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In this study, we successfully obtained crystalline silicon from silica powder using a metal-induced crystallization method. For this purpose, powders were first prepared from organosilicon compounds and finely dispersed aluminum particles, then their metal-induced crystallization was carried out by annealing at the temperature of 570 °C. Powders of organosilicon compounds (tetraethoxysilane and polyethylhydrosiloxane) were prepared by different technological operations in order to determine precisely the presence of carbon in the product. The results showed that the presence of carbon in silica powder affects the production of crystalline silicon. In silica powders containing no carbon, the formation of crystalline substances does not occur at the annealing temperature of 570 °C. The results of this study are of great importance for the production of polycrystalline silicon powders obtained at reduced temperatures.

Multilayer graphene (MLG) has attracted considerable attention as an interconnect material owing to its excellent electrical and mechanical properties. Several studies on the formation of MLG on insulators have been reported; however, the process temperature and shape controllability of MLG remain challenging. In this study, we investigated the formation of MLG strips for interconnect via metal-induced layer exchange (LE). The LE of strip-patterned amorphous carbon and Ni formed {002}-oriented high-crystallinity MLG strips at low temperatures (600 °C). While voids were formed inside the strip, continuous MLG was formed at the strip edge, likely due to the remarkable atomic diffusion at the edge. Smaller widths and larger thicknesses of the MLG strip allowed us to form uniform MLG strips without voids, and an electrical conductivity of 1100 S cm–1 was achieved. The technique developed in this study is unique because it overcomes the limitations of conventional MLG fabrication techniques and is promising for MLG interconnect applications. [ABSTRACT FROM AUTHOR]

In this study, we successfully obtained crystalline silicon from silica powder using a metal-induced crystallization method. For this purpose, powders were first prepared from organosilicon compounds and finely dispersed aluminum particles, then their metal-induced crystallization was carried out by annealing at the temperature of 570 °C. Powders of organosilicon compounds (tetraethoxysilane and polyethylhydrosiloxane) were prepared by different technological operations in order to determine precisely the presence of carbon in the product. The results showed that the presence of carbon in silica powder affects the production of crystalline silicon. In silica powders containing no carbon, the formation of crystalline substances does not occur at the annealing temperature of 570 °C. The results of this study are of great importance for the production of polycrystalline silicon powders obtained at reduced temperatures. [ABSTRACT FROM AUTHOR]

The thermal process of amorphous silicon thin film crystallization when combined with an aluminum (Al) film using a continuous wave (CW) laser is accompanied by additional interactions induced by the aluminum layer. This technique is frequently employed to optimize the crystallization process and enhance the quality of crystalline silicon by combining the thermodynamic effects of laser annealing with metal-induced crystallization (MIC). Hydrogenated amorphous silicon (a-Si:H) films were deposited using the plasma-enhanced chemical vapor deposition (PECVD) process on Corning glass substrates. An aluminum overcoat was deposited on the films. The specimens were irradiated with a continuous wave (CW) argon-ion (Ar +) laser beam of varying power density and duration. The samples were then annealed at 250 °C for 15 min to convert the amorphous silicon into polysilicon film. The grain size of the polycrystalline silicon films varies by varying the laser power density and the exposure time. The polysilicon grains acquired diameters ranging from 0.4 to 1.25 µm when the laser power density was set between 74.7 W/cm2 and 94.3 W/cm2. The grains with a size ranging between 1 and 2.5 µm showed plate-like and dendritic-like configurations when laser power densities changed between 31.4 and 74.7 W/cm2. The X-ray diffraction analysis (XRD) analysis revealed polycrystalline silicon with expected relative strengths. [ABSTRACT FROM AUTHOR]

