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  • 1.
    Ali, Amjad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan.;Univ Okara, Dept Phys, Okara 56300, Pakistan.
    Raza, Rizwan
    COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan.;Royal Inst Technol KTH, Dept Energy Technol, S-10044 Stockholm, Sweden..
    Khalil, R. M. Arif
    Bahauddin Zakariya Univ, Dept Phys, Multan 60800, Pakistan..
    Ahmad, M. Ashfaq
    COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan..
    Rafique, Asia
    COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan..
    Ullah, M. Kaleem
    COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan..
    Rehman, Amin Ur
    Lahore Univ, Dept Phys, Lahore 54000, Pakistan..
    Mushtaq, M. Naveed
    COMSATS Inst Informat Technol, Dept Phys, Lahore 54000, Pakistan..
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A potential electrolyte (Ce1-x CaxO2-delta) for fuel cells:Theoretical andexperimental study2018In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 44, no 11, p. 12676-12683Article in journal (Refereed)
    Abstract [en]

    First-principles calculations are performed using density function theory to explore the effects of dopant Ca in ceria (Ce1-x CaxO2-delta). The impact of oxygen vacancy on band gap and density of states is examined in doped ceria using generalized gradient approximations. Vacancy association and vacancy formation energies of the doped ceria are calculated to reveal the effect of dopant on ion conduction. The experimental study of the sample Ce0.875Ca0.125O2-delta) was performed to compare with the theoretical results. The obtained results from theoretical calculation and experimental techniques show that oxygen vacancy increases the volume, lattice constant (5.47315 angstrom) but decrease the band gap (1.72 eV) and bulk modulus. The dopant radius (1.173 angstrom) and lattice constant (5.4718 angstrom) are also calculated by equations which is close to the DFT lattice parameter. The result shows that oxygen vacancy shifts the density of states to lower energy region. Band gap is decreased due to shifting of valence states to conduction band. Vacancy formation shows a significance increase in density of states near the Fermi level. Density of states at Fermi level is proportional to the conductivity, so an increase in density of states near the Fermi level increases the conductivity. The experimental measured ionic conductivity is found to 0.095 S cm(-1) at 600 degrees C. The microstructural studies is also reported in this work.

  • 2. Araujo, C. Moyses
    et al.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ramzan, Muhammad
    Shukla, R.
    Jayakumar, O. D.
    Tyagi, A. K.
    Liu, Yi-Sheng
    Chen, Jeng-Lung
    Glans, Per-Anders
    Chang, Chinglin
    Blomqvist, Andreas
    Lizarraga, Raquel
    Holmström, Erik
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Guo, Jinghua
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites2014In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, p. 4686-Article in journal (Refereed)
    Abstract [en]

    We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

  • 3.
    Araujo, C. Moysés
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kapilashrami, Mukes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Jun, Xu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Jayakumar, Onattu D.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Wu, Yan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Århammar, Cecilia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Gehring, Gillian A.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Room temperature ferromagnetism in pristine MgO thin films2010In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 23Article in journal (Refereed)
    Abstract [en]

    Robust ferromagnetic ordering at, and well above room temperature is observed in pure transparent MgO thin films (<170 nm thick) deposited by three different techniques. Careful study of the wide scan x-ray photoelectron spectroscopy rule out the possible presence of any magnetic contaminants. In the magnetron sputtered films, we observe magnetic phase transitions as a function of film thickness. The maximum saturation magnetization of 5.7 emu/cm(3) is measured on a 170 nm thick film. The films above 500 nm are found to be diamagnetic. Ab initio calculations suggest that the ferromagnetism is mediated by cation vacancies.

  • 4. Bagchi, S.
    et al.
    Tomenius, H.
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ausmees, N.
    Intermediate filament-like proteins in bacteria and a cytoskeletal function in Streptomyces2008In: Molecular Microbiology, ISSN 0950-382X, E-ISSN 1365-2958, Vol. 70, no 4, p. 1037-1050Article in journal (Refereed)
    Abstract [en]

    Actin and tubulin cytoskeletons are conserved and widespread in bacteria. A strikingly intermediate filament (IF)-like cytoskeleton, composed of crescentin, is also present in Caulobacter crescentus and determines its specific cell shape. However, the broader significance of this finding remained obscure, because crescentin appeared to be unique to Caulobacter. Here we demonstrate that IF-like function is probably a more widespread phenomenon in bacteria. First, we show that 21 genomes of 26 phylogenetically diverse species encoded uncharacterized proteins with a central segmented coiled coil rod domain, which we regarded as a key structural feature of IF proteins and crescentin. Experimental studies of three in silico predicted candidates from Mycobacterium and other actinomycetes revealed a common IF-like property to spontaneously assemble into filaments in vitro. Furthermore, the IF-like protein FilP formed cytoskeletal structures in the model actinomycete Streptomyces coelicolor and was needed for normal growth and morphogenesis. Atomic force microscopy of living cells revealed that the FilP cytoskeleton contributed to mechanical fitness of the hyphae, thus closely resembling the function of metazoan IF. Together, the bioinformatic and experimental data suggest that an IF-like protein architecture is a versatile design that is generally present in bacteria and utilized to perform diverse cytoskeletal tasks.

  • 5.
    Belova, Liubov M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Hellwig, Olav
    Dobisz, Elizabeth
    Dahlberg, E. Dan
    Rapid preparation of electron beam induced deposition Co magnetic force microscopy tips with 10 nm spatial resolution2012In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 83, no 9, p. 093711-Article in journal (Refereed)
    Abstract [en]

    Magnetic force microscope Co spike tips with lateral magnetic resolution of 10 nm have been prepared. The Co spikes are grown by electron beam induced deposition of Co from Co-2(CO)(8) gas precursor. The high resolution Co spikes are fabricated at the spot of a tightly focused electron beam on the tip of commercial atomic force microscope cantilevers. Qualitative investigations indicate that a spike grown on a planar base of Co improves the signal to noise.

  • 6.
    Belova, Lyubov M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Dahlberg, E. D.
    Riazanova, Anastasiia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Mulders, J. J. L.
    Christophersen, C.
    Eckert, J.
    Rapid electron beam assisted patterning of pure cobalt at elevated temperatures via seeded growth2011In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 22, no 14, p. 145305-Article in journal (Refereed)
    Abstract [en]

    A new method of direct, rapid nano- to micro-scale patterning of high purity cobalt is presented. The method utilizes a combination of electron beam induced deposition (EBID) and seeded growth at elevated temperatures below the temperature of spontaneous thermal decomposition. Dicobalt octacarbonyl Co-2(CO)(8) is used as the precursor and carbon as a seed layer. Seeded deposition is carried out in the substrate temperature range from 55 to 75 degrees C. Deposition yield is significantly higher than conventional EBID and magnetotransport measurements indicate that resistivity, 22 mu Omega cm, and saturation magnetization, 1.55 T, are much closer to the corresponding values for bulk Co than those for standard EBID.

