Single Crystal Silicon Substrates Research Articles

Temperature Dependent Internal Friction Behavior of Single Crystal Germanium Studied by the Impulse Excitation Technique

The anelastic relaxation process in crystalline solids is influenced by various mechanisms including diffusion of atoms and point defects, grain boundary viscosity, dislocation, phase transformation, etc. To analyze the type and concentration of relaxing units participating in a particular activated process, measuring the internal friction is a well-known approach. A fundamental measure of internal friction can be defined as the ratio between the mechanical energy dissipated during one cycle in a unit volume and the maximum stored elastic energy per unit volume during that cycle [1]. The impulse excitation technique (IET) is a well-established mechanical spectroscopic technique analyzing the internal friction and Young’s modulus behaviour of materials as function of temperature [2]. IET measures the resonant frequency of a specimen by exciting it mechanically with an impulse tool. The resonance frequencies are characteristic for the sample material and are related to its stiffness, mass and geometry. The amplitude decay of a free vibration can be related to the internal friction, i.e. the dissipation of the vibration energy or damping. Measurement of the resonance frequency allows the calculation of Young's modulus E. This technique has been previously applied to determine the temperature dependent Young's modulus of single crystal silicon and germanium in the <100>, <110> and <111> crystallographic directions [3,4,5]. More and more, single crystal germanium and silicon layers and substrates are used together to process advanced nano-eletronic devices. The thermal stresses during crystal growth and device processing have an important impact on generation and diffusion of point defects and in the worst case also can lead to dislocation generation. Although the temperature dependent mechanical properties of silicon are well known, this is much less the case for germanium.In the present study, the impulse excitation technique was used to analyze the temperature dependence of the internal friction in single crystal Ge in the <111>, <100> and <110> directions between room and melting temperatures. A similar set-up was used as in [6] but equipped with a specimen chamber and specimen suspension system allowing heating the samples in an inert atmosphere up to the Ge melt temperature. Between room temperature and melt temperature, three internal friction peaks were observed for each crystallographic orientation after internal friction spectrum analysis, a typical spectrum is shown in the figure. The mechanism leading to these peaks is thermally activated. To interpret the observed internal friction peaks, various aspects such as activation energy of peaks, peak positions and relaxation time will be discussed. The origin of the relaxation peaks is associated with intrinsic point defect processes and/or extended defect formation.

Nanoindentation of polysilicon and single crystal silicon: Molecular dynamics simulation and experimental validation

This paper presents novel advances in the deformation behaviour of polycrystalline and single crystal silicon using molecular dynamics (MD) simulation and validation of the same via nanoindentation experiments. In order to unravel the mechanism of deformation, four simulations were performed: indentation of a polycrystalline silicon substrate with a (i) Berkovich pyramidal and a (ii) spherical (arc) indenter, and (iii and iv) indentation of a single crystal silicon substrate with these two indenters. The simulation results reveal that high pressure phase transformation (HPPT) in silicon (Si-I to Si-II phase transformation) occurred in all cases; however, its extent and the manner in which it occurred differed significantly between polycrystalline silicon and single crystal silicon, and was the main driver of differences in the nanoindentation deformation behaviour between these two types of silicon. Interestingly, in polycrystalline silicon, the HPPT was observed to occur more preferentially along the grain boundaries than across the grain boundaries. An automated dislocation extraction algorithm (DXA) revealed no dislocations in the deformation zone, suggesting that HPPT is the primary mechanism in inducing plasticity in silicon.

Preparation and Tribological Property of Novel Self-Assembled Composite Films on Silicon

Self-assembled composite films of APTES-GA-APTES were successfully prepared on single-crystal silicon substrates through the cross-linking reaction between glutaraldehyde (GA) and two layers of 3-aminopropyltriethoxysilane (APTES). The optimal time to deposit the GA layer on the APTES monolayer was 3 h, during which most amino groups of APTES reacted with the aldehyde groups of GA to form smooth and uniform APTES-GA composite films. The further deposition of another APTES layer led to the generation of three-layer APTES-GA-APTES composite films. Compared to the APTES self-assembled monolayers, the three-layer films displayed a similar surface morphology but a reduced friction coefficient from 0.23 to 0.15 and an extended wear life from 50 s to 820 s due to the introduction of GA.

