Far infrared absorption in bulk amorphous red phosphorous

Far infrared absorption measurements have been performed above 30 cm^?1 in bulk amorphous red P at 300 K. A number of low frequency spectral features are observed that are not present in the corresponding bulk amorphous As spectrum. Deep minima observed at 163 and 320 cm^?1 in α(ω) and in the Raman spectra suggest that the phonon density of states is essentially divided into 3 bands. A calculation of the mean effective charge of the bands indicates weak coupling to the lowest frequency band. A comparison with the results in a-As suggests a less rapid frequency variation in the infrared coupling parameter at low frequencies in a-$\text{P}$.     

The mass enhancement and the specific heat of disordered and amorphous metals

The reduction of the mean free path in metals causes a change of the electronphonon interaction and the Eliashberg function α²(Ω)F(Ω). The values of α²(Ω)F(Ω) for pure, disordered and amorphous lead are used to calculate the enhancement of the density of states and the electronic specific heat in these materials. In pure lead the cyclotron mass (1+λ) has a maximum at 11 °K and the Sommerfeld constant (γ) has a maximum at 5 °K. In disordered lead with a mean free path of about 70 Å, both, 1+λ and γ are almost constant in this temperature range. For amorphous lead there is no temperature range where 1+λ and γ are sufficiently constant. A measurement of the specific heat in disordered non-superconducting metals could answer the question whether these metals are closer to the superconducting state when their mean free path is reduced, a fact which is true for all weak-coupling superconductors.     

Specific heat and thermal conductivity of low-stress amorphous Si-N membranes

We present values of the specific heat and thermal conductivity from 3-300 K of low-stress amorphous silicon-nitride thin-films determined from measurements using a membrane-based microcalorimeter. The thermal conductivity has a temperature dependence often seen in amorphous solids, but the magnitude is large, with the expected plateau occurring at significantly higher temperatures than seen in other amorphous systems. Specific heat measurements show that the expected ‘peak’ in the vibrational spectrum also occurs at relatively high temperatures. The estimated phonon mean-free-path at 300 K is ≈5 Å, comparable to the inter-atomic spacing, as seen in other amorphous solids. Below ≈ 20 K the mean free path is comparable to or exceeds the thickness of the membrane, indicating that surface scattering dominates the thermal transport. This surface scattering is found to be either specular or diffuse, depending on details of the membrane processing, which affects both the thermal conductivity and specific heat below 10 K.     

The microscope structures of amorphous phosphorus

The microscopic structures of thin films of amorphous phosphorus have been investigated by Raman scattering. The thin films were deposited by vacuum evaporation at substrate temperatures T_s between 300 and 510K. The Raman spectra of the films were compared with vibrational spectra of different allotropes of phosphorus: orthohombic black P, bulk amorphous red P and Hittorf's P. The structure of the films with T_s ? 300K is built up of double layers similar to those of orthorhombic black P. For T_s?510K the thin films have a structure similar to bulk amorphous red P based on the pentagonal tubes of Hittorf's P. A continuous transformation from one structure to the other is indicated by the Raman spectra of the films at intermediate T_s. The Raman measurements support early determinations of the structures of amorphous phosphorus inferred from radial distribution functions.     

Raman scattering in amorphous boron

Raman scattering measurements have been performed at room temperature in thin film evaporated amorphous B and B_0.91C_0.09. The amorphous B spectrum indicates density of states features similar to those observed in infrared absorption as well as lower frequency scattering attributed to acoustic plus optic-like modes. The addition of C to amorphous B broadens the spectrum and shifts the lowest frequency peak to higher frequencies. A comparison of the amorphous B and broadened crystalline β-B Raman spectra indicates a number of similarities in peak frequencies that are consistent with similar short range order in both materials.     

