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1.
We investigate spin coherence time of electrons bound to phosphorus donors in silicon single crystals, employing a pulsed electron paramagnetic resonance technique. The samples were isotopically controlled so that they may possess different concentrations (about 5% and 100%) of 29Si, which is the only non-zero-spin (spin-1/2) stable isotope of Si. Both 29Si-concentration dependence and orientation dependence of the electron spin coherence time demonstrate that the decoherence is caused by spectral diffusion due to mutual flip-flops of the environmental nuclear spins. The detail analysis of spin echo decay curves enables the unique assignment of the host sites responsible for electron spin echo envelope modulation. 相似文献
2.
The current status of the problem of obtaining high-purity silicon isotopes 28Si, 29Si, and 30Si is analyzed. The scheme of obtaining monoisotopic silicon includes the stages of isotope separation in the form SiF4, synthesis and deep purification of isotopically enriched silane, obtaining polycrystalline silicon-28,-29, and-30, and growing
monocrystals. The basic problems and methods of their solution in the synthesis and deep purification of silane and obtaining
poly-and monocrystals of isotopically enriched silicon are discussed. Data characterizing the achieved level of chemical and
isotopic purity of high-purity monocrystals of silicon-28 with a main isotope content of more than 99.99% and silicon-29 and
silicon-30 with isotopic purity higher than 99% are presented. In monocrystalline 28Si, the boron content was 4.5 × 1013, the phosphorus content was 5 × 1011, the carbon and oxygen contents were <1 × 1016 at/cm3, and the specific resistance was 800 Ω cm.
The results of investigation of heat capacity, heat conduction, photoluminescence, and electron paramagnetic resonance spectra
for monoisotopic silicon-28 are presented. The heat conduction of monoisotopic silicon is increased considerably owing to
the reduced photon scattering on isotopic inhomogeneities. In the region of 20–30 K, the heat conduction of silicon-28 with
an isotopic purity of 99.98% is higher by a factor of 8 than the heat conduction of natural silicon.
Investigations of photoluminescence spectra in the magnetic field in the low-temperature region demonstrated the capability
of optical detection of nuclear spin states of a phosphorus admixture in high-purity silicon-28. p ]Topical questions for
further investigations and possible fields of practical application of high-purity isotopically enriched silicon are discussed. 相似文献
3.
A systematic study of geopolymers by 29Si and 27Al MAS NMR has been carried out in an attempt to understand polymer structural details. 27Al MAS NMR data shows that transient aluminium species are formed during the reaction of metakaolin with NaOH. Interaction of silicate anions with the aluminium sites of metakaolin was evident during the synthesis of geopolymers as observed from low field shift of 29Si MAS NMR resonance lines of silicate centres. As the reaction progresses, the coordination of aluminium (IV, V and VI) in metakaolin changes almost completely to IV. 29Si MAS NMR of selected compositions of the ternary system of sodium silicate, metakaolin and aqueous alkali reveals that geopolymerisation occurs in a distinct compositional region. At high alkalinity [> 30% (mol/mol) overall Na2O content], connectivity of silicate anions is reduced, consistent with poor polymerisation. At low alkalinity [<10% (mol/mol) overall Na2O content], a clear 29Si NMR resonance line due to unconverted metakaolin is observed. NMR spectra were recorded from a series of samples with a fixed Na2O content (20 mol%) and varied SiO2/Al2O3 ratio to observe aluminium substitution in the cross-linked silicon tetrahedra of polymer network. Aluminium insertion into the silicate network is confirmed from the observed 29Si NMR shift as a function of Si/Al ratio. The identification of the presence or absence of metakaolin in the cured geopolymer product is not possible even by 29Si NMR as the signal from metakaolin is indistinguishable from a broad 29Si NMR peak consisting of many resonance lines from the network of cross-linked silicon/aluminium tetrahedra. In an attempt to identify metakaolin signal, we prepared geopolymers with higher SiO2/Al2O3 molar ratios. Since aluminium substitutions in the silicate tetrahedral network are decreased, this results in better-resolved 29Si NMR lines. The 29Si NMR signal due to metakaolin is then distinguishable in the spectra of cured products in a series of samples with 3 to 11 mol% metakaolin. These results indicate that a geopolymer structure is a network of silicon/aluminium tetrahedra with some presence of unreacted metakaolin. The silicon/aluminium tetrahedra might have connectivity ranging from 1 to 4. 相似文献
4.
