Two-stage of Nanocones Formation by Laser Radiation on the Surface of Semiconductors

In this work we study mechanism of nanocones formation on a surface of elementary semiconductors by Nd:YAG laser radiation. A new mechanism of p-n junction formation by laser radiation in the elementary semiconductor as a first stage of nanocones formation is proposed. We explain this effect in following way: p-n junction is formed by generation and redistribution of intrinsic point defects in temperature gradient field – the Thermogradient effect, which is caused by strongly absorbed laser radiation. According to the Thermogradient effect, interstitial atoms drift towards the irradiated surface, but vacancies drift to the opposite direction – in the bulk of semiconductor. Since interstitials in Ge crystal are of n-type and vacancies are known to be of p-type, a n-p junction is formed. The mechanism is confirmed by appearance of diode-like current-voltage characteristics after i-Ge irradiation crystal by laser radiation. The second stage of nanocones formation is laser heating up of top layer enriched by interstitial atoms with its further plastic deformation due to compressive stress caused by concentration of interstitials in the top layer and vacancies in the buried layer. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3498

Characterization of Optical and Photoelectrical Properties of ZnO Crystals

We characterized optical and photoelectrical properties of undoped and Ga-doped ZnO layers differently grown on sapphire substrates by using complementary optical methods. Different stimulated emission threshold values for ZnO epitaxial layers grown by pulsed laser deposition and MBE methods were attributed to crystalline quality of the layers and the growth method used. Different carrier lifetimes in various ZnO epitaxial layers are explained by defect-related and intrinsic mechanisms of recombination

Laser induced SnS2-SnS phase transition and surface modification in SnS2 thin films

The SnS2 single-phase thin films were obtained by the close-spaced vacuum sublimation method. Laser irradiation of the SnS2 films provides evaporation of sulphur and hence phase transition to the SnS phase. Irradiation of the sample leads to the smoothing of the surface of the film. The electrical measurements of the irradiated samples show diode behaviour of the current-voltage dependencies. Two-layer n-SnS2/p-SnS heterojunction structure was formed.A thin film of SnS2 obtained by close-spaced vacuum sublimation was irradiated by an Nd:YAG laser (λ = 532 nm) using two intensities of laser radiation of 8.5 MW/cm2 and 11.5 MW/cm2. It was shown that laser irradiation leads to evaporation of sulphur from the surface, and the formation of SnS and Sn2S3 phases. The study of samples’ cross-section by energy dispersive X-ray analysis reveals that in the case of irradiation at 8.5 MW/cm2 intensity, the SnS layer is formed only at the surface of the initial SnS2 thin film. The application of more intensive radiation of 11.5 MW/cm2 leads to changes in chemical composition for the entire thin film. The formation of the predominant SnS phase, which includes a small amount of Sn2S3, was confirmed by the X-ray diffraction and Raman spectroscopy methods, as well as by measurements of optical reflectance and transmittance spectra. It was established that laser irradiation of the samples leads to the coalescence of grains accompanied by smoothing of the surface. The current-voltage characteristics of the ITO/SnxSy/Al samples show an ohmic behaviour in the case of non-irradiated intensity samples; for irradiated samples, the diode behaviour of I-V curves was observed. This is considered as evidence of the formation of p-SnS/n-SnS2 heterojunction by laser irradiation.This work was supported by the Ministry of Education and Science of Ukraine (Grant # 0115U000665c). A. Voznyi and Dr. V. Kosyak acknowledges Erasmus Mundus Ianus II program

Laser induced SnS2-SnS phase transition and surface modification in SnS2 thin films

