Specific features of the laser irradiation of thin molybdenum films

Laser irradiation of thin molybdenum films with a thickness of less than 100 nm is studied. An experimental hypothesis in accordance with which films of refractory metals can be laser-ablated owing to the formation of an intermediate oxide phase is experimentally proven. A threefold decrease in the thickness of the ablation region under the action of scanning laser radiation is interpreted.     

Pulsed laser treatment of gold and black gold thin films fabricated by thermal evaporation

The effect of pulsed laser treatment of metal, and metal blacks, was studied. Gold and black gold thin films were fabricated by thermal evaporation of gold in a vacuum and nitrogen atmosphere respectively. Black gold films were grown in a nitrogen atmosphere at pressures of 200 Pa and 300 Pa. UV pulsed laser radiation (λ = 266 nm, τ = 4 ns), with fluence ranging from 1 mJ·cm⁻² to 250 mJ·cm⁻² was used for the film treatment in a vacuum and nitrogen atmosphere. The nitrogen pressure was varied up to 100 kPa. Surface structure modifications were analyzed by optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDX) was used for chemical characterization of the samples. A significant dependence of the film optical and structural properties on laser treatment conditions (laser fluence, ambient pressure and number of applied pulses) was found. The threshold for observable damage and initiation of changes of morphology for gold and black gold surfaces was determined. Distinct modifications were observed for fluences greater than 106 mJ·cm⁻² and 3.5 mJ·cm⁻² for the gold and black gold films respectively. Absorbtivity of the black gold film is found to decrease with an increase in the number of laser pulses. Microstructural and nanostructural modifications after laser treatment of the black gold film were observed. EDX analysis revealed that no impurities were introduced into the samples during both the deposition and laser treatment.      

Specific features of the luminescence of silicate glasses with silver introduced by ion exchange

The luminescence spectra of silicate glasses with silver introduced by ion exchange have been investigated. It is shown that silver introduced into glass by ion exchange exists not only in the form of ions, but also as neutral atoms and charged and neutral molecular clusters, which provide intense luminescence in the visible spectral range. Cerium ions in glass facilitate the formation of neutral molecular silver clusters, due to which the luminescence intensity increases. It is shown that Ag _n -Ce ^x+ complexes can be formed in glass containing cerium ions and neutral molecular silver clusters.     

Specific features of hydrogenation of chromium-doped polycrystalline thin vanadium dioxide films

It has been found that hydrogen penetration into chromium-doped polycrystalline thin vanadium dioxide films occurs with a lower rate than in the case of pure vanadium dioxide films. It has been shown that hydrogenation of films with low chromium concentrations is accompanied by a decrease in the phase transition temperature below T _c = 340 K. However, at room temperature in these hydrogenated films, no traces of M1 monoclinic phase have been observed. As the chromium concentration increases, hydrogenation ceases to be accompanied by the decrease in the phase transition temperature.     

Space-selective co-precipitation of silver and gold nanoparticles in femtosecond laser pulses irradiated Ag, Au co-doped silicate glass

We report on space-selective co-precipitation of silver and gold nanoparticles in Ag⁺, Au³⁺ co-doped silicate glasses by irradiation of femtosecond laser pulses and subsequent annealing at high temperatures. The color of the irradiated area in the glass sample changed from yellow to red with the increase of the annealing temperature. The effects of average laser power and annealing temperature on precipitation of the nanoparticles were investigated. A reasonable mechanism was proposed to explain the observed phenomena.     

SERS activity of silver and gold nanostructured thin films deposited by pulsed laser ablation

The deposition power dependence of visible transmittance and refractive index of room temperature-deposited ZnO:Al thin films by RF magnetron sputtering has been studied. All films exhibited high visible transmittance and near-complete UV absorption. The refractive index of the films decreased continuously with an increase in the RF power at all photon energies in the visible and near-IR region, which has been partially attributed to the decreased packing density of the films. For each film, the refractive index exhibited strong frequency dispersion in the weak-absorption region. The origin of optical dispersion at different RF power has been discussed in the light of a single-oscillator model.     

Specific features of low-energy electron scattering by thin films of cubic crystals

The specific features of the electron states in thin films of cubic crystals are considered in the energy range above the vacuum zero of the crystal potential. It is demonstrated that bands of bound states embedded in the energy continuum can exist along particular directions of the two-dimensional Brillouin zone. These bands can substantially affect the intensity of low-energy electron scattering.     

