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1.
Epitaxial La1−xSrxMnO3 (LSMO) films were prepared by excimer laser-assisted metal organic deposition (ELAMOD) at a low temperature using ArF, KrF, and XeCl excimer lasers. Cross-section transmission electron microscopy (XTEM) observations confirmed the epitaxial growth and homogeneity of the LSMO film on a SrTiO3 (STO) substrate, which was prepared using ArF, KrF, and XeCl excimer lasers. It was found that uniform epitaxial films could be grown at 500 °C by laser irradiation. When an XeCl laser was used, an epitaxial film was formed on the STO substrate at a fluence range from 80 to 140 mJ/cm2 of the laser fluence for the epitaxial growth of LSMO film on STO substrate was changed. When the LaAlO3 (LAO) substrate was used, an epitaxial film was only obtained by ArF laser irradiation, and no epitaxial film was obtained using the KrF and XeCl lasers. When the back of the amorphous LSMO film on an LAO substrate was irradiated using a KrF laser, no epitaxial film formed. Based on the effect of the wavelength and substrate material on the epitaxial growth, formation of the epitaxial film would be found to be photo thermal reaction and photochemical reaction. The maximum temperature coefficient of resistance (TCR) of the epitaxial La0.8Sr0.2MnO3 film on an STO substrate grown using an XeCl laser is 4.0%/K at 275 K. XeCl lasers that deliver stabilized pulse energies can be used to prepare LSMO films with good a TCR.  相似文献   

2.
Ferromagnetic La0.7Sr0.3MnO3 (LSMO) and antiferromagnetic La0.33Ca0.67MnO3 (LCMO) layers were grown on SrTiO3 (STO) substrates by the pulsed laser deposition technique. LSMO films had rougher surfaces and larger grain sizes than LCMO films. Fully strained bilayers, in which each layer was as thin as 10 nm, were prepared by changing their stacking sequences, i.e. LSMO/LCMO/STO and LCMO/LSMO/STO. The former had higher TC (350 K) than the latter (300 K), and exchange bias effects were only observed in the former bilayers. This revealed that microstructures could play an important role in the transport and magnetic properties of manganese oxide thin films.  相似文献   

3.
La0.8Sr0.2MnO3 films were prepared on SrTiO3 (STO) and LaAlO3 (LAO) substrates using excimer laser-assisted metal organic deposition (ELAMOD). For the LAO substrate, no epitaxial La0.8Sr0.2MnO3 film was obtained by laser irradiation in the fluence range from 60 to 110 mJ/cm2 with heating at 500 °C. On the other hand, an epitaxial La0.8Sr0.2MnO3 film on the STO substrate was formed by laser irradiation in the fluence range from 60 to 100 mJ/cm2 with heating at 500 °C. To optimize the electrical properties for an IR sensor, the effects of the laser fluence, the irradiation time and the film thickness on the temperature dependence of the resistance and temperature coefficient of resistance (TCR: defined as 1/R·(dR/dT)) of the LSMO films were investigated. An LSMO film on the STO substrate that showed the maximum TCR of 3.9% at 265 K was obtained by the ELAMOD process using the KrF laser.  相似文献   

4.
Magnetic nanoparticles of La0.67Sr0.33MnO3 (LSMO) manganite were prepared by sol-gel method. Phase formation and crystal structure of the synthesized powder were examined by the X-ray diffraction (XRD) using the Rietveld analysis. The mean particle size was determined by the transmission electron microscopy (TEM). Infrared transmission spectroscopy revealed that stretching and bending modes are influenced by calcinations temperature. The temperature dependence of the ac magnetic susceptibility was measured at different frequencies and ac magnetic fields in the selected ranges of 40-1000 Hz and 80-800 A/m, respectively. The temperature dependence of ac susceptibility shows a characteristic maxima corresponding to the blocking temperature near room temperature. The frequency dependence of the blocking temperature is well described by the Vogel-Fulcher law. By fitting the experimental data with this law, the relaxation time τ0=1.7×10−12 s, characteristic temperature T0=262±3 K, anisotropy energy Ea/k=684±15 K and effective magnetic anisotropy constant keff=2.25×104 erg/cm3 have been obtained. dc Magnetization measurement versus magnetic field shows that some of LSMO nanoparticles are blocked at 293 K. The role of magnetic interparticle interactions on the magnetic behavior is also investigated.  相似文献   

