Single Se Research Articles

Imaging of Odontogenic Cysts and Tumors

Summary Although expert review of conventional radiographs may even reveal some of the more subtle features of jaw cysts and tumors#x2014;for example, focal areas of perforation—only 50% or fewer of all OKC, are identified on plain radiographs. The recurrence rate is estimated at 58.3% in a recent review.47 Combined CT and MR imaging is necessary for the full range of tissue morphology, including bony and soft tissue detail, and certain fluid characteristics. Magnetic resonance imaging is indispensable in evaluating most radiolucent lesions resembling a dental cyst, irrespective of the size or location of the lesion. Cyst contents can be characterized in a cost-effective manner by using a single T2-fast SE sequence, which can also accurately distinguish between most ameloblastomas and myxofibromas. The multiplanar, subtle soft tissue detail obtained provide the way for a definitive diagnosis as well as effective first procedure surgery. In the authors#x0027; experience, advanced MR imaging applications provide, for the first time, a reliable, noninvasive modality to determine the vitality of free vascularized microsurgical tissue transplantation grafts.

Raman Scattering Study of K3H(SeO4)2Single Crystal in High Temperature Phases

Raman scattering from the deuterated compound Rb 3 D(SeO 4 ) 2 single crystal is studied in the temperature range between 79.2 K and 480.0 K. A new Raman line appears at 827 cm -1 as much as 60 K below the superionic phase transition temperature, and does not depend on temperature and deuteration. It has been suggested that this line is caused by the stretching motion of a single Se–O in SeO 4 tetrahedra accompanied by the destruction and reconstruction of a hydrogen bond. In low temperature region, the dielectric constant of Rb 3 D(SeO 4 ) 2 , measured at 100 KHz, shows a λ-type anomaly at 93 K, while the observed Raman spectra are almost the same above and below this temperature.

Synthesis and Characterization of MoSe2 and WSe2 Nanoclusters

The synthesis, characterization, absorption, and emission spectra of MoSe2 and WSe2 nanoclusters are reported. These nanoclusters are about 3.5−6 nm (MoSe2, see graphic) and 4−7 nm (WSe2) in diameter, as measured by TEM imaging. The particles are strongly quantum confined and highly anisotropic. Electron diffraction results indicate that they are three-atoms thick, consisting of a single two-dimensional Se−Mo−Se or Se−W−Se trilayer.

Preparation of CulnSe 2 thin films by rapid thermal processing of Se-containing precursors

In this study, CuInSe2 thin films were prepared by the rapid thermal treatment (RTP) of metallic precursors in a close-spaced graphite container. The thermal diffusion process of selenium into the InSe/Cu/InSe precursor stacks critically influenced the structural properties (i.e., morphological features, formation of crystalline phases and in-depth compositional uniformity) of the films. In cases where pure elemental Se layers were incorporated into the stacks (i.e., InSe/Cu/InSe/Se), RTP treatment yielded compound films with poor structural properties. Single-phase material with uniform and dense surface morphologies was obtained when InSe/Cu/InSe precursors were reacted to an elemental Se atmosphere during RTP treatment. In these cases, single Se pellets were placed in close proximity to the samples in a partially closed graphite container. The container was then rapidly heated in 1 min to 550 °C, followed by a reaction period of 6 min at this temperature. X-ray fluorescence (XRF) Kα1,2 line intensity measurements from these specific samples, after different stages of etching, revealed a relatively high degree of in-depth compositional uniformity. The deposition of this high quality material with a relatively simple and rapid two-stage technique represents an important technological advantage.

Dynamics of Single Selenium Chains Confined in One-Dimensional Nanochannels ofAlPO4−5: Temperature Dependencies of the First- and Second-Order Raman Spectra

The temperature dependence of the Raman spectrum of single helical Se chains in nanochannels of ${\mathrm{AlPO}}_{4}\ensuremath{-}5$ was studied. Dramatic changes in the spectra due to structure transformations in this one-dimensional system are observed. The chains are found to be ordered at 77 K. Reversible weak disordering of the chains (mainly due to the large-amplitude torsional vibrations) occurs with increasing temperature. At temperatures above $\ensuremath{\sim}340\mathrm{K}$, a phase transition accompanied with a structural relaxation of the chains to the strongly disordered state with unfixed dihedral angles (``torsional melting'') is observed.

Selenium double donors in neutron transmutation doped, isotopically controlled germaniun

Far infrared photoconductivity and absorption measurements were performed on isotopically controlled 76Ge samples that were neutron irradiated to produce 77Se through double beta decay. The spectra exhibit ground state to bound excited state transitions which place the first ionization level of Se at E c -0.2688 eV. Hall effect measurements on compensated Ge:Se single crystals yield the second ionization level in the lower half of the band gap at E v +0.17 eV. Our experiments offer the first unambiguous identification of the deep donor level formed by single Se atoms on Ge lattice sites and verify earlier findings.

