Effect of annealing on the conduction mechanism in amorphous silicon

This paper reports the effect of annealing on conduction mechanisms in amorphous silicon films. High field transport is mainly by the Poole-Frenkel mechanism in unannealed films of amorphous silicon. As they are annealed, the conduction meachnism changes from Poole-Frenkel to space charge conduction. The films are fully annealed at 120°C for 15 h and any more annealing for longer periods does not change the I–V characteristics. From the measured values of threshold voltage at which space charge conduction sets in, the density of localized states around the Fermi level is calculated to be about 10¹⁷–10¹⁸/eV · cm³ which agrees very well with our results from other experimental techniques.     

Influence of annealing on nanocrystal formation in Ni amorphous alloy

An amorphous Ni alloy has been obtained as a ribbon by plasma-arc melt spinning in a copper water-cooled lining slag crucible. Ribbon samples have been annealed in a special cylindrical furnace at temperatures from 200 to 400°C for 1 h in Ar. It is established that nanocrystals in the alloy samples increase in size with increasing annealing temperature. The rise of resistivity upon annealing at temperatures below 300°C and its significant decrease at higher temperatures is consistent with the change in the amorphous alloy microstructure.     

The influence of laser annealing in the presence of longitudinal weak magnetic field on asymmetrical magnetoimpedance response of CoFeSiB amorphous ribbons

Asymmetrical magnetoimpedance (AMI) is very important to further improve micromagnetic sensor performance in terms of linearity and sensitivity. This behavior was investigated for Co_68.15Fe_4.35Si_12.5B₁₅ amorphous ribbons irradiated by a 1064 nm Nd:YAG pulsed laser in air and in the presence of 3 Oe longitudinal magnetic field with changing pulse repetition rate. Results indicate that for different pulse repetition rates, various types of AMI profiles appear. For the samples annealed in the presence of longitudinal field, because of induced anisotropy, rising in asymmetry factor takes place and another peak in the magnetoimpedance (MI) profile transpires.     

High-frequency magnetoimpedance on annealed amorphous magnetic wires with different magnetostriction constants

Amorphous Co-based and Fe-based magnetic wires having magnetostriction constants ranging from nearly zero positive values to large positive values, have been submitted to different thermal treatments (dc Joule heating and furnace annealing) to relax internal stresses produced during fabrication and to possibly induce different magnetic anisotropy. High-frequency (up to 6 GHz) magnetoimpedance GMI response has been studied as a function of frequency and thermal treatment in order to experimentally investigate the role of all these parameters on GMI.     

Torsion and tension stress induced transformation of surface magnetic structure in Co-rich amorphous microwires

The effect of torsion and tensile stress on the surface magnetic properties in Co-rich glass covered amorphous microwires has been studied. The magnetization reversal in microwires has been studied by magneto-optical Kerr effect. Calculations of hysteresis loop was performed taking into account the existence of helical magnetic anisotropy in the outer shell of the microwire. The comparative analysis of the results of the experiment and the calculation demonstrates that the observed transformation of the surface hysteresis is related to the variation of the angle of the helical surface structure.     

On-state behaviour and degradation effects in thin-film amorphous switching devices

The on-state behaviour of thin-film chalcogenide threshold switches was studied with special reference to the influence of electrode materials and the progressive effects of device degradation. For operations during the forming period, the on-state current-voltage characteristics remain identical for both rising and falling current. The on-state minimum voltage is found to be closely proportional to the square root of the electrode thermal conductivity and, in addition, shows some polarity dependence with dissimilar electrode combinations. This behaviour is interpreted in terms of a model in which the voltage drop across the on-state current channel is dominated by constrictions and associated hot spots near the channel/electrode boundaries. After forming and after a further number of operations depending both on electrode material and ambient temperature, one or more stable intermediate steps or “branches” develop in the I–V characteristic of the transition from off-state to on-state. The exact pattern shows some polarity dependence. Branching is identified with the progressive precipitation of tellurium-rich “islands” in the glass as the number of device operations increases and as a result of which the growth of the on-state channel proceeds via a number of “island-hopping” stages.     

Photo-enhanced crystallization by laser irradiation and thermal annealing in amorphous GeSe2

The laser irradiated crystallization process in amorphous GeSe₂ was studied by Raman scattering to discriminate between thermal and photo-induced contributions. Amorphous GeSe₂ crystallizes into a low-temperature (LT) form, LT-GeSe₂, and a high-temperature (HT) form, HT-GeSe₂. An amorphous sample was annealed at various temperatures and times in an electric furnace with and without laser irradiation. The laser power was adjusted to about 20 mW having a 0.4 mm spot size to determine the photo-induced effect. The difference between the thermal and laser irradiated crystallization process was discussed by considering the activation energy of crystallization. The activation energy due to laser irradiation above the band-gap energy was found to be smaller than that for the pure thermal crystallization process. We present a model for the photo-enhanced effect in which the lone-pair electrons of Se atoms are excited by the photons and the bond switching or atomic rearrangement occurs when the electrons relax through an electron–phonon interaction.     