Effect of O2 partial pressure on optical and electrical properties in Al doped ZnO thin films

Al doped ZnO (AZO) thin films were synthesised on single crystal silicon and quartz glass substrates by pulsed laser deposition method at different O2 partial pressure. The structure, composition, optical and electrical properties in AZO thin films were investigated. With the increase in O2 partial pressure, the crystalline quality of AZO thin films becomes poor, and the Al content in the films decreases from 6·3 to 4·3%. The former leads to the enhancement of grain boundary scattering, consequently Hall mobility will decrease. While the latter results in the decrease of carrier concentration. As a result, the electrical resistivity in AZO thin films increases from 2·18×10−4 to 13·40×10−4 Ω cm with increasing the O2 partial pressure. The increase of carrier concentration induces the widening of optical band gap due to the Burstein-Moss effect with the increase of O2 partial pressure. For AZO thin films grown by PLD method, the control of O2 partial pressure is a simple method to adjust the electrical resistivity, optical band gap and UV emission in the films.

Semiconductor behavior of nanocrystalline carbon

The study of the characteristics of nanocrystalline carbon films produced by deposition onto single-crystal silicon substrates from the vapor phase during the pyrolysis of methane in an electric field shows that there exists a reversible semimetal-semiconductor transition at temperatures higher than 560°C. The material contains a large number of tetrahedral nanoclusters in a pyrolytic carbon matrix. The mass density of the material is higher than 2.7 g cm−3. The manyfold increase in the conductivity of the composite upon heating is caused mainly by the transition of the clusters to the region of intrinsic conduction. Estimation of the thermal activation energy of the conductivity of the composite gives 0.78 eV.

P-type Sodium-doped Zinc Oxide Nanowire Arrays Grown by High-pressure Pulsed Laser Deposition

Sodium-doped ZnO (ZnO:Na) nanowire arrays were grown with high-pressure pulsed laser deposition (HP-PLD). The influence of growth pressure and thickness of gold catalyst layer on the growth of ZnO:Na nanowires were systemically studied. It is found that c-orientated ZnO nanowire arrays grow on single crystal silicon substrates under the optimized condition, e.g. gold catalyst layer’s thickness of 4.2 nm, growth pressure of 3.33×10 Pa and growth temperature of 875 °C. X-ray diffraction pattern and X-ray photoelectron spectroscope analyses indicate that Na is introduced into ZnO nanowires successfully. Optical fingerprints of sodium-related acceptors in the low-temperature (15 K) photoluminescence spectrum are observed, such as neutral acceptor-bound exciton emission (3.356 eV, AX), free-electron to neutral-acceptor emission (3.312 eV, (e, A)), and donor-to-acceptor pair emission (3.233 eV, DAP). ZnO:Na nanowire arrays grown on ZnO:Al/sapphire substrates form the pn junction. The corresponding I-V curve measurements exhibit a clear rectifying behavior of pn homojunction, which further indicates that such ZnO:Na nanowire is of p-type conductivity. 156 无 机 材 料 学 报 第 29卷

Fourier transform infrared, optical properties and Schottky junction application of 2-[(antipyrinyl)-hydrazono]-3-oxo-N-pyridin-2-yl-butyramide thin films

A new organic compound, 2-[(antipyrinyl)-hydrazono]-3-oxo-N-pyridin-2-yl-butyramide (AHPB) has been chemically synthesized and characterized using spectral and elemental analyses. Fourier transform infrared showed that the thermal evaporation is a suitable technique for obtaining chemically integrated AHPB films. The optical properties of AHPB films are investigated in the framework of spectrophotometeric measurements of transmittance and reflectance over the spectral range 200–2500nm, from which the absorption coefficient and refractive index are calculated. The films showed two indirect allowed transitions. The corresponding optical band gaps are evaluated as 2.29 and 2.5eV. Single oscillator model is applied for determining the dispersion parameters and the dielectric constant at high frequency. AHPB films are deposited onto p-type silicon single crystal substrates for fabricating Schottky junction in the configuration type of Au/AHPB/p-Si/Al. The electrical properties of the junction are discussed on the bases of the current–voltage characteristics measured in temperature range 298–373K. The ideality factor, potential barrier height and series resistance are evaluated as a function of temperature. With increasing temperature, the ideality factor and series resistance decrease, whereas the potential barrier height increases.