Raman Scattering Study of Cs 3H(SeO 4) 2 Single Crystal in High Temperature Phases

Raman scattering from the deuterated compound Rb 3 D(SeO 4 ) 2 single crystal is studied in the temperature range between 79.2 K and 480.0 K. A new Raman line appears at 827 cm -1 as much as 60 K below the superionic phase transition temperature, and does not depend on temperature and deuteration. It has been suggested that this line is caused by the stretching motion of a single Se–O in SeO 4 tetrahedra accompanied by the destruction and reconstruction of a hydrogen bond. In low temperature region, the dielectric constant of Rb 3 D(SeO 4 ) 2 , measured at 100 KHz, shows a λ-type anomaly at 93 K, while the observed Raman spectra are almost the same above and below this temperature.

Raman Scattering Study of Rb3H(SeO4)2Single Crystal in High Temperature Phases

Raman scattering from a single crystal of Rb 3 H(SeO 4 ) 2 has been observed in the frequency range between 20 cm -1 and 1000 cm -1 at phases I (482.6 K, 466.8 K, 443.3 K) and II (391.2 K, 301.2 K, 78.6 K). The measured spectra in phase II were assigned to the normal modes of SeO 4 tetrahedra vibration. In phase I, this compound shows high electric conductivity due to the hopping of protons. A new Raman line has been found at 826 cm -1 in this high temperature phase. It is suggested that this line is caused by the stretching mode of a single Se–O bond in SeO 4 tetrahedra, accompanied by destruction and reconstruction of hydrogen bonds.

Selenium-containing formate dehydrogenase H from Escherichia coli: a molybdopterin enzyme that catalyzes formate oxidation without oxygen transfer.

Formate dehydrogenase H, FDH(Se), from Escherichia coli contains a molybdopterin guanine dinucleotide cofactor and a selenocysteine residue in the polypeptide. Oxidation of 13C-labeled formate in 18O-enriched water catalyzed by FDH(Se) produces 13CO2 gas that contains no 18O-label, establishing that the enzyme is not a member of the large class of Mo-pterin-containing oxotransferases which incorporate oxygen from water into product. An unusual Mo center of the active site is coordinated in the reduced Mo(IV) state in a square pyramidal geometry to the four equatorial dithiolene sulfur atoms from a pair of pterin cofactors and a Se atom of the selenocysteine-140 residue [Boyington, J. C., Gladyshev, V. N., Khangulov, S. V., Stadtman, T. C., and Sun, P. D. (1997) Science 275, 1305-1308]. EPR spectroscopy of the Mo(V) state indicates a square pyramidal geometry analogous to that of the Mo(IV) center. The strongest ligand field component is likely the single axial Se atom producing a ground orbital configuration Mo(dxy). The Mo-Se bond was estimated to be covalent to the extent of 17-27% of the unpaired electron spin density residing in the valence 4s and 4p selenium orbitals, based on comparison of the scalar and dipolar hyperfine components to atomic 77Se. Two electron oxidation of formate by the Mo(VI) state converts Mo to the reduced Mo(IV) state with the formate proton, Hf+, transferring to a nearby base Y-. Transfer of one electron to the Fe4S4 center converts Mo(IV) to the EPR detectable Mo(V) state. The Y- is located within magnetic contact to the [Mo-Se] center, as shown by its strong dipolar 1Hf hyperfine couplings. Photolysis of the formate-induced Mo(V) state abolishes the 1Hf hyperfine splitting from YHf, suggesting photoisomerizaton of this group or phototransfer of the proton to a more distant proton acceptor group A-. The minor effect of photolysis on the 77Se-hyperfine interaction with [77Se] selenocysteine suggests that the Y- group is not the Se atom, but instead might be the imidazole ring of the His141 residue which is located in the putative substrate-binding pocket close to the [Mo-Se] center. We propose that the transfer of Hf+ from formate to the active site base Y- is thermodynamically coupled to two-electron oxidation of the formate molecule, thereby facilitating formation of CO2. Under normal physiological conditions, when electron flow is not limited by the terminal acceptor of electrons, the energy released upon oxidation of Mo(IV) centers by the Fe4S4 is used for deprotonation of YHf and transfer of Hf+ against the thermodynamic potential.

