Energy Position Of Peak Research Articles

Temperature invariance of quantum well modulators using a feedback circuit based on the quantum confined Stark effect

We report the design and performance characteristics of a voltage feedback circuit which can rapidly compensate for the temperature-dependent shift of the excitonic peak energy positions in quantum confined Stark effect modulators. The energy position remains invariant over a temperature shift of 10 degrees . The circuit is simple and can be operated with a single device or an array of modulators.

Interface trap transformation in radiation or hot-electron damaged MOS structures

The interface traps created by ionising radiation or hot-electron injection in MOS capacitors have been found to undergo significant changes with time over an extended period (many months). Immediately after radiation or hot-electron damage, an interface trap peak above the midgap ( approximately Ev+0.75 eV) invariably appears. This peak (designated peak 1), along with its background, would continuously change with time after damage, and the detailed time-dependent behaviour depends on the surface orientation of the Si substrate, processing history, gate bias and sample temperature. For samples made on (100) substrates, three separable regimes have been observed: (i) latent generation (peak 1 and its background increase with time), (ii) defect transformation (peak 1 gradually converts into peak 2 below the midgap, resulting in a double-peak interface trap distribution), and (iii) room-temperature annealing (the overall density of interface traps decreases with time). The focus of this paper is on the defect transformation process. For samples made on (111) samples, on the other hand, the most salient feature is the gradual shift of the energy position of peak 1 toward the valence band, and eventually a single-peak residing below the midgap is observed. In contrast to the (100) results, no discernible double-peak distribution has been found in (111) samples. Results on (110) samples are qualitatively similar to those on (111) samples, while (311) samples are similar to (100) samples. The various experimental parameters that affect the defect transformation process in both (100) and (111) samples will be discussed. While the (100) results are too complex to be explained satisfactorily based on existing theories at the present time, the (111) results will be interpreted in terms of the atomic relaxation of the dangling-bond defect at the (111)Si/SiO2 interface.

Evaluation of a galvanometric scanner for rapid tuning of CO2 lasers

Remote sensing of gaseous constituents in the atmosphere is possible with a single laser system operating at high (more than 100 Hz) pulse tuning rates so as to minimize the effects of atmospheric turbulence. This article investigates the possibility of using a galvanometric scanner as a rapid tuning device for both pulsed and continuous-wave CO2 lasers. Preliminary cw experiments, performed in anticipation of future heterodyne lidar development, indicated that lines could be switched at rates up to 77 Hz over the entire spectrum, while much greater rates were achieved by restricting the angular displacement of the galvanometer. When used with a transversely excited atmospheric (TEA) laser, the galvanometer was able to switch lines as fast as 140 Hz. However, amplitude-dependent position adjustments were necessary to compensate for settling time and/or thermal drift effects in order to obtain maximum energy output. A calibration curve was constructed and tested, but predictions of peak energy positions were accurate only for high gain lines. Using a 16-bit D to A converter with computer control, there was more than adequate resolution available to extract the maximum energy from each line, even at low gain line positions. Only a small amount (250 μrad maximum) of far-field beam wander was measured during tuning between any two lines at maximum tuning rates. Thus, it appears that tuning a CO2 laser at line switching rates greater than 70 Hz is possible, but requires a feedback mechanism and/or additional sensor for accurate positioning. Although the galvanometer itself is a relatively simple and compact device, practical utilization may require additional equipment or algorithms.

Energy effects in secondary ion emission of implanted and simultaneously sputtered argon

Two states of implanted argon (single atoms and solid argon bubbles) cause splitting in energy distributions of Ar + secondary ions emitted from metal and semiconductor surfaces under Ar + ion bombardment. Steady state conditions of the sputtered surfaces influence the Ar + energy peak position.

EFFECT OF ANNEALING ON THE BANDTAIL STATES IN a-SixC1-x:H FILMS

Photoluminescence (PL) spectra of annealed a-SixC1-x:H films were studied. The-widths of the exponential bandtails were determined by means of the temperature dependences of PL peak energy positions. The experimental results shows that PL peak energy positions shift towards the lower energy with annealing temperature increasing. The bandtail widths have been calculated according to the exponential bandtail model, the calculation shows that the bandtails contract with increase of annealing temperature. A discussion about the results has been given.

