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Showing papers on "Single crystal published in 1973"


Journal ArticleDOI
Marc Ilegems1, H.C. Montgomery1
TL;DR: Hall measurements for undoped and Zn-doped vapor-grown single crystal GaN on (0001) Al 2 O 3 layers with 298 K carrier concentrations (n -type) between 1·4×10 17 cm −3 and 9×10 19 cm−3 were reported in this paper.

180 citations


Journal ArticleDOI
TL;DR: In this article, single crystal aluminium surfaces were prepared by auto-epitaxy on these substrates and the work functions of the surfaces were determined photoelectrically, showing a linear relationship between surface atom density and work function for the three faces investigated.
Abstract: (100), (110) and (111) single crystal aluminium substrates were thoroughly outgassed by heating by electron bombardment in ultra high vacuum. Fresh single crystal surfaces were prepared by autoepitaxy on these substrates and the work functions of the surfaces were determined photoelectrically. The general effect of the deposition of an aluminium film on the substrate was to reduce the work function, but annealing the film at temperatures between 473 K and 573 K caused the work function to return to a constant value which was taken to be characteristic of the ordered surface. (100) aluminium surfaces were also prepared by epitaxy on potassium chloride crystals. The effect of argon ion bombardment on a bulk (110) aluminium surface is to increase the work function towards the polycrystalline value, but the characteristic value for the (110) face may be restored by annealing the crystal. There is a linear relationship between surface atom density and work function for the three faces investigated.

140 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined the properties of the 3-V compounds with respect to crystallography, surface topography, uniformity, residual strain and electrical and acoustic properties with emphasis on those orientations which are of particular interest to surface acoustic wave (SAW) device applications.
Abstract: Heteroepitaxial films of the III-V compounds, A1N, GaN and GaAs have been grown on insulating substrates by reactions involving Group III metal-organic compounds and Group V hydrides. The films were examined with respect to crystallography, surface topography, uniformity, residual strain, and electrical and acoustic properties with emphasis on those orientations which are of particular interest to surface acoustic wave (SAW) device applications. Aluminum nitride films up to 10 µm in thickness were grown on 1″ diameter sapphire substrates with a 5% to 10% thickness variation. The films, though characterized as single crystal by x-ray means, exhibited a grain-like structure and considerable surface faceting. The residual strain in the films depends on the crystallographic direction and increases substantially with film thickness. These films exhibit useful surface acoustic properties. Epitaxial GaN films are more easily prepared than A1N films but by contrast are semiconducting unless “doped” with Zn or Li during the growth process. Films of this material are similar crystallographically to A1N and preliminary results show that they exhibit piezoelectric properties. The lack of published data on the acoustic properties of GaN films is probably due to the difficulty in compensating the films to provide insulating layers in device structures. Preliminary results obtained on GaAs epitaxial layers are discussed briefly because of the semiconducting properties of this material.

123 citations


Journal ArticleDOI
TL;DR: In this article, a structural refinement of the five data sets has been performed and it has been shown that as the temperature approaches T c the oxygen atom approaches the position x, 1 3, 1 12, with respect to Ta at the origin, in space group R 3 c.

123 citations



Journal ArticleDOI
TL;DR: Pines et al. as mentioned in this paper employed the method of protonenhanced nuclear induction spectroscopy to find the eigenvalues and eigenvectors of the chemical shift tensors for the various 13C nuclei in a single crystal of durene (1, 2, 4, 5 −tetramethylbenzene).
Abstract: The method of proton‐enhanced nuclear induction spectroscopy [A. Pines, M. G. Gibby, and J. S. Waugh, J. Chem. Phys. 59, 569 (1973)] has been employed to find the eigenvalues and eigenvectors of the chemical shift tensors for the various 13C nuclei in a single crystal of durene (1, 2, 4, 5‐tetramethylbenzene). For each type of carbon the trace of the shielding tensor, Trσ agrees well with the isotropic shift σi found from spectra of liquid solutions. The well‐known tendency of σi to be smaller for aromatic than for aliphatic carbon is found to be ascribable largely to the very small shielding which occurs for the former when the applied field is in the plane of the ring and tangent to it at the C atom in question. The CH3 carbons have much less anisotropic shielding than do the ring carbons. The rather close coincidences between nominal bond directions and the eigenvectors of σ suggest that nonbonded interactions in the crystal play an unimportant role.

