STUDY OF RAMAN-SPECTRA OF ZNSE-ZNTE STRAINED LAYER SUPERLATTICES

The Raman spectra of the II-VI wide band-gap compound ZnSe-ZnTe semiconductor strained-layer superlattices have been studied. The relations between the Raman shifts of the longitudinal optical phonon modes and the superlattice-structure parameters have been determined. When the layer thickness exceeds 40 angstrom, the change of the LO phonon-mode frequency shifts with the layer thickness is minimal, whereas when the layer thickness is smaller than 40 angstrom, great shifts have been observed. We estimate that the critical thickness of ZnSe-ZnTe SLS is about 40 angstrom. We have also found that the shifts induced by strain are much larger than the red shifts due to confinement.

INFLUENCES OF ALLOY DISORDER AND INTERFACE ROUGHNESS ON OPTICAL-SPECTRA OF INGAAS/GAAS STRAINED-LAYER QUANTUM-WELLS

We present studies of alloy composition and layer thickness dependences of excitonic linewidths in InGaAs/GaAs strained-layer quantum wells grown by MBE, using both photoluminescence and optical absorption. It is observed that linewidths of exciton spectra increase with indium content and well size. Using the virtual crystal approximation, the experimental data are analyzed. The results obtained show that the alloy disorder is the dominant mechanism for line broadening at low temperature. In addition, it is found that the absorption spectra related to light hole transitions have varied from a peak to a step-like structure as temperature increases. This behavior can be understood by the indirect space transitions of light holes.

ENHANCEMENT EFFECT OF PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITED SIN CAPPING LAYER ON DIELECTRIC CAP QUANTUM-WELL DISORDERING

Quantum well disordering of GaAs/AlGaAs multiple quantum well(MQW) has been accomplished with only plasma enhanced chemical vapor deposited (PECVD) SiN cap layer growth. The amount of blue shift increases with SiN growing time. This result has been explained by the vacancy indiffusion during PECVD SiN growth. Rapid thermal annealing (RTA) of the sample after SiN cap layer growth at 850 degrees C for 35 s caused a larger amount of blue shift than those obtained without RTA. By considering the model of Al diffusion from AlGaAs barrier into GaAs QWs together with the result from photoluminescence (PL) measurement, Al diffusion coefficients were calculated. The Al diffusion coefficient due to PECVD SiN was estimated at about 3 x10(-17) cm(2)/s. It was possible to extract the effect of RTA on the QW disordering, which showed that the amount of the blue shift and the Al diffusion coefficient due only to RTA increases with SiN cap layer thickness as reported by Chi et al.(10))

Study on growth factors of intermetallic layer within hot-dipped 25% Al-Zn alloy coating on steel

25%Al-Zn alloy coating performs better than hot dip galvanized coating and 55%Al-Zn-Si coating with regard to general seawater corrosion protection. This study deals with the interfacial intermetallic layer's growth, which affects considerably the corrosion resistance and mechanical properties of 25%Al-Zn alloy coatings, by means of three-factor quadratic regressive orthogonal experiments, The regression equation shows that the intermetallic layer thickness decreases rapidly with increasing content of Si added to the Zn-Al alloy bath, increases with rise in bath temperature and prolonging dip time. The most effective factor that determined the thickness of intermetallic layer was the amount of Si added to Zn-Al alloy bath, while the effect of bath temperature and dip time on the thickness of intermetallic layer were not very obvious.

Effect of adding 0.3wt% Ni into the Sn-0.7wt% Cu solder - Part II: Growth of intermetallic layer with Cu during wetting and aging

The growth behavior of intermetallic layer with or without adding 0.3 wt% Ni into the Sn-0.7Cu solder was studied during the wetting reaction on Cu-substrate and thereafter in solid-state aging condition. The Cu-solder reaction couple was prepared at 255, 275 and 295 °C for 10 s. The samples reacted at 255 °C were then isothermally aged for 2-14 days at 150 °C. The reaction species formed for the Sn-0.7Cu/Cu and Sn-0.7Cu-0.3Ni/Cu soldering systems were Cu6Sn5 and (CuNi)6Sn5, respectively. The thickness of the intermetallic compounds formed at the solder/Cu interfaces and also in the bulk of both solders increased with the increase of reaction temperature. It was found that Ni-containing Sn-0.7Cu solder exhibited lower growth of intermetallic layer during wetting and in the early stage of aging and eventually exceeded the intermetallic layer thickness of Sn-0.7Cu/Cu soldering system after 6 days of aging. As the aging time proceeds, a non-uniform intermetallic layer growth tendency was observed for the case of Sn-0.7Cu-0.3Ni solder. The growth behavior of intermetallic layer during aging for both solders followed the diffusion-controlled mechanism. The intermetallic layer growth rate constants for Sn-0.7Cu and Sn-0.7Cu-0.3Ni solders were calculated as 1.41 × 10-17 and 1.89 × 10-17 m2/s, respectively which indicated that adding 0.3 wt% Ni with Sn-0.7Cu solder contributed to the higher growth of intermetallic layer during aging. © 2006 Elsevier B.V. All rights reserved.

