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Applied Surface Science (v.269, #)

Editorial Board (pp. ii).

Progress in Applied Surface, Interface and Thin Film Science 2012 Solar Renewable Energy News III, May 14–18, 2012, Florence, Italy (SURFINT-SREN III) by Emil Pincik Dr. (pp. 1-1).

Kinetics of atomic smoothing GaAs(001) surface in equilibrium conditions by I.O. Akhundov; V.L. Alperovich; A.V. Latyshev; A.S. Terekhov (pp. 2-6).

► Kinetics of GaAs(001) surface smoothing in equilibrium conditions is measured. ► Roughness, step length, Fourier spectra and correlation functions are analyzed. ► Smoothing is accompanied by narrowing the spectra of spatial frequencies. ► Length of monatomic steps is the best characteristic of step-terraced surfaces. ► The excess of step length is inversely proportional to the annealing time.The technique for preparing step-terraced GaAs surfaces by annealing in the conditions close to equilibrium is further developed. The kinetics of GaAs(001) surface flattening is experimentally measured. The step-terraced surface morphology formation is characterized by the evolution of root mean square roughness, total length of monatomic steps, and by Fourier and correlation analyses. It is shown that the excess of monatomic step length over the value for the ideal vicinal surface is the most adequate characteristic of the surface smoothing because it decreases inversely proportional with annealing duration.

Keywords: Surface smoothing; GaAs; Monatomic steps; Step-terraced morphology; Fourier analysis; Autocorrelation functions

The electronic properties of nickel phosphide surfaces: Angle-resolved and resonant photoemission studies by Kazuyuki Edamoto (pp. 7-11).

► The photoemission spectra of Ni₂P consist of a Ni 3d–P 3p hybrid band and a satellite. ► The satellite is associated with photoemission leading to a two-hole bound state. ► A P 3p-induced surface state is formed onNi2P(101¯0). ► The P segregation to the surface is brought about by annealing at 260–330°C. ► The 3d levels of surface Ni atoms are stabilized by bonding with segregated P atoms.The electronic structures of (1×1) Ni₂P(0001) andc(2×4)Ni2P(101¯0) have been investigated by photoemission spectroscopy (PES). For both surfaces, the valence PES spectra consisted of a Ni 3d–P 3p hybrid band (main band) and a satellite; the main band is observed at 0–4eV and the satellite is observed at 8eV. Resonant PES study showed that the satellite is associated with the photoemission process leading to a two-hole bound final state. On(101¯0), a P 3p-induced surface state is formed around 0.6eV along the boundary of the surface Brillouin zone of the c(2×4) lattice. The surface core-level shifts were observed in P 2p spectra for both surfaces; the surface components were shifted to the lower binding energy side by 0.9eV for (0001) and by 0.6eV for(101¯0). These results suggest that the coordination number of surface P atoms is much reduced from that in the bulk. The segregation behavior of P atoms in Ni₂P was investigated by Auger electron spectroscopy and PES. It was found that the segregation of P atoms proceeds by annealing at 260–330°C. The valence PES study showed that the 3d levels of the surface Ni atoms are stabilized through the bonding with segregated P atoms.

Keywords: Angle-resolved photoemission; Surface electronic phenomena; Phosphides; Low index single crystal surfaces

Evolution of the structure and hydrogen bonding configuration in annealed hydrogenated a-Si/a-Ge multilayers and layers by C. Frigeri; M. Serényi; A. Csik; Zs. Szekrényes; K. Kamarás; L. Nasi; N.Q. Khánh (pp. 12-16).

► We study hydrogenated amorphous Si/Ge multilayers annealed to form SiGe alloy. ► H is released from Si and Ge atoms on annealing. ► Annealing causes surface blistering. ► Released hydrogen is partially trapped in cavities that form blisters by increasing in size. ► Si di-hydrides are formed on the inner surfaces of the cavities/blisters.The evolution of the structure and of the hydrogen bonding configuration in hydrogenated a-Si/a-Ge multilayers prepared by RF sputtering is analyzed as a function of annealing. Single layers are also investigated to better evaluate the H behavior. IR absorption measurements show that H is released from its bonds to Si and Ge upon annealing. The mono-hydrides already disappear to a large extent for low annealing times (1 and 4h), being replaced by di-hydrides, especially in the case of Si. For 10h annealing both mono- and di-hydrides are almost completely destroyed. At the same time surface blisters form which, for the same annealing conditions, increase in size with increasing incorporated H in the as-deposited sample. It is concluded that the blisters in the multilayers are due to the trapping of the released H in cavities that increase in size upon annealing. The enlarged inner surface of the cavities is the candidate site for the formation of the di-hydrides at low annealing times, i.e., when the thermal energy supplied by the annealing is still insufficient to break all of them.

Keywords: Amorphous Si/Ge multilayer; Hydrogen; Annealing; IR absorption; Blister

Huge field-effect surface charge injection and conductance modulation in metallic thin films by electrochemical gating by M. Tortello; A. Sola; Kanudha Sharda; F. Paolucci; J.R. Nair; C. Gerbaldi; D. Daghero; R.S. Gonnelli (pp. 17-22).

► Novel polymer-gating field-effect experiments allow to reach a record induced surface charge density of 4×10¹⁵charges/cm². ► A modification of the double-step chronocoulometry method is very appropriate for the determination of the induced charge density. ► Huge resistance variations (up to 8%) are observed at room temperature in thin films of different metals (Au, Ag, Cu). ► These relative resistance variations are explained very well by a simple free-electron model that includes parallel resistive channels.The field-effect technique, popular thanks to its application in common field-effect transistors, is here applied to metallic thin films by using as a dielectric a novel polymer electrolyte solution. The maximum injected surface charge, determined by a suitable modification of a classic method of electrochemistry called double-step chronocoulometry, reached more than 4×10¹⁵charges/cm². At room temperature, relative variations of resistance up to 8%, 1.9% and 1.6% were observed in the case of gold, silver and copper, respectively and, if the films are thick enough (⩾25nm), results can be nicely explained within a free-electron model with parallel resistive channels. The huge charge injections achieved make this particular field-effect technique very promising for a vast variety of materials such as unconventional superconductors, graphene and 2D-like materials.

Keywords: Field-effect experiments; Electrochemical gating; Surface electron states; Conductivity of metals

Charging behavior of silicon nitride based non-volatile memory structures with embedded semiconductor nanocrystals by Zs.J. Horváth; P. Basa; T. Jászi; K.Z. Molnár; A.E. Pap; Gy. Molnár (pp. 23-28).

