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Experimental demonstration of on-chip two-octave supercontinuum generation in the mid-infrared wavelength, ranging from 3 to 13 µm (larger than 2500 cm-1), by using graded-index SiGe waveguides that allow dispersion tailoring and low propagation losses.

Photodetectors are fundamental components in most optoelectronic systems, therefore extending and controlling their spectral response is very appealing for a wide range of applications. In this paper, we propose and demonstrate two different dual band photodetectors which combine Ge and Si to selectively operate in the visible and near infrared spectral ranges.

We investigate spin transport in a set of $\text{Ge}/{\text{Si}}_{0.15}{\text{Ge}}_{0.85}$ multiple quantum wells (MQWs) as a function of the well thickness. We exploit optical orientation to photogenerate spin-polarized electrons in the discrete energy levels of the well conduction band at the $\mathrm{\ensuremath{\Gamma}}$ point of the Brillouin zone. After diffusion, we detect the optically oriented spins by means of the inverse spin-Hall effect (ISHE) taking place in a thin Pt layer grown on top of the heterostructure. The employed spin injection/detection scheme is sensitive to in-plane spin-polarized electrons, therefore, by detecting the ISHE signal as a function of the photon energy, we evaluate the spin polarization generated by optical transitions driven by the component of the light wave vector in the plane of the wells. In this way, we also gain insight into the electron spin-diffusion length in the MQWs. The sensitivity of the technique to in-plane spin-related properties is a powerful tool for the investigation of the in-plane component of the spin polarization in MQWs, which is otherwise commonly inaccessible.

Photonics integration in the mid-Infrared (mid-IR) spectral range, and more specifically the fingerprint region between 5 and 20 μm wavelength has garnered a great interest as it provides an immense potential for applications in spectroscopy and sensing. The unique vibrational and rotational resonances of the molecules at these wavelengths can be exploited for non-intrusive, unambiguous detection of the molecular composition of a broad variety of gases, liquids or solids, with a great interest for many high-impact applications. Fourier-transform spectrometers (FTS) are a particularly interesting solution for the on-chip integration due to their superior robustness against fabrication imperfections. However, the performance of current on-chip FTS implementations is limited by tradeoffs between bandwidth and resolution, for a given footprint. In this work we propose and experimentally demonstrate a new FTS approach that gathers the advantages of spatial heterodyning and optical path tuning by thermo-optic effect. The high resolution is provided by spatial multiplexing among different interferometers with increasing imbalance length, while the broadband operation is enabled by fine sampling interval of the optical path delay in each interferometer harnessing the thermo-optic effect. This novel approach overcomes the bandwidth-resolution tradeoff in conventional counterparts. The fabricated device enables a bandwidth as wide as 603 cm-1 (instead of 74 cm-1 with no-thermal tuning) near 7.7 μm wavelength, keeping a resolution better than 15 cm-1 with the same footprint. This device is fabricated in a Ge-rich graded-index SiGe platform with experimentally proven low loss operation up to 8.5 μm wavelength.

In 1989 an ancient burial consisting of a skeleton and a few objects was discovered at the Monte dei Cappuccini Monastery, in Torino (Italy). Anthropological analysis of the skeleton revealed that it belonged to a young man, and the archaeometric characterization of the objects suggested that most of them are compatible with the Medieval period. As a proper archeological survey was not conducted at the time of the finding, due to the religious nature of the site, a high-precision radiocarbon (14C) dating has been performed. The samples were processed with three different methods: besides the ultrafiltration (UF) treatment, we applied the “collagen” (COL) and the Longin-base (LB) methods. While UF and COL treatments provided compatible results, LB method returned ages older with respect the UF one, with significant disagreements in some cases and this evidence is supported by several measurements on the same individual. Thanks to the reduction of the uncertainty with the high number of measured samples and the availability of historical evidence, the possible age of the burial has been limited to the time interval 1464–1515 cal AD.