Comment on the low temperature specific heat of ferroelectrics,antiferroelectrics, and related materials

Lawless has reported accurate, low temperature (2–30°K) specific heat measurements (C_Exp) of a large number of ferroelectrics, antiferroelectrics, and related materials. A plot of C_Exp T^?3 vs. T (T is temperature) reveals an “excess’ specific heat in the 10–30K range. Lawless has interpreted and fit this excess heat with an Einstein term determining the number of oscillators and the Einstein frequence for each material. He has related these large number of extra oscillators to modes observed in some Raman experiments. Using a more realistic density of states, we suggest that the experimental data can be understood in terms of straightforward harmonic lattice dynamics and that there are no extra modes. The “extra” heat capacity merely arises from the differences between the more realistic density of states and that of a Debye solid.     

A cellular model for the specific heat of amorphous solids at low temperatures

The wave equation for a non-homogeneous continuum with a statistical mass-density distribution is studied as a model for the vibrational specific heat of amorphous solids. The frequency spectrum is calculated for the simple case of small homogeneous cells separated from each other by hard and soft boundary walls distributed at random. The usual bulk mode density is enhanced by a positive constant term yielding the specific heat AT + BT³. From experimental values of the constants A, an upper limit of about 70 Å is calculated for the average cell diameter in vitreous SiO₂ and GeO₂.     

Structural variation in a synchrotron‐induced contamination layer (a‐C:H) deposited on a toroidal Au mirror surface

A carbon layer deposited on an optical component is the result of complex interactions between the optical surface, adsorbed hydrocarbons, photons and secondary electrons (photoelectrons generated on the surface of optical elements). In the present study a synchrotron‐induced contamination layer on a 340 mm × 60 mm Au‐coated toroidal mirror has been characterized. The contamination layer showed a strong variation in structural properties from the centre of the mirror to the edge region (along the long dimension of the mirror) due to the Gaussian distribution of the incident photon beam intensity/power on the mirror surface. Raman scattering measurements were carried out at 12 equidistant (25 mm) locations along the length of the mirror. The surface contamination layer that formed on the Au surface was observed to be hydrogenated amorphous carbon film in nature. The effects of the synchrotron beam intensity/power distribution on the structural properties of the contamination layer are discussed. The I(D)/I(G) ratio, cluster size and disordering were found to increase whereas the sp²:sp³ ratio, G peak position and H content decreased with photon dose. The structural parameters of the contamination layer in the central region were estimated (thickness ? 400 Å, roughness ? 60 Å, density ? 72% of bulk graphitic carbon density) by soft X‐ray reflectivity measurements. The amorphous nature of the layer in the central region was observed by grazing‐incidence X‐ray diffraction.     

Surface characteristics and electrochemical behaviour of sputter-deposited NiTi thin film

Thin nanocrystalline amorphous NiTi film was deposited on Si substrate using DC magnetron sputtering. The as-deposited NiTi thin film was crystallized by heat treatment at 500 °C for 1 h. The crystal structure, surface morphology, microstructure and surface chemistry of the deposited films were studied using X-ray diffraction, atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy (XPS), respectively. Corrosion behaviour was assessed in Ringer’s solution at 37 °C by open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy as a function of exposure time. OCP values indicate that the tendency for the formation of a spontaneous oxide film is greater for the NiTi thin films than the bulk NiTi. Long time exposure to Ringer’s solution was found to have a great effect on the corrosion behaviour of the samples. Significantly low corrosion current density was obtained for the annealed NiTi film from the potentiodynamic polarization curves indicating a typical passive behaviour, but as-deposited film and bulk NiTi alloy exhibited breakdown of passivity at potentials approximately +1.4 V (vs. SCE). XPS showed that the oxide film formed on the annealed NiTi thin film mainly composed of Ti oxides, and no evidence of Ni was found up to 8.2 nm beneath the top surface, suggesting the excellent corrosion resistance of this sample in Ringer’s solution.     

