A study of the microstructure of thin a-C:H layers that orient liquid crystals

The surface structure of thin layers of a-C: H is studied by the method of island decoration, using silver films. The changes in the dimensions and density of silver particles is tracked by an electron microscope as a function of the thickness of the a-C: H layers. The electrical microprofile is discussed, along with the nature of the silver crystallization centers on the surface of the a-C: H layers. Zh. Tekh. Fiz. 68, 108–110 (January 1998)     

Hydrogen in amorphous and crystalline ytterbium films

Ytterbium vapor condensation on a liquid-helium cooled substrate in a hydrogen atmosphere is used to obtain Yb-H films containing up to 55 at.% hydrogen. Various thermodynamic and kinetic parameters of the transition of these films from the amorphous to the crystalline state (a→c transition) are investigated along with the electrical conductivity of these states. It is shown that the investigated properties of Yb-H films containing up to 40 at.% hydrogen are essentially indistinguishable from those of pure Yb films in the temperature interval 4.2–293 K. Increasing the hydrogen concentration to 55 at.% leads to an insignificant increase in the electrical resistivity, the kinetic temperature, and the activation energy of the a→c transition, and also to a decrease of the propagation speed of self-maintaining avalanche (explosive) crystallization. Reasons for the observed influence of hydrogen on the properties of Yb-H films are analyzed. The examined low-temperature Yb-H condensates can be characterized as a “frozen” solid solution of hydrogen in ytterbium in the temperature interval 4.2–293 K. Storing such films at room temperature leads to the formation of ionic ytterbium dihydride YbH₂. Fiz. Tverd. Tela (St. Petersburg) 41, 177–182 (February 1999)     

Influence of impurities on the low-temperature deformation of nanocrystalline copper

The influence of ZrO₂ particles on the low-temperature deformation of nanocrystalline copper produced by strong plastic deformation is investigated using equichannel angular pressing. A comparison is made between the deformation characteristics in tension and compression in the temperature range 4.2–400 K, measured for copper and the composite Cu:0.3 vol. % ZrO₂. It is shown that within 4.2–200 K the yield point σ _sm of the composite is higher than that for copper, attaining 680 MPa at 4.2 K, then the yield points are close in value up to room temperature, and diverge again as the temperature is raised. Possible causes of the dissimilar influence of an impurity on the strength and plasticity characteristics of nanocrystalline copper in various temperature intervals are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1639–1641 (September 1998)     

Photoluminescence of a-Si:H films grown by plasma-enhanced chemical vapor deposition and doped with erbium from the metallorganic compound Er(HFA)3·DME

Using standard low-temperature (<300 °C) plasma-enhanced chemical vapor deposition (PE CVD) technology, films of a Si(Er): H were obtained that emitted light in the neighborhood of 1.54 μm at room temperature. The Er source was the specially synthesized fluorine-containing metallorganic complex Er(HFA)₃·DME where HFA=CF₃C(O)CHC(O)CF₃ and DME=CH₃OCH₂CH₂OCH₃, which possesses a low transition temperature to the gas phase (of order 100 °C) at working pressures (0.1–0.5 Torr) for the PE CVD method. Distinctive features of the photoluminescence spectrum of a-Si(Er):H were investigated in the range 0.5–1.7 μm for T=77 and 300 K. The presence of photoconductivity in the synthesized films is evidence of their satisfactory electronic quality. Fiz. Tverd. Tela (St. Petersburg) 40, 1433–1436 (August 1998)     

Influence of structural deformations on the magnetic properties of Jahn-Teller complexes of divalent copper in CaxSr1−x F2 mixed crystals

Crystals of variable constituency Ca_xSr_1−x F₂:Cu (0⩽x⩽0.05, x≅0.5, 1.0⩾x⩾0.95) are investigated by EPR and x-ray structural analysis. The electron-Zeeman, intrinsic hyperfine, and ligand hyperfine interaction parameters are determined; they characterize the magnetic properties of the copper paramagnetic complexes formed in the crystals. Models of the molecular structures of these complexes are discussed, along with the influence of structural deformations and vibronic interactions on their magnetic properties. Fiz. Tverd. Tela (St. Petersburg) 40, 445–451 (March 1998)     