Polarized Raman spectra of selenium species confined in nanochannels of AlPO 4-5 single crystals

Selenium has been incorporated into the channels of AlPO 4-5 (AFI) single crystals by vapor adsorption as well as by molten Se injection. Results have been found to be similar for both methods. From Raman spectra, we have concluded that single helical Se chains and Se 8 molecules are formed inside the AFI channels. Moreover, we have found trigonal Se in meso-channels of AFI–Se crystals. Single chains and chains in trigonal Se are oriented along the c-axis of the AFI crystal. Se 8 molecules are mainly oriented by 4-fold axis along the c-axis of the AFI crystal.

Absorption and Raman spectra of Se 8-ring clusters in zeolite 5A

Samples with different weight ratio of Se to zeolite 5A (Se composition) have been prepared by loading Se into the cages of zeolite 5A and the measurements of the absorption and Raman spectra have been carried out for the prepared samples. The measured absorption edges of the samples are close and blue shifted to the value for monoclinic Se containing Se 8-ring, suggesting the formation of Se 8-ring clusters in the cages. The continuous and broadening features of the absorption spectra are interpreted by the strong electron-phonon coupling in Se 8-ring clusters. The sample with high Se composition has a red shift of the absorption band edge relative to the samples with less Se composition. It is tentatively attributed to the reason that with different Se composition, single Se 8-ring clusters and double Se 8-ring clusters are formed in the cages of zeolite 5A. A single broad band at about 262 cm −1 is observed in the Raman spectra, that gives the further support of the formation of Se 8-ring clusters.

Atomic structure of selenium inserted in zeolites of the Na-mordenite type

The atomic structure of Se incorporated with various amounts in both small and large pore zeolites of the Na-mordenite type is investigated by X-ray absorption spectroscopy (XAS). The results of the EXAFS analysis are compared to those obtained for hexagonal selenium. The distances of Se to its first and second Se neighbors are found to be 2.33 and 3.61 A, respectively, and attributed to intrachain distances, which are reduced with respect to those of hexagonal selenium. The lack of the Se-Se distance at 3.44 A confirms the loss of the first interchain bonds present in hexagonal Se and confirms the incorporation of single chains of Se in the channels of the mordenite in agreement with previous results given in the literature. Only small differences in the selenium environment are observed for the various contents of Se in mordenite. The presence of a peak around 4 A in the Fourier transforms of the EXAFS data of all the analyzed compounds is attributed to the partial overlap of the single Se chains present inside the mordenite channels.

A Study on Transmission Error in a Synchronous Belt Drive. Effect of Production Error in Polyurethane Belt.

Experiments on a transmission error having a period of one revolution of the belt in a polyurethane synchronous belt drive were performed in the quasi-static condition under an initial tention. The experimental results were compared with the computed results which used the results of measurement for the production error in the belt. It was confirmed that the transmisssion error is mainly caused by a single pitch error and the change of the product of the sectional area of the load carrying cords and the modules of elasticity of the belt, SE. In the case of the belt used in this study, the change of SE had the most influence on the transmission error. As the tendencies of the experimental results and the computed ones coincided well, the methods of measurement for the single pitch error and SE, and the methods for arrangement of these values used in order to compute the transmission error were right.

Laser Selective Area Epitaxy for the Potential of Optoelectronic Integration

ABSTRACTWe report for the first time the dopant behavior in laser assisted selective epitaxy of device quality GaAs films. DMZn and H2Se were used as p-type and n-type dopants respectively. Uniform doping was achieved by introducing TMGa, AsH3 and dopant gases simultaneously and was accompanied by a decrease in growth rate for both Zn and Se doping. For planar doping, several Se planes were embedded in a GaAs layer by simultaneously introducing AsH3 and H2Se during the LCVD process. A sheet carrier concentration in the 1012 – 1013 cm−2 range was obtained for a single Se plane. Hall data of these films will be discussed. It was found planar doping results in better electrical properties and better growth rate control.

Raman spectra of chalcogen chains isolated in zeolite matrixes

Raman spectra are reported for single Se and Te chains stabilised in the regular system of parallel channels of a mordenite dielectric matrix. The symmetric bond-stretching mode frequency is determined for Se chains (260 cm-1) and for Te chains (164 cm-1). The distinct bond-bending mode bands associated with ring-like and chain-like fragments and the Fermi resonance structure are found in the Se chain spectrum. A comparison of the spectra of chains with those of bulk materials is made. It is shown that the interchain interaction in trigonal Se and Te crystals weakens significantly the intrachain bonding. Confirmation is given for the amorphous Se and Te models that are based on slightly interacting chains with varying signs and magnitudes of dihedral angles.

