Jan Ivanco
Slovak Academy of Sciences, Institute of Physics, Department Member
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The electronic level alignment of the organic semiconductor para-sexiphenyl on a nanoscopically patterned substrate was investigated with ultraviolet photoemission spectroscopy, work function measurements and scanning tunnelling... more
The electronic level alignment of the organic semiconductor para-sexiphenyl on a nanoscopically patterned substrate was investigated with ultraviolet photoemission spectroscopy, work function measurements and scanning tunnelling microscopy. The results show that for increasing coverage on inhomogeneous surfaces, shifts in electronic level alignment occur, which are due to the change from local to average band alignment. The Cu(110)–(2×1)O stripe phase, used
Research Interests: Engineering, Materials Science, Chemistry, Nanoelectronics, Organic Semiconductors, and 15 moreOrganic Electronics, Molecular Electronics, Copper, Thin Film, Physical sciences, Nanostructures, Nanostructure, Photoemission Spectroscopy, Dipole, CHEMICAL SCIENCES, Scanning Electron Microscope, Photoemission, Potential Energy Surface, Tunnel Effect, and Scanning Microscope
The ability to control the interparticle distance in self-assembled arrays of nanoparticles plays an important role in a large number of applications, which require tunable electronic and photonic properties. Importantly,...
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ABSTRACT A method of observation of interface states for ultrathin insulating layer/semiconductor interfaces is developed by use of X-ray photoelectron spectroscopy (XPS) measurements under bias. The analysis of the energy shift of the... more
ABSTRACT A method of observation of interface states for ultrathin insulating layer/semiconductor interfaces is developed by use of X-ray photoelectron spectroscopy (XPS) measurements under bias. The analysis of the energy shift of the semiconductor core level as a function of the bias voltage gives energy distribution of interface states. When the atomic density of SiO2 layers is low (e.g., SiO2 layers formed at 350 °C), only one interface state peak is observed near the midgap, and it is attributed to isolated Si dangling bonds at the interface. For SiO2 layers with a high atomic density (e.g., SiO2 layers formed at 700 °C), on the other hand, two interface state peaks, one above and the other below the midgap, are observed, and they are attributed to Si dangling bonds interacting weakly with a Si or oxygen atom in SiO2. Interface states can be passivated by cyanide treatment which simply involves the immersion in cyanide solutions such as KCN and HCN solutions. When the cyanide treatment is applied to 〈indium tin oxide/SiO2/mat-textured single crystalline Si〉 metal-oxide-semiconductor (MOS) solar cells, the photovoltage is greatly increased, leading to a high conversion efficiency of 16.2%. When the cyanide treatment is performed on polycrystalline Si (poly-Si)-based MOS diodes, a greater effect in comparison to that for single crystalline Si-based MOS diodes is observed due to the elimination of defect states in poly-Si as well as Si/SiO2 interface states. The cyanide treatment can also increase the conversion efficiency of pn-junction single crystalline and poly-Si solar cells.
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NO2 and H2 gas sensing by few-layer graphene (FLG) were studied in dependence on the annealing and decoration of graphene by palladium nanoparticles (NPs). Graphene was deposited onto SiO2 (500 nm)/Si substrates by a modified... more
NO2 and H2 gas sensing by few-layer graphene (FLG) were studied in dependence on the annealing and decoration of graphene by palladium nanoparticles (NPs). Graphene was deposited onto SiO2 (500 nm)/Si substrates by a modified Langmuir-Schaefer technique. A solution of FLG flakes in 1-methyl-2-pyrrolidone was obtained by a mild sonication of the expanded milled graphite. FLG films were characterized by atomic force microscopy, X-ray diffraction, Raman spectroscopy, and the Brunnauer-Emmett-Teller method. Average FLG flake thickness and lateral dimension were 5 nm and 300 nm, respectively. Drop casting of Pd NP (6–7 nm) solution onto FLG film was applied to decorate graphene by Pd. The room temperature (RT) resistance of the samples was stabilized at 15 kΩ by vacuum annealing. Heating cycles of FLG film revealed its semiconducting character. The gas sensing was tested in the mixtures of dry air with H2 gas (10 to 10 000 ppm) and NO2 gas (2 to 200 ppm) between RT and 200 °C. The respon...