  • 7. Bhatt, P.
    et al.
    Kanciurzewska, A.
    Carlegrim, E.
    Kapilashrami, Mukes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Fahlman, M.
    Ferromagnetism above room temperature in nickel-tetracyanoethylene thin films2009In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 19, no 36, p. 6610-6615Article in journal (Refereed)
    Abstract [en]

    Room temperature ferromagnetic ordering is reported in Ni-tetracyanoethylene (TCNE) thin films fabricated on Au substrates using physical vapor deposition (PVD) under ultra high vacuum conditions. This technique enables the preparation of very clean films without having any kind of contamination from oxygen-containing species, solvents or precursor molecules. Film stoichiometry was obtained from X-ray photoelectron spectroscopy (XPS) measurements. XPS derived stoichiometry points to a similar to 1 : 2 ratio between Ni and TCNE resulting in Ni(TCNE)(x), x approximate to 2. No evidence of pure Ni metal in the in situ grown films was present in the XPS or the ultraviolet photoelectron spectroscopy (UPS) measurements within the detection limits of the techniques.

  • 8.
    Biswas, Anis
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Shirong, Wang
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Liubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    The effect of oxygen partial pressure during deposition in the magnetic properties of ZnO thin film2011In: Mater Res Soc Symp Proc, 2011, p. 117-122Conference paper (Refereed)
    Abstract [en]

    We have studied the magnetic properties of 100 nm thick ZnO thin films prepared by magnetron sputtering in different oxygen partial pressures (ratio of oxygen pressure to total pressure in deposition chamber, P Oxy). Only the films fabricated at P Oxy below ∼ 0.5 show room temperature ferromagnetism. The saturation magnetization at room temperature is initially found to increase as P Oxy increases and reaches maximum value of ∼ 5 emu/gm at P Oxy ∼ 0.3 and then starts to decrease and becomes diamagnetic for P Oxy &gt; 0.5. From small angle XRD study of structural properties of the films, we find that the lattice stress developed in the film along c-axis also exhibits a similar behavior with the variation of P Oxy. Thus, both the room temperature ferromagnetism and lattice stress appear to originate from the intrinsic defects present in the sample.

  • 9. Chen, J.
    et al.
    Lindberg, F.
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Forssgren, B.
    Gott, K.
    Lejon, J.
    Jasiulevicius, A.
    High resolution electron microscopy study on oxide films formed on nickel-base Alloys X-750, 182 and 82 in simulated high flow velocity BWR water conditions2011Conference paper (Refereed)
    Abstract [en]

    This work contributes to characterization of the oxide films formed on nickel-base alloys (Alloy X-750, Alloy 82 and Alloy 182) under simulated BWR water environments at ∼10 or 18 m/s with or without iron injection. HR SEM/TEM and FIB techniques were applied. The oxide thicknesses on different alloys were substantially different, ranging from 50 nm to 8 μm. For Alloy X-750 and Alloy 182 exposed without iron injection, similar oxide phase compositions consisting of sub-micron Fe2O3 and NiFe 2O4 grains as well as NiO were formed but with substantially different microstructures. For the corroded Alloy X-750 there was an additional dense layer of possibly Ni1.5Cr0.5O 3 in between the NiFe2O4 and NiO layers. On Alloy 82 which contained a relatively low Fe-content only a thin but dense film of Cr1.3Fe0.7O3 was seen. With iron injection the oxide films formed on Alloy 82 were similar to that on the Alloy 182 without iron injection, suggesting that iron injection may play a similar role as if the alloy had an elevated iron content. The implication of the observations for material corrosion behavior in BWRs is elaborated.

  • 10. Chia, Han-Jong
    et al.
    Guo, Feng
    Belova, Liubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    McMichael, R. D.
    Nanoscale Spin Wave Localization Using Ferromagnetic Resonance Force Microscopy2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 8, p. 087206-Article in journal (Refereed)
    Abstract [en]

    We use the dipolar fields from a magnetic cantilever tip to generate localized spin wave precession modes in an in-plane magnetized, thin ferromagnetic film. Multiple resonances from a series of localized modes are detected by ferromagnetic resonance force microscopy and reproduced by micromagnetic models that also reveal highly anisotropic mode profiles. Modeled scans of line defects using the lowest-frequency mode provide resolution predictions of (94.5 +/- 1.5) nm in the field direction, and (390 +/- 2) nm perpendicular to the field.

  • 11. Chia, Han-Jong
    et al.
    Guo, Feng
    Belova, Liubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    McMichael, R. D.
    Spectroscopic defect imaging in magnetic nanostructure arrays2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 4, p. 042408-Article in journal (Refereed)
    Abstract [en]

    We introduce a method for imaging defective structures in an array of magnetic nanodevices using ferromagnetic resonance force microscopy with contrast between normal and defective devices provided through differences in resonance condition. In a demonstration of this technique, two dimensional scans of an array resolve not only intentional differences in resonant field between 200 nm circular dots and an intentional oval "defect," but also smaller differences between the nominally identical circular dots in the array.

  • 12. Chia, Han-Jong
    et al.
    Guo, Feng
    Belova, Liubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    McMichael, R. D.
    Two-dimensional spectroscopic imaging of individual ferromagnetic nanostripes2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 18, p. 184406-Article in journal (Refereed)
    Abstract [en]

    We use ferromagnetic-resonance force microscopy to spectroscopically image the edge modes in individual 700 nm and 400 nm wide Permalloy stripes with a spatial resolution on the order of 200 nm. The imaging clearly identifies some resonances as edge modes in stripes in a case where mode identification by comparison with micromagnetic modeling is not clear. Combined spectroscopic and spatial scans reveal clear differences in the edge mode resonances at opposite edges of the stripes as well as inhomogeneity along the length of the stripe.

  • 13. Costanzi, Barry N.
    et al.
    Riazanova, Anastasia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Dahlberg, E. Dan
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    In situ manufacture of magnetic tunnel junctions by a direct-write process2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, no 22, p. 222401-Article in journal (Refereed)
    Abstract [en]

    In situ construction of Co/SiO2/Co magnetic tunnel junctions using direct-write electron-beam-induced deposition is described. Proof-of-concept devices were built layer by layer depositing the specific components one at a time, allowing device manufacture using a strictly additive process. The devices exhibit a magnetic tunneling signature which agrees qualitatively with the Slonczewski model of magnetic tunneling.

