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  • 1.
    Afrasiabi, Roodabeh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Jokilaakso, Nima
    KTH, School of Biotechnology (BIO), Protein Technology.
    Schmidt, Torsten
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Björk, P.
    Eriksson Karlström, Amelie
    KTH, School of Biotechnology (BIO), Protein Technology.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Effect of microwave-assisted silanization on sensing properties of silicon nanoribbon FETs2015In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 209, p. 586-595Article in journal (Refereed)
    Abstract [en]

    An important concern with using silicon nanoribbon field-effect transistors (SiNR FET) for ion-sensing is the pH-response of the gate oxide surface. Depending on the application of the FET sensor, this response has to be chemically manipulated. Thus in silicon oxide-gated pH-sensors with integrated sensor and reference FETS, a surface with high pH-sensitivity, compared to the bare gate oxide, is required in the sensor FETs (SEFET), whereas in the reference FETs (REFET) the surface has to be relatively pH-insensitive. In order to control the sensitivity and chemistry of the oxide surface of the nanoribbons, a silanization reagent with a functional group is often self-assembled on the SiNR surface. Choice of a silanization reaction that results in a self-assembled layer on a silicon oxide surface has been studied extensively over the past decades. However, the effect of various self-assembled layers such as monolayers or mixed layers on the electrical response of SiNR FETs in aqueous solution needs to be exploited further, especially for future integrated SEFET/REFET systems. In this work, we have performed a comprehensive study on 3-aminopropyltriethoxysilane (APTES) silanization of silicon oxide surfaces using microwave (MW) heating as a new biocompatible route to conventional methods. A set of complementary surface characterization techniques (ellipsometry, AFM and ATR-FTIR) was used to analyze the properties of the APTES layer deposited on the silicon surface. We have found that a uniform monolayer can be achieved within 10 min by heating the silanization solution to 75 degrees C using MW heating. Furthermore, electrical measurements suggest that little change in device performance is observed after exposure to MW irradiation. Real-time pH measurements indicate that a uniform APTES monolayer not only reduces the pH sensitivity of SiNR FET by passivating the surface silanol groups, but also makes the device less sensitive to cation concentration in the background electrolyte. Our silanization route proves promising for future chemical surface modification of on-chip REFETs.

  • 2.
    Afrasiabi, Roodabeh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Jokilaakso, Nima
    KTH, School of Biotechnology (BIO), Protein Technology.
    Schmidt, Torsten
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Eriksson Karlström, Amelie
    KTH, School of Biotechnology (BIO), Protein Technology.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Microwave-assisted silanization of SiNW-FET: characterization and effect on sensing propertiesManuscript (preprint) (Other academic)
  • 3.
    Afrasiabi, Roodabeh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Söderberg, Lovisa M.
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
    Jönsson, Håkan
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
    Björk, Per
    Acreo Swedish ICT AB, SE-164 40 Kista, Sweden.
    Svahn Andersson, Helene
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Integration of a Droplet-Based Microfluidic System and Silicon Nanoribbon FET Sensor2016In: Micromachines, ISSN 2072-666X, E-ISSN 2072-666X, Vol. 7, no 8Article in journal (Refereed)
    Abstract [en]

    We present a novel microfluidic system that integrates droplet microfluidics with a silicon nanoribbon field-effect transistor (SiNR FET), and utilize this integrated system to sense differences in pH. The device allows for selective droplet transfer to a continuous water phase, actuated by dielectrophoresis, and subsequent detection of the pH level in the retrieved droplets by SiNR FETs on an electrical sensor chip. The integrated microfluidic system demonstrates a label-free detection method for droplet microfluidics, presenting an alternative to optical fluorescence detection. In this work, we were able to differentiate between droplet trains of one pH-unit difference. The pH-based detection method in our integrated system has the potential to be utilized in the detection of biochemical reactions that induce a pH-shift in the droplets.

  • 4.
    Badel, Xavier
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Domeij, Martin
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Doping of electrochemically etched pore arrays in n-type silicon: processing and electrical characterization2005In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 152, no 4, p. G252-G258Article in journal (Refereed)
    Abstract [en]

    Silicon p-n diodes formed in the walls of deep pores have been electrically characterized. The pores were electrochemically etched in low-doped n-type silicon substrates, and the entire pore array was doped p(+) by boron diffusion at 1050 degrees C. Two different process flows were investigated to disconnect the p(+) layers from one pore to another. The first consists of removing a few micrometers of silicon at the top of the sample using reactive ion etching after diffusion while the second enables the prevention of doping at the top of the pore walls with an oxide, acting as a barrier during diffusion. Current-voltage and capacitance-voltage characteristics of p-n junctions are presented and related parameters, such as the serial resistance and the ideality factor are discussed. The results show good rectifying behavior of the diodes with a reverse current about four to five decades smaller than the forward current. Measurements with two pores connected in a transistor-like configuration (p(+)/n(-)/p(+)), were also performed. Device simulations were used to examine the device behavior. Finally, our results demonstrate that pores could work as individual detector pixels for moderate reverse voltages, suitable for radiation imaging applications.

  • 5.
    Badel, Xavier
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Galeckas, Augustinas
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kleimann, P.
    LENAC, Université Claude Bernard Lyon-I, Villeurbanne.
    Fröjdh, C.
    Mitthögskolan, Department of Electronics.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Improvement of an X-ray imaging detector based on a scintillating guides screen2002In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 487, no 1-2, p. 129-135Article in journal (Refereed)
    Abstract [en]

    An X-ray imaging detector has been developed for dental applications. The principle of this detector is based on application of a silicon charge coupled device covered by a scintillating wave-guide screen. Previous studies of such a detector showed promising results concerning the spatial resolution but low performance in terms of signal to noise ratio (SNR) and sensitivity. Recent results confirm the wave-guiding properties of the matrix and show improvement of the detector in terms of response uniformity, sensitivity and SNR. The present study is focussed on the fabrication of the scintillating screen where the principal idea is to fill a matrix of Si pores with a CsI scintillator. The photoluminescence technique was used to prove the wave-guiding property of the matrix and to inspect the filling uniformity of the pores. The final detector was characterized by X-ray evaluation in terms of spatial resolution, light output and SNR. A sensor with a spatial resolution of 9 LP/mm and a SNR over 50 has been achieved using a standard dental X-ray source and doses in the order of those used at the moment by dentists (around 25 mR).

  • 6.
    Badel, Xavier
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kumar, R. T. R.
    Atomic Physics Division, Stockholm University.
    Kleinmann, P.
    LENAC, Univ. Claude Bernard Lyon-I, Villeurbanne.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Formation of ordered pore arrays at the nanoscale by electrochemical etching of n-type silicon2004In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 36, no 1/3, p. 245-254Article in journal (Refereed)
    Abstract [en]

    Electrochemical etching has been studied to structure n-type silicon substrates at the nanoscale. In this work, well-ordered pore arrays with diameters in the range of 150-500 nm and depths up to 50 mum have been fabricated. The pores were successfully formed by anodic etching in (100)oriented n-type silicon wafers of low-resistivity, typically 1 Omegacm, using aqueous hydrofluoric acid solutions. The lithographic step was performed in a thermally grown oxide using a stepper and dry oxide etching technique. Two types of oxide openings and pitch sizes were tested. The smallest oxide opening realised at this stage was 0.5 mum for a pitch of 1 mum. Stable pore formation was obtained and the smallest pore size obtained was about 200 nm with an aspect ratio close to 100.