100 citations


Journal ArticleDOI
TL;DR: The hydrogen-deuterium exchange reaction takes place readily on a platinum single crystal with high Miller index (997), but not detatably on a single crystal of low Miller: index (111), and the difference in reactivity is attributed to the large density of atomic steps present on the high-index surface that are responsible for the dissociation of the diatomic molecules.
Abstract: The hydrogen-deuterium exchange reaction takes place readily on a platinum single crystal with high Miller index (997), but not detatably on a platinum single crystal of low Miller: index (111). The difference in reactivity is ascribed to the large density of atomic steps present on the high-index surface that are responsible for the dissociation of the diatomic molecules.

99 citations


Journal ArticleDOI
TL;DR: In this paper, single crystal samples have been irradiated in a high voltage (1 MeV) transmission electron microscope and the defects formed are described as a function of specimen temperature and compared with similar defects formed by proton irradiation in an accelerator-electron microscope link.
Abstract: Silicon single crystal samples have been irradiated in a high voltage (1 MeV) transmission electron microscope. The defects formed are described as a function of specimen temperature and compared with similar defects formed by proton irradiation in an accelerator-electron microscope link. The defects are contrasted with those obtained with heavy ions with particular regard to possible mechanisms for the crystalline to amorphous transition which was not seen for electron and proton bombardments. For irradiations at 450°C needle-shaped precipitates were formed on {113} planes.

95 citations


Journal ArticleDOI
TL;DR: In this article, the i.r. reflection and Raman spectra of single crystal specimens of cuprous oxide have been studied between 20 and 900 cm −1 over a wide temperature range.

93 citations


Journal ArticleDOI
TL;DR: In this article, a new polymorph of the layered compound tantalum disulfide, 4Hb-TaS 2, has been prepared in single crystal form, and measurements of magnetic susceptibility, electrical resistivity, and differential heat capacity show two first order transitions at 20 and 315°K.

88 citations


Journal ArticleDOI
TL;DR: In this article, the authors reported the single-crystal Raman and i.r. spectra of vanadium(V) oxide and absorption frequencies compared with those calculated using a simple transferred force field.
Abstract: Oriented single-crystal Raman and i.r. spectra of vanadium(V) oxide are reported and absorption frequencies compared with those calculated using a simple transferred force field. It is shown that departures from previously established oxide-group frequencies are due to the relative lightness of the vanadium atom.

Journal ArticleDOI
TL;DR: The scattering of hydrogen, deuterium, and rare gases from the (111) face of silver has been studied at ultrahigh vacuum as mentioned in this paper, where the surfaces were prepared by argon ion bombardment and high temperature annealing incident angles between 20° and 65° and surface temperatures between room temperature and 573°K.


Journal ArticleDOI
TL;DR: In this paper, a single crystal thin films of Bi substituted iron garnets have been grown by the liquid phase epitaxy technique and the growth conditions and compositions are presented together with the segregation coefficients of Bi and Pb as a function of growth temperature.
Abstract: Single crystal thin films of Bi substituted iron garnets have been grown by the liquid phase epitaxy technique. The growth conditions and compositions are presented together with the segregation coefficients of Bi and Pb as a function of growth temperature. The Faraday rotation and optical absorption have been measured for wavelengths between 0.7 and 0.46 μm. The superior magneto-optic properties (Faraday rotations of up to ten times larger than that observed for Y3Fe5O12) make these epitaxial layers attractive for magneto-optic devices. The influence of Pb incorporation on the optical properties of the films is discussed. Compositions of Bi and Ga(Al) substituted Gd3Fe5O12, which exhibit a magnetic compensation temperature near room temperature and high Faraday rotation, have also been prepared. The magnetic switching behaviour as a function of temperature has been determined. It shows that these films are especially suited for thermomagnetic recording using an argon ion laser at a wavelength of 5145 A.