  • 14.
    Davydova, Alexandra
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Tselikov, G.
    Dilone, D.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kabashin, A. V.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Fabrication of thin ZnO films with wide-range tuned optical properties by reactive magnetron sputtering2018In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 33, no 2, article id 025004Article in journal (Refereed)
    Abstract [en]

    We report the manufacturing of thin zinc oxide films by reactive magnetron sputtering at room temperature, and examine their structural and optical properties. We show that the partial oxygen pressure in DC mode can have dramatic effect on absorption and refractive index (RI) of the films in a broad spectral range. In particular, the change of the oxygen pressure from 7% to 5% can lead to either conventional crystalline ZnO films having low absorption and characteristic descending dependence of RI from 2.4-2.7 RIU in the visible to 1.8-2 RIU in the near-infrared (1600 nm) range, or to untypical films, composed of ZnO nano-crystals embedded into amorphous matrix, exhibiting unexpectedly high absorption in the visible-infrared region and ascending dependence of RI with values varying from 1.5 RIU in the visible to 4 RIU in the IR (1600 nm), respectively. Untypical optical characteristics in the second case are explained by defects in ZnO structure arising due to under-oxidation of ZnO crystals. We also show that the observed defect-related film structure remains stable even after annealing of films under relatively high temperatures (30 min under 450 degrees C). We assume that both types of films can be of importance for photovoltaic (as contact or active layers, respectively), as well as for chemical or biological sensing, optoelectronics etc.

  • 15.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Aristov, Andrey
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kabashin, Andrei V.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Particle-free inkjet printing of nanostructured porous indium tin oxide thin films2013In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 3, no 42, p. 19501-19507Article in journal (Refereed)
    Abstract [en]

    We report a simple, low-cost, single-step inkjet printing method for the fabrication of nanostructured, highly transparent and conductive ITO films, which completely avoids the use of ITO particles in the fabrication process. In our method, the inks are formed from a liquid solution presenting a properly selected mixture of indium and tin acetates. After jet printing, the ink is decomposed during a subsequent annealing step, in which the released CO2 gas bubbles control the ITO nucleation process to provide a porous film texture. We show that the fabricated ITO films are highly crystalline, stoichiometric, and nanoporous with controlled porosity. Electrical measurements show relatively low resistivity values for the films (down to 0.029 Omega cm) comparable to those of the best ITO thin films fabricated by other methods. Optical ellipsometry tests demonstrate a relatively high refractive index (1.5-1.7) and high transparency of the films over a wide region of the spectrum ranging from 500 to 1700 nm. Since the method does not require any pre-fabricated ITO particles, masks or templates, and enables the deposition of films on substrates of various materials and shapes, it can be employed for fabrication of nanoporous ITO films for a diversity of applications, including solar cell, bio- and chemical sensing, etc.

  • 16.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyuba
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    The art of tailoring inks for inkjet printing metal oxides2012Manuscript (preprint) (Other academic)
    Abstract [en]

    Inkjet printing has become a promising, efficient, inexpensive, scalable technique for materials deposition and mask-less patterning in many device applications. This article provides an introduction of the essentials of inkjet printing technology and ink preparation which remains a challenge especially for printing oxide transparent materials. After introducing the essentials of an inkjet printer and the process of the conversion of liquid ink into solid thin films of oxide materials, we present two approaches to the tailoring of inks, especially relevant for piezoelectric drop-on-demand ink jet printer: (1) the inks prepared from oxide particle suspensions (e.g., SiO2, TiO2, Fe3O4), and (2) metal-acetates precursor solutions for direct printing of thin films subsequently processed by calcination into the respective oxides like undoped and doped ZnO, MgO, ITO among others. The oxide films prepared this way using high purity precursors are free from undesirable contaminations, stoichiometric and when annealed appropriately produce smooth printed thin films. We place special emphasis upon preparation of inks that are stable without sediments over time so that the printing process is reliable and repeatable, and the obtained oxide films are dense and uniform. Also, for some of the inks containing multi-type acetates with possible phase separation even before calcinations we have developed a chelating procedure in order to tailor the films into single phase homogeneity. The films are characterized by optical microscope for micro features, high resolution SEM in a Nova600-Nanolab SEM/FIB system, and JEOL atomic force microscope for their morphology.

  • 17.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyuba
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Thermal anealing effects on Ag/TiO2 thin films prepared by ink-jet printingManuscript (preprint) (Other academic)
    Abstract [en]

    The effects of heat treatment on both the phase structure and the electronic band structure were studied for Ag/TiO2 composite films prepared by inkjet printing. Ag nanoparticles can form ‘metal-bridge’ to link TiO2 particles in the mesoporous structured films and improve the transport properties of the films. The distribution of Ag in the composite films shows dependence on the annealing conditions: Ag clusters were observed at high annealing temperature (>600 °C), and they can be annihilated by a longer time annealing. Comparing with pure TiO2 films, the decreased intensity of the photoluminescence (PL) emission spectra of Ag/TiO2 composite films indicates that the doped Ag atoms could act as traps to capture electron and inhabit the recombination of electron-hole pairs. From the identifiable PL emission peaks, the band structure of the films is deduced.

  • 18.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Hao
    Cent S Univ, Sch Phys & Elect, Hunan Key Lab Super Microstruct & Ultrafast Proc, Changsha 410083, Hunan, Peoples R China..
    Riazanova, Anastasiia
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Rao, K Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Tuning room temperature ferromagnetism of 'in-situ' inkjet printed Fe-doped ZnO films2019In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 34, no 5, article id 055006Article in journal (Refereed)
    Abstract [en]

    ZnO is a wide-band gap semiconductor widely used in optical and electric devices, associating with ferromagnetism at low dimension endowing its possibility for functional applications with magneto-optical and magneto-electric properties. We prepared ZnO and Fe-doped ZnO thin films 'in-situ' on substrate by inkjet printing, and tuned the room temperature ferromagnetism (RTFM) of the film by Fe-doping concentration, film thickness and post annealing temperature. It was found that by Fe doping the saturation magnetization (M-s) of the film can be enhanced by more than 4 folds comparing with the un-doped film, i.e. from 0.9 emu g(-1) for the ZnO film to 3.8 emu g(-1) for the Fe-doped ZnO film with comparable thickness. The enhancement was attributed to the introduction of un-paired 3d electrons which formed long range ferromagnetic ordering, as well as the consequent structure changes with smaller grains which increased the interface induced magnetism. By changing the annealing temperature and the film thickness, the defect-induced ferromagnetism was investigated. The RTFM shows thickness dependence with peak saturation magnetization value of 4.44 emu g(-1) for the 45 nm thick film. The work provides an effective way of tuning magnetism in ZnO based films for functional device applications.