  • 7.
    Badel, Xavier
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Electrochemical etching of n-type silicon based on carrier injection from a back side p-n junction2003In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 6, no 6, p. C79-C81Article in journal (Refereed)
    Abstract [en]

    A technique for electrochemical etching of n-type silicon in aqueous hydrofluoric acid is presented. This technique differs from photoelectrochemical etching because the holes (positive carriers) needed for the dissolution reaction to occur, are not photogenerated. The principle developed here is to inject these positive carriers using a p-n junction under forward bias formed at the back side of the sample. Drift-diffusion of holes through the wafer thickness allows a chemical dissolution reaction at the interface with the electrolyte. To enable holes diffusing through the wafer the minority carrier lifetime must be sufficiently high making the technique well adapted for high resistivity silicon. However, extension to low resistivity wafers has been achieved. Results show the possibility of forming pore arrays and diverse 3D structures.

  • 8.
    Badel, Xavier
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Janson, M. S.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Österman, J.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Formation of pn junctions in deep silicon pores for X-ray imaging detector applications2003In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 509, no 1-3, p. 96-101Article in journal (Refereed)
    Abstract [en]

    The formation of pn junctions in deep silicon pores has been studied for a new concept of X-ray imaging detectors. The sensitive part of the device is an array of CsI(Tl) columns formed by filling a silicon matrix of pores having pn junctions in their walls. Under X-ray illumination, the CsI(TI) scintillator emits photons that are collected by the pn junctions. Relatively high signal collection efficiency is expected. However, the formation of pn junctions inside pore walls represents a challenging step in the detector fabrication. In this work pore matrices were fabricated in n-type silicon by deep reactive ion etching and by photo-electrochemical etching. The pn junctions were formed either by boron diffusion or deposition of boron doped poly-silicon. Various techniques were used to analyze the transverse depth profiles of boron atoms at different pore depths. The study shows successful results for pn-junctions formed both by diffusion and by poly-silicon deposition.

  • 9.
    Badel, Xavier
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kleimann, P
    Norlin, B
    Koskiahde, E
    Valpas, K
    Nenonen, S.
    Petersson, Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Frojdh, C
    Metallized and oxidized silicon macropore arrays filled with a scintillator for CCD-based X-ray imaging detectors2004In: 2003 IEEE NUCLEAR SCIENCE SYMPOSIUM, CONFERENCE RECORD, VOLS 1-5, 2004, p. 1006-1010Conference paper (Refereed)
    Abstract [en]

    Silicon Charge Coupled Devices (CCD) covered with a scintillating film are now available on the market for use in digital medical imaging. However, these devices could still be improved in terms of sensitivity and especially spatial resolution by coating the CCD with an array of scintillating waveguides. In this work-, we fabricated such waveguides by first etching pores in silicon, then performing metallization or oxidation of the pore walls and finally filling the pores with CsI(TI). The resulting structures were observed using SEM and tested under X-ray exposure. The detector performances were also compared with simulations, indicating that the optimal pore depth for metallized macropore arrays is about 80 mum while it is around 350 mum for oxidized ones. This result, together with the roughness of the metal coating, explains why lower performances were measured experimentally with the metallized macropores. Indeed, our macropore arrays had depths in the range of 210-390 mum, which is favorable to oxidized structures.

  • 10.
    Badel, Xavier
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kleimann, P.
    LENAC, Univ.́ Claude Bernard Lyon-I, Villeurbanne.
    Norlin, B.
    Department of Information Technology, Mid-Sweden University, Sundsvall.
    Koskiahde, E.
    Metorex International Oy, Espoo.
    Valpas, K.
    Metorex International Oy, Espoo.
    Nenonen, S.
    Metorex International Oy, Espoo.
    Petersson, Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fröjdh, C.
    Department of Information Technology, Mid-Sweden University, Sundsvall.
    Metallized and oxidized silicon macropore arrays filled with a scintillator for CCD-based X-ray imaging detectors2004In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 51, no 3, p. 1001-1005Article in journal (Refereed)
    Abstract [en]

    Silicon charge-coupled devices (CCDs) covered with a scintillating film are now available on the market for use in digital medical imaging. However, these devices could still be improved in terms of sensitivity and especially spatial resolution by coating the CCD with an array of scintillating waveguides. In this paper, such waveguides were fabricated by first etching pores in silicon, then performing metallization or oxidation of the pore walls and finally filling the pores with CsI(TI). The resulting structures were observed using scanning electron microscopy and tested under X-ray exposure. Theoretical efficiencies of macropore arrays filled with CsI(TI) were also calculated, indicating that the optimal pore depth for metallized macropore arrays is about 80 mum while it is around 350 mum for oxidized ones. This result, together with the roughness of the metal coating, explains why lower SNR values were measured with the metallized macropores. Indeed, the macropore arrays had depths in the range of 210-390 mum, which is favorable to oxidized structures.

  • 11.
    Badel, Xavier
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Norlin, B.
    Department of Information Technology and Media, Mid-Sweden University, Sundsvall.
    Kleimann, P.
    LENAC, Université Claude Bernard Lyon-I, Villeurbanne.
    Williams, L.
    Applied Scintillation Technology, Harlow.
    Moody, S. J.
    Applied Scintillation Technology, Harlow.
    Tyrell, G. C.
    Applied Scintillation Technology, Harlow.
    Fröjdh, C.
    Department of Information Technology and Media, Mid-Sweden University, Sundsvall.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Performance of scintillating waveguides for CCD-based X-ray detectors2006In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 53, no 1, p. 3-8Article in journal (Refereed)
    Abstract [en]

    Scintillating films are usually used to improve the sensitivity of CCD-based X-ray imaging detectors. For an optimal spatial resolution and detection efficiency, a tradeoff has to be made on the film thickness. However, these scintillating layers can also be structured to provide a pixellated screen. In this paper, the study of CsI(TI)-filled pore arrays is reported. The pores are first etched in silicon, then oxidized and finally filled with CsI(TI) to form scintillating waveguides. The dependence of the detector sensitivity on pore depth, varied from 40 to 400 mu m here, follows rather well theoretical predictions. Most of the detectors produced in this work have a detective quantum efficiency of the incoming X-ray photons of about 25%. However, one detector shows that higher efficiency can be achieved approaching almost the theoretical limit set by Poisson statistics of the incoming X-rays. Thus, we conclude that it is possible to fabricate scintillating waveguides with almost ideal performance. Imaging capabilities of the detectors are demonstrated.

