Photoluminescence from Silicon Nanocrystals Formed by Pulsed-Laser Deposition

2003 ◽  
Vol 770 ◽  
Author(s):  
X. Y. Chen ◽  
Y. F. Lu ◽  
Y. H. Wu ◽  
B. J. Cho ◽  
W. D. Song ◽  
...  
Keyword(s):  
Ambient Pressure ◽  
Quantum Confinement Effect ◽  
Surface States ◽  
Peak Shift ◽  
Peak Position ◽  
Small Crystals ◽  
Before And After ◽  
Intensity Changes ◽  
Excitation Laser ◽  
Ar Gas

AbstractSi nanocrystals (NCs) consisting of small crystals from 1 to 20 nm were formed by pulsedlaser deposition (PLD) in inert Ar gas and reactive O2 gas. The oxygen content of the Si NCs increases with increasing O2 ambient pressure and nearly SiO2 stoichiometry is obtained when O2 pressure is higher than 100 mTorr. The optical absorption of the Si NCs shows an indirect band transition. Broad PL spectra are observed from Si NCs. The peak position and intensity of the PL band at 1.8–2.1 eV are dependent on excitation laser intensity, while intensity changes and blue shifts are observed after oxidation and annealing. The PL band at 2.55 eV displays vibronic structures with periodic spacing of 97 ± 9 meV, while no peak shift is found before and after oxidation and annealing. The as-deposited Si NCs show a polycrystal structure and crystallinity improves after annealing. Combined with the PL of Si NCs obtained by crumbling electrochemical-etched porous Si layer, the results give strong evidence that the PL band at 1.8–2.1 eV is due to the quantum confinement effect (QCE) in Si NC core while the PL band at 2.55 eV is related to the localized surface states at SiOx/Si interface.

Carbon Capture Performance of Amino-Modified MIL-101 at Room Temperature

2013 ◽  
Vol 395-396 ◽  
pp. 637-640
Author(s):  
Yi Yang ◽  
Zheng Ping Wang ◽  
Ling Meng ◽  
Lian Jun Wang
Keyword(s):  
Carbon Dioxide ◽  
Specific Surface ◽  
Pore Structure ◽  
Carbon Capture ◽  
Room Temperature ◽  
Ambient Pressure ◽  
Metal Organic Framework ◽  
Adsorption Properties ◽  
Carbon Dioxide Adsorption ◽  
Before And After

MIL-101, a metal-organic framework material, was synthesized by the high-temperature hydrothermal method. Triethylenetetramine (TETA) modification enabled the effective grafting of an amino group onto the surface of the materials and their pore structure. The crystal structure, micromorphology, specific surface area, and pore structure of the samples before and after modification were analyzed with an X-ray diffractometer, scanning electron microscope, specific surface and aperture tester, and infrared spectrometer. The carbon dioxide adsorption properties of the samples were determined by a thermal analyzer before and after TETA modification. Results show that moderate amino modification can effectively improve the microporous structure of MIL-101 and its carbon dioxide adsorption properties. After modification, the capacity of MIL-101 to adsorb carbon dioxide decreased only by 0.61 wt%, and a high adsorption capacity of 9.45 wt% was maintained after six cycles of adsorption testing at room temperature and ambient pressure.

Identification of Amber and the Copal under Heat Pressurized Process

2012 ◽  
Vol 554-556 ◽  
pp. 2112-2115
Author(s):  
Hui Li ◽  
Xuan Wang ◽  
Yong Zhu ◽  
Qin Ren
Keyword(s):  
Chemical Properties ◽  
Peak Position ◽  
Exothermic Peak ◽  
Endothermic Peak ◽  
Scanning Calorimetry ◽  
Natural Resin ◽  
Before And After ◽  
Artificial Heat ◽  
Physical And Chemical ◽  
And Chemical Properties