The effect of the aluminum layer on the kinetics and mechanism of aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) in (Al/a-Si)n multilayered films was studied using a complex of in situ methods (simultaneous thermal analysis, transmission electron microscopy, electron diffraction, and four-point probe resistance measurement) and ex situ methods (X-ray diffraction and optical microscopy). An increase in the thickness of the aluminum layer from 10 to 80 nm was found to result in a decrease in the value of the apparent activation energy Ea of silicon crystallization from 137 to 117 kJ/mol (as estimated by the Kissinger method) as well as an increase in the crystallization heat from 12.3 to 16.0 kJ/(mol Si). The detailed kinetic analysis showed that the change in the thickness of an individual Al layer could lead to a qualitative change in the mechanism of aluminum-induced silicon crystallization: with the thickness of Al ≤ 20 nm. The process followed two parallel routes described by the n-th order reaction equation with autocatalysis (Cn-X) and the Avrami–Erofeev equation (An): with an increase in the thickness of Al ≥ 40 nm, the process occurred in two consecutive steps. The first one can be described by the n-th order reaction equation with autocatalysis (Cn-X), and the second one can be described by the n-th order reaction equation (Fn). The change in the mechanism of amorphous silicon crystallization was assumed to be due to the influence of the degree of Al defects at the initial state on the kinetics of the crystallization process. [ABSTRACT FROM AUTHOR]

The phase composition, structure, and size of particles and agglomerates formed by annealing of the powder obtained from hydrophobizing organosilicon liquid in the presence of aluminum powder (5–10 wt %) were studied by X-ray diffraction, Fourier IR spectroscopy, and laser granulometry. The annealing temperature varied from 550 to 700°С influences the mean size of the individual particles, and the aluminum content influences the agglomerate size. An increase in the heat treatment temperature leads to a decrease in the mean diameter of separate particles. The samples containing 10% aluminum powder have the largest agglomerate size. In turn, the formation of the polycrystalline silicon phase from the amorphous silica-containing powder system in the temperature range of solid-phase reactions depends on the particle and agglomerate size. To obtain polycrystalline silicon from samples containing coarser agglomerates, it is necessary to raise the annealing temperature at equal process time. The minimal annealing temperature for the start of the polycrystalline silicon formation was 550°С, and the required amount of aluminum powder was 5%. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is very important for the applications of energy devices such as fuel cells and metal-air batteries. A powerful catalyst is essential for ORR. It is known that Pt is the most effective ORR catalyst, but it is expensive. In this work, we have developed a Pt-anchored nanoporous gold catalyst (named NPG-Pt) for ORR. The NPG films were prepared from two-layer Au/a-Ge precursors by a novel solid-phase reaction method. Then, NPG-Pt x catalysts were prepared by adsorption and electroreduction method (x = 2, 4, and 6, representing the cycle numbers of cyclic voltammetry). It was found that the NPG film with a good three-dimensional porous structure provides sufficient active sites and improves Pt utilization, which further enhances ORR performance. Among all NPG-Pt x catalysts, NPG-Pt 4 catalyst shows the highest specific and mass activity (1.75 mA cm−2 and 4.21 A mg Pt −1). The results of X-ray photoelectron spectroscopy analysis confirmed that the electron structure of the NPG-Pt 4 catalyst is more suitable than those of other NPG-Pt x catalysts, in which the d-band center shifts more negatively, which is beneficial for the optimal adsorption of oxygen-containing intermediates and the improvement of ORR activity. This work provides a realistic perspective for the development of promising nanoporous metal-based ORR catalysts. • Nanoporous gold films were fabricated using a novel solid-phase reaction method. • Pt nanoparticles were electrodeposited on the surface of NPG films. • The NPG-Pt 4 catalyst exhibits an enhanced ORR activity. [ABSTRACT FROM AUTHOR]

The influence of Au catalyst microstructure on the crystallization behavior of Ge thin films obtained by Au-induced crystallization method is studied. By improving the Au catalyst crystallinity by pre-annealing, the hole mobility of Ge thin film crystallized at 200°C is improved to nearly 150 cm2/Vs thanks to the increase in Ge grain size, which is fairly high for a Ge film as thin as 10 nm. It is found that the increase in Ge grain size originates from the recrystallization process at deep subeutectic temperature. This is attributed to the existence of a metastable AuGe alloy phase surrounding crystalline Ge, which is kinetically stabilized by a continuous flow of Ge atoms through the alloy phase and realizes a solution-like growth. The process using a kinetically stabilized metastable phase will open up the possibility to realize a novel cost-effective and low-temperature process to fabricate high-performance semiconductor devices on plastic substrates. [Display omitted] • A high hole mobility of ∼150 cm²/Vs is achieved for a 10 nm thick polycrystalline Ge film via Au-induced crystallization. • Larger Au grains with fewer grain boundaries suppressed Ge nucleation, leading to larger (111)-oriented Ge grains. • The existence of a recrystallization process is discovered as an additional factor promoting Ge grain growth. • Recrystallization is attributed to a metastable AuGe alloy surrounding crystalline Ge and realizing a solution-like growth. [ABSTRACT FROM AUTHOR]

