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1.
Laetitia Vincent Rym Boukhicha Cyrille Gardès Charles Renard Vy Yam Frédéric Fossard Gilles Patriarche Daniel Bouchier 《Journal of Materials Science》2012,47(4):1609-1613
We report detailed structural analysis of 〈111〉 oriented silicon nanowires (NWs) grown by UHV–CVD using the VLS process with
a gold catalyst. STEM-HAADF observations have revealed an unexpected inhomogeneous distribution of gold nanoclusters on the
NW surface. Gold is mainly distributed on three sides among the six {112}-sidewalls and is anchored on upward {111} facets.
This original observation brought us a new comprehension of the faceting mechanisms. The stability of the 〈111〉 growth direction
needs the formation of facets on {112}-sidewalls with energetically favorable planes. We demonstrate that the initial formation
of covered facets with a three-fold symmetry is driven by the formation of {111} Au/Si interfaces between the nucleated Si
NW and the Au droplet. 相似文献
2.
Morphological features of transgranular fracture facets in low temperature brittle fracture of 18Cr–18Mn–0.7N high nitrogen
austenitic steel have been studied by means of scanning electron microscopy and their formation mechanisms have been discussed.
The transgranular fracture facets are fairly coarse compared with intergranular fracture facets and annealing twin boundary
fracture facets. There are parallel steps and river patterns on the facets. Dual-surface observation indicated that these
patterns are parallel to {111} planes and of strict crystallographic features. Microstructure observation shows that there
are a lot of planar deformation structures formed prior to low temperature transgranular fracture. Transgranular fracture
originates from microcracks formed at the intersections of the deformation structures on different {111} planes. These microcracks
propagate toward adjacent microcracks on different {111} planes, forming transgranular fracture facets with steps and river
patterns. 相似文献
3.
The structures of martensites in a Cu–11.2 wt% Al–3 wt% Ni specimen, which was quenched from 1173 K, have been studied by
high resolution electron microscopy (HREM) and diffraction techniques. Two kinds of martensites, i.e. β′1 and γ′1, coexisting
adjacent to each other in the specimen were observed. The γ′1 matensite consists of microtwins with monoclinic structure.
Three variants of the twin structure, i.e. {1 2 1}, {2 1 0} and {1 0 1} twins, are arranged within a single plate. The β′1
martensite possesses basically ordered N9R structure, but mixed with thin 2H domains. Some diffraction spots of this martensite
shift along the [0 0 1] direction. In addition, extra weak reflections appear in the diffraction pattern due to heterogeneous
atomic displacements. The microstructural features of the martensites are examined and discussed.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
4.
Yasuyuki Kaneno Tetsuo Yamaguchi Takayuki Takasugi 《Journal of Materials Science》2006,41(20):6871-6880
The texture evolution during the hot-rolling and the recrystallization of B2-type Fe–48Al, Ni–50Al and Co–50Ti (expressed
by at.%) intermetallic compounds were investigated. By hot-rolling at 973 K, Fe–48Al showed a microstructure with coarse grains
elongated along rolling direction, while Ni–50Al and Co–50Ti showed a deformed microstructure featured by the heavily distorted
(elongated) grains and/or the deformation bands. The hot-rolling texture of Fe–48Al was composed of {111}<uvw>, while those
of Ni–50Al and Co–50Ti were composed of {111}<110> and {111}<112>, respectively. After annealing, the recrystallized grains
were preferentially nucleated at the grain boundaries for Fe–48Al, and in the heavily distorted regions or the deformation
bands for Ni–50Al and Co–50Ti. The orientations of the recrystallized grains were similar with those of the deformed matrix,
especially for Ni–50Al and Co–50Ti. The recrystallization textures were generally more dispersive than the hot-rolling texture.
Based on these results, the texture evolution during the hot rolling and the recrystallization of the B2-type intermetallic
compounds were discussed. 相似文献
5.
