Annealing effect on ion-beam-sputtered titanium dioxide film

We found that the extinction coefficient of ion-beam-sputtered titanium dioxide films first decreased with increasing annealing temperature then increased drastically when annealing temperature was increased above ~200 degrees C for 24 h of annealing time. The decreasing extinction coefficient with annealing temperature was attributed to a reduction in absorption owing to oxidation of the film by annealing. The film structure remained amorphous to 200 degrees C annealing temperature. The drastic increase of extinction coefficients above ~200 degrees C was associated with the appearance of an anatase polycrystalline structure and was attributed to scattering by the polycrystalline structure. With shorter annealing time the transition temperature from amorphous to polycrystalline anatase was higher. Guidance for reducing the optical loss of laser mirrors is proposed.     

Laser induced recrystallization in lead mercury chalcogenide semiconductor films

Evidence is presented showing that the transition from amorphous to polycrystalline or polycrystalline to expitaxial state occurs gradually in flash evaporated lead mercury chalcogenide semiconductor films, during the process of laser annealing using a CW argon ion laser. TEM examination shows complete crystallization of the lead rich polycrystalline films of lead mercury chalcogenide films deposited at 25°C.     

Crystalline amorphous semiconductor superlattice

A new class of superlattice, crystalline amorphous superlattice (CASL), by alternatively depositing two semiconductor materials, is proposed. CASL displays three states depending on the component materials' phase: both polycrystalline phases, both amorphous phases, and one polycrystalline phase while another amorphous phase. Using materials capable of reversible phase transition, CASL can demonstrate reversibility among three states. GeTe/Sb(2)Te(3) CASL has been synthesized and proved by x-ray reflectometry and TEM results. The reversible transition among three states induced by electrical and laser pulse was observed. The changes in the optical absorption edge, electrical resistivity, thermal conductivity, and crystallization temperature as a function of layer thickness are interpreted as quantum or nanoeffects. The unique properties of CASL enable the design of materials with specific properties.     

The influence of boron concentrations on structural properties in disorder silicon films

In this work we present a detailed structural of a series of B-doped hydrogenated microcrystalline silicon (μc-Si:H) films deposited by plasma-enhanced chemical vapor deposition (PECVD) and B-doped polycrystalline silicon (poly-Si) films produced by step-by-step laser crystallization process from amorphous silicon. The influence of doping on the structural properties and structural changes during the sequential crystallization processes were monitored by Raman spectroscopy. Unlike μc-Si:H films, that consist of a two-phase mixture of amorphous and ordered Si, partially crystallized sample shows a stratified structure with polycrystalline silicon layer at the top of an amorphous layer. With increasing doping concentration the LO-TO phonon line in poly-Si shift to smaller wave numbers and broadens asymmetrically. The results are discussed in terms of resonant interaction between optical phonons and direct intraband transitions known as a Fano resonance. In μc-Si:H films, on the other hand, the Fano effect is not observed. The increase of doping in μc-Si:H films suppressed the crystalline volume fraction, which leads to an amorphization in the film structure. The structural variation in both μc-Si:H and poly-Si films leads to a change in hydrogen bonding configuration.     

Laser induced single-crystal transition in polycrystalline silicon

Transition to single crystal of polycrystalline Si material underlying a Si crystal substrate of 〈100〉 orientation was obtained via laser irradiation. The changes in the structure were analyzed by reflection high energy electron diffraction and by channeling effect technique using 2.0 MeV He Rutherford scattering. The power density required to induce the transition in a 4500 ? thick polycrystalline layer is about 70 MW/cm² (50ns). The corresponding amorphous to single transition has a threshold of about 45 MW/cm².     

A contribution to the explanation of the electronic spectrum of amorphous materials

In this article the electronic spectrum is explained on the basis of a polycrystalline model of amorphous material. It is shown that from the given model the origin of the “tail profile” function can be derived which expresses the dependence of the density of states on energy. Taking into consideration the small density of states in the region of the tail, “the increase” of activation energy of amorphous materials in comparison with monocrystalline materials can easily be explained.     

