eV For Samples Research Articles

Annealing Behaviour of Deuterium in Silicon Doped Carbon Films

Annealing behaviour of deuterium in carbon films with different Si contents deposited by a pulsed arc discharge method in deuterium atmosphere was studied. The concentration profiles of D were measured by secondary ion mass spectrometry and elastic recoil detection techniques. A model taking into account diffusion, detrapping and trapping of D is used to describe the experimental depth profiles. Diffusion coefficients obtained for non-trapped D resulted in activation energies of 1.5 ± 0.2, 0.7 ± 0.2, 0.6 ± 0.2 and 1.2 ± 0.2 eV for samples containing 0, 6, 15 and 33 at.% of Si, respectively.

Dielectric response and complex impedance spectroscopy studies in pulsed laser ablated (Ba, Sr)TiO3 thin films

The dielectric response of pulsed laser ablated barium strontium titanate (Ba, Sr)TiO3 thin films was studied as a function of frequency, time and ambient temperature. Both time and frequency responses followed the ”universal power law’ pertaining to the universal dielectric response model theorized by Jonscher. Theoretical fits were used to compare the experimental results and determine the temperature dependence of the theoretical parameters such as n(T) and a(T) used in the universal model. Complex impedance spectroscopy was used to investigate the grain, grain boundary, and electrode/film interface responses. The complex spectroscopic plots revealed the major response originated from the bulk grains while in the case of polycrystalline samples the grain boundary contributed significantly. Arrhenius plot of the bulk resistance calculated from complex impedance diagrams showed a significant difference in the activation energy ranging from 1.17 to 1.23 eV for samples grown at different substrate temperatures.

Photoluminescence from transmuted impurities in neutron-transmutation-doped semi-insulating GaP

The transmuted impurities Ge and S in neutron-transmutation-doped (NTD) semi-insulating GaP were studied by a photoluminescence method. A broad emission was observed at 1.65 eV accompanied by a hump at ∼1.87 eV in samples annealed above 640°C. These emissions are attributed to Ge Ga–Ge P complex and S donor–Ge acceptor pair recombination, respectively, indicating the presence of the transmuted impurities. The formation of the complex defect was examined using a configuration coordinate model. The presence of the complex defects restricted the electrical activation of the transmuted impurities in NTD-GaP, forming a localized state.

Electronic structure and electron emission of lithium-containing amorphous hydrogenated carbon films

Amorphous hydrogenated carbon films were prepared by ion beam deposition. The degree of sp3 coordination and the density of the films were determined from ultraviolet photoelectron valence band spectra and electron energy loss spectra. The films prepared can be described as highly sp3 coordinated (about 80%) and of relatively high density (about 2.3 g/cm3). An indication of a negative electron affinity is found in the valence band spectra. In an attempt to lower the work function, lithium-containing a-C:H films were deposited by lithium evaporation from dispensers during deposition of the a-C:H films. Photoelectron spectra of these films reveal parallel shifts of the core levels and valence band to higher binding energies with respect to the spectra of pure amorphous hydrogenated carbon. These shifts can be attributed to a shift of the Fermi level due to a charge transfer from the lithium to the carbon matrix. From the onset of the valence band spectra at low kinetic energy and from total photoyield spectra the work function of the samples was determined independently. A reduction of the work function from 3.4 eV in pure a-C:H to 2.45 eV in samples containing 35 at. % lithium is observed.

Effect of Annealing Under Uniform Stress on Photoluminescence, Electrical and Structural Properties of Silicon

ABSTRACTEffect of increased pressure (up to 1.5GPa) during annealing of Cz-Si on creation of thermal donors (at 720 - 1000K) and visible luminescence (peaking at 1.7- 2.2eV for samples annealed at up to 1420K) is reported. The observed phenomena are related to stress - stimulated oxygen clustering / precipitation in Cz-Si resulting in creation of specific defects.