  • 19.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Cent S Univ, Sch Phys & Elect, Hunan Key Lab Super Microstruct & Ultrafast Proc, Changsha 410083, Hunan, Peoples R China..
    Liu, Fang
    Cent S Univ, Sch Phys & Elect, Hunan Key Lab Super Microstruct & Ultrafast Proc, Changsha 410083, Hunan, Peoples R China..
    Li, Tianli
    Cent S Univ, Sch Phys & Elect, Hunan Key Lab Super Microstruct & Ultrafast Proc, Changsha 410083, Hunan, Peoples R China..
    Zhang, Wenchao
    Cent S Univ, Sch Phys & Elect, Hunan Key Lab Super Microstruct & Ultrafast Proc, Changsha 410083, Hunan, Peoples R China..
    Xia, Huayan
    Cent S Univ, Sch Phys & Elect, Hunan Key Lab Super Microstruct & Ultrafast Proc, Changsha 410083, Hunan, Peoples R China..
    Rao, K. , V
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Inkjet printing Ag-TiO2 thin films with suppressed photoluminescence2019In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 34, no 10, article id 105027Article in journal (Refereed)
    Abstract [en]

    With ultraviolet sensitive photochemistry and photoelectric properties, TiO2 is attractive for applications like photocatalysis, photovoltaic devices, and sunscreen products, among others. By coating Ag on TiO2 surface, the sensitivity can be extended to visible light, endowing enhanced properties with potential new applications. In this work we inkjet print Ag-TiO2 films from particle suspensions, and investigate the structure, morphology, Ag distribution and the photoluminescence of the films It is found that Ag nanoparticles form bridges among TiO2 particles during the post-annealing. These metallic bridges can transport the excited electrons and suppress the recombination of electrons and holes with the photoluminescence of the film reduced by more than half. The work provides an industrial applicable, low-cost, environment friendly route of preparing Ag-TiO2 films for attractive photochemistry and photoelectric device applications.

  • 20.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Riazanova, Anastasia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Magnetic properties of inkjet printed Fe-doped ZnO thin filmsManuscript (preprint) (Other academic)
    Abstract [en]

    Magnetic properties in semiconductors show dependences on the substance itself (the doped element and the matrix), the states (e.g., bulk, nanoparticles, or film) and the preparation methods, which attract huge interest for both functional applications and fundamental science. As a widespread used semiconductor, ZnO and Fe-doped ZnO thin films were prepared via calcination of the as-prepared acetates precursor films printed by inkjet technique. Their room temperature (RT) magnetic properties were investigated to obtain the insight into the origin of RT ferromagnetism (FM). It was found that the grain size of the films was reduced by Fe-doping. For ~30 nm thick films, the saturation magnetization (MS) of 10 at.% Fe-doped ZnO (3.8 emu/g) is 4 times higher than that of pure ZnO thin film (0.9 emu/g) prepared with the same route. We attribute the enhancement to: (i) the introduction of Fe atoms with unpaired 3d electrons which contribute to magnetism; and (ii) the Fe-doping increase the defect in the lattice structure of the ZnO matrix. The effects of calcination temperature on RTFM of 10 at.% Fe-doped thin films were studied, and the temperature dependent MS was observed. The RTFM depended on film thickness as well, which shows an initial increase and then decrease with the maximum MS of 4.44 emu/g obtained from the ~45 nm 10 at.% Fe-doped ZnO film. Possible reasons for the observed phenomena were discussed.

  • 21.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Riazanova, Anastasia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Magnetism of Fe-doped MgO thin films prepared by inkjet printingManuscript (preprint) (Other academic)
    Abstract [en]

    We prepared MgO and Fe-doped MgO thin films by inkjet printing and investigated the room temperature ferromagnetism (RTFM) of the films. Films prepared from the same route show amorphous for pure MgO films while crystals for Fe-doped MgO thin films, indicating that the doped Fe atoms can improve the crystallinity of the films. The saturation magnetization of 10 at.% Fe-doped MgO film is ~5 times as much as that of pure MgO film with same thickness (~90 nm), implying the great enhancement of magnetism introduced by Fe-doping. The RTFM of 10 at.% Fe-doped MgO films shows dependence on calcination temperature and the film thickness, where the effects of defect and crystal structure on magnetism of films were discussed. From the L2,3-edge features, the coexistence of Fe2+ and Fe3+ cations in octahedral and tetrahedral sites of the crystals was deduced, which was consistent with the two lattice structures determined from X-ray diffraction. The unpaired 3d electrons in the lattices could interact with each other directly or mediated by anions/carriers, which contribute to the enhancement of RTFM in the Fe-doped films. The saturation magnetization of ~30 nm 10at.% Fe-doped MgO film was detected to be ~6.3 emu•cm-3 and the coercively was ~50 Oe.

  • 22.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Olsson, Richard T.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Particle size and magnetic properties dependence on growth temperature for rapid mixed co-precipitated magnetite nanoparticles2012In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, no 14, p. 145601-Article in journal (Refereed)
    Abstract [en]

    Magnetite nanoparticles have been prepared by co-precipitation using a custom-designed jet mixer to achieve rapid mixing (RM) of reactants in a timescale of milliseconds. The quick and stable nucleation obtained allows control of the particle size and size distribution via a more defined growth process. Nanoparticles of different sizes were prepared by controlling the processing temperature in the first few seconds post-mixing. The average size of the nanoparticles investigated using a Tecnai transmission electron microscope is found to increase with the temperature from 3.8 nm at 1 +/- 1 degrees C to 10.9 nm for particles grown at 95 +/- 1 degrees C. The temperature dependence of the size distribution follows the same trend and is explained in terms of Ostwald ripening of the magnetite nanoparticles during the co-precipitation of Fe2+ and Fe3+. The magnetic properties were studied by monitoring the blocking temperature via both DC and AC techniques. Strikingly, the obtained RM particles maintain the high magnetization (as high as similar to 88 A m(2) kg(-1) at 500 kA m(-1)) while the coercivity is as low as similar to 12 A m(-1) with the expected temperature dependence. Besides, by adding a drop of tetramethylammonium hydroxide, aqueous ferrofluids with long term stability are obtained, suggesting their suitability for applications in ferrofluid technology and biomedicine.