F. E. Cimilli H. Efeoğlu M. Sağlam A. Türüt 《Journal of Materials Science: Materials in Electronics》2009,20(2):105-112
The current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Ag/n-InP/In Schottky diodes have been studied in a wide temperature range by steps of 10 K. A decrease in the apparent barrier
height (BH), , an increase in the ideality factor, and a nonlinearity in the activation energy plot with a decrease in temperature have been seen. The experimental values of
BH and ideality factor for the devices were calculated as 0.61 eV and 1.18 at 320 K, 0.48 eV and 1.52 at 200 K, and 0.20 eV
and 3.89 at 70 K, respectively. An abnormal decrease in the experimental BH and an increase in the ideality factor n with a decrease in temperature have been explained by the barrier inhomogeneities at the metal–semiconductor (MS) interface.
From the temperature dependent I–V characteristics of the Ag/n-InP contact, that is, and A* as 0.79 and 0.55 eV, and 7.96 and , respectively, have been calculated from a modified vs. 1/T plot for the two temperature regions. The Richardson constant values are in close agreement with the value of known for n-type InP. Moreover, the difference between the apparent BHs obtained from the I–V and C–V characteristics has been attributed to the existence of Schottky BH inhomogeneity. 相似文献
6.
We have investigated the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Ru/Pt/n-GaN Schottky diodes in the temperature range 100–420 K. The calculated values of barrier height and ideality factor for the
Ru/Pt/n-GaN Schottky diode are 0·73 eV and 1·4 at 420 K, 0·18 eV and 4·2 at 100 K, respectively. The zero-bias barrier height (Φb0) calculated from I–V characteristics is found to be increased and the ideality factor (n) decreased with increasing temperature. Such a behaviour of Φb0 and n is attributed to Schottky barrier (SB) inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs)
at the metal/semiconductor interface. The current–voltage–temperature (I–V–T) characteristics of the Ru/Pt/n-GaN Schottky diode have shown a double Gaussian distribution having mean barrier heights (
[`(F)]\textb0 {\bar{{\Phi}}_{\text{b}0}} ) of 1·001 eV and 0·4701 eV and standard deviations (σ
0) of 0·1491 V and 0·0708 V, respectively. The modified ln (J0 /T2 )-( q2s 02/2k2T2 ){ln} ({{J}_{0} /{T}^{2}} )-( {{q}^{2}{\sigma} _{0}^{2}/{2}{k}^{2}{T}^{2}} ) vs 103/T plot gives
[`(F)]\textb0 \bar{{\Phi}}_{\text{b}0} and Richardson constant values as 0·99 eV and 0·47 eV, and 27·83 and 10·29 A/cm2K2, respectively without using the temperature coefficient of the barrier height. The difference between the apparent barrier
heights (BHs) evaluated from the I–V and C–V methods has been attributed to the existence of Schottky barrier height inhomogeneities. 相似文献
7.
M. T PEREZ-PRADO M. C CRISTINA O. A RUANO G GONZALEZ-DONCEL 《Journal of Materials Science》1997,32(5):1313-1318
Microstructural evolution on annealing of Al–5 wt% Ca–5 wt% Zn sheet alloy has been systematically investigated by means of
texture analysis and optical and transmission electron microscopy. Heat treatments in the temperature range of 100 to 540
°C for times between 0.11 (7 min) and 90.5 h have been performed. After annealing, the main texture component of the as- received
material, {1 1 3} <3 3 2>, was retained, whereas the minor components, {0 1 3} <3 1 0> and {0 1 1} <1 0 0>, showed clear changes
depending on the annealing conditions. Additional minor components appeared upon heat treatments. Continuous recrystallization,
subgrain accommodation by means of rotation and subsequent extensive grain growth are the processes which account for all
the microstructural changes observed.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
8.
