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Magnetic properties of inkjet printed Fe-doped ZnO thin films
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.ORCID iD: 0000-0003-4889-4210
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
(English)Manuscript (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.

National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-102018OAI: oai:DiVA.org:kth-102018DiVA: diva2:550341
Note

QS 2012

Available from: 2012-09-06 Created: 2012-09-06 Last updated: 2012-09-07Bibliographically approved
In thesis
1. Properties of Multifunctional Oxide Thin Films Despostied by Ink-jet Printing
Open this publication in new window or tab >>Properties of Multifunctional Oxide Thin Films Despostied by Ink-jet Printing
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ink-jet printing offers an ideal answer to the emerging trends and demands of depositing at ambient temperatures picoliter droplets of oxide solutions into functional thin films and device components with a high degree of pixel precision. It is a direct single-step mask-free patterning technique that enables multi-layer and 3D patterning. This method is fast, simple, easily scalable, precise, inexpensive and cost effective compared to any of other methods available for the realization of the promise of flexible, and/or stretchable electronics of the future on virtually any type of substrate. Because low temperatures are used and no aggressive chemicals are required for ink preparation, ink-jet technique is compatible with a very broad range of functional materials like polymers, proteins and even live cells, which can be used to fabricate inorganic/organic/bio hybrids, bio-sensors and lab-on-chip architectures. After a discussion of the essentials of ink-jet technology, this thesis focuses particularly on the art of designing long term stable inks for fabricating thin films and devices especially oxide functional components for electronics, solar energy conversion, opto-electronics and spintronics. We have investigated three classes of inks: nanoparticle suspension based, surface modified nanoparticles based, and direct precursor solution based. Examples of the films produced using these inks and their functional properties are:

1) In order to obtain magnetite nanoparticles with high magnetic moment and narrow size distribution in suspensions for medical diagnostics, we have developed a rapid mixing technique and produced nanoparticles with moments close to theoretical values (APL 2011 and Nanotechnology 2012). The suspensions produced have been tailored to be stable over a long period of time.

2)In order to design photonic band gaps, suspensions of spherical SiO2 particles were produced by chemical hydrolysis (JAP 2010 and JNP 2011 - not discussed in the thesis).

3) Using suspension inks, (ZnO)1-x(TiO2)x composite films have been printed and used to fabricate dye sensitized solar cells (JMR 2012). The thickness and the composition of the films can be easily tailored in the inkjet printing process. Consequently, the solar cell performance is optimized. We find that adding Ag nanoparticles improves the ‘metal-bridge’ between the TiO2 grains while maintaining the desired porous structure in the films. The photoluminescence spectra show that adding Ag reduces the emission intensity by a factor of two. This indicates that Ag atoms act as traps to capture electrons and inhibit recombination of electron-hole pairs, which is desirable for photo-voltaic applications.

4) To obtain and study room temperature contamination free ferromagnetic spintronic materials, defect induced and Fe doped MgO and ZnO were synthesized ‘in-situ’ by precursor solution technique (preprints). It is found that the origin of magnetism in these materials (APL 2012 and MRS 2012) is intrinsic and probably due to charge transfer hole doping.

5) ITO thin films were fabricated via inkjet printing directly from liquid precursors. The films are highly transparent (transparency >90% both in the visible and IR range, which is rather unique as compared to any other film growth technique) and conductive (resistivity can be ~0.03 Ω•cm). The films have nano-porous structure, which is an added bonus from ink jetting that makes such films applicable for a broad range of applications. One example is in implantable biomedical components and lab-on-chip architectures where high transparency of the well conductive ITO electrodes makes them easily compatible with the use of quantum dots and fluorescent dyes.

In summary, the inkjet patterning technique is incredibly versatile and applicable for a multitude of metal and oxide deposition and patterning. Especially in the case of using acetate solutions as inks (a method demonstrated for the first time by our group), the oxide films can be prepared ‘in-situ’ by direct patterning on the substrate without any prior synthesis stages, and the fabricated films are stoichiometric, uniform and smooth. This technique will most certainly continue to be a versatile tool in industrial manufacturing processes for material deposition in the future, as well as a unique fabrication tool for tailorable functional components and devices.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. x, 98 p.
Keyword
ink-jet printing, oixde, thin film, ink, suspension, dye sensitized solar cell, functional properties, magnetism, diluted magnetic semiconductors
National Category
Condensed Matter Physics Materials Engineering
Identifiers
urn:nbn:se:kth:diva-102021 (URN)978-91-7501-477-7 (ISBN)
Public defence
2012-09-25, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Vinnova
Note

QC 20120907

Available from: 2012-09-07 Created: 2012-09-06 Last updated: 2012-09-07Bibliographically approved

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