Size effects of static conduction in thin tantalum films

In thin tantalum films grown by pulsed laser deposition in a vacuum, the resistivity versus thickness dependence is found to oscillate. The oscillation periods equal 5.0 and 5.6 nm for α-and β-Ta films, respectively. This observation is interpreted as the quantum-size effect in thin tantalum films.     

Energy distribution of ions in plasma formed by laser ablation of metallic Nb and Ta targets

The laser plasma plume expansion induced by UV nanosecond irradiation from metallic Nb and Ta targets has been studied using Langmuir probe time-of-flight measurements. The ion current shape was measured as a function of the laser radiation flux at various probe-to-target distances. The ion velocity distribution and the ion energy spectra have been determined by measuring the time of flight of ions reaching the Langmuir probe. A multi-mode velocity distribution of ions has been revealed. The dependence of the amplitudes of the plume energy components on the plume scatter time and on the laser radiation flux has been investigated. The experimental time-of-flight data have been compared with a Maxwell velocity distribution. The threshold values of the laser intensity were determined for different distribution modes in the ion energy spectrum.     

Vanadium- and Titanium Dioxide-Based Memristors Fabricated via Pulsed Laser Deposition

Thin TiO _x and VO_{2 – x} films are fabricated via pulsed laser deposition from metal targets with the help of mask technologies. Their memristive properties are investigated using Au/TiO_x1/TiO_x2/Au and Au/VO₂/VO_{2 – x}/Au thin-film structures, and the possible mechanisms of resistive switching are discussed. The structures are obtained at room temperature in an oxygen atmosphere.     

The electron temperature distribution of laser erosion plume after ablation of a tantalum target with excimer laser in vacuum

The erosion plume resulting from an ablation of a tantalum target in vacuum with an excimer laser radiation (308 nm) was studied using the Langmuir probe technique. The spatial and temporal dependencies of the electron probe currents were obtained in real time. The electron temperature of different plume regions was determined from a series of I–U characteristics taken at different distances between the probe and the target. We determined that the plume electron temperature is non-uniform and has a maximum value in front of the plume.     

Determination of alkali metals by laser-induced atomic-ionization in flames

The technique of laser-induced atomic-ionization (AI) in flames has been used for direct determination of Na, K, Rb, and Cs in samples such as water, high-purity alkali metals and their salts and polymeric organosilicon compounds. Different procedures for sample introduction into the flame were studied: (a) the sample was placed onto the cathode of the detector (this gave limits of detection for Na and Cs of 4 x 10(-16) and 2 x 10(-15) g, respectively), (b) electrothermal vaporization and (c) aspiration of the sample into the flame. To reduce the interference of SiO(2) in the AI determination of K in polymeric organosilicon compounds (at the level of 10(-3)-10(-5)%), a procedure involved additional electrical heating of the FID cathode was developed. The efficiency of certain schemes for the laser stepwise and two-photon excitation of atoms was compared for determination of Na.     

Pulse laser deposition of vanadium dioxide films

Thin amorphous and crystalline films of VO₂ are obtained on (0001) sapphire substrates via pulsed laser deposition with the speed separation of particles under a variety of deposition conditions. The electrical and optical properties of the films in the vicinity of the phase transition in the temperature range of 20 to 100°C are studied. The temperature of transition (T_c) and the width of the hysteresis are found to be 67.5 and 3°C, respectively.     

Two-dimensional heterostructures based on ZnO

The multiple quantum wells (MQW) Mg_0.27Zn_0.73O/ZnO have been grown by the pulsed laser deposition method with different well widths L _w . The interface roughness of quantum wells was inherited from the bottom one and did not exceed 1 nm. We observed the quantum confinement effect showing up in the blue shift of the exciton peak in the low temperature (8 K) photoluminescence and absorption spectra at well width reduction. The exciton binding energy of the two-dimensional structures Mg_0.27Zn_0.73O/ZnO was two times higher in comparison with the bulk ZnO. It has been established that Einstein’s characteristic temperature Θ _E sharp increase with reduction of well width L _w up to L _w =2.6 nm. It has been revealed that the discontinuity ratio of conduction and valence bands in the heterostructure Mg_0.27Zn_0.73O/ZnO is 0.65/0.35. We demonstrated the abrupt increase in quantum efficiency at a reduction of the well width that allowed us to observe the optically excited stimulated emission in ZnO quantum wells with the excitation threshold of ∼210 kW/cm².     

Photoluminescence properties of thin nitrogen- and phosphorus-doped ZnO films fabricated using pulsed laser deposition

The production of n- and p-type high-quality film structures is a foreground task in tackling the problem of growing the light-emitting p-n junctions based on zinc oxide. The ZnO:N and ZnO:P thin-film samples are produced from ceramic targets using the pulsed laser deposition. Zn₃N₂, MgO, and Zn₃P₂ are introduced in the ZnO ceramic targets for the fabrication of the p-type ZnO films. Gases O₂ and N₂O are used as buffer gases. The thermal annealing of the ZnO films is employed. The resistance and photoluminescence (PL) spectra of the ZnO films are measured prior to and after annealing. The dependence of the ZnO PL peak amplitude and position prior to and after annealing on the level of doping with nitrogen and phosphorus is established. The PL characteristics of the films are studied at cw optical excitation using a He-Cd laser with a radiation wavelength of 325 nm. The PL spectra in the interval 300–700 nm are recorded by an HR4000 Ocean Optics spectrometer in the temperature range 10–400 K. The effect of the conditions for the film deposition on the PL spectra is analyzed. The effect of the N- and P-doping level of the ZnO films on the PL intensity of the films and the position of the PL bands in the UV region is investigated. The short-wavelength (250–400 nm) transmission spectra of the ZnO:P films are measured. The effect of the P-doping level on the band gap of the ZnO films is studied.