用SiCl4/H2气源沉积多晶硅薄膜光照稳定性的研究

对以SiH₄/H₂及SiCl₄/H₂为源气体、采用 等离子体增强化学气相沉积技术制备的非晶硅薄膜和多晶硅薄膜进行了光照稳定性的研究.实验表明，制备的多晶硅薄膜并没有出现 非晶硅中的光致衰减现象，其光电导、暗电导在光照过程中没有下降反而有所上升且电导率 变化快慢受氢稀释度的制约.多晶硅薄膜的光照稳定性可能来源于高的晶化度及Cl元素的存在. 关键词： 多晶硅薄膜 稳恒光电导效应 晶界 光致衰退效应     

Structural aspects of solid-state amorphization in Eu<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

X-ray diffraction studies of Eu₂(MoO₄)₃ single crystals were performed, which demonstrate that, in contrast to polycrystalline samples, these crystals do not exhibit amorphous-like diffraction patterns during the reverse transition from the high-pressure phase into the initial β phase; rather, the diffracted intensity in their diffraction patterns decreases significantly to the background. Such a diffraction pattern can be explained under the assumption that a single crystal is divided into small (nanoscopic) regions inside which the lattice parameters of the high-pressure phase and the initial β phase change continuously. The simultaneous recovery of the single-crystal state of the β phase from this intermediate state in all nanoscopic regions as the annealing temperature increases indicates that nanocrystals in this state are structurally correlated with each other. This result suggests that the halo-type diffraction patterns of polycrystalline samples reflect an intermediate state between the high-pressure phase and the β phase in every initial crystallite (as in the single crystals) rather than being caused by an amorphous structure of the sample. In this case, the total diffraction pattern of differently oriented crystallites gives an amorphous-like diffraction pattern reflecting the contributions from numerous various crystallographic planes involved in diffraction.     

Hydrogen mean force and anharmonicity in polycrystalline and amorphous ice

The hydrogen mean force from experimental neutron Compton profiles is derived using deep inelastic neutron scattering on amorphous and polycrystalline ice. The formalism of mean force is extended to probe its sensitivity to anharmonicity in the hydrogen-nucleus effective potential. The shape of the mean force for amorphous and polycrystalline ice is primarily determined by the anisotropy of the underlying quasi-harmonic effective potential. The data from amorphous ice show an additional curvature reflecting the more pronounced anharmonicity of the effective potential with respect to that of ice Ih.     

Electrical conductivity and equations of states of β-rhombohedral boron in the megabar dynamic pressure range

The pressure dependence of the conductivity of boron under conditions of a stepwise shock compression of megabaric range is studied. With this purpose, the following problems have been solved. The conductivity of boron has been measured in the range of dynamic pressures, where boron has different high-pressure phases. The equations of state of β-rhombohedral and amorphous boron have been constructed in a megabaric pressure range. The thermodynamic states of boron in the conditions of these experiments are calculated, which, in combination with the measurement data, made it possible to determine the change in the boron conductivity in the conditions of strong stepwise shock compression at dynamic pressures to 110 GPa. The increase in the conductivity of polycrystalline boron at megabar pressures is interpreted as a result of a nonmetal–metal transition.

     

Real-time in situ spectroscopic ellipsometry investigation of the amorphous to crystalline phase transition in Mo single layers

Molybdenum single layers were grown by ion beam sputter deposition onto [001] Si substrates. Argon or xenon was used as sputter gas. The layer growth was monitored by real-time in situ spectroscopic ellipsometry in the visible spectral region. A volume phase transition from amorphous to polycrystalline molybdenum layer growth was observed during the deposition process. The time regime of the phase transition as well as the layer thickness at which the phase transition occurs, depends on the sputter regime, especially on sputter species and deposition-pressure range. The thermodynamic approach of energy minimisation is discussed as the driving force for the Mo phase transition. A moderate backscattered particle bombardment of the growing molybdenum film provides the activation energy for the recrystallisation process. A self-diffusion-like process is made responsible for atomic rearrangement of the entire as-deposited thin-film volume. The molybdenum phase transition is connected to thin-film densification and therefore volume contraction. PACS 68.65.Ac; 81.15.Cd; 78.67.Pt     