The effect of the aluminum layer on the kinetics and mechanism of aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) in (Al/a-Si)n multilayered films was studied using a complex of in situ methods (simultaneous thermal analysis, transmission electron microscopy, electron diffraction, and four-point probe resistance measurement) and ex situ methods (X-ray diffraction and optical microscopy). An increase in the thickness of the aluminum layer from 10 to 80 nm was found to result in a decrease in the value of the apparent activation energy Ea of silicon crystallization from 137 to 117 kJ/mol (as estimated by the Kissinger method) as well as an increase in the crystallization heat from 12.3 to 16.0 kJ/(mol Si). The detailed kinetic analysis showed that the change in the thickness of an individual Al layer could lead to a qualitative change in the mechanism of aluminum-induced silicon crystallization: with the thickness of Al ≤ 20 nm. The process followed two parallel routes described by the n-th order reaction equation with autocatalysis (Cn-X) and the Avrami–Erofeev equation (An): with an increase in the thickness of Al ≥ 40 nm, the process occurred in two consecutive steps. The first one can be described by the n-th order reaction equation with autocatalysis (Cn-X), and the second one can be described by the n-th order reaction equation (Fn). The change in the mechanism of amorphous silicon crystallization was assumed to be due to the influence of the degree of Al defects at the initial state on the kinetics of the crystallization process.

Cr and Si thin films were sequentially deposited on fused silica substrates by electron beam evaporation. Two bilayer film geometries, one with Cr thin film at the bottom and the other with it on top of the Si thin film, were investigated. The thin films were deposited at 200, 400 and 500°C followed by annealing in vacuum. Thereafter, the bilayer films were post-deposition annealed at temperatures between 600 and 800°C in 50°C steps. Raman spectroscopy studies showed that the interdiffusion process resulted in the crystallization of the as-deposited amorphous Si films. The temperature at which the crystallization occurred was geometry dependent, being lower when the Si film was at the top and at higher substrate temperature in the reverse case. The onset of crystallization temperature and the extent of crystallization of Si were determined by investigating the Raman spectra of the films recorded after post-annealing at each temperature. In addition to crystalline Si, the formation of CrSi2 and Cr2O3 was also detected. Thus, under favourable conditions the crystallization of Si is not silicide mediated. Bilayers with Cr on top and deposited at 400ºC, the onset of crystallization occurred at 700ºC with a maximum crystallization fraction of 67%. In contrast, in the case of metal at the bottom geometry and deposited at 500ºC, the onset of crystallization occurred at a lower temperature of 600ºC. Significantly, the presence of silicides was detected in the Cr (top)/Si (bottom) geometry and there was absence of silicides in the reverse geometry. This study provides new insights into the behaviour of metal–Si interfaces with implications for semiconductor devices and solar cells. [ABSTRACT FROM AUTHOR]

The process of tin-induced crystallization of amorphous silicon under the influence of different types of laser irradiation was investigated using the method of Raman scattering by thin-film Si-Sn-Si structures. The dependences of the size and concentration of Si nanocrystals on the power of laser radiation was experimentally evaluated and analyzed. As sources of excitation pulse laser radiation with the pulses duration equal to 20 ns and 150 s and wavelengths equal to 535 and 1070 nm was used. The possibility of efficient tin-induced transformation of silicon from amorphous phase to crystalline one in the 200-nm thick layers of a-Si under the action of laser pulses with duration equal to 20 ns was shown. The spatial and temporal distributions of laser induced temperature rise was calculated to interpret experimental results.

