Ixs from polycrystalline samples

Neutron Brillouin scattering NBS is an inelastic neutron scattering near the forward direction. This technique is effective for observing coherent excitations in non-single-crystal samples, such as ferromagnetic spin waves in powder samples and acoustic phonons in liquids and polycrystals.

Such excitations can be observed by accessing the energy-momentum space around the zero momentum. Although the principle of NBS is not new, the recent progress of intense pulsed neutron sources provides opportunities to realize the experimental conditions for NBS more conveniently by utilizing neutrons with higher energies and higher resolutions.

The aim of NBS is to become a promising experimental method combined with intense pulsed neutrons for a wide range of scientific studies. Advanced Search. JPS Conf. Sorry, you do not have access to this content.

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Shinichi ItohYasuo Endoh. Online access to the content you have requested requires one of the following:. You have requested the following content:. Remember me. Choose from the following options:.Crystalline vs Polycrystalline. Although we define solids as crystalline or amorphous, in nature there are few examples of these pure forms.

Most of the time, they are mixed together or form variations. Polycrystalline is such a variation from the crystalline solids. Here, we will look into the differences between crystalline and polycrystalline in detail. Crystalline can be a crystal, composed of crystal, or resemble a crystal. Crystalline solids or crystals have ordered structures and symmetry.

The atoms, molecules, or ions in crystals are arranged in a particular manner, thus have a long-range order. In crystalline solids, there is a regular, repeating pattern; thus, we can identify a repeating unit. Examples are halite, salt NaCland quartz SiO 2. But, crystals are not restricted to minerals: they comprise most solid matters such as sugar, cellulose, metals, bones, and even DNA.

Crystals are formed by living organisms too. For example, calcite is produced by mollusks. There are water-based crystals in the form of snow, ice or glaciers. Crystals can be categorized according to their physical and chemical properties.

They are covalent crystals e. Crystals can have different shapes and colors. Crystals have an aesthetic value, and it is believed to have healing properties; thus, people use them to make jewelry. Other than being a crystal, some solids may resemble a crystal by adopting some of its properties. For example, these can be sparkly, transparent or clear, or have the structure similar to a crystal.

In nature, most of the time, crystals appear to have disrupted their long-range order. Polycrystalline are solids that are composed of many numbers of small crystals. These are arranged in different orientations and are bound by highly defective boundaries. The crystals in a polycrystalline solid are microscopic, and they are known as crystallites. These are also known as grains. There are solids, which are composed of a single crystal like gems, silicon single crystals. However, these occur very rarely in nature.

Most of the time solids are polycrystalline.Metrics details. Here, we review techniques and methodologies used to measure sound velocities in metals at megabar pressures, with specific focus on the compressional sound velocity of hexagonal close-packed iron.

ixs from polycrystalline samples

A critical comparison of literature results, coherently analyzed using consistent metrology pressure scale, equation of stateallows us to propose reference relations for the pressure and density dependence of the compressional velocity of hexagonal close-packed iron at ambient temperature.

Iron Fe has always attracted considerable interest in fundamental physics and chemistry, as well as materials science, due to its primary role in a great variety of technological applications. The physical properties of Fe at high pressure and high temperature also have unique relevance for Earth and planetary science, since all the telluric planets share the same basic layered nature: a central metallic core, made mostly of iron, surrounded by a silicate mantle and a thin, chemically differentiated crust.

Amongst the remote sensing techniques we have to rely on, seismology is certainly one of the most direct. However, to derive an accurate compositional model, these seismic observations have to be combined with experiments or calculations constraining the density and elastic properties of highly compressed candidate materials.

In this respect, compressional-wave V P and shear-wave V S sound velocities play a fundamental role, as two of the few parameters that can be directly compared with the seismic observations.

Since then, a large number of experimental and theoretical studies have addressed the sound velocities of solid iron at extreme conditions. Over the last 15 years, a great deal of effort has been devoted to the development of experiments capable of probing elasticity and sound velocity of opaque metallic samples at high static pressure, with iron providing much of the motivation.

