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1.
Anisotropic (elliptically polarized) photoinduced second harmonic generation (PISHG) in SiNxOy/Si1 1 1 films was proposed for contact-less monitoring of specimens with different nitrogen to oxygen (N/O) ratios. As a source for the photoinducing light, we used a nitrogen Q-switched pulse laser at wavelengths of 315, 337 and 354 nm as well as doubled frequency YAG–Nd laser wavelength (λ=530 nm). The YAG : Nd pulse laser (λ=1.06 μm; W=30 MW; τ=10–50 ps) was used to measure the PISHG. All measurements were done in a reflected light regime. We found that the output PISHG signal was sensitive to the N/O ratio and the film thickness. Measurements of the PISHG versus pumping wavelengths, powers, incident angles as well as independent measurements of the DC-electric field induced second harmonic generation indicate the major role played in this process by axially symmetric photoexcited electron–phonon states. The SiNxOy films were synthesized using a technique of chemical evaporation at low pressures. Films with thickness varying between 10 and 30 nm and with an N/O ratio between 0 and 1 were obtained. Electrostatic potential distribution at the Si1 1 1–SiNxOy interfaces was calculated. Comparison of the experimentally obtained and quantum chemically calculated PISHG data are presented. High sensitivity of anisotropic PISHG to the N/O ratio and film thickness is revealed. The role of the electron–phonon interactions in the dependencies observed is discussed. We have shown that the PISHG method has higher sensitivity than the traditional extended X-ray absorption fine structure spectroscopic and linear optical method for films with the N/O ratio higher than 0.50.  相似文献   

2.
The compositional dependence of the optical constants, the refractive index n, and the absorption index k, of the AsSe1−xTex thin films with 0<x<1.0 were determined in the spectral range of 400–2500 nm. The maximum value of the refractive index n, is shifted toward the long wavelength by increasing the Te content in the examined system. The values of the forbidden energy gap of the system have been determined and were correlated with the type and the amount of chemical bonds formed by the increasing Te content in the AsSe1−xTex glassy system. The value of the dispersion energy Ed exhibits low value at the composition containing the same atomic percent of Se and Te.  相似文献   

3.
Focused ion beam implantation of gallium and dysprosium was used to locally insulate the near-surface two-dimensional electron gas of AlxGa1−xN/GaN heterostructures. The threshold dose for insulation was determined to be 2×1010 cm−1 for 90 keV Ga+ and 1×109 cm−1 for 200 keV Dy2+ at 4.2 K. This offers a tool not only for inter-device insulation but also for direct device fabrication. Making use of “open-T” like insulating line patterns, in-plane gate transistors have been fabricated by focused ion beam implantation. An exemplar with a geometrical channel width of 1.5 μm shows a conductance of 32 μS at 0 V gate voltage and a transconductance of around 4 μS, which is only slightly dependent on the gate voltage.  相似文献   

4.
The band structure of HgTe quantum wells (QWs) has been determined from absorption experiments on superlattices in conjunction with calculations based on an 8×8 k·p model. The band structure combined with self-consistent Hartree calculations has enabled transport results to be quantitatively explained.Rashba spin–orbit, (SO) splitting has been investigated in n-type modulation doped HgTe QWs by means of Shubnikov–de Haas oscillations (SdH) in gated Hall bars. The heavy hole nature of the H1 conduction subband in QWs with an inverted band structure greatly enhances the Rashba SO splitting, with values up to 17 meV.By analyzing the SdH oscillations of a magnetic two-dimensional electron gas (2DEG) in modulation-doped n-type Hg1−xMnxTe QWs, we have been able to separate the gate voltage-dependent Rashba SO splitting from the temperature-dependent giant Zeeman splitting, which are of comparable magnitudes. In addition, hot electrons and Mn ions in a magnetic 2DEG have been investigated as a function of current.Nano-scale structures of lower dimensions are planned and experiments on sub-micrometer magneto-transport structures have resulted in the first evidence for ballistic transport in quasi-1D HgTe QW structures.  相似文献   