To develop high-efficiency multijunction solar cells onto inexpensive substrates, an innovative technique for growing a large-grained Ge layer on glass is strongly desired. We investigated the epitaxial growth of a light absorbing Ge film (500-nm thickness) on a large-grained (>100 μm) Ge seed layer (50-nm thickness) formed on glass by Al-induced layer exchange. After examining molecular beam epitaxy (MBE) and solid-phase epitaxy (SPE) for both methods, Ge layers with a low Al concentration were epitaxial grown at 350 °C. Microwave photoconductivity decay revealed that the MBE-Ge layer exhibited a short minority carrier lifetime owing to the rough surface. Conversely, the SPE-Ge layer was relatively flat and exhibited a long bulk minority carrier lifetime (5.6 μs), which is close to that of a single-crystal Ge. Therefore, the seed layer concept that combines SPE with Al-induced layer exchange is a promising way for fabricating ideal bottom cells for high-efficiency multijunction solar cells based on inexpensive substrates. • We propose applying Al-induced layer exchange (ALILE) of Ge to high-efficiency multijunction solar cells. • A 500-nm-thick Ge film is epitaxially grown on a large-grained (> 100 μm) Ge layer formed by ALILE. • Both molecular-beam epitaxy and solid-phase epitaxy (SPE) provide Ge layers with a low Al concentration at 350 °C. • The SPE-Ge layer exhibits a long minority carrier lifetime (5.6 μs), which is close to that of a single-crystal Ge. [ABSTRACT FROM AUTHOR]

Germanium-lead films have been investigated as a new direct-bandgap group IV alloy. GePb films were deposited on Si via thermal evaporation of Ge and Pb solid sources using the layer inversion metal-induced crystallization method for comparison with the current laser-induced recrystallization method. Material characterization of the films using x-ray diffraction analysis revealed highly oriented crystallinity and Pb incorporation as high as 13.5% before and 5.2% after annealing. Transmission electron microscopy, scanning electron microscopy, and energy-dispersive x-ray mapping of the samples revealed uniform incorporation of elements and complete layer inversion. Optical characterization of the GePb films by Raman spectroscopy and photoluminescence techniques showed that annealing the samples resulted in higher crystalline quality as well as bandgap reduction. The bandgap reduction from 0.67 eV to 0.547 eV observed for the highest-quality material confirms the achievement of a direct-bandgap material. [ABSTRACT FROM AUTHOR]

The solid state reaction between Cu and a-Si films was investigated at 150–200 °C by depth profiling with secondary neutral mass spectrometry. Intermixing was observed leading to the formation of a homogeneous Cu 3 Si layer at the interface. The growth of the crystalline silicide follows a parabolic law at 165 °C and 200 °C. At 150 °C a transition from linear to parabolic kinetics is observed. Combining with our previous experimental results showing linear kinetics at 135 °C [Acta Materialia, 61 (2013) 7173–7179], the temperature dependence of the linear and parabolic coefficients as well as the transition length can be estimated. [ABSTRACT FROM AUTHOR]

LiCoO 2 thin films were fabricated using the metal-induced crystallization (MIC) method. The condition to create the MIC effect was investigated. The location and thickness of the Al coating used to manufacture the LiCoO 2 cathode thin film electrodes were varied, and the structural and electrochemical characteristics of the LiCoO 2 thin film electrode were investigated by Raman spectroscopy, field emission scanning electron microscopy and charge-discharge tests. The degree of crystallization of LiCoO 2 increased in the order of uncoated LiCoO 2 (lowest), Al(coating)/LiCoO 2 /Al foil, and LiCoO 2 /Al(coating)/Al foil (highest), for identical heat treatment condition (600 °C, 1 h). The crystallization of LiCoO 2 occurred more quickly as the Al thickness decreased, and it is considered that crystallization of LiCoO 2 is delayed owing to the formation of an alloy between Li-Al when there is more Al. [ABSTRACT FROM AUTHOR]

The process of tin-induced crystallization of amorphous silicon under the influence of different types of laser irradiation was investigated using the method of Raman scattering by thin-film Si-Sn-Si structures. The dependences of the size and concentration of Si nanocrystals on the power of laser radiation was experimentally evaluated and analyzed. As sources of excitation pulse laser radiation with the pulses duration equal to 20 ns and 150 µs and wavelengths equal to 535 and 1070 nm was used. The possibility of efficient tin-induced transformation of silicon from amorphous phase to crystalline one in the 200-nm thick layers of a-Si under the action of laser pulses with duration equal to 20 ns was shown. The spatial and temporal distributions of laser induced temperature rise was calculated to interpret experimental results. [ABSTRACT FROM AUTHOR]