A. V. Gusev V. A. Gavva E. A. Kozyrev A. M. Potapov V. G. Plotnichenko 《Inorganic Materials》2011,47(7):691-693
A process has been developed for the preparation of single-crystal 29Si from 29Si-enriched silane. A silicon single crystal has been grown with a 29Si content over 99.9 at %. The oxygen and carbon concentrations in the crystal are under 1 × 1016 cm−3, and its resistivity exceeds 1 kΩ cm. 相似文献
5.
Jagjeet Kaur Ravi Shrivastava Vikas Dubey Yogita Parganiha 《Journal of Materials Science: Materials in Electronics》2016,27(4):3227-3233
Eu2+ and Tb3+ doped Ca2MgSi2O7 phosphors were synthesized by conventional solid-state reaction. The phase formation was confirmed by X-ray powder diffraction technique and refined lattice parameters were calculated by rietveld refinement process using Celref v3. The photoluminescence (PL) excitation and emission spectra were investigated. The phosphors exhibited broaden green emitting luminescence peaking at 520 nm when excited at 374 nm source. Morphological studies were carried out using Scanning electron microscopy (SEM) images of the sample with optimum PL emission. The dependence of photoluminescence intensity on co-dopant concentration and the kinetic parameters were also reported. Time resolved fluorescence spectroscopy (TRFS) is used to investigate the decay in luminescence signals with respect to time. The sample proved to be a good long lasting material, which makes it useful in emergency signs, textile printing, textile exit sign boards and electronic instrument dial pads etc. 相似文献
6.
Christopher L. Turner Dimitrios Koumoulis Gang Li Zoran Zujovic R. E. Taylor Richard B. Kaner 《Journal of Materials Science》2018,53(5):3309-3322
Understanding different bonding environments in various metal borides provides insight into their structures and physical properties. Polycrystalline aluminum diboride (AlB2) samples have been synthesized and compared both with a commercial sample and with the literature. One issue that arose is the relative ease with which boron-rich and aluminum deficient phases of aluminum borides can be presented in AlB2. Here, we report 27Al, 11B nuclear magnetic resonance (NMR) spectroscopy and first-principles calculations on AlB2 in order to shed light on these different bonding environments at the atomic level and compare the structural and electronic properties of the products of different preparations. Along with the aforementioned, the present study also takes an in-depth look at the nature of the 11B and 27Al nuclear spin–lattice relaxation recovery data for the AlB2 and other superhard materials. The nuclear spin–lattice relaxation has been measured for a static sample and with magic-angle spinning. The combination of NMR and band structure calculations highlights the synthetic challenges with superhard materials. 相似文献
7.
Tyryshkin AM Tojo S Morton JJ Riemann H Abrosimov NV Becker P Pohl HJ Schenkel T Thewalt ML Itoh KM Lyon SA 《Nature materials》2012,11(2):143-147
Silicon is one of the most promising semiconductor materials for spin-based information processing devices. Its advanced fabrication technology facilitates the transition from individual devices to large-scale processors, and the availability of a (28)Si form with no magnetic nuclei overcomes a primary source of spin decoherence in many other materials. Nevertheless, the coherence lifetimes of electron spins in the solid state have typically remained several orders of magnitude lower than that achieved in isolated high-vacuum systems such as trapped ions. Here we examine electron spin coherence of donors in pure (28)Si material (residual (29)Si concentration <50 ppm) with donor densities of 10(14)-10(15) cm(-3). We elucidate three mechanisms for spin decoherence, active at different temperatures, and extract a coherence lifetime T(2) up to 2 s. In this regime, we find the electron spin is sensitive to interactions with other donor electron spins separated by ~200 nm. A magnetic field gradient suppresses such interactions, producing an extrapolated electron spin T(2) of 10 s at 1.8 K. These coherence lifetimes are without peer in the solid state and comparable to high-vacuum qubits, making electron spins of donors in silicon ideal components of quantum computers, or quantum memories for systems such as superconducting qubits. 相似文献
8.