5.
Effect of the deposition temperature (200 and 500 °C) and composition of SmxCe1−xO2−x/2 (x = 0, 10.9–15.9 mol%) thin films prepared by electron beam physical vapor deposition (EB-PVD) and Ar+ ion beam assisted deposition (IBAD) combined with EB-PVD on structural characteristics and morphology/microstructure was investigated. The X-ray photoelectron spectroscopy (XPS) of the surface and electron probe microanalysis (EPMA) of the bulk of the film revealed the dominant occurrence of Ce4+ oxidation state, suggesting the presence of CeO2 phase, which was confirmed by X-ray diffraction (XRD). The Ce3+ oxidation states corresponding to Ce2O3 phase were in minority. The XRD and scanning electron microscopy (SEM) showed the polycrystalline columnar structure and a rooftop morphology of the surface. Effects of the preparation conditions (temperature, composition, IBAD) on the lattice parameter, grain size, perfection of the columnar growth and its impact on the surface morphology are analyzed and discussed.  相似文献   

6.
A pseudopotential formalism within the virtual crystal approximation in which the effects of composition disorder are involved is applied to the GaxIn1−xAsyP1−y quaternary alloys in conditions of lattice matching to GaAs, InP and ZnSe substrates so as to predict their energy band gaps. Very good agreement is obtained between the calculated values and the available experimental data for the alloy lattice matched to InP and GaAs. The alloy is found to be a direct-gap semiconductor for all y compositions whatever the lattice matching to the substrates of interest. The (ΓΓ) band-gap ranges and the ionicity character are found to depend considerably on the particular lattice-matched substrates suggesting therefore that, for an appropriate choice of y and the substrate, GaxIn1−xAsyP1−y could provide more diverse opportunities to obtain desired band gaps, which opens up the possibility of discovering new electronic devices with special features and properties.  相似文献   

7.
The magnetic susceptibility and magnetization are presented for polycrystalline samples of the alloy systems Cd1-xMnxTe 0 < x 0.1 and Sn1-xMnxTe 0 < 4 0.4. The magnetic measurements were performed between 2.3 K and 300 K in external magnetic fields up to 11 kOe. At sufficiently high temperatures the susceptibility can be described by a Curie-Weiss law. In the system Sn1-xMnxTe θp is positive. A linear dependence θpx was found with θp(0.4) = 49 K. In the series Cd1-xMnxTe θp changes sign. For θ < x < 0.04 θp is positive with a maximum θp ≈ 10 K at x = 0.02. In the region x #62; 0.04 θp becomes negative with θp = -35 K at x = 0.1. The effective spin value of manganese is Seff #62; 5/2 for all the samples. The investigation was done to check the assumption that ferromagnetic coupling may exist in tellurides of manganese if the shortest distance dMnMn is greater than 3.4 Å. This hypothesis has been stated. In the case θp #62; 0 the results are partly explained by the RKKY exchange coupling.  相似文献   

8.
Room temperature cathodoluminescence (RTCL) was obtained from Tm implanted AlxGa1−xN with different AlN contents (in the range 0≤x≤0.2) and from implanted InxAl1−xN with different InN contents (x=0.13 and 0.19) close to the lattice match with GaN. The Tm3+ emission spectrum depends critically on the host material. The blue emission from AlxGa1−xN:Tm peaks in intensity for an AlN content of x0.11. The emission is enhanced by up to a factor of 50 times with an increase of annealing temperature from 1000 to 1300 C. The blue emission from In0.13Al0.87N:Tm, annealed at 1200 C, is more than ten times stronger than that from AlxGa1−xN:Tm, x≤0.2. However, the intensity decreases significantly as the InN fraction increases from 0.13 to 0.19.  相似文献   

9.
Far-infrared reflectivity spectra of Pb1−xMnxTe (0.0001x0.1) single crystals were measured in the 10–250 cm−1 range at room temperature. The analysis of the far-infrared spectra was made by a fitting procedure based on the model of coupled oscillators. In spite of the strong plasmon–LO phonon interaction, we found that the long wavelength optical phonon modes of these mixed crystals showed an intermediate one–two mode behavior.  相似文献   