► The charging behavior of MNS and MNOS structures containing Si or Ge nanocrystals are studied. ► Exponential dependence of injected charge on the charging voltage is obtained and explained. ► Contradictory results of memory window measurements are obtained and discussed.The charging behavior of MNS (metal-nitride-silicon) and MNOS (metal-nitride-oxide-silicon) structures containing Si or Ge nanocrystals were studied by capacitance–voltage ( C– V) and memory window measurements and by simulation. Both the width of hysteresis of C– V characteristics and the injected charge exhibited exponential dependence on the charging voltage at moderate voltage values, while at high voltages the width of hysteresis of C– V characteristics and the injected charge exhibited saturation. The memory window for reference MNS structure without nanocrystals was wider than that for reference MNOS structures. The presence of nanocrystals enhanced the charging behavior of MNOS structures, but in MNS structures nanocrystals exhibited the opposite effect. The main conclusion is that the presence of nanocrystals or other deep levels close to the Si surface enhances the charge injection properties due to the increased tunneling probability, but nanocrystals or other deep levels located far from the Si surface in the nitride layer do not enhance, but even can degrade the charging behavior by the capture of charge carriers.

Keywords: Si and Ge nanocrystals; MNOS; Memory behavior; Silicon nitride

The distribution of elements in sequentially prepared MgB₂ on SiC buffered Si substrate and possible pinning mechanisms by Š. Chromik; A. Nishida; V. Štrbík; M. Gregor; J.P. Espinós; J. Liday; R. Durný (pp. 29-32).

► Superconducting MgB₂ thin films were prepared on SiC substrates by sequential method. ► XPS spectra indicate that SiC is not incorporated into MgB₂ film but the distribution of carbon and silicon in the film is observed. ► XPS spectra indicate a reaction between MgB₂ and MgO at higher temperature (830°C). ► XPS spectrum suggests the possibility of the substitution carbon for boron in MgB₂.MgB₂ thin films are prepared by sequential evaporation of boron and magnesium bilayers on SiC buffered Si substrates followed by an in situ annealing. Precursor Mg–B bilayers are deposited by electron beam evaporation at room temperature. The amount of B is varied so as to result in different thickness (15nm and 50nm) of stoichiometric MgB₂ final film after an in situ reaction with the excess Mg top layer in the vacuum. We show the distribution of the elements through the film.X-ray photoelectron spectroscopy analyses have shown that carbon is not free in the films (except the surface of the film) and silicon is in the compound form, too. In the case of the 15nm thick films we see a strong interdiffusion of the elements (C, B) and we observe a suppression of T_C of the film to 20K. We register different slope of theHC2(T) dependence – the lowest temperature value ofHC2 for the 15nm thick film exceeds the one for the 50nm thick film in spite of lower T_C. We suppose that δl pinning mechanism is dominant for the 15nm thick film.

Keywords: MgB; ₂; films; AES analysis; XPS analysis; Pinning

Interaction of non-equilibrium oxygen plasma with sintered graphite by Uroš Cvelbar (pp. 33-36).

► Evaluation of interactions of plasma species with surface, in our case predominatly neutral oxygen atoms and their consumption through processing. ► Surface heating due to extensive chemical interactions between the O atoms and graphite suface. ► Functionalization of the surface in respect to treatment time, where the number of the carbonyl groups is affected be increased surface temperature.Samples made from sintered graphite with grain size of about 10μm were exposed to highly non-equilibrium oxygen plasma created in a borosilicate glass tube by an electrodeless RF discharge. The density of charged particles was about 7×10¹⁵m⁻³ and the neutral oxygen atom density 6×10²¹m⁻³. The sample temperature was determined by a calibrated IR detector while the surface modifications were quantified by XPS and water drop techniques. The sample surface was rapidly saturated with carbonyl groups. Prolonged treatment of samples caused a decrease in concentration of the groups what was explained by thermal destruction. Therefore, the created functional groups were temperature dependent. The heating of samples resulted in extensive chemical interaction between the O atoms and samples what was best monitored by decreasing of the O atom density with increasing sample temperature. The saturation with functional groups could be restored only after cooling down of the samples and repeated short plasma treatment at low temperature.

Keywords: Plasma; Graphite; Oxygen; Interactions

Structural and electroluminescent properties of Si quantum dots/SiC multilayers by Yunjun Rui; Shuxin Li; Yunqing Cao; Jun Xu; Wei Li; Kunji Chen (pp. 37-40).

► Size-controllable Si QDs/SiC multilayers have been fabricated. ► Size-dependent EL was observed in the multilayers due to quantum confinement effect. ► EL is originated from radiative recombination of injected e–h pairs in Si QDs.Si quantum dots (QDs)/SiC multilayered structures were prepared by thermal annealing the hydrogenated amorphous silicon (a-Si:H)/hydrogenated amorphous silicon carbide (a-SiC:H) multilayers. The microstructures of annealed samples were investigated by Raman scattering, cross-sectional transmission electron microscopy, and Fourier transform infrared spectroscopy. The size of formed Si QDs can be controlled by the a-Si:H layer thickness and annealing conditions. Room temperature electroluminescence (EL) was observed and the EL peak energy was shifted with the size of the Si QDs formed in the annealed multilayers, which can be attributed to quantum confinement effect in Si QDs.

Keywords: PACS; 73.21.La; 78.67.Pt; 78.60.FiSilicon carbide; Si quantum dots; Multilayers; Electroluminescence

First principles calculations of magnetic properties of Rh-doped SnO₂(110) surfaces by F. Bouamra; A. Boumeddiene; M. Rérat; H. Belkhir (pp. 41-44).

► Ab initio study of magnetic properties of Rh-doped SnO₂(110) surfaces with CRYSTAL03 program. ► Different concentrations of Rh, from 0% to 26.31% this is corresponding to Sn48−2_xO₉₆Rh2_x( x=2, 3, 4, 5). ► Investigation of magnetic properties of thin films SnO₂(110) doped with Rh is based on density total (DOS) and projected (PDOS) analysis. ► System nature is concluded from Mulliken population analysis (PPAN).The magnetic properties of Rh-doped SnO₂(110) surface over a range of atomic Rh/Sn ratio from 9.09% to 26.31% have been calculated using a density functional theory (DFT) at the B3LYP level, as well as the spin-polarized total and projected density of states (DOS) of Rh atoms nearest-neighboring O and next-nearest neighboring Sn ions. An analysis of Mulliken population has been also done at the surface of SnO₂ in presence of the defects.

Keywords: Density functional calculations; Ferromagnetic; Magnetic moment; Transition metal; Rh-doped SnO; ₂; (1; 1; 0)

On the difference between optically and electrically determined resistivity of ultra-thin titanium nitride films by H. Van Bui; A.Y. Kovalgin; R.A.M. Wolters (pp. 45-49).

► We determined the resistivity of ultra-thin TiN films in the thickness range 0.65–20nm using both spectroscopic ellipsometry and electrical test structure methods. ► The comparison showed the considerable difference in resistivity obtained from the two methods for films thinner than 4nm. ► The significant difference was attributed to the scattering effects at grain boundaries and interfaces.This work reports on the determination and comparison of the resistivity of ultra-thin atomic layer deposited titanium nitride films in the thickness range 0.65–20nm using spectroscopic ellipsometry and electrical test structures. We found that for films thicker than 4nm, the resistivity values obtained by the two techniques are in good agreement. However, below 4nm, the comparison shows an increasing difference with decreasing film thickness. A difference with a factor of 3 was found at 1.8nm and increased up to hundreds at 0.65nm. We attribute this significant difference to the electron scattering effects at grain boundaries and interfaces which can not be fully taken into account by spectroscopic ellipsometry measurements.

