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In this work, we study the optical response of structures involving porous silicon and porous alumina in a multi-layered hybrid structure. We performed a rational design of the optimal sequence necessary to produce a high transmission and selective filter, with potential applications in chemical and biosensors. The combination of these porous materials can be used to exploit its distinguishing features, i.e., high transparency of alumina and high refractive index of porous silicon. We assembled hybrid microcavities with a central porous alumina layer between two porous silicon Bragg reflectors. In this way, we constructed a Fabry-Perot resonator with high reflectivity and low absorption that improves the quality of the filter compared to a microcavity built only with porous silicon or porous alumina. We explored a simpler design in which one of the Bragg reflectors is replaced by the aluminium that remains bound to the alumina after its fabrication. We theoretically explored the potential of the proposal and its limitations when considering the roughness of the layers. We found that the quality of a microcavity made entirely with porous silicon shows a limit in the visible range due to light absorption. This limitation is overcome in the hybrid scheme, with the roughness of the layers determining the ultimate quality. Q-factors of 220 are experimentally obtained for microcavities supported on aluminium, while Q-factors around 600 are reached for microcavities with double Bragg reflectors, centred at 560 nm. This represents a four-fold increase with respect to the optimal porous silicon microcavity at this wavelength. [ABSTRACT FROM AUTHOR]

Modulated photoconductivity has proved to be an excellent tool to probe the density of states of semiconductors. However, though a great deal of attention has been devoted to the high frequency regime for its simplicity of application, the modulated photoconductivity in the low frequency (LF-MPC) regime has been the object of researches only recently. In the case of a dominant species of states present in the forbidden gap, it was shown that LF-MPC is a good complementary technique to the high frequency method to extract different transport parameters. In this paper, we present a complete theoretical analysis of the LF-MPC experiment for the case when different species of traps are present. We solve the complete system of equations that describe the experiment, and we apply simplifying assumptions to deduce a simple formula relating the photocurrent phase shift to the density of states (DOS) at the majority carriers’ quasi-Fermi level. By means of numerical calculations, we discuss the accuracy of our development, and of previous approximate formulas, to reconstruct a given DOS. Finally, we present experimental and theoretical evidence that, under sensitization conditions, the sign of the phase shift of the modulated photocurrent reverses and the steady-state photoconductivity depends superlinearly on the generation rate. [ABSTRACT FROM AUTHOR]

An experimental technique to study the energy profile of localized states in the gap of amorphous semiconductors is proposed. The method is based on the relationship between the recombination lifetime and the density of states (DOS) at the quasi-Fermi level for trapped carriers. We use the modulated photocurrent experiment in the recombination-limited regime as a convenient method to measure the recombination lifetime. Measurements performed as a function of temperature allow the DOS above the Fermi energy to be determined. The accuracy and limitations of the method are studied by means of computer simulations. The experimental technique is applied to obtain the density of defect states of a hydrogenated amorphous silicon sample. [ABSTRACT FROM AUTHOR]

We have measured the temperature variation of the magnetic anisotropy of Ni nanowires (Ni NWs) embedded in freestanding porous anodized aluminum oxide membranes, using DC magnetometry and ferromagnetic resonance. Both techniques show a significant reduction of the uniaxial anisotropy with decreasing temperature. This decrease can be explained by magnetoelastic effects, as Ni NWs are subjected to stress due to the difference in thermal expansion coefficients between the nanocomposite materials. Matching our experimental findings with previously measured thermal strains along the Ni NW axis led us to estimate the perpendicular stress. Thus, we postulate the Ni NWs as nanometric differential stress sensors. [ABSTRACT FROM AUTHOR]

We have measured the thermal expansion of Ni nanowires (NWs) electrodeposited into self-organized nanoporous amorphous aluminum oxide (AAO) membranes without an Al substrate using X-ray diffraction between 110 K and 350 K. The results indicate an average thermal expansion of the Ni NWs—along the wire axis—of α ¯ NiNW = − 1.6 ± 1.5 × 10 − 6 K − 1 . Assuming a bulk-like thermal expansion of the isolated Ni NWs, this result indicates that AAO also has a negative thermal expansion. We estimate the thermal expansion of nanoporous AAO to be α AAO = − 5 ± 1 × 10 − 6 K − 1 . We show that data obtained previously on the thermal expansion of metallic NWs grown in the nanoporous AAO may be interpreted as originating from a negative thermal expansion of the matrix. [ABSTRACT FROM AUTHOR]