  • 12.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. University of Amsterdam, Netherlands .
    Qejvanaj, Fatjon
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Gregorkiewicz, Tom
    University of Amsterdam, Netherlands .
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Temporal correlation of blinking events in CdSe/ZnS and Si/SiO2 nanocrystals2014In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 453, p. 63-67Article in journal (Refereed)
    Abstract [en]

    Well passivated single Si/SiO2 nanoparticles obey mono exponential blinking statistics, whereas CdSe/ZnS quantum dots follow an apparent (truncated) power-law. Log-normal distributions are found to describe the interval length histograms at least as well as power-laws, while at the same time being more physically feasible and significantly easing the determination of the exponential cutoff in the ON-time distribution. The correlation of an ON- (OFF-)interval with its temporally displaced ON (OFF) neighbors, as well as that of intermixed intervals (ON with OFF and OFF with ON neighbors) has been studied. As expected from purely random processes, the correlation coefficients for events in silicon nanocrystals equal zero, whereas positive correlations between the pure and negative correlations between the mixed states in CdSe quantum dots hint at a switching process between two distinct blinking regimes that are slower than the blinking itself.

  • 13.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Qejvanaj, Fatjon
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Blinking Statistics and Excitation-Dependent Luminescence Yield in Si and CdSe Nanocrystals2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 4, p. 2202-2208Article in journal (Refereed)
    Abstract [en]

    ON-OFF intermittency or blinking is a phenomenon observed in single quantum emitters, which reduces their overall light emission. Even though it seems to be a fundamental property of quantum dots (QDs), substantial differences can be found in the blinking statistics of different nanocrystals. This work compares the blinking of numerous single, oxide-capped Si nanocrystals with that of CdSe/ZnS core-shell nanocrystals, measured under the same conditions in the same experimental system and over a broad range of excitation power densities. We find that ON- and OFF-times can be described by exponential statistics in Si QDs, as opposed to power-law statistics for the CdSe nanocrystals. The type of blinking (power-law or monoexponential) does not depend on excitation but seems to be an intrinsic property of the material system. Upon increasing excitation power, the duty cycle of Si quantum dots remains constant, whereas it decreases for CdSe nanocrystals, which is readily explained by blinking statistics. Both ON-OFF and OFF-ON transitions can be regarded as light-induced in Si/SiO2 QDs, while the OFF-ON transition in CdSe/ZnS nanocrystals is not stimulated by photons. The differences in blinking behavior in these systems will be discussed.

  • 14.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Sangghaleh, Fatemeh
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Fabricating single silicon quantum rods for repeatable single dot photoluminescence measurements2011In: Physica Status Solidi A-applications and materials science, ISSN 1862-6319, Vol. 208, no 3, p. 631-634Article in journal (Refereed)
    Abstract [en]

    A fabrication method for a matrix pattern of laterally separated silicon quantum rods was developed, consisting of a three-step recipe utilizing electron beam lithography (EBL), reactive ion etching (RIE), and oxidation. Photoluminescence (PL) measurements -images, spectra, and blinking-verified that the presented method results in a high number of luminescing single silicon quantum rods in well defined positions on the sample. These are suitable for single dot spectroscopy and repeatable measurements, even using different measurement methods and instruments. [GRAPHICS] Colorized scanning electron microscope images of undulating silicon nanowalls for controlled single quantum rod fabrication.

  • 15.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Valenta, Jan
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Controlled fabrication of individual silicon quantum rods yielding high intensity, polarized light emission2009In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 20, no 50, p. 1-5Article in journal (Refereed)
    Abstract [en]

    Elongated silicon quantum dots (also referred to as rods) were fabricated using a lithographic process which reliably yields sufficient numbers of emitters. These quantum rods are perfectly aligned and the vast majority are spatially separated well enough to enable single-dot spectroscopy. Not only do they exhibit extraordinarily high linear polarization with respect to both absorption and emission, but the silicon rods also appear to luminesce much more brightly than their spherical counterparts. Significantly increased quantum efficiency and almost unity degree of linear polarization render these quantum rods perfect candidates for numerous applications.

  • 16.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Valenta, Jan
    Sangghaleh, Fatemeh
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Blinking Statistics of Silicon Quantum Dots2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 12, p. 5574-5580Article in journal (Refereed)
    Abstract [en]

    The blinking statistics of numerous single silicon quantum dots fabricated by electron-beam lithography, plasma etching, and oxidation have been analyzed. Purely exponential on- and off-time distributions were found consistent with the absence of statistical aging. This is in contrast to blinking reports in the literature where power-law distributions prevail as well as observations of statistical aging in nanocrystal ensembles. A linear increase of the switching frequency with excitation power density indicates a domination of single-photon absorption processes, possibly through a direct transfer of charges to trap states without the need for a bimolecular Auger mechanism. Photoluminescence saturation with increasing excitation is not observed; however, there is a threshold in excitation (coinciding with a mean occupation of one exciton per nanocrystal) where a change from linear to square-root increase occurs. Finally, the statistics of blinking of single quantum dots in terms of average on-time, blinking frequency and blinking amplitude reveal large variations (several orders) without any significant correlation demonstrating the individual microscopic character of each quantum dot.

  • 17.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Valenta, Jan
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Mitsuishi, Kazutaka
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Transition from silicon nanowires to isolated quantum dots: Optical and structural evolution2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 4, p. 045404-Article in journal (Refereed)
    Abstract [en]

    The evolution of the structural and optical properties of a silicon core in oxidized nanowalls is investigated as a function of oxidation time. The same individual nanostructures are characterized after every oxidation step in a scanning electron microscope and by low-temperature photoluminescence, while a representative sample is also imaged in a transmission electron microscope. Analysis of a large number of recorded single-dot spectra and micrographs allows to identify delocalized and localized exciton emission from a nanowire as well as confined exciton emission of a nanocrystal. It is shown how structural transitions from one-to zero-dimensional confinement affect single-nanostructure optical fingerprints.

