D. Dimova-Malinovska

Preparation of thin porous silicon layers by stain etching

Abstract A method of preparation of thin (1000 A) porous silicon layers by chemical etching of c-Si in HF:HNO 3 :H 2 O=1:3:5 solution is reported wherein a thin Al film is deposited by evaporation on the silicon surface prior to etching. The method is characterized by no “incubation” period to the onset of the stain etching. The reaction between Al and HNO 3 produces the required holes for the very fast start of the chemical etching of Si. Using Al patterns deposited through a mask or prepared by photolithography it is possible to achieve selective formation of porous silicon. The porous silicon layers exhibit visible photoluminescence and when prepared on p-type c-Si and a shallow p–n c-Si homojunction the resulting heterostructures also display electroluminescence and photovoltaic properties.

Optical and electrical properties of R.F. magnetron sputtered ZnO:Al thin films

Optical and electrical properties of Al-doped ZnO films, deposited by R.F. magnetron sputtering, have been investigated as a function of preparation conditions in an attempt to develop transparent films with low electrical resistivity. The electrical resistivity as well as the Hall mobility of sputtered films depend on the R.F. power density and thickness of the films when it is less than about 300 nm. The free carrier concentration is almost independent on the film thickness and the R.F. power. The optical transmission of the films in the visible range does not depend on the thickness as well as on the R.F. power and is about 90% from the substrate transmission there. In the near-infrared, where the absorption is due to free carriers, the transmission depends strongly on the film thickness and on the preparation conditions.

Electrical, photoelectrical and electroluminescent properties of porous Si–c-Si heterojunctions

Abstract Porous silicon–c-Si heterojunctions have been formed by the method of stain etching. A ZnO highly conductive thin film was used as a front transparent contact. The transport mechanism, photovoltaic and electroluminescent properties have been studied. The heterojunctions show a wide spectral response, from 400 to 1000 nm. The spectral dependence of the photocurrent in the region 400–600 nm depends on the reverse bias. Electroluminescence from the device structure in the visible region has been observed under forward bias. A model based on tunneling of minority carriers through a narrow energy barrier between ZnO and porous Si and the presence of a spike barrier and a conduction band discontinuity at the interface porous Si/c-Si is suggested for describing the properties of the heterojunctions.

Nanostructured and Advanced Materials for Applications in Sensor, Optoelectronic and Photovoltaic Technology

Preface.- Invited Papers: Nanostructured materials based next generation devices and sensors A. Vaseashta.- Metal-induced crystallization an advanced technology for producing polycrystalline Si films on foreign substrates D. Dimova-Malinovska.- Electronic characterisation and modelling of disordered semiconductors J. M. Marshall, C. Main.- Spectroscopy of rare earth ions R. Reisfeld.- Nanostructured and advanced materials for bio-applications D. Dimova-Malinovska .-Transmission electron microscopy imaging of nanoparticulate matter H. Hofmeister.- Matrix embedded metal and semiconductor nanoparticles H. Hofmeister.- From nanoparticles to nanorods and nanowires H. Hofmeister.- ZnO - an advanced material for solar cell, optoelectronic and sensor applications D. Dimova-Malinovska.- Ion beam nanostructuring of materials J.-C. Pivin.- Porous silicon for sensor applications A.. Nassiopoulou.- Luminescent nanoparticles: Colloid synthesis and emission properties T. Gacoin.- Nanoparticles: Functionalization and elaboration of materials T. Gacoin.- Organized mesoporous thin films T. Gacoin.- Photovoltaics in the world S. M. Pietruszko.- Nano-structured materials for a hydrogen economy D. Perniu et al.- Nano-structured functional materials: The defect chemistry J. Schoonman.- Nano-structured materials for the conversion of sustainable energy J. Schoonman.- Seminar Papers: Double-walled carbon nanotubes: Synthesis and filling by l-D nanocrystals E. Flauhaut.- Kinetics of field-aided nickel induced lateral crystallisation of hydrogenated amorphous silicon A. J. Flewitt et al.- Silicon thin-film solar cells W. Fuhs.- Nanocavity structures produced by ion implantation into silicon for semiconductor applications R. E. Hurley et al.- Nanocrystal superlattices ofcopper, silver and gold, by nanomachining A..A.. Ponce et al.- Raman scattering from low-dimensional semiconductors D. Nesheva.- Selected Contributed Papers: Stress state and twin configuration of spheroidal silver nanoparticles in glass A. Berger et al.- Synthesis, characterization, photocatalytic and dielectric properties of nanosized strontium and barium titanates D.V. Demydov , K. J. Klabunde.- Properties of ss-FeSi2 quantum structures grown on silicon L. Dozsa et al.- Zinc oxide nanowires on non-epitaxial substrates from colloidal processing for gas sensing applications A. Sugunan et al.- Structural properties of poly-Si thin films obtained by aluminium-induced crystallization in different atmospheres V. Grigorov et al.- Challenges of growing CuAlSe2 by physical vapor deposition M. W. Haimbodi et al. Silicon-on-insulator thin films grown by liquid phase epitaxy I. Jozwik et al.- Recrystallization of CdTe under conditions of high temperature and pressure V. Mikli, J. Hue.- Prospective investigations of biofuel cells as sources for applications in nanobiotechnology I. Stamatin et al.- Electronic properties of a peanut-shaped C60 polymer J. Onoe .- The gel trapping technique: A novel method for characterizing the wettability of microparticles and the replication of particle monolayers V. N. Paunov, 0. J. Cayre .- Ideal nano-emitters and panel nano-devices based on 2D crystals of superconducting nanotubes V. V. Pokropivny et al.- Photoluminescence and XPS study of selenium treated porous silicon R. Jarimaviciute-Zvalioniene et al.- Synthesis and characterization of PbS nanocrystal assemblies T. Saraidarov, R. Reisfeld.- Laser assisted fragmentation of silver and copper nanoclusters in Si02 thin films M. Sendova et al.- Nd3+ photoluminescence in silica thin films M. Sendova-Vassileva et al.- Characterization of the metal-semiconductor interface for silicon carbide based sensors A. A. Woodworth et al.- Nanoparticles, nanoporous and carbon nanotube based devices for bio-molecular detection A. Vaseashta et al.- Crystallisation of apatite stoichiometric ionomer glasses for medical

