Fyzikální ústav

Nejnovější přírůstky:
2017-10-04
17:58
Back electrode influence on opto-electronic properties of organic photovoltaic blend characterized by Kelvin probe force microscopy
Čermák, Jan ; Miliaieva, Daria ; Hoppe, H. ; Rezek, Bohuslav
Organic photovoltaic (PV) system consisting of P3HT:PCBM blend layer was prepared with an aluminum (Al) back electrode. After the final thermal annealing the Al layer was partially removed. Kelvin Probe Force Microscopy (KPFM) was used to measure photovoltage response to illumination by a solar spectrum light as a function of time (up to 3 weeks). Comparison of the same KPFM measurement on the areas with and without Al revealed differences in both morphology and photovoltage response to illumination. The data are discussed with view to reducing degradation of organic PV devices.\n

Úplný záznam
2017-10-04
17:58
Correlated microscopy of electronic and material properties of graphene grown on diamond thin films
Rezek, Bohuslav ; Čermák, Jan ; Varga, Marián ; Tulic, S. ; Skákalová, V. ; Waitz, T. ; Kromka, Alexander
In this work we compare growth of graphene on diamond thin films that enable large area processing. We use films with different crystal size and surface roughness to obtain deeper insight into formation and properties of GoD. The diamond films are coated by a nm thin sputtered Ni layer and heated to 900°C in a forming gas atmosphere (H2/Ar) to initiate catalytic thermal CVD process. The samples are cleaned from residual Ni after the growth process. We employ scanning electron microscopy, Raman micro-spectroscopy and Kelvin probe force microscopy to correlate material, structural, and electronic properties of graphene on diamond. We show how grain size and grain boundaries influence graphene growth and material and electronic properties. For instance we show that the grain boundaries (with non-diamond carbon phases) in diamond films have an important role. They influence the electronic properties and they are beneficial for forming graphene on diamond higher quality.

Úplný záznam
2017-10-04
17:58
Spatially separated HOMO/LUMO at interface of polypyrrole physisorbed on oxidized nanodiamond facets
Matunová, Petra ; Jirásek, Vít ; Rezek, Bohuslav
Nanodiamond particles (NDs) have recently risen in popularity owing to their unique and perspective properties. Merging NDs with organic molecules, such as polypyrrole (PPy), into hybrid organic-semiconductor functional systems gives rise to potential applications in photovoltaics (PV), which is supported by prior experimentally observed charge transfer between bulk diamond and PPy. This work focuses on the most relevant (111) and (100) O-terminated ND facets with different coverage of surface terminating oxygens in ether, epoxide, ketone, and peroxide positions. We use density functional theory (DFT) computations employing B3LYP functional and 6-31G(d) basis set. Energetically the most favorable oxidized ND facets were further optimized with PPy in physisorbed configurations. Analysis of geometry, binding energy, HOMO-LUMO gap, and charge transfer was done on the relaxed PPy-ND structures. Multiple hydrogen bonds are formed between PPy amino groups and O atoms on ND surface.

Úplný záznam
2017-10-04
17:58
The deposition of germanium nanoparticles on hydrogenated amorphous silicon
Stuchlík, Jiří ; Volodin, V.A. ; Shklyaev, A.A. ; Stuchlíková, The-Ha ; Ledinský, Martin ; Čermák, Jan ; Kupčík, Jaroslav ; Fajgar, Radek ; Mortet, Vincent ; More Chevalier, Joris ; Ashcheulov, Petr ; Purkrt, Adam ; Remeš, Zdeněk
We reveal the mechanism of Ge nanoparticles (NPs) formation on the surface of the hydrogenated amorphous silicon (a-Si:H) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) on ITO and a on boron doped nanocrystalline diamond (BDD). The coating of Ge NPs on a-Si:H was performed by molecular beam epitaxy (MBE) at temperatures up to 450 °C. The Ge NPs were characterized by Raman spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The nanocrystalline Ge particles are conglomerates of nanocrystals of size 10-15 nm and quantum dots (QDs) with size below 2 nm embedded in amorphous Ge phase. After coating with Ge NPs the a-Si:H thin films show better adhesion on BDD substrates then on ITO substrates.