Current data sets, however, even including those based on indirect determinations, are generally limited to pressures of the order of to GPa at ambient temperature, and very few results exist at simultaneous high pressure and temperature.

Most importantly, different studies are not always in agreement. These limitations become very critical when attempting to estimate the nature and amounts of light elements, whose presence as impurities in the inner core is required to modify the density and velocity of iron to match seismic observations.

In this paper, we intend to briefly review the techniques for sound velocity determinations. Finally, the proposed velocity-density relationship will be discussed in relation to potential high-temperature effects.

Conversely, sound velocity measurements of iron under static compression turned out to be an experimental challenge. Conventional pulse-echo ultrasonic techniques require sample dimensions large enough to avoid overlap of successive acoustic echoes and, hence, experimental volumes of several cubic millimeters, hardly compatible with experimentation at megabar pressures. Gigahertz interferometry has been proposed as a possible solution to overcome these hindrances, but applications at very high pressure are still limited e.

Jacobsen et al. Only very recently, measurements of acoustic echoes in samples compressed in diamond anvil cells became possible thanks to the developments in time-resolved pump-probe techniques laser ultrasonicsboth in the nanosecond time scale Chigarev et al.The shape of the frequency distribution function g of the normal modes of vibration of a crystal determines an important part of its properties, since it contains many relevant elastic and thermodynamic information.

From the overall spectrum, temperature dependencies of the lattice contribution to the specific heat and the internal energy, the vibrational entropy, the mean force constant and the Debye temperature are obtained, whereas from the low frequency part the Debye velocity can be derived, giving access to aggregate elastic properties. Experimentally, gor the vibrational density of states VDOSis commonly determined by inelastic neutron scattering INS or by nuclear inelastic scattering.

Here, we show that inelastic X-ray scattering IXS offers an alternative experimental method. In analogy to coherent INS, inelastic scattering spectra of polycrystalline samples have to be recorded over a large range of momentum transfers Qbut due to the Q -dependence of the atomic form factor, this sampling range needs to be optimised.

We have developed semi-quantitative criteria, which are independent of any specific lattice dynamics model, and result only from simple symmetry considerations.

Monocrystalline and polycrystalline solar panels: what you need to know

The advantage of their use is that no a priori knowledge of the lattice properties is needed. The validity of our approach was checked by comparison of results for diamond with ab initio lattice dynamics calculations [1] and thermodynamic measurements. The momentum resolution was set to 0. As the spectrometer arm is equipped with five analysers, the spectra were recorded for two angular settings of the spectrometer arm, thus covering a Q-range from 60 to 75 nm -1 approximately and yielding ten IXS spectra.

For the data treatment we followed the same approach as for nuclear inelastic scattering, where the multiphonon term is eliminated simultaneously with the deconvolution of the data with the instrumental function [2]. Figure 16 shows the VDOS obtained, together with the result of an ab initio calculation [1].

The agreement is quite remarkable: the position of special points is nearly identical, and the high-energy peak, due to the overbending of the optical phonon branch, is clearly visible. The excellent quality of our experimental VDOS allowed the determination of several macroscopic parameters such as the specific heat at constant volume, the low- and high-temperature limit of the Debye temperature Dand the Debye velocity V D.

Table 1 shows a selection of our derived macroscopic parameters, compared to other experimental results. These values give an appropriate description of the macroscopic aggregate elasticity of diamond. Further experiments were performed on MgO, BN zincblende and wurtzite polymorphs and various ice polymorphs. The general applicability of the method for the study of elementary solids is easily estimated, showing that the VDOS can be determined with an appropriate accuracy for essentially all elemental solids.

One of the potential applications of this novel technique is the VDOS determination of samples submitted to very high pressures. In this case the signal level for elements heavier than, say, scandium should be sufficiently high to allow measurements on tiny amounts of samples as in a diamond anvil cell. It is worth noting that with respect to INS, the amount of material needed is orders less, and anomalous absorption like for B, Cd, Gd… or anomalously high cross-sections H are not present.