S. M. Rao J. K. Srivastava M. K. Wu B. H. Mok C. L. Chen M. C. Ling H.-L. Liu Y. Y. Chen J. C. Ho 《Journal of Superconductivity and Novel Magnetism》2011,24(4):1249-1262
We report here SQUID (magnetization) measurements, along with supporting specific heat, Raman, SEM (scanning electron microscope),
EDX (energy dispersive X-ray) and XRD (X-ray diffraction) measurements, on Cu-doped and undoped double perovskite Sr22+Y3+Ru5+O62-\mathrm{Sr}_{2}^{2+}\mathrm{Y}^{3+}\mathrm{Ru}^{5+}\mathrm{O}_{6}^{2-} (abbreviated as SrY2116) system grown as single crystal using high-temperature solution growth technique. These measurements
show the undoped system to be a nonmetallic (insulating) spin glass (SG) and the ∼5–30% Cu-doped (i.e. Cu-concentration/(Cu + Ru-concentration)
∼5–30%) system to be a spin glass superconductor (SGSC) with T
c (critical temperature) ∼28–31 K and superconducting volume fraction, f
sc∼2.2–9%. To mention, similar measurements done on undoped and Cu-doped BaY2116 and BaPr2116 systems show for them the same
(SG, SGSC) behaviors. However they show a decrease in T
c and f
sc when diamagnetic Y3+ ions are replaced by Pr3+ spins, presumably due to enhanced internal pair breaking, and also decreased Cu–O–Cu overlap, owing to Pr3+ presence; these phenomena are known to exist in the Pr123 compound, PrBa2Cu3O7−δ
(δ∼0), due to ∼10% of Pr3+ ions having tendency to occupy Ba2+ sites. Measurements done on undoped and Cu-doped SrHo2116 show similar SG and SGSC properties. Further, the undoped and Cu-doped
SrY2116 crystals grown by hydrothermal growth technique (i.e., grown using lower temperature and high pressure) show same
behaviors. From these investigations it can be said that the undoped Ru-double perovskites (A2BB′O6, B′=Ru) are SG systems and that Cu-doped Ru-double perovskites (A2BB′O
δ
, δ∼6, B′=Ru1−x
Cu
x
, 0<x≲0.3) are SG superconductors (SGSCs). Results are discussed. 相似文献
9.
The coarsening behavior of rod-shaped and spherical δ-Ni2Si precipitates in a Cu–1.86 wt% Ni–0.45 wt% Si alloy during aging at 823–948 K has been investigated by measuring both precipitate
size by transmission electron microscopy (TEM) and solute concentration in the Cu matrix by electrical resistivity. The rod-shaped
δ precipitates have an elongated shape along 〈[`5] 5 8 \overline{5} 5 8 〉m and a {110}m habit-plane facet. The coarsening theory of a spherical precipitate in a ternary alloy developed by Kuehmann and Voorhees
(KV) has been modified to a case of rod-shaped precipitates. The coarsening kinetics of average size of the rod-shaped and
spherical δ precipitates with aging time t obey the t
1/3 time law, as predicted by the modified KV theory. The kinetics of depletion of the supersaturation with t are coincident with the predicted t
−1/3 time law. Application of the modified KV theory has enabled calculation of the energies of sphere, {110}m and rod-end interfaces from the data on coarsening alone. The energy of the {110}m interface having a high degree of coherency to the Cu matrix is estimated to be 0.4 J m−2, the incoherent sphere-interface energy 0.6 J m−2, and the rod-end interface energy 5.2 J m−2. 相似文献
10.
We have studied the temperature dependence of carrier mobility (μ) in undoped and gadolinium-doped p-GaSe crystals. The results demonstrate that, in the temperature range 77–420 K, the carrier mobility in high-resistivity
p-GaSe〈Gd〉 crystals increases at low temperatures as a power law. At high temperatures, μ(T) has a maximum and varies roughly as $T^{ - \tfrac{3}
{2}}
$T^{ - \tfrac{3}
{2}}
. In addition, μ is a nonmonotonic function of gadolinium content. The observed anomalies in the temperature dependence of
carrier mobility in the crystals studied are due to partial disorder in these materials. The present experimental data can
be interpreted in terms of a two-barrier energy-band model of partially disordered semiconductors. 相似文献
11.
