Positron Lifetime Studies of Defect Structures in Bal-xKxBiO3

1990 ◽  
Vol 209 ◽  
Author(s):  
J.C. O'Brien ◽  
R.H. Howell ◽  
H.B. Radousky ◽  
P.A. Sterne ◽  
D.G. Hinks ◽  
...  
Keyword(s):  
Normal State ◽  
Room Temperature ◽  
Positron Lifetime ◽  
Theoretical Calculations ◽  
Defect Structures ◽  
Cryogenic Temperatures ◽  
Aging Effects ◽  
Temperature Dependent ◽  
Lifetime Measurements ◽  
Lifetime Studies

ABSTRACTTemperature-dependent positron lifetime experiments have been performed from room temperature to cryogenic temperatures on Ba1−xKxBiO3. for x=0.4 and 0.5. From the temperature dependence of the positron lifetime in the normal state, we observe a clear signature of competition between separate defect populations to trap the positron. Theoretical calculations of lifetimes of free or trapped positrons have been performed on Ba1−xKxBiO3, to help identify these defects. Lifetime measurements separated by long times have been performed and evidence of aging effects in the sample defect populations is seen in these materials.

Positron Lifetime Studies of Polyaniline Conducting Polymers

1995 ◽  
Vol 413 ◽  
Author(s):  
C. M. Huang ◽  
J. Liu ◽  
T. C. Sandreczki ◽  
Y. C. Jean
Keyword(s):  
Positron Annihilation ◽  
Room Temperature ◽  
Positron Lifetime ◽  
The Other ◽  
Chemical Compositions ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime ◽  
Positron Lifetimes ◽  
Lifetime Studies ◽  
Made In

ABSTRACTPositron annihilation lifetime measurements are made in a series of polyaniline polymers with different chemical compositions and protonation ratios at room temperature. Two positron lifetimes are observed in these materials: one is assigned to annihilation in the bulk and the other to voids created due to protonation. A relationship between conductivities and positron annihilation probabilities is found.

Temperature Dependent Thermopower and Resistance Measurements of CNT-MgB2 Composites

2012 ◽  
Vol 1407 ◽  
Author(s):  
Kofi W. Adu ◽  
Ruwantha Jayasingha ◽  
Danhao Ma ◽  
Gamini U. Sumanasekera
Keyword(s):  
Normal State ◽  
Room Temperature ◽  
Magnesium Diboride ◽  
Single Wall Carbon Nanotubes ◽  
Temperature Dependent ◽  
Temperature Resistance ◽  
Sample Composition ◽  
State Resistance ◽  
Resistance Data ◽  
Mgb2 Composites

ABSTRACTThe temperature dependent resistance R(T) and thermopower S(T) of sintered single wall carbon nanotubes (SWCNT) and magnesium diboride (MgB2) composites containing 5wt%, 10wt%, and 15wt% of SWCNTs have been measured and compared to their pure counterparts. The thermopower of both MgB2 (in the normal state) and SWCNT remain positive over the entire temperature range (10K to 300K) with room temperature values being ∼ 8μV/K and 57μV/K, respectively. The thermopower of the sintered composites decreased with decreasing temperature and switched from positive to negative near 70K. The superconducting critical temperature (Tc) of the samples ranges from 38K-41K. The room-temperature resistance ratio (RRR) is seen to depend on the sample composition. The temperature width (ΔT) is observed to increase with increasing SWCNT concentration. The normal state resistance data were fitted with the generalized Block-Grüneisen function obtaining Debye temperature of ∼ 900K.

TDPAC and Positron Lifetime Studies in Cold-Worked TiHf

1998 ◽  
Vol 12 (24) ◽  
pp. 1039-1049 ◽  
Author(s):  
R. Govindaraj ◽  
R. Rajaraman
Keyword(s):  
Cold Working ◽  
Positron Lifetime ◽  
Annealing Treatment ◽  
Lifetime Measurements ◽  
Annealing Step ◽  
Time Differential ◽  
Predominant Orientation ◽  
Cold Worked ◽  
Lifetime Studies ◽  
Complete Dissociation

Well annealed reference TiHf hcp samples are characterized by Time differential perturbed angular correlation (TDPAC) of 133–482 keV γ–γ cascade of 181 Ta and positron lifetime measurements to be free from lattice defects of detectable concentrations. TDPAC measurement on the 50% cold-worked sample shows that a fraction 0.16 of probe nuclei is associated with a cold-working induced defect which is interpreted to be faulted dislocation loop. The complete dissociation of these defects from Hf atoms is observed following the annealing treatment of the sample at 723 K. Predominant annihilation of positrons at dislocation kind of defects is observed by positron lifetime measurements in the cold-worked sample. Complete defect recovery of the sample is seen following the annealing step at 873 K, by positron lifetime measurements. XRD measurement of the cold-worked sample shows the predominant orientation of microcrystallites along [Formula: see text] direction.

