Amorphous Lattice Research Articles

Corrosion behavior of phosphorus containing zinc alloy deposits obtained from alkaline electrolyte

Zinc-alloy depositions are now largely used thanks to their good corrosion behaviour (as compared to zinc depositions). Phosphorus was introduced in the metallic matrix in order to increase the corrosion resistance of Zn-Ni platings. Strongly alkaline electrolytes were used (pH=12-12.5), in order to obtain Zn-Ni- P deposits. The characteristics of these depositions (chemical composition, structure) were studied in correlation with their performances of corrosion resistance. The qualitative analysis carried out by X-ray diffraction revealed that as part of Zn-Ni alloy, P reduces the grain size, also bringing about a tendency towards an amorphous crystal lattice. Korrosionsverhalten von Phosphor-enthaltenen Zinklegierungsabscheidungen aus alkalischen Elektrolyten Dank ihres guten Korrosionsverhaltens (verglichen mit Zinkbeschichtungen) werden Zinklegierungsabscheidungen vielfach eingesetzt. Um den Korrosionswiderstand der Zn-Ni- Überzüge zu erhöhen, wurde Phosphor in die metallischen Matrix eingebracht. Hierfür wurden stark alkalische Elektrolyten (pH = 12–12,5) verwendet. Die Eigenschaften dieser Abscheidungen (chemische Zusammensetzung, Struktur) wurde in Korrelation mit ihrem Korrosionswiderstandsverhalten untersucht. Die mittels Röntgenbeugung durchgeführte qualitative Analyse ergab, dass P als Teil der Zn-Ni Legierung die Korngröße reduziert sowie ein amorphes Kristallgitter begünstigt.

Plasma Deposition of Thin Carbon⧸Germanium Alloy Films from Organogermanium Compounds

Semiconductors based on group IV elements are widely used in the fields of micro-electronics, optics and photonics. The group IV alloys are processed using plasma enhanced chemical vapor deposition and its opto-electrical properties are a result of the material composition and structure. Infrared and Raman spectroscopy are complementary and powerful tools for providing these essential material characteristics. In this work, the vibrational modes present in hydrogenated, oxygenated and carbonated group IV alloys are investigated in a unique range of amorphous and nano-crystalline SiX≥0Ge1−X:H films and their alloys with C, O and Sn. Measurements are performed both post-deposition and following extended exposure to the ambient and de-ionized water. This comprehensive review is of value in the fields of material science and engineering as a single work of reference for group IV peak identification. Additionally, the effect of electrical screening, the influence of the dielectric medium on the peak frequency of a vibrational mode, is illustrated using the experimentally observed frequency shifts of X-O and X-H (X = C, Si, Ge) vibrational modes. All experimentally observed center frequencies of silicon hydride stretching modes in silicon solids and corresponding silicon-hydride configurations are identified using a straightforward Lorentz-Lorenz model approximation and considering all potential hydrogenated volume deficiencies within a tetrahedrally coordinated amorphous and nanocrystalline lattice. It shows that the stretching mode signature can reveal detailed information on the volume deficiencies in IV-valence alloys.

EPR investigation of a-Si:H aerosol particles formed under silane thermal decomposition

The dangling bond defects were investigated in a-Si:H particles formed under silane thermal decomposition in flow reactor. EPR together with hydrogen evolution method were used. The experimental results allowed us to conclude that there are two kinds of dangling bond defects in a-Si:H aerosol particles. The defects of the first kind are localized on the surface of interconnected microvoids and microchannels (surface dangling bonds) and those of the second kind are embedded in amorphous silicon network (volume dangling bonds). The thermal equilibration of dangling bonds and temperature dependence of equilibrium dangling bond concentration were investigated. It was found that at temperatures > 400 K the dangling bond concentrationNApplied Magnetic Resonance s reversibly depends on sample temperature. The volume dangling bond concentration increases with temperature increasing (the effective activation energy of dangling bond formationU > 0), and the surface dangling bond concentration decreases with temperature increasing (U < 0). It has been found that EPR line is considerably asymmetric for samples with high hydrogen content and for low hydrogen content the EPR line is weakly asymmetric. A conclusion was drawn that the asymmetry degree depends on amorphous silicon lattice distortions. This conclusion has been confirmed by EPR spectra simulations.

