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M D Ediger - One of the best experts on this subject based on the ideXlab platform.
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using deposition rate and Substrate Temperature to manipulate liquid crystal like order in a vapor deposited hexagonal columnar glass
Journal of Physical Chemistry B, 2021Co-Authors: Camille Bishop, Michael F Toney, Zhenxuan Chen, Harald Bock, M D EdigerAbstract:We investigate vapor-deposited glasses of a phenanthroperylene ester, known to form an equilibrium hexagonal columnar phase, and show that liquid crystal-like order can be manipulated by the choice of deposition rate and Substrate Temperature during deposition. We find that rate-Temperature superposition (RTS)-the equivalence of lowering the deposition rate and increasing the Substrate Temperature-can be used to predict and control the molecular orientation in vapor-deposited glasses over a wide range of Substrate Temperatures (0.75-1.0 Tg). This work extends RTS to a new structural motif, hexagonal columnar liquid crystal order, which is being explored for organic electronic applications. By several metrics, including the apparent average face-to-face nearest-neighbor distance, physical vapor deposition (PVD) glasses of the phenanthroperylene ester are as ordered as the glass prepared by cooling the equilibrium liquid crystal. By other measures, the PVD glasses are less ordered than the cooled liquid crystal. We explain the difference in the maximum attainable order with the existence of a gradient in molecular mobility at the free surface of a liquid crystal and its impact upon different mechanisms of structural rearrangement. This free surface equilibration mechanism explains the success of the RTS principle and provides guidance regarding the types of order most readily enhanced by vapor deposition. This work extends the applicability of RTS to include molecular systems with a diverse range of higher-order liquid-crystalline morphologies that could be useful for new organic electronic applications.
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vapor deposited glass structure determined by deposition rate Substrate Temperature superposition principle
Journal of Physical Chemistry Letters, 2019Co-Authors: Camille Bishop, Ankit Gujral, Michael F Toney, M D EdigerAbstract:We show that deposition rate substantially affects the anisotropic structure of thin glassy films produced by physical vapor deposition. Itraconazole, a glass-forming liquid crystal, was deposited at rates spanning 3 orders of magnitude over a 25 K range of Substrate Temperatures, and structure was characterized by ellipsometry and X-ray scattering. Both the molecular orientation and the spacing of the smectic layers obey deposition rate-Substrate Temperature superposition, such that lowering the deposition rate is equivalent to raising the Substrate Temperature. We identify two different surface relaxations that are responsible for structural order in the vapor-deposited glasses and find that the process controlling molecular orientation is accelerated by more than 3 orders of magnitude at the surface relative to the bulk. The identification of distinct surface processes responsible for anisotropic structural features in vapor-deposited glasses will enable more precise control over the structure of glassy materials used in organic electronics.
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influence of Substrate Temperature on the transformation front velocities that determine thermal stability of vapor deposited glasses
Journal of Physical Chemistry B, 2015Co-Authors: Shakeel S Dalal, M D EdigerAbstract:Stable organic glasses prepared by physical vapor deposition transform into the supercooled liquid via propagating fronts of molecular mobility, a mechanism different from that exhibited by glasses prepared by cooling the liquid. Here we show that spectroscopic ellipsometry can directly observe this front-based mechanism in real time and explore how the velocity of the front depends upon the Substrate Temperature during deposition. For the model glass former indomethacin, we detect surface-initiated mobility fronts in glasses formed at Substrate Temperatures between 0.68Tg and 0.94Tg. At each of two annealing Temperatures, the Substrate Temperature during deposition can change the transformation front velocity by a factor of 6, and these changes are imperfectly correlated with the density of the glass. We also observe Substrate-initiated fronts at some Substrate Temperatures. By connecting with theoretical work, we are able to infer the relative mobilities of stable glasses prepared at different Substrate...
J Bechara - One of the best experts on this subject based on the ideXlab platform.
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electrical and optical properties of pyrolytically electrostatic sprayed fluorine doped tin oxide dependence on Substrate Temperature and Substrate nozzle distance
Journal of Applied Physics, 2000Co-Authors: D Zaouk, Y Zaatar, A Khoury, C Llinares, J P Charles, J BecharaAbstract:Tin–oxide (SnO2) thin films were prepared by a modified spray technique called electrostatic spray pyrolysis. Their electrical and optical properties dependence on fluorine concentration, Substrate Temperature Ts, and the Substrate–nozzle distance Dsn was studied. Dsn and Ts seem to be interrelated for the optimization of good quality fluorine-doped SnO2 films. Films of about 9×10−4 Ω cm resistivity and high visible 85% transparency were obtained for a Substrate Temperature of 550 °C, a 6 cm Substrate nozzle distance, and 80% of hydrofluorhydric acid HF in the starting solution. These data are discussed in light of the kinetics reaction.