Keywords: Titanium nitride; Resistivity; Spectroscopic ellipsometry; Current–voltage characteristics

Acoustic spectroscopy and electrical characterization of Si/NAOS-SiO₂/HfO₂ structures by Peter Bury; Taketoshi Matsumoto; Ivan Bellan; Marián Janek; Hikaru Kobayashi (pp. 50-54).

The MOS structure prepared on n-type Si substrate with SiO₂/HfO₂ gate dielectric layers was formed by 5nm HfO₂ oxide deposited by atomic layer deposition on 0.6nm SiO₂ oxide film prepared with nitric acid oxidation of Si (NAOS) in ∼100% HNO₃ vapor. The set of this MOS structure was annealed in N₂ atmosphere at 200, 300 and 400°C for 10min to stabilize the structure, to decrease the interface states density and leakage current density. The both acoustic deep level transient spectroscopy (A-DLTS) and acoustoelectric response signal versus gate voltage dependence ( U_ac– U_g characteristics) were used to characterize the interface states and the role of annealing treatment, except ordinary electrical investigation represented by current–voltage and capacitance–voltage measurements. The main interface deep centers with activation energies ∼0.30eV typical for dangling-bond type defects were observed as well as a particular influence of annealing treatment on the interface states. The obtained results are analyzed and discussed.

Keywords: PACS; 73.40.Qv; 73.20.HbAcoustic DLTS; MOS structures; NAOS SiO; ₂; /HfO; ₂; oxide layer; Interface states

Modeling the reactive sputter deposition of N-doped TiO₂ for application in dye-sensitized solar cells: Effect of the O₂ flow rate on the substitutional N concentration by D.A. Duarte; J.C. Sagás; A.S. da Silva Sobrinho; M. Massi (pp. 55-59).

► Berg model was applied to simulate the deposition of N-doped TiO₂. ► N-doped TiO₂ is grown from chemisorption and oxidation of TiN. ► Substitutional N is mainly incorporated from oxidation of TiN.In this paper an original numerical model, based on the standard Berg model, was used to simulate the growth mechanism of N-doped TiO₂ deposited at different O₂ concentrations in the reactive gas mixture. For evaluation of the numerical model, films were deposited in the same conditions as those used in the numerical approach. Films were analyzed by profilometry, optical spectrophotometry, Rutherford back-scattering spectroscopy (RBS) and X-ray photoelectron spectroscopy (XPS). Results show that oxidation of TiN plays a fundamental role for incorporation of substitutional N in the TiO₂ lattice and the overall structure of the films, as well as, the chemical composition obtained from numerical model is in agreement to experimental data.

Keywords: N-doped TiO; ₂; Reactive sputter deposition; Berg model; Dye-sensitized solar cells

Ohmic contacts to p-GaP/n-ZnO core/shell nanowires based on Au metallization by A. Dujavová-Laurenčíková; S. Hasenöhrl; P. Eliáš; R. Stoklas; M. Blaho; I. Novotný; Z. Križanová; J. Novák (pp. 60-64).

► We report ohmic contacts to p-GaP/n-ZnO core/shell nanowires with radial pn heterojunction. ► The ohmic contacts were prepared using e-beam lithography and lift-off technique. ► ZnO shell was removed by wet chemical etching in KOH.This paper presents the technology of ohmic contacts to p-GaP/n-ZnO core/shell nanowires (NW) that have a radial pn heterojunction. To separately contact the GaP core and ZnO shell of an individual NW is not trivial as it requires two different types of ohmic metallization alloyed at different temperatures. The NWs were contacted using electron beam lithography and a lift-off technique in a two-step process: (1) the ZnO shell layer was removed from one NW end to reveal the GaP core onto which an Au/Zn alloy was deposited to contact GaP, (2) an Au/Al alloy was used to make contact to the ZnO shell layer.

Keywords: Core/shell nanowires; Ohmic contact; GaP; ZnO

Influence of deposition conditions on electrical and mechanical properties of Sm₂O₃-doped CeO₂ thin films prepared by EB-PVD (+IBAD) methods. Part 1: Effective relative permittivity by Mária Hartmanová; Vojtech Nádaždy; František Kundracik; Catina Mansilla (pp. 65-71).

► We have developed a facile method of creating a hydrophobic surface on a magnesium alloy by an immersion process. ► The distribution of micro-structure and roughness of the surface play critical roles from hydrophilic to hydrophobic. ► The hydrophobic coatings possess better corrosion resistance than magnesium alloy matrix.Study is devoted to the effective relative permittivity ɛ_r of CeO₂+ x. Sm₂O₃ thin films prepared by electron-beam physical vapour deposition and ionic beam-assisted deposition methods; ɛ_r was investigated by three independent ways from the bulk parallel capacitance C_p, impedance capacitance C_imp, and accumulation capacitance C_acc in dependence on the deposition conditions (deposition temperature, dopant amount x and Ar⁺ ion bombardment during the film deposition) used. Investigations were performed using impedance spectroscopy, capacitance–voltage and current–voltage characteristics as well as deep level transient spectroscopy. Results obtained are described and discussed.

Keywords: CeO; ₂; +; x; Sm; ₂; O; ₃; thin films; Relative permittivity; Impedance spectroscopy; Deep level transient spectroscopy; Electron beam-physical vapour deposition; Ionic beam assisted deposition

Zinc-doped gallium phosphide nanowires for photovoltaic structures by Stanislav Hasenöhrl; Peter Eliáš; Ján Šoltýs; Roman Stoklas; Agáta Dujavová-Laurenčíková; Jozef Novák (pp. 72-76).

► We studied the influence of the dopant precursor DEZn on GaP nanowire growth in a set of six samples with gradually increased DEZn molar fraction in the reactor. ► Precursor influence on the nanowire shape was observed in SEM. ► Measurements of NW field-effect transistor (NW-FET) devices showed the influence of the DEZn molar fraction on the nanowire electrical parameters. ► When the DEZn molar fraction exceeds 9×10⁻⁶, nanowire growth is hindered and only small stumps and kinked wires are grown.The GaP–ZnO core–shell nanowire (NW) heterojunction integrated on top of a multi-junction solar cell can extend its spectral sensitivity region toward shorter wavelengths, enhance the photon absorption, and reduce the surface light reflection. We report on the preparation of the Zn-doped GaP cores for such heterostructure NWs. Problems with NW Zn doping are addressed. A small amount of diethylzinc (DEZn) vapor added to the reactor slightly increased the axial and radial growth rates, which resulted in moderate increase in NW tapering. A further increase in the DEZn molar fraction in the reactor suppressed the tapering (lower radial growth rate) but the axial growth rate was increased. When the DEZn molar fraction exceeded 9×10⁻⁶, the NW growth was hindered; only small stumps and kinked wires grew. The measurement of NW electrical transport parameters showed that DEZn compensated native n-type impurities at small vapor pressures ( χ_DEZn∼1×10⁻⁸ to 1×10⁻⁷); the NWs exhibited n-type conductivity or were compensated. GaP NWs of p-type with a hole concentration p∼1×10¹⁸cm⁻³ were grown only in a very narrow interval of DEZn vapor pressures ( χ_DEZn∼1–6×10⁻⁶).