Iron silicide formed in a-Si:Fe thin films by magnetron co-sputtering and ion implantation

Thin films containing iron silicides are prepared by two methods. The first one consists in depositing a-Si:H:Fe thin films by magnetron co-sputtering followed by rapid thermal annealing (RTA). The second one is ion implantation of Fe in a-Si:H thin films and RTA treatment. The samples are characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Rutherford back-scattering (RBS). FTIR spectra show absorption bands typical for β-FeSi 2 at 263, 293, 308, 345 and 425 cm -1 . It is shown that the optimal concentration of Fe in the co-sputtered films to obtain β-FeSi 2 is 35-40% and the optimal RTA temperature is 900°C. XPS spectra show that β-FeSi 2 is formed in as-deposited and annealed co-sputtered a-Si:H:Fe and implanted a-Si:H thin films.

Structural, optical and electrical properties of V doped ZnO thin films deposited by r.f. magnetron sputtering

Structural, optical and electrical properties of V doped ZnO thin films deposited by r.f. magnetron co-sputtering on glass substrates at different temperature, Ts, between 150°C and 500°C are studied. The EDS analyses indicate that the average vanadium content in the films is in the range of 0.86–0.89 at. %. XRD spectra demonstrate preferential (002) crystallographic orientation with c-axis perpendicular to the substrate surface and grains sizes of the films about 21–29 nm. The band gap energy, Eg, values are in the range of 3.44–3.47 eV. The deposited V doped ZnO films have low resistivity − (2–8). 10−3 Ω cm. Raman spectra show vibrational phonons modes typical for ZnO. Comparison with the structural, optical and electrical properties of thin films ZnO and ZnO:Al is given.

Room-temperature photoluminescence from Tb3+ ions in SiO2 and a-SiC:H thin films deposited by magnetron co-sputtering

The laser excited photoluminescence (PL) of SiO 2 and a-SiC:H thin films doped with Tb deposited by co-sputtering has been studied. In the case of SiO 2 :Tb the PL is due to 4f-4f transitions of Tb 3 + ions starting from the 5 D 4 level which is resonantly excited by the 488 nm Ar + laser line. The PL in this case has no temperature quenching from 18 K up to room temperature. The inhomogeneous broadening of the PL bands predominates over the homogeneous one. In the case of a-SiC:H:Tb a broad band covering the whole visible spectrum is observed. It is tentatively assigned to a recombination centre created by the Tb impurity.

Mixing of metals in Si with 4.5 MeV Au ions

Abstract The mechanism of ion beam mixing of Fe, Er, Pd, Ag, Au layers embedded in a-Si, a-SiC, a-Si:H or a-SiC:H under 4.5 MeV Au irradiation is studied by means of RBS and TEM. Contrary to what is generally observed for irradiation at lower energies recoil implantation contributes significantly to the process by forcing atoms to enter in solid solution into the matrix. Insoluble species migrate over some distance before precipitating in nanometric clusters. Fe, Pd and Er form silicides, growing either by unidirectional diffusion of Si in the metal layer or two-dimensional diffusion of recoil implanted atoms parallel to this layer. But hydrogenation of the matrix promotes a diffusion of Er in a-Si:H and enhances the diffusion rate of noble metals in a-SiC:H.

Sensitivity of Co doped ZnO films to NH3 at room temperature - influence of the deposition temperature

The sensitivity was studied of undoped ZnO films and doped with Co (ZnO:Co) to exposure to NH3. The films were deposited by magnetron sputtering of a sintered ZnO target and co-sputtering of the ZnO target with Co chips on its surface. The influence of the substrate temperature, Ts, on the properties of the films was studied. The structural and optical properties of the undoped and Co doped ZnO films were studied by X-ray diffraction spectroscopy (XRD) and optical transmittance and reflectance. The optical band gap of the films was calculated. The variation of the sensitivity of films deposited at different Ts with the NH3 concentration is presented. The results demonstrate that the Co doped ZnO films have a higher sensitivity to ammonia and their sensitivity increases with Ts.

A novel laser-liquid-solid interaction process for hydroxyapatite formation on porous silicon

The mechanism of hydroxyapatite (HA, Ca10(PO4)6(OH)2) growth on the surface of porous silicon (PS) was examined. PS layers were prepared by electrochemical or chemical etching of n-type Si with (111) orientation, and p-type Si with (100) orientation. HA growth was induced by two methods: a simple soaking process in a simulated body fluid (SBF) and a novel Laser-Liquid-Solid Interaction (LLSI) process which allowed interaction between a scanning laser beam and the PS substrate immersed in the SBF. The grown layers were investigated by light microscopy, electron microprobe analysis, Raman spectroscopy and X-ray diffraction. Differently doped Si substrates with different crystallographic orientation and electrical resistivity were used and their effect on the HA growth, as well as the effect of the laser energy were examined.