Journal ArticleDOI
TL;DR: In this article, a single crystal of a bismuth-substituted gadolinium iron garnet was measured in the near-infrared region and the optical absorption coefficient was observed in this wavelength region.
Abstract: Faraday rotation and optical absorption of a single crystal of bismuth‐substituted gadolinium iron garnet were measured in the near‐infrared region. In spite of the remarkable increase of rotation by the bismuth substitution, no appreciable increase of absorption coefficient was observed in this wavelength region.

Journal ArticleDOI
TL;DR: In this paper, X-ray scattering studies in single-crystal beryllium reveal an anisotropy in both the plasmon dispersion and linewidth, and by comparing the data with random-phase approximation-type theory which includes band structure, they can begin to separate the contributions from the lattice and from true many-body interactions to the temporally and spatially dependent response of an interacting electron gas at metallic densities.
Abstract: X-ray scattering studies in single-crystal beryllium reveal for the first time an anisotropy in both the plasmon dispersion and linewidth. By comparing the data with random-phase-approximation-type theory which includes band structure, we can begin to separate the contributions from the lattice and from the true many-body interactions to the temporally and spatially dependent response of an interacting electron gas at metallic densities.

Journal ArticleDOI
TL;DR: In this article, a new concept of the α1-relaxation mechanism of high-density polyethylene is proposed based on the mechanical properties observed in the α-temperature range for as-grown single crystal mats and for samples of bulk crystallized material.
Abstract: A new concept of the nature of the α1-relaxation mechanism of high-density polyethylene is proposed. This concept is based on the mechanical properties observed in the α-temperature range for as-grown single crystal mats and for samples of bulk crystallized material. The decomposition of the α-multiple-relaxation process into separate α1 and α2-processes was carried out using several different assumptions. These were based on the magnitude of activation energy, on the absorption curve profile of the α2-mechanism, and on the morphological aspects of hollow pyramidal single crystal and lamellar platelets. Based on the paracrystalline analysis proposed by Hosemann, it is suggested that the lamellar platelets of bulk spherulites are composed of a mosaic block structure. These mosaic blocks have diameters of 130∼180 A, heights of 170∼400 A, and intermosaic block distances of several angstroms with specific values depending upon the annealing temperature. The magnitude of the energy dissipation produce...

Journal ArticleDOI
TL;DR: The crystal structure of tin(II) chloride dihydrate, SnCl2·2H2O has been determined by a single crystal X-ray diffractometer technique as discussed by the authors.
Abstract: The crystal structure of tin(II) chloride dihydrate, SnCl2·2H2O has been redetermined by a single crystal X-ray diffractometer technique. The crystal is monoclinic, space group P21⁄c with a=9.313, b=7.250, c=8.970 A, β=114°55′ and Z=4. The structure was solved by three-dimensional Patterson and electron density syntheses. An anisotropic least-squares refinement, based on 1695 independent reflections gave an R value of 0.04. The tin(II) atom forms a pyramidal complex with two chlorine atoms and one oxygen atom; the bond lengths in the pyramid are Sn–O, 2.33 and Sn–Cl, 2.50 and 2.56 A and the bond angles are 86.9, 85.0, and 87.9°. These results support a view that the bonding in dichloroaquotin(II) complex is considerably ionic in character. This crystal consists of double layers of the aquocomplex, SnCl2·(OH2), parallel to (100) with intervening layers of the second water molecules. Both kinds of the water molecules are linked together by hydrogen bonds of 2.74, 2.79, and 2.80 A into two-dimensional networ...