Guojia Fang - One of the best experts on this subject based on the ideXlab platform.
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comprehensive investigation of structural electrical and optical properties for zno al films deposited at different Substrate Temperature and oxygen ambient
Journal of Applied Physics, 2008Co-Authors: Binzhong Dong, Guojia Fang, Xingzhong Zhao, Dayu Zheng, Yuanping SunAbstract:c-axis oriented polycrystalline ZnO:Al (AZO) films were deposited at different Substrate Temperature (Ts) and oxygen ambient (PO2) by pulsed laser deposition. It is found that with the increase in Ts and PO2, the 2θ position of AZO (0002) shifts to higher angle, which can be attributed to the different amounts and species of defects in AZO films. Furthermore, the full width at half maximum of 2θ and (0002) rocking curve indicate the different crystalline qualities for AZO films grown at different conditions. At the same time, the carrier concentration decreases with the increase in Ts and PO2 for most of the samples; however, the Hall mobility usually attains its maximum at proper Ts and PO2. Moreover the transport of electrons may be governed by different mechanisms for AZO films grown at different conditions. The AZO transmission spectra show that the ultraviolet absorption edge and infrared transparency limit shift toward longer wavelength with the increase in Ts and PO2, which are due to the changes o...
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influence of Substrate Temperature on electrical and optical properties of p type semitransparent conductive nickel oxide thin films deposited by radio frequency sputtering
Applied Surface Science, 2008Co-Authors: Lei Ai, Guojia Fang, Longyan Yuan, Mingjun Wang, Chun Li, Qilin Zhang, Jun Li, Xingzhong ZhaoAbstract:Abstract Nickel oxide thin films were deposited on fused silica and Si(1 0 0) Substrates at different Substrate Temperatures ranging from room Temperature to 400 °C using radio frequency reactive magnetron sputtering from a Ni metal target in a mixture of O 2 and Ar. With the increase of Substrate Temperature, nickel oxide films deposited on the Si Substrates exhibit transition from amorphous to poly-crystalline structures with different preferred orientations of NiO(2 0 0) and (1 1 1). The films deposited at higher Temperature exhibit higher Ni 2+ /Ni 3+ ratio. With Substrate Temperature increasing from room Temperature to 400 °C, the electrical resistivities of nickel oxide films increase from (2.8 ± 0.1) × 10 −2 to (8.7 ± 0.1) Ω cm, and the optical band-gap energies increase from 3.65 to 3.88 eV. A p-nickel oxide/n-zinc oxide heterojunction was fabricated to confirm the p-type conduction of nickel oxide thin film, which exhibited a steadily rectifying behavior.
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effect of Substrate Temperature on the growth and photoluminescence properties of vertically aligned zno nanostructures
Journal of Crystal Growth, 2006Co-Authors: Guojia Fang, Xingzhong ZhaoAbstract:Vertically well-aligned ZnO nanoridge, nanorod, nanorod-nanowall junction, and nanotip arrays have been successfully synthesized on Si (100) Substrates using a pulsed laser deposition prepared ZnO film as seed layer by thermal evaporation method. Experimental results illustrated that the growth of different morphologies of ZnO nanostructures was strongly dependent upon Substrate Temperature. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed that the ZnO nanostructures were single crystals with a wurtzite structure. Compared with those of the other nanostructures, the photoluminescence (PL) spectrum of nanorod-nanowall junctions showed the largest intensity ratio of ultraviolet (UV) to yellow-green emission and the smallest full-width at half-maximum (FWHM) of the UV peak, reflecting the high optical quality and nearly defect free of crystal structure. The vertical alignment of the nanowire array on the Substrate is attributed to the epitaxial growth of the nanostructures from the ZnO buffer layer. The growth mechanism was also discussed in detail. (c) 2006 Elsevier B.V. All rights reserved.