Copper-induced changes in the properties of arsenic chalcogenides

The influence of the presence of Cu in the amount between 1% and 6% in arsenic chalcogenide glasses is examined through a study of the electronic energy levels by means of x-ray photoelectron and x-ray emission spectroscopy, through an investigation of the low-energy tunneling systems by means of phonon echoes at 0.37 K, and through an examination of the photodarkening and the photoinduced dichroism caused by polarized Ar+ laser irradiation. Possible links between the various effects are examined. The Cu atoms become an integral part of the amorphous lattice structure and strongly influence the photodarkening, but they do not have a significant effect on the tunneling systems or the dichroism. It is concluded that the tunneling levels and the dichroism involve only local configurations, while the photodarkening involves larger-scale areas of the lattice.

Insight on the microscopical structure of a-C and a-C:H thin films through electron spin resonance analysis

Abstract In this paper it is shown that electron spin resonance can be used as a tool for structural investigation of amorphous carbon thin films. Interesting information on the amorphous lattice is obtained from the analysis of the features of the ESR signal. Some representative examples will be discussed. For instance, it will be shown that different degrees of structural disorder exist in the various films, that regions having different local structure exist in sputtered amorphous carbon, and that in soft polymeric a-C:H the unpaired spins have a very weak interaction with the lattice.

Hydrogen Energetics and Transport Kinetics in Amorphous Silicon Hydride

AbstractTo understand the electrical properties and behavior of amorphous silicon, it is imperative to understand the behavior of hydrogen in the amorphous silicon lattice. Although considerable effort has been extended to study hydrogen trapping in a-Si:H, the energetics and populations of the traps remain unresolved. We have developed a reaction diffusion model which includes multiple bulk trapping mechanisms, bulk transport, and realistic surface processes. The model results are compared with existing hydrogen temperature programmed evolution data, isothermal hydrogen evolution experiments, and thermal quenching experiments. We find consistently good fits for all three types of experiments with a shallow trap depth of 1.5 eV and deep trap depth of 1.8–1.9 eV below the mobility level, with 20–30% of hydrogen present in the deep trap. The difference of 0.3–0.4 eV between the two trap depths is similar to the defect formation activation energy and suggests a defect formation mechanism which involves movement of hydrogen from a deep to a shallow trap.

Bonding and diffusion in hydrogenated amorphous silicon by tight-binding molecular dynamics

The structural and bonding properties of hydrogenated amorphous silicon are investigated by tight-binding molecular dynamics. The formation of clusters and chains of hydrogen atoms is observed when quenching a hydrogenated liquid silicon sample to room temperature. In addition, the high-temperature stability of the amorphous network is investigated as a function of the hydrogen content of the sample. The amorphous silicon lattice is found to be unstable at high temperature when the hydrogen content is above 10%.

Long-range structural relaxation in the Staebler-Wronski effect

X-ray photoemission spectroscopy (XPS) has been used to study the structural changes of device-quality a-Si:H between the annealed state (A) and the light-soaked state (B). The XPS spectra show a reversible shift of about 0.1 eV of the Si 2p peak to lower binding energy without a corresponding shift of the Si 2s peak in going from state A to state B. Density functional calculations on a Si 6H 14 prototype molecule are also presented which suggest that the Si core energy levels may indeed be shifted by comparable amounts when small structural rearrangements are forced upon the structure. The change in the Si 2p peak is too large to be caused by a rearrangement of the amorphous lattice restricted to the immediate surroundings of the defects responsible for the Staebler-Wronski effect (defect density: < 10 17 cm −3). It is proposed instead that the formation of dangling bonds under exposure to light is also accompanied by long-range structural rearrangements of the amorphous network. Results obtained by other groups are discussed which, in our opinion, also indicate the presence of long-range structural rearrangement during the Staebler-Wronski effect.

Thermostability of amorphous bubble lattices in garnet films

It is experimentally shown that amorphous bubble lattices formed in thin uniaxial garnet films are more thermostable than regular or cluster bubble lattices. The obtained experimental results are explained within the framework of a thermodynamical approach using the concept of the domain chemical potential.