  • 18.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Valenta, Jan
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Mitsushi, Kazutaka
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Transition fromsilicon nanowires to isolated quantum dots: Optical and structural evolution2009Manuscript (preprint) (Other (popular science, discussion, etc.))
  • 19.
    Cavallaro, Sara
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Horak, Josef
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Protein Engineering.
    Haag, Petra
    Karolinska Inst, Karolinska Univ Hosp, Dept Oncol Pathol, Theme Canc,Patient Area,Pelvis, Akad Straket 1, S-17164 Stockholm, Sweden..
    Gupta, Dhanu
    Karolinska Inst, Clin Res Ctr, Dept Lab Med, S-17177 Stockholm, Sweden.;Evox Therapeut Ltd, Oxford OX4 4HG, England..
    Stiller, Christiane
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Protein Engineering.
    Sahu, Siddharth S.
    Uppsala Univ, Angstrom Lab, Dept Solid State Elect, Box 534, SE-75121 Uppsala, Sweden..
    Gorgens, Andre
    Karolinska Inst, Clin Res Ctr, Dept Lab Med, S-17177 Stockholm, Sweden.;Evox Therapeut Ltd, Oxford OX4 4HG, England.;Univ Duisburg Essen, Univ Hosp Essen, Inst Transfus Med, D-45122 Essen, Germany..
    Gatty, Hithesh K.
    Uppsala Univ, Angstrom Lab, Dept Solid State Elect, Box 534, SE-75121 Uppsala, Sweden..
    Viktorsson, Kristina
    Karolinska Inst, Dept Oncol Pathol, Karolinska Univ Hosp, Theme Canc,Patient Area,Head & Neck Lung & Skin, Akad Straket 1, S-17164 Solna, Sweden..
    El Andaloussi, Samir
    Karolinska Inst, Clin Res Ctr, Dept Lab Med, S-17177 Stockholm, Sweden.;Evox Therapeut Ltd, Oxford OX4 4HG, England..
    Lewensohn, Rolf
    Karolinska Inst, Dept Oncol Pathol, Karolinska Univ Hosp, Theme Canc,Patient Area,Head & Neck Lung & Skin, Akad Straket 1, S-17164 Solna, Sweden..
    Eriksson Karlström, Amelie
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Protein Engineering. KTH Royal Inst Technol, Sch Engn Sci Chem Biotechnol & Hlth, Dept Prot Sci, AlbalNova Univ Ctr, S-10691 Stockholm, Sweden..
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics. KTH Royal Inst Technol, Sch Engn Sci, Dept Appl Phys, S-16440 Kista, Sweden..
    Dev, Apurba
    Uppsala Univ, Angstrom Lab, Dept Solid State Elect, Box 534, SE-75121 Uppsala, Sweden..
    Label-Free Surface Protein Profiling of Extracellular Vesicles by an Electrokinetic Sensor2019In: ACS SENSORS, ISSN 2379-3694, Vol. 4, no 5, p. 1399-1408Article in journal (Refereed)
    Abstract [en]

    Small extracellular vesicles (sEVs) generated from the endolysosomal system, often referred to as exosomes, have attracted interest as a suitable biomarker for cancer diagnostics, as they carry valuable biological information and reflect their cells of origin. Herein, we propose a simple and inexpensive electrical method for label-free detection and profiling of sEVs in the size range of exosomes. The detection method is based on the electrokinetic principle, where the change in the streaming current is monitored as the surface markers of the sEVs interact with the affinity reagents immobilized on the inner surface of a silica microcapillary. As a proof-of-concept, we detected sEVs derived from the non-small-cell lung cancer (NSCLC) cell line H1975 for a set of representative surface markers, such as epidermal growth factor receptor (EGFR), CD9, and CD63. The detection sensitivity was estimated to be similar to 175000 sEVs, which represents a sensor surface coverage of only 0.04%. We further validated the ability of the sensor to measure the expression level of a membrane protein by using sEVs displaying artificially altered expressions of EGFR and CD63, which were derived from NSCLC and human embryonic kidney (HEK) 293T cells, respectively. The analysis revealed that the changes in EGFR and CD63 expressions in sEVs can be detected with a sensitivity in the order of 10% and 3%, respectively, of their parental cell expressions. The method can be easily parallelized and combined with existing microfluidic-based EV isolation technologies, allowing for rapid detection and monitoring of sEVs for cancer diagnosis.

  • 20. Chen, Si
    et al.
    Nyholm, Leif
    Jokilaakso, Nima
    KTH, School of Biotechnology (BIO), Molecular Biotechnology.
    Karlström, Amelie Eriksson
    KTH, School of Biotechnology (BIO), Molecular Biotechnology.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Smith, Ulf
    Zhang, Shi-Li
    Current Instability for Silicon Nanowire Field-Effect Sensors Operating in Electrolyte with Platinum Gate Electrodes2011In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 14, no 7, p. J34-J37Article in journal (Refereed)
    Abstract [en]

    Current instability is observed for silicon nanowire field-effect transistors operating in electrolytes with Pt gate electrodes. A comparative study involving an Ag/AgCl-reference gate electrode reveals that the effect results from a drift in the potential at the Pt-electrode/electrolyte interface. In a phosphate buffer saline of pH 7.4, the stabilization of the potential of the Pt electrode was found to require approximately 1000 s. A concurrent potential drift, with a comparable time constant, occurring at the electrolyte/oxidized-nanowire interface rendered a complex device current response which complicated the interpretation of the results.

  • 21.
    Chulapakorn, T.
    et al.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Ottosson, M.
    Uppsala Univ, Dept Chem, Angstrom Lab, Inorgan Chem, POB 538, SE-75121 Uppsala, Sweden..
    Primetzhofer, D.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    Moro, M. V.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT).
    Luminescence of silicon nanoparticles from oxygen implanted silicon2018In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 86, p. 18-22Article in journal (Refereed)
    Abstract [en]

    Oxygen with a kinetic energy of 20 keV is implanted in a silicon wafer (100) at different fluences, followed by post-implantation thermal annealing (PIA) performed at temperatures ranging from 1000 to 1200 degrees C, in order to form luminescent silicon nanoparticles (SiNPs) and also to reduce the damage induced by the implantation. As a result of this procedure, a surface SiOx layer (with 0 < x < 2) with embedded crystalline Si nanoparticles has been created. The samples yield similar luminescence in terms of peak wavelength, lifetime, and absorption as recorded from SiNPs obtained by the more conventional method of implanting silicon into silicon dioxide. The oxygen implantation profile is characterized by elastic recoil detection (ERD) technique to obtain the excess concentration of Si in a presumed SiO2 environment. The physical structure of the implanted Si wafer is examined by grazing incidence X-ray diffraction (GIXRD). Photoluminescence (PL) techniques, including PL spectroscopy, time-resolved PL (TRPL), and photoluminescence excitation (PLE) spectroscopy are carried out in order to identify the PL origin. The results show that luminescent SiNPs are formed in a Si sample implanted by oxygen with a fluence of 2 x 10(17) atoms cm(-2) and PIA at 1000 degrees C. These SiNPs have a broad size range of 6-24 nm, as evaluated from the GIXRD result. Samples implanted at a lower fluence and/or annealed at higher temperature show only weak defect-related PL. With further optimization of the SiNP luminescence, the method may offer a simple route for integration of luminescent Si in mainstream semiconductor fabrication.

  • 22. Chulapakorn, T
    et al.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Suvanam, Sethu Saveda
    KTH, School of Information and Communication Technology (ICT).
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Primetzhofer, D
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT).
    Influence of swift heavy ion irradiation on the photoluminescence of Si-nanoparticles and defects in SiO22017In: Nanotechnology, Vol. 28, article id 375606Article in journal (Refereed)
    Abstract [en]

    The influence of swift heavy ion (SHI) irradiation on the photoluminescence (PL) of silicon nanoparticles (SiNPs) and defects in SiO2-film is investigated. SiNPs were formed by implantation of 70 keV Si+ and subsequent thermal annealing to produce optically active SiNPs and to remove implantation-induced defects. Seven different ion species with energy between 3-36 MeV and fluence from 10(11)-10(14) cm(-2) were employed for irradiation of the implanted samples prior to the thermal annealing. Induced changes in defect and SiNP PL were characterized and correlated with the specific energy loss of the employed SHIs. We find that SHI irradiation, performed before the thermal annealing process, affects both defect and SiNP PL. The change of defect and SiNP PL due to SHI irradiation is found to show a threshold-like behaviour with respect to the electronic stopping power, where a decrease in defect PL and an anticorrelated increase in SiNP PL after the subsequent thermal annealing are observed for electronic stopping exceeding 3-5 keV nm(-1). PL intensities are also compared as a function of total energy deposition and nuclear energy loss. The observed effects can be explained by ion track formation as well as a different type of annealing mechanisms active for SHI irradiation compared to the thermal annealing.