We investigate the morphology and crystalline structure of Au/Ge films in a wide range of temperatures by in situ TEM heating. Au/Ge films with Au mass thickness of 0.2–0.3 nm and Ge thickness of 5 nm were produced in vacuum by the sequential deposition of components on a carbon substrate at room temperature. It has been shown that particles with an average size of 4 nm, formed by Au film de-wetting, melt on the germanium substrate at temperatures 110–160 °C, which are below the eutectic temperature for the bulk. The effect of crystallization-induced capillary motion of liquid eutectic particles over Ge surface has been found in this work. Formation of metastable fcc phase of Ge has been observed at the liquid–germanium interface and behind the moving particle. Formation of a liquid phase with its subsequent crystallization at the metal–semiconductor interface seems to play a key role in the metal-induced crystallization effect. [ABSTRACT FROM AUTHOR]

Gold-induced crystallization (GIC) of amorphous germanium (a-Ge) using bilayer and multilayer films was performed through electron beam evaporation on glass substrates. The GIC of a-Ge was studied while the post-annealing temperature was varied between 250 and 550 °C for a fixed annealing time. The structure of polycrystalline Ge films was investigated by employing X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM). In both the bilayer and multilayer films the crystallization of a-Ge took place from 250 °C. The amount of crystallization fractioning and film quality were improved as the annealing temperature increased. However, preferentially (220) oriented crystalline Ge was formed in the bilayer films, indicating a micro-crystalline structure of the Ge. In the multilayer configuration (111) oriented crystalline Ge was observed indicating a poly-crystalline structure of the Ge. Scanning electron microscopy (SEM) images clearly highlight the grain size difference between these structures, especially for annealing temperatures above 400 °C. [ABSTRACT FROM AUTHOR]

Large-grained polycrystalline GeSn layers on glass are achieved through the layer exchange between a-Ge and Sn-doped Al layers. The thicker Sn layers, inserted below Al layers, provided the faster growth velocity, resulting in the smaller grain size of the GeSn layer. Controlling the Sn thickness (10 nm) and the growth temperature (300 °C) allowed for approximately 80% (111)-oriented GeSn layer with grains having an average size of 40 μm. The lower growth temperature led to the higher Sn content in GeSn: 300 °C resulted in a Sn content of 2%. These findings are meaningful to researches related to GeSn on insulators for fabricating advanced electrical and optical devices on inexpensive substrates as well as on Si platforms. [ABSTRACT FROM AUTHOR]

Ultrathin Si films in the nanometer range are extensively used for electronic and optoelectronic devices. Their mechanical properties have a high impact on the durability of the devices during lifetime. Here, fragmentation and buckling of 8–103 nm thin amorphous and polycrystalline (poly-) Si films on polyimide substrates have been studied by in situ light microscopy, Raman spectroscopy and resistance measurements. Generally, a smaller film thickness and a compressive residual stress delays the fracture of the film. The fracture strength of poly-Si films is larger compared to that of amorphous Si films while the adhesion to the substrate is better for amorphous Si compared to poly-Si. The onset delamination as a function of film thickness differs for the two phases and is described by two different models. Thin-film models for fracture toughness (amorphous Si: K 1C = 1.49 ± 0.22, poly-Si: K 1C = 3.36 ± 1.37) are applied, discussed, and found to be consistent with literature values. [ABSTRACT FROM AUTHOR]

An interfacial thermodynamic model is applied for understanding the phase transformation occurring in Pd/ a -Si (amorphous Si) bilayered system. The results of calculations indicate that, upon annealing, Si atoms diffuse into Pd grain boundary (GB) and crystallize at temperature above 460 °C, and Pd 2 Si phase forms at both Pd GB and Pd/ a- Si interface. c -Si (crystalline Si) grains nucleated at Pd GB grow laterally. Pd 2 Si grains nucleated at both Pd GB and Pd/ a- Si interface grow laterally and vertically. [ABSTRACT FROM AUTHOR]