NMR study on amorphous dense Kondo CeCu6

Abstract The NMR spectrum and spin-lattice relaxation rate 1/T1 of Cu nuclei in an amorphous CeCu6 alloy were measured. The spectrum is very broad, and 1/T1 has a distribution, probably because of many inequivalent Cu sites, the anisotropy in 1/T1 and the amorphous lattice arraement. The largest component of 1/T1 is independent of temperature T, and the smallest one is nearly proportional to T. These results are very similar to those obtained for crystalline CeCu6.

Time-dependent evolution of the structure and chemical bonds in diamond-like carbon films generated by the hot filament chemical vapour deposition method

The chemical structure of inhomogeneous amorphous carbon films grown for different lengths of time in a hot filament chemical vapour deposition reactor from a methane-hydrogen mixture has been investigated by electron energy loss spectroscopy (EELS) and Raman spectroscopy. The changes in EELS and Raman spectral shapes allowed us to monitor the time-dependent structural evolution of the films, from an amorphous lattice with a noticeable fraction of sp 3-bonded hydrogenated carbon atoms to a prevalence of microcrystalline graphitic domains. The depth profile of hydrogen in the grown film for 120 min has been measured by the 1H( 15N, αγ) 12C nuclear reaction analysis technique. The low value of the hydrogen content (less than 4 at.%) is consistent with the structure of this carbon film which has a density of 1.9 g cm -3. By the combined use of Rutherford backscattering spectrometry and nuclear reaction analysis the mean carbon coverage thickness was found to be 22±5 nm. Secondary ion mass spectrometry measurements confirmed this conclusion.

Properties of p-type amorphous silicon carbide window layers prepared using boron trifluoride

Abstract One set (A) of undoped and three sets (B, C and D) of doped hydrogenated amorphous silicon carbide samples have been made in the framework of a research plan for obtaining high quality p-type window layers by radiofrequency glow discharge of silane-based gas mixtures. The samples of sets A and B were made using different RF-power-density to mass-flow ratios for various methane percentages in the gas mixture. The best carbon incorporation in the amorphous silicon lattice was obtained at the highest RF-power density. The properties of sets C and D, prepared using different RF-power densities and silane and methane propertions have been analysed as functions of the concentration of borom trifluoride with respect to silane. In both cases, the optical gap E G , after a slight initial decrease, remains at a value of approximately 2.1 eV without quenching in the dopiong ranges covered. The best conductivity obtained is 2 × 10 −7 (μ cm) −1 . IR spectra allow to associate these features with the structural quality of the films.

Induced flux creep as a novel technique for detecting alternating magnetic fields: Study of YBa 2Cu 3O 7−x thin film at 0.006–100 MHz

A new mechanism for detecting AC magnetic fields, based on induced flux creep ([1] S.M. Vatnik and S.N. Smirnov, Phys. Lett. A, submitted), has been studied in detail. The amorphous flux lattice approximation, widely used for the description of flux creep, has been shown to be inconsistent with experimental results in a field range chosen in studies of both induced flux creep and stationary I–V characteristics. A technique has been proposed for determining the pinning energy from stationary I–V characteristics.

A hole burning study of excitonic states of chain molecules in glasses

Thermal broadening of spectral holes burnt into excitonic states of long chain molecular aggregates of pseudoisocyanine iodide is investigated over a temperature range from 350 mK to 80 K. The results differ very much from the usual behavior of small molecules in glasses. We found that extended states are almost completely decoupled from the amorphous host lattice and spectral diffusion effects play a minor role. The homogeneous linewidth is independent of temperature below 10 K. Above, thermal broadening occurs in two steps: there is a weak onset around 15 K and a strong onset around 65 K. The data can be fitted by a superposition of two exponentials.

Trends in materials development for magnetic recording heads

Magnetic recording technology is in a transition stage from ferrite heads and low coercivity oxide media to high coercivity metallic media, and thin film heads with high frequency response. This paper reviews some of the possibilities for improvements in existing magnetic materials and the main direction of development of new materials for magnetic heads. Amorphous alloys, multilayers, microcrystalline alloys, amorphous and crystalline artificial lattice structures are, and will continue to be, the focal point of magnetic head materials research.