Effect of Sb content on the phase composition of CoSb x nanofilms grown on a heated substrate

We have studied the phase composition and crystal structure of CoSb x (1.82 ≤ x ≤ 4.16) nanofilms (30 nm) grown by molecular beam epitaxy on oxidized single-crystal silicon substrates at a temperature of 200°C, followed by heat treatment in vacuum at temperatures from 300 to 700°C. The as-grown films were found to be polycrystalline, with no preferential orientation. The effect of Sb content on the phase composition of the films was consistent with equilibrium phase diagram data for bulk Co-Sb materials. Vacuum annealing at temperatures above 450–500°C led to Sb sublimation not only from the crystalline phase but also from the antimonides, thereby increasing the percentages of the CoSb and CoSb2 phases and reducing the amount of CoSb3. The 30-nm-thick CoSb x (1.8 ≤ x ≤ 4.16) films were thermally stable at temperatures of up to 350°C.

Focused ion beam fabrication and magneto-electrical transport properties of La0.67Ca0.33MnO3 nanobridge

La0.67Ca0.33MnO3 particle films with an average particle size of ~150 nm were grown on single-crystal silicon substrate using pulsed electron deposition technique and then focused ion beam was introduced to fabricate nanobridge in size of 300 × 900 nm on the particle film. The magneto-transport properties of both samples were studied. For the film, there is only one resistance peak at 182 K in temperature-dependent resistance (R–T) curves, which is far lower than ferromagnetic–paramagnetic transition temperature (TC) of 250 K. When compared to the film, double peaks were observed in both R–T curves and magnetoresistance dependent on temperature (MR–T) curves of the nanobridge, one peak is at 186 K, which is very close to metal–insulator transition temperature (TP) of film, the other one is at 250 K, which is close to the TC of film, and these two peaks caused separately by grain and grain boundary (GB), which demonstrated that the electrical transport behavior of grain was separated from that of GB.

The Determination of the Effective Radius of the Tip of the Probe of an Atomic Force Microscope Using Monodispersed Silicon Oxide Nanoparticles

A method of constructing samples of a monodispersed ensemble of spherical particles of silicon oxide with a diameter of 26.6 ± 3.5 nm, distributed uniformly on the surface of a single-crystal silicon substrate of area 1 cm2 with a mean particle surface density of about 0.5 particles/μm2 is developed. The use of the test structure obtained to determine the effective radius of the tip of the probe of a scanning atomic-force microscope is demonstrated.

A chemical route to fabricate Lu2Si2O7:Ce3+ micro-column structured films

Lu2Si2O7 (LPS):Ce3+ micro-column structured films have been prepared on silicon substrate by a chemical method which combines Si nanowire array wafers with dip-coating method. In the processing, the Si nanowire array wafers are obtained via a metal-assisted chemical etching route on single-crystal silicon (100) substrate at first step. The produced Si nanowire array wafers not only serve as guide–templates for the fabrication of LPS:Ce3+ films in a columnar fashion, but also provide Si sources for further reacting with lutetium sources at high temperatures to form LPS:Ce3+ micro-column structured films. XRD analysis indicates that as-prepared films are crystallized into a monoclinic Lu2Si2O7 phase along with an amorphous silicon oxide phase, and the latter phase ascribes to the oxidation of Si nanowire arrays. The as-prepared LPS:Ce3+ films exhibit a columnar-array structure and a uniform morphology according to SEM and TEM observations. The UV photoluminescence spectra illustrate the characteristic excitation and emission spectrum of Ce3+ ions in the host of LPS. X-ray induced emission spectrum reveals a similar shape with UV excited emission spectrum peaking at 378nm. Furthermore, the LPS:Ce3+ micro-column structured films present a fast decay time of about 3425ns. These experiments have demonstrated that the film technique thus developed is possible to fabricate column-like luminescent films of large scale with low cost.

Single mask fabrication process for movable MEMS devices

The current work reports on the realization of movable micromachining devices using self-aligned single-mask fabrication process. Only dry etching process utilizing inductively coupled plasma reactive ion etching was used to release 3D micro structures from single crystal silicon substrate. No wet etching process is required to release the structures as is the case with silicon on insulator (SOI) wafers. Also the developed process does not require an SOI substrate and accordingly dispensing with the application of a wet etching step, thus yielding uniform structures without stiction. The optimized process was applied to realize thermally actuated microgrippers. The article presents the development of the fabrication process and demonstrates the operation of the fabricated device. The optimized process provides an avenue for low cost fabrication of movable micromachining devices without the use of complicated wet etching steps typically associated with SOI substrates.