Low-temperature (≤ 300 °C) formation of orientation-controlled large-grain (≥ 10 μm) Ge-rich (≥ 50%) SiGe crystals on insulator are realized by the gold-induced layer-exchange technique. Stacked structures of a-Si 1 − x Ge x (0 ≤ x ≤ 1)/Au/SiO 2 are employed as starting materials. Here, thin-Al 2 O 3 layers are introduced as diffusion barrier at a-SiGe/Au interfaces to suppress random bulk-nucleation and make (111)-oriented interface-nucleation on SiO 2 dominant. For samples with Ge fraction of 80%–100%, (111)-oriented large-grains (≥ 10 μm) are obtained through layer-exchange during annealing at 250 °C. On the other hand, layer-exchange for Ge fraction of 50% does not proceed at 250 °C. This phenomenon is attributed to retardation of lateral growth by introduction of Si. To enhance lateral growth, increase of annealing temperature is examined. As a result, (111)-oriented large-grains (≥ 10 μm) are realized for SiGe with Ge fraction of 50%–100%, having uniform composition profiles, by annealing at 300 °C. This technique is very useful to realize high-performance flexible electronics, employing plastic substrates (softening temperature: ~ 350 °C). [ABSTRACT FROM AUTHOR]

[Display omitted] • We examine mechanism and kinetics of metal-induced crystallization in Ag/Ge films. • We revealed that the MIC process occurs through intermediate phases. • Metastable AgGe hcp phase was identified at the reaction front at 450 °C. • MIC process is activated if the size of Ag nanoparticles exceeds a critical value. The initial stages of interfacial interactions between Ag nanoparticles and amorphous Ge (a-Ge) films, in particular the mechanism and kinetics of metal-induced crystallization (MIC) of a-Ge films are investigated herein. Unsupported Ag-Ge films formed by PVD were used as a model. In situ high-resolution (S)TEM and low-loss monochromated STEM-EELS techniques were used for real-time observation of the nucleation and growth of crystalline Ge and intermediate phases, as well as mapping of chemical elements at the reaction zone. We show that crystallization is activated at the metal–semiconductor interface around ≈200 °C, followed by lateral crystallization of a-Ge film at temperatures above ≈400 °C. It was revealed that the MIC process occurs through intermediate phases. Metastable Ag 0.8 Ge 0.2 hcp phase was identified at the reaction front at elevated temperatures, thus revealing the non-equilibrium melting of a eutectic alloy as the most probable mechanism of Ag-induced crystallization of a-Ge film. We show that the MIC process is activated only if the size of Ag nanoparticles exceeds a critical value, which is ≈8 nm in our case and equal to the thickness of the a-Ge film. [ABSTRACT FROM AUTHOR]

Fabricating large-grained polycrystalline Ge (poly-Ge) thin films on conducting-layer coated glass is a promising approach to lower the manufacturing cost of high-efficiency III-V tandem solar cells. We investigated the self-organizing formation of poly-Ge/Al/glass structures by using Al-induced layer exchange. The layer exchange between amorphous Ge and Al layers was completed at a low temperature of 350°C. Forming the interlayer between Ge and Al, i.e., limiting the diffusion of Ge to Al lowered the Ge nucleation rate and then enlarged the grain size of the resulting poly-Ge layer. The natively oxidized Al interlayer, formed by exposing a thin Al membrane (2-nm thickness) to air for 180 min, led to the poly-Ge with grains 46 μm in size. Moreover, the Ge layer was highly (111)-oriented. This Ge/Al/glass structure appears promising for use in the bottom cell of the III-V semiconductor based tandem solar cells, as well as in the epitaxial templates for aligned nanowires and other advanced materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Graphene was formed by Cu-induced crystallization of amorphous carbon at 300 °C. • A combined experimental approach including AES, XPS, Raman spectroscopy and HRTEM was used. • Graphene formation occurs at the Cu top surface, Cu grain boundaries and the Cu/a-C interface. • The process may provide a promising support for synthesizing Cu/graphene composites at low temperatures. Graphene or graphene-like carbon-reinforced copper matrix composites have gained extensive application prospects in aerospace and electronic fields due to their high electrical, thermal conductivity and excellent machining performance. The preparation of Cu/graphene composites at a relatively low temperature is highly demanded for practical applications. Herein, we develop an approach for synthesizing few-layer graphene (FLG) by contacting amorphous carbon (a-C) with Cu at a low annealing temperature of 300 °C. The mechanism of such low-temperature growth of graphene was discussed by the combined experimental methods of scanning electron microscopy, Auger electron spectroscopy, cross-sectional transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. It is found that the formation of FLG is mediated by the grain-boundary (GB) diffusion, interfacial diffusion and surface diffusion of carbon atoms simultaneously. The high density of Cu GBs can provide a fast diffusion path for "free" C atoms in the a-C sublayer, and the graphene layer was formed at the Cu GBs, at the Cu/a-C interface and on top of the Cu layer where carbon atoms are present. The Cu-induced growth of graphene at low temperatures may provide a promising support for synthesizing Cu/graphene composites in the future. [ABSTRACT FROM AUTHOR]