Silicon oxide conductivity of hydrogen ion implanted polysilicon thin film transistors

The influence of hydrogen ion implantation into the channel polysilicon of polysilicon thin film transistors on gate oxide conductivity has been investigated. Data for effective tunnelling barriers at the gate oxide/channel polysilicon interface are presented. A value of 1.2eV for samples with boron doped channel polysilicon is calculated. For hydrogenated boron doped samples tunnelling barriers higher than 2.1eV are obtained. The tunnelling barriers for phosphorus doped samples are impurity concentration dependent and decrease with increasing phosphorus concentration in the range 3 × 10 17 to 3 × 10 19 cm −3.

Optical Properties of Nano Crystalline InP in Opal 3-Dimensional Gratings

AbstractOpal consists of a three dimensional array of silica balls with diameter in the range 150 -350 nm and acts as a 3-D grating. Within the microcrystals (a few hundred microns) of opal there is typically 5% variation in ball diameter arranged in a fee structure. Using a specially modified MOCVD process InP can be grown within the voids between the touching silica balls. These interconnecting voids are approximately 1/5 and 2/5 the silica sphere diameter, Raman spectroscopy confirms the crystallinity of the InP for two samples loaded with 2.5 volume % of InP. The LO phonon is shifted to the red by 10 cm−l from the bulk value of 345 cm−1, while the TO phonon is shifted 22 cm−l to the blue from the bulk value of 303.7 cm−l. This shift is attributed to strain in the nanocry stals.The half width of the reflectance is dependent upon InP loading with the 2.5 vol.% samples giving 0.19 eV and the lower loaded 0.4 vol. % giving 0.17 eV for samples with the same ball diameter. Photoluminescence emission near 1.7 eV is attributed to confined InP compared with a bulk value of 1.4 eV. The energy of the emission is determined by the combined contribution of the laterally confined InP and its interaction with the opal matrix.

Cadmium-hydrogen shallow acceptor complexes in germanium

The transmuted impurities Ge and S in neutron-transmutation-doped (NTD) semi-insulating GaP were studied by a photoluminescence method. A broad emission was observed at 1.65 eV accompanied by a hump at ∼1.87 eV in samples annealed above 640°C. These emissions are attributed to GeGa–GeP complex and S donor–Ge acceptor pair recombination, respectively, indicating the presence of the transmuted impurities. The formation of the complex defect was examined using a configuration coordinate model. The presence of the complex defects restricted the electrical activation of the transmuted impurities in NTD-GaP, forming a localized state.

Spontaneous and stimulated photoluminescence of CdSe/CdS Stark superlattices

Photoluminescence properties of CdSe/CdS intrinsic Stark superlattices are studied mainly by means of nanosecond optical spectroscopy. The blue-shift induced by increasing screening of the internal piezoelectric fields with increasing excitation power reaches nearly 0.4eV for samples with large periods. At excitation levels above 2 to 20MW/cm2 stimulated emission is observed depending on temperature. Measurements by the stripe-length method give gem maximum values around 103cm-1.

Mn2+Internal Emission and Excitonic Emission of MBE-Grown Cd1-xMnxTe –Dependence on Substrate Temperature and Magnetic Field

It has been reported that there exists Mn-related photoluminescence at 2.0 eV in addition to excitonic emission in Cd 1- x Mn x Te with x more than 0.3 grown by conventional methods. We have investigated dependence of these luminescence lines on substrate temperature, T s , in MBE-grown Cd 0.6 Mn 0.4 Te crystals. A large broad line was observed at around 2.05 eV in samples grown at high T s at about 400°C whereas a sharp line at around 2.17 eV evolved in samples grown at T s =320–340°C. Both of these lines were seen in the case of T s =380°C. Measurement of the magnetic field dependence of the peak positions up to 40 T revealed that the former assigned as Mn related luminescence shows no observable Zeeman shift. On the other hand, the later is assigned as the excitonic emission because of the large shift to lower energy in the magnetic field. The experimental results suggest that the Mn-related photoluminescence at 2.0 eV is affected strongly by crystal imperfections, probably the vacancy type defects. On...

