scholarly journals Electrospun Semi-Alicyclic Polyimide Nanofibrous Membrane: High-Reflectance and High-Whiteness with Superior Thermal and Ultraviolet Radiation Stability for Potential Applications in High-Power UV-LEDs

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1977
Author(s):  
Xinxin Zhi ◽  
Huasen Wang ◽  
Xinying Wei ◽  
Yan Zhang ◽  
Yuancheng An ◽  
...  
Keyword(s):  
Thermal Treatment ◽  
Elevated Temperatures ◽  
Average Molecular Weight ◽  
Radiation Stability ◽  
Solid Content ◽  
High Dose ◽  
Pristine Sample ◽  
Resin Solution ◽  
Uv Leds ◽  
High Reflectance

Polymeric nanofibrous membranes (NFMs) with both high whiteness and high thermal and ultraviolet (UV) stability are highly desired as reflectors for ultraviolet light-emitting diodes (UV-LEDs) devices. In the current work, a semi-alicyclic and fluoro-containing polyimide (PI) NFM with potential application in such kinds of circumstances was successfully fabricated from the organo-soluble PI resin solution via a one-step electrospinning procedure. In order to achieve the target, a semi-alicyclic PI resin was first designed and synthesized from an alicyclic dianhydride, 3,4-dicarboxy-1,2,3,4,5,6,7,8-decahydro-1-naphthalenesuccinic dianhydride (or hydrogenated tetralin dianhydride, HTDA), and a fluoro-containing diamine, 2,2-bis[4-(4-amino-phenoxy)phenyl]hexafluoropropane (BDAF), via an imidization procedure. The derived PI (HTDA-BDAF) resin possessed a number-average molecular weight (Mn) higher than 33,000 g/mol and was highly soluble in polar aprotic solvents, such as N,N-dimethylacetamide (DMAc). The electrospinning solution was prepared by dissolving the PI resin in DMAc at a solid content of 25–35 wt%. For comparison, the conventional high-whiteness polystyrene (PS) NFM was prepared according to a similar electrospinning procedure. The thermal and UV stability of the derived PI and PS NFMs were investigated by exposure under the UV-LED (wavelength: 365 nm) irradiation. Various thermal evaluation results indicated that the developed PI (HTDA-BDAF) NFM could maintain both the high reflectance and high whiteness at elevated temperatures. For example, after thermal treatment at 200 °C for 1 h in air, the PI (HTDA-BDAF) NFM exhibited a reflectance at a wavelength of 457 nm (R457) of 89.0%, which was comparable to that of the pristine PI NMF (R457 = 90.2%). The PI (HTDA-BDAF) NFM exhibited a whiteness index (WI) of 90.88, which was also close to that of the pristine sample (WI = 91.22). However, for the PS NFM counterpart, the R457 value decreased from the pristine 88.4% to 18.1% after thermal treatment at 150 °C for 1 h, and the sample became transparent. The PI NFM maintained good optical and mechanical properties during the high dose (2670 J/cm2) of UV exposure, while the properties of the PS NFM apparently deteriorated under the same UV aging.

Effect of Annealing on the Structure of Buried SiO2 Layers Formed By Elevated Temperature High Dose Oxygen Implantation

1985 ◽  
Vol 53 ◽  
Author(s):  
S.J. Krause ◽  
C.O. Jung ◽  
S.R. Wilson ◽  
R.P. Lorigan ◽  
M.E. Burnham
Keyword(s):  
Single Crystal ◽  
Oxide Layer ◽  
Elevated Temperatures ◽  
Superficial Layer ◽  
Silicon On Insulator ◽  
High Dose ◽  
Threading Dislocations ◽  
Heater Temperature ◽  
Buried Oxide ◽  
Structural Differences