Transformations of hydrocarbon radicals moving along a stainless steel tube

Transport of exhausted thermonuclear fuel in the ITER divertor and pumping duct was modeled on a specially designed dc glow discharge setup using mass spectrometry, optical and electron microscopy, and electron probe microanalysis. Transport and deposition of hydrocarbon radicals transferred in an H₂/C _x H _yx mixture through a hollow stainless steel anode at a total mixture pressure of 8–212 Pa and a methane content to 15 mol % were considered. It was shown that deposition of radicals and ions (CH₃, C₂H₃, C₂H₅) with kinetic energies of 0.03–3 eV on the anode inner surface at 600 K was suppressed to a large extent. In the temperature range of 600–800 K, deposition of ions and radicals with kinetic energy of ~3 eV was partially restored with the formation of soft a-C:H films, while thermalized radicals were not condensed.     

Charge displacement induced by intercalation of graphite-like nanoclusters in amorphous carbon with copper

Interaction of an impurity Cu atom with carbon in copper-intercalated graphite-like nanoclusters in a-C:H has been considered in a simple tight-binding approximation. Clusters with simple configurations were used to show that partial ionization of Cu gives rise to metallization of a semiconductor cluster and to a substantial charge redistribution in the latter. The presence of copper initiates in the cluster internal polarization with components directed both normal to the graphene-fragment plane and parallel to it. The lowering of the cluster symmetry induced by copper intercalation activates the Raman band G in the IR spectrum of a-C:H. Fiz. Tverd. Tela (St. Petersburg) 41, 868–870 (May 1999)     

Determination of the degree of crystallinity of poly(vinyl alcohol) by FTIR spectroscopy

Quantitative correlations between the intensity of the crystalline band at 1144 cm⁻¹ (A ₁₁₄₄) normalized to the intensity of the C–O stretching band at 1094 cm⁻¹ (A ₁₀₉₄) in IR spectra of PVA films and the degree of crystallinity (α) of these films measured by an x-ray diffraction method were investigated. It was found that α and A ₁₁₄₄/A ₁₀₉₄ were related by the linear dependence α (%) = a + b(A ₁₁₄₄/A ₁₀₉₄) with correlation coefficient 0.999 for α values in the range 18–60%.     

One-phonon Raman spectra of carbon in composite films prepared by modification of amorphous hydrogenated carbon by copper and cobalt

One-phonon visible-range Raman spectra of a-C: H〈Cu〉 and a-C: H〈Co〉 composite films with comparable metal and carbon contents were studied in the frequency region 1200–1700 cm^?1 including the carbon sp²-bond vibrations. Broad bands G and D characteristic of unmodified a-C: H films, as well as some additional features, are observed experimentally in the spectra. By unfolding the spectra into Gaussian components, it was possible to follow the variation of Raman shifts and of contributions of individual components to the spectrum as a function of metal content and thermal annealing. The data obtained, complemented by available information on carbon sp²-coordinated systems, show that incorporation of Cu or Co favors growth and ordering of graphite-like nanoclusters in a-C: H, the effect being substantially stronger in the case of Co. It is shown that the process of metal-stimulated graphitization includes carbon bond breaking with the formation of short chainlike fragments and their linkage with the formation of aromatic-ring nanoclusters. A qualitatively similar sp²-structure rearrangement takes place under thermal annealing. For the Cu and Co concentrations studied, the linear dimensions L _a of graphite-like clusters are estimated to vary from ～0.8 nm in unannealed a-C: H to ～1.0 and ～1.2 nm in annealed a-C: H〈Cu〉 and a-C: H〈Co〉, respectively. The number of aromatic rings in these clusters is approximately estimated to increase from 12 to 16 (for Cu) and 20 (for Co).     