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The Fe2O3 and CoFe2O4 nanoparticle-based Langmuir-Blodgett lms for sensingof nitrogen dioxide (NO2) and acetone vapours have been explored. Both the sensitivity of thechemiresistors and dynamic properties, such as the response/recovery... more
The Fe2O3 and CoFe2O4 nanoparticle-based Langmuir-Blodgett lms for sensingof nitrogen dioxide (NO2) and acetone vapours have been explored. Both the sensitivity of thechemiresistors and dynamic properties, such as the response/recovery time, have been probed independence of the number of nanoparticle monolayers and working temperatures. The responseof 23 at the NO2 concentration of 1 ppm has been monitored suggesting the pertinent sensitivityin the deep sub-ppm range, i.e. approaching the canine detection limit, and likewise implyingthe supposable detection of nitrate-based explosives.
Research Interests: Engineering, Nanoelectronics, Organic Semiconductors, Organic Electronics, Molecular Electronics, and 14 moreCopper, Ultraviolet, Thin Film, Physical sciences, Nanostructures, Nanostructure, Photoemission Spectroscopy, Dipole, CHEMICAL SCIENCES, Scanning Electron Microscope, Work Function, Photoemission, Potential Energy Surface, and Tunnel Effect
This work reports on the X-ray photoemission spectroscopy (XPS) measurements of the As-rich GaAs(001) surface properties developing due to the different thicknesses of the undoped silicon overlayers. We analyzed the bond nature on the... more
This work reports on the X-ray photoemission spectroscopy (XPS) measurements of the As-rich GaAs(001) surface properties developing due to the different thicknesses of the undoped silicon overlayers. We analyzed the bond nature on the silicon–GaAs interface depending on the silicon thickness which was connected with observed variations in surface Fermi level positions. Further, the Au\Si\n-GaAs metal-semiconductor contacts were prepared on
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ABSTRACT The electronic properties of molecular films are analysed with the consideration of the molecular orientation. The study demonstrates that surfaces of electroactive oligomeric molecular films can be classified—analogously to the... more
ABSTRACT The electronic properties of molecular films are analysed with the consideration of the molecular orientation. The study demonstrates that surfaces of electroactive oligomeric molecular films can be classified—analogously to the elemental surfaces—by their intrinsic work functions. The intrinsic work function of molecular films is correlated with their ionisation energies; again, the behaviour is analogous to the correlation existing between the first ionisation energy of elements and the work function of the corresponding elemental surfaces. The proposed intrinsic work-function concept suggests that the mechanism for the energy-level alignment at the interfaces associated with molecular films is virtually controlled by work functions of materials brought into the contact.
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ABSTRACT Here the morphology, molecular orientation and electronic structure of in situ prepared para-sexiphenyl (6P) and α-sexithiophene (6T) films studied with atomic force microscopy, near edge X-ray absorption fine structure... more
ABSTRACT Here the morphology, molecular orientation and electronic structure of in situ prepared para-sexiphenyl (6P) and α-sexithiophene (6T) films studied with atomic force microscopy, near edge X-ray absorption fine structure spectroscopy and valence band photoemission are presented. Attention is given to the differences between different organic crystallite orientations and the pitfalls in the interpretation of area averaging surface sensitive techniques that can arise from inhomogeneities in the films, which commonly occur even on single crystal inorganic substrates. The growth of organic–organic heterostructures is then considered for sexithiophene films grown on homogeneous upright (6P(001)) and lying (6P(203)) crystalline films. In both cases, the orientation of the substrate molecules is imposed on the molecules of the second species and thick films of upright-on-upright or lying-on-lying could be produced. The organic substrates are thus shown to be excellent templates for further organic film growth that do not require the stringent UHV conditions of inorganic templates.
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ABSTRACT The chemical and electronic structure of indium on copper phthalocyanine CuPc contacts is addressed. Both core levels and valence band evolutions were inspected during the incremental formation of the indium CuPc interface. In... more
ABSTRACT The chemical and electronic structure of indium on copper phthalocyanine CuPc contacts is addressed. Both core levels and valence band evolutions were inspected during the incremental formation of the indium CuPc interface. In contrast to the previous study [V. Y. Aristov et al., Phys. Rev. B 72, 165318 2005 ], our results suggest that the In CuPc system is not a reactive one. This is corroborated by the absence of reactive components in the C amp; 8201;1s and N amp; 8201;1s regions. A component shifted toward high binding energy in the In amp; 8201;4d spectrum and gap states the latter emerging between the highest occupied molecular orbital and the Fermi level, which were regarded as an evidence of a reaction between In and CuPc are consistently interpreted in terms of the final state effect of finite indium nanoclusters exposed at the CuPc surface.