ABSTRACTOxygen has been implanted into Si wafers at high doses and elevated temperatures to form a buried SiO2 layer for use in silicon-on-insulator (SOI) structures. Substrate heater temperatures have been varied (300, 400, 450 and 500°C) to determine the effect on the structure of the superficial Si layer through a processing cycle of implantation, annealing, and epitaxial growth. Transmission electron microscopy was used to characterize the structure of the superficial layer. The structure of the samples was examined after implantation, after annealing at 1150°C for 3 hours, and after growth of the epitaxial Si layer. There was a marked effect on the structure of the superficial Si layer due to varying substrate heater temperature during implantation. The single crystal structure of the superficial Si layer was preserved at all implantation temperatures from 300 to 500°C. At the highest heater temperature the superficial Si layer contained larger precipitates and fewer defects than did wafers implanted at lower temperatures. Annealing of the as-implanted wafers significantly reduced structural differences. All wafers had a region of large, amorphous 10 to 50 nm precipitates in the lower two-thirds of the superficial Si layer while in the upper third of the layer there were a few threading dislocations. In wafers implanted at lower temperatures the buried oxide grew at the top surface only. During epitaxial Si growth the buried oxide layer thinned and the precipitate region above and below the oxide layer thickened for all wafers. There were no significant structural differences of the epitaxial Si layer for wafers with different implantation temperatures. The epitaxial layer was high quality single crystal Si and contained a few threading dislocations. Overall, structural differences in the epitaxial Si layer due to differences in implantation temperature were minimal.

Amorphous Phase Formation During Ion Mixing of Ti/Si Bilayers at Elevated Temperature

1988 ◽  
Vol 100 ◽  
Author(s):  
K. Maex ◽  
R. F. De Keersmaecker ◽  
M. Van rossum ◽  
W. F. Van Der Weg
Keyword(s):  
Elevated Temperature ◽  
Thermal Treatment ◽  
Diffusion Couple ◽  
Amorphous Phase ◽  
Phase Formation ◽  
Multilayer Structure ◽  
Elevated Temperatures ◽  
Binary Diffusion ◽  
Amorphous Phase Formation

ABSTRACTThe amorphous phaseformation in Ti-Si bilayers upon ion mixing at elevated temperatures and in Ti-Si multilayers upon thermal treatment was studied. In the case of ion mixing with 5×1015 cm−2 Xe atoms at temperatures around 240°C a 100nm thick amorphous Ti-Si alloy is formed with a very homogeneous Ti:Si=3 :4 composition. Thermal treatment of the Ti-Si multilayer structure at similar temperatures also yields amorphous silicide layers. The results are interpreted according to the evolution in a planar binary diffusion couple, where the Si and Ti concentrations in the reacted layer are dictated by thermodynamic and kinetic arguments.

Profile broadening of high dose germanium implants into (100) silicon at elevated temperatures due to channeling

1998 ◽  
Vol 83 (7) ◽  
pp. 3565-3573 ◽  
Author(s):  
A. Nejim ◽  
A. P. Knights ◽  
C. Jeynes ◽  
P. G. Coleman ◽  
C. J. Patel
Keyword(s):  
Elevated Temperatures ◽  
High Dose

Electrical and dielectric sensitivities to thermal processes in carbon nanofiber/high-density polyethylene composites

2011 ◽  
Vol 18 (1-2) ◽  
pp. 51-60 ◽  
Author(s):  
Tian Liu ◽  
Weston Wood ◽  
Bin Li ◽  
Brooks Lively ◽  
Wei-Hong Zhong
Keyword(s):  
Dielectric Properties ◽  
Thermal Treatment ◽  
High Density Polyethylene ◽  
Ac Conductivity ◽  
Elevated Temperatures ◽  
Carbon Nanofiber ◽  
Polymeric Materials ◽  
High Density ◽  
Heating Process ◽  
Thermal Processes

AbstractOwing to the huge interface region existing in a polymer nanocomposite, the effects of thermal processes on properties of nanocomposites are much more complicated than in a pure polymer. It is therefore important to determine the effects of thermal processes on nanocomposites with different interfacial interactions between the nanofillers and the polymer matrix. It is also important to explore the performance changes for nanocomposites under elevated temperatures over pure polymers. In this investigation, we examined the correlation of thermal treatment with dielectric properties of carbon nanofiber (CNF) reinforced high-density polyethylene nanocomposites. The thermal treatment of specimens was conducted for up to 120 h at 87°C and 127°C. Then, alternating current (AC) conductivity and dielectric properties were tested after definite intervals of time. Their changing rates over treatment time were analyzed. The results revealed the approximate linear relationships of AC conductivity and dielectric constant vs. heating time. Modified CNF reinforced nanocomposites had less influence by the heating treatments exhibiting better thermal resistance. The change rates of AC conductivity σ and dielectric properties have higher sensitivity to the treatment at a higher temperature. This study provides potential for further research on application of electrical and dielectric signals to detect the effects of heating process on lifetime of polymeric materials.