5.
This paper reports the growth and spectroscopic characterization of Er3+:Sr3Y(BO3)3 crystal. Er3+:Sr3Y(BO3)3 crystal with dimensions up to ∅20×35 mm3 has been grown by Czochralski method. The polarized spectroscopic properties of Er3+:Sr3Y(BO3)3 crystal were investigated. Based on the Judd-Ofelt theory, the effective intensity parameters Ωt were obtained: Ω2=1.71×10−20 cm2, Ω4=1.39×10−20 cm2, Ω6=0.74×10−20 cm2 for π-polarization, and Ω2=1.77×10−20 cm2, Ω4=1.44×10−20 cm2, Ω6=0.65×10−20 cm2 for σ-polarization. The emission cross-section σem was calculated to be 4.75×10−21 cm2 for π-polarization at 1536 nm and 6.30×10−21 cm2 for σ-polarization at 1537 nm. The investigated results showed that Er3+:Sr3Y(BO3)3 crystal may be regarded as a potential laser host material for 1.55 μm IR solid-state lasers.  相似文献   

6.
Liang Sun  Feng-yun Guo  Li-li Liu  Wei Cai  Yu-heng Xu 《Optik》2009,120(11):514-518
OH-absorption properties of the optical damage region in a series of codoped In/Mg:LiNbO3 crystals with various Li/Nb ratios have been investigated. The OH-associated vibrational peak at 3507 cm−1 is confirmed to occur in crystals with Li/Nb ratio of 0.94. For codoped In/Mg:LiNbO3 crystals with Li/Nb ratio of 1.05 and 1.20, the OH-associated vibrational peaks are detected at 3536 and 3507 cm−1 as well. A new peak at 3518 cm−1 attributed to a (InNb)2−-OH-(MgNb)3− defect center is revealed in crystals with Li/Nb ratio 1.38. When the “In-Mg threshold” concentration is reached, the optical damage resistance ability of codoped In/Mg:LiNbO3 crystals is greatly improved.  相似文献   

7.
This paper reports the spectral properties of Nd3+:Ca2Nb2O7. The spectral parameters of Nd3+ in Nd3+:Ca2Nb2O7 crystal have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained. The parameters of line strengths Ωλ are Ω2=4.967×10−20 cm2, Ω4=5.431×10−20 cm2, Ω6=5.693×10−20 cm2. The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 122 μs, 103 μs and 84.4%, respectively. The fluorescence branch ratios calculated: β1=0.425, β2=0.479, β3=0.091, β4=0.004. The emission cross section at 1068 nm is 6.204×10−20 cm2.  相似文献   

8.
The effect of Ba(La)TiO3 doping on the structure and magnetotransport properties of La2/3Sr1/3MnO3(LSMO)/xBa(La)TiO3 (x=0.0, 1.0, 5.0 mol%) have been investigated. The X-ray diffraction patterns and microstructural analysis show that BaTiO3 and LSMO phases exist independently in BaTiO3-doped composites. The metal-insulator transition temperature (TMI) decreases whereas the maximum resistivity increases very quickly by the increase of BaTiO3 doping level. The partial substitution of Ba by La(0.35 mol%) results in a decrease in resistivity of LSMO/xBa(La)TiO3 composites. Magnetoresistance of BaTiO3-doped composites decreases monotonously in the temperature range 200-400 K in a magnetic field of 5 T, which is completely different from that of LSMO compound. The value of MR decreases at low field (H<1 T) and increases at high fields (H>1 T) with increasing the BaTiO3 doping level at low temperatures below 280 K. These investigations reveal that the magnetotransport properties of LSMO/xBa(La)TiO3 composites are dominated by spin-dependent scattering and tunneling effect at the LSMO/BaTiO3/LSMO magnetic tunnel junction.  相似文献   