Optical and structural characterization of ultrananocrystalline diamond/hydrogenated amorphous carbon composite films deposited via coaxial arc plasma

Ultrananocrystalline diamond/hydrogenated amorphous carbon composite films were deposited in the ambient of hydrogen by coaxial arc plasma deposition. The film compositions and chemical bonding structures were investigated by X-ray diffraction, X-ray photoemission and hydrogen forward scattering spectroscopies. The sp³/(sp²+sp³) ratio and hydrogen content in the film were estimated to be 64% and 35?at.%, respectively. The optical parameters and the optical dispersion profile were determined by using a variable angle spectroscopic ellipsometer at 55°, 65° and 75° angle of incidence in the photon energy range of 0.9–5?eV. Combinations of multiple Gaussian, and Tauc-Lorentz or Cody-Lorentz dispersion functions are used to reproduce the experimental data. Results of ellipsometry showed a refractive index of approximately 2.05 (at 2eV) and optical band gap of 1.63?eV. The imaginary part of dielectric function exhibited a peak at 3.8?eV, which has assigned to π-π* electron transitions. Furthermore, Electron spin resonance measurements implied the existence of dangling bonds, which might have a partial contribution to the optical absorption properties of the deposited films. A correlation between optical parameters and structural profile of the deposited films is discussed.     

Temperature dependence of anomalous and ordinary Raman scattering in β-AgI

We report careful measurements of the temperature dependence of Raman scattering in β-AgI, with particular emphasis on the region 12°K to 150°K. Our main result is that the anomalous features in the Raman spectra of β-AgI are definitely first order. Furthermore from the temperature dependence of the anomalous scattering intensity we infer the possibility of a first partial disordering in the Ag⁺ sublattice at about 50°K.     

Conversion electron Mössbauer study of amorphous FeSi thin films

Amorphous FeSi films deposited at 77 K and at room temperature were studied by CEMS. The CEMS reflection spectra for bulk FeSi show quadrupole splittings, ΔE_S, larger by ～ 0.04 mm sec^?1 than ΔE_B - the ones shown by transmission spectra.For amorphous FeSi films ΔE was found (a) to decrease with the thickness of the film, and (b) to be by 25% larger for an amorphous film than for a crystallized one (of the same thickness).The crystallization was found to start at 240°C for a 300 Å thick film.     

Low temperature thermal properties of PbI2

The heat capacity and thermal conductivity of a large (56.5 g) crystal of PbI₂ have been measured in the temperature region 0.5 < T < 3.9°K. Analysis of the heat capacity data yields a value of the limiting apparent Debye characteristic temperature θ₀^c = 99.4 (±0.3)°K, which corresponds to an average lattice wave velocity of 1.151 (±0.005) × 10⁵ cm sec^?1. It is consistent with a wave velocity estimated from neutron scattering experiments, but not with one determined from Brillouin spectra. The heat capacity data also show that dispersion of the low frequency waves is not unusual, as might have been expected for a layer-type crystal. The apparent thermal conduction is found to be surprisingly small in the crystal.     

Messung der spezifischen Wärme von abschreckend kondensierten Indium-, Blei- und Wismut-Schichten bei tiefer Temperatur

Thin metal films are evaporated onto a cooled Be-foil at 25–32 °K in high vacuum. After condensation the films have a large degree of disorder. The specific heat is measured in the temperature range from 5–8 °K after condensation and after annealing. No differences in the specific heat are found for disordered and annealed In- and Pb-films. The specific heat of amorphous Bi-films, however, is 1.7 times larger than that of crystalline films. The results are discussed together with investigations of disordered films by superconducting tunneling.     

Calculation of vibrational relaxation times in gaseous cyanogen

A calculation of vibrational relaxation times in gaseous cyanogen at 300°K is presented. It is suggested that two well separated dispersion regions should be found in sound velocity measurements at ultrasonic frequencies, the higher frequency region being associated with the relaxation of the combined vibrational specific heat contributions of the two lowest modes and the lower frequency region being associated with the relaxation of the corresponding contribution of the next highest mode.     