10.
High-pressure photoluminescence (PL) experiments (at 9 K) are reported for GaAs1−xNx/GaAs quantum wells having N compositions (x=0.0025, 0.004) in the dilute regime where the GaAs1−xNx alloy conduction band (CB) evolves rapidly by incorporation of N-pair states. Under increasing pressure, the PL spectra exhibit several new N-pair features that derive from CB-resonant states at 1 atm. Two of these features appear strongly at sub-band-gap energies for P29 kbar in the x=0.0025 sample, but are absent for all pressures in the x=0.004 sample. Several competing PL assignments due to bound-exciton recombination at NNi pairs (i=1–4 is the anion separation) are considered in light of prior findings for N-doped (1017 cm−3) GaAs. The absence of certain PL features in the x=0.004 sample shows that N-pair states mix into the CB-continuum via a selective process, and this selectivity offers an important test for band-structure calculations in dilute GaAs1−xNx alloys.  相似文献   

11.
A linear dependence of the reciprocal susceptibility on the temperature similar to a Curie-Weiss-law with positive values of the paramagnetic Curie temperature θp was found for the (Cr1-xFex)1+Sb ternary system in an intermediate range of x between the antiferromagnetic end members (x = 0 and 1). A magnetization appears below θp with temperature and external field dependences, for fields below a critical applied field, which are unusual for ferromagnetic substances. A remanence is found only far below θp. In this temperature range the magnetization depends on the time elapsed after changing the applied field and on the magnetic as well as on the thermal history. These phenomena are investigated and an interpretation of the observed behavior is discussed using the model of the magnetic structure for mictomagnets.  相似文献   

12.
Perovskite-type La(Cr1−xMnx)O3+δ (0.0x1.0) was synthesized using a sol–gel process. The crystal structure of La(Cr1−xMnx)O3+δ changes from orthorhombic to rhombohedral at x=0.6. The Mn4+ ion content increases monotonically in the range 0.2x1.0. The magnetic measurement of La(Cr1−xMnx)O3+δ indicates that a Mn3+ ion is a high-spin state with (d)3(dγ)1. The variation of the average (Cr, Mn)-O distance is explained by ionic radii of the Cr3+, the Mn3+, the Mn4+ ions. Since the log σT–1/T curve is linear and the Seebeck coefficient (α) is independent of temperature, it is considered that La(Cr1−xMnx)O3+δ is a p-type semiconductor and exhibits the hopping conductivity.  相似文献   

13.
We present a reliable method for growing single crystals of Y1−xPrxBa2Cu3O7−δ high-Tc superconductors in ZrO2 crucibles. This method results in crystals with greatly improved superconducting properties compared to crystals grown with the previously reported methods which use Al2O3 crucibles. We describe techniques for crystal growth in both Al2O3 and ZrO2 crucibles using an excess of BaCo3 and CuO as the flux. The crystals were characterized by means of DC magnetic-susceptibility measurements, electrical-resistivity measurements, and electron microprobe analysis. The effects of Al contamination on the conditions for crystal growth and on the superconducting properties of the crystals are found to be quite significant.  相似文献   

14.
15.
We report a comprehensive analyzes of the Fourier transform infrared (FTIR) absorption and Raman scattering data on the structural and vibrational properties of dilute ternary GaAs1−xNx,[GaP1−xNx] (x<0.03) alloys grown on GaAs [GaP] by metal organic chemical vapor deposition (MOCVD) and solid source molecular beam epitaxy (MBE). By using realistic total energy and lattice dynamical calculations, the origin of experimentally observed N-induced vibrational features are characterized. Useful information is obtained about the structural stability, vibrational frequencies, lattice relaxations and compositional disorder in GaNAs (GaNP) alloys. At lower composition (x<0.015) most of the N atoms occupy the As [P] sublattice {NAs[NP]}—they prefer moving out of their substitutional sites to more energetically favorable locations at higher x. Our results for the N-isotopic shifts of local mode frequencies compare favorably well with the existing FTIR data.  相似文献   

