The Electronic Structure of a-Si,Ge:H Alloys

1994 ◽  
Vol 336 ◽  
Author(s):  
F. Zhong ◽  
J.D. Cohen ◽  
J. Yang ◽  
S. Guha
Keyword(s):  
Thermal Emission ◽  
Drive Level ◽  
Optical Methods ◽  
Defect States ◽  
Thermal Transitions ◽  
Defect Band ◽  
Time Resolved ◽  
Photocurrent Spectroscopy ◽  
First Time ◽  
Negative Signal

ABSTRACTWe have carried out a detailed study of the energy distribution of deep defects for high quality glow discharge a-Si,Ge:H alloys using both thermal emission and optical Methods: drive-level capacitance profiling, transient photocapacitance and photocurrent plus modulation photocurrent spectroscopy. Four distinct bands of transitions involving defect states have been identified: two associated with thermal transitions, and the other two related to optical transitions. We have, for the first time, observed a negative signal in the photocapacitance spectra at photon energies near 1.2eV. This striking aspect verifies the presence of a distinct defect band above Ep from which electron thermal emission is greatly suppressed. Our Measurements also disclose a fairly narrow defect band below the Fermi level which contrasts with the defect properties observed in a-Si:H. Time resolved photocapacitance spectra indicate that this defect band exhibits configuration relaxation.

scholarly journals Photoresponse from single upright-standing ZnO nanorods explored by photoconductive AFM

2013 ◽  
Vol 4 ◽  
pp. 208-217 ◽  
Author(s):  
Igor Beinik ◽  
Markus Kratzer ◽  
Astrid Wachauer ◽  
Lin Wang ◽  
Yuri P Piryatinski ◽  
...  
Keyword(s):  
Density Functional ◽  
Zno Nanorods ◽  
Density Functional Theory Calculations ◽  
Band Gap Energy ◽  
Ambient Conditions ◽  
Defect States ◽  
Time Resolved ◽  
Photocurrent Spectroscopy ◽  
Upright Standing ◽  
Photocurrent Spectra

Background: ZnO nanostructures are promising candidates for the development of novel electronic devices due to their unique electrical and optical properties. Here, photoconductive atomic force microscopy (PC-AFM) has been applied to investigate transient photoconductivity and photocurrent spectra of upright-standing ZnO nanorods (NRs). With a view to evaluate the electronic properties of the NRs and to get information on recombination kinetics, we have also performed time-resolved photoluminescence measurements macroscopically. Results: Persistent photoconductivity from single ZnO NRs was observed for about 1800 s and was studied with the help of photocurrent spectroscopy, which was recorded locally. The photocurrent spectra recorded from single ZnO NRs revealed that the minimum photon energy sufficient for photocurrent excitation is 3.1 eV. This value is at least 100 meV lower than the band-gap energy determined from the photoluminescence experiments. Conclusion: The obtained results suggest that the photoresponse in ZnO NRs under ambient conditions originates preferentially from photoexcitation of charge carriers localized at defect states and dominates over the oxygen photodesorption mechanism. Our findings are in agreement with previous theoretical predictions based on density functional theory calculations as well as with earlier experiments carried out at variable oxygen pressure.

scholarly journals Defect States in SiC/GaN- and SiC/AlGaN/GaN- Heterostructures Characterized by Admittance and Photocurrent Spectroscopy

1999 ◽  
Vol 4 (S1) ◽  
pp. 388-396
Author(s):  
H. Witte ◽  
A. Krtschil ◽  
M. Lisker ◽  
J. Christen ◽  
F. Scholz ◽  
...  
Keyword(s):  
Modulation Frequency ◽  
Schottky Contact ◽  
Peak Shift ◽  
Optical Transitions ◽  
Defect States ◽  
Defect Band ◽  
Transition Energies ◽  
Photocurrent Spectroscopy ◽  
Voltage Dependent ◽  
Related Defect

Deep defect levels in n-type GaN/AlN/6H-SiC- and GaN/AlGaN/6H-SiC- heterostructures grown by Metallorganic Vapor Phase Epitaxy were analyzed by Thermal and Optical Admittance and Photocurrent Spectroscopy. The various thermal and optical transitions in the spectra originating from both the Schottky contact as well as the GaN/SiC- and AlGaN/GaN-heterojunctions were separated. This was achieved by variation of the modulation frequency, the use of different contact arrangements and by comparison with reference spectra from GaN/Sapphir samples and SiC substrates. In the GaN/AlGaN/SiC structures a bias voltage dependent peak shift was found which is correlated to an interface related defect distribution. In additionally to, SiC related defects, defect-band-transitions involving defects with transition energies at 2.2eV, 1.85eV, EG-(470±40) meV and EG-(65-95) meV were found for the GaN layer.