This work explores the use of Ge-rich graded-index Si

International audience; This work explores the use of Ge-rich graded-index Si 1-x Ge x rib waveguides as building blocks to develop integrated nonlinear optical devices for broadband operation in the mid-IR. The vertical Ge gradient concentration in the waveguide core renders unique properties to the guided optical mode, providing tight mode confinement over a broadband mid-IR wavelength range from λ = 3 µm to 8 µm. Additionally, the gradual vertical confinement pulls the optical mode upwards in the waveguide core, overlapping with the Ge-rich area where the nonlinear refractive index is larger. Moreover, the Ge-rich graded-index Si 1-x Ge x waveguides allow efficient tailoring of the chromatic dispersion curves, achieving flat anomalous dispersion for the quasi-TM optical mode with D ≤ 14 ps/nm/km over a ~ 1.4 octave span while retaining an optimum third-order nonlinear parameter, γ eff. These results confirm the potential of Ge-rich graded-index Si 1-x Ge x waveguides as an attractive platform to develop mid-IR nonlinear approaches requiring broadband dispersion engineering.

There is significant interest to develop cheap CMOS compatible sensors that operate in the mid-infrared (MIR). To meet these requirements, Ge-on-Si is proving to be an exciting platform. There is the potential to realize waveguide integrated quantum well infrared photodetectors (QWIPs) based on Ge quantum wells (QWs). Intersubband absorption from p-Ge QWs has been demonstrated in the important atmospheric transmission window of 8-13 μm. An alternative strategy for sensing in the MIR is demonstrated through highly n-type doped Ge plasmonic antennas. These antennas demonstrate vibrational sensing of polydimethylsiloxane (PDMS) spin coated layers at 12.5 μm wavelength. These demonstrate enhanced sensing capabilities due to the localized hot spots of the antenna resonant modes.

Effective monolithic integration strategies for high quality quantum III-V nanostructure fabrication on Si will be introduced. The methodologies presented range from ultrathin planar Ge virtual substrates for the integration of single photon emitters with high temperature stability to advanced three-dimensional Ge growths strategies.

Hydrogenated nanocrystalline silicon (nc-Si:H) is an attractive material for photovoltaic applications, mainly due to its higher stability against Staebler-Wronski effects with respect to amorphous silicon. Notwithstanding its promising properties, its physical characteristics have been only in recent times investigated and many questions are still open. As an example, the investigation of the transport mechanisms has up to now led to controversial results. This is mainly due to the complexity of this material, as several phases coexist: crystalline nano-grains, nanocrystalline columns, hydrogenated amorphous Si (a-Si:H), defects, grain-boundaries and voids. The doping process further increases the complexity of the system as dopant atoms can segregate at nanocrystals or at the boundaries between different phases. Recently [1], the investigation of the electrical transport mechanisms and routes has revealed the major importance of percolation conduction through the network of connected disordered tissue encapsulating the columns in fully-crystalline undoped μc-Si:H, while different results [2] are in favor of an hopping assisted conduction mechanism. The present contribution deals with an extended study of the conduction mechanisms at both macroscopic and microscopic levels of hydrogenated nanocrystalline Si thin films grown in different conditions. The films have been deposited by Low Energy Plasma Enhanced Chemical Vapor Deposition (LEPECVD) using SiH4 and H2 precursor gases, the deposition temperatures ranged from 200 to 400°C, the SiH4 dilution ratios from 1% to 50%. The films were deposited on several substrates: crystalline Si, glass, glass covered with ITO or ZnO. The crystal fraction, as measured by Raman spectroscopy, ranged from 25 to 75% [3]. p-doped layers were obtained by varying the using B2H6 dilution rates. Both doped and undoped films were examined. Sub-micron resolution current maps have been obtained by conductive atomic force microscopy (C-AFM) applying a fixed voltage to a conductive tip. In the undoped samples all the maps obtained present a clear evidence of enhanced conduction in the nanocrystals, while the disordered tissue surrounding the nano-grains (constituted mainly by amorphous region) is mostly nonconductive (fig.1). This result was obtained for all the undoped films examined whatever the substrate is. The conduction, furthermore, occurs mainly at the Si nanocrystallites independently of the crystalline fraction of the films examined, while the spatial distribution and the concentration of conductive nano-grains significantly changes as a function of the film deposition parameters [3]. Doped films show a quite different behavior: nanocrystals are still more conductive than the surrounding tissue, but the most conductive nanocrystals are mainly located within the “valley” of the structure, i.e. at the boundaries between the columns (fig.2). For undoped material, conductivity measurements as a function of temperature revealed a Meyer Neldel Rule (MNR) for materials grown at a dilution factor between 1 and 6% and temperature range from 240 to 340 K. It is, thus, likely that these materials have a similar microstructure and that the conduction involves the amorphous phase, our MNR parameters being close to the one found for amorphous silicon. However, since the activation energy values is low and the conductivity relatively high, it is also possible that the conduction occurs through the crystalline phase as well, in agreement with C-AFM results. At higher dilution factors we observe a decrease in conductivity up to typical values for amorphous which seems more sensitive to the silane flow than to the dilution. We observe a strong enhancement of conductivity while increasing the doping ratio up to a threshold from which the conductivity decreases. Most probably, after saturating the substitutional sites, additional boron atoms will be incorporated on interstitial site in whic...