  • 23. Chulapakorn, T.
    et al.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Suvanam, Sethu Saveda
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Linnros, Jan T.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Primetzhofer, D.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    MeV ion irradiation effects on the luminescence properties of Si-implanted SiO2-thin films2016In: Physica Status Solidi (C) Current Topics in Solid State Physics, ISSN 1862-6351, Vol. 13, no 10-12, p. 921-926Article in journal (Refereed)
    Abstract [en]

    The effects of MeV heavy ion irradiation at varying fluence and flux on excess Si, introduced in SiO2 by keV ion implantation, are investigated by photoluminescence (PL). From the PL peak wavelength (λ) and decay lifetime (τ), two PL sources are distinguished: i) quasi-direct recombination of excitons of Si-nanoparticles (SiNPs), appearing after thermal annealing (λ &gt; 720 nm, τ ∼ μs), and ii) fast-decay PL, possibly due to oxide-related defects (λ ∼ 575-690 nm, τ ∼ ns). The fast-decay PL (ii) observed before and after ion irradiation is induced by ion implantation. It is found that this fast-decay luminescence decreases for higher irradiation fluence of MeV heavy ions. After thermal annealing (forming SiNPs), the SiNP PL is reduced for samples irradiated by MeV heavy ions but found to stabilize at higher level for higher irradiation flux; the (ii) band vanishes as a result of annealing. The results are discussed in terms of the influence of electronic and nuclear stopping powers.

  • 24. Chulapakorn, T.
    et al.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Suvanam, Sethu Saveda
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Wolff, M.
    Primetzhofer, D.
    Possnert, G.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits. Uppsala University, Sweden.
    Si-nanoparticle synthesis using ion implantation and MeV ion irradiation2015In: Physica Status Solidi (C) Current Topics in Solid State Physics, ISSN 1862-6351Article in journal (Refereed)
    Abstract [en]

    A dielectric matrix with embedded Si-nanoparticles may show strong luminescence depending on nanoparticles size, surface properties, Si-excess concentration and matrix type. Ion implantation of Si ions with energies of a few tens to hundreds of keV in a SiO<inf>2</inf> matrix followed by thermal annealing was identified as a powerful method to form such nanoparticles. The aim of the present work is to optimize the synthesis of Si-nanoparticles produced by ion implantation in SiO<inf>2</inf> by employing MeV ion irradiation as an additional annealing process. The luminescence properties are measured by spectrally resolved photoluminescence including PL lifetime measurement, while X-ray reflectometry, atomic force microscopy and ion beam analysis are used to characterize the nanoparticle formation process. The results show that the samples implanted at 20%-Si excess atomic concentration display the highest luminescence and that irradiation of 36 MeV 127I ions affects the luminosity in terms of wavelength and intensity. It is also demonstrated that the nanoparticle luminescence lifetime decreases as a function of irradiation fluence.

  • 25.
    Dev, Apurba
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Uppsala University, Sweden.
    Horak, J.
    Kaiser, A.
    Yuan, X.
    Perols, A.
    Björk, P.
    Karlström, A. E.
    Kleimann, P.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Electrokinetic effect for molecular recognition: A label-free approach for real-time biosensing2016In: Biosensors & bioelectronics, ISSN 0956-5663, E-ISSN 1873-4235, Vol. 82, p. 55-63Article in journal (Refereed)
    Abstract [en]

    We present a simple and inexpensive method for label-free detection of biomolecules. The method monitors the changes in streaming current in a fused silica capillary as target biomolecules bind to immobilized receptors on the inner surface of the capillary. To validate the concept, we show detection and time response of different protein-ligand and protein-protein systems: biotin-avidin and biotin-streptavidin, barstar-dibarnase and Z domain-immunoglobulin G (IgG). We show that specific binding of these biomolecules can be reliably monitored using a very simple setup. Using sequential injections of various proteins at a diverse concentration range and as well as diluted human serum we further investigate the capacity of the proposed technique to perform specific target detection from a complex sample. We also investigate the time for the signal to reach equilibrium and its dependence on analyte concentration and demonstrate that the current setup can be used to detect biomolecules at a concentration as low as 100 pM without requiring any advanced device fabrication procedures. Finally, an analytical model based on diffusion theory has been presented to explain the dependence of the saturation time on the analyte concentration and capillary dimensions and how reducing length and inner diameter of the capillary is predicted to give faster detection and in practice also lower limit of detection. © 2016 Elsevier B.V.

  • 26.
    Domeij, Martin
    et al.
    KTH, Superseded Departments, Electronics.
    Breitholtz, Bo
    KTH, Superseded Departments, Electronics.
    Hillkirk, Leonardo
    KTH, Superseded Departments, Electronics.
    Linnros, Jan
    KTH, Superseded Departments, Electronics.
    Östling, Mikael
    KTH, Superseded Departments, Electronics.
    Dynamic avalanche in 3.3-kV Si power diodes1999In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 46, no 4, p. 781-786Article in journal (Refereed)
    Abstract [en]

    Measurements of the safe reverse recovery limit were performed for 3.3-kV Si power diodes using a novel optical experimental technique. In this experiment, influence of the junction termination is effectively eliminated by optical generation of a laterally-localized carrier plasma. The turn-off failures observed in measurements at two temperatures showed no temperature dependence and could not be reproduced in ordinary one-dimensional (1-D) or two-dimensional (2-D) device simulations. To simulate the stability of the current density toward current filamentation, two 1-D diodes with an area ratio 1:19 and a 10% difference in initial carrier plasma level, were simulated in parallel. This resulted in a strongly inhomogeneous current distribution, and a rapid reverse voltage fall resembling the measured turn-off failures. Inhomogeneous current distribution in these simulations appears as the current decay ceases due to impact ionization, in qualitative agreement with a current instability condition proposed by Wachutka [1].

  • 27.
    Domeij, Martin
    et al.
    KTH, Superseded Departments, Electronics.
    Breitholtz, Bo
    KTH, Superseded Departments, Electronics.
    Linnros, Jan
    KTH, Superseded Departments, Electronics.
    Ostling, Mikael
    KTH, Superseded Departments, Electronics.
    Avalanche injection in high voltage Si PiN diodes1997In: Physica scripta. T, ISSN 0281-1847, Vol. T69, p. 134-137Article in journal (Refereed)
    Abstract [en]

    An experimental technique using optical excitation by a YAG laser pulse for studying avalanche injection in power devices is demonstrated This technique enables the creation of high uniform excess carrier concentrations in an optically defined device volume, involving very little heating. A method for determining the onset of avalanche multiplication, by studying the time integral of the reverse recovery current, is proposed. A PiN diode is observed to turn off from avalanching at a dissipated power density of more than 200 kW/cm(2).