  • 23.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Olsson, Richard T.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rapid mixing: A route to synthesize magnetite nanoparticles with high moment2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, no 22, p. 222501-Article in journal (Refereed)
    Abstract [en]

    We demonstrate the impact of rapid mixing of the precursors in a time scale of milliseconds on the reaction rate and magnetic properties of co-precipitated magnetite with a custom-made mixer. The mixed volume is directed into a desk-top AC susceptometer to monitor the magnetic response from the growing particles in real-time. These measurements indicate that the reaction is mostly completed within a minute. The obtained superparamagnetic nanoparticles exhibit a narrow size distribution and large magnetization (87 Am(2) kg(-1)). Transmission electron micrographs suggest that rapid mixing is the key for better crystallinity and a more uniform morphology leading to the observed magnetization values.

  • 24.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Takahiko, Tamaki
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Co-precipitation of iron oxide nanoparticles by rapid mixingArticle in journal (Other academic)
    Abstract [en]

    Synthesis of Magnetite appears to be a topic of continued interest because of its versatility and the variety applications. Among the chemical techniques to synthesize Fe3O4, co-precipitation approach although very common, seems to be extremely sensitive to the consequences of nucleation, growth and most of all the rate of the reaction involved. This work is an attempt to demonstrate the complexities of obtaining monodispersed nanosized Fe3O4 particles. We consider the role of rapid mixing and its consequences on co-precipitation at ice-point, room temperature and boiling water temperatures on the magnetic properties of Fe3O4. We obtained crystallites varying in the range from 6.6 nm (grown in ice-water) to 7.9 nm (grown in boiling water) as determined from the broadening of XRD diffraction peaks using the Scherrer approach. With the increase of the particle size, the saturate magnetization of iron oxides increases from 52 emu/g to 63 emu/g, and the coercivity increases from 0.5 Oe to 7.9 Oe. Layers of nanosized magnetic particles on glass substrates show unusual wavelength dependence of Faraday rotation loops which show a reversal phenomenon in the sign of the magnetization around 550.

  • 25.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Voit, Wolfgang
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kyndiah, Adrica
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Wu, Yan
    Faculty of Materials Science and Chemical Engineering, China University of Geosciences.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Room temperature ferromagnetism of Fe-doped ZnO and MgO thin films prepared by ink-jet printing2012In: MRS Proceedings, 2012Conference paper (Refereed)
    Abstract [en]

    Room temperature magnetic properties of un-doped, as well as 10 at.% Fe-doped ZnOand MgO single-pass layer of ink-jet printed thin films have been investigated to obtain insightinto the role of the band gaps and mechanisms for the origin of ferromagnetic order in thesematerials. It is found that on doping with Fe, the saturation magnetization is enhanced by severalfoldin both systems when compared with the respective un-doped thin films. For a ~28 nm thickfilm of Fe-doped ZnO (Diluted Magnetic Semiconductor, DMS) we observe an enhancedmoment of 0.465 μB/Fe atom while it is around 0.111μB/Fe atom for the doped MgO (DilutedMagnetic Insulator, DMI) film of comparable thickness. Also, the pure ZnO is far moreferromagnetic than pure MgO at comparable low film thicknesses which can be attributed todefect induced magnetism originating from cat-ion vacancies. However, the film thicknessdependence of the magnetization and the defect concentrations are found to be significantlydifferent in the two systems so that a comparison of the magnetism becomes more complex forthicker films.

  • 26.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Volotinen, Tarja
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kulkarni, S. K.
    Indian Institute of Science Education and Research, India.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Effect of Fe3O4 nanoparticles on the optical transmission properties of 3D magnetic photonic crystals2010In: Physics ReviewArticle in journal (Other academic)
    Abstract [en]

    Magnetic and optical properties of three-dimensional magnetic photonic crystals (MPCs), consisting of silica spheres in the size range 190-680nm embedded with 8, 9 and 13 nm Fe3O4 nanoparticles, have been investigated. All the PC-films, with and without embedded magnetic nanoparticles, show five band gaps at well defined wavelengths in their optical transmission spectrum. The band gaps are found to be a linear function of the constituent sphere size in the MPC films. From the slope of this function, the deduced refractive index for the constituents in the films is found to increase with the concentration of the embedded magnetite nanoparticles. The observed shifts in the photonic band gaps PBGs in the films is qualitatively explained in terms of the variations of refractive index and the contrast index difference arising from the concentration of the embedded nanoparticles. We also find that the angular dependence of PBG positions for MPCs at small incidence angles is strongly dependent on the p- and s- polarization states of the incident light. The polarization sensitivity of PBGs to the Fe3O4 concentration is also discussed.  

  • 27.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Volotinen, Tarja
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kulkarni, S. K.
    Indian Institute of Science Education and Research, India.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Enhanced linear sphere size dependence of photonic band gaps for 3D nanocomposite magnetic photonic crystals2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550Article in journal (Other academic)
    Abstract [en]

    Silica spheres in the size range (70-650) nm, containing embedded nano-sized magnetic iron oxide particles have been synthesized and arranged into 3D-face-centered-cubic (fcc) structured magnetic photonic crystals (MPCs) with the (111) crystal plane parallel to the glass substrate surface. Five photonic band gaps (PBGs) are observed in the optical transmission spectra measured over UV-Vis-near IR range for MPCs. The peak wavelengths of the PBGs (λC) are found to increase linearly with the sphere size (Φ). Furthermore, on embedding magnetic nanoparticles the position of PBGs is shifted to higher wavelengths. In addition, the average refractive index, 1.5 ± 0.1, obtained for the MPCs from the slopes of λC(Φ) is found to be larger than the reported value of 1.349 for pure silica PCs.

  • 28.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Volotinen, Tarja T.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kulkarni, S. K.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Effect of embedding Fe3O4 nanoparticles in silica spheres on the optical transmission properties of three-dimensional magnetic photonic crystals2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 10, p. 103501-Article in journal (Refereed)
    Abstract [en]

    Magnetic and optical properties of three-dimensional fcc-structured magnetic photonic crystals (MPCs), consisting of SiO2 spheres, in the size range 260-680 nm, embedded with 0-6.4 wt % Fe3O4 nanoparticles have been investigated. In the wide spatial angle transmission spectra for these crystals at normal incidence of light in the UV-visible range, five photonic band gaps (PBGs) due to Bragg diffraction from different crystal planes have been observed. The Bragg wavelengths (lambda(B)) of PBGs in both the nonmagnetic and MPCs of the same structure are found to depend linearly on the sphere size. From the slope of this linear function the calculated effective refractive index is found to increase with the concentration of the magnetite nanoparticles in the MPCs, and is consistent with the result calculated from the average dielectric constant. We also find lambda(B) of PBGs are dependent on the angle of the incidence of the light. Furthermore, for small angles this angular dependency is more strongly dependent on the polarization of incident light for MPCs than for the non-MPCs. Thus, magnetic nanocomposite PCs can be designed to incorporate additional functionality in the development of potential magneto-optical devices.