Keywords: Nanowires; Gallium phosphide; Doping; MOCVD

Structure analysis of CoFeBSiNb(Ga) pseudobulk metallic glasses by J. Hosko; I. Janotova; P. Svec; I. Matko; D. Janickovic; P. Svec Sr. (pp. 77-80).

► CoFeBSiNb ribbons and trilayers were prepared by modified planar flow casting. ► Samples were annealed up to 1100K, Fe₂B and (Co–Fe)₂₃B₆ were determined by XRD. ► Increased thickness has no influence on final microstructure. ► Ga addition into base composition slightly changes microstructure at 1100K. ► Ga affects the kinetics of crystallization and new phase was observed α(Fe–Co).Rapidly quenched Co–Fe based ferromagnetic amorphous ribbons and pseudobulk metallic glasses are attractive group of materials for structural and functional use. In the present contribution, structure of as-cast and annealed Co–Fe–B–Si–Nb pseudobulk metallic glasses with increased thickness was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, influence of a small addition of gallium (2 at.%) into base composition on structure of the ribbon was investigated.

Keywords: Ribbon; Pseudobulk metallic glasses; Planar flow casting; Transmission electron microscopy; X-ray diffraction

Sputtered ITO for application in thin-film silicon solar cells: Relationship between structural and electrical properties by J. Hotovy; J. Hüpkes; W. Böttler; E. Marins; L. Spiess; T. Kups; V. Smirnov; I. Hotovy; J. Kováč (pp. 81-87).

► The relationship between structural and electrical properties of RF magnetron-sputtered ITO thin layers was studied. ► ITO layers grown at surprisingly low temperature of 125°C exhibited remarkably high value of Hall mobility of 49cm²/Vs. ► It was revealed that high Hall mobility is related to domain formations on surface as observed by AFM and SEM. ► ITO layers were applied as front contacts in μc-Si:H solar cells on rigid and flexible substrates (maximum efficiency: 8.4%).Indium tin oxide (ITO) thin films for application in thin-film silicon solar cells with superior electrical and optical properties (resistivity ranging from 1.4 to 8.4×10⁻⁴Ωcm; transparency of >80%) have been investigated. ITO layers were deposited by radio-frequency (RF) magnetron sputtering process at different argon gas pressures and substrate temperatures ranging from room temperature to 280°C. The main goal was to identify the relationship between structural and electrical properties. Generally, ITO layers were rather smooth with granular topography; electro-optically superior layers exhibited substantially different surface morphology of large, well-organized domain formations. Hall mobility of remarkably high value of 49cm²/Vs (resistivity of 2.6×10⁻⁴Ωcm) was achieved for the ITO layers, which were deposited at surprisingly low temperature of 125°C. ITO process has been successfully applied, even at room temperature, to fabricate front contacts for microcrystalline silicon solar cells, exhibiting excellent performance on both rigid and flexible substrates.

Keywords: ITO; Surface morphology; Microstructure; Hall mobility; Electrical properties; μc-Si:H; Nip solar cell

The effect of neutron irradiation on the properties of SiC and SiC(N) layer prepared by plasma enhanced chemical vapor deposition by Jozef Huran; Albín Valovič; Pavol Boháček; Valery N. Shvetsov; Alexander P. Kobzev; Sergey B. Borzakov; Angela Kleinová; Mária Sekáčová; Juraj Arbet; Vlasta Sasinková (pp. 88-91).

► The influence of neutron irradiation on the properties of SiC and SiC(N) layer was investigated. ► Silicon carbide (SiC) and nitrogen-doped silicon carbide (SiC(N)) layers were deposited by PECVD technology. ► No significance effect on the IR spectra band features after neutron irradiation was observed. ► Raman spectroscopy results of SiC and SiC(N) showed decrease in Raman band feature intensity after neutron irradiation. ► The measured currents after irradiation are greater (up to 100 times) than the current before irradiation for all samples.Amorphous silicon carbide (a-SiC) is an excellent alternative passivation layer material for silicon solar cells especially working in hard and space environment. Silicon carbide (SiC) and nitrogen-doped silicon carbide (SiC(N)) layers were deposited on P-type Si(100) substrates at various deposition conditions by means of plasma enhanced chemical vapor deposition (PECVD) technology using silane (SiH₄) methane (CH₄) and ammonium (NH₃) gas as precursors. The concentration of elements in layers was determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analytical method simultaneously. Chemical compositions were analyzed by Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. Irradiation of samples by fast neutrons with fluence 1.4×10¹⁴cm⁻² was used. No significance effect on the IR spectra band features after neutron irradiation was observed. Intensity of Raman spectra band features was decreased after neutron irradiation. The measured currents after irradiation are greater (up to 100 times) than the current before irradiation for all samples.

Keywords: Silicon carbide layer; Plasma CVD; Neutron irradiation; Structural and electrical characterization

Characteristics of the electromagnetic interference shielding effectiveness of Al-doped ZnO thin films deposited by atomic layer deposition by Yong-June Choi; Su Cheol Gong; David C. Johnson; Stephen Golledge; Geun Young Yeom; Hyung-Ho Park (pp. 92-97).

► Al-doped ZnO thin film. ► Modified pulse sequence atomic layer deposition. ► Most effective pulse sequence of Al-doped ZnO thin films is DEZ/N₂/TMA/N₂/H₂O/N₂. ► 6.5dB of EMI-SE with 131nm thick Al-doped ZnO thin film.The structural, optical, and electrical properties of Al-doped ZnO (ZnO:Al) thin films deposited by atomic layer deposition (ALD) with a modified precursor pulse sequence were investigated to evaluate the electromagnetic interference shielding effectiveness (EMI-SE). A Zn–Al–O precursor exposure sequence was used in a modified ALD procedure to result in better distribution of Al³⁺ ions in the ZnO matrix with the aim of reducing the formation of complete nano-laminated structures that may form in the typical alternating ZnO and Al₂O₃ deposition procedure. The ALD dopant concentration of the ZnO:Al films was varied by adjusting the dopant deposition intervals of the ZnO:ZnAlO precursor pulse cycle ratios among 24:1, 19:1, 14:1, and 9:1. The lowest obtained resistivity and average transmittance in the visible region (380-780nm) were 5.876×10⁻⁴Ωcm (carrier concentration of 6.02×10²⁰cm⁻³ and Hall mobility of 17.65cm²/Vs) and 85.93% in the 131nm thick ZnO:Al(19:1) film, respectively. The average value of the EMI-SE in the range of 30MHz to 1.5GHz increased from 1.1dB for the 121nm thick undoped ZnO film to 6.5dB for the 131nm thick ZnO:Al(19:1) film.

