Optical Reflectance Studies Research Articles

Synthesis of graphite-SbCl 5 and optical tests of its environmental stability

Details of the synthesis of stage 2 to stage 5 graphite-SbCl 5 are presented. The samples were prepared by the reaction of highly oriented pyrolytic graphite with SbCl 5 in a closed Pyrex tube by a two-temperature technique. We characterized our samples by X-ray diffractograms of the (001) reflections. The X-ray data were analyzed for the various c axis repeat distances and we found that I c( n) = 9.37 + ( n − 1)3.35 ± 0.02 Å where n is the stage number of the compound. This results is in good agreement with previous work. Results of optical reflectance studies on samples measured in situ and on samples exposed to laboratory air for several months are presented. These studies indicate that SbCl 5 intercalates into graphite to form an environmentally stable synthetic metal.

Transport and optical properties of polythiazyl bromides: (SNBr 0.4) x

Electrical transport and optical reflectance studies have been carried out on metallic derivatives of (SN) x; (SNBr 0.4) x and (SNBr 0.25) x. The average room temperature conductivity of (SNBr 0.4) x is 3.8 × 10 4 (ω-cm) -1 with temperature dependence characteristics of metallic behavior. Resistance ratios depend on sample perfection. Analysis of the optical reflectance data for light polarized along the (SN) x chains yields [ h ̷ ]ω p = 4.8 eV indicating little or no charge transfer upon bromination.

53. Quantitative optical reflectivity studies of graphitizable carbons prepared from coal-tar pitch, polyvinylchloride and acenaphthylene

53. Quantitative optical reflectivity studies of graphitizable carbons prepared from coal-tar pitch, polyvinylchloride and acenaphthylene

Synchrotron radiation as a new tool within photon-beam technology

Synchrotron radiation is now playing an increasingly important role in recent developments of new light sources. Synchrotron light emitted from a relativistic electron beam has a radiation pattern which makes it a unique source. The advantages with this type of radiation can be summarized as (a) continuous spectrum extending from the ir to the x-ray region, (b) strongly polarized, (c) highly collimated, (d) pulsed structure allowing time-resolution spectroscopy, and (e) high intensity making feasible the use of monochromators with narrow band pass. The Stanford Synchrotron Radiation Project has been in operation since May 1974 as a U.S. National Facility for uv and x-ray research in many disciplines using the radiation from the storage ring SPEAR at the Stanford Linear Accelerator Center. The radiation spectrum is characterized by the critical energy which varies as E3 (E=electron-beam energy) and is 11 keV for E=4 GeV. Useful flux is available out for approximately five times the critical energy. Five monochromators now share the beam run and cover the entire wavelength region from the visible to the hard x-ray region. Several experimental groups are involved in research programs including (a) uv and x-ray photoelectron spectroscopy, (b) optical reflectance and transmission studies, (c) soft x-ray absorption and extended x-ray absorption fine structure (EXAFS) studies, (d) low-angle scattering studies of certain biological materials, and (e) x-ray diffraction studies of protein crystals and other materials.

Optical reflection studies of lattice disorder in iodine implanted CdS

Abstract Optical reflectivity spectra (3.45 to 5.90 eV) of CdS implanted with 40 keV I+ are presented for doses between 5 × 1013 and 1 × 1016 ions/cm2 and for isochronal anneals up to 550°C. Typical peaks (E 1: A, B) present in crystalline CdS decrease with increasing dose until they are no longer resolvable; however, a prominent saturation observed in Si and somewhat in GaAs is not found for doses up to 1 × 1016 ions/cm2. Correlation with similar results obtained from the Rutherford scattering technique suggests the reflection variations are damage related and verifies previous results that anobservable amorphous layer is not formed. Annealing tends to increase the peaks with complete restoration occurring for doses 7 × 1014 ions/cm2 annealed at 500°C.

Electrical and Optical Properties of Amorphous vs Crystalline GeTe Films

Ac and dc conductivity, tunneling, and optical transmission and reflectance studies have been made on amorphous and crystalline (rhombohedral and NaCl) GeTe films (80 Å to 10 μ thick) prepared by evaporation and by sputtering. The crystalline films behave like a p-type degenerate semiconductor with Fermi level ∼0.3–0.5 eV in the valence band, resistivity ∼10−4 Ω cm, carrier concentration ∼1020 to 1021/cm3, Hall mobility ∼25–120 cm2/V sec, and a small, positive (metallic) temperature coefficient of resistivity. Amorphous films show a high resistivity which increases exponentially from ∼103 to >1010 Ω cm as the temperature decreases from 300–77 K, corresponding to an activation energy of 0.3–0.4 eV. The ac conductivity increases as ωn(n < 1) to approach a constant value above ω = 90 kc. Simultaneously, the activation energy for conduction decreases continuously to a nearly zero value. The conductivity also increases rapidly as a high power of the electric field at >104 V/ cm. The near infrared indices of amorphous and crystalline structures are 4.0 and 5.6, respectively. The optical absorption edge is nearly the same (∼0.8 eV) for the crystalline and amorphous films. A tentative explanation of the transport behavior of amorphous films is possible in terms of conduction by two parallel mechanisms: (a) in the conduction band by intrinsically excited carriers, and (b) by a hopping process in the trap-like localized levels above the Fermi level in the valence band.

Magnetic properties of V2O3-Al2O3 solid solutions

The magnetic susceptibilities of dilute solid solutions of V2O3 in corundum (α-Al2O3) have been measured over the temperature range 77–500°K, and at V3+ ion concentrations from 1 to 9 mole %. Lattice parameter and optical reflectance studies confirm the existence of a corundum phase over this concentration range. The magnetic moment of the V3+ ion is lower than the spin-only value and it decreases linearly with increasing concentration. The result is explained in terms of pair-wise interactions between V3+ ions, analogous to those in V2O3. The system also shows a large temperature independent paramagnetism of ca. 650 × 10–6, which is attributed to the trigonal component of the cubic crystal field present in the corundum structure.

Band Structure of Silicon, Germanium, and Related Semiconductors

A comprehensive survey of recent optical and cyclotron resonance experiments in semiconductors is given. By combining all available data, a categorical classification of eight principal levels in the valence and conduction bands of Si and Ge is proposed. Six of these levels occupy the same relative positions in the two crystals. Two of the levels are "sensitive" to the detailed differences in crystal potential; even these levels are much more nearly alike than previous theoretical work on Si indicated. The position of the two "sensitive" levels is shown to depend on one universal parameter, common to Si, Ge, and probably grey Sn, in both the experimental and theoretical band structures. The six insensitive levels are predicted quite accurately by theory.Experimental data on III-V compound semiconductors are consistent with the classification of levels in Si and Ge. It is suggested that a decisive test of the classification can be obtained from optical reflectivity studies of wurtzite crystals in the ultraviolet.