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《Current Applied Physics》2010,10(4):1221-1226
Good quality ammonium dihydrogen phosphate single crystals have been grown by: (i) Sankaranarayanan–Ramasamy (SR) method and (ii) SR method with slotted ampoule. The grown crystals were subjected to UV–Vis spectroscopy, high-resolution X-ray diffractometer, dielectric, piezoelectric and laser damage threshold studies. Compared to the (1 0 0) plane of the conventional method grown ADP crystal and 〈1 0 0〉 directed SR method grown ADP crystal, the crystal grown by SR method with slotted ampoule has higher growth rate, higher optical transparency, high crystalline perfection, low dielectric loss, high piezoelectric charge coefficient and high laser damage threshold due to diffusion of segregated impurities away from the growing crystal in the slotted ampoule growth. 相似文献
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Structures of monolayer nickel nitride (NiN) on Cu(0 0 1) surface are studied by X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Formations of Ni–N chemical bonds and NiN monolayer at the surface are confirmed by XPS on the N-adsorbed Cu(0 0 1) surfaces after Ni deposition and subsequent annealing to 670 K. A c(2 × 2) structure is always observed in the LEED patterns, which is a quite contrast to the (2 × 2)p4g structure observed usually at the N-adsorbed Ni(0 0 1) surface. Atomic images by STM indicate the mixture of Ni–N and Cu–N structures at the surface. Density of the trenches on the N-saturated surface decreases and the grid pattern on partially N-covered surfaces becomes disordered with increasing the Ni coverage. These results are attributed to the decrease of the surface compressive stress at the N-adsorbed Cu surface by mixing Ni atoms. 相似文献
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F. Allegretti G. Parteder L. Gragnaniello S. Surnev F.P. Netzer A. Barolo S. Agnoli G. Granozzi C. Franchini R. Podloucky 《Surface science》2010,604(5-6):529-534
We report on an interface-stabilized strained c(4 × 2) phase formed by cobalt oxide on Pd(1 0 0). The structural details and electronic properties of this oxide monolayer are elucidated by combination of scanning tunneling microscopy data, high resolution electron energy loss spectroscopy measurements and density functional theory. The c(4 × 2) periodicity is shown to arise from a rhombic array of Co vacancies, which form in a pseudomorphic CoO(1 0 0) monolayer to partially compensate for the compressive strain associated with the large lattice mismatch (~9.5%) between cobalt monoxide and the substrate. Deviation from the perfect 1:1 stoichiometry thus appears to offer a common and stable mechanism for strain release in Pd(1 0 0) supported monolayers of transition metal rocksalt monoxides of the first transition series, as very similar metal-deficient c(4 × 2) structures have been previously found for nickel and manganese oxides on the same substrate. 相似文献
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The chemical properties of structurally well-defined PdRu/Ru(0 0 0 1) monolayer surface alloys [H. Hartmann, T. Diemant, A. Bergbeiter, J. Bansmann, H.E. Hoster, R.J. Behm, Surf. Sci. in press, doi:10.1016/j.sucs.2008.10.055.] and a Pd monolayer on Ru(0 0 0 1) were studied by temperature programmed desorption and infrared reflection absorption spectroscopy using CO as probe molecule. IR experiments on the PdRu/Ru(0 0 0 1) surface alloys demonstrate that CO adsorption on Ru sites resembles that on pure Ru(0 0 0 1) (on-top adsorption), while adsorption on the Pd sites occurs on both multifold coordinated and on-top sites, similar to CO on Pd(1 1 1). A significant destabilization of CO adsorption on Pd sites for both, surface alloys and the Pd monolayer film, compared to pure Pd(1 1 1) surfaces is attributed to a combination of geometric strain and vertical electronic ligand effects; an additional variation in the CO adsorption bond strength in the surface alloys is attributed to changes in the neighboring surface atom shell (lateral ligand effects). The chemical modifications introduced by PdRu surface alloy formation are compared with findings for deuterium adsorption on the same surface alloys; effects of the two-dimensional (2D) distribution of surface atoms are illustrated by comparison with CO adsorption on PtRu/Ru(0 0 0 1) surface alloys, where in contrast to the pronounced 2D phase segregation in PdRu/Ru(0 0 0 1) the surface atoms are essentially randomly distributed. 相似文献