  • 29.
    Fang, Mei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Volotinen, Tarja T.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kulkarni, Sulabha K.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Designing photonic band gaps in SiO(2)-based face-centered cubic-structured crystals2011In: Journal of Nanophotonics, ISSN 1934-2608, Vol. 5, p. 053514-Article in journal (Refereed)
    Abstract [en]

    We designed face-centered cubic-structured (fcc) photonic crystals whose lattice parameters were tuned by varying the size of the constituent spherical silica particles in the range 100 to 520 nm. From wide-angle optical transmission investigations and Gaussian fitting of the absorbance spectra over UV-Vis-Near IR range, we found that in these crystals the Bragg wavelengths of the photonic band gaps (PBGs) corresponding to the reflected crystal planes linearly increase with the size of the spheres as expected. From this data, the average refractive index along the different crystal planes of the fcc structure was found to be in the 1.24 to 1.32 range. The Bragg wavelengths were tuned between 400 and 1100 nm. Thus, photonic crystals of the same structure can be designed to tune the Bragg wavelengths of PBGs by selecting the sphere size. These studies open up possibilities to design a new class of "smart" photonic crystals consisting of dielectric entities of sub-micron silica spheres with added functionality from magnetic or piezoelectric nanoparticles embedded in them.

  • 30.
    Fang, Mej
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Voit, Wolfgang
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Wu, Y.
    Lyubov, Belova
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    'In-situ' preparation of metal oxide thin films by inkjet printing acetates solutions2013In: Mater Res Soc Symp Proc, 2013, p. 13-20Conference paper (Refereed)
    Abstract [en]

    Direct printing of functional oxide thin films could provide a new route to low-cost, efficient and scalable fabrications of electronic devices. One challenge that remains open is to design the inks with long term stability for effective deposition of specific oxide materials of industrial importance. In this paper, we introduce a reliable method of producing stable inks for 'in-situ' deposition of oxide thin films by inkjet printing. The inks were prepared from metal-acetates solutions and printed on a variety of substrates. The acetate precursors were decomposed into oxide films during the subsequent calcination process to achieve the 'in-situ' deposition of the desired oxide films directly on the substrate. By this procedure we have obtained room temperature contamination free ferromagnetic spintronic materials like Fe doped MgO and ZnO films from their acetate(s) solutions. We find that the origin of magnetism in ZnO, MgO and their Fe-doped films to be intrinsic. For a 28 nm thick film of Fe-doped ZnO we observe an enhanced magnetic moment of 16.0 emu/cm3 while it is 5.5 emu/cm3 for the doped MgO film of single pass printed. The origin of magnetism is attributed to cat-ion vacancies. We have also fabricated highly transparent indium tin oxide films with a transparency &gt;95% both in the visible and IR range which is rather unique compared to films grown by any other technique. The films have a nano-porous structure, an added bonus from inkjetting that makes such films advantageous for a broad range of applications.

  • 31.
    Fischer, Andreas C.
    et al.
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Malm, Gunnar B.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Kolahdouz, Mohammadreza
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Radamson, Henry
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Gylfason, Kristinn B.
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Stemme, Göran
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    3D Free-Form Patterning of Silicon by Ion Implantation, Silicon Deposition, and Selective Silicon Etching2012In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 22, no 19, p. 4004-4008Article in journal (Refereed)
    Abstract [en]

    A method for additive layer-by-layer fabrication of arbitrarily shaped 3D silicon micro- and nanostructures is reported. The fabrication is based on alternating steps of chemical vapor deposition of silicon and local implantation of gallium ions by focused ion beam (FIB) writing. In a final step, the defined 3D structures are formed by etching the silicon in potassium hydroxide (KOH), in which the local ion implantation provides the etching selectivity. The method is demonstrated by fabricating 3D structures made of two and three silicon layers, including suspended beams that are 40 nm thick, 500 nm wide, and 4 μm long, and patterned lines that are 33 nm wide.

  • 32.
    Fischer, Andreas C.
    et al.
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Gylfason, Kristinn B.
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Belova, Liubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Malm, Gunnar B.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Kolahdouz, Mohammadreza
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rikers, Yuri G.M.
    FEI Electron Optics.
    Stemme, Göran
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    3D Patterning of Si Micro and Nano Structures by Focused Ion Beam Implantation, Si Deposition and Selective Si Etching2012Conference paper (Other academic)
  • 33.
    Fischer, Andreas C.
    et al.
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Gylfason, Kristinn B.
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Belova, Lyubov M.
    Malm, Gunnar B.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Radamson, Henry H.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Kolahdouz, M.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rikers, Y. G. M.
    Stemme, Göran
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Layer-by-layer 3D printing of Si micro- and nanostructures by Si deposition, ion implantation and selective Si etching2012In: 12th IEEE Conference on Nanotechnology (IEEE-NANO), 2012, IEEE conference proceedings, 2012, p. 1-4Conference paper (Refereed)
    Abstract [en]

    In this paper we report a method for layer-by-layer printing of three-dimensional (3D) silicon (Si) micro- and nanostructures. This fabrication method is based on a sequence of alternating steps of chemical vapor deposition of Si and local implantation of gallium (Ga+) ions by focused ion beam (FIB) writing. The defined 3D structures are formed in a final step by selectively wet etching the non-implanted Si in potassium hydroxide (KOH). We demonstrate the viability of the method by fabricating 2 and 3-layer 3D Si structures, including suspended beams and patterned lines with dimensions on the nm-scale.

  • 34.
    Fischer, Andreas
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Sokka, Ilia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Belova, Liubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Synthesis, structure, and magnetic properties of some layered compounds based on long-chain sulfonium cations and complex cobalt and copper anions2013In: Zeitschrift für Anorganische und Allgemeines Chemie, ISSN 0044-2313, E-ISSN 1521-3749, Vol. 639, no 14, p. 2613-2617Article in journal (Refereed)
    Abstract [en]

    Two new materials of the composition ({CH3(CH2) 15(CH3)2S}+)2[CoBr 4]2- (1) and ({CH3(CH2) 15(CH3)2S}+)2[CuBr 4]2- (2 and 3), of which the latter exists in two polymorphs, were synthesized. The materials display the synthetically targeted structures, comprising of layers of complex metal ions and layers of long-chain sulfonium cations. The crystal structures of the materials were determined. The interlayer distances are around 24 Å, with metal-metal distances about 8 Å. The magnetic properties of 1 were investigated, and the material is paramagnetic. ({CH3(CH2)15(CH3) 2S}+)2[CuBr4]2 is polymorphic. Both polymorphs crystallize with triclinic symmetry.