Details a study which performed isothermal annealing on a hydrogenated amorphous silicon sample deposited at low temperature in a glow discharge reactor. Dependence of dark conductivity and photoconductivity on annealing time; Experimental procedures; Equation for computing the variation in photoconductivity.

Studies the amorphous silicon carbide samples by infrared and visible spectroscopy. Evolution of the 2000-2100 cm[sup-1] absorption band; Phases related to the Si-H bonds environments that exist; Factors that have the most important effect on the behavior of the band.

Examines the kinetics of oxidation in high-pressure direct current-sputtered amorphous silicon (Si). Information on the two mechanisms of oxidation; Comparison between the density of α-Si and &alpha-Ge; Consequences of the existence of porous structure; Approximation of the total absorbance spectrum of the mixture.

Presents a study which investigated the role of surface in sputtered amorphous silicon. Method of the study; Results and discussion; Conclusion.

Presents a study which reported the room-temperature cathodoluminescence (CL) of diamond like films produced by glow discharge. Details on the growth of films of crystalline diamond on substrates; Characteristics of CL spectra of diamonds; Details on the infrared spectra of the samples; Description of the normalized room-temperature CL of the samples.

Studies the oxidation of hydrogenated amorphous silicon carbide films prepared by glow-discharge decomposition of gaseous mixtures of silane and methane by using infrared absorption spectroscopy. Infrared differential absorbance spectrum of a carbon-rich sample obtained after six month room-temperature exposure to air; Overview of differential absorption spectra resulting from the oxidation of a sample; Presence of a large fraction of CH[sub3] precursor radical.

In this work, a series of boron-doped microcrystalline silicon samples [μcSi:H(B)] were deposited by plasma--enhanced chemical vapor deposition, using silane (SiH4) diluted in hydrogen, and diborane (B2H6) as a dopant gas. The concentration of B2H6 in SiBL4 was varied in the range of 0-100 ppm. The density of states was obtained from the thermally stimulated conductivity technique and compared with results obtained by the modulated photoconductivity methods. To e×plain the poor agreement between the density of states obtained from the thermally stimulated conductivity and the other methods, it is shown by means of numerical simulations that the density of states is very sensitive to e×perimental errors introduced in the calculation of the μnτn product (mobility of electron × lifetime of the electron). The thermally stimulated conductivity method is applied here for the first time to calculate the density of defect states in the forbidden band of μc-Si:H samples. [ABSTRACT FROM AUTHOR]

Addresses criticisms on a study which examined the dependence of the stretching band of silicon hydride bonds in a-SiC:H on carbon content. Overview of the research findings; Basis of the arguments; Explanation for the growth in oxidation peak.

We report the results of enhanced nickel induced crystallization of intrinsic hydrogenated amorphous silicon thin films under vacuum conditions. Crystallization was performed by conventional furnace annealing at both atmospheric pressure and vacuum or low pressure conditions (≈10-6 Torr) for comparison. We have investigated the influence of low pressure during annealing on the resulting polycrystalline films by means of optical microscopy, ultraviolet reflectance, and photoacoustic spectrometry measurements. A faster crystallization and a smaller grain size were observed when the process is carried out under vacuum, with an annealing time reduction of more than 50%. We discuss, from a thermodynamical viewpoint, some possible causes by which vacuum annealing influences incubation and nucleation stages due to the presence of mobile hydrogen atoms inside the amorphous silicon matrix. Large grains with diameters of 30 and 100 μm were obtained at vacuum and atmospheric pressure, respectively. [ABSTRACT FROM AUTHOR]

Presents an errata to an article published in the 'Journal of Applied Physics,' published as of 1991. Details of the errata.