Elaboration and characterization of barium silicate thin films

Room temperature depositions of barium on a thermal silicon oxide layer were performed in ultra high vacuum (UHV). In-situ X-ray photoelectron spectroscopy (XPS) analyses were carried out as well after exposure to air as after subsequent annealings. These analyses were ex-situ completed by secondary ion mass spectrometry (SIMS) profiles and transmission electron microscopy (TEM) cross-sectional images. The results showed that after air exposure, the barium went carbonated. Annealing at sufficient temperature permitted to decompose the carbonate to benefit of a barium silicate. The silicate layer was formed by interdiffusion of barium with the initial SiO₂ layer.     

Magnetoconductivity of thin epitaxial silver films

The magnetoconductance (MC) of thin epitaxial Ag films on Si(111) surfaces is studied as a function of film thickness (1–125 monolayers (ML)) at 20 K under ultra high vacuum (UHV) conditions. Three different regimes of magnetoconductance are observed depending on the degree of disorder in the films which is controlled by film thickness and annealing procedures. Thick films (d>3 ML) with diffuse electron transport show in the case of large elastic scattering times ₀ a classical, negative MC B ² and in the case of small ₀ a positive MC due to weak localization effects. The MC of thin films (d<2 ML) which have a conductance smaller than e ²/h, i.e. localized electron states, is negative again.     

Laser reflectance relaxation spectroscopy: Determination of thermal diffusivity in thin films of gold

The technique of thermal modulation is applied to the study of transient thermal properties of thin films of Au. Relaxation spectra as seen in the reflected laser light give a value for the thermal diffusivity of Au as κ ? 1.2 cm²/sec, comparable to previous data for the bulk metal. Versatility and potentials of the laser reflectance relaxation spectroscopy are discussed.     

Polarization properties of porous gold and silver films

Using the method of polarization modulation of electromagnetic radiation and the Kretschmann geometry, we perform comparative studies of surface plasmon resonance in porous and continuous gold and silver films. The spectral dependences of the polarization difference of the reflection coefficients of nano-composites are obtained for the first time and are supplemented by angular characteristics of this parameter. We show that these dependences characterize particular features of the optical properties related to the structure, morphology, and topology of porous films. We reveal that surface plasmon-polaritons and local plasmons in porous films can be excited both by radiation that is p polarized with respect to the plane of incidence, as is the case with continuous films, and by s polarized radiation. We demonstrate that the measurement results can yield information on the structural properties of films, such as their thickness, roughness height, degree of dispersion of nanoparticles, and so on.     

Specific features of the formation of optical waveguides in silicate glass at high energy and doze of electron irradiation

The formation of an optical waveguide in silicate glass that contains alkali-metal ions is experimentally studied under electron irradiation at an energy of 50 keV and a doze of 25–50 mC/cm². A gradient waveguide with a maximum variation in the refractive index of 0.01–0.04 is formed in the glass due to irradiation. It is demonstrated that a variation in the refractive index results from both field migration of alkalimetal ions to the region of negative space charge and structural modifications in the glass related to the destruction of glass structure by high-energy electrons.     

掺Yb硅酸盐玻璃的热漂白性能研究

采用传统高温熔融法制备了掺Yb硅酸盐玻璃, 玻璃组成为 60SiO₂-12Al₂O₃-28CaO-1.0 mol%Yb₂O₃. 将玻璃分成两组, 一组经总剂量3 kGy的Co⁶⁰γ辐射源辐射, 另一组做空白对照. 然后测试了玻璃未辐射、辐射后及热漂白后的吸收谱和近红外发光谱. 实验结果表明: 一定的热处理会使得玻璃在辐射过程中产生的色心缺陷发生分解, 即辐射后的玻璃在300–900 nm波段的吸收系数显著地降低了, 在400 nm处未经辐射、经3 kGy辐射以及热漂白后的玻璃吸收系数分别是0.93, 2.9, 1.89 cm^-1. 另外, 玻璃的近红外发光强度明显增强, 在1028 nm处未经辐射、经3 kGy辐射以及热漂白后的玻璃近红外发光相对强度分别是588, 261, 436, 从而极大地改善了玻璃的光学性能. 所以一定的热处理可以使辐射后的玻璃产生热漂白的现象. 研究结果为进一步发展抗辐射玻璃材料提供了新的实验依据.     

The resistivity of thin gold films

Results are obtained on the D.C. electrical resistivity of evaporated gold films on KBr substrates as a function of thickness and temperature. These show that the conduction electrons are not specularly reflected at the sample surface but nevertheless the temperature dependent part of the resistivity is independent of sample thickness. Comparison of the results with Fuchs-Sondheimer theory for the effects of sample thickness upon the resistivity yield a maximum specularity of approximately 0.64 for <100> films on KBr.     