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ABSTRACT The electronic structure of highly-ordered copper phthalocyanine (CuPc) thin films is unravelled. The deconvolution of the well-resolved valence band spectra allowed an extraction of energy levels of particular molecular orbitals... more
ABSTRACT The electronic structure of highly-ordered copper phthalocyanine (CuPc) thin films is unravelled. The deconvolution of the well-resolved valence band spectra allowed an extraction of energy levels of particular molecular orbitals in the low binding energy part of the π-band, an approach which is often neglected in the data analysis. Quantitative analysis of the incidence photon energy dependence of the particular orbitals was exerted to address their character in terms of the contribution of constituent atoms. The line shape of the valence band was found to be closely related to the molecular orientation in the films. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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The effect of the ultrathin interfacial layer of silicon nitride deposited by remote plasma-enhanced chemical vapor deposition technique on the Schottky barrier characteristics of Au/n-GaAs contacts is investigated. The changes of both... more
The effect of the ultrathin interfacial layer of silicon nitride deposited by remote plasma-enhanced chemical vapor deposition technique on the Schottky barrier characteristics of Au/n-GaAs contacts is investigated. The changes of both capacitance-voltage and current-voltage characteristics, in dependence on the interfacial layer thicknesses are discussed and explained on the basis of the surface passivation. The influence of thermal annealing on
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ABSTRACT We report a modification by thin silicon nitride intralayers of the Au/n-GaAs)(100) Schottky barrier height. Thin intralayers were obtained by nitridation of evaporated Si films on decapped GaAs substrates in an argon-nitrogen... more
ABSTRACT We report a modification by thin silicon nitride intralayers of the Au/n-GaAs)(100) Schottky barrier height. Thin intralayers were obtained by nitridation of evaporated Si films on decapped GaAs substrates in an argon-nitrogen mixture plasma. The nitridation was performed at a beam energy <40 eV, with 573 K sample temperature. Gold was deposited to study in situ the Schottky barrier formation process with x-ray photoelectron spectroscopy. Internal photoemission spectroscopy and current-voltage measurements were used to evaluate the barrier modification on fully formed interfaces. Such a modification was analyzed in terms of theoretical calculations of the dipole created by the substrate-intralayer bonds. (C) 1997 American Institute of Physics.
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ABSTRACT This Letter reports the impact of the evaporation rate on the crystallographic phase formation of vacuum deposited α-sexithiophene thin films studied by X-ray diffraction methods. The experiments reveal the formation of two... more
ABSTRACT This Letter reports the impact of the evaporation rate on the crystallographic phase formation of vacuum deposited α-sexithiophene thin films studied by X-ray diffraction methods. The experiments reveal the formation of two crystal phases, one of which is a thermodynamically stable phase occurring at low rates, while the second is favored by high rates. This second phase exhibits an increased layer spacing and diffraction features typical for two-dimensional crystals which are laterally ordered but without interlayer correlations of the molecular positions. This disordered layered phase comprises molecules of nonuniform conformations, and is kinetically induced.
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Heavily doped (100) GaAs:Si substrates were exposed for up to 32 min to H2 + Ar discharges while keeping the substrates at 300°C. Both direct and remote mode plasma exposures were conducted with the aim of comparing the respective... more
Heavily doped (100) GaAs:Si substrates were exposed for up to 32 min to H2 + Ar discharges while keeping the substrates at 300°C. Both direct and remote mode plasma exposures were conducted with the aim of comparing the respective plasma-induced damages. After the remote hydrogen plasma treatment, not only the amount of charge released from plasma-induced deep levels in Al/GaAs diodes in the course of a DLTS scan had been reduced, moreover, the zero-bias crossover EFT of the Fermi level and the trap level could be shifted up to EC − EFT ≈ 0.01 eV. The latter shift was not connected with any changes of the Al/GaAs barrier height which was found to be essentially insensitive to the plasma treatment (φB ≈ 0.8 eV). Nevertheless, the distributed damage-related energy levels of all processed substrates could be characterized by a unique dependence of the capture cross-section σ on the activation enthalpy ΔE of the corresponding charge deep-level transient spectroscopy (DLTS) peaks as σ = σ0exp(ΔEE0), E0 being a constant. Finally, we constructed an equivalent ln σ versus ΔE plot for charge DLTS data of Al/Si3N4/GaAs metal-insulator-semiconductor (MIS) structures with silicon nitride layers prepared in the same reactor at comparable temperatures, and included it in the Al/GaAs-related data. The combined data provided a single plot that exhibits two perfectly jointed branches differing in respective slopes. As expected, shallow Si-donor passivation could be detected too, the efficiency of the latter reaching 90% under the direct mode hydrogen plasma conditions.