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influence of Substrate Temperature and post treatment on the properties of zno al thin films prepared by pulsed laser deposition
Applied Surface Science, 2005Co-Authors: Xin Chen, Guojia Fang, Wenjie Guan, Xiaona ZhaoAbstract:Abstract Highly transparent conductive Al 2 O 3 doped zinc oxide (AZO) thin films have been deposited on the glass Substrate by pulsed laser deposition technique. The effects of Substrate Temperature and post-deposition annealing treatment on structural, electrical and optical properties of AZO thin films were investigated. The experimental results show that the electrical resistivity of films deposited at 240 °C is 6.1 × 10 −4 Ω cm, which can be further reduced to as low as 4.7 × 10 −4 Ω cm by post-deposition annealing at 400 °C for 2 h in argon. The average transmission of AZO films in the visible range is 90%. The optical direct band gap of films was dependent on the Substrate Temperature and the annealing treatment in argon. The optical direct band gap value of AZO films increased with increasing annealing Temperature.
M Boomashri - One of the best experts on this subject based on the ideXlab platform.
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influence of Substrate Temperature on structural and optical properties of zno thin films prepared by cost effective chemical spray pyrolysis technique
Superlattices and Microstructures, 2016Co-Authors: A S Enigochitra, P Perumal, C Sanjeeviraja, D Deivamani, M BoomashriAbstract:Abstract Over the past few decades semiconductor metal oxides have stimulated research interests owing to their important role in fundamental research and future applications in the field of energy conversion and sensors. So the present research work has been focused on the synthesis, growth mechanisms and physical properties of ZnO thin films prepared by cost-effective chemical spray pyrolysis technique. Desirable properties of thin films can be easily tailored by chemical spray pyrolysis technique by optimising the spray parameters. ZnO thin films were deposited on glass Substrates with various Substrate Temperatures ranging from 573 K to 723 K. The influence of Substrate Temperature on structural, morphological and optical properties have been analyzed via XRD, SEM, UV–VIS–NIR spectroscopy, PL studies respectively. The Structural study reveals that all the spray deposited ZnO thin films have polycrystalline nature with preferential orientation along (100) plane. Optical studies show that the direct band gap values increases from 3.14 to 3.20 eV. PL studies shows that the intensity of emission peaks differ according to the Substrate Temperature. Smooth and uniform morphology obtained from SEM analysis. The optical transmittance observed in the visible region is more than 85% for all films other than 573 K as Substrate Temperature.
Boubaker Benhaoua - One of the best experts on this subject based on the ideXlab platform.
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influence of Substrate Temperature and cobalt concentration on structural and optical properties of zno thin films prepared by ultrasonic spray technique
Superlattices and Microstructures, 2012Co-Authors: Said Benramache, Boubaker BenhaouaAbstract:Abstract Pure and Cobalt doped zinc oxide were deposited on glass Substrate by Ultrasonic spray method. Zinc acetate dehydrate, Cobalt chloride, 4-methoxyethanol and monoethanolamine were used as a starting materials, dopant source, solvent and stabilizer, respectively. The ZnO samples and ZnO:Co with Cobalt concentration of 2 wt.% were deposited at 300, 350 and 400 °C. The effects of Substrate Temperature and presence of Co as doping element on the structural, electrical and optical properties were examined. Both pure and Co doped ZnO samples are (0 0 2) preferentially oriented. The X-ray diffraction results indicate that the samples have polycrystalline nature and hexagonal wurtzite structure with the maximum average crystallite size of ZnO and ZnO:Co were 33.28 and 55.46 nm. An increase in the Substrate Temperature and presence doping the crystallinity of the thin films increased. The optical transmittance spectra showed transmittance higher than 80% within the visible wavelength region. The band gap energy of the thin films increased after doping from 3.25 to 3.36 eV at 350 °C.
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effect of Substrate Temperature on the stability of transparent conducting cobalt doped zno thin films
Journal of Semiconductors, 2012Co-Authors: Said Benramache, Boubaker Benhaoua, Foued ChabaneAbstract:Transparent conducting Co doped ZnO thin films have been fabricated by Ultrasonic spray. The thin films were deposited at three different Substrate Temperatures of 300, 350 and 400 °C. The obtained films had a hexagonal wurtzite structure with a strong (002) preferred orientation. The maximum crystallite size value of the film deposited at 350 °C is 55.46 run. Spectrophotometer (UV-vis) of a Co doped ZnO film deposited at 350 °C shows an average transmittance of about 90%. The band gap energy increased from 3.351 to 3.362 eV when the Substrate Temperature increased from 300 to 350 °C. The electrical conductivity of the films deposited at 300, 350 and 400 °C were 7.424, 7.547 and 6.743 (Ω·cm)−1 respectively. The maximum activation energy value of the films at 350 °C was 1.28 eV, indicating that the films exhibit a n-type semiconducting nature.