Atom-Nucleus Hybrid State of 9 Be

A new concept of “atom-nucleus hybrid state” is proposed to explain the second 9ΣBe peak observed in the (K-, π-) reaction at CERN. The explanation is based on coupling among the isotriplet states of 8Be*(16.63 MeV) with corresponding isotriplet of Σ particles. The Coulomb interaction between 8B and Σ- prepares a shallow atomic bound state with a narrow conversion width. The coupling of strong interaction between the two states (8B + Σ-) and (8Be*+ Σ0) pushes down the energy of resonance state and it is expected to reproduce the correct energy position and level width of the second peak of the observed 9ΣBe hypernuclear spectrum.

On the bonding and reactivity of CO 2 on metal surfaces

We present ab-initio valence-bond calculations on free and coordinated CO 2. By analogy to transition-metal complexes with coordinated CO 2 three different coordination geometries for the CO 2 molecule are considered: (a) pure carbon coordination, (b) pure oxygen coordination, (c) mixed carbon-oxygen coordination. It is shown that pure oxygen ((b) geometry) and mixed carbon-oxygen coordination ((c) geometry) are more favourable than pure carbon coordination. In all cases studied, the bonding between the CO 2 moiety and the metal atom is described best as a CO 2 − anion interacting with a Ni cation. On the basis of the theoretical calculations, many observed and expected features (some already known and some predicted) of the interaction of CO 2 and metal surfaces can be discussed. The electron transfer to the CO 2 moiety drives the observed bent geometry of the coordinated CO 2 molecule and is accompanied by an elongation of the CO bond distance with respect to the free molecule. The bond elongation leads to a drastic lowering of the asymmetric CO stretching frequency, and a change in the relative energy position of the photoelectron peaks. We also consider intermolecular interaction between the CO 2 − anion and surrounding neutral CO 2 molecules via “solvation” in analogy to results of recent gas-phase cluster experiments. On the basis of the deduced metal-CO 2 bonding scheme the reactivity of coordinated CO 2 is investigated. Three reaction channels are considered: (a) dissociation into CO and O −, (b) oxidation to CO 3 − and CO 3 2−, (c) disproportionation of CO 2 − + CO 2 to CO 3 − and CO. On the basis of energetic considerations we argue that dissociation is likely to occur on transition-metal surfaces, while oxidation to carbonate species is more likely on noble metals due to the low binding energies for the dissociation products, namely oxygen and CO on these surfaces.

Usefulness of thermoluminescence in herbicide research

Many herbicides of different chemical structure inhibit photosynthetic electron flow by interrupting the photosyn‐thetic electron flow by interrupting the photosynthetic electron transport chain between the primary acceptor (QA) and the secondary acceptor (QB) of photosystem 2 (PS2). Thermoluminescence (TL) originates from PS2, and the bands of the glow curve can be related to the charge recombination between positively charged donors and negatively charged acceptors. The glow curve of TL is strongly influenced by addition of PS2 herbicides. The herbicide treatment shifts the peak position and activation energy of the TL band related to QA, suggesting that herbicide binding affects the midpoint redox potential not only of Q B but also that of QA. On the basis of the band shift the herbicides of various chemical structures can be classified into different “thermodynamical” groups which relfect the differences in the binding properties of these herbicides. As a new approach TL seems to be a useful technique...

Tunneling hot-electron transfer amplifier: A hot-electron GaAs device with current gain

Tunneling hot-electron transfer amplifier (THETA) devices, based on GaAs-AlGaAs heterojunctions, were fabricated and tested. Hot-electron transfer (α) through a 1100-Å base in excess of 70% was found at 4.2 K. This resulted in a corresponding current gain ( β) in a common emitter configuration of about 2.3. In the temperature range of 4.2–80 K and under constant biasing conditions, α was nearly temperature independent. Electron energy distributions for motion normal to the layers and electron total energy loss while traversing the device were estimated. Typical widths of the energy distributions were less than 200 meV, and both widths and energy peak positions were only slightly dependent on temperature and initial injection energy.