With the mechanical resonance damped using a perforated back-plate underneath the sensing diaphragm, a piezoresistive aero-acoustic microphone with improved high-frequency characteristics is demonstrated. The sensing diaphragm and the damper back-plate were monolithically integrated in one process flow. The microphone was calibrated using a high-voltage electrical spark-discharge acoustic N-wave source. A sensitivity of ~0.33 μV/V/Pa, a bandwidth of ~520 kHz at 3-dB attenuation, and a significant damping of the mechanical resonance were realized. [ABSTRACT FROM AUTHOR]

Semiconductor germanium (Ge) in contact with some metals, such as Al, Pd, and Au, etc., is a class of distinctive materials with non-integer dimensions (D) that differ from integer dimensional materials, such as nanoparticles (0D), nanowires/nanorods//nanotubes/nanoribbons (1D), and thin films (2D). In this article, we describe our efforts toward understanding the annealing strategies and perspectives of metal-induced crystallization for the amorphous Ge embedded in Al, Pd, and Au matrices prepared by high vacuum thermal evaporation techniques, highlighting contributions from our laboratory. First, we present the Al-induced crystallization of amorphous Ge and formation processes of fractal Ge patterns. In addition, the fractal Ge patterns induced by Pd nanoparticles with solid-state reactions will be summarized in detail. Temperature-dependent properties of resistance and fractal dimension in Pd/Ge bilayer films will be expounded. In particular, the nonlinear optical properties are discussed in detail. Finally, we will emphasize the in situ observations by transmission electron microscopy and multi-fractal analysis for the fractal Ge patterns induced by Au nanoparticles. Moreover, the polycondensation-type fractal Ge patterns with non-integer dimensions, thick branches and smooth edges, and metastable gamma-Au0.6Ge0.4are further investigated. The computer simulation indicated that the experimental results are good agreement with the simulation patterns, which were carried out by a ripening mechanism of non uniform grains. This review may provide a novel insight to modulate their competent performance and promote rational design of micro/nanodevices. [ABSTRACT FROM AUTHOR]

Abstract: Al-induced crystallization (AIC) of amorphous Si x Ge1−x (a-Si x Ge1−x ) solid solutions, with compositions over the entire range of the isomorphous Si–Ge system, was investigated. The crystallization progress was monitored in detail, at low temperatures from 150 to , by in situ X-ray diffraction while gradually increasing the annealing temperature until crystallization was completed, allowing for an evaluation of the crystallization kinetics. The formation of single-phase crystalline Si x Ge1−x solid solutions upon AIC of a-Si x Ge1−x (0 x 1) was observed at all annealing temperatures. Concentration–depth profiling by Auger electron spectroscopy provided a detailed insight into the diffusion processes occurring in the early stage of the low-temperature AIC process and the intriguing phenomenon of layer exchange of the Al and a-Si x Ge1−x sublayers. On the basis of evaluation of the Si and Ge diffusion coefficients, the results suggest that, upon AIC, both Si and Ge atoms diffuse at comparable rates into the Al layer in the low temperature range investigated. The degree of completeness of the layer-exchange process after full crystallization is a function of the a-Si x Ge1−x composition; complete layer exchange occurs for all Al/a-Si x Ge1−x specimens containing more than 27at.% Si. [Copyright &y& Elsevier]