The SnS2 single-phase thin films were obtained by the close-spaced vacuum sublimation method. Laser irradiation of the SnS2 films provides evaporation of sulphur and hence phase transition to the SnS phase. Irradiation of the sample leads to the smoothing of the surface of the film. The electrical measurements of the irradiated samples show diode behaviour of the current-voltage dependencies. Two-layer n-SnS2/p-SnS heterojunction structure was formed.A thin film of SnS2 obtained by close-spaced vacuum sublimation was irradiated by an Nd:YAG laser (λ = 532 nm) using two intensities of laser radiation of 8.5 MW/cm2 and 11.5 MW/cm2. It was shown that laser irradiation leads to evaporation of sulphur from the surface, and the formation of SnS and Sn2S3 phases. The study of samples’ cross-section by energy dispersive X-ray analysis reveals that in the case of irradiation at 8.5 MW/cm2 intensity, the SnS layer is formed only at the surface of the initial SnS2 thin film. The application of more intensive radiation of 11.5 MW/cm2 leads to changes in chemical composition for the entire thin film. The formation of the predominant SnS phase, which includes a small amount of Sn2S3, was confirmed by the X-ray diffraction and Raman spectroscopy methods, as well as by measurements of optical reflectance and transmittance spectra. It was established that laser irradiation of the samples leads to the coalescence of grains accompanied by smoothing of the surface. The current-voltage characteristics of the ITO/SnxSy/Al samples show an ohmic behaviour in the case of non-irradiated intensity samples; for irradiated samples, the diode behaviour of I-V curves was observed. This is considered as evidence of the formation of p-SnS/n-SnS2 heterojunction by laser irradiation.This work was supported by the Ministry of Education and Science of Ukraine (Grant # 0115U000665c). A. Voznyi and Dr. V. Kosyak acknowledges Erasmus Mundus Ianus II program

Post-growth treatment of SnxSy thin films

In this study, the effect of post-growth thermal annealing and laser irradiation on phase composition, structural, optical and electrical properties of SnS2 obtained by the close-spaced sublimation on ITO substrates was studied. It was found, by using EDS, XRD and Raman methods that as-grown samples have single phase SnS2 structure and their chemical composition is close to stoichiometric

Investigating the Superconducting Properties and Surface Morphology of Sputtered Nb Films on Cu Due to Laser Treatment

Bulk niobium is currently the material of choice for superconducting radio frequency (SRF) cavities and is a well matured process. However, it is possible that SRF cavities could be further improved beyond bulk Nb by sputtering thin Nb films onto Cu cavities. Copper has a greater thermal conductivity than Nb and is also easier to machine, while sputtering films on the surface reduces the amount of Nb used to fabricate the whole cavity. However, sputtering Nb on Cu produces other issues, for example, the surface quality of the Cu affects the quality of the Nb deposited on the surface and therefore the superconducting parameters. As the Nb on the surface is not perfect, the magnetic field produced by the RF can enter the cavity earlier than expected, producing RF losses, which can in turn lead to a quench. One approach is to treat the Nb post deposition by irradiating the surface using a laser to polish the surface of the Nb and increase the surface magnetic field that the cavity can maintain while remaining in the Meissner state. A magnetic field penetration experiment designed and built at Daresbury Laboratory has been used to measure the field of full flux penetration to characterize the effect of the laser treatment on the superconducting properties of the Nb. Surface characterization and the response of the Nb in a dc magnetic field have also been performed to try and provide an explanation for the change in the superconducting properties. The results demonstrate that the laser treatment can lead to an increase in the magnetic field at which the flux penetrates from one side of the sample to the other, thus it could potentially improve the performance of Nb coated RF cavities

Post-growth treatment of SnxSy thin films

In this study, the effect of post-growth thermal annealing and laser irradiation on phase composition, structural, optical and electrical properties of SnS2 obtained by the close-spaced sublimation on ITO substrates was studied. It was found, by using EDS, XRD and Raman methods that as-grown samples have single phase SnS2 structure and their chemical composition is close to stoichiometric

UV-light-induced curing of branched epoxy novolac resin for coatings

UV-light induced curing of the branched epoxy novolac resin (ENR) is reported. Cross-linked ENR coatings with a thickness of 150 µm were produced by the cationic photopolymerization of poly((phenyl glycidyl ether)-co-formaldehyde), which was photoinitiated by bis(4-dodecylphenyl)-iodonium hexaflurorantimonate. ENR crosslinking efficiency of UVlight polymerization accomplished by Hg-lamp with a power of 1 kW continuous irradiation was investigated as a function of the photoinitiator content and UV curing time. Optimal cross-linking properties were observed for photoinitiator concentration of 1.5%, and curing time 5 min. It was found that higher Vickers hardness of the polymer resulted in an increased cross-linking density of the developed chain network. UV irradiation time longer than 6 min results in the photodegradation of the polymer. This was confirmed by scanning electron microscopy investigations of polymer surface microstructure, as well as complemented by Fourier transform infrared (FTIR), ultraviolet-visible (UV-VIS) and Raman spectroscopy measurements that evidence the oxygen containing groups. Furthermore, the developed ENR photopolymerization technology can be used to obtain protective coatings for applications in power generation and maritime industries where thermal curing processes and two-component resin hardening are unacceptable