Characteristics of the material improvement process for silicon on sapphire by solid phase epitaxial regrowth

A comprehensive matrix study of the material modification of chemical vapor deposited silicon on sapphire has been made. The modification is effected by applying twice the process of ion implantation with 28 Si+ ions followed by solid phase epitaxial regrowth (SPEG) induced by furnace annealing. The matrix consisted of varying the fluences for the first and second implantation from just above the critical fluence for forming an amorphous phase to 7×1015cm−2. The defect reduction was studied for each sample of the matrix. This study has shown that the density of defects at the silicon/sapphire interface and silicon surface depends on both implantations. The deposited damage energy peak position is estimated to occur at a depth ∼Rp for a substrate temperature of 330 K during implantation. The position of the damage peak affects the estimated damage at the silicon sapphire interface which controls the aluminum outdiffusion. The major reduction in the defect density has already occurred for fluences of the two implantations such that the amorphous regions terminate within about 200 Å of each other. Using the width of the random yield portion of the channeled spectra for MeV 3He+ ions overestimates the width of the amorphous layer.

Electronic structure of a cobalt monolayer on Cu(100)

Abstract Angular resolved photoemission spectra using synchrotron radiation have been measured for different amounts of cobalt evaporated on Cu(100). At room temperature cobalt grows layer-bylayer forming well-ordered layers in registry with the substrate, as judged by AES, LEED and UPS measurements. The energy position and linewidth of the Cu peaks remain unchanged when cobalt is deposited onto the surface, suggesting a rather weak interaction between the d-bands of Co and Cu. The two-dimensional band structure of the monolayer of cobalt has been determined. We have obtained a value for the magnetic exchange splitting of ΔEexch = 0.80 ± 0.15 eV, which is nearly identical to the bulk value. A shift in the energy positions of the critical points for the monolayer versus bulk of cobalt is interpreted in terms of a narrower 2D density of states in the monolayer as compared to the bulk. A resonant valence-band two-electron satellite has been found. The correlation energy and screening effects of the two d-holes are very similar to the corresponding bulk values, while the decreased intensity of the satellite at resonance compared to the one for Co(0001) suggests that there are more d-states relative to s-states in the monolayer than in a bulk cobalt single crystal, in agreement with recent models of the valence band electronic structure at surfaces.

Electronic structure of a cobalt monolayer on Cu(100)

Angular resolved photoemission spectra using synchrotron radiation have been measured for different amounts of cobalt evaporated on Cu(100). At room temperature cobalt grows layer-bylayer forming well-ordered layers in registry with the substrate, as judged by AES, LEED and UPS measurements. The energy position and linewidth of the Cu peaks remain unchanged when cobalt is deposited onto the surface, suggesting a rather weak interaction between the d-bands of Co and Cu. The two-dimensional band structure of the monolayer of cobalt has been determined. We have obtained a value for the magnetic exchange splitting of ΔE exch = 0.80 ± 0.15 eV, which is nearly identical to the bulk value. A shift in the energy positions of the critical points for the monolayer versus bulk of cobalt is interpreted in terms of a narrower 2D density of states in the monolayer as compared to the bulk. A resonant valence-band two-electron satellite has been found. The correlation energy and screening effects of the two d-holes are very similar to the corresponding bulk values, while the decreased intensity of the satellite at resonance compared to the one for Co(0001) suggests that there are more d-states relative to s-states in the monolayer than in a bulk cobalt single crystal, in agreement with recent models of the valence band electronic structure at surfaces.