  • 28.
    Domeij, Martin
    et al.
    KTH, Superseded Departments, Electronics.
    Breitholtz, Bo
    KTH, Superseded Departments, Electronics.
    Linnros, Jan
    KTH, Superseded Departments, Electronics.
    Östling, Mikael
    KTH, Superseded Departments, Electronics.
    Avalanche Injection in High Voltage Si P-i-N Diodes Measurements and Device Simulations1997In: ISPSD '97: Proceedings of the International Symposium on Power Semiconductor Devices and ICs, 1997, p. 125-Conference paper (Other academic)
  • 29.
    Domeij, Martin
    et al.
    KTH, Superseded Departments, Electronics.
    Breitholtz, Bo
    KTH, Superseded Departments, Electronics.
    Linnros, Jan
    KTH, Superseded Departments, Electronics.
    Östling, Mikael
    KTH, Superseded Departments, Electronics.
    Reverse Recovery and Avalance Injection in High Voltage SiC PIN Diodes1998In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 264-268, p. 1041-Article in journal (Other academic)
  • 30.
    Elfström, Niklas
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Eriksson Karlström, Amelie
    KTH, School of Biotechnology (BIO).
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Silicon Nanoribbons for Electrical Detection of Biomolecules2008In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, no 3, p. 945-949Article in journal (Refereed)
    Abstract [en]

    Direct electrical detection of biomolecules at high sensitivity hat recently been demonstrated using semiconductor nanowires. Here we demonstrate that semiconductor nanoribbons, in this case, a thin sheet of silicon on an oxidized silicon substrate, can approach the same sensitivity extending below the picomolar concentration regime in the biotin/streptavidin case. This corresponds to less than similar to 20 analyte molecules bound to receptors on the nanoribbon surface. The micrometer-size lateral dimensions of the nanoribbon enable optical lithography to be used, resulting in a simple and high-yield fabrication process. Electrical characterization of the nanoribbons is complemented by computer simulations showing enhanced sensitivity for thin ribbons. Finally, we demonstrate that the device can be operated both in inversion as well as in accumulation mode and the measured differences in detection sensitivity are explained in terms of the distance between the channel and the receptor coated surface with respect to the Debye screening length. The nanoribbon approach opens up for large scale CMOS fabrication of highly sensitive biomolecule sensor chips for potential use in medicine and biotechnology.

  • 31.
    Elfström, Niklas
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Juhasz, Robert
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Engfeldt, Torun
    KTH, School of Biotechnology (BIO).
    Eriksson Karlström, Amelie
    KTH, School of Biotechnology (BIO).
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Surface Charge Sensitivity of Silicon Nanowires: Size Dependence2007In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 7, no 9, p. 2608-2612Article in journal (Refereed)
    Abstract [en]

    Silicon nanowires of different widths were fabricated in silicon on insulator (SOI) material using conventional process technology combined with electron-beam lithography. The aim was to analyze the size dependence of the sensitivity of such nanowires for biomolecule detection and for other sensor applications. Results from electrical characterization of the nanowires show a threshold voltage increasing with decreasing width. When immersed in an acidic buffer solution, smaller nanowires exhibit large conductance changes while larger wires remain unaffected. This behavior is also reflected in detected threshold shifts between buffer solutions of different pH, and we find that nanowires of width > 150 nm are virtually insensitive to the buffer pH. The increased sensitivity for smaller sizes is ascribed to the larger surface/volume ratio for smaller wires exposing the channel to a more effective control by the local environment, similar to a surrounded gate transistor structure. Computer simulations confirm this behavior and show that sensing can be extended even down to the single charge level.

  • 32.
    Elfström, Niklas
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Avalanche breakdown in surface modified silicon nanowires2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 10, p. 103502-1-103502-3Article in journal (Refereed)
    Abstract [en]

    The electrical conductance of semiconductor nanowires can be changed by charges present on the nanowire surface. At high surface charge density, however, the nanowire channel may be quenched leading to a large shift in the I-DS-V-DS characteristics. In this letter, the authors demonstrate that this shift in V-DS is related to an avalanche effect in the nanowire. Silicon nanowires were fabricated in a top-down approach and the nanowire surface charge density was modified through buffer solutions of different pH values. Computer simulations using representative surface charge and interface charge densities clearly reproduce the data and unambiguously demonstrate the avalanche effect.

  • 33.
    Elfström, Niklas
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Biomolecule detection using a silicon nanoribbon: Accumulation mode versus inversion mode2008In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 19, no 23, p. 235201-Article in journal (Refereed)
    Abstract [en]

    Silicon nanoribbons were fabricated using standard optical lithography from silicon on insulator material with top silicon layer thicknesses of 100, 60 and 45 nm. Electrically these work as Schottky-barrier field-effect transistors and, depending on the substrate voltage, electron or hole injection is possible. The current through the nanoribbon is extremely sensitive to charge changes at the oxidized top surface and can be used for biomolecule detection in a liquid. We show that for detection of streptavidin molecules the response is larger in the accumulation mode than in the inversion mode, although not leading to higher detection sensitivity due to increased noise. The effect is attributed to the location in depth of the conducting channel, which for holes is closer to the screened surface charges of the biomolecules. Furthermore, the response increases for decreasing silicon thickness in both the accumulation mode and the inversion mode. The results are verified qualitatively and quantitatively through a two-dimensional simulation model on a cross section along the nanoribbon device.

  • 34.
    Elfström, Niklas
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Sensitivity of silicon nanowires in biosensor applications2008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, no PART 5Article in journal (Refereed)
    Abstract [en]

    A 2-dimensional simulation tool was designed to investigate the threshold voltage behaviour for a silicon nanowire constructed in a top down approach on silicon on insulator (SOI) material. The simulation shows, assuming a positive charge of +1.10(11) cm(-2) between the silicon/silicon dioxide interface and negatively charged surface states on top of the nanowire that the threshold voltage increases with decreasing height of the nanowire.

  • 35. Galeckas, A.
    et al.
    Grivickas, P.
    Grivickas, V.
    Bikbajevas, V.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Temperature dependence of the absorption coefficient in 4H-and 6H-silicon carbide at 355 nm laser pumping wavelength2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 191, no 2, p. 613-620Article in journal (Refereed)
    Abstract [en]

    We report on the absorption coefficient at 355 nm laser wavelength for 4H- and 6H-SiC over a wide temperature range. The measurements were carried out using a depth- and time-resolved free-carrier-absorption technique. The values of the absorption coefficient for the fundamental E perpendicular to

  • 36. Galeckas, A.
    et al.
    Hallén, Anders.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Majdi, S.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Pirouz, P.
    Combined photoluminescence-imaging and deep-level transient spectroscopy of recombination processes at stacking faults in 4H-SiC2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 23Article in journal (Refereed)
    Abstract [en]

    We report on electronic properties of single- and double-layer stacking faults in 4H-SiC and provide an insight into apparent distinctions of recombination-enhanced defect reactions at these faults. Photoluminescence imaging spectroscopy and deep-level transient spectroscopy experiments reveal key constituents of radiative recombination and also provide firm evidence of nonradiative centers at E-V+0.38 eV responsible for recombination-enhanced mobility of silicon-core partial dislocations. A comprehensive energy level model is proposed allowing for a qualitative description of recombination activity at different types of stacking faults and the corresponding bounding partial dislocations.