Effect of annealing temperature on the structural and optical properties of amorphous Sb2Te2Se thin films

Thin films of Sb₂Te₂Se were prepared by conventional thermal evaporation of the presynthesized material on Corning glass substrates. The chemical composition of the samples was determined by means of energy‐dispersive X‐ray spectrometry. X‐ray diffraction studies on the as‐deposited and annealed films revealed an amorphous‐to‐crystalline phase transition. The as‐deposited and annealed films at T _a = 323 and 373 K are amorphous, while those annealed at T _a= 423 and 473 K are crystalline with a single‐phase of a rhombohedral crystalline structure as that of the source material. The unit‐cell lattice parameters were determined and compared with the reported data. The optical constants (n , k ) of the investigated films were determined from the transmittance and reflectance data at normal incidence in the spectral range 400–2500 nm. The analysis of the absorption spectra revealed non‐direct energy gaps, characterizing the amorphous films, while the crystalline films exhibited direct energy gaps. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hall resistivity of a magnetic amorphous alloy — Effects of thermal cycling and annealing

We have studied the effects of thermal cycling and annealing on the Hall resistivity ?_H and electrical resistivity ? of an amorphous magnetic material, Metglas 2826A. Thermal cycling up to 600 K has no significant effect on ? but changes ?_H, especially at T > 300 K. Annealing at higher temperatures T_a affects ?_H more strongly that it influences ?. For T_a = 650 K the Curie temperature jumps by ～300 K and this, combined with X-ray data, is regarded as being symptomatic of the onset of crystallization. It is demonstrated that, for a fixed T, the variation of the extraordinary Hall coefficient R₁ is simply correlated with that of ? for both the amorphous material and the annealed (crystallized) specimens. Furthermore, for a given T_a, the variations of R₁ and ? as functions of temperature exhibit the same formal relationship. The temperature dependence of ? in the annealed specimens is rendered plausible in terms of recent theories of disordered materials. Room-temperature studies of electron spin resonance and the field dependence of the magnetization are also reported.     

Flux Bridgman growth and the influence of annealing temperatures on PL properties of ZnO single crystals

Transparent ZnO crystals were obtained by the flux Bridgman method from high temperature solution of 22 mol% ZnO‐78 mol% PbF₂ system. The influence of annealing temperatures on the photoluminescence (PL) of ZnO crystal was investigated. An ultraviolet emission peak at about 379 nm was observed in PL spectra and the peak position has a weak blueshift for annealed samples. A green band centered at 523 nm appeared in the annealed samples and its intensity enhanced with the increase of annealing temperatures, while the intensity of the ultraviolet peak decreased considerably. However, the ultraviolet emission peak became the strongest after annealing at 1000 °C. This phenomenon was considered to be associated with oxygen vacancy and F^‐ impurities induced by the PbF₂ flux. The results show that high temperature annealing in air seems helpful for improving the PL properties of ZnO crystal. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetostatic properties of amorphous and nanostructured Fe73.5Si13.5B9Cu1Nb3 wires

We present the results of experimental investigations of magnetostatic properties of Fe-based amorphous wires with diameter about 100 μm. The samples were annealed at different conditions. The as-quenched sample had a weak increase (about 5%) of the magnetization with magnetic field decrease – the negative differential magnetic permeability could be observed in its hysteresis loops. The coercive force was about 0.2 Oe. The conventional annealing decreased the value of the saturation field down to 5 Oe without change of the coercive force value. When the annealing was accompanied with torsion stress the coercive force became less than 50 mOe. After the current annealing any peculiarities disappeared in magnetization in a weak magnetic field.     

The relaxation behaviour of strenght and fracture toughness of amorphous metal-metalloid alloys

The effect of an annealing treatment on crack and fracture kinetics and on mechanical properties of Fe₄₀Ni₄₀P₁₀B₆ and Fe₅Co₇₀Si₁₅B₁₀ amorphous ribbons — both pure and with defined impurities — was investigated by in-situ tensile experiments in SEM. The effect of relaxation processes on tensile strength, microhardness and fracture toughness was analysed. A result of technological interest is the increase of fracture toughness after an annealing treatment in the temperature range T_ann. = (0.55 … 0.6) · T_cryst.. This effect will be enhanced by defined chemical impurities, and it can be well interpreted by a model of fracture toughness variation during a temper process. In this model the deformation behaviour cannot be described within the scope of a homogeneous solid, but it is determined by a relationship between closely localized deformation instabilities.     