Hydrogen bond formation and anion ordering in superconducting (TMTSF) 2ClO 4 and (TMTSF) 2AsF 6

An examination of the low temperature (125K) X-ray diffraction determined structure of (TMTSF) 2C10 4, the only ambient pressure organic superconductor known, reveals a previously unseen nearest-neighbor hydrogen bonding environment surrounding the anion resulting in short oxygen atom to methyl-hydrogen atom interactions that are likely responsible for the ordering of the C10 4 - anion associated with a transition observed at 24K. 1 Superconductivity is observed in (TMTSF) 2ClO 4 only when the anions adopt an ordered (relaxed 1) configuration. In contrast to the previously reported single short Se…0 distance, the 0…H-C contacts are both short and numerous. The observed librational motion of the perchlorate anion provides further support for the importance of the 0…H interactions in the pinning of the anion. Additional discussion regarding the influence of F…H hydrogen bonds on the AsF 6 - anion disorder in (TMTSF) 2AsF 6, a superconductor under applied pressure only, is also presented.

Site inequivalence inFe1+xNb3−xSe10

${\mathrm{Fe}}_{1+x}{\mathrm{Nb}}_{3\ensuremath{-}x}{\mathrm{Se}}_{10}$ has a novel structure made up of trigonal prismatic and octahedral coordinated metal atoms. The Se atoms are of two major types, those bound in Se pairs and single Se atoms, and while only Nb cations are found on the trigonal sites and the Fe (along with the remaining Nb) is found on the octahedral sites. To permit the study of the effects of disorder and site inequivalence on the electronic structure of this compound, the x-ray photoelectron spectra of the core and valence electrons were examined. The spectra show two distinct types of Se. The relative intensities of the two Se spectra and comparisons with the spectra of related compounds identify the Se at greater binding energy with the closely spaced Se pairs in the trigonal chains and those at smaller binding energy with the rest of the Se atoms. The spectra of the Nb atoms in the two different sites were not resolved and differ by not more than 0.2 eV in binding energy. However, the Nb $3d$ spectra showed more broadening than in similar compounds, probably due to the Nb site inequivalence and disorder intrinsic to the octahedral chains. All Nb atoms are consequently chemically similar. Chemical shifts indicate an oxidation state for Nb in ${\mathrm{Fe}}_{1+x}{\mathrm{Nb}}_{3\ensuremath{-}x}{\mathrm{Se}}_{10}$ between these of Nb${\mathrm{Se}}_{2}$ and Nb${\mathrm{Se}}_{3}$. The spectra of the Fe atoms were relatively broad, and showed no resolved structure. These results are consistent with a recent semiempirical tight-binding band calculation which suggests that the conduction-electron density is low and resides mainly on the trigonal prismatic chain.

The absorption spectra of single selenium and tellurium chains in dielectric matrix channels

The absorption spectra are reported for single Se and Te chains stabilized in the regular system of parallel channels of mordenite dielectric matrix. A conclusion is made that the Se(Te) chain located in the mordenite channel has no D 3 symmetry as the dihedral angle of the chain varies randomly. A correlation is found between absorption spectra of the Se(Te) chain and amorphous Se(Te).

Formation of heavily doped n-type layers in GaAs by multiple ion implantation

N-type layers in GaAs with high free electron concentrations have been produced by multiple implantation of Ga, As, or P with dopant species such as Se, Si, or Ge. The implants that have been investigated include Si, Si + P, Ge, Ge + As, Se, and Se + Ga. The multiple implants Si + P, Ge + As, and Se + Ga gave higher peak carrier concentrations, especially at lower anneal temperatures, than did the respective single implants Si, Ge, and Se. In fact, Ge when implanted alone produced a p-type layer while the Ge + As multiple implant produced an n-type layer. Multiple implants with Si and Ge as dopants showed significant thermal diffusion during the anneal. Multiple implants of Ga with Se, on the other hand, resulted in reduced thermal diffusion in comparison with single Se implants.

Formation of heavily dopedn-type layers in GaAs by multiple ion implantation

N-type layers in GaAs with high free electron concentrations have been produced by multiple implantation of Ga, As, or P with dopant species such as Se, Si, or Ge. The implants that have been investigated include Si, Si + P, Ge, Ge + As, Se, and Se + Ga. The multiple implants Si + P, Ge + As, and Se + Ga gave higher peak carrier concentrations, especially at lower anneal temperatures, than did the respective single implants Si, Ge, and Se. In fact, Ge when implanted alone produced a p-type layer while the Ge + As multiple implant produced an n-type layer. Multiple implants with Si and Ge as dopants showed significant thermal diffusion during the anneal. Multiple implants of Ga with Se, on the other hand, resulted in reduced thermal diffusion in comparison with single Se implants.