Minwoo Park 《Journal of Materials Science》2005,40(15):3945-3949
The effects of Si addition and of deposition temperature on the precipitation processes of Al2Cu (θ) and Si particles in Al-Cu-Si alloy films were studied with in-situ hot stage transmission electron microscopy (TEM). Deposition of an Al-1.5Cu-1.5Si (wt%) film at 305∘C, in the three-phase, Al(α)-Al2Cu-Si region resulted in formation of fine, uniformly distributed spherical θ -phase particles due to the coprecipitation of the θ and Si phase particles during deposition. For deposition in the two-phase, Al(α)-Si region (435∘C), fine θ -phase particles precipitated during wafer cooldown, while coarse Si nodules formed at the sublayer interface during deposition. In-situ heat treatment of the film revealed that excess Si existed in a supersaturated Al matrix. Si addition decreased film susceptibility to corrosion induced by the θ -phase precipitates, since extensive Cu segregation can be reduced by coprecipitation at 305∘C and the Al matrix supersaturated with Si reduced galvanic action with respect to the θ -phase precipitate. 相似文献
9.
A. D. Bulanov V. A. Gavva A. Yu. Sozin M. F. Churbanov T. V. Kotereva Yu. P. Kirillov A. Yu. Lashkov O. Yu. Troshin T. G. Sorochkina O. Yu. Chernova N. V. Abrosimov L. V. Shabarova 《Inorganic Materials》2018,54(10):977-983
This paper examines sources of carbon impurities in polycrystalline monoisotopic 28Si prepared by a hydride method. Analytical data on the concentrations of carbon-containing impurities in volatile silicon compounds (28SiH4 and 28SiH4), process gases (Ar and H2), and polycrystalline 28Si are used to identify the major sources of carbon in the polycrystalline 28Si prepared by the hydride method. These are the starting 28SiH4 and calcium hydride used in 28SiH4 conversion into 28SiH4. The rate of carbon intake into polycrystalline silicon from the apparatus material during the monosilane pyrolysis process does not exceed 9 × 1011 cm–2 h–1. Polycrystalline silicon has been precipitated from monosilane with different concentrations of hydrocarbon impurities. At hydrocarbon concentrations in the range 10–4 to 10–3 mol %, the carbon concentration in the monosilane correlates with that in the silicon obtained from it. High-purity monosilane has been used to prepare polycrystalline 28Si samples with concentrations of carbon impurities in the range (0.8–2.3) × 1015 cm–3. Based on calculations of the carbon impurity distribution along the length of a zone-refined ingot, we examine the effect of the initial carbon concentration in the starting polycrystal on the yield of single-crystal monoisotopic 28Si. Requirements are formulated for the carbon concentration in polycrystalline 28Si which ensure a high yield of single crystals with parameters suitable for metrological applications. 相似文献
10.
M. N. Brekhovskikh S. P. Solodovnikov L. V. Moiseeva I. A. Zhidkova V. A. Fedorov 《Inorganic Materials》2018,54(7):713-715
We have studied electron paramagnetic resonance spectra of europium- and gadolinium-activated ZBLAN-type fluorohafnate glasses, using the composition 58HfF4 · 20BaF2 · 2LaF3 · 3AlF3 · 17NaF as an example. The ratio of the concentration of free Eu2+ and Gd3+ ions to that of ions in clusters has been quantitatively evaluated for the first time. The percentage of free ions has been shown to increase significantly with decreasing activator concentration. At activator concentrations of 1.25 mol % EuF2 and 1 mol % GdF3, the activator ions predominantly form clusters and only a small fraction of Eu2+ and Gd3+ are present as individual ions, whereas at 0.1 mol % EuF2 the concentration of free ions is comparable to that of ions in the clusters. 相似文献
11.