Amber and copal belong to the natural resin, which are similar and transitional in the physical and chemical properties. The artificial heat-pressurized treatment is contributed to the polymerization of the natural copal, and turns into green, yellow-green and deep orange-yellow copal. It is very difficult to identify amber from the heat- pressurized treatment copal only based on the gemological parameters.The thermal behavior of amber and the copal before and after heat-pressurized treatment were analyzed by means of differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy(FTIR) and nuclear magnetic resonance(NMR). The results show that amber exists an evident endothermic peak around 123~132°C, and copal reveals an obvious endothermic peak at about 174~178°C, and the heat pressurized treatment copal occurs a clear exothermic peak around 150~152°C. The differences between endothermic or exothermic transition and peak position reveal occurring thermal oxidation or the bond breaking or the melting, which are of great significance in the identification.

The Accuracy of Financial Analysts' Forecasts after Mergers

1994 ◽  
Vol 9 (3) ◽  
pp. 465-483 ◽  
Author(s):  
In-Mu Haw ◽  
Kooyul Jung ◽  
William Ruland
Keyword(s):  
Financial Analysts ◽  
Forecast Accuracy ◽  
Capital Intensity ◽  
Financial Leverage ◽  
Prediction Bias ◽  
Before And After ◽  
Intensity Changes ◽  
Industry Diversification

This paper examines forecasts developed by financial analysts before and after mergers. The study finds that forecast accuracy decreases sharply after mergers. These accuracy reductions tend to be more pronounced when financial leverage changes, when the merger does not provide earnings or industry diversification, when the purchase method of accounting is used to record the transaction, when capital intensity changes, and when the size of the target corporation is large compared to the size of the acquiring corporation. The data also show that reductions in forecast accuracy after mergers tend to be temporary. Accuracy returns to approximately the premerger level within four years after the merger. The study also finds that overprediction bias increases sharply in the year immediately following the merger. This increase in over-prediction bias, however, is also temporary. Overprediction bias returns to approximately the premerger level within the four-year postmerger study period.

Impact of damaging and recovery on the temperature dependence of the work function of oxide electrodes in fluorescent lamps

2021 ◽  
Vol 96 (1) ◽  
pp. 11301
Author(s):  
Reinhard Langer ◽  
Irina Paul ◽  
Reinhard Tidecks
Keyword(s):  
Ultraviolet Radiation ◽  
Temperature Dependence ◽  
Work Function ◽  
Surface States ◽  
Strong Increase ◽  
Thermal Excitation ◽  
Cold Starting ◽  
Fluorescent Lamps ◽  
Oxide Electrodes ◽  
Before And After

In the present work the work function of electrons for oxide cathodes in operating fluorescent lamps is measured before and after damaging the cathodes by cold starting of the lamp. A strong increase of the absolute value and a decrease of the temperature dependence of the work function is observed. The values recover partly after operating the lamp for a certain time. The results are interpreted as the consequence of a thin metallic layer generated during cold starting at the surface of the oxide and its effect on the depletion of electrons of donor-like colour centres (appearing in the oxide due to oxygen vacancies) under the ultraviolet radiation present in an operating fluorescent lamp, and on the magnitude and temperature dependence of the work function in the plated regions, invoking the patch effect to generate an averaged value of the work function, which is then assumed to be observed experimentally. Moreover, barium surface states are considered, yielding reasonable values for the not plated regions, when calculating the work function, as well for the assumption of a depletion of also these states by ultraviolet radiation, as also when only regarding a thermal excitation of the surface states applying the Fowler equation. Finally, a model of a diffusion governed dynamical equilibrium yielding a T3∕2 dependence for the donor concentration is proposed.