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《Surface science》2003,470(1-2):9-18
First principles total energy studies are performed to investigate the energetics, and the atomic structure of the adsorption of germane (GeH4), and digermane (Ge2H6) on the Si(0 0 1)-c(2 × 4) surface. It has been observed experimentally that adsorption of Ge2H6 is a dissociative process, which first yields GeH3 and then GeH2 fragments as products. We first study the adsorption of GeH2 considering two different models; the intra-row and the on-dimer geometries. Our results show that the on-dimer site is more stable than the intra-row geometry by 0.44 eV. This is not a surprise since in the absence of H atoms, adsorption in the on-dimer site leaves no dangling bonds. In contrast, when the GeH2 fragment is considered together with two H atoms, the intra-row geometry is favored energetically as compared with the on-dimer site, in good agreement with experiment. Similar results have been previously obtained for the adsorption of SiH2 on Si(0 0 1). Digermane adsorption is explored according to two different geometries. In the first one, we have considered the adsorption as two GeH3 fragments, while in the second, we have considered the adsorption as two GeH2 fragments plus 2 H fragments. In good agreement with experiments, it is found that the latter geometry is energetically more favorable. 相似文献
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Hisashi Yoshida Akinori Okamoto Seigi Mizuno Hiroshi Tochihara 《Surface science》2010,604(5-6):535-540
Low-energy electron diffraction (LEED) have been used to determine the Cu(0 0 1)–c(4 × 4)-Sn structure formed at 300 K. It is demonstrated that a structural model suggested by scanning tunneling microscopy observations is correct: The model consists of one substitutional Sn atom and four Sn adatoms in the unit cell. Optimum parameters of the determined c(4 × 4) structure reveal that Sn adatoms laterally are displaced by 0.30 Å away from ideal fourfold-hollow sites along the 〈100〉 directions. It is proposed that such displacements of the Sn adatoms cause the formation of a network of octagonal rings on Cu(0 0 1). The substitutional Sn atom is located at each center of the octagonal rings. The formation conditions of the network are discussed. 相似文献
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Takuhiro Kakiuchi Shogo Hashimoto Narihiko Fujita Masatoshi Tanaka Kazuhiko Mase Shin-ichi Nagaoka 《Surface science》2010,604(9-10):L27-L30
Topmost-surface-sensitive Si-2p photoelectron spectra of a clean Si(1 0 0)-2 × 1 surface have been measured using Si-2p photoelectron Si-L23VV Auger coincidence spectroscopy (Si-2p–Si-L23VV PEACS). The escape depth of the PEACS electrons is estimated to be ~1.2 Å. The results support the assignments of the Si up-atoms, the Si down-atoms, the Si 2nd-layer, and the Si bulk proposed in previous researches. The Si-2p component with a binding energy of ?0.23 eV relative to the bulk Si-2p3/2 peak, is shown to originate mainly from the topmost surface. Site selectivity of PEACS is indicated to be achieved to some degree by carefully selecting the kinetic energy of the Auger electrons. Since PEACS can be applied to any surface, the present study opens a new approach to identify PES components. 相似文献
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Structural, energetic and electronic properties of water molecules adsorbed on β-Si3N4 (0 0 0 1) surface, at various coverages, are investigated using density functional theory. At low coverages (θ ? 0.5), it is found that all H2O molecules undergo spontaneous dissociation forming hydroxyl (OH) and imino (NH) groups where the reactive sites are identified, a result shown for the first time using ab initio theory. For higher coverages (θ > 0.5), only partial dissociation takes place where some of the molecules stay intact being bound via H-bond in good agreement with experimental findings. The driving force for the water dissociation has been identified to be dangling bonds on lower coordinated N and Si surface atoms showing that not all surface atoms are reactive corroborating with previous experimental findings. 相似文献