9.
The transport properties of Sr0.98La0.02SnO3−δ in the system Sr1−xLaxSnO3−δ, after which the pyrochlore La2Sn2O7 appears, were investigated over the temperature range 4.2-300 K. The oxide was found to be n-type semiconductor with concomitant reduction of Sn4+ into Sn2+. The magnetic susceptibility was measured down to 4.2 K and is less than 3×10−5 emu cgs mol−1 consistent with itinerant electron behavior. The electron is believed to travel in a narrow band of Sn:5s character with an effective mass ∼4 mo. The highest band gap is 4.32 eV and the optical transition is directly allowed. A further indirect transition occurs at 4.04 eV. The electrical conductivity follows an Arrhenius-type law with a thermal activation of 40 meV and occurs by small polaron hopping between nominal states Sn4+/2+. The linear increase of thermo-power with temperature yields an electron mobility μ300 K (2×10−4 cm2 V−1 s−1) thermally activated. The insulating-metal transition seems to be of Anderson type resulting from random positions of lanthanum sites and oxygen vacancies. At low temperatures, the conduction mechanism changes to a variable range hopping with a linear plot Ln ρ−1 vs. T−4. The photo electrochemical (PEC) measurements confirm the n-type conductivity and give an onset potential of −0.46 VSCE in KOH (1 M). The Mott-Schottky plot C−2-V shows a linear behavior from which the flat band potential Vfb=+0.01 VSCE at pH 7 and the doping density ND=1.04×1021 cm−3 were determined.  相似文献   

10.
In this work, new LaSi3N5:Ce3+ phosphors have been synthesized by solid-state reaction. Rietveld refinement of the crystal structure of La1−xCexSi3N5 reveals that Ce atoms substituted for La atoms occupy 4a crystallographic positions. Broad emission and excitation bands observed were attributed to the transitions between the doublet ground state of the 4f1 configuration and the crystal field components of the 5d1 excited state. At 77 K, the centroid and crystal field splitting εcfs of the 5d levels of Ce3+ in LaSi3N5:Ce3+ compounds were valuated at 33.4×103 and 11.3×103 cm−1, respectively. The zero-phonon line and the Stokes shift were measured to be 26.0×103 and 5.0×103 cm−1, respectively.  相似文献   

11.
In a three-components fluorophosphate glass system, the introduction of H3BO3 brings some valuable influence to the spectroscopic and thermal properties of the glasses. With H3BO3 increases from 2 to 20 mol%, Ω6, Sed4I13/2, FWHM, Tg and fluorescence lifetime change from 3.21×10−20 cm2, 1.77×10−20 cm2, 45 nm, 480 °C and 8.8 ms to 4.66×10−20 cm2, 2.11×10−20 cm2, 50 nm, 541 °C and 7.4 ms, respectively. σabs, σemi, FWHM×τf×σemi has a maximum when H3BO3 is 11 mol%. Tg and TxTg increases with H3BO3 introduction. Results showed that in fluorophosphate glasses, proper amount of B2O3 can be used as a modifier to suppress upconversion and improve spectroscopic properties, broadband property and crystallization stability of the glasses while keeps the fluorescence lifetime relatively high.  相似文献   

12.
<正>We fabricated La_(1-x)Sr_xMnO_3/Si(LSMO/Si) heterojunctions with different Sr doping concentrations(x = 0.1, 0.2,0.3) in LSMO and studied the Sr content influence on magnetoresistance(MR) ratio.The hetero junctions show positive MR and high sensitivity of MR ratio in a low applied magnetic field.The MR ratio is dependent on Sr content and the low Sr doping in LSMO causes a large positive MR in LSMO/Si junctions.The MR ratio for 0.1 Sr doping in the LSMO/Si heterostructure is 116%in 100 Oe(1 Oe=79.5775 A/m) at 210 K.The mechanism for the positive MR dependence on the doping density is considered to be the competition between the tunneling rate of electrons in e_g~1↑to t_(2g)↓band and that to e_g~2↑band at the interface region of LSMO.The experimental results are in agreement with those observed in La_(0.9)Sr_(0.1)MnO_3/SrNb_(0.01)Ti_(0.99)O_3 p-n junction.The results indicate that choosing low doping concentration to improve the low field sensitivity of the heterojunction devices is a very efficacious method.  相似文献   

13.
Temperature dependences of the Hall coefficient, Hall mobility and thermoelectric properties of Ni-doped CoSb3 have been characterized over the temperature range from 20 to 773 K. Ni-doped CoSb3 is an n-type semiconductor and the conduction type changes from n-type to p-type at around 450 K. The temperature for the transition from n-type to p-type increased with increasing Ni content x. The Seebeck coefficient reaches a maximum value near the transition temperature. The electrical resistivity indicates that Co1−xNixSb3 is a typical semiconductor when x≤0.03 and a degenerate semiconductor when x>0.03. Thermal conductivity analyses show that the lattice component is predominant at lower temperatures and carrier and bipolar components become large at temperatures higher than the transition temperature. The thermoelectric figure of merit reaches a maximum value close to the transition temperature and the largest value, 4.67×10−4 K−1 at 600 K, was obtained for x=0.05.  相似文献   