Indium oxide thin-film holographic recorders grown by excimer laser reactive sputtering

2 O₃) thin films on glass substrates is performed by pulsed laser ablation of a metallic indium target in an oxygen atmosphere. X-ray diffraction analysis verifies that a transition, from amorphous to polycrystalline film growth, occurs at a temperature of 150 °C. Films grown under optimized conditions exhibit optical transmission higher than 80% in the visible light. Ultraviolet radiation (λ= 325 nm) induced dynamic holographic recording in films deposited at specific temperature and oxygen pressure settings is also demonstrated. Received: 25 April 1997/Accepted: 27 May 1997     

相变区硅薄膜拉曼和红外光谱分析

采用等离子体增强化学气相沉积(PECVD)技术制备了一系列不同氢稀释率下的硅薄膜,采用拉曼散射光谱和傅里叶红外光谱技术研究了非晶/微晶相变区硅薄膜的微观结构变化,将次晶结构(paracrystalline structure)引入到非晶/微晶相变区硅薄膜结构中,提出了次晶粒体积分数(f_p),用来表征硅薄膜中程有序程度。结果表明,氢稀释率的提高导致硅薄膜经历了从非晶硅到微晶硅的相变过程,在相变区靠近非晶相的一侧,硅薄膜表现出氢含量高、结构致密和中程有序度高等特性,氢在薄膜的生长中主要起到表面钝化作用。在相变区靠近微晶相的一侧,硅薄膜具有氢含量低、晶化率高和界面体积分数小等特性,揭示了氢的刻蚀作用主控了薄膜生长过程。采用扫描电子显微镜对样品薄膜的表面形貌进行分析,验证了拉曼散射光谱和傅里叶红外光谱的分析结果。非晶/微晶相变区尤其是相变区边缘硅薄膜结构特性优良,在太阳能电池应用中适合用作硅基薄膜电池本征层。     

Morphological transformations of vanadium oxide films during low-temperature reduction in hydrogen electron cyclotron resonance plasma

Morphological transformations of amorphous vanadium oxide films obtained by the sol-gel method and polycrystalline V₂O₅ films are studied during their low-temperature (295–623 K) reduction in a hydrogen electron cyclotron resonance plasma. The morphology of films is analyzed using atomic force microscopy and high-resolution electron microscopy. It is found that a homogeneous amorphous film during the reduction process transforms to an island film and then bulk amorphous islands of a regular shape appear. These islands resemble microcrystals, and their concentration depends on the temperature and the reduction time. The low-temperature reduction of polycrystalline V₂O₅ films leads to their amorphization; however, the microcrystals in the polycrystalline film do not change their shape in this process. A mechanism of the reduction process is proposed. This mechanism explains the regularities of morphological transformations in amorphous sol-gel films of vanadium oxides based on the suggestion of a competition between the ion-stimulated nucleation and growth of nuclei of the crystalline phase and the amorphization of the growing nuclei.     

Soft Magnetic Materials in a Bulk Form Prepared by Powder Compaction

The amorphous, nanocrystalline and polycrystalline ferromagnetic alloys are known as materials with excellent soft magnetic properties. These attractive magnetic properties are challenge for researchers to extend investigation of these materials with the aim to broaden their technical exploitation. The shape in which amorphous, nanocrystalline and polycrystalline materials are usually prepared, is in many cases not suitable shape for application, therefore it is logical to attempt to prepare such material in a more “bulk” form, for example in the form of a cylinder or a ring, that would be more convenient for industrial applications. One of the ways to prepare material in bulk form is to compact the powder. There is rational assumption that the non-magnetostrictive alloys (amorphous Co-Fe-Si-B, nanocrystalline Fe-Nb-Cu-Si-B, and polycrystalline Ni-Fe) may be suitable for the preparation of bulk samples by high-pressure compression, because mechanical stress does not induce magnetic anisotropy in ferromagnetic material during preparation process.We observed that milling of ribbons prepared by rapid quenching method leads to the increase of coercivity, which is caused by the increase of the fraction of magnetization vector rotation in the magnetization processes (the fraction of domain wall motion decreases). After long milling the powder particles become single-domain and can be magnetized by the magnetization vector rotation only, exhibiting maximum value of coercivity.Consolidation of powder with high value of coercivity leads to the “magnetic contact” between powder particles resulting in the decrease of coercivity to the value comparable with that for as-spun ribbons.     