Patent
28 Nov 1973
TL;DR: In this paper, a single crystal electrode is formed as an epitaxial layer on a single silicon chip substrate and by a process which includes vapor or sputter depositing an electrode-forming material, preferably palladium, upon the unheated exposed areas of the silicon substrate.
Abstract: In a semiconductor switch device wherein upon the application of a voltage in excess of the threshold voltage value at least one current conducting filamentous path is formed of relatively low resistance, there is provided one or more electrodes comprising a single crystal of conductive material which has a smooth face contacting the amorphous semiconductor material. The single crystal electrode is preferably formed as an epitaxial layer on a single silicon chip substrate and by a process which includes vapor or sputter depositing an electrode-forming material, preferably palladium, upon the unheated exposed areas of the silicon substrate. A subsequent annealing process grows a single crystal epitaxial layer of the deposited palladium and the silicon on the substrate. The semiconductor material forming the switch device is then directly deposited on this epitaxial layer.

Journal ArticleDOI
TL;DR: In this paper, three independent approaches are discussed for the quantitative calibration of tin adsorbed on the surface of iron monitored by Auger electron spectroscopy, and two of the approaches involved measurement of the substrate and condensate electron intensities at stages during the condensation of tin or stannic oxide on pure iron.


Journal ArticleDOI
TL;DR: The pyramidal nonplanar conformation of the oxonium ion has been confirmed in the first single crystal neutron diffraction study of a salt containing discrete H3O+ cations in an isolated state as discussed by the authors.
Abstract: The pyramidal nonplanar conformation of the oxonium ion has been confirmed in the first single crystal neutron diffraction study of a salt containing discrete H3O+ cations in an isolated state, p‐toluenesulfonic acid monohydrate (H3O+CH3C6H4SO3−). All H atoms have been located to high precision and the cation has molecular dimensions O–H=1.011(8) (the numbers within parentheses here and throughout the paper are the estimated standard deviations in the least significant digits), 1.013(8), and 1.008(8) A with H–O–H angles of 110.7(5), 109.2(5), and 111.2(5)°. The oxygen atom is 0.322(4) A out of the plane of the three hydrogen atoms. Although unrestricted by crystal symmetry, the ion has essentially C3ν symmetry. O–H separations are characteristic of those found in similarly strongly H‐bonded systems where the O...O separations are fairly short at 2.53 A.The structure was determined using 1732 independent three‐dimensional intensities measured using a neutron wavelength of 1.142 A. The crystals are monoclin...


Journal ArticleDOI
TL;DR: In this article, the emission spectra of phthalocyanine single crystals and evaporated films were investigated in the near infrared, and the authors discussed the S-T interaction caused by central metals.
Abstract: The emission spectra of phthalocyanine single crystals and evaporated films were investigated in the near infrared. In a H 2 Pc single crystal, several fluorescence peaks were observed between 760 mµ∼1 µ. In a CuPu single crystal, one phosphorescence band with fine structures was observed at 1.12 µ. However, no fluorescence was observed between 700 mµ∼1 µ. In ZnPc single crystals, both the fluorescence peaks and the phosphorescence peak at 1.15 µ were observed. In CoPc and NiPc, no emission was observed. These emission spectra were discussed in connection with S-T interaction caused by central metals. The phosphorescence was decreased markedly with raising temperature. In the evaporated film, a fairly broad emission band was observed which was attributed to the excimer emission tentatively. By the thermal treatment of this film, this broad band changes to the emission band of the single crystal.