Defects in Electron Irradiation Te-Doped GaSb Studied by Positron Lifetime Spectroscopy

2008 ◽  
Vol 607 ◽  
pp. 140-142
Author(s):  
H. Li ◽  
J.Y. Ke ◽  
J.B. Pang ◽  
Bo Wang ◽  
Z. Wang
Keyword(s):  
Electron Irradiation ◽  
Irradiation Dose ◽  
Room Temperature ◽  
Positron Lifetime ◽  
Rydberg States ◽  
Average Lifetime ◽  
Shallow Trap ◽  
Lifetime Measurements ◽  
Positron Lifetime Spectroscopy ◽  
Antisite Defects

Defects induced by electron irradiation in Te-doped liquid-encapsulated Czochralski–grown GaSb were studied by the positron lifetime spectroscopy. The lifetime measurements under room temperature indicated there were VGa-related defects with a characteristic lifetime of 298 ps in the heavily Te-doped as-grown GaSb samples. The average lifetime increased with the increase of irradiation dose in lightly Te-doped GaSb,but the behavior was opposite in the heavily Te-doped samples. It should be due to the shift of Fermi level in heavily Te-doped GaSb and the occurrence of gallium vacancies in different charge states. In the temperature dependence measurements carried out on heavily Te-doped samples, we observed positron shallow trap, and this shallow trap should be attributed to positrons forming hyrogenlike Rydberg states with GaSb antisite defects.

scholarly journals Minority Carrier Lifetime Measurements on 4H-SiC Epiwafers by Time-Resolved Photoluminescence and Microwave Detected Photoconductivity

2019 ◽  
Vol 963 ◽  
pp. 313-317
Author(s):  
Jan Beyer ◽  
Nadine Schüler ◽  
Jürgen Erlekampf ◽  
Birgit Kallinger ◽  
Patrick Berwian ◽  
...  
Keyword(s):  
Room Temperature ◽  
Carrier Lifetime ◽  
Minority Carrier ◽  
Minority Carrier Lifetime ◽  
Temperature Dependent ◽  
Lifetime Measurements ◽  
Time Resolved ◽  
Excess Carrier ◽  
Time Resolved Photoluminescence ◽  
Different Thickness

Temperature dependent microwave detected photoconductivity MDP and time-resolved photoluminescence TRPL were employed to investigate the carrier lifetime in CVD grown 4H-SiC epilayers of different thickness. The minority carrier lifetime may be found from both theMDP and defect PL decay at room temperature for all epilayers, whereas the near bandedge emission (NBE) decay is much faster for thin epilayers (<17 μm) due to the substrate proximity and only follows the minority carrier lifetime for thicker samples at lower excess carrier concentrations.

TEMPERATURE-DEPENDENT STUDIES IN SOME HOMOLOGUES OF ALKYLOXY CYANOBIPHENYL EMPLOYING POSITRON LIFETIME SPECTROSCOPY

2000 ◽  
Vol 14 (18) ◽  
pp. 1927-1938 ◽  
Author(s):  
M. SHARMA ◽  
C. KAUR ◽  
K. CHANDRAMANI SINGH ◽  
P. C. JAIN
Keyword(s):  
Positron Annihilation ◽  
Nematic Phase ◽  
Structural Changes ◽  
Positron Lifetime ◽  
Temperature Dependent ◽  
Lifetime Measurements ◽  
Positron Lifetime Spectroscopy ◽  
Crystalline Polymorphism

Some homologues of alkyloxy cyanobipheny1 (6OCB, 8OCB, 9OCB, 10OCB) have been investigated by employing positron lifetime spectroscopy. In each of these compounds, temperature dependent positron lifetime measurements have been carried out, both in the heating as well as cooling cycles. Besides detecting many interesting features like solid-crystalline polymorphism, anti-parallel bimolecular association, formation of cybotactic groups in the nematic phase, positron annihilation parameters have been able to reveal anomalous structural changes taking place in these compounds.

Defect and Dislocation Density Parameters of 5251 Al Alloy Using Positron Annihilation Lifetime Technique

2012 ◽  
Vol 332 ◽  
pp. 17-25 ◽  
Author(s):  
M.A. Abdel-Rahman ◽  
M. Elsayed ◽  
Ahmed G. Attallah ◽  
A.A. Ibrahim ◽  
Emad A. Badawi
Keyword(s):  
Cross Section ◽  
Positron Lifetime ◽  
Defect Density ◽  
Theoretical Calculations ◽  
Linear Increase ◽  
Trapping Efficiency ◽  
Al Alloy ◽  
Trapping Rate ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime

The result of positron lifetime measurements of a defected 5251 Al alloy is reported. Positron lifetime is measured as a function of the thickness reduction of the sample which shows a nearly linear increase and then becomes constant; which can be considered to be a reason for the defect movement saturation. The trapping rate, trapping efficiency, trapping cross-section, defect concentration and defect density of positrons are also measured for the sample concerned. The behaviors of these parameters are matched with theoretical calculations. Data are analyzed using the PATFIT88 computer program.