Keywords: ZnO; Al-doped ZnO; Atomic layer deposition; Transparent conducting oxides; Electromagnetic shielding effectiveness

Significant increasing of onset temperature of FM transition in LSMO thin films by Štefan Chromik; Vladimír Štrbík; Edmund Dobročka; Agáta Dujavová; Marián Reiffers; Jozef Liday; Marianna Španková (pp. 98-101).

► Transition temperature metal insulator above 400K. ► Increased onset temperature of ferromagnetic transition. ► Magnetization of LSMO film at 398K. ► Microstructure with distorted orthorhombic unit cells.La_0.67Sr_0.33MnO₃ (LSMO) thin films with a significant increased onset temperature of ferromagnetic transition were prepared using an on-axis dc magnetron sputtering from a stoichiometric ceramic target onto one-side polished MgO (001). The highest temperature of insulator-metal transition was observed at T_P=416K. Magnetization hysteresis curves taken at T=398K indicate the beginning of the ferromagnetic transition above 400K. The negative magnetoresistance reaches 15% at a temperature of 400K. We show that the LSMO thin films with increased temperature values of resistance peak T_P and Curie temperature T_C are characteristic by a proper microstructure with distorted orthorhombic unit cells. This microstructure is developed during the layer growth, it is not caused by the underlying substrate and it is linked with an appropriate pseudocubic out-of-plane lattice parameter a_c^⊥, splitted Bragg reflections in rocking curves and as well as in reciprocal space maps.

Keywords: Ferromagnetic thin film; Curie temperature; Magnetoresistance; Metal-insulator transition

The study of structure of Fe–B–P based metallic glasses by I. Janotova; J. Hosko; P. Svec; I. Matko; D. Janickovic; P. Svec Sr.; T. Gemming; M. Stoica (pp. 102-105).

► Amorphous materials in form of ribbons were prepared by planar flow casting. ► Kinetics of crystallization was investigated by DSC and TGA. ► Samples were annealed at 773K, bcc-Fe, Fe₃B and Fe₂₃B₆ were determined by XRD. ► In situ XRD using linear heating confirmed three-stage transformation. ► Cu addition into base composition leads to more regular grain morphology.Rapidly quenched (RQ) Fe–B–P alloys with addition of Co and Cu exhibit excellent soft magnetic and mechanical properties. A system of the type (Fe85−_zCo_zB₁₅)100− x−_yP_xCu_y with x=3, 4, 5; y=0, 1 and z=0, 21at.% has been prepared by planar flow casting in form of thin ribbons. Selected properties in as-cast state and after controlled annealing targeted to produce fine-grain structure were determined. The effect of the substitution of Fe for Co and the additions of P and Cu on structure in nanocrystalline state was investigated. These systems were investigated by thermogravimetry (TGA) and by differential scanning calorimetric (DSC) measurements. The structure was investigated by XRD and TEM (HREM).

Keywords: Metallic glasses; Soft magnetic materials; Iron–boron alloys, Nanocrystalline structure

FT IR spectroscopy of silicon oxide layers prepared with perchloric acid by M. Kopani; M. Mikula; M. Takahashi; J. Rusnák; E. Pinčík (pp. 106-109).

► Formation of stoichiometric SiO₂ layer with lowest density after chlorine oxidation ► KCN/HCN passivation contributes to formation of SiN, SiO and SiOH bonds at the expense of SiCl bonds. ► SiCN could not be identified due to overlapping of detected signal with absorption induced by CO₂.Chlorine oxidation is important methods for improvement of many properties such as passivation of mobile oxide charge, breakdown strength or enhancement of the minority-carrier lifetime in the underlying silicon. In this study we consider effects influencing the density of SiO₂ layers formed by three different methods: thermal oxidation at 850°C, low temperature oxidation method by use of nitric acid – HNO₃ (NAOS) and HClO₄ afterward passivated with KCN/HCN solutions. Thicknesses of SiO₂ layers determined by both capacitance–voltage ( C– V) and XPS revealed fast oxidation rate compared with samples prepared by thermal oxidation. FT IR measurement showed that all absorption spectra are almost similar. Higher absorption of the sample prepared in HClO₄ was observed. No SiCl bonds were visible. Calculated atomic density of the SiO₂ layer obtained from IR measurements was lowest for sample formed in HClO₄. Chlorine oxidation results in higher oxidation rate (higher thickness) and formation of stoichiometric SiO₂ layer with lower density. Following KCN/HCN passivation causes formation of SiN, SiO and SiOH bonds at the expense of SiCl bonds.

Keywords: Infrared spectroscopy; Passivation; Silicon oxide; Perchloric acid; KCN treatment

Sputtered TiO₂ thin films with NiO additives for hydrogen detection by I. Kosc; I. Hotovy; V. Rehacek; R. Griesseler; M. Predanocy; M. Wilke; L. Spiess (pp. 110-115).

► The effect of NiO additives on the properties of TiO₂ films was studied. ► Conductively combined p/n type gas sensitive material was presented. ► Inversion of conductivity response type was observed. ► The critical H₂ concentration was function of operating temperature.The effect of NiO additives and post-deposition treatment by rapid thermal annealing on the properties of TiO₂ thin films has been studied. The structural, compositional and H₂ sensing parameters have been investigated by X-ray diffraction (XRD), glow discharge optical emission spectrometry (GDOES), scanning electron microscopy (SEM) and by electrical measurements. In the range of annealing temperatures from 500°C to 700°C crystallization started and the structure changed from amorphous to polycrystalline. The NiO modified sensing films exhibit enhanced and improved sensing behavior to hydrogen at relatively low operating temperatures. The inversion of the conductivity type of response due to different H₂ concentrations has been observed. The critical H₂ concentration causing break of the p-type response to n-type response was identified. The temperature dependence of this critical concentration as a function of operating temperature was studied. Moreover, change of response type due to different annealing temperatures was achieved.

Keywords: Gas; Sensors; Sputtering; Hydrogen; TiO; ₂; NiO

2D irregular structure in the LED surface patterned by NSOM lithography by Ivana Kubicova; Dusan Pudis; Jaroslava Skriniarova; Jaroslav Kovac; Jaroslav Kovac Jr.; Jan Jakabovic; Lubos Suslik; Jozef Novak; Anton Kuzma (pp. 116-119).

Display Omitted► Effect of irregular structure surface on emission properties of the light emitting diode is investigated. ► NSOM lithography was used to pattern 2D irregular structure on the emitting surface of GaAs-based LED. ► Enhancement of radiation 1.2–1.5 times from the patterned air holes in comparison with the surrounding surface was proven.This contribution presents near-field scanning optical microscope (NSOM) in illumination mode as effective tool for semiconductor device surface patterning. Though the effect of periodic structure application on the light emitting diode (LED) surface is well known, for the first time, the effect of irregular structure is investigated. The non-contact mode of the NSOM lithography was used to pattern two-dimensional irregular structure on the emitting surface of GaAs/AlGaAs-based LED. The structure was patterned in the upper confinement AlGaAs layer and the enhancement of radiation 1.2–1.5 times from the patterned air holes in comparison with the surrounding surface was proven, which is similar to the enhancement of light extraction efficiency published for periodic structure application.