Journal ArticleDOI
TL;DR: In this article, it was shown that the birefringence of AIIBIVC2V crystals with the chalcopyrite structure depends on the anisotropic polarizability of the A-C bonds.
Abstract: We have found that, as a consequence of the experimentally observed geometrical regularity of the BC4 tetrahedra in AIIBIVC2V crystals with the chalcopyrite structure, the birefringence of the crystals depends on the anisotropic polarizability of the A–C bonds only. This has allowed us to predict the birefringence of several AIIBIVC2V crystals for which reliable experimentally determined values are not available. To provide additional crystal structure data, as required for the predictions, we have refined the structural parameters of ZnGeP2 and ZnSiAs2 by the method of least squares with counter measured single crystal x‐ray diffraction data; the positional parameters (estimated standard errors in parentheses) are xP=0.25816 (0.00044) and xAs=0.26575 (0.00012). Final values of the conventional agreement index R were 0.029 and 0.022 for ZnGeP2 and ZnSiAs2, respectively. The GeP4 and SiAs4 tetrahedra are regular within experimental error. Experimentally determined bond distances are: Zn–P, 2.375 (0.002) ...

Journal ArticleDOI
TL;DR: The electronic absorption spectra of the iron-porphyrin chromophore are still not well understood despite the attention they command in physical, chemical, and biological investigations, and considerable new insight can be gained from investigations using polarized light.
Abstract: The electronic absorption spectra of the iron-porphyrin chromophore are still not well understood despite the attention they command in physical, chemical, and biological investigations. The spectra are characterized by broad, overlapping bands and generally remain diffuse even at very low temperatures. Metal d + d and metalligand charge transfer type transitions may appear in the same frequency region and are often obscured in the ordinary solution spectrum by the intense absorption of the porphyrin pi electron system. For these reasons, few convincing spectral assignments have been made for other than porphyrin n -+ n* transitions. Nevertheless, from investigations using polarized light, considerable new insight can be gained into the origin of these exceedingly rich and complex spectra. The most informative polarized light experiment is the measurement of the anisotropic absorption of plane polarized light by single crystals. The unique experimental result obtained from the single crystal experiment is the molecular direction in which plane polarized light is maximally absorbed, i.e., the direction of the electric dipole transition moment. This parameter is of paramount importance in elucidating optical transition mechanisms since it can lead directly to the symmetry of the excited state, thereby providing a critical test of theoretical descriptions of the chromophore’s electronic structure. With pure porphyrin or metalloporphyrin derivatives, there are serious experimental problems in obtaining a polarized -single crystal absorption spectrum. Because the chromophore concentration is so high (generally 2-5 M), extraordinarily thin crystal samples are required for measurements even in regions of only moderately intense absorption. Preparation of such thin crystals generally leads to small crystal faces, marginally suitable for absorption measurements even when microspectrophotometric techniques are employed. In the case of the triclinic tetraphenyl porphin crystal, this experimental difficulty was circumvented by Anex and Umans who measured the polarized specular reflectance spectrum and obtained

Journal ArticleDOI
TL;DR: The electrical resistivity of hexagonal synthetic single crystals and natural crystals of MoS 2 intercalated with alkali metals (K, Rb and Cs) has been measured.


Journal ArticleDOI
TL;DR: A pressure-temperature (P-T) section of the phase equilibrium diagram for Nb2 O5 has been determined and the superstructure of L-Nb2O5 was indexed on the basis of similarities to the known superstructures of L/O5 and confirmed with single crystal electron diffraction data.
Abstract: A pressure-temperature (P-T) section of the phase equilibrium diagram for Nb2O5 has been determined. Four single phase regions, H-Nb2O5, B-Nb2O5, and two L-Nb2O5 areas, were characterized by x-ray powder diffraction data. The superstructure of L-Nb2O5 was indexed on the basis of similarities to the known superstructures of L-Ta2O5 and confirmed with single crystal electron diffraction data. The correct unit cell is orthorhombic with a = 6.168, b = 29.312, c = 3.938 A, with the b axis 8 times the subcell (8 × 3.664 A).

Journal ArticleDOI
Abstract: Second order perturbation solutions are given to the general experimental hamiltonian : where the axes of the g, D and A tensors may be non-collinear. The effects of the non-collinearities are discussed in terms of the modifications of the E.S.R. parameters for both single crystal and polycrystalline samples. The principles are illustrated for the E.S.R. of the formyl radical from published single crystal and powder data.