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A sample structure and method for superlateral-growth (SLG) enhancement in excimer-laser crystallization has been implemented and realized. The proposed sample structure is a Si film/buffer film/light-absorptive (LA) film/glass-stacked structure, with the irradiation of laser light from underneath a substrate. The influence of the absorption coefficient α of the LA film has been found to be critical in this structure. By increasing α from 0 to 12,000 cm−1, diameter of SLG grain has increased from 0.8 to 10 μm, with the solidification term increased from 75 to 1050 ns, respectively. The radius of SLG grain was shown to be proportional to the solidification term with a slope of 5 m/s. This result suggests the average SLG growth rate is constant at 5 m/s, irrespective of the solidification term of Si film. The applicability of present method to both sequential lateral solidification method and micromelt seeding method was demonstrated. Overcoming of Si agglomeration has been shown to be important for applying the present method to the sequential lateral solidification (SLS) method.
A process suitable for preparing metal-insulator-metal thin film capacitors with submicron insulating layers and top electrodes with cm-scale dimensions is presented. Most importantly, this process does not require sophisticated deposition equipment or a clean room environment. The key to large area yield is co-firing the insulator film with a non-dewetting electrode during the dielectric crystallization/densification anneal. We propose a mechanism of electrode dewetting during the high temperature anneal where the metal laterally retreats from geometric asperities that compromise the integrity of the insulating layer. This behavior is driven by surface energy minimization, which promotes metal migration away from the regions of high curvature. This methodology is not material specific, and only requires a top electrode with a large contact angle to the dielectric in question. Using this technique, functional thin film capacitors with 2.5 cm lateral dimensions and 1 μm dielectric thicknesses can be routinely prepared.
The structural model for metallic glasses and the topological instability criterion for multicomponent alloy systems have been combined to formulate a design protocol for bulk metallic glasses (BMGs). New Ni-Nb-Zr bulk metallic glasses with high corrosion resistance have been discovered. The experimental results in literature also support the use of this approach as a practically efficient method to select bulk metallic glass-forming compositions.
We recently reported the chemical vapor deposition growth of binary Ge1–ySny and ternary Ge1–ySixSny alloys directly on Si wafers using SnD4, Ge2H6 (di-germane), SiH3GeH3, and (GeH3)2SiH2 sources. Ge1–ySny is an intriguing infrared (IR) material that undergoes an indirect-to-direct band-gap transition for y < 0.1. In addition, we have found that Ge1–ySny layers have ideal properties as templates for the subsequent deposition of other semiconductors: (i) they are strain-relaxed and have low threading-defect densities (105 cm−2) even for films thinner than 1 μm; (ii) their low growth temperatures between 250 and 350 °C are compatible with selective growth, and the films possess the necessary thermal stability for conventional semiconductor processing (up to 750 °C, depending on composition); (iii) they exhibit tunable lattice constants between 5.65 Å and at least 5.8 Å, matching InGaAs and related III-V systems; (iv) their surfaces are extremely flat; (v) they grow selectively on Si and not on SiO2; and (vi) the film surface can be prepared by simple chemical cleaning for subsequent ex situ epitaxy. The incorporation of Sn lowers the absorption edges of Ge. Therefore, Ge1–ySny is attractive for detector and photovoltaic applications that require band gaps lower than that of Ge. Spectroscopic ellipsometry and photoreflectance experiments show that the direct band gap is halved for as little as y = 0.15. Studies of a Ge0.98Sn0.02 sample yield an absorption coefficient of 3500 cm−1 at 1675 nm (0.74 eV). Thus, IR detectors based on Ge0.98Sn0.02 could easily cover the L-(1565–1625 nm) and C-(1530–1565 nm) telecomm bands. Photoluminescence studies show band-gap emission on thin GeSn layers sandwiched between higher band-gap SiGeSn barriers. We have made advances in p- and n-doping of GeSn and present results on electrical characterizations. Hall measurements reveal mobilities as high as of 600 cm2/V-s and background p-dopant concentrations in the 1016 cm−3 range for samples with nominal composition and thickness of Ge0.98Sn0.02 and ∼500 nm, respectively. GeSn also has application in band-to-band laser heterodiodes. The ternary system Ge1–x–ySixSny grows on Ge1–ySny-buffered Si. It represents the first practical group IV ternary alloy, because C can only be incorporated in minute amounts to the Ge–Si network. The most significant feature of Ge1–x–ySixSny is the possibility of independent adjustment of the lattice constant and band gap. For the same value of the lattice constant, one can obtain band gaps differing by >0.2 eV, even if the Sn concentration is limited to the range y < 0.2. This property can be used to develop a variety of novel devices, from multicolor detectors to multiple-junction photovoltaic cells. A linear interpolation of band-gap lattice constants between Si, Ge, and α–Sn shows that it is possible to obtain SiGeSn with a band gap and a lattice constant larger than that of Ge. We shall use this feature to make a tensile-strained Ge-on-SiGeSn telecomm detector with improved performance. To date, record high tensile strain (0.40%) has been achieved in Ge layers grown on GeSn-buffered Si where the strain is systematically tuned by adjusting the lattice constant in the buffer. A tensile-strain-induced direct gap of Ge can be used also for laser diodes and electroptical modulators.