Keywords: Near-field scanning optical microscope; NSOM lithography; Light emitting diode; Irregular structure

Plume study by ion probe and morphology control during pulsed laser deposition of Sm1−_xNd_xNiO₃ by S. Lafane; T. Kerdja; B.D. Ngom; S. Abdelli-Messaci; S. Malek (pp. 120-124).

► We study the effect of oxygen pressure on ion dynamics and films microstructure. ► The ambient oxygen affects the ion dynamics when exceeding a threshold pressure. ► Three ionic components were observed in a certain range of oxygen pressure. ► Clusters formation and deposition were discussed. ► A correlation between the ion dynamics and the films microstructure was obtained.Plume dynamics was studied by ion probe diagnostics for Sm1−_xNd_xNiO₃ thin film deposition. The fluence was set at 2Jcm⁻² and the oxygen pressure was varied from vacuum to 1mbar. At vacuum and low oxygen pressure the ion expansion is free. A modulation of the ion kinetic energy can be done for pressures beyond 2×10⁻²mbar. In such case, the kinetic energy of the ions depends on the distance from the target. Depending on the oxygen pressure, different components of the ion flow were observed due to the ion-oxygen gas interaction and cluster formation. A correlation between the ion dynamics regarding the target–substrate distance and the morphology of the films deposited on (100) silicon substrate at 0.2mbar was obtained.

Keywords: PLD; Ion probe; Film morphology

The effect of multiwalled carbon nanotube doping on the CO gas sensitivity of TiO₂ xerogel composite film by Jin-Seok Lee; Tae-Jung Ha; Min-Hee Hong; Chang-Sun Park; Hyung-Ho Park (pp. 125-128).

Display Omitted► TiO₂ xerogel composite film containing MWCNTs(0.01wt%) to CO gas sensor application. ► Seven times higher sensitivity of the composite film than pure TiO₂ xerogel film. ► Well dispersion of MWCNTs in TiO₂ xerogel with 1.5 times increased surface area. ► n–p junction structure of TiO₂ xerogel coated on MWCNTs.A simple sol–gel method was applied for the synthesis of 0.01wt% multiwalled carbon nanotubes (MWCNTs)-doped TiO₂ xerogel composite film. The film's CO gas sensing properties were then evaluated. Doped MWCNTs were coated with TiO₂ and distributed on a TiO₂ xerogel matrix. The TiO₂ xerogel showed an anatase structure after heat treatment at 450°C under vacuum. The specific surface area of the composite material was larger than the pure TiO₂ xerogel material. The CO gas sensitivity of the MWCNTs(0.01wt%)-doped TiO₂ xerogel composite film was found to be seven times higher than that of pure TiO₂ xerogel film and to have good stability. This higher gas-sensing property of the composite film was due to both an increase of specific surface area and the n–p junction structure of the TiO₂ xerogel coated on MWCNTs. The electrons generated from TiO₂ after adsorption of CO gas induces electron transfer from the TiO₂ to the MWCNTs. This induces a characteristic change in the MWCNTs from p-type to n-type, and the resistance of MWCNTs-doped TiO₂ xerogel composite sensor is therefore decreased.

Keywords: TiO; ₂; xerogel; MWCNTs; CO gas sensor; Solvothermal drying; Sensitivity; Response time; Recovery time

Optical absorption and charging effect in nano-crystalline Ge/SiN x multilayers by Cong Li; Jun Xu; Ling Xu; Wei Li; Xiaofan Jiang; Shenghua Sun; Kunji Chen (pp. 129-133).

► Nanocrystalline Ge(nc-Ge)/SiN x multilayers with various size of nc-Ge are fabricated. ► The size-dependent optical absorption and band gap are observed. ► The carrier transport mechanism is dominated by space-charge limited current process. ► The charging storage effect is achieved in SiN x/nc-Ge/SiN x sandwiched structures.Nanocrystalline Ge (nc-Ge)/SiN x multilayers and sandwiched structures were fabricated by thermally annealing amorphous Ge/SiN x layered films at 600°C. The evolution of microstructure before and after annealing was studied by various characterization techniques, which reveals the formation of nc-Ge after annealing. The tunable optical absorption and band gap were observed by changing the grain size of nc-Ge. The study on carrier transport behavior of nc-Ge/SiN x MLs indicated that the transport process was dominated by space-charge limited current mechanism. Furthermore, the charging storage effect in SiN x/nc-Ge/SiN x floating gate structures was demonstrated due to both the electron and hole injection processes.

Keywords: Nanocrystalline Ge; Optical absorption; Carrier transport; Charging effect

Asymptotic properties of the variables of the roughness surface by A. Macurova; D. Macura (pp. 134-137).

► The variables as the roughness surfaces, the durability of the cutting tool, and the cutting forces are investigated with low cutting speed. ► The functions of the relations have the asymptotic properties as boundedness and non-boundedness. ► The mathematical dependence of the investigated variables are described by the one operator.The authentic technological process is described by the presented relation expressed by the consensus of the experiment. Theoretical information and new aspects on calculation of the roughness values of the cut surface for the chosen materials are being presented. The properties of the cut surface are being described by specific dependency of the cutting force at the cutting speed.

Keywords: PACS; 89.20.Bb; 81.20.Wk; 02.30.Tb; 06.20.JrDurability; Cutting speed; Roughness surface

Quantification of In_xGa1−_xP composition modulation by nanometric scale HAADF simulations by C.E. Pastore; M. Gutiérrez; D. Araújo; E. Rodríguez-Messmer (pp. 138-142).

► Use of scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) to quantify composition modulation. ► Quantification of composition modulation in In_xGa1−_xP layer. ► Absolute variation in Indium content in In_xGa1−_xP layer of 4.25%. ► The compositional variation of the compound affects the E_g, causing negative effects on the overall efficiency of the device.Multijunction solar cell efficiency is highly sensitive to structural and chemical variations. These variations can be quantified at nm scale in InGaP/InGaAs/Ge multijunctions using transmission electron microscopy modes, e.g. diffraction contrast (DC-CTEM) and high angle annular dark field (STEM-HAADF). These studies determined the structure and the composition modulation of InGaP layers with sensitivity below 1% of In composition. To quantify the In-related variation, STEM-HAADF profiles are compared to numerically simulated ones. The fit with the experimental contrast shows local variations of 4.25%In for distances below 30nm.

Keywords: Electron microscopy; Photovoltaic; Germanium; InGaP; Phase separation

Behaviour of amorphous silicon carbide in Au/a-SiC/Si heterostructures prepared by PECVD technology using two different RF modes by Milan Perný; Miroslav Mikolášek; Vladimír Šály; Michal Ružinský; Vladimír Ďurman; Milan Pavúk; Jozef Huran; Juraj Országh; Štefan Matejčík (pp. 143-147).