Improved Thermal Performance of SOI Using Compound Buried Layer

The buried oxide (BOX) layer in silicon on insulator (SOI) was replaced by a compound buried layer (CBL) containing layers of SiO2, polycrystalline silicon (polysilicon), and SiO2. The undoped polysilicon in the CBL acted as a dielectric with a higher thermal conductivity than SiO2. CBL provides a reduced thermal resistance with the same equivalent oxide thickness as a standard SiO2 buried layer. Thermal resistance was further reduced by lateral heat flow through the polysilicon. Reduction in thermal resistance by up to 68% was observed, dependent on polysilicon thickness. CBL SOI substrates were designed and manufactured to achieve a 40% reduction in thermal resistance compared with an 1.0-μm SiO2 BOX. Power bipolar transistors with an active silicon layer thickness of 13.5 μm manufactured on CBL SOI substrates showed a 5%-17% reduction in thermal resistance compared with the standard SOI. This reduction was dependent on transistor layout geometry. Between 65% and 90% of the heat flow from these power transistors is laterally through the thick active silicon layer. Analysis confirmed that CBL SOI provided a 40% reduction in the vertical path thermal resistance. Devices employing thinner active silicon layers will achieve the greater benefit from reduction in vertical path thermal resistance offered by CBL SOI.

Magnetic Characteristics of a High-layer-number NiFe/FeMn Multilayer

We report the static & dynamic magnetic characteristics of a high-layer-number NiFe/FeMn multilayer test structure with potential applications in broadband absorber and filter devices. To allow fine control over the absorption linewidths and to understand the mechanisms governing the resonances in a tailored structure similar to that expected to be used in real world applications, the multilayer was intentionally designed to have layer thickness and interface roughness variations. Magnetometry measurements show the sample has complex hysteresis loops with features consistent with single ferromagnetic film reversals. Structural characterisation by transmission electron microscopy allows us to correlate the magnetic properties with structural features. Analysis of resonance frequencies from broadband ferromagnetic resonance measurements as a function of field magnitude and orientation provide values of the local exchange bias, rotatable anisotropy, and uniaxial anisotropy fields for specific layers in the stack and explain the observed mode softening. The linewidths of the multilayer are adjustable around the bias field, approaching twice that seen at larger fields, allowing control over the bandwidth of devices formed from the structure.

Mixed layer characteristics and hydrography off the west and east coasts of India

In this thesis, a detailed attempt has been made to understand the general hydrography of the upper 300m of the water column, in the eastern Arabian Sea and the western Bay of Bengal, the two contrasting basins in the northern Indian Ocean, using recently collected data sets of Marine Research-Living Resources (MR-LR) assessment programme, funded by Department of Ocean Development, from various cruises, pertaining to different seasons. Initially it discuss the general hydrography of the west and east coasts of India are covered, in the context of mixed layer processes. The study describes the materials and methods . To compare the hydrography of the AS and BOB, a unique MLD(Mixed Layer Depth) definition for AS and BOB is essential, for which the 275 CTD profiles were used. A comparison has been made among the various MLD criteria with the actual MLD. The monthly evolution of MLD, barrier layer thickness and the role of atmospheric forcing on the dynamics of the mixed layer in the AS and BOB were studied. The general hydrography along the west coast of India is described. The upwelling/downwelling, winter cooling processes, in the context of chemical and biological parameters, are also addressed. Finally the general hydrography of the Bay of Bengal is covered. The most striking feature in the hydrography are the signature of an anticyclonic subtropical gyre during spring intermonsoon and a cold core eddy during winter monsoon. The TTS(Typical Tropical Structure) of the euphotic layer was also investigated.