Investigation of Ion Beam Mixing of Iron Marker Layers in Aluminum Oxide by RBS

ABSTRACTThin films made with a thin embedded marker layer of iron or iron oxide in amorphous alumina were ion mixed with 210 keV Ar over a temperature range of RT to 750°C in vacuum. The dose range was 5×l015-7×l016ions/cm2with an average dose rate of 4.5×1012ions/cm2-sec. The resulting marker distributions were analyzed using RBS. Spreading of the iron RBS peak due to mixing into the alumina matrix was observed in the Fe2O3marker samples and was clearly seen to be a function of temperature (>400°C) and dose, whereas for the Fe marker sample, no such temperature dependence was observed. An activation energy for the thermally assisted ion mixing in the Fe2O3marker sample was determined to be 0.69 eV in comparison to an activation energy of 1.77 eV for samples that underwent only a thermal treatment.

Oxygen diffusion in YBCO: an isothermal thermogravimetric study

The kinetics of oxygenation/deoxygenation in YBa 2Cu 3O 7−δ has been studied with thermogravimetry. Experiments were conducted at various constatn temperatures on powder samples subjected to an abrupt change in ambient oxygen partial pressure. The processes are found to be diffusion-controlled, with an activation energy of 1.3 eV for samples with oxygen deficiencies δ near 0.1. The chemical diffusion coefficient at 500°C is determined as 10 −10 cm 2/s, two to three orders of magnitude smaller than values measured from sintered samples.

Effects of Fluorine Implantation into Hydrogenated Amorphous Silicon

ABSTRACTMultiple-energy implantation of fluorine into rf glow discharge deposited hydrogenated amorphous silicon (a-Si:H) thin films has been performed. It is found that the optical gap decreases with the implanted fluorine concentration CF from 1.56 eV for the unimplanted sample to 1.40 eV for the sample with CF of 3×1021 cm−3. Results of the Staebler-Wronski experiment show that the ratio between the electrical conductivity before and after illumination, as well as the ratio between the photo- and dark conductivity, decrease also with Cp. Electrical measurements show that there is significant decrease in the conductivity activation energy Ea with CF for samples annealed at or below the substrate temperature TS during deposition. But for samples annealed at temperatures higher than TS, Ea was found to change back to values close to that of the unimplanted sample. A large shift to higher energy for one peak in the photoluminescence spectra at 77K has been observed, from 1.34 eV of the unimplanted sample to around 1.6 eV for the implanted samples, though with almost one order of magnitude weakening in intensity. It is also observed that ESR splitting has been induced in the fluorine implanted samples. The g-factors of the two resonances are determined to be 2.003 and 2.006, respectively. For the g=2.006 resonance, the spin density increases markedly after implantation but is essentially independent on CF before annealing and effectively reduced or eliminated after annealing. For the g=2.003 resonance, the spin density increases rapidly with CFp especially in the range from CF = 1×1020 to 1×1021 cm−3 before annealing and reduces only slightly after annealing.

Optical and electrical energy gap investigations in low-temperature glassy carbon layers

The optical and electrical energy gaps of low-temperature glassy carbon obtained from polyfurfuryl alcohol in the range of heat-treatment temperature HTT=300–800 °C have been compared. Optical absorption were measured in the energy range of 0.4–3.5 eV. The optical energy gap is 1.8 eV for samples heat-treated at 300 °C and decreases with HTT to 0.05 for HTT=800 °C. The mobility gap changes from 1.2 to 0.08 eV in the range of HTT=400–700 °C. The differences between the optical and the electrical energy gaps apparently decreases with increasing HTT. These results support the suggestion that in the low-temperature glassy carbon a large number of localized states exist, the band edges of the valence and conduction bands are not sharp and deviations from the Tauc plot for the optical absorption may exist.