Basavaraj Angadi V. M. Jali M. T. Lagare N. S. Kini A. M. Umarji 《Bulletin of Materials Science》2002,25(3):191-196
The low thermal expansion ceramic system, Ca1-xSr{x}Zr4P6O24, for the compositions with x = 0, 0.25, 0.50, 0.75 and 1 was synthesized by solid-state reaction. The sintering characteristics
were ascertained by bulk density measurements. The fracture surface microstructure examined by scanning electron microscopy
showed the average grain size of 2.47 μm for all the compositions. The thermal expansion data for these ceramic systems over
the temperature range 25–800°C is reported. The sinterability of various solid solutions and the hysteresis in dilatometric
behaviour are shown to be related to the crystallographic thermal expansion anisotropy. A steady increase in the amount of
porosity and critical grain size with increase in x is suggested to explain the observed decrease in the hysteresis. 相似文献
12.
The transient current were analysed by considering the effect of variation of forming time, temperature, field and composition
of blend specimens. Measurements indicated that transient charging and discharging currents exhibited thermally activated
character but did not show mirror image behaviour at different temperatures and field values. The log I\emph{I}–log t\emph{t} plots were found to follow the Curie–Von Schweidler law with the value of decay constant ‘n\emph{n}’ lying in the range of 0·029–2·9456. These observed characteristics also indicated that the transient charging in PVF:PVDF
fluoro polyblends occur partly due to orientation of dipoles but predominantly due to trapped space charges and hopping of
charge carriers amongst localized states. The modification in transient behaviour on blending PVDF with PVF have been explained
on the basis of plasticization effect which increases free volume and molecular mobility and T
g
modification in the trap structure. 相似文献
13.
K. Zelonka M. Sayer A. P. Freundorfer J. Hadermann 《Journal of Materials Science》2006,41(12):3885-3897
Stoichiometric barium strontium titanate (BST) films of composition
with thickness >2 μm have been fabricated on Si/SiO2/Pt substrates by hydrothermal sol-gel composite processing. This film deposition technique involves the treatment of a spun-on
sol-gel composite film, formed from a suspension of a powder in an aqueous BST sol-gel, at temperatures from 100–200°C at
a pressure of 1–15 atm. An initial hydrolysis procedure eliminates dissolution of the dried sol-gel during the hydrothermal
treatment. Glancing angle X-ray diffraction shows excellent crystallinity and stoichiometry in the BST films with no evidence
of new phases created during processing. Scanning electron micrography and atomic force microscopy show densification of the
film structure and the development of a bridging microstructure. Transmission electron micrography indicates that while much
of the sol-gel derived matrix phase is amorphous a more crystalline interface occurs with the powder particles. The relative
permittivity and loss tangent of the films are measured using a parallel plate capacitor technique in the frequency range
1–100 kHz. At 100 kHz relative permittivities of the films range from ɛr = 400–1200 and loss tangents lie in the range 0.05 < tan δ < 0.10, depending on the parameters of film preparation. The film
structure and morphology and the electrical studies suggest that the microstructure of the films evolves by deposition of
the sol-gel derived BST on the underlying powder, resulting in an electrically interconnected microstructure in which the
sol-gel derived material bridges between the high permittivity powder particles. 相似文献
14.