A correction to the nanoindentation technique taking into account the elastic recovery at extremely shallow contact depths was proposed. Using a high-sensitivity nanoindentation system with a sharp indenting tip, the magnitude of the elastic recovery could be obtained directly from very low-force load–unload curves, which was then used to correct the contact area used for hardness measurements. Nanoindentation experiments were performed on a standard fused quartz sample and, compared to standard nanoindentation techniques, the proposed method was found to be more accurate at ultrashallow indenting depths of <3 nm.
The three-dimensional nanostructured SiO2-based microshells of diatoms have been converted into nanocrystalline BaTiO3 via a series of shape-preserving reactions. The microshells, obtained as diatomaceous earth, were first exposed to a surfactant-induced dissolution/reprecipitation process [C.E. Fowler, et al., Chem. Phys. Lett.398, 414 (2004)] to enhance the microshell surface area, without altering the microshell shape. The SiO2 microshells were then converted into anatase TiO2 replicas via reaction with TiF4 gas and then humid oxygen. Hydrothermal reaction with a barium hydroxide-bearing solution then yielded three-dimensional nanocrystalline microshell replicas composed of BaTiO3. The enhanced surface area of the surfactant-treated microshells resulted in faster conversion into phase-pure BaTiO3 at 100 °C.
The undercooling of flip-chip Pb-free solder bumps was investigated by differential scanning calorimetry (DSC) to understand the effects of solder composition and volume, with and without the presence of an under bump metallurgy (UBM). A large amount of the undercooling (as large as 90 °C) was observed with Sn-rich, flip-chip size solder bumps sitting in a glass mold, while the corresponding undercooling was significantly reduced in the presence of a wettable UBM surface. In addition, the solidification of an array of individual solder bumps was monitored in situ by a video imaging technique during both heating-up and cooling-down cycles. Data obtained by the optical imaging method were used to complement the DSC thermal measurements. A random solidification of the array of bumps was demonstrated during cooling, which also spans a wide temperature range of 40–80 °C. In contrast, an almost simultaneous melting of the bumps was observed during heating.
We have found a new route for preparing Pt containing perovskites. Ba containing perovskite powder, (La0.7Sr0.2Ba0.1)ScO3–δ (LSBS), reacted with Pt foil at 1898 K in air, and formed ultramarine colored Pt containing perovskite, (La0.7Sr0.2Ba0.1)(Sc,Pt)O3–δ, without changing the GdFeO3-type structure. The chemical compositions of the samples before and after firing, measured with inductively coupled plasma (ICP) optical emission spectrometry, were La: Sr: Ba: Sc = 0.70(1): 0.206(4): 0.101(2): 0.98(2) and La: Sr: Ba: Sc: Pt = 0.70(1): 0.197(4): 0.085(2): 0.95(2): 0.0062(2), respectively. The reaction proceeded not only at the interface between perovskite powder and Pt foil, but also over whole powder surface. We name this new preparation method the “solid-phase elution (SE) method”, because the process involves elution of Pt ions from the Pt foil to the LSBS perovskite lattice. It is expected that we can control the amount of Pt introduced into perovskites by using the SE method after optimizing the reaction time and temperature.
We report the studies on the effect of grain alignment on lateral carrier transport in nominally 〈001〉-oriented aligned-crystalline silicon (ACSi) films on polycrystalline substrates. With improving grain alignment, energy barrier height at the grain boundaries was reduced from 150 to less than 1 meV, and both conductivity and Hall mobility became less sensitive to hydrogen passivation. This suggests that the dangling bonds in ACSi films are a major source of trapping sites, and that they become less dominant with improving grain alignment. These results demonstrate that improving grain alignment enhances the lateral carrier transport in small-grained (≤1 μm) polycrystalline silicon films, by reducing dangling bond density at the grain boundaries.