Defect States in SiC/GaN-and SiC/AlGaN/GaN-Heterostructures Characterized by Admittance and Photocurrent Spectroscopy

1998 ◽  
Vol 537 ◽  
Author(s):  
H. Witte ◽  
A. Krtschil ◽  
M. Lisker ◽  
J. Christen ◽  
F. Scholz ◽  
...  
Keyword(s):  
Modulation Frequency ◽  
Schottky Contact ◽  
Peak Shift ◽  
Optical Transitions ◽  
Defect States ◽  
Defect Band ◽  
Transition Energies ◽  
Photocurrent Spectroscopy ◽  
Voltage Dependent ◽  
Related Defect

AbstractDeep defect levels in n-type GaN/AlN/6H-SiC- and GaN/AlGaN/6H-SiC- heterostructures grown by Metallorganic Vapor Phase Epitaxy were analyzed by Thermal and Optical Admittance and Photocurrent Spectroscopy. The various thermal and optical transitions in the spectra originating from both the Schottky contact as well as the GaN/SiC- and AlGaN/GaNheterojunctions were separated. This was achieved by variation of the modulation frequency, the use of different contact arrangements and by comparison with reference spectra from GaN/Sapphir samples and SiC substrates. In the GaN/AlGaN/SiC structures a bias voltage dependent peak shift was found which is correlated to an interface related defect distribution. In additionally to, SIC related defects, defect-band-transitions involving defects with transition energies at 2.2eV, 1.85eV, EG-(470±40) meV and EG-(65-95) meV were found for the GaN layer.

Seeking for magnetic fields in rotating disk/jets with ALMA polarimetry

2018 ◽  
Vol 14 (A30) ◽  
pp. 128-129
Author(s):  
Francesca Bacciotti ◽  
Josep Miquel Girart ◽  
Marco Padovani
Keyword(s):  
Linear Polarization ◽  
Thermal Emission ◽  
Rotating Disk ◽  
Polarization Angle ◽  
T Tauri ◽  
Magnetic Signatures ◽  
Dust Evolution ◽  
First Time ◽  
Crucial Ingredient ◽  
Polarization Fraction

AbstractThe Atacama Large Millimeter/submillimeter Array (ALMA) is providing important advances in studies of star formation. In particular, polarimetry can reveal the disk magnetic configuration, a crucial ingredient in many processes, as, for example, the transport of angular momentum. We analized ALMA Band 7 (870 μm) polarimetric data at 0.”2 resolution for the young rotating disk/jet systems DG Tau and CW Tau, to find magnetic signatures. From the Stokes I, U, Q maps, we derive the linear polarization intensity, $P = \sqrt {{Q^2} + {U^2}} $ , the linear polarization fraction, and the polarization angle. The alignment of the latter with the disk minor axis (Fig. 1) shows that self-scattering of dust thermal emission rather than magnetic alignment dominates the polarization in both targets (Bacciotti et al. 2018). However, several dust properties can be diagnosed comparing the polarization data with the models of self-scattering (e.g. Kataoke et al. 2017, Yang et al. 2017). The maximum grain size turns out to be in the range 50 - 70 μm for DG Tau and 100 - 150 μm for CW Tau. The asymmetry of the polarized intensity in DG Tau, observed for the first time around a T Tauri star, indicates that the disk is flared. Moreover, the observed belt-like feature may betray the presence of a disk substructure. In contrast, the polarization maps of CW Tau indicate that here the grains have settled to the disk midplane. Polarimetry is thus very important in studies of the dust evolution.

scholarly journals Experimental Investigation of the Pumping of a Model-Concrete through Pipes

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1161
Author(s):  
Martin A. Haustein ◽  
Moritz N. Kluwe ◽  
Rüdiger Schwarze
Keyword(s):  
Pressure Loss ◽  
Plug Flow ◽  
Particle Migration ◽  
Test Plant ◽  
Flow Profile ◽  
Time Resolved ◽  
Rheological Measurements ◽  
Lubricating Layer ◽  
Image Velocimetry ◽  
First Time

Many practical aspects of processing fresh concrete depend on its rheology, such as the pumping of the material. It is known that a lubricating layer is formed in the process, which significantly reduces the pumping pressure. However, these phenomena can hardly be considered in the usual rheological measurements. A main problem is the optical inaccessibility of the material, which prevents estimations about, e.g., the thickness of the plug flow or particle migration. In this paper, the pneumatic pumping of a transparent model concrete is performed by means of a test plant. The flow profile over the entire pipe cross-section is resolved in time and space via Particle Image Velocimetry (PIV) measurements. This allows the comparison with the analytical flow profile from rheological measurements of the material using the Buckingham–Reiner equation. A reduction of the pressure loss to around 60% induced through segregation of the material is found. These measurements reflect the rheology of the material under realistic pumping conditions including particle migration. This makes it possible for the first time to observe a transparent material with concrete-like rheology under pulsating pumping conditions and to compare the true and calculated time-resolved pressure loss.

