ZnTe（ZnTe：Cu）多晶薄膜的XPS研究

用共蒸发法在室温下制备了ZnTe及ZnTe：Cu多晶薄膜，测量了电导率温度曲线，发现不掺杂的ZnTe薄膜的暗电导随温度的增加而线形增加，呈常规的半导体材料特征；掺Cu的ZnTe薄膜在温度较低时，lnσ随温度升高而缓慢增加，随后缓慢降低，达到一极小值，当温度继续升高时又陡然增加，呈现异常现象。用XPS研究了N2气氛下退火前后表面状态，发现不掺Cu的ZnTe薄膜呈现富Te现象。掺Cu后Te氧化明显，以ZnTe形式存在的Te明显减少；ZnTe：Cu薄膜中Zn的含量在退火前后变化明显，退火前，Zn主要以ZnTe形式存在，退火后Zn原子向表面扩散，使表面成分更加均匀，谱峰变宽；退火时，部分Cu原子进入晶格形成CuxTe相，引起载流子浓度变化，导致ZnTe：Cu多晶薄膜的电导温度关系异常。     

Mechanisms of high-speed deformation of polycrystalline copper

The mechanisms of high-speed deformation of ultrafine-grained copper produced during severe plastic deformation by equal-channel angular pressing were analyzed using numerical modeling in comparison with those in the case of coarse-crystalline copper. The activity of annihilation processes during nonconservative motion and double cross slip of dislocations was estimated. Their effect on the macroscopic behavior of samples is shown.     

Fabrication of large-grain polycrystalline Ge films using absorptive films

Amorphous germanium (a-Ge) films in samples with or without an absorptive film are crystallized by short-pulse XeF excimer laser crystallization (ELC). An in situ time-resolved optical reflection and transmission (TRORT) monitoring system combining a cw He-Ne probe laser, a digital oscilloscope and two photodetectors is developed to investigate the melting and resolidification dynamics of Ge films during ELC. TRORT measurements reveal that the longest melt duration is prolonged from 250 to 1000 ns by adding absorptive films in the samples. Absorptive films are shown to be effective in improving the melt duration of the molten state and the grain size of polycrystalline Ge films. The grain size with a diameter of approximately 12 μm can be fabricated in the superlateral growth regime for 90-nm-thick a-Ge films at room temperature in air by single-shot ELC.     

Laser scribing of polycrystalline thin films

We have investigated the use of several different types of lasers for scribing of the polycrystalline materials used for thin-film solar cells: CdTe, CuInGaSe₂ (CIGS), ZnO, SnO₂, Mo, Al, and Au. The lasers included four different neodymium–yttrium–aluminum garnet (Nd:YAG) (both 1064 and 532 nm wavelengths), a Cu vapor (511/578 nm), an XeCl excimer (308 nm), and a KrF excimer (248 nm). Pulse durations ranged from 0.1 to 250 ns. We found that the fundamental and frequency-doubled wavelengths of the Nd:YAG systems work well for almost all of the above materials except for the transparent conductor ZnO. The diode-laser-pumped Nd:YAG was particularly convenient to use. For ZnO the uv wavelengths of the two excimer lasers produced good results. Pulse duration was found generally not to be critical except for the case of CIGS on Mo where longer pulse durations (≥250 ns) are advantageous. The frequently observed problem of ridge formation along the edges of scribe lines in the semiconductor films can be eliminated by control of intensity gradients at the film through adjustment of the focus conditions.     

Faceted grain boundaries in polycrystalline films

A theoretical model is proposed for describing a new mechanism of misfit-stress relaxation in polycrystalline films, namely, the formation of faceted grain boundaries whose facets are asymmetric tilt boundaries. The ranges of parameters (the film thickness, misfit parameter, angle between facets) in which the nucleation of faceted grain boundaries is energetically favorable are calculated. The nucleation of faceted grain boundaries is shown to be facilitated as the film thickness increases.     

Strength and plastic deformation of polycrystalline diamond composites

ABSTRACT

The use of nanopolycrystalline diamond has allowed a systematic study on deformation of polycrystalline diamond composites (PCDCs). Bulk PCDCs samples containing either Co or SiC as a binding agent were deformed under high pressure and temperature to strains up to 18% at strain rates ～10^?5?s^?1. All samples exhibit strong work hardening. The strength of PCDCs depends on the amount and type of binding agents and is consistently weaker than that of diamond single crystals. The weakening may be due to the binder materials, which play an important role in affecting grain boundary structures. In SiC-based PCDC, significant grain fragmentation occurs. Nearly all grain boundaries are wetted by SiC after large deformation, resulting in lower strength. In Co-based PCDC, the microstructure is dominated by dislocations, deformation twins, and separated grain boundaries. The density of deformation twins increases significantly with strain, with the twin domain width reaching as low as 10–20?nm at 14% strain.     