Luminescence of II-VI Semiconductor Nanoparticles

2014 ◽  
Vol 222 ◽  
pp. 1-65 ◽  
Author(s):  
B.P. Chandra ◽  
V.K. Chandra ◽  
Piyush Jha
Keyword(s):  
Band Gap ◽  
Data Storage ◽  
Quantum Confinement Effect ◽  
Ultrafine Particle ◽  
Surface States ◽  
Emission Spectra ◽  
Volume Ratio ◽  
Blue Shift ◽  
Band Gap Energy ◽  
Molecular Engineering

Nanoparticle or an ultrafine particle is a small solid whose physical dimension lies between 1 to 100 nanometers. Nanotechnology is the coming revolution in molecular engineering, and therefore, it is curiosity-driven and promising area of technology. The field of nanoscience and nanotechnology is interdisciplinary in nature and being studied by physicists, chemists, material scientists, biologists, engineers, computer scientists, etc. Research in the field of nanoparticles has been triggered by the recent availability of revolutionary instruments and approaches that allow the investigation of material properties with a resolution close to the atomic level. Strongly connected to such technological advances are the pioneering studies that have revealed new physical properties of matter at a level intermediate between atomic/molecular and bulk. Quantum confinement effect modifies the electronic structure of nanoparticles when their sizes become comparable to that of their Bohr excitonic radius. When the particle radius falls below the excitonic Bohr radius, the band gap energy is widened, leading to a blue shift in the band gap emission spectra, etc. On the other hand, the surface states play a more important role in the nanoparticles, due to their large surface-to-volume ratio with a decrease in particle size (surface effects). From the last few years, nanoparticles have been a common material for the development of new cutting-edge applications in communications, energy storage, sensing, data storage, optics, transmission, environmental protection, cosmetics, biology, and medicine due to their important optical, electrical, and magnetic properties.

CONTROLLED SYNTHESIS AND CHARACTERIZATION OF CERIUM-DOPED ZnS NANOPARTICLES IN HMTA MATRIX

2011 ◽  
Vol 10 (03) ◽  
pp. 487-493 ◽  
Author(s):  
K. VIJAI ANAND ◽  
R. MOHAN ◽  
R. MOHAN KUMAR ◽  
M. KARL CHINNU ◽  
R. JAYAVEL
Keyword(s):  
Quantum Confinement Effect ◽  
Average Particle Size ◽  
Surface States ◽  
Deep Trap ◽  
Average Particle ◽  
Zns Nanoparticles ◽  
Selected Area Electron Diffraction ◽  
Luminescence Process ◽  
Photoluminescence Studies

Cerium-doped ZnS nanoparticles have been synthesized through hydrothermal method. The nanoparticles were stabilized using hexamethylenetetramine (HMTA) as surfactant in aqueous solution. The average particle size of the prepared samples is about 2 nm. The structure of the as-prepared ZnS nanoparticles is cubic (zinc blende) as demonstrated by X-ray powder diffraction (XRD) and selected area electron diffraction (SAED) analysis. TEM results showed that the synthesized nanoparticles were uniformly dispersed in the HMTA matrix without aggregation. The UV–Vis absorption spectra of the prepared ZnS nanoparticles show a considerable blueshift in the absorption band edge compared to bulk ZnS indicating a strong quantum confinement effect. Formation of HMTA-capped ZnS nanoparticles was confirmed by FTIR studies. Photoluminescence studies showed that the relative emission intensity of Ce3+ -doped ZnS nanoparticles is higher than that of undoped ZnS nanoparticles, which is due to the enhancement of radiative recombination in the luminescence process. The PL spectra showed two emission peaks at around 420 nm and 442 nm, which may be attributed to deep-trap emission or defect-related emission of ZnS and presence of various surface states.

Suppression of SiC surface roughening during high-temperature annealing by atmospheric control using purified Ar gas

2010 ◽  
Vol 25 (4) ◽  
pp. 708-710 ◽  
Author(s):  
Atsushi Ogura ◽  
Daisuke Kosemura ◽  
Shingo Kinoshita
Keyword(s):  
Surface Roughness ◽  
High Temperature ◽  
Surface Roughening ◽  
Annealing Atmosphere ◽  
High Temperature Annealing ◽  
Force Microscopy ◽  
Atomic Force ◽  
Before And After ◽  
Furnace Tube ◽  
Ar Gas