Hydrogenated nanocrystalline silicon films (nc-Si:H) is a very promising material for photovoltaic applications. Notwithstanding its interesting properties, many issues regarding its electronic and optical properties and the influence of structural defects on them are not completely understood yet. This is due to the fact that nc-Si:H is a very complex material due to the coexistence of different phases: crystalline nano-grains, nanocrystalline columns, hydrogenated amorphous Si (a-Si:H), defects and voids. Surface Photovoltage Spectroscopy (SPS) [1] is a valuable method for the non-contact and non-destructive investigation of several semiconductor properties, such as optical band-gap, defect-related optical transitions, Van Hove singularities or phase inhomogeneities. Hydrogenated nanocrystalline Si films for photovoltaic applications were analysed by SPS. The films have been deposited by Low Energy Plasma Enhanced Chemical Vapor Deposition on different substrates (crystalline Si, oxidized crystalline Si, glass, glass covered by transparent conductive oxide), at deposition temperature around 200 °C and SiH4 dilution ratio d= [SiH4]/([SiH4]+[H2]) ranging from 1% to 50%. The crystal fraction, measured by Raman spectroscopy, ranges from 25 to 75%. Surface Photovoltage spectra allowed for the determination of defect states, energy gap and Urbach tails in the films. Several characteristics of the films were obtained: slight n-type conductivity, optical gap around 1.5 eV, Urbach tails around 50meV and the presence of intra-gap transitions relevant to defective states. One example of a surface photovoltage spectrum of highly crystalline nc-SI:H film is reported in Fig.1, while a sketch of the band structure of the film, as obtained by SPS, is shown in fig.2. Intra-gap transitions in nc-Si:H are often attributed to dangling bonds. In the present study, a tentative identification of the defects responsible of such transitions has been carried out: as SPV spectra measured before and after H etching showed a very similar behavior, thus intra gap transitions should be not related only with dangling bonds, that should reduce their concentration after H-induced passivation. Optical transitions (around 1.86 eV and 1.14 eV) were also detected and attributed to the optical gap of the amorphous phase and crystalline phases, respectively. The comparison between films grown at different dilution ratios and with different cristallinity has allowed us to localize the defects responsible for intra-gap optical transitions, i.e. to attribute them to a certain phase in the material. The role played by the different phases on the optical properties of the film is also clarified. One of the most interesting physical issues regarding photovoltaic applications concerns the optical properties, in this respect SPS is a valuable tool as it allows the determination of optical properties in a non-destructive and non-contact mode.

Structural analysis of nanocrystalline Silicon layers deposited on oxidized and non-oxidized silicon substrates and on glass substrates by low-energy plasma-enhanced chemical vapour deposition technique was fulfilled by means of transmission electron microscopy. Low magnification and high resolution observations of specimens performed in plan-view and cross section are described and discussed. These results are compared to those obtained by atomic force microscopy study. Growth modes and relevant structural changes are tentatively correlated to elaboration parameters.