Temperature dependence of amorphous and interface phases in the Fe80Nb7Cu1B12 nanocrystalline alloy

Temperature measurements (77–625 K) of Fe₈₀Nb₇Cu₁B₁₂ nanocrystalline alloy prepared from amorphous precursor annealed for 1 h at 470^°C and 620^°C are presented. Structural and magnetic behaviours of the crystalline phase, the amorphous residual matrix, and the interface zone between crystalline grains and the amorphous phase are studied by distributions of hyperfine magnetic fields. Magnetic regions are developing in the retained amorphous phase with rising temperature of annealing. They can be suppressed, however, at high enough measuring temperatures turning the amorphous matrix into paramagnetic state. As a consequence, the respective spectral components do not interfere so much and the role of interface zone can be studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

Streuung von Helium-Atomstrahlen in Edelgasen

The scattering of Helium atomic beams in rare gases is investigated by measurements of total elastic scattering cross sections. With the device described the dependence of total scattering cross sections of the relative velocity of the scattering atoms was measured. For variation of the beam velocity in the range of 1:8 a He beam source was used which could be cooled down with liquid helium from room temperature to 4.8 °K. The detector is of the universal-detector-type. A Wien filter is used as mass filter. The lowest detectable particle density is 6.3 · 10³ He-atoms/cm³. The measured scattering cross sections are in qualitative agreement with the theory ofBernstein.     

The annealing of damage in ion implanted gallium arsenide

Photoluminescence measurements at 77°K and Rutherford scattering of 450 keV protons were used to study radiation damage and annealing in ion implanted GaAs. The characteristic band edge luminescence (8225 Å) in GaAs is completely quenched by ion implantation. Photoluminescence measurements on samples which were isochronally annealed show a single annealing stage at 600°C. A luminescence peak at 9140 Å is introduced into the spectra of all implanted and annealed samples. This peak is attributed to an acceptor level created by As vacancies. The intensity of the peak is greatly reduced by protecting the surface of implanted layers with SiO₂ during annealing. Rutherford scattering measurements on isochronally annealed samples reveal two annealing stages. A 300°C annealing stage is observed on samples which have an initial aligned yield less than random while a 650°C stage is observed on samples which have an initial aligned yield equal to random.     

Raman scattering and short range order in amorphous germanium

Variations in short range order of amorphous Ge films are determined from a combination of depolarized Raman scattering, optical absorption, and previous radial distribution function studies. An estimated minimum value of the bond angle width of Δθ ? 9°, obtained for evaporated, anneal stable a-Ge differs significantly from a recent EXAFS estimate. The maximum disorder observed in dc sputtered films deposited at ～90K indicates that an ～20% variation in bond angle width is possible in a-Ge. Substantial modification of the Raman spectrum of the low temperature film annealed at 300K also demonstrates that lower temperature structural relaxation processes involve changes in short range order.     

Structural and magnetic properties of Co-C composite films and Co/C multilayer films

CoC composite films and Co/C multilayer films have been prepared by a method incorporating ion beam sputtering and plasma chemical vapor deposition. It has been found that the structure and magnetic properties of both the Co-C composite and the Co/C multilayer films depend strongly on the substrate temperature during deposition. The Co-C composite film deposited at room temperature is amorphous, with relatively low saturation magnetization and coercivity. On the other hand, the film deposited at 250 °C is composed of fine Co crystallites separated by amorphous C or Co-C phase. As a result, both the saturation magnetization and coercivity are increased compared with the film deposited at room temperature. When deposited at room temperature, the Co/C multilayer film exhibits good periodicity, with a period of 70 nm (Co: 40 nm, C: 30 nm) and sharp and flat Co-C interfaces. High magnetization (602 emu/cm³) and low coercivity (1.6 Oe) are obtained for such a film. However, increasing the substrate temperature to 250 °C was found to be detrimental to the magnetic properties due to the formation of cobalt carbide at the Co-C interface. Received: 11 July 2000 / Accepted: 13 July 2000 / Published online: 30 November 2000