From silver nanoparticles to thin films: Evolution of microstructure and electrical conduction on glass substrates

Silver nanoparticles embedded in a dielectric matrix are investigated for their potential as broadband-absorbing optical sensor materials. This contribution focuses on the electrical properties of silver nanoparticles on glass substrates at various morphological stages. The electrical current through thin films, consisting of silver nanoparticles, was characterized as a function of film thickness. Three distinct conductivity zones were observed. Two relatively flat zones (“dielectric” for very thin films and “metallic” for films thicker than 300-400 Å) are separated by a sharp transition zone where percolation dominates. The dielectric zone is characterized by isolated particle islands with the electrical conduction dominated by a thermally activated tunneling process. The transition zone is dominated by interconnected silver nanoclusters—a small increase of the film thickness results in a large increase of the electrical conductivity. The metallic conductivity zone dominates for thicknesses above 300-400 Å.     

Specific features of holographic recording of diffraction gratings in thin films of fullerene-containing organic systems

Thin films based on fullerene-containing polyimides COANP and PNP were studied using methods of dynamic holography under conditions of Raman-Nath diffraction. A significant increase in the diffraction efficiency of the fullerene-containing samples was detected, and the threshold of the transition from phase grating to amplitude grating was determined. The qualitative explanation of the results is based on the spectral features and the thermal properties of the systems under study.     

Pulsed laser deposition of silicate phosphor thin films

Three types of silicate phosphor thin films, emitting in the red-green-blue (RGB) primary colors, were fabricated by pulsed laser deposition, including manganese and lead doped calcium silicate (CaSiO₃:MnPb) for red color, manganese doped zinc silicate (Zn₂SiO₄:Mn) for green color and cerium doped yttrium silicate (Y₂SiO₅:Ce) for blue color. A correlation was observed between photoluminescence intensity with film crystallinity and surface morphology. RGB phosphor thin films with excellent color saturation were obtained. Luminescence mechanisms for these phosphor thin films are discussed.     

Excimer laser-assisted annealing of silicate glass with ion-synthesized silver nanoparticles

The effect of KrF excimer laser radiation on a composite layer consisting of sodium-potassium silicate glass with silver nanoparticles is studied as a function of the number of laser nanosecond pulses. The silver nanoparticles are synthesized by ion implantation. The measured optical absorption of the composite layer demonstrates that the silver nanoparticle size decreases monotonically as the number of laser pulses increases. Rutherford backscattering shows that laser annealing is accompanied by silver diffusion into the bulk of the glass and partial metal evaporation from the sample surface. The detected decrease in the silver nanoparticle size is discussed in terms of simultaneous melting of silver nanoparticles and the glass matrix due to the absorption of laser radiation.     

Anisotropic magnetoresistance in thin inhomogeneous gold films

We investigate the magnetoresistance (MR) of thininhomogeneous gold films applying the magnetic field perpendicular as well as parallel to the film plane. The MR-data show a strong anisotropy which can be well explained within the theory of weak electron localization (WEL) in 2d for both field orientations. The important results is that fitting the MR-data for both orientations by the corresponding theoretical expressions we obtain nearly identical values for the phase coherence lengthsL and its temperature dependence. This confirms (i) the correctness of the fitting process and (ii) the validity of the theory. From this we conclude that WEL in 2d can also be used to describe the MR ofinhomogeneous films.     

Power-law scaling of proton conductivity in amorphous silicate thin films

Amorphous hafnium silicate, a-Hf_0.1Si_0.9O_x, thin film with thickness of 32, 41, 55, 80, 110, 120, 180 and 320 nm was prepared by multiple spin-cast process and the proton conductivity across the films was measured at intermediate temperatures (100-400 °C) in dry atmosphere. The morphologically- and compositionally-uniform films were prepared on a substrate as confirmed by SEM, RBS and XPS measurements. a-Hf_0.1Si_0.9O_x thin film clearly revealed the H/D isotope effect on ionic conductivity, indicating that protonic conduction is dominant in the measured temperature range. The films did not reveal thickness-dependent proton conductivity in dry air and the σ at given temperatures is almost constant at any thickness. No increment of σ in a-Hf_0.1Si_0.9O_x thin films by reduction of thickness might be related to the absence of the highly-conductive acid network with mesoscopically-sized length because of the relatively low concentration of Brønsted acid sites inside films.