Hydrogenated nanocrystalline silicon (nc-Si:H) is a very promising material for photovoltaic applications. Notwithstanding its wide application as the intrinsic layer in solar cells, many issues regarding its electronic and optical properties are not completely understood. The present contribution aims to report on electrical and optical characterization of nanocrystalline Si thin films grown by low energy plasma enhanced chemical vapour deposition (LEPECVD) as starting material for Si based thin film solar cells. Optical and electrical properties were studied in order to understand the role played by electronic levels associated with defect states and to study the electrical conduction mechanisms at the nanoscale. Optical and electrical characterizations were carried out by surface photovolage spectroscopy (SPS) and conductive atomic force microscopy (C-AFM), respectively.

Hysteretic behaviour, as found in the dump combustor facility at GALCIT, allows nonlinear active control of the instability, demonstrated recently by Knoop et al. (1996). As in that work, pulses of secondary fuel, based on a simple on/off control law, have been successfully used to drive the transition between the two modes present in the hysteretic region, thereby reducing the amplitude of the pressure oscillations with minimal use of fuel. In order to clarify the origin of the phenomenon, high speed shadowgraph images of the flowfield during the transition between 'unstable' and stable burning have been taken, showing distinctive features that may help in modeling the observed behaviour. A preliminary parametric study (type of injector, duration of pulses, type of secondary flow) has also been conducted, showing that the transition can be obtained over a broad range of conditions.

One of the fundamental ingredients for quantum cryptography and quantum information applications is the fabrication of single and entangled photon emitters. Single photon emitter should produce exactly a single photon on demand, should work not only at cryogenic temperature and should be easy to produce and to integrate on existing electronic devices. In this work, we present the fabrication and characterization of single photon emission from high quality GaAs quantum dots (QDs) by droplet epitaxy (DE) and from impurity centers in AlGaAs layers grown on Si through a thin Ge buffer layer deposited by Low Energy Plasma Enhanced Chemical Vapour Deposition (LEPECVD). The deposition of a thin Ge layer by LEPECVD and subsequent annealing cycles allow for the reduction of threading dislocation density down to few 107 cm-2. DE is an intrinsically low thermal budget technique, being performed at temperatures between 200 and 350 °C. This makes DE perfectly suited for the implementation of growth procedures compliant with back-end integration of III-V nanostructures on CMOS. GaAs QDs with a density of few 108 cm-2 and a mean height of 8 nm are fabricated by DE inside a Al0.3Ga0.7As barrier. Bright and sharp emission lines are observed in a micro-photoluminescence experiment around 700 nm, with pure radiative excitonic lifetime and clear evidence of exciton-biexciton cascade. The achievement of quantum photon statistics is directly proved by antibunching in the second order correlation function as measured with a Hanbury Brown and Twiss interferometer up to T=80 K, thus making the single photon emitter working at liquid nitrogen temperature and compatible with present CMOS technology. The optical quality of the GaAs quantum dots grown on Si substrate is almost comparable with quantum dots directly grown on GaAs substrates. We also show that the epitaxial growth of thin layers of Al0.3Ga0.7As on GaAs buffer layers grown on Si and Ge substrates allows to obtain a single photon source by exploiting the strewn and unintentional contamination with defects of the Al0.3Ga0.7As. Very bright and sharp single photoluminescence lines are observed in confocal microscopy. These lines behave very much as single excitons in QDs, but their realization is by far much easier, since it does not require 3D nucleation or spatially selective doping. The photon antibunching is demonstrated by time resolved Hanbury Brown and Twiss measurements. In both cases (GaAs QDs by DE and impuritues in AlGaAs layer) it is clearly demonstrated a new procedure for the integration of high efficient light emitters, based on III-V semiconductors, directly on Si substrates, and opening the route to wide applications to optoelectronics, photonics and quantum information technology.

