Temperature dependence of the optical properties of ZnSe films deposited on quartz substrate

ZnSe thin films were deposited by pulsed laser ablation on quartz substrate. The films were investigated by different characterization techniques, such as X-ray diffraction, Raman microspectroscopy, absorption, reflectivity, and photoluminescence spectroscopy. The XRD analysis showed the formation of cubic phase polycrystalline films. The Raman spectra confirmed the formation of ZnSe by the presence of TO and LO peaks at 202 cm^-1 and 252 cm^-1, respectively. The analysis of absorption and reflectivity measurements permits evaluation of the band gap and excitonic energy at low temperature and the temperature dependence of the energy gap. The photoluminescence measurements indicated the possibility of obtaining intrinsic band-band radiative emission up to room temperature. PACS 52.38.Mf; 78.55.-m; 78.55.Et     

New laser-induced fluorescence scheme for simultaneous OH and NO detection by a single laser set-up

In this communication, we propose a new laser-induced fluorescence (LIF) scheme that allows the simultaneous detection of OH and NO by a single laser set-up. OH is detected by the second harmonic (SH) of a dye laser tuned to the (0,0)-band of the 3064 ? system, while its third harmonic (TH) is used to detect NO through excitation of the (2,0)-band of the γ system. This scheme is presented and discussed within the framework of its potential use in field instruments for the measurement of tropospheric OH concentration. Received: 8 March 2002 / Revised version: 22 April 2002 / Published online: 8 August 2002     

On the Measurement of N2(A3Σ u + ) Metastable in N2 Surface-Dielectric Barrier Discharge at Atmospheric Pressure

The N₂(A³Σ _u ⁺ ) metastable has been investigated in an AC surface dielectric barrier discharge (surface-DBD) at atmospheric pressure in N₂ by Optical–Optical Double Resonance–Laser Induced Fluorescence spectroscopy (OODR-LIF) and by Optical Emission Spectroscopy (OES). The discharge is single-side produced by metallic stripes (comb-like electrode on a dielectric layer). The OODR-LIF measurements have been carried out in space afterglow above the plasma layer. The measurement was time resolved during the AC high voltage cycle and space resolved around the metallic/dielectric stripes. The space afterglow N₂(A) density does not evidence significant variation in the voltage cycle. The density is higher above the dielectric strip than on the metallic one. N₂(A) density in the space afterglow has been estimated to be about 10¹¹ cm^?3. The plasma layer, not accessible by OODR-LIF, has been investigated by OES through NOγ and Herman infrared bands. The estimated N₂(A) maximum density in the plasma layer is higher than 10¹² cm^?3.     

Microwave characterization of YBa2Cu3O7−x thin films grownin situ by Off-axis magnetron sputtering

Summary Superconducting films of YBa₂Cu₃O_7−x were depositedin situ on LaAlO₃ substrates using single-target 90° off-axis sputtering. The obtained films have tipicalT _c values of 91K. Surface resistance measurements on as-grown films reach 1.1 mΩ at 77K and 10GHz; whilst on ion-etched patterned resonant linesR _s (77K, 10GHz) it is about 10mΩ. Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994.     

Superconducting properties of polycrystalline YBCO prepared by a pyrolytic process

Il Nuovo Cimento D - Polycrystalline YBCO was prepared by a pyrolytic process starting from citrate and tartrate precursors. The effect of the precursor on the superconducting properties was...     

Effects of the indium doping on structural and optical properties of CdSe thin films deposited by laser ablation technique

Thin films of n-type CdSe have been grown on a quartz substrate by laser ablating a target obtained by mixing CdSe and metallic In powders. The effects of different doping concentration of In have been investigated. X-ray diffraction spectra show that at low In density only the CdSe lattice is present in the deposited film, whereas CdIn₂Se₄ and InSe compounds are deposited at higher In concentration. Band gap narrowing and band tails are observed in the absorption spectra when the In concentration increases. Photoluminescence spectra show band-band recombinations from 10 K to room temperature. Received 27 September 2002 Published online 11 April 2003 RID="a" ID="a"e-mail: giuseppe.perna@ba.infn.it     

Controlling semiconductor/metal junction barriers by incomplete, nonideal molecular monolayers

We study how partial monolayers of molecular dipoles at semiconductor/metal interfaces can affect electrical transport across these interfaces, using a series of molecules with systematically varying dipole moment, adsorbed on n-GaAs, prior to Au or Pd metal contact deposition, by indirect evaporation or as "ready-made" pads. From analyses of the molecularly modified surfaces, we find that molecular coverage is poorer on low- than on high-doped n-GaAs. Electrical charge transport across the resulting interfaces was studied by current-voltage-temperature, internal photoemission, and capacitance-voltage measurements. The data were analyzed and compared with numerical simulations of interfaces that present inhomogeneous barriers for electron transport across them. For high-doped GaAs, we confirm that only the former, molecular dipole-dependent barrier is found. Although no clear molecular effects appear to exist with low-doped n-GaAs, those data are well explained by two coexisting barriers for electron transport, one with clear systematic dependence on molecular dipole (molecule-controlled regions) and a constant one (molecule-free regions, pinholes). This explains why directly observable molecular control over the barrier height is found with high-doped GaAs: there, the monolayer pinholes are small enough for their electronic effect not to be felt (they are "pinched off"). We conclude that molecules can control and tailor electronic devices need not form high-quality monolayers, bind chemically to both electrodes, or form multilayers to achieve complete surface coverage. Furthermore, the problem of stability during electron transport is significantly alleviated with molecular control via partial molecule coverage, as most current flows now between, rather than via, the molecules.     

Electrical and optical properties of natural and synthetic melanin biopolymer

Natural and synthetic melanin have been investigated by means of optical, electrical and photoelectronic measurements. Optical measurements evidence absorption curves which allow to estimate optical gap for synthetic melanin, by using Tauc’s method. Dark conductivity and photoconductivity measurements were performed as a function of temperature and for different duration of thermal treatments. It has been evidenced that both quantities are thermally activated and thermal treatments play a very important role as far as gap states are concerned.