Fabrication by Spin-Coating and Optical Characterization of Poly(styrene-co- acrylonitrile) Thin Films

The optical characteristics of poly(styrene-co- acrylonitrile) thin films obtained by spin- coating of polymer blend in tetrahydrofuran were investigated by spectroscopic ellipsometry, spectrophotometry, and atomic force microscopy. Film thickness can be broadly varied by changing the polymer concentration.The film thickness dependence on PSAN concentration shows a non- linear behavior that can be explained by a concentration-dependent viscosity. According to previously proposed models, prepared solutions are close to the concentrated solution regime. Films show a broad transparency range and refractive index independent of film thickness. The refractive index values range from 1.55 to 1.6 in the visible range. Thermal treatment revealed good stability of the films up to 220 °C and a progressive deterioration for larger temperatures, with evident damage at 300 °C. UV- induced photodegradation was observed and results showed a progressive decrease of transmittance in the range between 200 and 300 nm but PSAN thin films show no changes when exposed to light from a solar illuminator. These investigations indicate that PSAN is an excellent candidate for thin film polymer-based optical uses like interference coatings or encapsulation of solar cell

Depth profiling of Cr-ITO dual-layer sample with secondary ion mass spectrometry using MeV ions in the low energy region

This work explores the possibility of depth profiling of inorganic materials with Megaelectron Volt Secondary Ion Mass Spectrometry using low energy primary ions (LE MeV SIMS), specifically 555 keV Cu ²⁺ , while etching the surface with 1 keV Ar ⁺ ions. This is demonstrated on a dual-layer sample consisting of 50 nm Cr layer deposited on 150 nm In2O5Sn (ITO) glass. These materials proved to have sufficient secondary ion yield in previous studies using copper ions with energies of several hundred keV. LE MeV SIMS and keV SIMS depth profiles of Cr-ITO dual-layer are compared and corroborated by atomic force microscopy (AFM) and time-of-flight elastic recoil detection analysis (TOF-ERDA). The results show the potential of LE MeV SIMS depth profiling of inorganic multilayer systems in accelerator facilities equipped with MeV SIMS setup and a fairly simple sputtering source

Influence of RF excitation during pulsed laser deposition in oxygen atmosphere on the structural properties and luminescence of nanocrystalline ZnO:Al thin films

Thin ZnO:Al layers were deposited by pulsed laser deposition in vacuum and in oxygen atmosphere at gas pressures between 10 and 70 Pa and by applying radio-frequency (RF) plasma. Grazing incidence small angle x-ray scattering and grazing incidence x-ray diffraction (GIXRD) data showed that an increase in the oxygen pressure leads to an increase in the roughness, a decrease in the sample density, and changes in the size distribution of nanovoids. The nanocrystal sizes estimated from GIXRD were around 20 nm, while the sizes of the nanovoids increased from 1 to 2 nm with the oxygen pressure. The RF plasma mainly influenced the nanostructural properties and point defects dynamics. The photoluminescence consisted of three contributions, ultraviolet (UV), blue emission due to Zn vacancies, and red emission, which are related to an excess of oxygen. The RF excitation lowered the defect level related to blue emission and narrowed the UV luminescence peak, which indicates an improvement of the structural ordering. The observed influence of the deposition conditions on the film properties is discussed as a consequence of two main effects: the variation of the energy transfer from the laser plume to the growing film and changes in the growth chemistry

Manipuliranje Diracovim elektronima pomoću nanometarske modulacije epitaksijalnoga grafena

Structurally modulated graphene presents a new variety of this 2D material which offers a possibility of electronic band engineering and promises to extend a wide range of possible applications of graphene from straintronics, optoelectronics and spintronics, coatings, sensors for batteries, etc. Motivated by these prospects, and a small number of experimental realizations of the modulated graphene systems, we have synthesized and studied epitaxial graphene on stepped Ir(332) substrate. The system was studied with a comprehesive set of experimental techniques which gave the insight into structural characteristics (scanning tunneling microscopy, STM, atomic force microscopy, AFM, and low energy electron diffraction, LEED), electronic band structure (angle-resolved photoemission spectroscopy, ARPES, scanning tunneling spectroscopy, STS, and density functional theory, DFT) and the nature of the inherent strain (polarized Raman spectroscopy). The graphene on Ir(332) caused a severe surface restructuring, consisting of formation of large (111) terraces and (331) step bunches, giving the substrate and graphene a new periodicity. We found that the new periodicity as well as the graphene rotation can be controlled through variation of growth parameters. Furthermore, we found that the ordering of modulated graphene depends on the graphene rotation, which was connected to the size of the moiré unit cell. Measurements of the electronic band structure showed the Dirac cone anisotropy which was attributed to the 1D periodicity present in the system. Additionally, graphene’s local density of states dependent heavily on the specific morphological motifs, which was connected to the measured difference in doping between the graphene on terraces or on step bunches, and to the site specific interaction calculated using DFT. The DFT calculations showed that the graphene binding is strongest on the step edges, which drives the surface restructuring. Furthermore, we have accomplished to transfer graphene from Ir(332) onto SiO2 terminated Si wafer, where the graphene modulation was preserved after the transfer. Such periodically nano-modulated graphene showed inherent presence of uniaxial strain, which is necessary for potential applications.Grafen je heksagonalna mreža ugljikovih atoma debljine jednog atomskog sloja s dva atoma u bazi. Veze između susjednih ugljikovih atoma su 1.42 Å udaljene tzv. σ veze formirane sp^2 hibridizacijom orbitala. Preostala p_z orbitala, okomita na ravninu grafena, formira π vezu. Snažna σ veza je odgovorna za iznimnu grafensku elastičnost i otpornost na deformacije, dok je π veza odgovorna za većinu odličnih elektronskih svojstava

Fractal nature of hard carbon prepared from C60 fullerene

International audienc