Hopping conductivity in polycrystalline diamond films

The results of the experimental study of the conductivity of a polycrystalline diamond film by dielectric spectroscopy are presented. A diamond film about 200 μm thick was grown by microwave plasma-assisted chemical vapor deposition for 180 h. Two pronounced local peaks in the frequency dependence of the conductivity were observed. The relevant frequencies were temperature-dependent. These data permit us to hypothesize that the hopping mechanism of conductivity occurs in the polycrystalline diamond film. Two types of electrically active centers with different activation energies and relaxation times are involved in the conductivity.     

Variation of internal stresses as a function of deformation and distance from sources in Cu–Al polycrystalline alloys

Internal stress fields in deformed Cu–Al polycrystalline alloys are studied via TEM. The sources of such stresses are determined. Internal stress fields are measured as a function of distance from different sources. The effect grain size has on the formation of internal stresses is determined.     

Compressive stress in polycrystalline volmer-weber films

The Volmer-Weber mode for growing polycrystalline films, which comprises island, network, and channel stages before the films become continuous, is well known for its complex stress behavior with compressive and tensile stress alternating in the initial three growth stages. Recently, two new mechanisms for the compressive stress have been proposed [Phys. Rev. Lett. 88, 156103 (2002); 89, 126103 (2002)], which account for the reversibility of stress generation and relaxation. We show that the two mechanisms play only minor roles for the development of compressive stress, which is confirmed to be due to capillarity effects in the precoalescence stage.     

Temperature coefficient of resistivity of polycrystalline films

The expression for the temperature coefficient of the resistivity of a polycrystalline metal film is derived. A significant result is that the fast fall off of TCR of polycrystalline films with decreasing thickness can be explained if grain boundary scattering is taken into account.     

Thermal properties of manganese-doped ZnO polycrystalline films

The thermal conductivity and heat capacity of manganese-doped zinc oxide polycrystals have been studied in the temperature range 30–300 K. A substantial influence of the secondary phase or MnO clusters formed as a result of doping on the temperature dependences of thermophysical properties of polycrystalline zinc oxide films has been shown.     

Anomalous Hall effect in polycrystalline Ni films

We systematically studied the anomalous Hall effect in a series of polycrystalline Ni films with thickness ranging from 4 to 200 nm. It is found that both the longitudinal and anomalous Hall resistivity increased greatly as film thickness decreased. This enhancement should be related to the surface scattering. In the ultrathin films (4–6 nm thick), weak localization corrections to anomalous Hall conductivity were studied. The granular model, taking into account the dominated intergranular tunneling, has been employed to explain this phenomenon, which can explain the weak dependence of anomalous Hall resistivity on longitudinal resistivity as well.     

Cyclic deformation of aluminium and its alloys

The formation of slip bands is the main mechanism of cyclic deformation in pure Al. Their density, orientation and heights in polycrystalline Al were investigated during cycling. Types, sizes and densities of precipitates are responsible for the mode of cyclic deformation in AlCu4 pure alloy. In technical Al alloys intermetallic phases have detrimental effects on deformation homogeneity and largely govern the fatigue mechanism of the material and especially microcrack initiation.     

Dynamic structure formation during high-temperature deformation of polycrystalline oxides

We have studied the changes in 2-dimensional, nonautonomous phases produced by transformation-transport processes in polycrystalline systems. We show there are conditions under which it is possible to grow vortex structures in grain boundary layers under dynamical conditions, and that these structures can be stable under static conditions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 69–75, August, 1995.     

Photoacoustic spectroscopy of diamond powders and polycrystalline films

Photoacoustic spectroscopy is used to study optical absorption in diamond powders and polycrystalline films. The photoacoustic spectra of diamond powders with crystallite sizes in the range from ∼100 μm to 4 nm and diamond films grown by chemical vapor deposition (CVD) had a number of general characteristic features corresponding to the fundamental absorption edge for light with photon energies exceeding the width of the diamond band gap (∼5.4 eV) and to absorption in the visible and infrared by crystal-structure defects and the presence of non-diamond carbon. For samples of thin (∼10 μm) diamond films on silicon, the photoacoustic spectra revealed peculiarities associated with absorption in the silicon substrate of light transmitted by the diamond film. The shape of the spectral dependence of the amplitude of the photoacoustic signal in the ultraviolet indicates considerable scattering of light specularly reflected from the randomly distributed faces of the diamond crystallites both in the polycrystalline films and in the powders. The dependence of the shape of the photoacoustic spectra on the light modulation frequency allows one to estimate the thermal conductivity of the diamond films, which turns out to be significantly lower than the thermal conductivity of single-crystal diamond. Fiz. Tverd. Tela (St. Petersburg) 39, 1787–1791 (October 1997)