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21.
Darius H. Torchinsky David Hsieh J.L. Luo Nuh Gedik 《Journal of Physics and Chemistry of Solids》2011,72(5):519-522
We report on band-dependent quasiparticle dynamics in the hole-doped Ba-122 pnictides measured by ultrafast pump-probe spectroscopy. In the superconducting state of the optimal and over hole-doped samples, we observe two distinct relaxation processes: a fast component whose decay rate increases linearly with excitation density and a slow component whose relaxation is independent of excitation strength. We argue that these two components reflect the recombination of quasiparticles in the two hole bands through intraband and interband processes. We also find that the thermal recombination rate of quasiparticles increases quadratically with temperature in all samples. The temperature and excitation density dependence of the decays indicates fully gapped hole bands and nodal or very anisotropic electron bands. 相似文献
22.
C.?T.?Hsieh J.?T.?LueEmail author 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,35(3):357-364
The electron spin resonance (ESR) spectrometer, a very sensitive instrument with fast detecting window to explore quantum phase transitions for magnetic nanoparticles, was exploited to study the fascinating interplay between thermal and quantum fluctuations in the vicinity of a quantum critical point. We have measured ESR in ferrofluid samples containing nanosize particles of Fe2O3. The evolution of the ESR spectrum with temperature suggests that quantum tunneling of spins occurs in single domain magnetic particles in the low temperature regime. The effects of various microwave fields, particle sizes, and temperatures on the magnetic states of single domain spinel ferrite nanoparticles are investigated. We can consistently explain experimental data assuming that, as the temperature decreases, the spectrum changes from superparamagnetic (SPR) to blocked SPR and finally evolves quantum superparamagnetic behaviour as the temperature lowers down further. A nanoparticle system of a highly anisotropic magnetic material can be qualitatively specified by a simple quantum spin model, or by the Heisenberg model with strong easy-plane anisotropy.Received: 29 August 2003, Published online: 15 October 2003PACS:
76.30.-v Electron paramagnetic resonance and relaxation - 75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.) - 05.30.-d Quantum statistical mechanics - 75.50.Dd Nonmetallic ferromagnetic materials 相似文献
23.
Nanosized ZnOs were synthesized on the surface of α brass coated a film of nickel catalyst at 500-700 °C under atmosphere of O2 and CH4 gases. The nanosized ZnOs have shapes including pillar, leaf, sheet and rod, which were determined by the synthesis temperature and the flow rates of O2 and CH4 gases. The nanosized ZnOs were characterized by electron microscopy including transmission electron microscope for crystal structure, morphology and high resolution images, both field emission scanning electron microscope and scanning electron microscope for morphology, and energy dispersive X-ray spectroscope equipped in electron microscope for chemical composition. A mechanism was proposed for the growth of nanosized ZnO obtained in this work. 相似文献
24.
The photo-induced electron and hole transfer across the semiconductor-dielectric interface in trap-dominated p-type organic field-effect transistors has been investigated. It has been observed that the transfer of electrons into the dielectric results in a decrease of the field-effect mobility of polarons, suggesting that additional shallow traps are generated in the conduction channel. Using this effect, the dependence of the field-effect mobility on the density of shallow traps, mu(N), has been measured, which allowed us to estimate the average polaron trapping time, tau_{tr}=50+/-10 ps, and the density of shallow traps, N0=(3+/-0.5) x 10(11) cm(-2), in the channel of single-crystal tetracene devices. 相似文献
25.
Four-point impedance spectroscopy of solid materials systems is severely hampered by unavoidable voltage-divider effects associated with the reference electrodes. As demonstrated by test circuit studies and experiments with Pt/YSZ/Pt cells (with embedded silver reference electrodes), high impedance reference electrodes can produce distorted and erroneous impedance data. The relationships between these data and the sample properties (conductivity, dielectric constant) and instrument limitations (input impedance/capacitance) are derived. Successful four-point impedance measurements on conductive systems require large effective dielectric constants, which may be unattainable in bulk solids, but are often associated with internal interfaces. 相似文献
26.
