scholarly journals Quantum Phenomena in Nanomaterials: Coherent Superpositions of Fine Structure States in CdSe Nanocrystals at Room Temperature

2019 ◽  
Vol 123 (51) ◽  
pp. 31286-31293 ◽  
Author(s):  
Elisabetta Collini ◽  
Hugo Gattuso ◽  
Luca Bolzonello ◽  
Andrea Casotto ◽  
Andrea Volpato ◽  
...  
Keyword(s):  
Fine Structure ◽  
Room Temperature ◽  
Cdse Nanocrystals ◽  
Quantum Phenomena

Electrophoretic Deposition of CdSe Nanocrystals for Photovoltaic Applications

2007 ◽  
Vol 1031 ◽  
Author(s):  
Nathanael Smith ◽  
Kevin J Emmett ◽  
Sandra J Rosenthal
Keyword(s):  
Titanium Dioxide ◽  
Electrophoretic Deposition ◽  
Room Temperature ◽  
Tio2 Thin Film ◽  
Cdse Nanocrystals ◽  
Photovoltaic Devices ◽  
Photovoltaic Applications ◽  
Nanocrystalline Titanium ◽  
Alternative Techniques

AbstractCdSe nanocrystals chemically linked to nanocrystalline titanium dioxide substrates form a promising material for nanostructured photovoltaic devices. The usual method for attaching the nanocrystals to the titanium dioxide substrate is by means of a linking molecule (such as mercaptopropionic acid) or in-situ growth. In this paper, we report the use of an alternative technique, electrophoretic deposition (EPD), to directly deposit already formed CdSe nanocrystals onto the substrate. In EPD, a voltage is established between two electrodes that are immersed in a solution of nanocrystals. At room temperature, a fraction of the nanocrystals are thermally charged, and these charged nanocrystals migrate to the electrodes and adhere to the surface. A significant advantage of EPD over the use of linking molecules is the speed with which the nanocrystals are deposited: EPD takes only a few minutes, compared to the several hours required for the alternative techniques. Additionally, we have fabricated initial photovoltaic devices based on electrophoretically deposited CdSe nanocrystals on a planar TiO2 thin film.

Symmetry Breaking Induced Activation of Nanocrystal Optical Transitions

MRS Advances ◽  
2018 ◽  
Vol 3 (14) ◽  
pp. 711-716 ◽  
Author(s):  
Peter C. Sercel ◽  
Andrew Shabaev ◽  
Alexander L. Efros
Keyword(s):  
Optical Properties ◽  
Fine Structure ◽  
Symmetry Breaking ◽  
Semiconductor Nanocrystals ◽  
Radiative Lifetime ◽  
Multipole Expansion ◽  
Cdse Nanocrystals ◽  
Coulomb Center ◽  
Charged Center ◽  
Positively Charged

ABSTRACTWe have analysed the effect of symmetry breaking on the optical properties of semiconductor nanocrystals due to doping by charged impurities. Using doped CdSe nanocrystals as an example, we show the effects of a Coulomb center on the exciton fine-structure and optical selection rules using symmetry theory and then quantify the effect of symmetry breaking on the exciton fine structure, modelling the charged center using a multipole expansion. The model shows that the presence of a Coulomb center breaks the nanocrystal symmetry and affects its optical properties through mixing and shifting of the hole spin and parity sublevels. This symmetry breaking, particularly for positively charged centers, shortens the radiative lifetime of CdSe nanocrystals even at room temperature, in qualitative agreement with the increase in PL efficiency observed in CdSe nanocrystals doped with positive Ag charge centers [A. Sahu et.al., Nano Lett. 12, 2587, (2012)]. The effect of the charged center on the photoluminescence and the absorption spectra is shown, with and without the presence of compensating charges on the nanocrystal surface. While spectra of individual nanocrystals are expected to shift and broaden with the introduction of a charged center, configuration averaging and inhomogeneous broadening are shown to wash out these effects. The presence of compensating charges at the NC surface also serves to stabilize the band edge transition energies relative to NCs with no charge centers.

Evaluation of Plastic Workability Limit of Magnesium Alloy by Cavitations in High Temperature Uni and Biaxial Test

2012 ◽  
Vol 735 ◽  
pp. 67-72
Author(s):  
Kunio Funami ◽  
Daisuke Yamashita ◽  
Kohji Suzuki ◽  
Masafumi Noda
Keyword(s):  
Fine Structure ◽  
High Temperature ◽  
Magnesium Alloy ◽  
Grain Boundary ◽  
Room Temperature ◽  
Grain Boundary Sliding ◽  
Az31 Magnesium Alloy ◽  
Temperature Deformation ◽  
Alloy Plate ◽  
Boundary Sliding

Abstract. This study examined the critical plastic formability limit of a fine-structure AZ31 magnesium alloy plate under warm and high temperature based on the strength of a magnesium alloy that has cavities at room temperature. The cyclic hot free-forging process as pre-form working following rolling at a light reduction ratio fabricated a fine-structure AZ31 magnesium alloy plate. The appearance of the cavities was examined in detail together with changes in the structure and preparation methods before further damage at high temperatures with increasing uni-and biaxial plastic deformation. The allowable deformation limit in the super plasticity process can be estimated from the strength of the deformed material and forming limit diagram (FLD) at room temperature. During high-temperature deformation, cavities are produced by stress concentrations at grain boundary triple points and striation bands due to grain boundary sliding. The cavitations growth behavior is dependent upon deformation conditions, and a high percentage of large cavities occupy the sample surface as a large amount of grain boundary sliding is present, i.e., as uniform elongation grows larger, the cavity size also increases. In a case where 200% uniaxial strain was applied to a fine-grained structure material at a temperature of 623K under a strain rate of 10-4s-1, the tensile strength at room temperature decreased about 13%, and elongation was 10% less, compared with that of a material to which no load was applied due to the influence of cavities. In a case of biaxial deformation, the values were 28% lower. It is possible to draw a FLD based on the cavity incidence fraction .