Hydrogen chemisorption on silicon (100) 2 × 1

Changes in the valence band density of states (DOS) of a (100) silicon surface that accompany he chemisorption of atomic hydrogen onto that surface are deduced from a study of the changes in the L 2,3VV Auger lineshape. Complementary changes in the conduction band DOS are inferred from changes in L 2,3VV-core-level characteristic loss spectra (CLS). The chemisorbed hydrogen layer is identified as the dihydride phase from low energy electron diffraction measurements. Upon hydrogen adsorption the DOS at the top of the valence band decreases and new energy levels associated with the Si-H bonds appear lower in the band. Assuming that the Auger signal from the hydrogen covered sample consists of a superposition of a signal from silicon atoms bonded to hydrogen in the dihydride layer and an elemental-Si signal from the substrate, a N( E) difference spectrum with features due only to the dihydride is obtained by subtracting the background corrected, loss deconvoluted L 2,3VV signal for a clean (100)Si surface rom the corresponding signal for the hydrogen covered surface. Comparisons of the energy position of the major peak in this difference spectrum with that of the main peak in a gas phase silane Si-L 2,3VV spectrum, and of the corresponding Auger energy calculated empirically, indicate a hole—hole interaction energy of ~8 eV for the two-hole final state in the gaseous system and zero for the dihydride surface system. Hydrogen induced changes in the conduction band DOS are less apparent than those of the valence band DOS with only the possibility of a decrease in the DOS at the bottom of the conduction band being inferred from the CLS measurements. Electron stimulated desorption of hydrogen from the dihydride layer is adduced from changes in the Auger lineshape under electron beam irradiation of the surface. Hydrogen induced changes in the near-elastic electron energy loss spectra (ELS) are also reported and compared with previously published ELS results.

A computer simulation of the surface channeling of MeV heavy charged particles

Abstract The surface channeling of 1.5 MeV N+ ions incident near the [011] direction on the (100) surface and near the [001] direction on the (110) surface of Ge crystals has been studied using computer simulation. The trajectories of ions incident at angles near the critical angle for axial channeling were traced. The energy spectra, the angular distributions and the reflection-depth distributions of scattered ions were obtained. The calculated energy spectra for both directions are found to be composed of a surface peak and a broad peak, the latter being at the low energy side of the surface peak. The height of the surface peak and the energy position of the broad peak are found to depend on the azimuthal component and the tilt component of the incident angle, respectively. This result is explained to be due to the focusing effect of channeled ions deffected by the atomic rows at the surface. It is shown that the calculated angular distributions of scattered ions form a half-ring pattern and clear dips ...

Photoemission study of the bulk and surface electronic structure of single crystals of gold

Angle-resolved energy distributions for photoelectrons emitted from the (111), (110), and (100) crystal faces of Au are presented for photon energies in the range 7.0-11.6 eV. The variation of peak-energy positions as a function of photon energy and electron emission angle has been studied. We have found very good qualitative agreement between the experimental results and the predictions of the three-step model applied to a relativistic-augmented-plane-wave band structure. To fit the theoretical peak-energy positions to the experimental data, it is necessary to lower bands Nos. 3, 4, and 5 (numbered from the bottom of the valence-band complex) by on the average 0.2 eV and to raise band No. 6 by 0.2 eV along the $\ensuremath{\Gamma}K$ symmetry line. Considerable emission must also be attributed to nondirect processes such as phonon-assisted nondirect transitions, scattering of electrons excited in direct transitions, and surface photoemission. A shoulder due to nondirect processes is always seen at -2.3 eV, whenever the emission due to direct transitions is low. The dispersion of the surface state in the $L$ gap has been measured. A parabolic fit to the data gives ${E}_{0}=0.45\ifmmode\pm\else\textpm\fi{}0.05$ eV and ${m}^{*}=(0.37\ifmmode\pm\else\textpm\fi{}0.05){m}_{0}$. We also report measurements on the local work function for the three low-index crystal faces.

Angular-resolved photoemission from low-index crystal faces of silver—bulk and surface contributions

The angular-resolved energy distributions for photoelectrons emitted from the (111), (110), and (100) crystal faces of Ag are presented for photon energies in the range 7.0-11.6 eV. The variation of peak energy positions as functions of emission angle and photon energy are compared with a calculation assuming direct transitions between the bulk energy bands (relativistic augmented plane wave). All primary cone emission from the calculation has been observed and found to vary in agreement with the simple theory. Angular-resolved secondary cone emission is identified in two cases. Some observed structures are also assigned to surface photoemission mechanisms: Surface photoemission where the final state is evanescent in the bulk, or surface state photoemission where the initial state is localized at the surface.