Low-voltage driven ZnS:Mn MIS and MISIM thin film electroluminescent devices with Eu2O3 insulator layer

AC thin film electroluminescent devices of MIS and MISIM have been fabricated with a novel dielectric layer of Eu2O3 as an insulator. The threshold voltage for light emission is found to depend strongly on the frequency of excitation source in these devices. These devices are fabricated with an active layer of ZnS:Mn and a novel dielectric layer of Eu2O3 as an insulator. The observed frequency dependence of brightness-voltage characteristics has been explained on the basis of the loss characteristic of the insulator layer. Changes in the threshold voltage and brightness with variation in emitting or insulating film thickness have been investigated in metal-insulator-semiconductor (MIS) structures. It has been found that the decrease in brightness occurring with decreasing ZnS layer thickness can be compensated by an increase in brightness obtained by reducing the insulator thickness. The optimal condition for low threshold voltage and higher stability has been shown to occur when the active layer to insulator thickness ratio lies between one and two.

Loss of nerve fiber layer in HIV positive patients and comparative patterns in a series of cases in Bucaramanga, Colombia

Objective: The objective of this study is to conduct a description of the features of optic neuropathy associated with Human Immunodeficiency Virus in relation to their possible incidence within our population, regarding that there is no data in our population in terms of frequency of this pathology (1,2). Methodology: Descriptive cross-sectional study of a clinical series of patients infected with human immunodeficiency virus, but AIDS, and the thickness of optic nerve´s layer of fibers studied with OCT technology (optical coherence tomography), patients were cited once captured. OCT was performed by the same observer, by taking 3 shots and picking the one with better reliability. Patients were given personally to the Ophthalmologic Foundation of Santander to conduct the review called OCT (optical coherence tomography). Results: In terms of viral load variable, we found a clear correlation in which validates the hypothesis that lower viral load means a thicker layer of fibers finding statistically significant differences for the 6 hours in right eye and 12 and 6 hours in left eye. Comparison between the known nomogram of fiber layer thickness for the population of Bucaramanga, Santander and thickness found in our sample, we note a clear decrease in the upper and lower quadrants, specifically in 7 hours and 11 hours, being more important in 7 hours, showing statistically significant differences. Conclusions: The pattern  of thinning of the nerve fiber layer in HIV positive patients without AIDS, and antiretroviral treatment type HAART, showed a statistically significant thinning targeted at 7 hours and 11 hours, being higher in first. Viral load figures have a direct relation with loss fiber layer, showing a statistically significant difference for the 6 and 12 hours.

Retinal nerve fibre layer thinning associated with diabetic peripheral neuropathy

Aims
To investigate the relationship between retinal nerve fibre layer thickness and peripheral neuropathy in patients with Type 2 diabetes, particularly in those who are at higher risk of foot ulceration.

Methods
Global and sectoral retinal nerve fibre layer thicknesses were measured at 3.45 mm diameter around the optic nerve head using optical coherence tomography (OCT). The level of neuropathy was assessed in 106 participants (82 with Type 2 diabetes and 24 healthy controls) using the 0–10 neuropathy disability score. Participants were stratified into four neuropathy groups: none (0–2), mild (3–5), moderate (6–8), and severe (9–10). A neuropathy disability score ‡ 6 was used to define those at higher risk of foot ulceration. Multivariable regression analysis was performed to assess the effect of neuropathy disability scores, age, disease duration and retinopathy on RNFL thickness.

Results
Inferior (but not global or other sectoral) retinal nerve fibre layer thinning was associated with higher neuropathy disability scores (P = 0.03). The retinal nerve fibre layer was significantly thinner for the group with neuropathy disability scores ‡ 6 in the inferior quadrant (P < 0.005). Age, duration of disease and retinopathy levels did not significantly influence retinal nerve fibre layer thickness. Control participants did not show any significant differences in thickness measurements from the group with diabetes and no neuropathy (P > 0.24 for global and all sectors).

Conclusions
Inferior quadrant retinal nerve fibre layer thinning is associated with peripheral neuropathy in patients with Type 2 diabetes, and is more pronounced in those at higher risk of foot ulceration.

Retinal nerve fiber layer analysis using GDx® in 49 patients with chronic phase DUSN

To describe retinal nerve fiber layer changes in late-stage diffuse unilateral subacute neuroretinitis eyes and compare these results with healthy eyes observed through nerve fiber analyzer (GDx®). Methods: This is a retrospective case-control study in which 49 eyes in late-stage diffuse unilateral subacute neuroretinitis were examined from May/97 to December/ 01. First, eyes with diffuse unilateral subacute neuroretinitis and healthy contralateral eyes (Control Group I) were statistically matched. Subsequently, eyes with diffuse unilateral subacute neuroretinitis were compared with eyes of healthy patients (Control Group II). Results: Eyes from Control Groups I and II had higher relative frequency of “within normal limits” status. Eyes from the diffuse unilateral subacute neuroretinitis (DUSN) Group had higher frequency of “outside normal limits” and “borderline” status. Control Groups I and II had absolute values different from the DUSN Group regarding all parameters (p<0.05), except for Symmetry in Control Groups I and II, Average thickness and Superior Integral in control group II. Conclusion: Patients with late-stage diffuse unilateral subacute neuroretinitis presented presumed decrease in nerve fiber layer thickness shown by GDx®. Retinal zones with larger vascular support and larger amount of nerve fibers presented higher decrease in the delay of the reflected light measured by the nerve fiber analyzer