14.
We report on the first Raman data of Cu substituted La1−ySryMn1−xCuxO3 (0≤x≤0.10 and 0.17≤y≤0.3, accordingly in order to have the same Mn4+/[Mn4++Mn3+] ratio), collected in the frequency range 100-900 cm−1 and at room temperature, with parallel (eies) and crossed (eies) polarizations of the incident (ei) and scattered (es) light. Spectra were fitted with a Drude-Lorentz model, and peaks at 190-220 and 430 cm−1, together with two broad structures centered at near 500 and 670 cm−1, have been found. We also have observed that the A1g mode is substantially shifted with increasing Cu substitution. The A1g phonon shift is a linear function of the tolerance factor t and the rhombohedral angle αr, thus following the structural changes of the MnO6 octahedra in the system.  相似文献   

15.
A series of Er3+/Yb3+-co-doped 60Bi2O3-(40−x) B2O3 -xGa2O3 (BBGA x=0, 4, 8, 12, 16 mol%) glasses have been prepared. The absorption spectra, emission spectra, fluorescence lifetime of Er3+:4I13/2 level and thermal stability were measured and investigated. Three Judd-Ofelt intensity parameters Ωt (t=2,4,6) (Ω2=(4.67-5.93)×10−20 cm2, Ω4=(1.50-1.81)×10−20 cm2, Ω6=(0.92-1.17)×10−20 cm2) of Er3+ ions were calculated by Judd-Ofelt theory. It is found that the Ω6 first increases with the increase of Ga2O3 content from 0 to 8 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section () of Er3+: 4I13/24I15/2 transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=69-76 nm) of the 4I13/24I15/2 transition of Er3+ ions were measured. The results indicate that these new BBGA glasses can be used as a candidate host material for potential broadband optical amplifiers.  相似文献   

16.
We report measured Lorentz O2-broadening and O2-induced pressure-shift coefficients of CH3D in the ν2 fundamental band. Using a multispectrum fitting technique we have analyzed 11 laboratory absorption spectra recorded at 0.011 cm−1 resolution using the McMath-Pierce Fourier transform spectrometer, Kitt Peak, Arizona. Two absorption cells with path lengths of 10.2 and 25 cm were used to record the spectra. The total sample pressures ranged from 0.98 to 339.85 Torr with CH3D volume mixing ratios of 0.012 in oxygen. We report measurements for O2 pressure-broadening coefficients of 320 ν2 transitions with quantum numbers as high as J″ = 17 and K = 14, where K″ = K′ ≡ K (for a parallel band). The measured O2-broadening coefficients range from 0.0153 to 0.0645 cm−1 atm−1 at 296 K. All the measured pressure-shifts are negative. The reported O2-induced pressure-shift coefficients vary from about −0.0017 to −0.0068 cm−1 atm−1. We have examined the dependence of the measured broadening and shift parameters on the J″, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = −J″, J″, and J″ + 1 in the QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.4%. The O2-broadening and pressure shift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results of the broadening coefficients are generally larger than the experimental data. Using for the trajectory model an isotropic Lennard-Jones potential derived from molecular parameters instead of the spherical average of the atom-atom model, a better agreement is obtained with these data, especially for |m| ? 12 values (11.3% for the first calculation and 8.1% for the second calculation). The O2-pressure shifts whose vibrational contribution are either derived from parameters fitted in the QQ-branch of self-induced shifts of CH3D or those obtained from pressure shifts induced by Xe in the ν3 band of CH3D are in reasonable agreement with the scattered experimental data (17.0% for the first calculation and 18.7% for the second calculation).  相似文献   

17.
In this paper, we report measured Lorentz N2-broadening and N2-induced pressure-shift coefficients of CH3D in the ν2 fundamental band using a multispectrum fitting technique. These measurements were made by analyzing 11 laboratory absorption spectra recorded at 0.0056 cm−1 resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 10.2 and 25 cm. The total sample pressures ranged from 0.98 to 402.25 Torr with CH3D volume mixing ratios of 0.01 in nitrogen. We have been able to determine the N2 pressure-broadening coefficients of 368 ν2 transitions with quantum numbers as high as J″ = 20 and K = 16, where K″ = K′ ≡ K (for a parallel band). The measured N2-broadening coefficients range from 0.0248 to 0.0742 cm−1 atm−1 at 296 K. All the measured pressure-shifts are negative. The reported N2-induced pressure-shift coefficients vary from about −0.0003 to −0.0094 cm−1 atm−1. We have examined the dependence of the measured broadening and shift parameters on the J″, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = −J″, J″, and J″ + 1 in the QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.7%. The N2-broadening and pressure-shift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results of the broadening coefficients are in good overall agreement with the experimental data (8.7%). The N2-pressure shifts whose vibrational contribution is derived from parameters fitted in the QQ-branch of self-induced shifts of CH3D, are also in reasonable agreement with the scattered experimental data (20% in most cases).  相似文献   