Since the scattering strengths for neutrons and X-rays are essentially different, it opens the possibility to extract directly the partial densities of states in at least binary systems from combined measurements. Pavone et al. B, 48 Kohn and A. Chumakov, Hyperfine Interactions Zouboulis, M.Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer.

In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride h-BN films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration.

By performing equilibrium molecular dynamics EMD simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures.

Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. The great success of graphene 123 with its extraordinary combination of high thermal conductivity 45mechanical strength 6 and electrical properties 7 raised an ongoing attention towards other two-dimensional 2D materials.

Numerous experimental and theoretical studies have confirmed the outstanding and broad prospects for the application of 2D materials: from flexible nanoelectronics to aerospace structures.

However, the high electrical conductivity of graphene forbids its application in devices where the building blocks are required to be electrically insulating. Nevertheless, several other 2D materials with inherent semiconducting properties have been fabricated such as hexagonal boron-nitride h-BN 8molybdenum disulfide MoS 2 9 and triazine-based graphitic carbon nitride g-C 3 N 4 nanosheets Among the available 2D semiconducting materials h-BN possesses the highest thermal conductivity and mechanical strength 111213 Similarly to graphene, h-BN presents a honeycomb lattice in which carbon atoms are replaced with alternating pairs of boron and nitrogen atoms.

Because of this similarity in atomic structure, graphene and h-BN have been proposed as candidates for the construction of hetero-structures with tuneable physical properties 15 Analogous to graphene, chemical vapor deposition CVD is the major route to produce large-scale h-BN films 17 However, crystal growth during the CVD method yields polycrystalline structures.

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Therefore, CVD grown h-BN films consist of different grains which are connected by grain boundaries throughout the sample. Grains with different growth orientations match together through grain boundaries that include various types of topological defects. Like all other known materials, these defects in CVD grown h-BN films affect their intrinsic physical properties.

Defects along the grain boundaries cause stress concentration and phonon scattering. In particular, these effects could lead to lower mechanical strength and thermal conductivity 192021 In polycrystalline structures, as the grain size decreases, more grain boundaries form resulting in higher defect concentrations.

Accordingly, a comprehensive understanding of the effects of grain size on the physical properties of h-BN films is of crucial importance. From the experimental or the theoretical point of view, few studies exist concerning the atomic structure of grain boundaries in h-BN films.

Meanwhile, a transmission electron microscope study of CVD grown h-BN films indicates that the grain boundaries consist mainly of pentagon-heptagon pairs rather than square-octagon pairs Both theoretical calculations and experiments also reveal that defect pairs in h-BN grain boundaries include homo-nuclear boron-boron or nitrogen-nitrogen bonds, which are higher in energy than heteronuclear boron-nitrogen bonds inside the grains.

To date, heat conduction in polycrystalline h-BN films has not been addressed neither theoretically nor experimentally. Because of the complexity of such experimental studies at the nanoscale, computer simulations offer an alternative approach 25 In the present work, we conducted classical molecular dynamics MD simulations to provide detailed information concerning the influence of grain size on the thermal conductivity of polycrystalline h-BN sheets.

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Additionally, we investigated the thermal conductivity of macroscopic films using the finite element FE method. In our FE models, all grain boundaries were assumed to present an effective contact conductance. This effective thermal conductance was estimated by fitting the FE results to those obtained by MD simulations.

Our atomistic-continuum multiscale modelling reveals that CVD grown h-BN films can exhibit high thermal conductivity, remarkably close to that of monocrystalline, defect-free sheets.Read this paper on arXiv. Phonon dispersion relations and vibrational density of states are reported and the phonon eigenvectors analysed by a detailed comparison of scattering intensities. The experimentally validated calculation is used to identify the vibration contributing most to the first peak in the density of vibrational states.