Low-temperature formation (~150°C) of Ge films on insulator is investigated for realization of advanced flexible devices. We propose utilization of Sn as catalyst to enhance the crystallization at low-temperatures. By annealing (150–200°C) of a-Ge/Sn stacked structures formed on insulators, the composition distributions of Ge/Sn layers are inverted, and Sn/poly-Ge stacked structures are obtained. The results demonstrate that the crystallization occurs at 150°C, which is slightly below the eutectic temperatures. This Sn-induced crystallization technique is useful to obtain poly-Ge on low-cost flexible substrates (softening temperature: ~200°C). [ABSTRACT FROM AUTHOR]

Abstract: We lowered the crystallization temperature of amorphous TiO2 thin films using a Cu catalyst as either a bottom or cap layer. The Cu bottom layer reduced the crystallization temperature of TiO2 by ~30°C. Depth profile analyses by Rutherford backscattering spectrometry revealed that a very small amount of Cu was sufficient to induce full crystallization of the TiO2 film. Depositing the Cu cap layer and annealing at 210°C for 3h yielded a transparent anatase TiO2 thin film upon wet-etching the Cu cap. [Copyright &y& Elsevier]

With the development of practical thin-film batteries, multilayer graphene (MLG) is being actively investigated as an anode material. Therefore, research on determining a technique to fabricate thick MLG on arbitrary substrates at low temperatures is essential. In this study, we formed an MLG with controlled thickness at low temperatures using a layer exchange (LE) technique and evaluated its anode properties. The LE technique enabled the formation of a uniform MLG with a wide range of thicknesses (25-500 nm) on Ta foil. The charge/discharge characterization using coin-type cells revealed that the total capacity, which corresponded to Li intercalation into the MLG interlayer, increased with increasing MLG thickness. In contrast, cross-sectional transmission electron microscopy showed a metal oxide formed at the MLG/Ta interface during annealing, which had small Li capacity. MLG with sufficient thickness (500 nm) exhibited an excellent Coulombic efficiency and capacity retention compared to bulk graphite formed at high temperatures. These results have led to the development of inexpensive and reliable rechargeable thin-film batteries.

Abstract: An approach to deposit polycrystalline silicon layers on amorphous substrates is presented. It is shown that metastable amorphous silicon can be transformed into its more stable microcrystalline structure at a temperature below 330°C via an intermediate liquid solution stage. In particular, the interaction of liquid indium nanodroplets in contact with amorphous silicon is shown to lead to the formation of circular polycrystalline domains. Crystallinity of these domains is analyzed by micro-Raman spectroscopy. The droplet size necessary for the onset of crystallization is related to the temperature of the film. Full coverage of the substrate with microcrystalline silicon has been obtained at 320°C within less than one hour. These films might act as seeding layers for further enlargement by steady-state liquid phase epitaxy. [Copyright &y& Elsevier]

Ni-metal-induced crystallization (MIC) of amorphous Si (α-Si) has been employed to fabricate low-temperature polycrystalline silicon thin-film transistors (TFTs). However, the Ni residues degrade the device performance. In this study, a new method for manufacturing MIC-TFTs using drive-in Ni-induced crystallization with a chemical oxide layer (DICC) is proposed. Compared with that of MIC-TFTs, the on/off current ratio ( I/ I) of DICC-TFTs was increased by a factor of 9.7 from 9.21 × 10 to 8.94 × 10. The leakage current ( I) of DICC-TFTs was 4.06 pA/ μm, which was much lower than that of the MIC-TFTs (19.20 pA/ μm). DICC-TFTs also possess high immunity against hot-carrier stress and thereby exhibit good reliability. [ABSTRACT FROM AUTHOR]

Abstract: Ni-metal-induced crystallization (MIC) of amorphous Si (α-Si) has been used to fabricate low-temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs). The current crystallization technology, however, often leads to trap Ni and NiSi2 precipitates, which degrade the device performance. In this study, a new manufacturing method for poly-Si TFTs using drive-in Ni induced crystallization (DIC) was proposed. In DIC, F+ implantation was used to drive Ni in the α-Si layer. It was found that the electrical performance (especially leakage current) and thermal stability of DIC-TFTs were improved due to the reduction of Ni concentration and passivation of trap states near the SiO2/poly-Si interface. [ABSTRACT FROM AUTHOR]