Heterojunctions of TiO2 nanoparticle film and c-Si with different Fermi level positions

The photovoltaic properties of heterojunctions of titanium dioxide (TiO2) nanoparticle films with single crystal silicon (c-Si) substrates with different Fermi level (E f) positions were studied. The TiO2 nanoparticles of rutile and anatase structures were studied without any sintering process. To clarify the photovoltaic properties, the characteristics of the heterojunction solar cells of TiO2 nanoparticle films with p-Si and n-Si substrates were investigated, where several Si substrates with different resistivities were used. The I–V characteristics of p-Si/TiO2 heterojunction showed the rectifying behavior and photovoltaic effect. The n-Si/TiO2 heterojunction also showed good rectifying characteristics; however, the conversion efficiency was extremely lower than that of p-Si/TiO2 heterojunction. The conversion efficiencies of various Si/TiO2 (rutile) heterojunction solar cells against the Fermi level E f of c-Si showed the maximum in the p-doped region. The photovoltaic properties of the Si/TiO2 heterojunction also depended on the crystal structure of TiO2, and the conversion efficiency of anatase is higher than that of rutile, which was attributed to the higher carrier mobility of anatase.

BaTiO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;/&amp;gamma;-Fe&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;颗粒膜的介电性质和磁电性质

Composite films of Ag/BaTiO3/γ-Fe2O3/ZnO structure were grown on an n-type silicon (100) single crystal substrate by high vacuum magnetron-ion beam composite sputtering system in this article. The comparative study of dielectric and magnetic along with ferromagnetic properties of BaTiO3/γ-Fe2O3 granular films at annealing temperature is 300℃, 400℃ and 500℃ respectively. Experimental investigation shows that it have high capacitance and large dielectric constant, namely, capacitance of 633.93 pF and dielectric constant of 10.233 under 500℃ annealing condition. All the samples are good ferromagnetic and ferroelectricity, however, it have largest saturated magnetic moment of 103.3 emμ/cm3 and remanent electric polarization of 9.13×10-1 μm/cm2 under 400℃, 500℃ annealing condition respectively. At the same time, the coercive electric field and the remanent electric polarization have no obvious change when magnetic fields are 0 T and 1.0 T. At 200 K, the hysteresis loop has obvious change when magnetic field is 0.5 T.

Photosensitive Heterostructures on the Basis of Nanocrystal Porous Silicon

In this work the investigations of technology, morphology, electric and photoelectric properties of the silicon photosensitive structures have been represented. The structures included layers of the silicon carbide and the porous silicon. The porous layer was formed on the surface of the single crystal silicon substrates by the method of electrolytic etching in fluoride containing solutions. Plates with different microrelief surface (polished, honed, textured) were used. Carbidization of the samples leading to the formation of heterostructures on SiC/Si was conducted by the method of gas endotaxin in a hydrogen stream in a vertical reactor with cold walls and a graphite container. The structure and composition of the SiC/Si heterostructures on the different surface structures of poly − and single crystal silicon, including surface of porous silicon layer have been investigated. We show that in the process of endotaxy of all types of surfaces forms a single crystal silicon carbide phase of cubic modification. The morphology of the resultant structures has been investigated by scanning and transmission electron microscopes. Different filiform formations were found on the pore − free surface, which are identified as silicon carbide, and the cylindrical or conical structures of the unclear nature were observed on the porous surface. The current − voltage and current − power curves have been plotted for all types of the structures, the general appearance of which indicates the presence of several potential barriers. The photoelectric properties of the structures have been analyzed along with the prospect of their use in solar cells.