Cryogenic atomic force microscopy

1991 ◽  
Vol 49 ◽  
pp. 54-55
Author(s):  
K. A. Fisher ◽  
M. G. L. Gustafsson ◽  
M. B. Shattuck ◽  
J. Clarke
Keyword(s):  
Room Temperature ◽  
Rapid Freezing ◽  
Cryogenic Temperatures ◽  
Soft Or ◽  
Electrically Conductive ◽  
Force Microscopy ◽  
Flexible Molecules ◽  
Advantages And Disadvantages ◽  
Atomic Force ◽  
Chemical Perturbation

The atomic force microscope (AFM) is capable of imaging electrically conductive and non-conductive surfaces at atomic resolution. When used to image biological samples, however, lateral resolution is often limited to nanometer levels, due primarily to AFM tip/sample interactions. Several approaches to immobilize and stabilize soft or flexible molecules for AFM have been examined, notably, tethering coating, and freezing. Although each approach has its advantages and disadvantages, rapid freezing techniques have the special advantage of avoiding chemical perturbation, and minimizing physical disruption of the sample. Scanning with an AFM at cryogenic temperatures has the potential to image frozen biomolecules at high resolution. We have constructed a force microscope capable of operating immersed in liquid n-pentane and have tested its performance at room temperature with carbon and metal-coated samples, and at 143° K with uncoated ferritin and purple membrane (PM).

(111) Monocrystalline Nickel Films

1972 ◽  
Vol 30 ◽  
pp. 512-513
Author(s):  
T.E. Pratt ◽  
R.W. Vook
Keyword(s):  
Film Thickness ◽  
Deposition Rate ◽  
Room Temperature ◽  
Narrow Range ◽  
High Vacuum ◽  
Residual Pressure ◽  
Temperature Dependent ◽  
Deposition Parameters ◽  
Transmission Electron ◽  
Substrate Temperatures

(111) oriented thin monocrystalline Ni films have been prepared by vacuum evaporation and examined by transmission electron microscopy and electron diffraction. In high vacuum, at room temperature, a layer of NaCl was first evaporated onto a freshly air-cleaved muscovite substrate clamped to a copper block with attached heater and thermocouple. Then, at various substrate temperatures, with other parameters held within a narrow range, Ni was evaporated from a tungsten filament. It had been shown previously that similar procedures would yield monocrystalline films of CU, Ag, and Au.For the films examined with respect to temperature dependent effects, typical deposition parameters were: Ni film thickness, 500-800 A; Ni deposition rate, 10 A/sec.; residual pressure, 10-6 torr; NaCl film thickness, 250 A; and NaCl deposition rate, 10 A/sec. Some additional evaporations involved higher deposition rates and lower film thicknesses.Monocrystalline films were obtained with substrate temperatures above 500° C. Below 450° C, the films were polycrystalline with a strong (111) preferred orientation.

Temperature Dependent Line-Shape of the Silicon Dangling Bond EPR-Resonance in Polycrystalline Silicon

1996 ◽  
Vol 452 ◽  
Author(s):  
N. H. Nickel ◽  
E. A. Schiff
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Polycrystalline Silicon ◽  
Room Temperature ◽  
Dangling Bond ◽  
Temperature Dependent ◽  
Paramagnetic Resonance ◽  
Temperature Electron ◽  
Motional Narrowing ◽  
G Value ◽  
Electron Paramagnetic

AbstractThe temperature dependence of the silicon dangling-bond resonance in polycrystalline (poly-Si) and amorphous silicon (a-Si:H) was measured. At room temperature, electron paramagnetic resonance (EPR) measurements reveal an isotropie g-value of 2.0055 and a line width of 6.5 and 6.1 G for Si dangling-bonds in a-Si:H and poly-Si, respectively. In both materials spin density and g-value are independent of temperature. While in a-Si:H the width of the resonance did not change with temperature, poly-Si exhibits a remarkable T dependence of ΔHpp. In unpassivated poly-Si a pronounced decrease of ΔHpp is observed for temperatures above 300 K. At 384 K ΔHpp reaches a minimum of 5.1 G, then increases to 6.1 G at 460 K, and eventually decreases to 4.6 G at 530 K. In hydrogenated poly-Si ΔHpp decreases monotonically above 425 K. The decrease of ΔHpp is attributed to electron hopping causing motional narrowing. An average hopping distance of 15 and 17.5 Å was estimated for unhydrogenated and H passivated poly-Si, respectively.

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