Natural crystals are usually twinned [ 2 ]. It furthermore exhibits a mass density 2.

No document with DOI "10.1.1.1080.3311"

These observations strongly suggest that, similar to crystals, the excess of vibrational states in glasses originates from the piling up of the acoustic-like branches near the boundary of the pseudo-Brillouin zone. A measurement of the full dispersion relation and the investigation of the vibration contributing most to the first peak in the VDOS is not reported.

Dynamical matrices and derived properties are calculated from first principles and compared to experiment. The distribution of low energy features over reciprocal space is analysed by x-ray diffuse scattering.

ixs from polycrystalline samples

The scattering intensities are confronted to calculated thermal diffuse scattering TDS and compared to predictions from a rigid unit model [ 16 ] and electron diffraction [ 17 ]. Selected regions in reciprocal space are further investigated using inelastic x-ray scattering IXS which is also used to measure the dispersion relation along selected directions and the VDOS.

Finally, the observed displacement patterns are put into relation with atomic motions reported for vitreous silica [ 18 ] to make the connection to the Boson peak. An octahedral single crystal with 0. One major twin and some mosaic spread were observed during the x-ray diffuse scattering. One domain could be isolated for the experimental study thanks to the small x-ray beam size, and only a small contribution from the other twins was observed. The samples revealed pure single-phase patterns.

The crystalline quality was checked by x-ray diffuse scattering. Clear patterns of diffraction rings without noticeable effects of structural disorder were observed. Monochromatic X-rays with The sample was rotated with an increment of 0. The orientation matrix and geometry of the experiment were refined using the CrysAlis software package.

The spectrometer was operated at Energy transfer scans were performed at constant momentum transfer Q in transmission geometry along selected directions in reciprocal space. Further details of the experimental setup and the data treatment can be found elsewhere [ 21 ]. IXS spectra were taken at momentum transfers chosen away from the Debye-Scherrer rings. The data combine measurements with 1. The elastic peak in the IXS spectra was subtracted using the instrumental resolution function determined from a polymethylmethacrylate PMMA sample at momentum transfers close to the maximum of its structure factor.

We apply the local density approximation LDA with the exchange correlation functional by Perdew and Zunger [ 26 ] and use the plane-wave formalism with norm-conserving pseudopotentials of the optimised form [ 27 ].Effective date : A polycrystalline silicon wafer is provided.

The polycrystalline silicon wafer, includes a plurality of silicon grains, wherein the carbon content of the polycrystalline silicon wafer is greater than 4 ppma, and the resistivity of the polycrystalline silicon wafer is greater than or equal to 1. A solar cell is a photoelectric device which generates electric energy by absorbing sunlight and performing photovoltaic conversion by means of a photovoltaic effect. Currently, solar cell materials are mainly silicon materials, as silicon is the second most accessible element on earth and has advantages of having low material cost, is nontoxic, has a high stability and the like, and the application of silicon in the semiconductor field has had a profound foundation.

Solar cells mainly made from silicon material are divided into three types, i. Using polycrystalline silicon as the raw material of a solar cell is mainly based on the consideration of cost. As compared with monocrystalline silicon manufactured by the existing Czochralski method CZ method and floating zone method FZ methodthe cost of the polycrystalline silicon is much cheaper relatively.

The polycrystalline silicon used for manufacturing solar cells is conventionally produced by using a general casting process.

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In brief, the silicon with a high purity is melted in a mold e. Then, the polycrystalline silicon ingot is generally cut into square wafers, which will be assembled into a cell by a solar cell manufacturer. The Journal of Crystal Growth, p.

As disclosed in the conventional method as described above, and generally conventionally understood, in the crystal-growing process volatile carbon monoxide gas can be easily generated and, if the content of the carbon monoxide incorporated into a silicon melt is too high, the carbon and oxygen will segregate and separately precipitate or otherwise be incorporated into the solidified crystal formed from the melt.