This study investigates ultra-thin potassium chloride (KCl) films on the Si(1 0 0)-2 × 1 surfaces at near room temperature. The atomic structure and growth mode of this ionic solid film on the covalent bonded semiconductor surface is examined by synchrotron radiation core level photoemission, scanning tunneling microscopy and ab initio calculations. The Si 2p, K 3p and Cl 2p core level spectra together indicate that adsorbed KCl molecules at submonolayer coverage partially dissociate and that KCl overlayers above one monolayer (ML) have similar features in the valance band density of states as those of the bulk KCl crystal. STM results reveal a novel c(4 × 4) structure at 1 ML coverage. Ab initio calculations show that a model that comprises a periodic pyramidal geometry is consistent with experimental results. 相似文献
27.
Chih-Kai Huang Chia-Yin Chen Jin-Lin Han Chii-Chang Chen Meng-Dan Jiang Jen-Sung Hsu Chia-Hua Chan Kuo-Huang Hsieh 《Journal of nanoparticle research》2010,12(1):199-207
The silver nanoparticles (Ag NPs) have been immobilized onto silica microspheres through the adsorption and subsequent reduction
of Ag+ ions on the surfaces of the silica microspheres. The neat silica microspheres that acted as the core materials were prepared
through sol–gel processing; their surfaces were then functionalized using 3-mercaptopropyltrimethoxysilane (MPTMS). The major
aims of this study were to immobilize differently sized Ag particles onto the silica microspheres and to understand the mechanism
of formation of the Ag nano-coatings through the self-assembly/adsorption behavior of Ag NPs/Ag+ ions on the silica spheres. The obtained Ag NP/silica microsphere conglomerates were characterized by field-emission scanning
electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). Their electromagnetic
wave shielding effectiveness were also tested and studied. The average particle size of the obtained Ag NPs on the silica
microsphere was found that could be controllable (from 2.9 to 51.5 nm) by adjusting the ratio of MPTMS/TEOS and the amount
of AgNO3. 相似文献
28.
We describe the structural properties and electrical characteristics of thin thulium oxide (Tm2O3) and thulium titanium oxide (Tm2Ti2O7) as gate dielectrics deposited on silicon substrates through reactive sputtering. The structural and morphological features of these films were explored by X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and atomic force microscopy, measurements. It is found that the Tm2Ti2O7 film annealed at 800 °C exhibited a thinner capacitance equivalent thickness of 19.8 Å, a lower interface trap density of 8.37 × 1011 eV−1 cm−2, and a smaller hysteresis voltage of ∼4 mV than the other conditions. We attribute this behavior to the Ti incorporated into the Tm2O3 film improving the interfacial layer and the surface roughness. This film also shows negligible degrees of charge trapping at high electric field stress. 相似文献
29.
Po-Tsung Hsieh 《Physica B: Condensed Matter》2008,403(1):178-183
ZnO thin films were prepared by reactive RF magnetron sputtering at various deposition temperatures. They were annealed in oxygen ambient at various annealing temperatures. The microstructures and photoluminescence characteristics of ZnO films were investigated. The grain size of the ZnO thin film that was deposited at room temperature (RT) after annealing exceeded that of the film that was deposited at . Excess Zn atoms were considered to be present in the ZnO film that was deposited at RT, so the film was non-stoichiometric ZnO. No visible emission of either of the ZnO films deposited at the two temperatures was observed before annealing. Following annealing at high temperature, the green emission from the ZnO film that was deposited at RT was stronger than that of the film that was deposited at . The relationship between the non-stoichiometry of the thin film and the visible emission was discussed. The luminescent centers that correspond to green emission are defects; the concentration of defects was higher in the ZnO thin film that was deposited at RT than in the film that was deposited at . 相似文献
30.
Hsieh HT Psaltis D Beyer O Maxein D von Korff Schmising C Buse K Sturman B 《Optics letters》2005,30(17):2233-2235
Spatial gratings are recorded holographically by two femtosecond pump pulses at 388 nm in lithium niobate (LiNbO3) crystals and read out by a Bragg-matched, temporally delayed probe pulse at 776 nm. We claim, to our knowledge, the first holographic pump-probe experiments with subpicosecond temporal resolution for LiNbO3. An instantaneous grating that is due mostly to the Kerr effect as well as a long-lasting grating that results mainly from the absorption caused by photoexcited carriers was observed. The Kerr coefficient of LiNbO3 for our experimental conditions, i.e., pumped and probed at different wavelengths, was approximately 1.0 x 10(-5) cm2/GW. 相似文献