S. A. Kulyukhin N. A. Konovalova I. A. Rumer M. P. Gorbacheva L. V. Mizina 《Radiochemistry》2010,52(5):515-522
Sorption of 131I and 137Cs from a solution simulating NPP trap waters on various inorganic and organic sorbents was studied. The highest degree of
131I recovery (>99%) can be attained with Fizkhimin granulated sorbents based on coarsely porous silica gel containing Ag and
Ni in 1: 4 ratio, with K
d for 131I exceeding 105 ml g−1 at V/m = 103 ml g−1 and contract time of the solid and liquid phases of 120 min. Elevation of the solution temperature to 40°C does not affect
the degree of 131I and 137Cs recovery. The degree of 137Cs recovery in all the experiments did not exceed 35%. The degree of 131I recovery by coprecipitation with AgCl and Ag4[Fe(CN)6] was about ∼96% and only 65%, respectively. 相似文献
12.
J. Thirumalai R. Chandramohan T. A. Vijayan 《Journal of Materials Science: Materials in Electronics》2011,22(8):936-943
Monodispersed Gd2O2S:Eu3+ nanostructures with tunable morphologies have been selectively fabricated by solvothermal method in the presence of stable
inorganic precursors avoiding metalorganic precursors. The size and morphology of the products were controlled successfully
by adjusting the reaction conditions. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy
(SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and X-ray photoelectron spectroscopy
(XPS). The corresponding UV absorption and photoluminescence excitation spectra show a significant blue-shift confirming the
quantum confinement effect. A possible growth mechanism for the formation of monodispersed Gd2O2S:Eu3+ nanocrystals has been proposed. The luminescence mechanism and the size dependence of their fluorescence properties are also
discussed. 相似文献
13.
S. A. Kulyukhin E. P. Krasavina L. V. Mizina I. A. Rumer N. V. Tanashchuk N. A. Konovalova A. S. Murachev V. V. Sergeev 《Radiochemistry》2005,47(6):575-581
Sorption of 85Sr, 137Cs, 22Na, and 152Eu on solid mixed potassium neodymium ferrocyanide KNd[Fe(CN)6]·4H2O from neutral, acidic, and alkaline media and also coprecipitation of these radionuclides with KNd[Fe(CN)6]·4H2O in its formation from a homogeneous solution were studied. It was found that 85Sr and 22Na do not noticeably coprecipitate with solid KNd[Fe(CN)6]·4H2O and are not sorbed by this substance. In aqueous medium, depending on the cesium concentration in solution, from 80 to 98% of 137Cs coprecipitates with solid KNd[Fe(CN)6]·4H2O. In this case, the distribution coefficient Kd depends on both the cesium concentration in solution and solution pH. Within 30 min of contact of the solid and liquid phases, the degree of recovery of 137Cs from aqueous solution with KNd[Fe(CN)6]·4H2O is approximately 95.0% of the initial amount. 152Eu coprecipitates with solid KNd[Fe(CN)6]·4H2O during its formation from a homogeneous solution to 98–99.9%. The degree of recovery of 152Eu from aqueous solution with KNd[Fe(CN)6]·4H2O precipitate within 60 min of contact of the solid and liquid phases is 70.3% of the initial amount. 相似文献
14.
Guo-Qing Zheng K. Katayama M. Kandatsu N. Nishihagi S. Kimura M. Hagiwara K. Kindo 《Journal of Low Temperature Physics》2010,159(1-2):280-283
We report the 59Co-NMR observation by spin-echo method at pulsed high magnetic fields up to 48 T. The 22 mm bore-resistive coil magnet with an inductance of 7.59 mH has a total time duration of 50 ms. After discharging the capacitor bank, NMR signals were observed near the maximum field. By repeatedly pulsing the RF sequence around the maximum field, spin echoes at different fields were recorded to give the NMR spectrum. 相似文献
15.
Rongfang Wang Xingming Wei Ronghuan Qin Pingfang Tao Liqin Qin Haichuang Liang 《Journal of Materials Science》2017,52(12):6994-6998
High-quality ZnSe:Eu, Mn quantum dots (QDs) with white light emitting were synthesized via a green preparation method in an aqueous solution using thioglycolic acid as a stabilizing agent. The composition of the QDs could be flexibly controlled by varying the amount of Eu or Mn cation. The effects of reflux time and Eu2+ ion dopant concentration on the luminescence properties were systematically investigated. The obtained QDs were characterized by photoluminescence spectrometry, X-ray powder diffraction, and high-resolution transmission electron microscopy. The proposed method formed cubic ZnSe:Mn2+, Eu2+ QDs with the maximum emission peak at 460 and 580 nm. In the optimal condition, the quantum yields of ZnSe:Mn2+, Eu2+ QDs could reach 27.68%. The CIE color coordinates were (0.328, 0.334), which agreed with those of pure white light (0.33, 0.33). The results verified that the ZnSe:Mn2+, Eu2+ QDs exhibited potential in light-emitting diode applications. 相似文献
16.