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The substrate reactions of three common oxygen sources for gate oxide deposition on the group III rich InAs(0 0 1)-(4 × 2)/c(8 × 2) surface are compared: water, hydrogen peroxide (HOOH), and isopropyl alcohol (IPA). Scanning tunneling microscopy reveals that surface atom displacement occurs in all cases, but via different mechanisms for each oxygen precursor. The reactions are examined as a function of post-deposition annealing temperature. Water reaction shows displacement of surface As atoms, but it does not fully oxidize the As; the reaction is reversed by high temperature (450 °C) annealing. Exposure to IPA and subsequent low-temperature annealing (100 °C) show the preferential reaction on the row features of InAs(0 0 1)-(4 × 2)/c(8 × 2), but higher temperature anneals result in permanent surface atom displacement/etching. Etching of the substrate is observed with HOOH exposure for all annealing temperatures. While nearly all oxidation reactions on group IV semiconductors are irreversible, the group III rich surface of InAs(0 0 1) shows that oxidation displacement reactions can be reversible at low temperature, thereby providing a mechanism of self-healing during oxidation reactions. 相似文献
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《Superlattices and Microstructures》2001,30(2):75-80
In this work, the electronic structure and disorder effects in copper halides alloys are studied by means of the full potential linearized augmented plane wave (FLAPW) method. The calculated bowing parameter shows that the main contribution is due to the relaxation effects, though the charge transfer remains relatively significant, while the volume deformation contribution is negligible. The total bowing is found to be small in the three studied alloys. Results agree well with experimental and available theoretical works. 相似文献
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In this paper, we investigated the performance of multi terabits DWDM system consisting of hybrid optical amplifier RAMAN-EDFA for different data format such as non-return to zero (NRZ), return to zero (RZ) and differential phase shift keying (DPSK). We find that in 64 × 10 and 96 × 10 Gbps, RZ is more adversely affected by nonlinearities, where as NRZ and DPSK is more affected by dispersion. We further show that RZ provide good quality factor (13.88 dB and 15.93 dB for 64 and 96 channels), less eye closure (2.609 dB and 3.191 dB for 64 and 96 channels) and acceptable bit error rate (3.89 × 108 and 1.24 × 109 for 64 and 96 channels) at the respective distance as compare to other existing modulation format. We further investigated the maximum single span distance covered by using existing data formats. 相似文献
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Recent interests in mixed metal oxide nanostructured materials especially IrxRu1−xO2 compounds have been mainly driven by the technological application as electrocatalyst and electrode materials. We present room temperature Raman scattering results of single crystalline IrxRu1−xO2 (0 ≤ x ≤ 1) nanowires grown by atmospheric pressure chemical vapor deposition. We observed that the Eg, the A1g, and the B2g phonon modes of a single IrxRu1−xO2 nanowire are blue-shifted linearly with respect to the Ir contents from which we could get stoichiometry information. We also observed that the asymmetric lineshape and the broadening of the full width at half maximum of the Eg mode that involves the out-of-plane oxygen vibration. The unusual asymmetric broadening of the Eg phonon can be explained by the activation of the non-zone-center phonons due to substitutional disorder present in the system. We also found that there is a mixed mode of the A1g and the B2g phonons due to the substitutional disorder, in the range of 630–750 cm−1. 相似文献