Chlorine chemisorption on silicon and germanium surfaces: Photoemission polarization effects with synchrotron radiation

The electronic states due to saturation Cl coverage on Si(111)2 \ifmmode\times\else\texttimes\fi{} 1, Si(111)7 \ifmmode\times\else\texttimes\fi{} 7, Si(100)2 \ifmmode\times\else\texttimes\fi{} 1, and Ge(111)2 \ifmmode\times\else\texttimes\fi{} 1 surfaces have been investigated with uv photoemission techniques employing synchrotron radiation. The energy position of the Cl-induced peaks in the photoemission spectra did not provide enough information to clearly identify the chemisorption geometry for each surface. Photon polarization effects have helped to solve this problem by determining the energy position of the ${p}_{z}$-like contributions to the density of filled states. The Cl adatoms have been found to occupy covalent onefold coordinated sites on Si(111)2 \ifmmode\times\else\texttimes\fi{} 1 and threefold ionic sites on Ge(111)2 \ifmmode\times\else\texttimes\fi{} 1. Both the above configurations coexist on Si(111)7 \ifmmode\times\else\texttimes\fi{} 7, while for Si(100)2 \ifmmode\times\else\texttimes\fi{} 1 the Cl-Si bonds are still covalent, but they are probably tilted with respect to the surface normal. Constant-initial-state curves reveal three Cl-induced structures in the density of empty states above the vacuum level. None of these empty state peaks seems to be related to the $\ensuremath{\sigma}$-antibonding states of the Si-Cl covalent bond on Si(111)2 \ifmmode\times\else\texttimes\fi{} 1 which are therefore probably located below the vacuum level.

Orientation dependent growth and luminescence of selective GaAs-Sn LPE

Heavily Sn doped selective structures were grown by GaAs liquid phase epitaxy (LPE) both into circular holes and into 〈011〉 orientated stripes. An orientation dependent edge overgrowth of the original etched hole with the preferred directions 〈100〉, 〈111〉 and 〈110〉 was observed. It is shown that the kinetic processes, becoming visible with selective epitaxy only, are compatible with the well known diffusion controlled growth in the case of layer growth. An epitaxial mesa structure with completely smooth surfaces suitable for practical applications is reported. Scanning photo- and cathodo-luminescence measurements were carried out. A luminescence intensify profile influenced by the different preferred directions was found. The different luminescence intensities are interpreted as being caused by different doping concentrations. This interpretation is confirmed by the peak energy position and the half-width of luminescence bands. A donor concentration ratio of N D100: N D111: N D110≌1:0.85:0.7 has been found.

Red pair luminescence in GaP:Cu

Investigations of the luminescent properties of high-ohmic Cu-doped GaP-crystals in the red spectral region (1.5-1.9 eV) with emphasis on broad band type emissions are reported. A dominant broad bell-shaped emission is found, centred at about 1.67 eV at 4 K. At low temperatures, this peak clearly shifts to higher energy with increasing excitation intensity, and non-exponential decay with emission persisting up to several minutes is observed. From those observations, the radiative mechanism for this emission at low temperatures sbelow ∼ 100 K) is believed to involve strongly phonon-coupled pair-transitions between (hallow donors and deep Cu-acceptors. The anomalous temperature dependence of the peak-energy position and emission intensity indicates that at higher temperatures (above ∼ 200 K) the radiative process involved is a transition between free elctrons and the same Cu-acceptor, also with strong phonon coupling. These observations imply a binding energy of 0.53 ± 0.03 eV for the corresponding Cu-acceptor. The excitation spectrum for this emission exhibits a dominant contribution from direct gap photon energies at low temperatures. Evidence for the existence of another Cu-related acceptor at about 0.7 eV above the valence band is also reported.

Glow Peak Analysis of Pure and Doped Naphthalene Thermoelectret

Polarization current for pure and doped naphthalene thermoelectrets is investigated. The thermal depolarization of the electret is used as a technique to investigate trapped polarization. Doped crystals with alpha and beta naphtol present new independent peaks in addition to the pure matrix peaks. The peaks are analyzed quantitatively for total integrated charge and activation energy by the initial rise method. The OH vibrational band of the impurities was used as an optical probe to detect their presence in the solid. Charges trapped in the dielectric absorption process corrected for the released charge at the low‐temperature depolarization, compare satisfactorily with the total integrated glow peak charge for both pure and doped samples. It was possible to differentiate between alpha and beta naphtol through the electret behavior using the glow peak position and activation energy of the peaks. The electret state is shown to be due to electronic carriers, trapped in a set or sets of exponentially distributed traps, as indicated by the atn dependence of the polarization current on time.