Correlation between lithium storage and diffusion properties and electrochromic characteristics of WO3 thin films

As essential electrochromic(EC) materials are related to energy savings in fenestration technology,tungsten oxide(WO3) films have been intensively studied recently.In order to achieve better understanding of the mechanism of EC properties,and thus facilitate optimization of device performance,clarification of the correlation between cation storage and transfer properties and the coloration performance is needed.In this study,transparent polycrystalline and amorphous WO3 thin films were deposited on SnO2:F-coated glass substrates by the pulsed laser deposition technique.Investigation into optical transmittance in a wavelength range of 400-800 nm measured at a current density of 130 μA·cm-2 with the applied potential ranging from 3.2 to 2.2 V indicates that polycrystalline films have a larger optical modulation of ～ 30% at 600 nm and a larger coloration switch time of 95 s in the whole wavelength range compared with amorphous films(～ 24% and 50 s).Meanwhile,under the same conditions,polycrystalline films show a larger lithium storage capacity corresponding to a Li/W ratio of 0.5,a smaller lithium diffusion coefficient(2×10-12cm2·s-1 for Li/W=0.24) compared with the amorphous ones,which have a Li/W ratio of 0.29 and a coefficient of ～2.5×10-11cm2·s-1 as Li/W=0.24.These results demonstrate that the large optical modulation relates to the large lithium storage capacity,and the fast coloration transition is associated with fast lithium diffusion.     

Superionic behavior in the xAgI–(1−x)CsAg2I3 polycrystalline system

A superionic phase behavior (with DC ionic conductivities higher than 0.01 S/cm) has been observed in xAgI–(1−x)CsAg₂I₃ (x≈0.67) polycrystalline system grown by slow evaporation using AgI and CsI powders (molar ratio Cs/Ag=0.25) as starting salts and an aqueous solution of HI as solvent. The transition from the normal-to- the superionic state is first-order with a hysteretic behavior in temperature centered at about 116 °C as reflected by thermal (DSC) and electrical conductivity measurements. This mixture is composed of CsAg₂I₃ and AgI crystalline phases and an additional amorphous AgI phase that explains the glassy-type behavior observed in the superionic phase transition.     

Electrical properties of film heterojunctions of cadmium selenide and amorphous selenium

Results are presented from a study of the volt-ampere characteristics of polycrystalline layers of cadmium selenide and amorphous layers of selenium, as well as the electrical and photoelectric characteristics of CdSe-Se heterojunctions. The experimental data and a theoretical examination of heterojunctions composed of a crystalline semiconductor and an amorphous semiconductor are used to propose an energy-band model for heterojunctions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 65–70, November, 1990.     

Compton profiles of trigonal and amorphous selenium

Compton profiles of trigonal and amorphous Selenium were measured with ²⁴¹Am γ-radiation using two crystalline and amorphous samples of identical geometric dimensions. As a result the difference profiles of amorphous and polycrystalline Se are reported and discussed. The valence electron Compton profile of the polycrystalline phase is compared to SCOPW-calculations by Krusius.     

Estimation of thermal expansion and thermal conductivity coefficients of amorphous dielectrics at high temperatures

Expressions for estimation of the thermal linear expansion coefficients and of the thermal conductivities of amorphous dielectrics above the Debye temperature are obtained. It is shown that for the compounds of the chemical composition corresponding to the rare-earth magnesium hexaaluminates taken as an example these parameters for amorphous compounds are less than for polycrystalline.