J. Miškinis

XRD, XPS, SEM/EDX and broadband impedance spectroscopy study of pyrophosphate (LiFeP2O7 and Li0.9Fe0.9Ti0.1P2O7) ceramics

LiFeP2O7 and Li0.9Fe0.9Ti0.1P2O7 were synthesised by solid-state reaction and ceramics were sintered. The structure of compounds was studied in the temperature range 300–700 K by X-ray diffraction. Ceramics’ surfaces were investigated by scanning electron microscope. Binding energies of Fe 2p, P 2p and O 1s core levels at ceramics’ surfaces have been determined by X-ray photoelectron spectroscopy and different valence states of Fe and P were detected. Elemental compositions of the compounds were studied by energy dispersive X-ray spectrometer. Impedance spectroscopy was performed in the frequency range 10 Hz–3 GHz and in the temperature interval 400–700 K. The changes of the activation energy of ionic conductivity at 528 and 550 K for LiFeP2O7 and Li0.9Fe0.9Ti0.1P2O7, respectively, were found. The phenomena can be related to disordering in the unit cells of the compounds.

Preparation and characterization of Li2.9Sc1.9−y Y y Zr0.1(PO4)3 (where y = 0, 0.1) solid electrolyte ceramics

The solid electrolyte Li2.9Sc1.9− y Y y Zr0.1(PO4)3 (where y = 0, 0.1) compounds belong to monoclinic symmetry (space group P21/n) at room temperature. The Zr 3d, Sc 2p, P 2p, Y 3d, O 1s, and Li 1s core level X-ray photoelectron spectra (XPS) were fitted. The Li ions in ceramics without Y occupy two different positions and in the ceramics with Y they occupy one position in the lattice. The deconvolutions of the Zr 3d, P 2p, Sc 2p, and Y 3d core level XPS are associated with different valence states on the surfaces of the investigated ceramics. Anomalies of enthalpy, change of activation energy of ionic conductivity, anomalies of dielectric permittivity in the temperature range 420–520 K of investigated compounds were found. The phenomena are related to diffuse structure phase transition in the compounds. At temperatures 600 and 900 K, the compounds belong to orthorhombic symmetry (space group Pbcn).

Doping of silicon by carbon during laser ablation process

Effect of laser ablation on properties of remaining material was investigated in silicon. It was established that laser cutting of wafers in air induced doping of silicon by carbon. The effect was found to be more distinct by the use of higher laser power or UV radiation. Carbon ions created bonds with silicon in the depth of silicon. Formation of the silicon carbide type bonds was confirmed by SIMS, XPS and AES measurements. Modeling of the carbon diffusion was performed to clarify its depth profile in silicon. Photo-chemical reactions of such type changed the structure of material and could be a reason for the reduced quality of machining. A controlled atmosphere was applied to prevent carbonization of silicon during laser cutting.

Formation of ohmic contacts on semi-insulating GaAs by laser deposition of In

A method for producing ohmic contacts on semi-insulating GaAs by laser ablation with subsequent laser deposition of In is proposed. The contacts are formed at room temperature; thus, the high-temperature annealing used in other technologies is excluded. The ohmic properties of the contacts are retained in a range of currents that is several orders of magnitude wide, regardless of the direction of current. The electric potential is distributed linearly along the sample, and the current is limited only by the bulk resistivity of the material itself. The method is promising for the formation of high-precision arrays of ohmic contacts that penetrate the whole thickness of the sample in the fabrication of microelectronic devices.