In this study, a constitutive analysis of the flow responses of Ti–6Al–4V under various strain rates [(e)\dot] \dot{\varepsilon } was conducted by separately quantifying the hardening and softening effects of microstructure, interstitial solute and deformation
heating on the total stress. For this purpose, a series of compression tests on an extra-low interstitial grade alloy with
equiaxed, lamellar, or bimodal microstructures was performed at
10 - 3 £ [(e)\dot] £ 10 \texts - 1 10^{ - 3} \le \dot{\varepsilon } \le 10\;{\text{s}}^{ - 1} until the metal fractured, and the results were compared to those of the commercial grade alloy. The thermal stress σ* increased with an increasing interstitial solute concentration; the athermal stress increased in the order of equiaxed, lamellar,
and bimodal microstructures. Load–unload–reload tests revealed that the flow softening at a relatively high [(e)\dot] \dot{\varepsilon } was likely caused by deformation heating rather than by microstructure change; thus flow softening was attributed to a decrease
in σ*. Finally, a mechanical threshold stress model was extended to capture those observations; the modified model can provide
a reasonable prediction of flow stress in Ti–6Al–4V with different microstructures and interstitial solute concentrations. 相似文献
15.
Magnetic susceptibility and effective magnetic moment of the Nd3+ and Co3+ ions in NdCo1 ? x Ga x O3
N. N. Lubinskii L. A. Bashkirov A. I. Galyas S. V. Shevchenko G. S. Petrov I. M. Sirota 《Inorganic Materials》2008,44(9):1015-1021
The magnetic susceptibility of NdCo1 − x
Ga
x
O3 (x = 0, 0.1, 0.3, 0.5, 0.7, 0.8, 0.9, 1) has been measured at temperatures from 80 to 950 K. The effective magnetic moments
(μeff) due to the magnetic moments of the Co3+ and Nd3+ ions have been determined in the temperature ranges of Curie-Weiss behavior, 130–370 and 600–940 K, and have then been used,
together with the effective magnetic moment of Nd3+ (3.62μB or 4.20μB), to evaluate the effective magnetic moment of Co3+ in NdCo1 − x
Ga
x
O3. For the solid solutions with < 2.83μB, we have determined the fractions of intermediate-and low-spin Co3+ ions. In the range 2.83μB < < 4.90μB, we have determined the fraction of high-spin Co3+ ions. The results indicate that, in the temperature range 130–370 K, the Co3+ ions in NdCo1 − x
Ga
x
O3 with x = 0, 0.5, 0.8, and 0.9 are in the intermediate-and high-spin states, and the fraction of high-spin Co3+ ions gradually increases from 10% at x = 0 to 67% at x = 0.9. In the solid solutions with x = 0.1, 0.2, 0.3, and 0.7, more than half of the Co3+ ions are in the low-spin state, and the rest are in the intermediate-spin state. In the temperature range 600–940 K, the
Nd3+ ions are in the ground and excited states, with theoretically predicted of of 3.62μB and 5.52μB, respectively. Because of the significant uncertainty in in this temperature range, has been determined less accurately compared to the range 130–370 K.
Original Russian Text ? N.N. Lubinskii, L.A. Bashkirov, A.I. Galyas, S.V. Shevchenko, G.S. Petrov, I.M. Sirota, 2008, published
in Neorganicheskie Materialy, 2008, Vol. 44, No. 9, pp. 1137–1143. 相似文献
16.
C. D. Marioara S. J. Andersen A. Birkeland R. Holmestad 《Journal of Materials Science》2008,43(14):4962-4971
The orientations Si-crystals take in aluminium, in an alloy with composition Al–1.3at%Si, were investigated by transmission
electron microscopy. Hardness was measured for isothermal heat-treatments at 175 °C and 260 °C. Conditions analysed by TEM
were 17 h at 175 °C and an additional 3 h at 260 °C, both containing a high density of small Si-crystals, the finest corresponding
to 175 °C. Two main orientation relationships were found: The first accounted for approximately 60% of Si precipitates in condition 17 h_175 °C. Despite a high number density and
well-aligned interfaces, the Si precipitates have negligible influence on hardness. Findings are consistent with Ge particles
in Al–Ge alloys. 相似文献
17.
Some preliminary results of dislocation analysis and associated glide systems in as-grown as well as in superplastically deformed
β silicon nitride are presented. Transmission electron microscopy observations using the weak-beam technique, are reported.