  • 35. Fraerman, A. A.
    et al.
    Belova, Lyubov M.
    KTH, Superseded Departments, Materials Science and Engineering.
    Gribkov, B. A.
    Gusev, S. A.
    Klimov, A. Y.
    Mironov, V. L.
    Nikitushkin, D. S.
    Pakhomov, G. L.
    Rao, K. Venkat
    KTH, Superseded Departments, Materials Science and Engineering.
    Shevtsov, V. B.
    Silaev, M. A.
    Vdovichev, S. N.
    Magnetic force microscopy to determine vorticity direction in elliptical Co nanoparticles2004In: Physics of low-Dimensional structures, ISSN 0204-3467, Vol. 1-2, p. 35-40Article in journal (Refereed)
    Abstract [en]

    We present a magnetic force microscopy investigation into the magnetic properties of arrays of Co nanoparticles fabricated by electron be am lithography. Vorticity directions are determined in zero applied magnetic fields. Experimental dependence of height on stable magnetic states of the particles is investigated. The statistics of the vorticity direction distribution is discussed.

  • 36.
    Gu, Ziyan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Co-existence of Superconductivity and Ferromagnetism in melt-spun Ni-Bi Compounds2005In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326Article in journal (Other academic)
  • 37.
    Gu, Ziyan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Owens, Frank J.
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Magnetic Patterning of Kapton-H Polyimide films via UV laser, and Hot stamping2005Article in journal (Other academic)
  • 38. Guo, Feng
    et al.
    Belova, Liubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    McMichael, R. D.
    Parametric pumping of precession modes in ferromagnetic nanodisks2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 10, p. 104422-Article in journal (Refereed)
    Abstract [en]

    We report on the parametric excitation of magnetic precession modes in nanodisks using a parallel pumping configuration. The excitations are detected using a ferromagnetic resonance force microscopy method, and the parallel-pumped spectra reveal nonlinear characteristics including instability thresholds and multiple, narrow, sawtooth-shaped resonances. These characteristics are in accord with analytical theory and micromagnetic modeling results. Modeled mode profiles of the excitations show that higher-order standing spin-wave modes with both even and odd symmetries are excited under parallel pumping.

  • 39. Guo, Feng
    et al.
    Belova, Liubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    McMichael, R. D.
    Spectroscopy and Imaging of Edge Modes in Permalloy Nanodisks2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, no 1, p. 017601-Article in journal (Refereed)
    Abstract [en]

    We report ferromagnetic resonance force microscopy of confined spin-wave modes with improved, 100 nm resolution. The ferromagnetic resonance spectra in Permalloy disks (diameters ranging from 100 to 750 nm) distinguish multiple edge modes, and the images reveal distinct precession patterns. The fundamental edge mode also provides a new, localized probe of the magnetic properties of the film edge; rotation of the applied field reveals large edge property variations in nominally circular disks. As a function of disk diameter, the number of observed edge modes agrees with modeling.

  • 40. Guo, Feng
    et al.
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    McMichael, Robert D.
    Nonlinear ferromagnetic resonance shift in submicron Permalloy ellipses2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 6, article id 064426Article in journal (Refereed)
    Abstract [en]

    We report a systematic study of nonlinearity in the ferromagnetic resonance of a series of submicron Permalloy ellipses with varying aspect ratios. At high excitation powers, the resonances are found to shift to higher or lower applied field. We focus here on the sign of the shift and its dependence on the applied field and shape-induced anisotropy of the ellipses. Using ferromagnetic resonance force microscopy, we find that the measured nonlinear coefficient changes sign as a function of anisotropy field and applied field in qualitative agreement with a macrospin analysis. This macrospin analysis also points to origins of the nonlinearity in a combination of hard-axis in-plane anisotropy and precession ellipticity. In comparison of the macrospin predictions with both experimental and micromagnetic modeling results, we measure/model values of the nonlinear coefficient that are more positive than predicted by the macrospin model. The results are useful in understanding nonlinear physics in nanomagnets and applications of spin-torque oscillators.

  • 41. Gupta, A.
    et al.
    Ganin, A. Y.
    Sharma, P.
    Agnihotri, V.
    Belova, Lyubov M.
    KTH, Superseded Departments, Materials Science and Engineering.
    Rao, K. V.
    Kozlov, M. E.
    Zakhidov, A. A.
    Baughman, R. H.
    Synthetic magnetic opals2002In: Pramana (Bangalore), ISSN 0304-4289, E-ISSN 0973-7111, Vol. 58, no 06-maj, p. 1051-1059Article in journal (Refereed)
    Abstract [en]

    We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.

  • 42.
    Gylfason, Kristinn B.
    et al.
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Fischer, Andreas C.
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Gunnar Malm, B. Gunnar
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Radamson, Henry H.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Process considerations for layer-by-layer 3D patterning of silicon, using ion implantation, silicon deposition, and selective silicon etching2012In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 30, no 6, p. 06FF05-Article in journal (Refereed)
    Abstract [en]

    The authors study suitable process parameters, and the resulting pattern formation, in additive layer-by-layer fabrication of arbitrarily shaped three-dimensional (3D) silicon (Si) micro- and nanostructures. The layer-by-layer fabrication process investigated is based on alternating steps of chemical vapor deposition of Si and local implantation of gallium ions by focused ion beam writing. In a final step, the defined 3D structures are formed by etching the Si in potassium hydroxide, where the ion implantation provides the etching selectivity.

  • 43. Hodgkins, Robert P.
    et al.
    Ahniyaz, Anwar
    Parekh, Kinnari
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Bergstroem, Lennart
    Maghemite nanocrystal impregnation by hydrophobic surface modification of mesoporous silica2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 17, p. 8838-8844Article in journal (Refereed)
    Abstract [en]

    Here, we report the design of a hybrid inorganic/organic mesoporous material through simultaneous pore engineering and hydrophobic surface modification of the intramesochannels to improve the uptake of superparamagnetic maghemite nanocrystals via impregnation techniques. The mesoporous material of the SBA-15 type was functionalized in situ with thiol organo-siloxane groups. Restricting the addition of the thiol organo-siloxane to 2 mol % yielded an inorganic/organic hybrid material characterized by large pores and a well-ordered hexagonal p6mm mesophase. The hydrophobic surface modification promoted the incorporation of 7.5 nm maghemite (gamma-Fe2O3) nanocrystals, prepared through temperature-control led decomposition of iron pentacarbonyl in organic solvents. The hydrophobic, oleic acid capped superparamagnetic maghemite nanocrystals were incorporated into the porous network via wet impregnation from organic suspensions. Combining diffraction, microscopy, and adsorption data confirmed the uptake of the nanocrystals within the intramesochannels of the silica host. Magnetization dependencies on magnetic field at different temperatures show a constriction in the loop around the origin, which indicates immobilization of maghemite nanocrystals inside the thiol-functionalized silica host.