Investigation of the transition from multilayer to granular films in the cobalt-copper system

Cobalt-copper films obtained by pulsed electrolytic deposition from a single electrolyte are investigated. The continuous transition from Co/Cu multilayer films to films of inhomogeneous Cu/Co alloys can be traced on the basis of an x-ray structural investigation, as well as nuclear magnetic resonance and magnetoresistance measurements. An explanation for the observed phenomena is proposed. Zh. Tekh. Fiz. 67, 89–91 (December 1997)     

Peculiarities and thermal stability of microstructure and strength properties of Ti–Al–Si–O–C–N films

Peculiar relationship between the composition and fine structure and the variations in strength properties of nanostructured and nanocomposite, high-carbon, high-oxygen Ti–Al–Si–N films are investigated using Auger spectroscopy, electron microscopy, X-ray structural analysis and hardness measurements. It is shown that a TiN-based phase can form in these films, which exhibits nanocrystalline or two-level grain structure distributed in the x-ray amorphous phase whose volume fraction is 20–50%. The grain-structure character can be deliberately changed by incorporating aluminum or silicon into the films. It is found out that irrespective of their structural state and composition the films demonstrate high thermal stability of superhardness and microstructure up to the temperatures Т ≈ 1173 K. Hardness is seen to decrease at Т ≥ 1273 K as a result of dislocation recovery, stress relaxation and early recrystallization. It is suggested that the high strength properties demonstrated by these films are due to the presence of dislocation substructure and high shear resistance of the x-ray amorphous phases along nanocrystallite boundaries. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 57–65, November, 2008.     

Thermal stability of submicrocrystalline copper strengthened with HfO2 nanoparticles in the temperature range 20–500 °C

The thermal stability of the yield stress and Young’s modulus was investigated in ultrafinegrained copper (99.98%) and a Cu-HfO₂ composite obtained by intensive plastic deformation using the method of equichannel angular pressing. It is shown that both the pure copper and the composite strengthened with HfO₂ nanoparticles demonstrate in this state a high yield stress (σ _0.2≈400 MPa). When the two-hour annealing temperature T _a is increased above 200 °C, the yield stress in pure copper decreases to 40 MPa at T _a=400 °C, whereas in the Cu-HfO₂ composite, high yield stresses are conserved up to T _a=500 °C. A recovery stage of Young’s modulus is found at around 200 °C both in pure copper and in the Cu-HfO₂ composite. It is concluded that this stage reflects the transition of the grain boundaries from a nonequilibrium to an equilibrium state, and the high-strength properties of the materials are determined mainly by the grain size and depend weakly on the grain-boundary structure. Fiz. Tverd. Tela (St. Petersburg) 40, 1268–1270 (July 1998)     

Surface plasmon resonance detection using amorphous carbon/Au multilayer structure

Surface plasmon resonance (SPR) can be used to detect the change in reflective index on a metal surface. In this report, we propose detection of the SPR can easily be applied to estimate the thickness of the amorphous carbon (a-C:H) films. To detect changes in film thickness using SPR, devices with an a-C:H/Au structure were fabricated. The a-C:H films were deposited by electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD) and sputtering, and the obtained film densities were 1.4 and 1.6 g/cm³, respectively. By the deposition of an 11-nm thick a-C:H film on a Au layer by sputtering, the SPR angle changed from 44.90° to 47.05°. For a-C:H deposited by ECR-CVD, the SPR angle was shifted from 44.24° for Au without the a-C:H layer to 58.44° after deposition of 45 nm thick a-C:H film. In both systems of the SPR angle increased with increasing the film thickness. The rate at which the SPR angle shifted depended on the a-C:H film density. These results show that the thickness of an a-C:H film can be determined by the SPR angle shift on an a-C:H layer using a-C:H/Au device with an a-C:H film of the same density.     

Experimental indication of macroscopic polarization parallel to the tilt plane in free-standing films of ferroelectric liquid crystals 8SI* and DOBAMBC

Optical reflectivity and x-ray studies have been conducted on free-standing films and bulk samples of ferroelectric liquid crystals near the smectic-A-smectic-C ^* transition. A tilt plane rotation with respect to the direction of an applied electric field is found in the ferroelectric films above the bulk transition temperature. Whereas the macroscopic polarization is perpendicular to the tilt plane at low temperature, it is parallel to the tilt plane at elevated temperature. The temperature dependence of the average tilt angle is measured. Zh. éksp. Teor. Fiz. 116, 1329–1334 (October 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

X-ray diffraction investigations of the crystallographic parameters and thermal expansion of β-BaB2O4 crystals

