Electronic properties of very thin native SiO2/a-Si:H interfaces and their comparison with those prepared by both dielectric barrier discharge oxidation at atmospheric pressure and by chemical oxidation

The contribution deals with electronic properties of thin oxide/amorphous hydrogenated silicon (a-Si:H) measured by capacitance-voltage (C-V) and charge version of deep level transient spectroscopy (Q-DLTS). The interest was focused on the studies of the interface properties of very thin dielectrics formed by dielectric barrier discharge (DBD) or natively on the a-Si:H layer. These properties were compared with those of oxide layers prepared by chemical oxidation in HNO3. The DBD was used for the preparation of a very thin SiO2 layer on a-Si:H for the first time to our knowledge. Preliminary electrical measurements confirmed that a very low interface states density was detected in the case of the native oxide/a-Si:H and DBD oxide/a-Si:H

Negative ions formed in N₂/CH₄/Ar discharge – a simulation of Titan's atmosphere chemistry

The formation of negative ions produced in a negative point-to-plane corona discharge fed by a Ar/N2//CH4/ gas mixture has been studied using mass spectrometry. The measurements were carried out in flowing regime at ambient temperature and a reduced pressure of 460 mbar. The CN ? anion has been found to be the most dominant negative ion in the discharge and is believed to be the precursor of heavier negative ions such as C3/N ? and C5/N ? . The most likely pathway for the formation of such molecular anions is H-loss dissociative electron attachment to HCN, H3/CN and H5/CN formed in the discharge. These same anions have been detected in Titan's atmosphere and the present experiments may provide some novel insights into the chemical and physical mechanisms prevalent in Titan's atmosphere and hence assist in the interpretation of results from the Cassini Huygens space mission

Corona discharge experiments in admixtures of N2 and CH4: a laboratory simulation of Titan's atmosphere

A positive corona discharge fed by a N2:CH4 mixture (98:2) at atmospheric pressure and ambient temperature has been studied as a laboratory mimic of the chemical processes occurring in the atmosphere of Titan, Saturn's largest moon. In-situ measurements of UV and IR transmission spectra within the discharge have shown that the main chemical product is C2H2, produced by dissociation of CH4, with small but significant traces of ethane and HCN, all species that have been detected in Titan's atmosphere. A small amount (0.2 %) CH4 was decomposed after 12 minutes of treatment requiring an average energy of 2.7 kWh/g. After 14 minutes the discharge was terminated due to the formation of a solid yellow deposit on the central wire electrode. Such a deposit is similar to that observed in other discharges and is believed to be an analogue of the aerosol and dust observed in Titan's atmosphere and is composed of chemcial species commonly knonw as 'tholins'. We have also explored the electrical properties of the discharge. The admixture of methane into nitrogen caused an increase in onset voltage of the discharge and consequently led to a reduction in the measured discharge current

Studies of resistance switching effects in metal/YBa2Cu3O7-x interface junctions

Current-voltage characteristics of planar junctions formed by an epitaxial c-axis oriented YBa2Cu3O7-x thin film micro-bridge and Ag counter-electrode were measured in the temperature range from 4.2 K to 300 K. A hysteretic behavior related to switching of the junction resistance from a high-resistive to a low-resistive state and vice-versa was observed and analyzed in terms of the maximal current bias and temperature dependence. The same effects were observed on a sub-micrometer scale YBa2Cu3O7-x thin film - PtIr point contact junctions using Scanning Tunneling Microscope. These phenomena are discussed within a diffusion model, describing an oxygen vacancy drift in YBa2Cu3O7-x films in the nano-scale vicinity of the junction interface under applied electrical fields.Comment: To be published in Applied Surface Science

Effect of crystallographic anisotropy on the resistance switching phenomenon in perovskites

Resistance switching effects in metal/perovskite contacts based on epitaxial c-axis oriented Y-Ba-Cu-O (YBCO) thin films with different crystallographic orientations have been studied. Three types of Ag/YBCO junctions with the contact restricted to (i) c-axis direction, (ii) ab-plane direction, and (iii) both were designed and fabricated, and their current-voltage characteristics have been measured. The type (i) junctions exhibited conventional bipolar resistance switching behavior, whereas in other two types the low-resistance state was unsteady and their resistance quickly relaxed to the initial high-resistance state. Physical mechanism based on the oxygen diffusion scenario, explaining such behavior, is discussed.Comment: The final version was published in Journal of Applied Physics (2012

Organic chemistry of NH₃ and HCN induced by an atmospheric abnormal glow discharge in N₂-CH₄ mixtures

The formation of the chemical products produced in an atmospheric glow discharge fed by a N2-CH4 gas mixture has been studied using Fourier Transform InfraRed (FTIR) and Optical Emission Spectrometry (OES). The measurements were carried out in a flowing regime at ambient temperature and pressure with CH4 concentrations ranging from 0.5% to 2%. In the recorded emission spectra the lines of the second positive system CN system and the first negative system of N2 were found to be the most intensive but atomic Hα, Hβ, and C (247 nm) lines were also observed. FTIR-measurements revealed HCN and NH3 to be the major products of the plasma with traces of C2H2. These same molecules have been detected in Titan's atmosphere and the present experiments may provide some novel insights into the chemical and physical mechanisms prevalent in Titan's atmosphere with these smaller species believed to be the precursors of heavier organic species in Titan's atmosphere and on its surface

Optical absorption edge and luminescence in phosphorous-implanted Cu₆PS₅X (X = I, Br) single crystals

Implantation of Cu6PS5X (X = I, Br) single crystals was carried out for different values of fluence with using P⁺ ions; the energy of ions was 150 keV. For the implanted Cu₆PS₅X crystals, the structural studies were performed using the scanning electron microscopy technique and energy-dispersive X-ray spectroscopy. Spectrometric studies of optical absorption edge and luminescence were carried out within the temperature range 77…320 K. The influence of ionic implantation on luminescence spectra, parameters of Urbach absorption edge, parameters of exciton-phonon interaction as well as ordering-disordering processes in Cu₆PS₅X (X = I, Br) superionic conductors have been studied

Optical absorption edge and luminescence in phosphorous-implanted Cu₆PS₅X (X = I, Br) single crystals

Implantation of Cu₆PS₅X (X = I, Br) single crystals was carried out for different values of fluence with using P+ ions; the energy of ions was 150 keV. For the implanted Cu₆PS₅X crystals, the structural studies were performed using the scanning electron microscopy technique and energy-dispersive X-ray spectroscopy. Spectrometric studies of optical absorption edge and luminescence were carried out within the temperature range 77…320 K. The influence of ionic implantation on luminescence spectra, parameters of Urbach absorption edge, parameters of exciton-phonon interaction as well as ordering-disordering processes in Cu₆PS₅X (X = I, Br) superionic conductors have been studied