An axial magnetic field of 0.1 T was applied to ZrF4–BaF2–LaF3–AlF3NaF fibers during heating to the glass crystallization temperature. Scanning electron microscopy and x-ray diffraction were used to identify crystal phases. It was shown that fibers exposed to the magnetic field did not crystallize, while fibers not exposed to the field did crystallize. A hypothesis based on magnetic work was proposed to explain the results, and was tested by measuring the magnetic susceptibilities of the glass and crystal.
This paper describes a new method to synthesize AlN nanowires by the nitridation of Ti3Si0.9Al0.1C2 solid solution. Single-crystalline AlN nanowires with the hexagonal wurtzite structure can be easily prepared using this method. In particular, the resulting AlN nanowires display a new growth orientation of 〈1011〉 besides 〈1000〉 and 〈0001〉. This work indicates that MN+1AXN compounds are promising raw reactants to synthesize one-dimensional (1D) nanostructures of nitrides and oxides.
The effect of process parameters on the plasma deposition of μc-Si:H solar cells is reviewed in this article. Several in situ diagnostics are presented, which can be used to study the process stability as an additional parameter in the deposition process. The diagnostics were used to investigate the stability of the substrate temperature during deposition at elevated power and the gas composition during deposition at decreased hydrogen dilution. Based on these investigations, an updated view on the role of the process parameters of plasma power, heater temperature, total gas flow rate, and hydrogen dilution is presented.
The complex dielectric permittivity of electrically lossy, porous Al2O3–SiC composites was measured as a function of frequency over the range of 0.001 to 18 GHz. These composites were fabricated by an infusion method of incorporating SiC polymer precursor into porous alumina disks. Repeat polymer infusions and pyrolysis steps to 1000 °C were carried out, with some samples undergoing an additional air fire prior to each subsequent step. Generally, it was found that for non-air-fired samples, moderate, controllable losses were attainable over a broad frequency range. By contrast, the dielectric loss attainable for air-fired samples was generally very low. For all samples, various aspects of the variation of permittivity components ϵ′ and ϵ″ with frequency were analyzed, with a view to determine the various factors contributing to dielectric response. Microstructure analysis using scanning electron microscopy was also performed.
In the course of a systematic field study, anisotropic alkali and alkaline earth vanadates have been accessed through a straightforward, one-step hydrothermal process. They are formed quantitatively from V2O5 and alkali- or alkaline earth halide solutions after a few days of autoclave treatment in the temperature range between 100 and 220 °C. The presence of ionic additives leads to an interplay between the formation of isotropic crystalline phases and the production of fibrous oxide materials, such as a novel magnesium vanadate. The influence of the hydrothermal parameters and of the alkali/alkaline earth halides on the emerging phases and morphologies has been investigated in the course of a systematic study. The results are compared with other vanadate- and transition metal oxide-based hydrothermal systems, and the emerging trends are discussed with respect to the development of predictive synthetic concepts for nanostructured vanadium oxides.
Bi-doped sodium–potassium aluminosilicate glasses were synthesized and characterized. Broadband near-infrared (IR) emission covered the whole telecommunication wavelength region, with a maximum peak at about 1250 nm, a full width at half-maximum of about 370 nm, and a lifetime longer than 420 μs. The present glasses are potential materials for tunable lasers and optical amplifiers. The decrease of active Bi center concentration with the increase of Na2O content and the addition of CeO2are first reported here, and the IR emission center in sodium–potassium aluminosilicate glasses might be ascribed to low-valence-state bismuth, most probably, Bi+.
A brief review is given of electrical properties of magnetoelectric, multiferroic materials, with emphasis on magnetocapacitance effects, nanostructures, integration into real random access memories, and critical phenomena, including defect dynamics near phase transitions.
We report on the one-phonon Raman scattering spectra from the following M2AC MAX-phase ternary carbides: Ti2AlC, V2AlC, Cr2AlC, Nb2AlC, Ta2AlC, Ti2InC, Hf2InC, V2GeC, Cr2GeC, V2AsC, and Nb2AsC. We also report the results of calculations of the Γ-point, Raman-active phonon energies for these phases based on density functional theoretical simulations, including the effect of the k-point sampling on the convergence of phonon energies. Good agreement between all measured and calculated Γ-point Raman-active optical phonon energies is obtained.
The strain rate dependence of plastic deformation of Ce60Al15Cu10Ni15 bulk metallic glass was studied by nanoindentation. Even though the ratio of room temperature to the glass transition temperature was very high (0.72) for this alloy, the plastic deformation was dominated by shear banding under nanoindentation. The alloy exhibited a critical loading rate dependent serrated flow feature. That is, with increasing loading rate, the alloy exhibited a transition from less prominent serrated flow to pronounced serrated flow during continuous loading but from serrated to smoother flow during stepped loading.