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The current–voltage (I–V) characteristics of the nanosized metal–semiconductor contacts formed between the epitaxially grown ErSi2 islands and p-Si(0 0 1) substrate are measured in situ by the scanning tunneling microscope. Experimental results show that the current densities passing through the nanocontacts are five orders of magnitude larger than that of the macroscopic ones and have an obvious dependence on the contact area. Especially, it is found that I–V characteristics of the contacts are sensitive to the sample surface adsorption. Our investigations indicate that surface conduction plays an important role in the electrical transport process from ErSi2 islands to the Si(0 0 1) substrate. Furthermore, for the nanocontacts with surface currents suppressed effectively, the ideality factor and the effective Schottky barrier height are estimated by using the standard thermionic emission model. Our analysis suggests that the current through the interface between ErSi2 nanoislands and the p-Si(0 0 1) substrate is enhanced due to the effects of tunneling and image force lowering. 相似文献
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《Solid State Ionics》2009,180(40):1613-1619
Materials of the LiTi2 − xZrx(PO4)3 series (0 ≤ x ≤ 2) were prepared and characterized by powder X-ray (XRD) and neutron diffraction (ND), 7Li and 31P Nuclear Magnetic Resonance (NMR) and Electric Impedance techniques. In samples with x < 1.8, XRD patterns were indexed with the rhombohedral R3̅c space group, but in samples with x ≥ 1.8, XRD patterns display the presence of rhombohedral and triclinic phases. The Rietveld analysis of the LiTi1.4Zr0.6(PO4)3 neutron diffraction (ND) pattern provided structural information about intermediate compositions. For low Zr contents, compositions deduced from 31P MAS-NMR spectra are similar to nominal ones, indicating that Zr4+ and Ti4+ cations are randomly distributed in the NASICON structure. At increasing Zr contents, differences between nominal and deduced compositions become significant, indicating some Zr segregation in the triclinic phase. The substitution of Ti4+ by Zr4+ stabilizes the rhombohedral phase; however, electrical performances are not improved in expanded networks of Zr-rich samples. Below 300 K, activation energy of all samples is near 0.36 eV; however, above 300 K, activation energy is near 0.23 eV in Ti-rich samples and close to 0.36 eV in Zr-rich samples. The analysis of electrical data suggests that the amount of charge carriers and entropic terms are higher in Zr-rich samples; however, the increment of both parameters does not compensate lower activation energy terms of these samples. As a consequence of different contributions, the bulk conductivity of Zr-rich samples, measured at room temperature, is one order of magnitude lower than that measured in Ti-rich samples. 相似文献
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M. Sauvage-Simkin Y. Garreau R. Pinchaux A. Coati A. Ouerghi B. Etienne 《Surface science》2010,604(3-4):415-419
In view of understanding silicon incorporation in the δ doping process of GaAs (0 0 1), Si atoms have been deposited, under UHV, on a α(2 × 4) arsenic terminated substrate. In the low coverage regime, a transition to a less As rich (3 × 2) reconstructed Si–GaAs (0 0 1) surface was observed whose atomic structure has been investigated by grazing incidence X-ray diffraction performed in situ. Silicon is found to occupy not only a Ga substitutional site, precursor of a donor dopant but also to form nuclei for neutral clusters, on a template made by the (3 × 2) GaAs (0 0 1) reconstructed surface observed by Martrou et al. [Phys. Rev. B 72 (2005) 241307®]. The maximum surface concentration of donor-like silicon is estimated at 1.04 × 1014 cm?2 (1/6th monolayer). 相似文献
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F. Tielens M. Calatayud R. Franco J.M. Recio J. Pérez-Ramírez C. Minot 《Solid State Ionics》2009,180(14-16):1011-1016
The structural, energetic, and thermodynamic properties of the Co3 ? sAlsO4 (s = 0, 1, 2, and 3) crystal family are studied using periodic DFT calculations. We provide a quantitative discussion of the cation distribution effect on the cell parameter, the oxygen Wyckoff position, the interatomic distances and the energies of the structures. It is demonstrated that the low cobalt containing CoAl2O4 spinel is the most stable structure of the Co3 ? sAlsO4 (s = 0, 1, 2, and 3) crystal family. 相似文献
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Physics of the Solid State - The processes of electric charge transfer (conductivity) and mass transfer (diffusion) in La1 ‒ ySryF3 – y superionic... 相似文献