scholarly journals Conducting Membranes and Coatings made from Redispersable Nanoscaled Crystalline SnO2:Sb Particles

1998 ◽  
Vol 520 ◽  
Author(s):  
C. Goebbert ◽  
M. A. Aegerter ◽  
D. Burgard ◽  
R. Nass ◽  
H. Schmidt
Keyword(s):  
Thermal Treatment ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Sol Gel ◽  
Total Porosity ◽  
Solid Content ◽  
Visible Range ◽  
Inorganic Membranes ◽  
Separation Processes

ABSTRACTInorganic membranes prepared by the sol gel method are promising candidates for use as filters in separation processes. Conducting supported membranes and coatings have been produced from redispersable nanoscaled crystalline Sb-doped SnO2 powders with a Sb content up to 5 mole % (with respect to Sn). The crystalline particles are monosized (≅4 nm) and fully redispersable in aqueous solution at pH ≥ 8 with a solid content up to 70 wt. %. By thermal treatment at different temperatures and times, the pore size diameter of the material can be adjusted from 4 to 20 nm with a very narrow pore size distribution (∼ ±1 nm) and a total porosity of 63 %, practically independent of the sintering parameters. Uniaxial pressed substrates present similar characteristics with however larger pore size distribution (±5 nm) and 80 % total porosity. Their resistance decreases with sintering temperature and time down to 4 Ω (800 °C 8 h). Fully dispersed aqueous solutions of the powder (25 wt. %) were used to prepare transparent conducting coatings on glass or ceramics by spin-coating. After thermal treatment (1 hour at 550 °C) single layers 200 nm thick exhibited a typical specific electrical resistance ρ = 2.5·10−2 ωcm with transmission in the visible range measured against air of 90%.

scholarly journals Component Resolved IR Bleaching Study of the Blue LM-OSL Signal of Various Quartz Samples

2008 ◽  
Vol 32 (-1) ◽  
pp. 79-85 ◽  
Author(s):  
George Polymeris ◽  
Nafiye Kiyak ◽  
George Kitis
Keyword(s):  
Thermal Treatment ◽  
Elevated Temperatures ◽  
Decomposition Analysis ◽  
Fast Component ◽  
Initial Component ◽  
Quartz Sample ◽  
Synthetic Quartz ◽  
Medium Components ◽  
Infra Red

Component Resolved IR Bleaching Study of the Blue LM-OSL Signal of Various Quartz Samples The present work provides an initial component resolved analysis concerning the effect of infra-red (IR) exposure at elevated temperatures on the blue LM-OSL signal of quartz (stimulated at 470 nm). The study was performed on a total of seven quartz samples, among which five originated from Turkey, one from Greece and one synthetic quartz sample. For these quartz samples, the presence of 6 or even 7 independent LM-OSL components was previously reported, after the application of a computerized decomposition analysis. IR bleaching of each one of these components is studied and compared to the respective signal reduction due to the same thermal treatment solely. It is clearly demonstrated that IR stimulation at temperatures above 50°C does not deplete only the fast component in most sedimentary quartz samples studied. Net depletion of fast and medium components resulting from IR exposure is sample-dependent and occurs faster as the stimulation temperature increases. Weak IR bleaching of slow components is also reported in some cases, being more effective for stimulation temperatures up to 100°C. No depletion of either the medium or the slow components was detected for stimulation temperatures above 150°C. Finally, IR does not stimulate any of the LM-OSL components in the case of the synthetic quartz sample.