Influence of Bi1−xSbx and Sb overlayers on the annealing behaviour of Ag films

Annealing of thin Ag films covered by Bi_1−xSb_x (x = 0.09) and Sb overlayers, respectively, has been investigated by measuring the electrical resistance. Material exchange by diffusion leading to the formation of an intermetallic phase between Ag and Sb was found to be mainly responsible for the annealing effects. By X-ray and electron diffraction the intermetallic compound has been identified as the ε-phase Ag₃Sb. The diffusion processes due to annealing were studied by SIMS. A correlation between the measured resistance and electron micrographs of the cross-sectional film structure was found.     

Bonding rearrangement in amorphous silicon nitrides deposited by hot-wire chemical vapor deposition upon thermal annealing

The bonding rearrangement upon thermal annealing of amorphous silicon nitride (a-SiN_x:H) films deposited by hot-wire chemical vapor deposition was studied. A wide range of N/Si atom ratio between 0.5 and 1.6 was obtained for the a-SiN_x:H sample series by varying the source gases ratio only. Evolutions of Si–N, Si–H and N–H bonds upon annealing were found to depend strongly on the N/Si atom ratio of the films. According to the above observations, we propose possible reaction pathways for bonding rearrangement in a-SiN_x:H with different N/Si ratios.     

The influence of annealing atmosphere on the optical properties of flower‐like ZnO

The influence of annealing atmosphere on the optical properties of flower‐like ZnO is investigated. The flower‐like ZnO is composed of nanosheets. Annealing at 500°C results in the increase of the thickness of nanosheets and the enhancement of UV emission. PL spectra results show that the annealing atmosphere affects the visible emission band, which is sensitive to intrinsic and surface defects in the flower‐like ZnO. The vibrational properties of the flower‐like ZnO annealing in different atmospheres are characterized by Raman spectra. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The influence of solute distribution on the high nucleation density of Al crystals in amorphous aluminum alloys

An extension of a previous model that describes the role of solute atoms on glass formability leads to the conclusion that solute distribution plays an important role in the formation and stability of amorphous metals. A random distribution of solutes is shown to produce local solute-depleted regions (on the size scale of the mean inter-solute spacing) that provide preferred sites for the formation of crystalline nuclei. The possibility that these solute-depleted regions are responsible for the exceptionally high number density of critical Al nuclei is explored for three Al-Y binary alloys using a computer simulation. Up to 10⁷ Y atoms were placed at random locations in the system, and the number of solute-free regions were counted as a function of the size of these regions. The experimentally observed number density of critical nuclei (∼3 × 10²¹ m⁻³) is reproduced for a critical nucleus about 5 Al atoms in diameter, containing ∼60 Al atoms in an fcc array. Good agreement with previous suggestions of the size of a critical nucleus (about 6 atoms in diameter, containing about 100 atoms) support the conclusion that the current model provides a reasonable physical explanation for the quenched-in features responsible for the exceptionally high nucleation density in some amorphous Al alloys.     

Crystallization-nitriding process of FeSiB and FeSiBCuNb ribbons: influence of additive (Cu,Nb) pair and nitrogen on structure, magnetic and magnetostrictive parameters

Both conventional thermal treatments (CTTs) and nitriding thermochemical treatments (NTTs) are used to crystallize Fe₇₄Si₁₄B₁₂ and Fe_73.5Si_13.5B₉Cu₁Nb₃ melt spun ribbons. For the FeSiB sample, nitrogen is detected throughout the whole thickness, while nitrogen is observed only in the periphery of the (Cu–Nb) containing sample. Nitrogen diffusion is related to the crystallization. The remaining phase in the nanocrystallized FeSiBCuNb sample slows down the nitrogen diffusion. This kind of treatment applicated to FeSiBCuNb sample enables the formation of nanocrystallites with a grain size that is slightly smaller than that obtained following a CTT.     

A FTIR study on low hydration saccharide amorphous matrices: Thermal behaviour of the Water Association Band

We report a study on the thermal behaviour of the infrared Water Association Band (WAB) in dry binary saccharide-water systems (containing trehalose, sucrose, maltose, and raffinose). This is a follow-up of preceding studies on analogous carboxymyoglobin-saccharide-water ternary systems, which pointed out a mutual protein-matrix influence (coupling). A comparison between binary and ternary systems, for all the saccharides studied, evidences a reduction in the residual water content in the latter and, except for trehalose, a sizable modification in the thermal behaviour, which is discussed in terms of structure and hydrogen bonding properties of the sugars. The study allowed us also to improve the definition of Spectra Distance, which is useful to roughly evaluate the system thermal evolution.