Ablation of silicon by picosecond pulses of laser radiation

UV laser radiation with picosecond pulse duration was applied for ablation of silicon. Micro-drilling and cutting of silicon wafers were performed by 266-nm radiation. The effect of laser fluence on ablation rate and drilling depth was investigated.Laser affected layer of a bulk material near cutting wall was investigated. SEM, AES, XPS and SIMS techniques were applied for analysis of a cross-section of the cut. The Ar-ion beam etching was used to make the depth profile of the layer. Elemental composition of subsurface layer and its thickness were estimated.Investigation was inspired by the promise of application of short pulse lasers for formation of microstructures used in production of sensors and high power pulsed microwave detectors.UV laser radiation with picosecond pulse duration was applied for ablation of silicon. Micro-drilling and cutting of silicon wafers were performed by 266-nm radiation. The effect of laser fluence on ablation rate and drilling depth was investigated.Laser affected layer of a bulk material near cutting wall was investigated. SEM, AES, XPS and SIMS techniques were applied for analysis of a cross-section of the cut. The Ar-ion beam etching was used to make the depth profile of the layer. Elemental composition of subsurface layer and its thickness were estimated.Investigation was inspired by the promise of application of short pulse lasers for formation of microstructures used in production of sensors and high power pulsed microwave detectors.

The influence of crystallite and interface region properties on the CdSe layer photoconductivity

Abstract The CdSe polycrystalline layer was analyzed by means of ESCA, SIMS, photoconductivity and Hall effect methods, and surface and bulk phenomena were researched. The activation of photoconductivity during the thermal treatment in air with and without CdCl 2 was investigated. It was found that the oxide formation decreased, if the chlorine was in the ambient, which caused the achievement of a higher compensation level. The prevalence of Cd or Se vacancies in the formation determined the conductivity and photosensitivity of the polycrystalline layer. Thermal quenching, persistent conductivity and the percolation regime at low temperatures were analyzed as well.

Synthesis and characterization of Li1/3Ce2/3PO4 and LiCe2/3PO4 ceramics

Li1/3Ce2/3PO4 and LiCe2/3PO4 compounds were synthesized by a solid state reaction and studied by x-ray diffraction and thermogravimetric analysis. At room temperature the investigated compounds exhibit monoclinic symmetry (space group P 21/n) with four formula units in the lattice. The compounds are stable up to 1200 K in air and show no weight loss. The ceramic samples were fabricated with varying sintering times. The surfaces of the ceramics were studied by scanning electron microscopy. The increase of sintering time of the ceramics leads to an increase of the grain size of the materials. The results of an x-ray photoelectron spectroscopy study have shown that the external electric field changes the Li amount on the surfaces of the ceramic samples. The electric properties of the samples were investigated by complex impedance spectroscopy in the frequency range from 50 to 1.2 × 109 Hz in the temperature range from 300 to 650 K. Varying the sintering time of the ceramics affects the values of the total conductivity, activation energy, dielectric permittivity and dielectric losses of the ceramics.

Self-organized nanoclusters of semiconductor compounds on vicinal Si surfaces and its influence on carrier recombination in Si

Abstract The self-organized nanocluster ensembles of ZnSe, CdSe and PbS were grown by laser ablation on vicinal Silicon (111) surfaces. The properties of the layers were investigated by XPS (X-rays photoelectron spectroscopy) and Auger spectroscopy. The properties of the semiconductor-clustered layer on single Si crystal structure were investigated by deep level transient spectroscopy (DLTS) and by microwave absorption induced by light pulse excitation. The clustered layer and multilayer structure modified the recombination at the Si surface and created additional carrier capture centres. Absolute values of surface recombination rate, s, were determined by the method of asymptotic lifetime amplitude. An increase of s is caused by formation of PbS clusters, while for CdSe clusters, this dependence was found to be weaker. Structures with barriers or flat conduction bands were grown on the silicon surface using different doping concentrations of layers.

Growth of CdSe clusters by laser ablation and mass spectroscopy of ion flow

Laser evaporation of CdSe has been analyzed by ion flow mass spectrometry and ultrafine spectrum structure was found. It was proposed the different strength atom bonds and plasma effects were responsible for additional mass spectrum components. The CdSe cluster growth on different substrates was investigated and a clear evidence of substrate structure influence on a cluster distribution was found. The two step mechanism of cluster growth regulation was demonstrated.