Nerve fiber layer in glaucomatous hemifield loss: a case-control study with time- and spectral-domain optical coherence tomography

Purpose: To evaluate the retinal nerve fiber layer measurements with time-domain (TD) and spectral-domain (SD) optical coherence tomography (OCT), and to test the diagnostic ability of both technologies in glaucomatous patients with asymmetric visual hemifield loss. Methods: 36 patients with primary open-angle glaucoma with visual field loss in one hemifield (affected) and absent loss in the other (non-affected), and 36 age-matched healthy controls had the study eye imaged with Stratus-OCT (Carl Zeiss Meditec Inc., Dublin, California, USA) and 3 D OCT-1000 (Topcon, Tokyo, Japan). Peripapillary retinal nerve fiber layer measurements and normative classification were recorded. Total deviation values were averaged in each hemifield (hemifield mean deviation) for each subject. Visual field and retinal nerve fiber layer "asymmetry indexes" were calculated as the ratio between affected versus non-affected hemifields and corresponding hemiretinas. Results: Retinal nerve fiber layer measurements in non-affected hemifields (mean [SD] 87.0 [17.1] mu m and 84.3 [20.2] mu m, for TD and SD-OCT, respectively) were thinner than in controls (119.0 [12.2] mu m and 117.0 [17.7] mu m, P<0.001). The optical coherence tomography normative database classified 42% and 67% of hemiretinas corresponding to non-affected hemifields as abnormal in TD and SD-OCT, respectively (P=0.01). Retinal nerve fiber layer measurements were consistently thicker with TD compared to SD-OCT. Retinal nerve fiber layer thickness asymmetry index was similar in TD (0.76 [0.17]) and SD-OCT (0.79 [0.12]) and significantly greater than the visual field asymmetry index (0.36 [0.20], P<0.001). Conclusions: Normal hemifields of glaucoma patients had thinner retinal nerve fiber layer than healthy eyes, as measured by TD and SD-OCT. Retinal nerve fiber layer measurements were thicker with TD than SD-OCT. SD-OCT detected abnormal retinal nerve fiber layer thickness more often than TD-OCT.

Parametric Analysis of Effective Material Properties of Thickness-Shear Piezoelectric Macro-Fibre Composites

A previous study on the characterization of effective material properties of a d(15) thickness-shear piezoelectric Macro-Fibre Composite (MFC) made of seven layers (Kapton, Acrylic, Electrode, Piezoceramic Fibre and Epoxy Composite, Electrode, Acrylic, Kapton) using a finite element homogenization method has shown that the packaging reduces significantly the shear stiffness of the piezoceramic material and, thus, leads to significantly smaller effective electromechanical coupling coefficient k(15) and piezoelectric stress constant e(15) when compared to the piezoceramic fibre properties. Therefore, the main objective of this work is to perform a parametric analysis in which the effect of the variations of fibre volume fraction, Epoxy elastic modulus, electrode thickness and active layer thickness on the MFC effective material properties is evaluated. Results indicate that an effective d(15) MFC should use relatively thick fibres having relatively high shear modulus and relatively stiff epoxy filler. On the other hand, the electrode thickness does not affect significantly the MFC performance.

Parametric analysis of effective material properties of thickness-shear piezoelectric macro-fibre composites

A previous study on the characterization of effective material properties of a d15 thickness-shear piezoelectric Macro-Fibre Composite (MFC) made of seven layers (Kapton, Acrylic, Electrode, Piezoceramic Fibre and Epoxy Composite, Electrode, Acrylic, Kapton) using a finite element homogenization method has shown that the packaging reduces significantly the shear stiffness of the piezoceramic material and, thus, leads to significantly smaller effective electromechanical coupling coefficient k15 and piezoelectric stress constant e15 when compared to the piezoceramic fibre properties. Therefore, the main objective of this work is to perform a parametric analysis in which the effect of the variations of fibre volume fraction, Epoxy elastic modulus, electrode thickness and active layer thickness on the MFC effective material properties is evaluated. Results indicate that an effective d15 MFC should use relatively thick fibres having relatively high shear modulus and relatively stiff epoxy filler. On the other hand, the electrode thickness does not affect significantly the MFC performance.