  • 37. Galeckas, A.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Breitholtz, B.
    Bleichner, H.
    Application of optical emission microscopy for reliability studies in 4H-SiC p(+)/n(-)/n(+) diodes2001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, no 2, p. 980-984Article in journal (Refereed)
    Abstract [en]

    An optical emission microscopy technique with spatial and spectral resolution capabilities is applied for stability studies of 4H-SiC material properties. From the example of a 4H-SiC p(+)/n(-)/n(+) diode imaged at different stages of electrical overstress the mechanism of degrading performance is directly unveiled. We correlate this phenomenon with irreversible structural changes within the active region created by a nonuniform heating related stress. The stress-generated features are interpreted as multiple stacking faults spreading throughout the whole base region and nucleated in the vicinity of built-in defects and process-induced structural deficiencies.

  • 38. Galeckas, A.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Frischholz, M.
    Grivickas, V.
    Optical characterization of excess carrier lifetime and surface recombination in 4H/6H-SiC2001In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 79, no 3, p. 365-367Article in journal (Refereed)
    Abstract [en]

    The high-injection lifetime and surface recombination parameters have been investigated in as-grown 4H and 6H-SiC epilayers subjected to various process treatments. A depth-resolved optical transient absorption technique was utilized to evaluate the influence of film thickness and surface treatment on carrier lifetime. We demonstrate that besides polishing and ion implantation, both natural and thermal oxidation may also result in lifetime reduction due to enhanced surface losses. Moreover, a long-term stability test has revealed a substantial degradation of lifetime characteristics, consistent with a spontaneous surface oxidation and slow relaxation of SiO2/SiC interface states. We show that for common film thickness < 100 mum, the effective lifetime is dominated by surface leakage, which is found, generally, to be higher in 4H compared to 6H-SiC.

  • 39. Galeckas, A.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Lindstedt, M.
    Characterization of carrier lifetime and diffusivity in 4H-SiC using time-resolved imaging spectroscopy of electroluminescence2003In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 102, no 03-jan, p. 304-307Article in journal (Refereed)
    Abstract [en]

    We report on time- and spectrally resolved studies of recombination radiation in 4H-SiC by combining imaging spectroscopy and gated optical emission microscopy techniques. An insight into the basic characteristics of 3D carrier dynamics was attained by combining data of electroluminescence imaged from the backside and from the cross-sectional plane of a forward biased PN structures. We demonstrate the potential and efficiency of this method in mapping minority carrier lifetime and diffusivity parameters and also in locating and analysis of the structural defects in the active area. Finally, a detrimental impact of the intrinsic growth-related and long-term operation-induced defects on the carrier transport properties was directly revealed and quantified.

  • 40. Galeckas, A.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Pirouz, P.
    Recombination-enhanced extension of stacking faults in 4H-SiC p-i-n diodes under forward bias2002In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 81, no 5, p. 883-885Article in journal (Refereed)
    Abstract [en]

    The extension of stacking faults in a forward-biased 4H-SiC PiN diodes by the recombination-enhanced motion of leading partial dislocations has been investigated by the technique of optical emission microscopy. From the temperature dependence of the measured velocity of the partials, an activation energy of 0.27 eV is obtained. Based on this and analysis of the emission spectra, a radiative recombination level of 2.8 eV for the stacking fault, and two energy levels for the partial dislocation, a radiative one at 1.8 eV and a nonradiative at 2.2 eV, have been determined.

  • 41. Galeckas, A.
    et al.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Pirouz, P.
    Recombination-induced stacking faults: Evidence for a general mechanism in hexagonal SiC2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 96, no 2Article in journal (Refereed)
    Abstract [en]

    We report on optically induced nucleation and expansion of stacking faults in hexagonal SiC structures. The activation energy for partial dislocation glide under optical excitation is found to reduce to 0.25 +/- 0.05 eV, which is about 2 eV lower than for pure thermal activation. From the measurements of thermal activation and below-gap excitation spectroscopy of dislocation glide, we conclude that the elementary process controlling expansion of stacking faults is kink pair nucleation aided by the phonon-kick mechanism. We propose that solitons on 30 degrees Si(g) partials with a silicon core act as deep 2.4 eV+E-V trap sites, readily providing electron-hole recombination energy to enhance the motion of dislocations. Our results suggest that this is a general mechanism of structural degradation in hexagonal SiC.

  • 42.
    Galeckas, Augustinas
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Hallen, Anders
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schoner, A.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Pirouz, P.
    Investigation of structural stability in 4H-SiC structures with heavy ion implanted interface2006In: Silicon Carbide and Related Materials 2005, Pts 1 and 2, 2006, Vol. 527-529, p. 395-398Conference paper (Refereed)
    Abstract [en]

    We investigate the possibility of controlling formation of stacking faults (SFs) at the interface region by implanting the 4H-SiC substrate with low-energy antimony ions (75 keV Sb+) prior to conventional CVD growth of the homoepitaxial layers. This approach is based on the solidsolution hardening concept, according to which interaction of impurity atoms with dislocations makes the motion of the latter more difficult. Photoluminescence imaging spectroscopy is employed to investigate incorporation of Sb+ implants at the buried interface and also to assess its impact on structural degradation. Spectral results are analyzed considering both the onset of n-type doping and irradiation damage. The latter factor was estimated separately from supplementary measurements of high-energy (2.5 MeV H+) proton-irradiated 4H-SiC epilayers. We compare results of optically stimulated SF formation in virgin and Sb implanted regions and provide a comprehensive picture of the defect evolution, including microscopic details of the imminent nucleation sites.

  • 43.
    Galeckas, Augustinas
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Kortegaard Nielsen, Hanne
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Svensson, Bengt G.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Pirouz, P
    Investigation of stacking fault formation in hydrogen bombarded 4H-SiC2005In: SILICON CARBIDE AND RELATED MATERIALS 2004 / [ed] Nipoti, R; Poggi, A; Scorzoni, A, 2005, Vol. 483, p. 327-330Conference paper (Refereed)
    Abstract [en]

    The effects of hydrogen and proton irradiation on stacking fault formation in 4H-SiC are investigated by an optical pump-probe method of imaging spectroscopy. We report optically stimulated nucleation and expansion of stacking faults (SFs) in 0.6 keV H-2(+) implanted n-/n+ and p+/n-/n+ structures. The activation enthalpy for recombination enhanced dislocation glide (REDG) in hydrogenated samples (&SIM; 0.25 eV) is found to be similar to that in a virgin material. Our results indicate that SFs mainly nucleate at the internal n-/n+ interface, beyond reach of hydrogen, thus justifying minor SF passivation effect. No REDG could be initiated optically in 2.5 MeV proton irradiated samples due to radiation defects providing alternative recombination channels to bypass the REDG mechanism. The radiation damage was verified by DLTS, revealing several new levels below E-C in the range 0.4-0.80 eV, and by PL, showing the onset of D-center related luminescence band and concurrent increase of the nonradiative recombination rate.