► Au/a-Si1−_xC_x/c-Si(p)/Al structures were prepared by PECVD deposition technique. ► Electrical and dielectrical properties of amorphous silicon carbide a-Si1−_xC_x:H films were studied ( C– V and I– V measurements). ► AFM and FTIR were used to study the surface of prepared films.Amorphous silicon carbide a-SiC (or more accurate a-Si1−_xC_x) thin films were prepared within Au/a-Si1−_xC_x/c-Si(p)/Al structures by PECVD deposition technique. Thin silicon carbide films on (100) silicon substrates were deposited using two different RF modes, i.e. placing the substrates either on electrically powered or grounded electrode. FTIR spectroscopy method was used for characterization of chemical bond states in the structure. Morphology of surface was analysed by AFM. C– V measurements on the prepared heterostructures were performed to evaluate the charge transport properties within the Au/a-Si1−_xC_x/c-Si(p)/Al structures. Temperature dependences of forward (FW) current–voltage ( I– V) characteristics of Au/a-Si1−_xC_x/c-Si(p)/Al structures are shown and analysed in this paper. Parameters as saturation current and activation energies were calculated from forward biased I– V curves.

Keywords: CVD technology; Electrical properties; C; –; V; measurements

About electrical properties of passivated SiO₂/Si structures prepared electro-chemically in HClO₄ solutions by Emil Pinčík; Hikaru Kobayashi; Jaroslav Rusnák; Masao Takahashi; Robert Brunner (pp. 148-154).

► New experimental results of passivation process of Si MOS structures in KCN and/or HCN solutions are presented. ► MOS samples annealed under bias at temperatures up to 500K were investigated. ► Mutual relation between density of interface defect states and flat-band voltage of C– V curves has been found.The contribution mainly presents results obtained on passivated SiO₂/Si structures prepared in HClO₄ solutions. The cleaned Si (100) wafers were immersed in 1M HClO₄ aqueous solutions and oxidized under positive bias. Results obtained on wet chemically prepared SiO₂/Si structures are compared with corresponding ones obtained on MOS formed by thermal oxidation at 850°C. Resulting oxide thicknesses of the layer prepared by electrochemical and thermal manners are ∼15nm and ∼7.5nm, respectively. All of prepared SiO₂/Si structures were passivated in HCN or KCN solutions. Low density of interface defect states below the level of ∼10¹¹eV⁻¹cm⁻² was determined on structures with the SiO₂ layer prepared electrochemically, passivated in aqueous HCN solutions, and annealed in vacuum at low temperatures. It has been shown that residual interface electron traps detected by Q-DLTS or C– V method after passivation procedures on electrochemically prepared samples can be partly transformed to mobile and/or immobile charged particles which shift the flat-band voltage of MOS and increase the magnitude of hysteresis of C– V curves.

Keywords: PACS; 73.20.±r; 78.55.Ap; 81.16±c; 85.40±eVery thin SiO; ₂; Passivation of MIS; HCN; KCN; Charge version of DLTS; C; –; V

Quantitative analysis of cathodoluminescence phenomena in InGaN/GaN QW by Monte Carlo method by J. Priesol; A. Šatka; F. Uherek; D. Donoval; P. Shields; D.W.E. Allsopp (pp. 155-160).

► CL spectra from InGaN/GaN SQW on nanopyramid were analysed by Monte Carlo method. ► Influence of electron beam parameters to the evolution of CL spectra was assessed. ► The InGaN/GaN recombination ratio rapidly decreases with increasing beam energy E_pe. ► The recombination in InGaN depends on diffusion length L in GaN and incidence angle. ► The recombination in InGaN reaches maximum at E_pe in dependence on L.In this paper, cathodoluminescence from InGaN/GaN single quantum wells grown on the facets of the GaN nano-pyramids has been quantitatively studied by Monte Carlo method. The influence of primary electron beam energy and the nanopyramid angle on generation of electron–hole pairs in individual parts of nanostructure has been studied by Monte Carlo simulations. The evolution of the GaN- and InGaN-related cathodoluminescence spectral lines with primary electron beam energy and angle of incidence has been assessed from the recombination rates in individual parts of the structure and compared with cathodoluminescence spectra measured at various beam energies. The possibility to determine the diffusion length of generated carriers in the structures like InGaN/GaN quantum wells using developed Monte Carlo simulator and CL measurements has been demonstrated.

Keywords: Spectral cathodoluminescence; InGaN/GaN quantum well; Nanopyramids; Monte Carlo simulation

Effect of 2D photonic structure patterned in the LED surface on emission properties by Dusan Pudis; Lubos Suslik; Jaroslava Skriniarova; Jaroslav Kovac; Jaroslav Kovac Jr.; Ivana Kubicova; Ivan Martincek; Stefan Hascik; Peter Schaaf (pp. 161-165).

► Influence of large and short period 2D PhC structures patterned in the LEDs surface was documented. ► Large period structure (2.4μm) achieved light extraction efficiency improvement based on diffraction on surface roughness. ► Short period (470nm) PhC structure is working as an effective radiation outcoupler using photonic band gap effect. ► 2D PhC LEDs show evident improvement of the light extraction efficiency based on different light outcoupling mechanisms.In this paper, effect of two-dimensional photonic crystal surface pattern on the emission properties of the GaAs/AlGaAs based light emitting diode (LED) is demonstrated. For surface patterning of the LED, the interference lithography based on a double-exposure process by two-beam interference optical field was used. Prepared photonic crystal structure in the LED surfaces was analyzed by atomic force microscope and scanning electron microscope. Emitting properties of the LEDs were investigated by L( I) measurements. Effect of large and short period of two-dimensional photonic structure on light extraction efficiency was documented.

Keywords: PACS; 81.16.Nd; 42.25.Hz; 85.60.Jb; 78.67.PtPhotonic crystal structure; Interference lithography; Optoelectronic device; Light emitting diode

GlyHisGlyHis immobilization on silicon surface for copper detection by Sabrina Sam; Anne Chantal Gouget-Laemmel; Jean-Noël Chazalviel; François Ozanam; Noureddine Gabouze (pp. 166-170).

Display Omitted► Covalent immobilization of GlyHisGlyHis peptide on SiH surface using multistep strategy. ► ATR-FTIR and AFM characterization of the surface at each stage of the functionalization. ► Electrochemical detection of copper using the peptide-modified electrode. ► The recorded cyclic voltammograms showed a surface reversible process. ► Potential role of peptide-modified silicon in developing strategies for metals detection.Hybrid nanomaterials based on organic layer covalently grafted on semi-conductor surfaces appear as promising systems for innovative applications, especially in sensor field. In this work, we focused on the functionalization of silicon surface by the peptide GlyHisGlyHis, which forms stable complexes with metal ions. This property is exploited to achieve heavy metals recognition in solution. The immobilization was achieved using multi-step reactions: GlyHisGlyHis was anchored on a previously prepared carboxyl-terminated silicon surface using N-ethyl-N′-(3-dimethylaminopropyl)-carbodiimide (EDC)/N-hydroxysuccinimide (NHS) coupling agents. This scheme is compatible with the mild conditions required for preserving the probe activity of the peptide. At each step of the functionalization, the surface was monitored by infrared spectroscopy Fourier transform (FTIR) in ATR (attenuated total reflexions) geometry and by atomic force microscopy (AFM). Electrochemical behaviour of such prepared electrodes was carried out in the presence of copper ions by means of cyclic voltammetry. The recorded cyclic voltammograms showed a surface reversible process corresponding to the Cu²⁺/Cu⁺ couple in the complex Cu–GlyHisGlyHis immobilized on the silicon surface. Copper ions concentrations down than μM where detected. These results demonstrate the potential role of peptide-modified silicon electrodes in developing strategies for simple and fast detection of toxic metals in solution.