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2017-10-04
17:58
Preparation of zinc oxide nanorods colloid from thin layers
Mičová, Júlia ; Remeš, Zdeněk ; Chang, Yu-Ying ; Neykova, Neda
The interest in ZnO (zinc oxide) nanoparticles is increasing due to low cost of their processing as well as the ability of fabricating ZnO nanostructures with controllable morphology such as size, shape and orientation. Our choice of method of the preparation of the nanostructured thin ZnO layers is the hydrothermal growth of ZnO nanorods on glass substrates coated by the nucleation layer deposited by the reactive magnetron sputtering. We have developed and optimized conditions of the thin layer growth with controllable dimensions of nanorods followed by the ultrasound peeling. The colloid of ZnO nanorods was characterized by measuring the size of particles using the dynamic light scattering (DLS) and the scanning electron microscopy (SEM). We found that the dynamic light scattering (DLS) can’t be directly used for size evaluation of ZnO nanorods due to their non- sperical shape. \n

Úplný záznam
2017-10-04
17:58
Hydrogen plasma treatment of ZnO thin films
Chang, Yu-Ying ; Neykova, Neda ; Stuchlík, Jiří ; Purkrt, Adam ; Remeš, Zdeněk
ZnO is an attractive wide band gap semiconductor with large exciton binding energy, high refractive index, high biocompatibility and diversety of nanostructure shapes which makes it suitable for many applications in the optoelectronic devices, optical sensors, and biosensors. We study the effect of hydrogen plasma treatment of the nominally undoped ZnO thin film deposited by DC reactive magnetron sputtering of Zn target in the gas mixture of argon and oxygen plasma. The SEM images show that the crystal size increases with film thickness. We confirm, that the electrical conductivity significantly increases after hydrogen plasma treatment by 4 orders of magnitude. Moreover, the increase of the infrared optical absorption, related to free carrier concentration, was detected below the optical absorption edge by the photothermal deflection spectroscopy.\n

Úplný záznam
2017-10-04
17:58
The intrinsic submicron ZnO thin films prepared by reactive magnetron sputtering
Remeš, Zdeněk ; Stuchlík, Jiří ; Purkrt, Adam ; Chang, Yu-Ying ; Jirásek, Vít ; Štenclová, Pavla ; Prajzler, V. ; Nekvindová, P.
The DC reactive magnetron sputtering of metallic target in oxide atmosphere is a simple method of depositing the intrinsic (undoped) nanocrystalline layers of metal oxides. We have optimized the deposition of the intrinsic ZnO thin films with submicron thickness 50−500 nm on fused silica glass substrates and investigated the localized defect states below the optical absorption edge down to 0.01 % using photothermal deflection spectroscopy from UV to IR. We have shown that the defect density, the optical absorptance and the related optical attenuation in planar waveguides can be significantly reduced by annealing in air at 400 °C.

Úplný záznam
2017-10-04
17:58
Transfer of electrons or holes between localized states. Application to polymer electric conductivity
Král, Karel ; Menšík, Miroslav
Basing on the quantum transport formalizm a formula for the irreversible transfer of charged particles has been introduced by us recently. This formula is expected to be suitable for the theoretical description of the electron or hole transfer between quantum dots, other nanoparticles, molecules, and so on. We discuss shortly the main physical properties of the formula. We also demonstrate the use of the formula for the theoretical analysis of the electronic physical properties of some electrically conductive polymers.\n

Úplný záznam
2017-10-04
17:58
Mechanical properties of Cr-DLC layers prepared by hybrid laser technology
Písařík, Petr ; Jelínek, Miroslav ; Remsa, J. ; Tolde, Z.
Diamond like carbon (DLC) layers have excellent biological properties for use in medicine for coating implants, but poor adhesion to biomedical alloys (titanium alloys, chromium alloys and stainless steel). The adhesion can be improved by doping the DLC layer by chromium, as described in this article. Chromium doped diamond like carbon layers (Cr DLC) were deposited by hybrid deposition system using KrF excimer laser (deposition diamond like carbon - graphite target) and\nmagnetron sputtering (deposition chromium - chromium target). Carbon and chromium contents were determined by wavelength dispersive X-ray spectroscopy.\n

Úplný záznam
2017-10-04
17:58
DLC/TI thin films properties prepared by hybrid laser technologies
Mikšovský, Jan ; Jelínek, Miroslav ; Písařík, Petr ; Kocourek, Tomáš ; Remsa, J. ; Jurek, Karel
Layers of diamond-like carbon are usable in many fields of industry as well as in medicine. Many scientific groups have worked with different types of deposition techniques to prepare DLC layers with improved or unique properties. The DLC properties could be improved by various dopations. In this study, we focused on DLC layers doped by titanium, prepared by hybrid laser depositions. Two techniques were used: Dual pulse laser deposition (DualPLD) and pulse laser deposition in combination with magnetron sputtering (PLD/MS). Preliminary tests for morphology, wettability, adhesion, hardness, corrosion, friction and wearability were examined. DLC samples were prepared on Si(100) wafer and on Ti6Al4V alloy substrates with titanium concentration from pure up to 25 at.%. Friction of the prepared layers ranged from 0.09 to 0.18. The films exhibited very low wear for loads 1 N and 2 N.\n

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