18.
By using diamond anvil cell (DAC), high-pressure Raman spectroscopic studies of orthophosphates Ba3(PO4)2 and Sr3(PO4)2 were carried out up to 30.7 and 30.1 GPa, respectively. No pressure-induced phase transition was found in the studies. A methanol:ethanol:water (16:3:1) mixture was used as pressure medium in DAC, which is expected to exhibit nearly hydrostatic behavior up to about 14.4 GPa at room temperature. The behaviors of the phosphate modes in Ba3(PO4)2 and Sr3(PO4)2 below 14.4 GPa were quantitatively analyzed. The Raman shift of all modes increased linearly and continuously with pressure in Ba3(PO4)2 and Sr3(PO4)2. The pressure coefficients of the phosphate modes in Ba3(PO4)2 range from 2.8179 to 3.4186 cm−1 GPa−1 for ν3, 2.9609 cm−1 GPa−1 for ν1, from 0.9855 to 1.8085 cm−1 GPa−1 for ν4, and 1.4330 cm−1 GPa−1 for ν2, and the pressure coefficients of the phosphate modes in Sr3(PO4)2 range from 3.4247 to 4.3765 cm−1 GPa−1 for ν3, 3.7808 cm−1 GPa−1 for ν1, from 1.1005 to 1.9244 cm−1 GPa−1 for ν4, and 1.5647 cm−1 GPa−1 for ν2.  相似文献   

19.
The trap levels in nominally undoped Ga3InSe4 crystals were investigated in the temperature range of 10-300 K using the thermally stimulated currents technique. The study of trap levels was accomplished by the measurements of current flowing along the c-axis of the crystal. During the experiments we utilized a constant heating rate of 0.8 K/s. Experimental evidence is found for one hole trapping center in the crystal with activation energy of 62 meV. The analysis of the experimental TSC curve gave reasonable results under the model that assumes slow retrapping. The capture cross-section of the trap was determined as 1.0×10−25 cm2 with concentration of 1.4×1017 cm−3.  相似文献   

20.
In this paper, we report measured Lorentz self-broadening and self-induced pressure-shift coefficients of 12CH3D in the ν2 fundamental band (ν0 ≈ 2200 cm−1). The multispectrum fitting technique allowed us to analyze simultaneously seven self-broadened absorption spectra. All spectra were recorded at the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory (NSO) on Kitt Peak, AZ with an unapodized resolution of 0.0056 cm−1. Low-pressure (0.98-2.95 Torr) as well as high-pressure (17.5-303 Torr) spectra of 12C-enriched CH3D were recorded at room temperature to determine the pressure-broadening coefficients of 408 ν2 transitions with quantum numbers as high as J″ = 21 and K = 18, where K″ = K′ ≡ K (for a parallel band). The measured self-broadening coefficients range from 0.0349 to 0.0896 cm−1 atm−1 at 296 K. All the measured pressure-shifts are negative. The reported pressure-induced self-shift coefficients vary from about −0.004 to −0.008 cm−1 atm−1. We have examined the dependence of the measured broadening and shift parameters on the J″, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = −J″, J″, and J″ + 1 in the QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 3.6%. A semiclassical theory based upon the Robert-Bonamy formalism of interacting linear molecules has been used to calculate these self-broadening and self-induced pressure-shift coefficients. In addition to the electrostatic interactions involving the octopole and hexadecapole moments of CH3D, the intermolecular potential includes also an atom-atom Lennard-Jones model. For low K (K ? 3) with |m| ? 8 the theoretical results of the broadening coefficients are in overall good agreement (3.0%) with the experimental data. For transitions with K approaching |m|, they are generally significantly underestimated (8.8%). The theoretical self-induced pressure shifts, whose vibrational contribution is derived from results in the QQ-branch, are generally smaller in magnitude than the experimental data in the QP-, and QR-branches (15.2%).  相似文献   

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