Ellipsometric studies of electronic interband transitions inCdxHg1−xTe

Ellipsometric measurements of the dielectric constant of ${\mathrm{Cd}}_{x}{\mathrm{Hg}}_{1\ensuremath{-}x}\mathrm{Te}$ alloys were performed at room temperature between 1.8 and 5.5 eV for samples covering the whole range of concentrations. The dependence of the ${E}_{1}$, ${E}_{1}+{\ensuremath{\Delta}}_{1}$, and ${E}_{2}$ threshold energies on $x$ was obtained: It is quadratic for ${E}_{1}$ and ${E}_{1}+{\ensuremath{\Delta}}_{1}$ and linear within experimental error for ${E}_{2}$. An upwards bowing is found for the spin-orbit splitting ${\ensuremath{\Delta}}_{1}$ as a function of $x$. The effect of alloying in broadening the observed structures is relatively small. However, a large decrease of excitonic effects in the ${E}_{1}$ and ${E}_{1}+{\ensuremath{\Delta}}_{1}$ gaps due to alloying has been observed. These results are discussed in the light of recent coherent-potential-approximation calculations.

Steady-state creep characteristics of carbon black loaded butadiene rubber

The temperature dependence of tensile creep of butadiene rubber (BR) loaded with different concentrations of carbon black ISAF was tested under different applied stresses. The steady creep rate showed a dependence on stress, temperature and carbon black content. The energy-activating steady creep was of order 0.15 eV for samples containing 20 phr of ISAF carbon black and reached a value of 0.37 eV for samples containing 80 phr of carbon black. This was attributed to the blocking of motion of the molecular segments by the carbon black. This view point was confirmed by the activation volume which was found to decrease with the increase of carbon black content.

Infrared photoluminescence in polyacetylene

More extensive photoluminescence measurements of polyacetylene reveal a broad new emission band between 1.2 and 1.6 eV in samples with various isomeric contents. The peak energy and the intensity of this low energy luminescence decrease as the cis fraction decreases, but the band is still present in fully converted trans samples. These characteristics suggest that the infrared emission either is due to perturbed fragments of cis polyacetylene or is unquenched 1Ag luminescence from segments of trans (CH) x.

Electrical properties of vanadium phosphate glasses containing antimony and arsenide oxide

Both DC and AC resistivity of some vanadium phosphate glasses containing antimony or arsenic oxide have been measured over a wide temperature range. These glasses contain a finite concentration of Sb3+ and possibly As3+ ions. The data indicate that below 200K conduction takes place via carriers excited to localised states at the band edge which is separated from the Fermi level by approximately 0.08 eV in glasses containing antimony oxide and approximately 0.04 eV in samples containing arsenic oxide. The origin of these states is ascribed to some bond formation between As3+ or Sb3+ and the V4+ ions.

Optical Absorption Spectrum of AgF

The optical absorption of thin films of silver monofluoride has been investigated in the visible and ultraviolet region of the spectrum at room and low temperatures. Exciton peaks have been observed at 4.63 and 6.34 eV for samples at 4.8 \ifmmode^\circ\else\textdegree\fi{}K. The first exciton peak is considerably lower in energy than might be expected on the basis of the trend set by the other silver halides. This unusually low energy has led us to speculate that the band structure of AgF may be quite different from those of the other silver halides.

Recombination Centers in Gamma-Irradiated Arsenic-Doped Germanium

A comprehensive investigation has been performed of the properties of recombination centers introduced in As-doped Ge by Co60 gamma rays. Materials of three resistivities were used: ~0.2, ~1 and ~8 Ω-cm. Measurements of lifetime versus temperature were made at low excess densities following various anneals. Numerous measurements of lifetime as a function of excess density with temperature as a parameter and with different annealing histories were performed. The position of the recombination center was observed to shift slightly with anneal temperature from Ev + 0. 346 ±.005 eV for room temperature stable defects to 0. 322 ±0.003 eV for samples which have been annealed in the range of ~70°C to ~120°C. These values are based on excess density measurements and assume unity statistical weight. The possible error from this assumption is estimated to be ±0.02 eV. The variation of electron capture probability with temperature was indicated by comparison with temperature dependence data; it varies approximately as T3/4. The hole-to-electron capture probability ratio near room temperature is 400 ±30 %. The arsenic atom appears to play no significant role in the process of recombination center creation or annihilation.