The lattice parameters a and c of β-BaB₂O₄ crystals have been measured in the temperature range 80–300 K by the x-ray diffraction method. The thermal expansion coefficients α are calculated from the measured values of the parameters. A substantial anisotropy of the thermal expansion is found. It is shown that the thermal expansion coefficient α _c along the c axis is an order of magnitude greater than the thermal expansion coefficient α _a in a plane perpendicular to this axis. It is established that α _a becomes negative in the temperature range 80–190 K. Fiz. Tverd. Tela (St. Petersburg) 39, 1038–1040 (June 1997)     

Employment of absorbing a-C:H films in reflective liquid-crystal light modulators

The effectiveness of employing a-C:H films as light-blocking layers in reflective liquid-crystal light modulators with a-Si:H and a-Si:C:H photosemiconductor layers is investigated. The possibility of reducing the light flux penetrating into a photosemiconductor by 100 fold using an a-C:H film with a thickness of 1 μm and an extinction coefficient equal to 5×10⁴ cm⁻¹ at a wavelength of 632.8 nm is demonstrated. Zh. Tekh. Fiz. 69, 80–81 (March 1999)     

Critical conditions for spontaneous relaxation in self-organizing dissipative film systems

It is established that the necessary conditions for spontaneous relaxation of elastic strain energy in a copper-As₆₀Se₄₀ self-organizing dissipative heterostructure is that the elastic deformation energy and the temperature must reach their threshold values. It is shown that in the temperature range 270–340 K the spontaneous relaxation of elastic deformation energy is accompanied by structural-chemical ordering and anomalous diffusion of copper into the glassy chalcogenide semiconductor layer. The maximum concentration of copper dissolved in the films is 40 at. %. Conductivity inversion from p to n type is observed in doped layers obtained by this method. Zh. Tekh. Fiz. 69, 128–129 (August 1999)     

Metamagnetism and magnetostriction of the Ising antiferromagnet DyCrO3

The magnetostriction of the Ising antiferromagnet DyCrO₃ during metamagnetic transitions induced by a magnetic field applied along the a and b axes of the crystal is investigated experimentally and theoretically. The magnetostriction measurements performed in the temperature range 1.5–4.2 K in magnetic fields up to 3 T clearly reveal the two-step character of the transition from the original antiferromagnetic structure to the ferromagnetic structure with the intermediate formation of a low-symmetry structure (when H is parallel to the a axis). The unusual behavior of the magnetostriction discovered during the magnetizing process provides information on the nature of magnetostriction in rare-earth Ising metamagnets. Fiz. Tverd. Tela (St. Petersburg) 39, 668–670 (April 1997)     

Hydrogen-induced-intrinsic transport in undoped microcrystalline silicon

It is demonstrated that microcrystalline silicon (μc-Si:H) of intrinsic character can be produced by post-growth atomic hydrogen treatment. Undoped μc-Si:H films with a dark-conductivity activation energy (E _a) of about 0.20 eV were grown by plasma-enhanced chemical vapor deposition, and then subsequently exposed to an atomic hydrogen plasma. The hydrogen treatment is shown to result in a gradual increase in the E _a with increasing treatment time, followed by saturation at about 0.57 eV, a value observed for truly intrinsic μc-Si:H films. In the saturated state, the dark conductivity is on the order of 10⁻⁷ S/cm. The dark conductivity prefactor is found to follow the Meyer–Neldel rule. It is proposed that charge transport takes place in amorphous-like tissue surrounding the crystalline grains. The results are attributed to the Fermi level shift due to a change in the gap state distribution.     

Magnetic quantum oscillations in the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

The interlayer magnetoresistance of the organic superconductor κ-(BEDT-TTF)₂Cu[N(CN)₂)Br is measured at ambient pressure and under pressures of up to 12.5 kbar. In addition to the slow Shubnikov-de Haas oscillations with a frequency of ≃150 T observed at P⩾5 kbar, rapid oscillations attributed to the magnetic breakdown orbit enveloping an area equal to 100% of the area of the Brillouin zone are found to emerge above B=20 T. The latter oscillations are observed at ambient pressure as well as under pressures of up to 9 kbar. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 190–194 (10 August 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.