  • 44.
    Galeckas, Augustinas
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kuznetsov, A.Y.
    Chassagne, T.
    Ferro, G.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Grivickas, V.
    Optical investigation of the built-in strain in 3C-SiC epilayers2004In: SILICON CARBIDE AND RELATED MATERIALS 2003, PRTS 1 AND 2 / [ed] Madar, R; Camassel, J, 2004, Vol. 457-460, p. 657-660Conference paper (Refereed)
    Abstract [en]

    The impact of the residual strain ranging from -2.5 GPa to + 0.436 GPa on the electronic properties of 3C-SiC/Si(100) heteroepitaxial layers is investigated by imaging PL spectroscopy. An anomalous above band-gap emission is observed in the blue/green region of spectrum and is tentatively attributed to the manifestation of defect-rich SiC/Si interfaces. A direct correlation of the accumulated strain with the energy gap and the temperature dependence of the band-gap are determined from the analysis of the peak shifts in the fundamental luminescence spectra. The differential pressure coefficient of the band-gap is found to be dE(G)/dp = -5 meV/GPa at room temperature. The observed energy gap narrowing in the temperature interval from 70 to 320 K can be described by the Varshni equation E-G = 2.417 - alphaT(2) (beta + T)(-1) with the parameters alpha = 3.4x10(-4) eV/K and beta = 700 K.

  • 45. Grivickas, P.
    et al.
    Galeckas, A.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Syvajarvi, M.
    Yakimova, R.
    Grivickas, V.
    Tellefsen, J. A.
    Carrier lifetime investigation in 4H-SiC grown by CVD and sublimation epitaxy2001In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 4, no 03-jan, p. 191-194Article in journal (Refereed)
    Abstract [en]

    Depth-resolved carrier lifetime measurements were performed in low-doped epitaxial layers of 4H silicon carbide samples. The technique used was a pump-and-probe technique where carriers are excited by an above-bandgap laser pulse and probed by free carrier absorption. Results from chemical vapour deposition samples show that lifetimes as high as 2 mus may be observed in the mid-region of 40 mum thick epilayers. For epilayers grown by the sublimation method decay transients were characterised by a fast (few nanoseconds) initial recombination, tentatively assigned to the 'true' lifetime, whereas a slow tail of several hundred microsecond decay time was assigned to trapping centres. From the saturation of this level at increased pumping we could derive the trapping concentration and their depth distribution peaking at the epilayer/substrate interface.

  • 46. Grivickas, P.
    et al.
    Grivickas, V.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Excitonic absorption above the Mott transition in Si2003In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 91, no 24Article in journal (Refereed)
    Abstract [en]

    We present experimental evidence for the existence of excitonic states above the excitonic Mott transition in both highly doped and highly excited silicon. Previous limitations to resolve the fundamental absorption edge of Si at dense carrier plasmas are overcome employing a novel spatially and time-resolved spectroscopy. We show that the obtained density dependent excess absorption at 75 K represents an excitonic enhancement effect, which is attributed to persisting many-body interactions.

  • 47. Grivickas, P.
    et al.
    Grivickas, V.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Galeckas, A.
    Fundamental band edge absorption in nominally undoped and doped 4H-SiC2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 12Article in journal (Refereed)
    Abstract [en]

    Fundamental band edge absorption is investigated in nominally undoped (n < 1014 cm(-3)) and heavily doped (n similar to 8 x 10(18) cm(-3)) 4H-SiC by a spectroscopy technique based on spatially and time-resolved free-carrier absorption. The spectra are extracted over a wide absorption range (0.02-500 cm(-1)) at temperatures from 75 to 450 K. The experimental results are supported by an indirect transition theory with a unique set of dominating momentum-conserving phonons, showing good correlation with earlier findings of differential absorption measurements at 2 K. Exciton binding energy of 30 +/- 10 meV is derived from fitting the data at 75 K. The detected polarization anisotropy of absorption with respect to c axis is shown to be consistent with the selection rules for the corresponding phonon branches. An analytical model related to constant degree of involved phonons describes well the obtained energy gap variation with temperature. Finally, doping induced band gap narrowing is characterized above the impurity-Mott transition and compared with theoretical calculations in the random phase approximation. The shape of the fundamental absorption edge at high carrier concentrations is discussed in terms of excitonic enhancement above the Mott transition, as recently detected in Si.

  • 48. Grivickas, P.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Grivickas, V.
    Carrier diffusion characterization in epitaxial 4H-SiC2001In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 16, no 2, p. 524-528Article in journal (Refereed)
    Abstract [en]

    Carrier diffusivity has been experimentally determined in low-doped n-type epitaxial 4H-SiC over a wide injection range using a Fourier transient grating technique. The data showed that, with injection, the diffusion coefficient increased from a minority-hole diffusivity D-h = 2.3 cm(2)/s to an ambipolar diffusivity D-a = 4.2 cm(2)/s at approximately 10(16) cm(-3) with a substantial decrease occurring at higher injections. The derived D-h value corresponded to a minority-hole drift mobility of mu (h) = 90 cm(2)/Vs, about 30% lower than available majority-hole mobilities. Also. the temperature dependence of the ambipolar diffusivity in the 296-523 K range has been determined. It followed a power law D-a similar to T-1.3 which notably differed from the expected one using the majority-hole mobility temperature dependence.

  • 49. Grivickas, V.
    et al.
    Bikbajevas, V.
    Allakhverdiev, K.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Two-photon indirect absorption in GaSe2008In: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY, 2008Conference paper (Refereed)
    Abstract [en]

    Two-photon absorption (TPA) in GaSe is detected in the narrow (about kT) spectral range above the indirect exciton energy for E⊥c light polarization. The appearance of TPA enhancement within narrow spectral region links to the resonant Raman scattering and anti-Stockes photoluminescence previously identified in GaSe. Extracted TPA coefficient is of the order of 10 cm/W and 5-10 times exceeds ones obtained previously for lower quanta energies.

  • 50. Grivickas, V.
    et al.
    Bikbajevas, V.
    Gavryushin, V.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Strong photoacoustic pulses generated in TlGaSe2 layered crystals2008In: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY, 2008, Vol. 100, no PART 4Conference paper (Refereed)
    Abstract [en]

    Periodic deflections of infrared probe beam in TlGaSe2 crystal after its lateral excitation by laser pulse with photon energy near the band gap are observed. Such deflections arise from travelling of the acoustic pulse within sample which, in turn, is produced by optical pump pulse through photoacoustic effect. The photoacoustic pulse is generated within thin region near the crystal excited face, much shorter then the light penetration depth. In the case of volume excitation photoacoustic pulse is also generated in the region near back face as well. Tentative explanation of the generation mechanism is discussed.

123 1 - 50 of 145
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