Keywords: Silicon functionalization; Peptide immobilization; Cyclic voltammetry

Electrocatalytic and photocatalytic activity of Pt–TiO₂ films on boron-doped diamond substrate by Tanţa Spătaru; Maria Marcu; Nicolae Spătaru (pp. 171-174).

► Pt–TiO₂ films were electrodeposited on boron-doped diamond (BDD) electrodes. ► BDD substrate enables more efficient separation of photogenerated charge carriers. ► On TiO₂ films, the active surface area of Pt particles is strongly enhanced. ► Pt/TiO₂/BDD electrodes show promising photocatalytic activity for CH₃OH oxidation.In the present work boron-doped diamond (BDD) polycrystalline films were used as support for direct anodic deposition of hydrous titanium oxide, and continuous TiO₂ coatings were obtained by appropriately adjusting the deposition charge. The photoelectrochemical activity of the TiO₂/BDD electrodes was investigated and it was found that, in terms of charge carriers separation efficiency, conductive diamond is a much better support for TiO₂, compared to traditional carbonaceous materials such as glassy carbon. Further electrochemical deposition of platinum particles on the oxide-coated conductive diamond enabled the formation of a composite with enhanced electrochemically active surface area. The electrocatalytic and photocatalytic properties of the Pt/TiO₂/BDD electrodes thus obtained were also scrutinized and it appeared that these hybrid systems also exhibit promising features for methanol anodic oxidation.

Keywords: Titanium oxide; Electrodeposition; Boron-doped diamond; Methanol oxidation

Electrical characterization of the A_IIIB_V-N heterostructures by capacitance methods by Ľubica Stuchlíková; Ladislav Harmatha; Miroslav Petrus; Jakub Rybár; Ján Šebok; Beata Ściana; Damian Radziewicz; Damian Pucicki; Marek Tłaczała; Arpád Kósa; Peter Benko; Jaroslav Kováč; Peter Juhász (pp. 175-179).

► Three MQW InGaAsN/GaAs heterostructures with various nitrogen ratios were compared. ► CV method and Deep Level Transient Spectroscopy measurements were used. ► Fluctuations in CV curves around 0V are due to free carriers’ emission from QW. ► DLTS shows that the similar system of defects is present in all samples. ► Multilevel evaluation confirmed the presence of deep level ET1 in all samples.This paper highlights the electrical characterization of three types of the multiple quantum well (MQW) InGaAsN/GaAs heterostructures labelled NI58n, NI59n and NI66n with the nitrogen concentration of about 0.4% and indium content of 12.1%, 13.5% and 13.0%, respectively, using capacitance methods. These MQW InGaAsN/GaAs heterostructures were grown by atmospheric pressure metal organic vapour phase epitaxy (APMOVPE) at various growth conditions. The capacitance-voltage and DLTS measurements of these structures were performed utilizing the measurement system BIORAD DL8000.The CV characteristics measured at different temperatures on all heterostructures show very fine fluctuations of capacitance in the voltage range around 0V, which is suggested to be a result of free carriers’ emission from quantum wells. The absence of GaAs “cap” layer in one of the samples shifted its CV characteristic to lower values of capacity.According to the DLTS measurement it is highly probable that the similar system of defects is present in all samples. The presence of the deep level ET1 is clear in all samples and its parameters were calculated by multi level evaluation (the activation energy of the defect which is approx. Δ E_T=0.62eV, value of effective capture cross-section of the defect σ_T is about 10⁻¹⁶cm², and defects concentration N_T is about 10¹⁴cm⁻³).

Keywords: MQW InGaAsN/GaAs; Deep Level Transient Fourier Spectroscopy; Capacitance voltage measurements; Deep energy levels; Schottky diodes; Dilute nitrides

Electrochemical gas sensors based on polypyrrole-porous silicon by Fatma-Zohra Tebizi-Tighilt; Fawzi Zane; Naima Belhaneche-Bensemra; Samia Belhousse; Sabrina Sam; Nour-Eddine Gabouze (pp. 180-183).

► Polymerization of pyrrole into regularly nanostructured Si/PS and Si/oxide PS from CH₃CN solution was investigated. ► The polymerization process showed different characteristic stages in both potential and current transients. ► The oxidation of PS has a preferential nucleation of PPy at the pore bottom, and deposition of PPy inside the pores followed by polymerization at the outer surface. ► The results presented in this work show that Si/oxide PSi/PPy and Si/PS/PPy structures can be used as a sensor for CO₂ gas. ► These sensors are extremely sensitive, have a good response and recovery time.This work consists in elaborating a gas sensor based on porous silicon and a polypyrrole obtained by covalent grafting and studying its answer in different environments. At first, we were interested in the formation of the nanoporous layers by cyclovoltammetric (CV) in a hydrofluoric acid solution followed by an electrochemical grafting of the polypyrrole (PPy) on the porous silicon and oxide porous silicon surfaces.The various interfaces were characterized using different techniques such as Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). Finally, a series of electric characterizations to study the answer of the structures in the contact of the carbon dioxide was achieved.

Keywords: Electrochemical synthesis; Porous silicon; Polypyrrole; Gas sensors

Surface potential patterning of hydroxyapatite films by focused electron beam: Influence of the electron energy by Martin Truchly; Tomas Plecenik; Katarina Secianska; Maros Gregor; Miroslav Zahoran; Melinda Vargova; Marian Mikula; Branislav Grancic; Gustav Plesch; Syed A.M. Tofail; Peter Kus; Andrej Plecenik (pp. 184-187).

► Surface potential of hydroxyapatite films was locally modified by electron beam. ► Resulting surface potential domains were examined by Kelvin probe force microscopy. ► Size of the domains strongly depends on the incident electron energy. ► Minimal domain size is limited by the e-beam diameter and its interaction volume. ► Smaller domains obtained by using smaller current compensated by longer irradiation.Surface potential (SP) of biomaterials surfaces is known to significantly influence adsorption of biological cells and biomolecules. Its modifications thus play an important role in biological and medical applications. In this work, focused electron beam typically available in scanning electron microscopes has been used to create micro-domains with modified SP on nano-crystalline hydroxyapatite thin films. The resulting SP distribution has been studied by the Kelvin probe force microscopy technique as a function of the incident electron energy in the range from 3 to 30keV for varying beam current, i.e. speed of the charge injection. Factors limiting minimal size of such SP patterns are discusses.

Keywords: Kelvin probe force microscopy; Surface potential; Hydroxyapatite; Electron beam

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