  • 44. Jonas, Kristina
    et al.
    Tomenius, Henrik
    Kader, Abdul
    Normark, Staffan
    Roemling, Ute
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Melefors, Oejar
    Roles of curli, cellulose and BapA in Salmonella biofilm morphology studied by atomic force microscopy2007In: BMC Microbiology, ISSN 1471-2180, E-ISSN 1471-2180, Vol. 7Article in journal (Refereed)
    Abstract [en]

    Background: Curli, cellulose and the cell surface protein BapA are matrix components in Salmonella biofilms. In this study we have investigated the roles of these components for the morphology of bacteria grown as colonies on agar plates and within a biofilm on submerged mica surfaces by applying atomic force microscopy (AFM) and light microscopy. Results: AFM imaging was performed on colonies of Salmonella Typhimurium grown on agar plates for 24 h and on biofilms grown for 4, 8, 16 or 24 h on mica slides submerged in standing cultures. Our data show that in the wild type curli were visible as extracellular material on and between the cells and as fimbrial structures at the edges of biofilms grown for 16 h and 24 h. In contrast to the wild type, which formed a three-dimensional biofilm within 24 h, a curli mutant and a strain mutated in the global regulator CsgD were severely impaired in biofilm formation. A mutant in cellulose production retained some capability to form cell aggregates, but not a confluent biofilm. Extracellular matrix was observed in this mutant to almost the same extent as in the wild type. Overexpression of CsgD led to a much thicker and a more rapidly growing biofilm. Disruption of BapA altered neither colony and biofilm morphology nor the ability to form a biofilm within 24 h on the submerged surfaces. Besides curli, the expression of flagella and pili as well as changes in cell shape and cell size could be monitored in the growing biofilms. Conclusion: Our work demonstrates that atomic force microscopy can efficiently be used as a tool to monitor the morphology of bacteria grown as colonies on agar plates or within biofilms formed in a liquid at high resolution.

  • 45.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyuba
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Effects of hole doping in the ferromagnetic semiconductor Mn-doped ZnO thin film studied by x-ray magnetic circular dichoism2009In: "Solid state devices and materials(SSDM2009)" held in Japan(7-9 october 2009), 2009Conference paper (Other academic)
  • 46.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Rao, K Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyuba
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Åkerstedt, Josefin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Defect induced magnetic anisotropy in undopted ZnO thin filmsArticle in journal (Other academic)
  • 47.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Upadhyay, Ramesh Venkataramaia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Belova, Liubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Effect of synthesis techniques on the magnetic properties of Mn-doped ZnO2008In: Magnetic Materials / [ed] Ghoshray, A; Bandyopadhyay, B, 2008, Vol. 1003, p. 255-257Conference paper (Refereed)
    Abstract [en]

    Mn-doped ZnO thin films have been prepared using three different routes, namely, magnetron sputtering technique, Pulsed Laser Deposition technique using targets from powders synthesized by solid state, and chemical method. Films deposited using sputtering technique in absence of nitrogen pressure gives higher magnetic moment per Mn atom, than is the case with films prepared by PLD indicating that ferromagnetism in the DMS systems is highly sensitive to processing conditions.

  • 48.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Xu, Jun
    Biswas, Anis
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Tamaki, Takahiko
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sharma, P.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Belova, Lyuba
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Coexistence of ultraviolet photo-response and room-temperature ferromagnetism in polycrystalline ZnO thin films2010In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, ISSN 0167-577X, Vol. 64, no 11, p. 1291-1294Article in journal (Refereed)
    Abstract [en]

    The coexistence of ultraviolet (UV) photoconductivity (PC) and room-temperature ferromagnetism (RTFM) is observed in polycrystalline ZnO thin films deposited by unbalanced magnetron sputtering under high oxygen pressure. A significant increase in PC (similar to 870% to 40000%) is observed with increasing film thickness and the consequent structural disorder and film porosity. In contrast, the saturation magnetization (M(S)) at room temperature is found to decrease from 1.02 emu/g to 0.53 emu/g with increasing film thickness from 50 to 150 nm.

  • 49.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Xu, Jun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Carlegrim, Elin
    Fahlman, Mats
    Experimental evidence for ferromagnetism at room-temperature in MgO thin films2010In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 22, no 34, p. 345004-Article in journal (Refereed)
    Abstract [en]

    Ferromagnetic ordering at room temperature (RTFM) in MgO thin films deposited by RF magnetron sputtering under various atmospheric conditions and temperatures is reported. A saturation magnetization (MS) value as high as 1.58 emu g(-1) is (0.046 mu B/unit cell) observed for a 170 nm film deposited at RT under an oxygen pressure of 1.3 x 10(-4) mbar. In contrast, films deposited at elevated temperature (under an identical oxygen pressure), or at higher oxygen pressures, as well as under a nitrogen atmosphere at RT show significantly suppressed magnetization. The ferromagnetic order in the MgO matrix is believed to be defect induced

  • 50.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Xu, Jun
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    On the defect induced ferromagnetic ordering above room-temperature in undoped and Mn doped ZnO thin films2009In: NOVEL MATERIALS AND DEVICES FOR SPINTRONICS / [ed] Sanvito S, Heinonen O, Dediu VA, Rizzo N, Warrendale, PA: MATERIALS RESEARCH SOCIETY , 2009, Vol. 1183, p. 3-8Conference paper (Refereed)
    Abstract [en]

    Evidence for long range ferromagnetic order above room-temperature, RTFM, in pristine ZnO, In2O3, TiO2 nanoparticles and thin films, containing no nominal magnetic elements have been reported recently. This could question the origin of RTFM in doped dilute alloys if for example the ZnO matrix itself develops a defect induced magnetic order with a significant moment per unit cell. In this presentation we report a systematic study of the film thickness dependence of RTFM in pure ZnO deposited by DC Magnetron Sputtering. We observe a maximum in the saturation magnetization, Ms, value of 0.62 emu/g (0,018 ÎŒB/unit cell), for a -480 nm film deposited in an oxygen ambience of appropriate pressure. Above a thickness of around 1 ÎŒm the films are diamagnetic as expected. We thus see a sequential transition from ferromagnetism to para- and eventual diamagnetism as a function of film thickness in ZnO. We also find that in such a ZnO matrix with a maximum intrinsic defect induced moment, on doping with Mn the maximum enhanced Ms value of 0.78 emu/g is obtained for 1 at. % Mn doping. With this approach of appropriate doping in a defect tailored matrix, we routinely obtain RTFM in both undoped and Mn- doped ZnO thin films.

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