16.
The use of focused ion beam implantation doping of an inverted GaAs/Al1−xGaxAs heterostructure during a growth interruption allows for the lateral modulation of the heterostructure doping. Hence, laterally patterned two dimensional electron gases (2DEGs) are obtained with no further processing steps required. We have performed the direct writing of a 2DEG with a Hall-bar pattern, such that only the application of ohmic contacts was necessary and the sample surface remained unharmed otherwise. The 2DEG has an electron density of 3.6×1011 cm−2 and an electron mobility of 4.8×105 cm2/V s, as determined by magnetotransport measurements. A conventional mesa-etched Hall-bar with almost identical electronic properties has also been studied. Different behaviour of the longitudinal as well as the transversal magnetoresistance for the two Hall-bars is observed and can be concluded to be due to a different confinement potential.  相似文献   

17.
In this paper, we present our recent experimental results of magnetic and transport properties of Gd1−xLaxMn2Ge2 intermetallic compounds with the ThCr2Si2-type layered structure. The results obtained indicate that, in GdMn2Ge2, a first-order transition from a collinear antiferromagnetic to a collinear ferrimagnetic state appears with decreasing temperature at Tt3, below the Néel temperature TN. In Gd1−xLaxMn2Ge2 compounds with x=0.05 and 0.075, after ordering ferrimagnetically at Tt1, two kinds of first-order transitions from a canted ferrimagnetic to a non-collinear antiferromagnetic state and from a non-collinear antiferromagnetic to a reentrant canted ferrimagnetic state occur at Tt2 and Tt3. In Gd0.925La0.075Mn2Ge2, a field-induced metamagnetic transition from non-collinear antiferromagnetism to canted ferrimagnetism occurs at relatively low fields, accompanied by fractal like multi-step transitions, the so called “devil's stair-case”. Furthermore, a negative giant magnetoresistance (GMR) effect (Δρ/ρ15%) was observed at the field-induced metamagnetic transition. The mechanism of this negative GMR was clarified by comprehensive measurements of the resistivity on single crystals Gd0.925La0.075Mn2Ge2 and TbMn2Ge2. With further increasing x, only canted ferrimagnetism appears with a compensation temperature for 0.10<x<0.40, whereas no compensation behavior appears for x>0.50. The phase diagram obtained indicates that the overall magnetism is controlled by the Mn–Mn intralayer distance in the tetragonal c-plane, reflecting the two-dimensional arrangement of Mn atoms.  相似文献   

18.
A set of SnTe/Sn1−xEuxTe superlattice (SL) samples with increasing nominal Eu content x up to 0.28 was successfully grown on (1 1 1) BaF2 substrates by molecular beam epitaxy. A complete structural characterization was performed by triple-axis X-ray diffractometry and reciprocal space mapping. The X-ray results showed that, despite the phase separation that normally occurs for unstrained Sn1−xEuxTe layers with x0.02, an SL stack with homogeneous individual layers can be formed for SL samples with a nominal Eu content up to 0.16. No SL satellite peak structure could be identified for samples with x values higher than 0.24. The structural parameters of the individual layers that compose the SL were determined using a best-fit simulation procedure which compared the calculated X-ray spectra to the measured (2 2 2) ω/2Θ scans. The strain information used in the simulation was obtained from the reciprocal space maps measured around the (2 2 4) lattice point.  相似文献   

19.
We report experimental data on the temperature and concentration dependences of the Nernst coefficient in the normal state for the YBa2Cu3 − xCoxOyceramic samples with increasing Co content up tox = 0.3. The Nernst coefficient is positive, and its value increases almost linearly withx. The temperature dependences ofQhave been analyzed on the basis of a narrow band model, together with data on other transport coefficients. Using a complex quantitative analysis of four transport coefficients, we were able to estimate the carrier mobility and to elucidate a character of the energy dependence of the relaxation time.  相似文献   

20.
The effect of oxygen nonstoichiometry and barium cation substitution on the structure and superconducting properties of Bi2Ba2−xMxCuO6 +δ(M = Sr, Ru, Rh, Pd, In, Sb or Pb;xchanged from 0 to 0.2) were studied. The cation-substituted samples annealed in oxygen flow contain a superconducting phase withTcinitnear 95 K.  相似文献   

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