A. A. Masalov O. G. Vyagin I. I. Ganina Yu. V. Malyukin I. M. Zenya N. G. Starzhinskii 《Technical Physics Letters》2009,35(2):154-157
Cerium-activated lutetium oxyorthosilicate Lu2SiO5:Ce3+ (LSO:Ce) and coactivated LSO:Ce,Dy and LSO:Ce,Yb crystals have been synthesized by the sol-gel technique. It is shown that
the introduction of coactivator (Yb and Dy) ions influences the energy storage in LSO:Ce, thus making it possible to control
the afterglow and thermoluminescence in these crystals. The observed effect is related to the electron properties of coactivator
ions (donor against acceptor), which determine the recharge of electron traps in LSO crystals. 相似文献
17.
Vijay Singh R. P. S. Chakradhar J. L. Rao Ho-Young Kwak 《Journal of Materials Science》2011,46(7):2331-2337
An efficient red emitting ZnAl2O4:Cr3+ powder phosphor material was prepared at furnace temperatures as low as 500 °C by using the combustion method. The prepared
powders were analyzed by X-ray diffraction and scanning electron microscopy techniques. The optical properties were studied
using photoluminescence technique. The EPR spectra exhibit an intense resonance signal at g = 3.74 which is attributed to Cr3+–Cr3+ pairs, and the weak resonance signal of at g = 1.97 is attributed to Cr3+ single ion transition. The spin population (N) has been evaluated as a function of temperature. The excitation spectrum exhibits two broad bands in the visible region
which are characteristic of Cr3+ ions in octahedral symmetry and the emission spectrum exhibits zero-phonon line frequencies along with vibronic frequencies.
The crystal field parameter (Dq) and Racah parameters (B and C) have been evaluated and discussed. 相似文献
18.
The phenomenon of phase-coherent precession of magnetization in superfluid 3He and the related effects of spin superfluidity are based on the true Bose-Einstein condensation of magnons. Several different states of coherent precession have been observed in 3He-B: homogeneously precessing domain (HPD); persistent signal formed by Q-balls at very low temperatures; coherent precession with fractional magnetization; and two new modes of coherent precession in compressed aerogel. Here we present evidence of magnons Bose-Einstein condensation in 3He-A in a compressed aerogel. 相似文献
19.
V. I. Korepanov K. Zh. Bekmyrza V. M. Lisitsyn E. A. Garibin P. E. Gusev A. A. Demidenko M. A. Krutov I. A. Mironov V. M. Reiterov K. S. Baktybekov 《Inorganic Materials》2012,48(6):625-629
We have studied the pulsed cathodoluminescence spectra and kinetics of CaF2:Yb2+,Yb3+ (3 mol % YbF3) single crystals and pressed samples under excitation with nanosecond electron pulses and determined the characteristic times
and intensities of nanosecond and microsecond emission decay components at temperatures from 15 to 300 K. The results demonstrate
that deformation pressing in vacuum at 1150°C followed by annealing in a CF4 atmosphere at 1180°C has an insignificant effect on the emissive properties of CaF2:Yb2+,Yb3+. 相似文献
20.
Fe-doped SiO2/TiO2 composite nanoparticles were directly prepared by sol-gel-hydrothermal process, and characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), thermal gravimetry (TG), X-Ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectra (DRS). It was found that the Fe3 + was well dispersed in solid solution of SiO2/TiO2 composite nanoparticles that was about 10 nm with spherical morphology and rich silica layer external surface. It could effectively offer broadband shield for both UVB (290–320 nm) and UVA (320–400 nm). The results of Photodecomposition of methylene blue showed that the photoactivity of Fe-doped SiO2/TiO2 composite was minimized due to the addition of iron ion. 相似文献