Assay of creatine kinase isoenzyme MB in serum with time-resolved immunofluorometry

1990 ◽  
Vol 36 (9) ◽  
pp. 1679-1683 ◽  
Author(s):  
E S Lianidou ◽  
T K Christopoulos ◽  
E P Diamandis
Keyword(s):  
Creatine Kinase ◽  
Laser Excitation ◽  
Solid Phase ◽  
Time Resolved ◽  
Creatine Kinase Isoenzyme ◽  
Phase Complex ◽  
Precision And Accuracy ◽  
Accuracy Indices ◽  
First Time ◽  
Creatine Kinase Isoenzyme Mb

Abstract We describe the first time-resolved immunofluorometric assay for creatine kinase (EC 2.7.3.2) isoenzyme MB (CK-MB) in serum. The assay is based on the formation of the complex: solid-phase anti-CK-MB-CK-MB-biotinylated anti-CK-BB-streptavidin-BCPDA-Eu3+, where anti-CK-MB and anti-CK-BB are monoclonal antibodies against the CK isoenzymes MB and BB, respectively, and BCPDA is the europium chelator 4,7-bis(chlorosulfophenyl)-1,10-phenanthroline-2,9-dicarboxylic acid. The solid-phase complex is fluorescent and is measured on the dry solid-phase (microtiter well) in a specially designed time-resolved fluorometer that uses laser excitation. The assay requires 25 microL of serum and is not affected by the presence of either CK-MM (up to 5000 micrograms/L) or CK-BB (up to 1000 micrograms/L) in the sample. Precision and accuracy indices for the assay were satisfactory.

scholarly journals Early results from a diagnostic 1.3 cm survey of massive young protostars

2012 ◽  
Vol 8 (S287) ◽  
pp. 497-501
Author(s):  
Crystal L. Brogan ◽  
Todd R. Hunter ◽  
Claudia J. Cyganowski ◽  
Remy Indebetouw ◽  
Rachel Friesen ◽  
...  
Keyword(s):  
Massive Star ◽  
Thermal Emission ◽  
Young Stellar Objects ◽  
Large Array ◽  
Stellar Objects ◽  
Very Large Array ◽  
Early Results ◽  
Wide Range ◽  
First Time ◽  
24 Ghz

AbstractWe have used the recently-upgraded Karl G. Jansky Very Large Array (JVLA) to conduct a K-band (~24 GHz) study of 22 massive young stellar objects in 1.3 cm continuum and a comprehensive set of diagnostic lines. This survey is unique in that it samples a wide range of massive star formation signposts simultaneously for the first time. In this proceeding we present preliminary results for the 11 sources in the 2-4 kpc distance bin. We detect compact NH3 cores in all of the fields, with many showing emission up through the (6,6) transition. Maser emission in the 25 GHz CH3OH ladder is present in 7 of 11 sources. We also detect non-thermal emission in the NH3 (3,3) transition in 7 of 11 sources.

Thermal Transformation of Hydrogen Bonds in a-SiC:H Films: Structural and Optical Properties

2005 ◽  
Vol 864 ◽  
Author(s):  
Andrey V. Vasin ◽  
Sergey P. Kolesnik ◽  
Andrey A. Konchits ◽  
Vladimir S. Lysenko ◽  
Alexey N. Nazarov ◽  
...  
Keyword(s):  
Light Emission ◽  
Vacuum Annealing ◽  
Thermal Transformation ◽  
Vacuum Treatment ◽  
Nonradiative Recombination ◽  
Defect States ◽  
Paramagnetic Defect ◽  
Paramagnetic Resonance ◽  
First Time ◽  
Hydrogenated Amorphous

AbstractHydrogenated amorphous silicon carbide (a-SiC:H) films have been deposited using magnetron sputtering technique. Investigation of the effect of the vacuum annealing temperature on photoluminescence properties and paramagnetic defects, and its correlation with structural transformation of a-SiC:H have been performed. Significantly enhanced light emission efficiency after low-temperature vacuum treatment (450 °C) is found due to enhanced passivation of paramagnetic defects associated with carbon-rich chemically disordered structure. Subsequent high-temperature vacuum annealing results in a decrease of luminescent intensity that is associated with increase of carbon related paramagnetic defect states, shown to be the primary nonradiative recombination centres. For the first time silicon-related dangling bonds in a-SiC:H have been detected reliably by electron paramagnetic resonance measurements in annealed samples.

Spatio-Temporal Development of Supercavitation Over an Impulsively Launched Projectile

2006 ◽  
Author(s):  
C. J. Weiland ◽  
P. P. Vlachos
Keyword(s):  
High Speed ◽  
Temporal Development ◽  
Two Phase ◽  
Time Resolved ◽  
Gas Gun ◽  
Supercavitating Flow ◽  
Image Velocimetry ◽  
Spatio Temporal ◽  
Asymmetric Vortices ◽  
First Time

Supercavitation inception and formation was studied over blunt projectiles. The projectiles were fired using a gas gun method. In this method, projectiles are launched under the action of expanding detonation gases. Both qualitative and quantitative optical flow diagnostics using high speed digital imaging were used to analyze the spatio-temporal development of the supercavitating flow. For the first time, quantification of the supercavitation was achieved using Time Resolved Digital Particle Image Velocimetry (TRDPIV) detailing the two phase flow field surrounding the translating projectiles and the gas vapor bubble. Experimental results indicate that the supercavity forms at the aft end of the projectile and travels forward along the direction of projectile travel. The impulsive start of the projectile generates two asymmetric vortices which are shed from the blunt nose of the projectile. The vortices interact with the moving cavity and subsequently deform. This interaction is believed to directly contribute to the instabilities in the flight path.

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