We report on triggered single photon emission from GaAs quantum dots, grown on Si substrates and obtained by means of fabrication protocols compatible with the monolithic integration on Si based microelectronics. Very bright and sharp individual exciton lines are resolved in the spectra and can be followed up to 150 K. The nature of quantum emitters of single photon pulses can be measured up to liquid nitrogen temperature by Hanbury Brown and Twiss interferometric correlations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4726189]

Monolithic integration of dissimilar materials with Si microelectronics by hetero-epitaxial growth, a process by means of which all the components are manufactured on the same piece of Si substrate, has been an active research topic for many years. The epitaxial growth of layers differing in lattice parameter and thermal expansion coefficients poses, however, a number of problems detrimental to device processing, yield and performance, such as dislocations, wafer bowing or even layer cracks. The latter become especially relevant at larger layer thicknesses, required for a number of applications, such as high-brightness LEDs, power electronic devices, multi-junction solar cells. We eliminated these disadvantages by a new approach in which layers are partitioned into arrays of disconnected single crystals by a mechanism of self-limited lateral growth. Our approach, tested so far for group IV epitaxy, consists of the following steps. First a Si substrate is patterned into high-aspect ratio pillars or ridges by conventional photolithography and deep reactive ion etching, to expose limited areas on which to grow Ge and Si 1-xGe x layers. Subsequent epitaxial growth by low energy plasma enhanced chemical vapor deposition (LEPECVD) takes advantage both of geometric shielding of the growth species arriving at the patterned substrate surface, as well as of growth parameters (e.g. low temperature, high growth rate) designed to limit the surface diffusion length, thus favoring vertical over lateral growth. This results in a uniform space-filling array of three dimensional epitaxial crystals. Surprisingly, the observed self-limited lateral expansion leaves an air gap between the neighboring crystals of the order of just several tens of nanometers, thus preventing their coalescence. The formation of these arrays was found to be remarkably independent of the thickness of the deposit and the details of the substrate patterns. It does not even depend on the lattice and thermal mismatch, as a comparison of pure Si, Si0.6Ge0.4 alloy and pure Ge crystal arrays shows. Threading dislocations are expelled to the edges of faceted crystals, leaving the bulk of the material defect-free. Cracks can neither form nor propagate, and wafer bending, often precluding further processing, is minimized. The crystalline quality, tilt and strain of the Ge and Si 1-xGe x crystals were investigated by high resolution X-ray diffraction (XRD) with reciprocal space mapping (RSM) around the Si(004) and Si(224) reflections. The results provided evidence for the nearly perfect crystal structure of the epitaxial material, and showed the crystals grown on the Si pillars to be strain-free. Synchrotron submicron diffraction experiments performed with a focused (300x500 nm) X-ray beam revealed tilted small tilt of epitaxial Ge crystals with respect to the Si pillars. Faceted crystals with height, size and shape tunable over a wide range by growth and substrate parameters, are shown to be defect-free by transmission electron microscopy and defect etching. The electrical properties of p-i-n heterojunctions between the epitaxial crystals and the Si-substrate and the interplay between surface and volume effects were investigated by in-situ SEM conductivity experiments. The measured I-V characteristics showed clear diode behavior with dark currents of the order of 10 -4 A/cm 2. While we have provided the proof of concept only for group IV semiconductors, we believe the new mode of hetero-epitaxial crystal growth to be applicable to most materials combinations used for the fabrication of semiconductor devices. The novel approach opens up the possibility of fabricating monolithically integrated X-ray or particle detectors requiring tens or even hundreds of microns of epitaxial material. © 2012 IEEE.

InGaAs/GaAs quantum wells (QWs) grown on micro-patterned Ge/Si substrates by metal organic vapor phase epitaxy are investigated by electron microscopy and spatially resolved photoluminescence (PL) spectroscopy. The lattice parameter mismatch of GaAs and Si is overcome by a Ge buffer layer grown by low-energy plasma enhanced chemical vapor deposition. The GaAs crystals form truncated pyramids whose shape is strongly affected by the geometry of the underlying pattern consisting of 8 micrometers deep and 3–50 micrometers wide square Si pillars. Comparing the measured PL energies with calculations performed in the effective mass approximation reveals that the QW Emission energies are significantly influenced by the GaAs morphology. It is shown that the geometry favors indium diffusion during growth from the inclined facets towards the top (001) facet. The Si pillarsize dependent release of thermally induced strain observed in the PL measurements is confirmed by X-ray diffraction.