4H-silicon carbide (SiC) wafers were annealed at 1300 and 1600 °C for 30 min and 60 min in a conventional and purified Ar atmosphere. The surface roughness before and after annealing was evaluated by atomic force microscopy. The surface roughness before annealing was approximately 2.37 nm in root mean square. The roughness, after annealing for 30 min at 1300 and 1600 °C in a conventional Ar furnace, was increased to 4.53 and 14.9 nm, respectively. The roughness, after annealing for 60 min, was 5.01 and 19.1 nm, respectively. In this study, the G3 grade Ar gas (99.999%) was supplied in the conventional furnace tube. When the Ar gas was purified to an impurity concentration of less than 1 ppb, and it was supplied in the leak-tight furnace tube, the roughness after 30-min annealing improved 4.27 and 6.93 nm at 1300 and 1600 °C, respectively. The roughness after 60-min annealing was also reduced to 3.54 and 9.28 nm, respectively. We assume that a significant reduction of H2O concentration in the annealing atmosphere might play an important role in suppressing surface roughening of SiC during high-temperature annealing.

Evolution of photoluminescence from Si nanocrystals embedded in a SiO2 matrix prepared by reactive pulsed laser deposition

2009 ◽  
Vol 24 (7) ◽  
pp. 2259-2267 ◽  
Author(s):  
Fang Fang ◽  
Wei Zhang ◽  
Jian Sun ◽  
Ning Xu ◽  
Jiang Zhu ◽  
...  
Keyword(s):  
Room Temperature ◽  
Annealing Temperature ◽  
Pulsed Laser ◽  
Average Diameter ◽  
Peak Position ◽  
Nitrogen Atmosphere ◽  
Film Deposition ◽  
Structural Variations ◽  
Si Nanocrystals ◽  
Before And After

Photoluminescence (PL) properties of SiOx thin films deposited by pulsed laser ablation of Si in a reactive oxygen ambient and annealed in a nitrogen atmosphere were studied at room temperature. Raman spectroscopy, Fourier transform infrared spectroscopy, and optical transmission measurements were used to characterize the deposited films before and after annealing and complement the PL studies. Strong PL due to quantum confinement was observed at room temperature from Si nanocrystals with an average diameter of approximately 5 nm at 325-nm light excitation. An apparent dependence of PL on the oxygen pressure for film deposition was observed. A detailed analysis of the effects of the annealing temperature revealed a significant PL evolution in luminescence intensity, spectrum profile, peak position, and spectrum range with the annealing temperature ranging from 300 to 1200 °C. Structural variations induced by thermal annealing of the films deposited at different oxygen pressures were also discussed on the basis of their correlation with the PL evolution.

Functional Patency of the Cochlear Aqueduct

1982 ◽  
Vol 91 (2) ◽  
pp. 209-215 ◽  
Author(s):  
Björn Carlborg ◽  
Barbara Densert ◽  
Ove Densert
Keyword(s):  
Cerebrospinal Fluid ◽  
Inner Ear ◽  
Middle Ear ◽  
Ambient Pressure ◽  
Ear Canal ◽  
Cochlear Aqueduct ◽  
Pressure Release ◽  
Release Capacity ◽  
Before And After ◽  
Pressure Changes

The perilymphatic (P P) and cerebrospinal fluid (P CSF) pressures were investigated in relation to pressure variations in the ear canal, middle ear and intracranial compartment before and after occlusion of the cochlear aqueduct (CA). Experiments using intracranial infusion showed that the CA was responsible for a perfect hydrodynamic balance between the CSF and the perilymph. There are indications of additional pressure release factors but their capacities were not sufficient to prevent the appearance of a longstanding and substantial pressure gradient following occlusion of the CA. A gradual P P build-up, from zero to its original level after the CA was opened and occluded, indicated perilymph production within the labyrinth. Investigation of pressure transfer from the ear canal and middle ear to the perilymph showed that the CA was the major pressure release route from the cochlea. Occlusion of the CA reduced the compliance of the inner ear and severely reduced the pressure release capacity. In such a situation the inner ear is almost incapable of equilibrating ambient pressure changes.

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