Synthesis of Ni2+‐doped ZnAl2O4/ZnO Composite Phosphor Film with Largely Enhanced Polychromatic Emission via a Single‐Source Precursor

Ni2+‐doped ZnAl2O4/ZnO composite films were successfully fabricated on single crystal silicon substrates through a single‐source precursor route, which mainly involved slurry coating of Ni–Zn–Al‐layered double hydroxide precursor followed by calcination at elevated temperatures. Material characterization has been presented using a combination of X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectra, Raman spectra, UV–vis diffuse reflectance spectra, and fluorescence spectroscopy measurements. The results showed that Ni2+ ions could be uniformly doped in the two‐phase ZnO and ZnAl2O4 lattices. A broadened and intense polychromatic emission peak covering the whole visible region was obtained over 4.3 mol% Ni2+‐doped ZnAl2O4/ZnO composite film, which was attributed to the presence of an appropriate number of luminescent Ni2+centers in the ZnO and ZnAl2O4 double host matrix, thus largely enhancing the related transition. We believe that such unique ZnAl2O4/ZnO films can open up a new opportunity for advanced applications of composite phosphors.

The microstructure and mechanical behavior of Mg/Ti multilayers as a function of individual layer thickness

We have used magnetron sputtering to deposit magnesium and titanium layers alternately onto a single-crystal silicon substrate with equal individual layer thickness (h, from 2.5 to 200nm) to form multilayers. We have investigated the mechanical behavior of the multilayers and its dependence on h. Transmission electron microscopy and X-ray diffraction analyses suggest that the multilayers exhibit strong texture with respect to Mg (0002) and Ti (0002) with an epitaxial growth pattern. Two primary orientation relationships between Ti and Mg have been identified, depending on h. Instrumented nanoindentation and microcompression have been used to examine the hardness/strength and the strain rate sensitivity of the multilayers. Based on nanoindentation, we have found that the strength of these multilayers generally increases as h is decreased. The microcompression measured strength is remarkably higher than that derived from indentation. The Hall–Petch law can be used to interpret the increase in strength at relatively large h (>50nm), while the confined layer slip model provides a better explanation for the relationship between strength and h at smaller h. We have also attempted to present an in-depth discussion about the applicability of relevant strengthening mechanisms on these hexagonal close-packed/hexagonal close-packed multilayers.

Effect of chemisorption of donor and acceptor gases on the semiconductor-metal phase transition in vanadium dioxide films

Heterophase textured films of vanadium dioxide on single-crystal silicon substrates have been synthesized by the sol-gel method from solutions of triethoxyvanadyl VO(OEt)3 in methyl cellosolve CH3OCH2CH2OH. The effect of ozone and ethanol vapor chemisorption on the parameters of the semiconductor-metal phase transition in vanadium dioxide VO2(B) has been studied. It has been found that the transition temperature increases in a reducing atmosphere and decreases in an oxidizing atmosphere.

Synthesis of aligned arrays of “Microropes” of silica nanowires by gas-jet electron beam plasma chemical vapor deposition method

For the first time, aligned arrays of bundles (“microropes”) of silica nanowires were synthesized from a monosilane-hydrogen mixture by gas-jet electron beam plasma chemical vapor deposition method. The synthesis was performed on single-crystal silicon substrates coated by micron-sized particles of stannic catalyst. A bundle (“microrope”) of silica nanowires each of which is about 15 nm in diameter grows from a catalyst particle. It seems that the synthesis proceeds by the vapor-liquid-solid mechanism, and several nanowires grow synchronously from the surface of one catalyst particle. The “microrope” growth rate was about 25 nm/s at a synthesis temperature of 400°C. A possible growth model was proposed to explain these results.

Nano-porous Silicon Microcavity Sensors for Determination of Organic Fuel Mixtures

We present the preparation and characteristics of liquid-phase sensors based on nano-porous silicon multilayer structures for determination of organic content in gasoline. The principle of the sensor is a determination of the cavity-resonant wavelength shift caused by refractive index change of the nano-porous silicon multilayer cavity due to the interaction with liquids. We use the transfer matrix method (TMM) for the design and prediction of characteristics of microcavity sensors based on nano-porous silicon multilayer structures. The preparation process of the nano-porous silicon microcavity is based on electrochemical etching of single-crystal silicon substrates, which can exactly control the porosity and thickness of the porous silicon layers. The basic characteristics of sensors obtained by experimental measurements of the different liquids with known refractive indices are in good agreement with simulation calculations. The reversibility of liquid-phase sensors is confirmed by fast complete evaporation of organic solvents using a low vacuum pump. The nano-porous silicon microcavity sensors can be used to determine different kinds of organic fuel mixtures such as bio-fuel (E5), A92 added ethanol and methanol of different concentrations up to 15%.