UV Picosecond-Laser Induced Bulk Modifications and Luminescence in Single-Crystal Diamond

Bulk laser-graphitized microstructures have been fabricated in type IIa single-crystal 1.2-mm-thick diamond plates by UV laser irradiation with 10-ps pulses at λ=355 nm wavelength. It is found that the crystallographic-plane-dependent character of structural modifications in the bulk is influenced by the laser wavelength and the direction of the laser beam incidence relative to a given crystallographic direction (<100> or <110>) in the diamond plates. High-order Stokes Raman lasing is observed during UV laser irradiation and bulk modifications of single-crystal diamond. It is shown that the formation of bulk microstructures results in dramatic changes in the behavior of the stimulated Raman scattering in diamond. The formation and migration of the 3H defects (self-interstitial related centers) is also found to take place in the course of bulk microstructuring with UV ps-pulses. Important limitations of the bulk microstructuring caused by high internal stresses in laser-modified regions resulting in ‘uncontrollable’ damage of the diamond single crystals are discussed

Anisotropic conductivity of Nd_{1.85}Ce_{0.15}CuO_{4-\delta} films at submillimeter wavelengths

The anisotropic conductivity of thin Nd$_{1.85}$Ce$_{0.15}$CuO$_{4-\delta}$ films was measured in the frequency range 8 cm$^{-1}<\nu <$ 40 cm$^{-1}$ and for temperatures 4 K $<T<300$ K. A tilted sample geometry allowed to extract both, in-plane and c-axis properties. The in-plane quasiparticle scattering rate remains unchanged as the sample becomes superconducting. The temperature dependence of the in-plane conductivity is reasonably well described using the Born limit for a d-wave superconductor. Below T_{{\rm C}%} the c-axis dielectric constant $\epsilon_{1c}$ changes sign at the screened c-axis plasma frequency. The temperature dependence of the c-axis conductivity closely follows the linear in T behavior within the plane.Comment: 4 pages, 4 figure

Doping dependence of the gap anisotropy in LCCO studied by millimeter-wave spectroscopy

We measure the penetration depth of optimally doped and underdoped La2-xCexCuO4 in the millimeter frequency domain (4 - 7 cm-1) and for temperatures 2 K < T < 300 K. The penetration depth as function of temperature reveals significant changes on electron doping. It shows quadratic temperature dependence in underdoped samples, but increases almost exponentially at optimal doping. Significant changes in the gap anisotropy (or even in the gap symmetry) may account for this transition.Comment: 4 pages, 4 figure

Femtosecond laser-induced periodic surface structures on diamond-like nanocomposite films

We study the formation of laser-induced periodic surface structures (LIPSS) on diamond-like nanocomposite (DLN) a-C:H:Si:O films and titanium-doped DLN films during femtosecond (fs) laser ablation processing with linearly-polarized beams of IR and visible fs-lasers (wavelengths 1030 nm and 515 nm, pulse duration 320 fs, pulse repetition rates 100 kHz-2 MHz, scanning beam velocity 0.04–0.4 m/s). The studies are focused on (i) comparison of high spatial frequency LIPSS (HSFL) and low spatial frequency LIPSS (LSFL) formed on DLN and Ti-DLN films by IR fs-laser processing, (ii) effects of the pulse repetition rate on the parameters of LIPSS formed on the DLN and Ti-DLN films, (iii) Raman spectroscopy analysis of the LIPSS-structured films with application for ultrathin surface graphitization, and (iv) relationship between the fs-laser-induced surface graphitization and LIPSS formation on the films. A variety of the HSFL and LSFL have been produced on the surface of DLN and Ti-DLN films, with all the LIPSS being oriented perpendicular to the beam polarization direction. The HSFL periods are varied from ~80 to 240 nm and the LSFL periods are varied from 355 to 840 nm, depending on the fs-laser irradiation conditions (wavelength, fluence, pulse repetition rate) and films properties. Various plasmonic effects such as the superposition of the HSFL and LSFL and emergence of very unusual sinusoid-like structures on the DLN and Ti-DLN films are presented and discussed

STM-Untersuchungen von Diamant- und DLC-Schichten: Siehe auch: Physica status solidi, A 145(1994), S.393-400.

Methodological problems of the applicability of scanning tunneling microscopy (STM) for the characterization of poorly conductive diamond and diamond-like carbon films are discussed. The sensitivity of STM to variation of the surface relief is characterized by a decay length d. It is shown that d depends on the serial resistance R of the sample seen by a tunneling microscope. For R<10 M Omega d is less than 1 nm that enables to image the samples with reasonable quality and correct reproduction of surface corrugations

Peculiarities of Field Electron Emission from CVD Diamond Films

Results are reported on characterization of the field electron emission from diamond films grown by dc arc discharge plasma CVD onto Si substrates from CH4-H2 gas mixtures. The field electron emission was observed at 15-20 V/µm. Emission current-voltage dependences were studied for films prepared at different CVD conditions and post-growth surface treatment/ modification (ultrathin metal and metal oxide coatings, MW-plasma processing, laser-induced surface graphitization). Features of emission current versus applied field behaviour (including a hysteresis phenomenon, vacuum arc initiation) and ultralow (0.1-0.5 eV) values of effective work function derived from Fowler-Nordheim plot fitting are discussed. A high vacuum scanning tunneling-field emission microscope was applied for simultaneous mapping of field electron emission inten-sity, topography and work function to study electronic and structural properties of field emission centers

Femtosecond-laser surface modification and micropatterning of diamond-like nanocomposite films to control friction on the micro and nanoscale.

Laser surface micropatterning (texturing) of hard materials and coatings is an effective technique to improve tribological systems. In the paper, we have investigated the laser-induced surface modifications and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H,Si:O) using IR and visible femtosecond (fs) lasers, focusing on the improvement of frictional properties of laser-patterned films on the micro and macroscale. The IR and visible fs-lasers, operating at λ = 1030 nm and λ = 515 nm wavelengths (pulse duration 320 fs and pulse repetition rate 101 kHz), are used to fabricate different patterns for subsequent friction tests. The IR fs-laser is applied to produce hill-like micropatterns under conditions of surface graphitization and incipient ablation, and the visible fs-laser is used for making microgroove patterns in DLN films under ablation conditions. Regimes of irradiation with low-energy IR laser pulses are chosen to produce graphitized micropatterns. For these regimes, results of numerical calculations of the temperature and graphitized layer growth are presented to show good correlation with surface relief modifications, and the features of fs-laser graphitization are discussed based on Raman spectroscopy analysis. Using lateral force microscopy, the role of surface modifications (graphitization, nanostructuring) in the improved microfriction properties is investigated. New data of the influence of capillary forces on friction forces, which strongly changes the microscale friction behaviour, are presented for a wide range of loads (from nN to μN) applied to Si tips. In macroscopic ball-on-disk tests, a pair-dependent friction behaviour of laser-patterned films is observed. The first experimental data of the improved friction properties of laser-micropatterned DLN films under boundary lubricated sliding conditions are presented. The obtained results show the DLN films as an interesting coating material suitable for laser patterning applications in tribology. ACKNOWLEDGMENTS This work was supported by the Russian Science Foundation under Project No. 15-12-00039