Experimental Tem and Image Simulation of Dislocations in Ti3A1

1994 ◽  
Vol 364 ◽  
Author(s):  
JÖrg M.K. Wiezorek ◽  
S. A. Court ◽  
C.J. Humphreys
Keyword(s):  
Fine Structure ◽  
Room Temperature ◽  
Stacking Faults ◽  
Antiphase Boundary ◽  
Computational Techniques ◽  
Image Simulation ◽  
Prism Plane ◽  
Weak Beam ◽  
Transmission Electron ◽  
Beam Technique

AbstractThe fine structure and the character of a dislocations on prism planes have been determined for room-temperature deformed polycrystalline Ti3Al using a combination of experimental and computational techniques of transmission electron microscopy (TEM). Within the resolution limits of the weak-beam technique the fine structure of prism plane a dislocations in Ti3Al is found to be planar and to comprise only a single ribbon of antiphase boundary and no experimentally observable stacking faults.

scholarly journals The Determination of Interfacial Structure and Phase Transitions in Al/Cu and Al/Ni Interfaces by Means of Surface Extended X-Ray Absorption Fine Structure

1991 ◽  
Vol 238 ◽  
Author(s):  
E. V. Barrera ◽  
S. M. Heald
Keyword(s):  
Fine Structure ◽  
Room Temperature ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Interfacial Structure ◽  
Reaction Products ◽  
X Ray ◽  
Absorption Fine ◽  
Reaction Zones ◽  
X Ray Absorption

ABSTRACTSurface extended x-ray absorption fine structure (SEXAFS) was used to investigate the interfacial conditions of Al/Cu and Al/Ni shallow buried interfaces. Previous studies using glancing angle extended x-ray absorption fine structure, x-ray reflectivity, photoemission, and SEXAFS produced conflicting results as to whether or not the interfaces between Al and Cu and Al and Ni were reacted upon room temperature deposition. In this study polycrystalline bilayers of Al/Cu and Al/Ni and trilayers of Al/Cu/Al and Al/Ni/Al were deposited on tantalum foil at room temperature in ultra high vacuum and analyzed to evaluate the reactivity of these systems on a nanometer scale. It became overwhelming apparent that the interfacial phase reactions were a function of the vacuum conditions. Samples deposited with the optimum vacuum conditions showed reaction products upon deposition at room temperature which were characterized by comparisons to standards and by least squares fitting to be CuAl2 and NiAl3 respectively. The results of this study showed that the reacted zone thicknesses were readily dependent on the deposition parameters. For both Al on Cu and Al on Ni as well as the metal on Al conditions 10A reaction zones were observed. These reaction zones were smaller than that observed for bilayers of Al on Cu (30Å) and Al on Ni (60Å) where deposition rates were much higher and samples were much thicker. The reaction species are evident by SEXAFS, where the previous photoemission studies only indicated that changes had occurred. Improved vacuum conditions as compared to the earlier experiments is primarily the reason reactions on deposition were seen in this study as compared to the earlier SEXAFS studies.

Exciton Fine Structure of CdSe/CdS Nanocrystals Determined by Polarization Microscopy at Room Temperature

ACS Nano ◽  
2015 ◽  
Vol 9 (8) ◽  
pp. 7992-8003 ◽  
Author(s):  
Stefano Vezzoli ◽  
Mathieu Manceau ◽  
Godefroy Leménager ◽  
Quentin Glorieux ◽  
Elisabeth Giacobino ◽  
...  
Keyword(s):  
Fine Structure ◽  
Room Temperature ◽  
Polarization Microscopy ◽  
Cds Nanocrystals

Study on Initial Kinetics of CdSe Nanocrystals by a Combination of in Situ X-ray Absorption Fine Structure and Microfluidic Reactor

2009 ◽  
Vol 113 (43) ◽  
pp. 18608-18613 ◽  
Author(s):  
Z. H. Sun ◽  
H. Oyanagi ◽  
M. Uehara ◽  
H. Nakamura ◽  
K. Yamashita ◽  
...  
Keyword(s):  
Fine Structure ◽  
Cdse Nanocrystals ◽  
X Ray ◽  
Absorption Fine ◽  
Microfluidic Reactor ◽  
X Ray Absorption ◽  
Kinetics Of

Formation of Reactive Clusters in Pd-Y Zeolite by Reduction-Reoxidation Treatment

1992 ◽  
Vol 57 (4) ◽  
pp. 817-825 ◽  
Author(s):  
Hiroshige Matsumoto ◽  
Shuji Tanabe
Keyword(s):  
Fine Structure ◽  
Room Temperature ◽  
Reactive Species ◽  
Temperature Programmed Reduction ◽  
Y Zeolite ◽  
X Ray ◽  
Absorption Fine ◽  
Temperature Programmed ◽  
X Ray Absorption

Preparation of a finely dispersed Pd-Y zeolite has been investigated by temperature-programmed reduction (TPR) and extended X-ray absorption fine structure (EXAFS) techniques. Upon the treatment by a sequence of calcination, reduction, and reoxidation, the original Pd(NH3)42+ ions in the zeolite transformed to reactive species, which were reduced with hydrogen at room temperature and characterized as small PdO clusters of about 25 Pd atoms.

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