The Effects of Low-Energy-Nitrogen-Ion Implantation on the Tribological and Microstructural Characteristics of AISI 304 Stainless Steel

1994 ◽  
Vol 116 (4) ◽  
pp. 870-876 ◽  
Author(s):  
R. Wei ◽  
B. Shogrin ◽  
P. J. Wilbur ◽  
O. Ozturk ◽  
D. L. Williamson ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Elevated Temperatures ◽  
Wear Behavior ◽  
Plasma Nitriding ◽  
Low Energy ◽  
304 Stainless Steel ◽  
High Dose ◽  
Ion Energy ◽  
Wear Resistant ◽  
Nitrogen Ion

The effects of nitrogen implantation conditions (ion energy, dose rate, and processing time) on the thickness and wear behavior of N-rich layers produced on 304 stainless-steel surfaces are examined. Surfaces implanted at elevated temperatures (≈400°C) with 0.4 to 2 keV nitrogen ions at high dose rates (1.5 to 3.8 mA/cm2) are compared to surfaces implanted at higher energies (30 to 60 keV) and lower current densities (0.1 to 0.25 mA/cm2). The most wear-resistant surfaces are observed when the implanted-ion energy is near 1 keV and the dose is very large (> 2 × 1019 ions/cm2). Typically, surfaces implanted under these optimum conditions exhibit load-bearing capabilities at least 1000 times that of the untreated material. Some comparisons are also made to surfaces processed using conventional plasma-nitriding. Samples treated using either process have wear-resistant surface layers in which the nitrogen is in solid solution in the fcc phase. It is argued that the deep N migration (> 1 μm) that occurs under low-energy implantation conditions is due to thermal diffusion that is enhanced by a mechanism other than radiation-induced vacancy production.

Ion Beam Synthesis By Tungsten Implantation Into 6h-Silicon Carbide At Elevated Temperatures

1996 ◽  
Vol 423 ◽  
Author(s):  
Hannes Weishart ◽  
W. Matz ◽  
W. Skorupa
Keyword(s):  
Silicon Carbide ◽  
Tungsten Carbide ◽  
Elevated Temperatures ◽  
Rutherford Backscattering Spectrometry ◽  
Ion Beam ◽  
Bimodal Distribution ◽  
High Dose ◽  
Electrically Conductive ◽  
Implantation Temperature ◽  
High Dose Implantation

AbstractWe studied high dose implantation of tungsten into 6H-silicon carbide in order to synthesize an electrically conductive layer. Implantation was performed at 200 keV with a dose of 1×1017 W+cm−2 at temperatures of 90°C and 500°C. The samples were subsequently annealed either at 950°C or 1100°C. The influence of implantation and annealing temperatures on the reaction of W with SiC was investigated. Rutherford backscattering spectrometry (RBS), x-ray diffiraction (XRD) and Auger electron spectroscopy (AES) contributed to study the structure and composition of the implanted layer as well as the chemical state of the elements. The implantation temperature influences the depth distribution of C, Si and W as well as the damage production in SiC. The W depth profile exhibits a bimodal distribution for high temperature implantation and a customary gaussian distribution for room temperature implantation. Formation of tungsten carbide and silicide was observed in each sample already in the as-implanted state. Implantation at 90°C and annealing at 950°C lead to crystallization of W2C; tungsten silicide, however, remains amorphous. After implantation at 500°C and subsequent annealing at 11007deg;C crystalline W5Si3 forms, while tungsten carbide is amorphous.

scholarly journals Структура и термоэлектрические свойства пленочных композитов на основе CoSi

2019 ◽  
Vol 53 (6) ◽  
pp. 784
Author(s):  
В.С. Кузнецова ◽  
С.В. Новиков ◽  
Ч.К. Ниченаметла ◽  
И. Кальво ◽  
М. Вагнер-Ритц
Keyword(s):  
Thin Films ◽  
Chemical Vapor Deposition ◽  
Thermal Treatment ◽  
Vapor Deposition ◽  
Multilayer Structure ◽  
Elevated Temperatures ◽  
Layer Structure ◽  
Chemical Vapor ◽  
Structural Data ◽  
Temperature Dependences

Properties of Co-Si thin films produced by thermal treatment of Co and Si layers are studied in this article. Co/Si layers were produced by chemical vapor deposition. The two-layer structure was annealed at elevated temperatures for the formation of cobalt silicide. Thermoelectric properties of the film structures were investigated in the temperature range 300-800 K. Temperature dependences of thermopower and resistivity as well as structural data indicate the formation a multilayer structure with Si-rich and Co-rich layers.

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