The oxygen-containing sites of a solidified ingot are known to behave as gettering sites for impurities and the influence the mechanical strength of a wafer formed therefrom, which can increase the effect of other crystal defects on degrading the crystal quality.

Furthermore, the carbon incorporated in the conventional method as described above can easily generate a silicon carbide precipitate through the reaction between the carbon and silicon in the melt, which may reduce the shunt resistance R shunt of a cell, thereby causing more electric leakage phenomenon.

Therefore, it is believed by those of ordinary skills in the art that, the too-high carbon and oxygen content causes the aforementioned instance, and thus the photovoltaic conversion efficiency is degraded. The aforementioned description is only used for providing the background technology, rather than admitting that the aforementioned description discloses the subject matter of the disclosure.

The aforementioned description does not constitute the prior art of the disclosure, and any of the aforementioned description should not be considered as any part of the disclosure. An embodiment of the disclosure provides a polycrystalline silicon column having a crystal-growing direction. The aforementioned polycrystalline silicon column includes a plurality of silicon grains growing along a crystal-growing direction, wherein in the crystal-growing direction, the average grain size of the silicon grains and the resistivity of the polycrystalline silicon column have opposite variation in their trends.

Another embodiment of the disclosure provides a polycrystalline silicon column having a crystal-growing direction. The aforementioned polycrystalline silicon column includes a plurality of silicon grains growing along a crystal-growing direction, wherein in the crystal-growing direction, the average grain size of the silicon grains and the oxygen content of the polycrystalline silicon column have opposite variation in their trends.

A further embodiment of the disclosure provides a polycrystalline silicon column having a crystal-growing direction. The aforementioned polycrystalline silicon column includes a plurality of silicon grains growing along a crystal-growing direction, wherein in the crystal-growing direction, the average grain size of the silicon grains and the defect area ratio of the polycrystalline silicon column have the same variation in their trends, and the overall average defect area ratio of the polycrystalline silicon column is less than or equal to 2.

ixs from polycrystalline samples

Another embodiment of the disclosure provides a polycrystalline silicon wafer including a plurality of silicon grains, wherein the polycrystalline silicon wafer has a carbon content greater than 4 parts per million atoms ppmaand a resistivity greater than or equal to 1. A further embodiment of the disclosure provides a polycrystalline silicon wafer including a plurality of silicon grains, wherein the polycrystalline silicon wafer has a carbon content greater than 4 ppma, and an oxygen content greater than or equal to 5.

Yet a further embodiment of the disclosure provides a polycrystalline silicon wafer including a plurality of silicon grains, wherein the polycrystalline silicon wafer has a carbon content greater than 4 ppma, and an average defect area ratio less than or equal to 1. The polycrystalline silicon column of the disclosure has a higher carbon content, and especially the bottom section thereof has a higher carbon content and a lower defect area ratio, such that the polycrystalline silicon wafer manufactured by cutting the polycrystalline silicon column also has a higher carbon content and a lower defect area ratio, and therefore a higher photovoltaic conversion efficiency.

The technical features and advantages of the disclosure summarized relatively widely above make the detailed description of the disclosure hereafter better understood. Other technical features and advantages constituting the subject matter of the claims of the disclosure will be described hereafter.

It should be understood by those of ordinary skills in the art of the disclosure that, the object of the disclosure can be achieved by modifying or designing other structures or processes.

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It should also be understood by those of ordinary skills in the art of the disclosure that, such an equivalent construction cannot depart from the spirit and scope of the disclosure as defined by the accompanying claims. Aspects of the disclosure will be understood best by reading the following detailed description in connection with the drawings.

It should be noted that, according to the standard implementation of the industry, various features are not drawn to scale. In practical, for clarity of discussion, dimensions of various features may be arbitrarily increased or decreased.

INXS - Disappear

The following disclosure provides many different embodiments and examples to implement different features of the application. The particular examples of elements and configurations are described hereafter so as to simplify the disclosure of the application.


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