Active control of longitudinal pressure oscillations in a combustion chamber is studied theoretically by means of a low order model obtained by systematic reduction from a complete representation. The formulation is based on the derivation of a generalized wave equation that accommodates the effects of mean flow, combustion, noise and control action. By using spatial averaging, the equations describing the dynamics of the chamber are reduced to a set of coupled ordinary differential equations, representing the motions of a system of coupled oscillators. The form of the resulting equations is particularly convenient for model reduction and for introducing feedback control terms, while retaining all physical processes. The oscillator equations are then rewritten in state-space form. Simulations are carried out to investigate in a unified fashion various aspects of the problem. These include the influences of noise, parameter uncertainties, unmodeled modes and a single timedelay. A criterion is derived that guarantees stability of the controlled closed-loop system in the presence of those quantities. The particular controller used here is based on a standard LQR design, but any design technique can be used as long as the stability criterion is fulfilled.

Considerable data exists suggesting that the response functions for many solid propellants tend to have higher values, in some ranges of frequencies, than predicted by the conventional QSHOD theory. It is a familiar idea that such behavior is associated with dynamical processes possessing characteristic times shorter than that of the thermal wave in the condensed phase. The QSHOD theory, and most of its variants, contains only the dynamics of that process, which normally has a characteristic frequency in the range of a few hundred hertz. Two previous works seeking to correct this deficiency (T'ien, 1972; Lazima and Clavin, 1992) have focused their attention on including the dynamics of the thermal wave in the gas phase. Both include effects of diffusion that complicate the analysis although the second achieves some simplification by applying the ideas of 'activation energy asymptotics'. While their results differ in detail, both works show influences at frequencies higher than those near the broad peak of the response due to the thennal wave. Recent theoretical work and simulations show that a combustion response function based on simple pressure coupling is not enough to explain the characteristics of the instability observed experimentally. Namely, differences in the shape of the response function fail to reproduce the differences observed experimentally in the characteristics of the limit cycle reached by combustion chambers with propellants of different chemical (or physical) composition. On the other hand, velocity coupling in the combustion response seems a promising mechanism able to predict the changes in the unstable modes observed experimentally and to produce considerable effect on the shape of the resulting limit cycle. The Baum and Levine model is used as a starting point in the investigation of velocity coupling. Other models, in which the mass burning rate is modified by some function of the velocity, are also investigated through direct time-simulation and by the use of a continuation method. Modeling of particle damping at high frequency constitutes a serious consideration in the modeling of the interaction of combustion dynamics and chamber acoustics. The effect of particle size distribution is analyzed by considering an experimental particle size distribution. The ultimate goal of this work is to find a link between the global dynamics of the combustion chamber and small changes in the combustion dynamics, caused by differences in propellant chemical composition or physical characteristics (for example, particle size and distribution). Response functions are shown for realistic ranges of the chief parameters characterizing the dynamics of the propellant. The results are also incorporated in the dynamical analysis of a small rocket motor to illustrate the consequences of the combustion dynamics for the stability and nonlinear behavior of unsteady motions in a motor.