[0 0 0 1] {1 0 1 0} and 1/3〈1 2 1 0〉 {1 0 1 1} glide systems have been characterized. In the basal plane, a superposition
of two hexagonal networks built with screw dipoles has been observed. Both a sequence extended node–constricted node and partial
dislocations have been identified in these networks which clearly evinces dislocation dissociation in β-silicon nitride following
the reaction 1/3〈2 1 1 0〉→1/3 〈1 0 1 0〉+1/3 〈1 1 0 0〉.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
18.
Wands I Shepherd DE Hukins DW 《Journal of materials science. Materials in medicine》2008,19(6):2417-2421
Calcium alginate was reinforced with hydroxyapatite (HA) particles, whose dimensions were a few micrometres, with mass fraction,
m
f, values in the range 0–0.8. Cylindrical samples of these composite materials were subjected to cyclic compression in the
frequency range f = 0.001–20 Hz; in these tests a sinusoidal load of amplitude 1 N was applied either side of a static compression of 2 N.
Storage and loss moduli, E′ and E′′, respectively, were found to be independent of particle size; however, E′ increased with frequency consistent with the materials undergoing a glass transition. Above frequencies of about 0.05 Hz,
for all materials. For each frequency, the dependence of the moduli on log10 f could be represented by a third order polynomial; these equations can be used to calculate E′ and E′′ for a range of compositions. Approximate values of are predicted by a Reuss model. 相似文献
19.
Che-Yi Wen Chun-Chia Huang Huy-Zu Cheng Hong-Yang Lu 《Journal of Materials Science》2008,43(1):123-131
Orientation relationships between the growth direction of carbon nanotubes and encapsulated residual iron-containing particles
have been determined using transmission electron microscopy. The nanotubes that are prepared by Fe-catalysed chemical vapour
deposition on sol–gel Fe(NO3)3-tetraethyl orthosilicate substrates are the helical multiwall type. Nanoscale particles of both the low-temperature α-Fe
(ferrite) and high-temperature γ-Fe (austenite) were found in the cavity of the carbon nanotubes with
, and parallel to the tube growth direction, respectively. Cementite Fe3C, the most abundant Fe-containing phase in present samples was also found to be entrapped in nanotubes with or parallel to the tube axis. The metastable retention of γ-Fe particles at room temperature is ascribed to the strain energy
induced at the particle-nanotube interface due to volume expansion upon the γ- → α-Fe phase transformation. The decomposition
of initially high aspect-ratio, rod-shape particles into a string of ovulation, while encapsulated in carbon nanotubes is
accounted for by the Rayleigh instability. Ovulation leading to reduced particle size has also contributed to increase the
surface energy term that counterbalances the total free energy change of phase transformation from γ- to α-Fe and further
aids to the metastable retention of γ-Fe. 相似文献
20.
Martensite plates in β′1 shape memory alloys commonly form self-accommodating groups of four plate variants with habit plane normals clustered about
a {1 1 0} pole of the parent phase. In the present work, the crystallography of martensitic transformation in a Cu–Al–Ni–Mn
shape memory alloy has been investigated with particular emphasis on accurate habit plane determination. The characteristically
high martensite start (M
s) temperature of β′1 alloys makes it impossible to analyse samples containing isolated plates within a β1 grain at ambient temperature. However, the parent β1 grain orientation has been determined in this work by means of a new method of junction plane trace analysis, which is based
on the knowledge that the junction planes are precisely {1 1 0}β1 planes. The mutual consistency of the experimental results indicates that this technique of junction plane traces analysis
is a viable method for determining the parent β1 grain orientation. Habit plane normals were determined by two surface trace measurements and referred to the parent crystal
basis by using the β1 grain orientation matrix. The habit plane normal was determined to be close to {1 5 5}β1 with the scatter in a series of mean value determinations being less than ± 1.2°.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献