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... FP Netzer Institut für Experimentalphysik, Karl-Franzens-Universität Graz A-8010 Graz (Austria) E-mail: michael.ramsey@uni-graz.at [**] Supported by the ... On the one hand, high substrate temperatures are often used to try and... more
... FP Netzer Institut für Experimentalphysik, Karl-Franzens-Universität Graz A-8010 Graz (Austria) E-mail: michael.ramsey@uni-graz.at [**] Supported by the ... On the one hand, high substrate temperatures are often used to try and promote crystallinity, which will lead to type I. On ...
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ABSTRACT This Letter reports the impact of the evaporation rate on the crystallographic phase formation of vacuum deposited α-sexithiophene thin films studied by X-ray diffraction methods. The experiments reveal the formation of two... more
ABSTRACT This Letter reports the impact of the evaporation rate on the crystallographic phase formation of vacuum deposited α-sexithiophene thin films studied by X-ray diffraction methods. The experiments reveal the formation of two crystal phases, one of which is a thermodynamically stable phase occurring at low rates, while the second is favored by high rates. This second phase exhibits an increased layer spacing and diffraction features typical for two-dimensional crystals which are laterally ordered but without interlayer correlations of the molecular positions. This disordered layered phase comprises molecules of nonuniform conformations, and is kinetically induced.
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The strain-resistance transduction of commercially available In 2 O 3 /Au/Ag layered films supported by polyethyl-ene terephthalate (PET) foil was studied. A colossal gauge factor as high as about 60,000 was observed upon a strain of 1%.... more
The strain-resistance transduction of commercially available In 2 O 3 /Au/Ag layered films supported by polyethyl-ene terephthalate (PET) foil was studied. A colossal gauge factor as high as about 60,000 was observed upon a strain of 1%. Such ultra-high response is presumably owing to conductivity derived from the tunnelling current across cracks formed in the strained In 2 O 3 film; the cracks – as visualized by scanning electron microscopy – are oriented perpendicularly to the strain vector and are noted for their uniform width across the sample. It is further demonstrated that the standardly defined gauge factor is incommensurate for strain sensors with transduc-tion based on the tunnelling current and a redefined formula for the gauge factor was proposed.
The energy level alignment of sexithiophene monolayer and multilayer films grown on a variety of well-defined substrates with different work functions is presented in this study. The ionization potential of the films as measured by... more
The energy level alignment of sexithiophene monolayer and multilayer films grown on a variety of well-defined substrates with different work functions is presented in this study. The ionization potential of the films as measured by valence band photoemission is found to have two distinct values that differ by ˜0.8 eV depending on substrate and/or growth conditions of the films. The results suggest the necessity of considering the variance of the ionization potential for the correct interpretation of energy level alignment obtained by photoemission; we demonstrate that the commonly reported absence of the relation between the band alignment and the substrate work function is partly determined by extrinsic effects. These are induced by varying electronic properties of solid films in addition to the intrinsic effects of the interfaces.
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Even though the term `organic electronics' evokes rather organic devices, a significant part of its scope deals with physical properties of `active elements' such as organic films and interfaces. Examination of the film growth and... more
Even though the term `organic electronics' evokes rather organic devices, a significant part of its scope deals with physical properties of `active elements' such as organic films and interfaces. Examination of the film growth and the evolution of the interface formation are particularly needful for the understanding a mechanism controlling their final properties. Performing such experiments in an ultra-high vacuum allows both to `stretch' the time scale for pseudo real-time observations and to control properties of the probed systems on the atomic level. Photoemission technique probes directly electronic and chemical structure and it has thereby established among major tools employed in the field. This review primarily focuses to electronic properties of oligomeric molecular films and their interfaces examined by photoemission. Yet, it does not aspire after a complete overview on the topic; it rather aims to otherwise standard issues encountered at the photoemission cha...