Considerable data exists suggesting that the response functions for many solid propellants tend to have higher values, in some ranges of frequencies, than predicted by the conventional QSHOD theory. It is a familiar idea that such behavior is associated with dynamical processes possessing characteristic times shorter than that of the thermal wave in the condensed phase. The QSHOD theory, and most of its variants, contains only the dynamics of that process, which normally has a characteristic frequency in the range of a few hundred hertz. Two previous works seeking to correct this deficiency (T’ien, 1972; Lazima and Clavin, 1992) have focused their attention on including the dynamics of the thermal wave in the gas phase. Both include effects of diffusion that complicate the analysis although the second achieves some simplification by applying the ideas of ‘activation energy asymptotics’. While their results differ in detail, both works show influences at frequencies higher than those near the broad peak of the response due to the thermal wave. The work reported in this paper has the primary purpose of constructing a simple model of the problem so that the possible dynamics of the thin region adjacent to the interface of the condensed phase may be incorporated and investigated in heuristic fashion, with and without approximations in the gas phase. It is well known from many observations, both with high-speed films and from pictures taken with scanning electron microscopes, that the surface of a burning solid propellant is certainly not smooth and in general contains both liquid and solid particles. For metallized propellants the agglomeration of aluminum drops is an important process affected, for example, by small amounts of impurities or additives. The dynamics of this region may be significant to the response of a burning propellant to external disturbances, but this phenomenon has not been previously been studied. In OUT analysis we include both phenomenological modeling of that surface layer as well as the thermal waves in both the gas and solid phase. Particular attention is given to the selection of the boundary conditions and their effect on the solution of the problem. Assumptions made in the analytical approach are tested against direct numerical integration of the relevant equations. Response functions are shown for realistic ranges of the chief parameters characterizing the dynamics of solid phase and surface layer. The results are also incorporated in the dynamical analysis of a small rocket motor to illustrate the consequences of the combustion dynamics for the stability and nonlinear behavior of unsteady motions in a motor. That is part of the primary objective of the Caltech MURl program, to understand the influences of propellant composition and chemistry on the global dynamical behavior of a solid rocket combustor by connecting the microscopic and macroscopic through the response function.

This paper is a report of work in progress, part of the Caltech MURI Program: Novel Energetic Materials to Stabilize Rocket Motors. The primary technical objective of the MURI Program is to understand the connections between propellant composition and chemistry, and the dynamical behavior observed in solid propellant rocket motors. Here we are concerned with the theoretical framework in which chamber dynamics are investigated; and certain aspects of combustion dynamics represented by the response function which is ultimately the macroscopic realization of the propellant chemistry and combustion. Some results are given to illustrate possible influences of the frequency spectrum of the response function on linear and nonlinear motions in a solid rocket. A simple model is described which is extended eventually to provide a way to model phenomenologically some of the observed characteristics of the combustion dynamics of a burning solid propellant.

Erratum to: Nanoscale Res. Lett.DOI 10.1007/s11671-010-9689-8The authors’ affiliations have been published incorrectly.Correct authors’ affiliations:S.Bietti,C.Somaschini,E.Sarti ,N.Koguchi,S.Sanguinetti(*)L-NESS and Dipartimento di Scienza dei Materiali,Universita’ di Milano Bicocca, Via Cozzi 53, 20125Milano, Italye-mail: stefano.sanguinetti@mater.unimib.itG. Isella, D. Chrastina, A. FedorovCNISM, L-NESS and Dipartimento di Fisica delPolitecnico di Milano, Via Anzani 42, 22100 Como, Italy

Hydrogenated nanocrystalline silicon (nc-Si:H) is a very promising material for photovoltaic applications. Notwithstanding its wide application as instrinsic layer in solar cells, many issues regarding its electronic and optical properties are not completely understood. The influence of crystal defects and impurities on the physical properties of nc-Si:H is not completely explored yet. The present contribution aims to report on defective states associated with crystal defects and impurities in nc-Si:H films grown by low-energy plasma enhanced chemical vapor deposition (LEPECVD) technique. Electronic levels associated to defect states were investigated by surface photovoltage spectroscopy (SPS) and the role of defects and impurities on the conduction mechanisms at a microscopic level were investigated by conductive atomic force microscopy (C-AFM). The results will be compared with structural analyses

Hydrogenated nanocrystalline silicon for photovoltaic application has been investigated by scanning force microscopy studies. Morphological properties as well as electrical properties have been investigated with high spatial resolution by scanning force microscopy analyses (AFM, Atomic Force Microscopy and C-AFM conductive AFM). Transmission Electron Microscopy (TEM) studies have been also carried out for structural characterization. The main problem regarding the electronic properties is to understand where the current flows. Actually the question has remained unresolved due to conflicting literature data. The present contribution aims to clarify which of the material phases mainly contributes to the conduction mechanisms.