Magnetic hysteresis and crystallization studies on metallic glass alloy Fe67Co18B14Si1

Magnetic hysteresis studies were carried out on Metglas 2605 Co(Fe67Co18B14Si1) samples, cut parallel and perpendicular to the ribbon axis and annealed at different temperatures. The samples annealed at 450°C for 2 hr show a coercive force of 8·75 Oe and 0·60 Oe in the parallel and perpendicular directions respectively. Electron probe micro analysis studies revealed the onset of primary crystallization at 400°C and a gradual displacement of B and Si from the lattice as the annealing temperature was increased to 450°C. The observed large coercive force is due to an increase in anisotropy resulting from an intergrowth pattern of the type Fe x Co1 −x , 0·3<x<1·0, including boron containing phases such as (FeCo)B, (FeCo)2B, (FeCo)3B, developed by the displacement of and Si from the original amorphous lattice.

Linear excitations and the stability of the hard sphere glass

We extend Fixman’s self-consistent phonon theory of the thermodynamic properties and fluctuations of the hard sphere crystal to an amorphous lattice. In doing so we develop a theory of lattice vibrations in amorphous materials via a perturbation theory around the Einstein oscillator approximation. This development is analogous to the mean spherical model description of electronic excitations in liquids. The theory exhibits a mechanical instability rather close to computer simulated glass transitions, suggesting the possibility that the simulations probe only linear stability because of the short simulation times.

Computer simulation of vortex pinning in type II superconductors. II. Random point pins

Pinning of vortices in a type II superconductor by randomly positioned identical point pins is simulated using the two-dimensional method described in a previous paper (Part I). The system is characterized by the vortex and pin numbers (N v ,N p ), the vortex and pin interaction ranges (R v ,R p ), and the amplitude of the pin potentialA p . The computation is performed for many cases: dilute or dense, sharp or soft, attractive or repulsive, weak or strong pins, and ideal or amorphous vortex lattice. The total pinning forceF as a function of the mean vortex displacementX increases first linearly (over a distance usually much smaller than the vortex spacing and thanR p ) and then saturates, fluctuating about its average\(\bar F\). We interpret\(\bar F\) as the maximum pinning forcej c B of a large specimen. For weak pins the prediction of Larkin and Ovchinnikov for two-dimensional collective pinning is confirmed:\(\bar F\)=const·\(\bar W\)/R p c66, where\(\bar W\) is the mean square pinning force andc 66 is the shear modulus of the vortex lattice. If the initial vortex lattice is chosen highly defective (“amorphous”) the constant is 1.3–3 times larger than for the ideal triangular lattice. This finding may explain the often observed “history effect”. The function\(\bar F\)(A p ) exhibits a jump, which for dilute, sharp, attractive pins occurs close to the “threshold value” predicted for isolated pins by Labusch. This jump reflects the onset of plastic deformation of the vortex lattice, and in some cases of vortex trapping, but isnot a genuine threshold. For strong pins\(\bar F\)∼(N p \(\bar W\))1/2 approaches the direct summation limit. For both weak and strong pinningj c B is related to the mean squareactual (not maximum) force of each pin. This mean square in general is not proportional toA p 2 but, due to relaxation of the vortex lattice, may be smaller or larger than its rigid-lattice limit. Therefore, simple power lawsj c ∼n p A p 2 orj c ∼n p A p in general donot hold except for very weak or unphysically strong pinning.

Statistics of Two-Dimensional Amorphous Lattice

Etude d'un reseau spatialement aleatoire forme de carres et de triangles equilateraux juxtaposes. Quand on fait varier le rapport entre le nombre de carres et le nombre de triangles, le reseau passe d'un reseau triangulaire a un reseau carre en passant par diverses formes de reseaux amorphes. On definit une mecanique statistique du reseau en affectant un poids statistique de Boltzmann approprie aux carres et aux triangles

Some elements of physico-chemical crystallography of the vitreous state

Using the notions about amorphous lattices and quaside-fects, the various kinds of defects in glass forming substances, the interaction between defects and amorphous lattices and the display of this interaction in the properties of glasses and glass forming melts are considered.