Defining Swelling Kinetics in Block Copolymer Thin Films: The Critical Role of Temperature and Vapour Pressure Ramp

We studied the kinetics of swelling in high-χ lamellar-forming poly(styrene)-block- poly(lactic acid) (PS-b-PLA) block copolymer (BCP) by varying the heating rate and monitoring the solvent vapour pressure and the substrate temperature in situ during solvo-thermal vapour annealing (STVA) in an oven, and analysing the resulting morphology. Our results demonstrate that there is not only a solvent vapour pressure threshold (120 kPa), but also that the rate of reaching this pressure threshold has a significant effect on the microphase separation and the resulting morphologies. To study the heating rate effect, identical films were annealed in a tetrahydrofuran (THF) vapour environment under three different ramp regimes, low (rT<1 °C/min), medium (2<rT<3 °C/min) and high (rT>4 °C/min), for 60, 90 and 120 min, respectively, while the solvent vapour pressure and the substrate temperature were measured in real time. The translational order improved significantly with increasing the heating rate. The solvent mass uptake calculated for the different ramp regimes during annealing is linearly proportional to time, indicating that the swelling kinetics followed Case II diffusion. Two stages of the swelling behaviour were observed: (i) diffusion at the initial stages of swelling and (ii) stress relaxation, controlled at later stages. Films with a faster rate of increase in vapour pressure (rP>2 kPa/min) reached the pressure threshold value at an early stage of the swelling and attained a good phase separation. According to our results, highly ordered patterns are only obtained when the volume fraction of the solvent exceeds the polymer volume fraction, i.e., (φs≥φp), during the swelling process, and below this threshold value (φs=0.5), the films did not obtain a good structural order, even at longer annealing times.

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Characterization of Microcrystalline Transition from Amorphous Silicon as a Function of Hydrogen Dilution and Substrate Temperature of Hot-wire CVD

MRS Proceedings ◽

10.1557/proc-715-a17.2 ◽

2002 ◽

Vol 715 ◽

Author(s):

Keda Wang ◽

Haoyue Zhang ◽

Jian Zhang ◽

Jessica M. Owens ◽

Jennifer Weinberg-Wolf ◽

...

Keyword(s):

Substrate Temperature ◽

Sudden Change ◽

Chemical Vapor ◽

Threshold Value ◽

Ir Absorption ◽

Sudden Increase ◽

Hot Wire ◽

Hydrogen Dilution ◽

Integral Absorption ◽

Two Peaks

Abstracta-Si:H films were prepared by hot wire chemical vapor deposition. One group was deposited at a substrate temperature of Ts=250°C with varied hydrogen-dilution ratio, 0<R<10; the other group was deposited with fixed R=3 but a varied Ts from 150 to 550°C. IR, Raman and PL spectra were studied. The Raman results indicate that there is a threshold value for the microstructure transition from a- to μc-Si. The threshold is found to be R ≈ 2 at Ts = 250°C and Ts ≈ 200°C at R=3. The IR absorption of Si-H at 640 cm-1 was used to calculate the hydrogen content, CH. CH decreased monotonically when either R or Ts increased. The Si-H stretching mode contains two peaks at 2000 and 2090 cm-1. The ratio of the integral absorption peaks I2090/(I2090+I2090) showed a sudden increase at the threshold of microcrystallinity. At the same threshold, the PL features also indicate a sudden change from a- to μc-Si., i.e. the low energy PL band becomes dominant and the PL total intensity decreases. We attribute the above IR and PL changes to the contribution of microcrystallinity, especially the c-Si gain-boundaries.

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Fabrication of Metastable Crystalline Nanocomposites by Flash Annealing of Cu47.5Zr47.5Al5 Metallic Glass Using Joule Heating

Nanomaterials ◽

10.3390/nano10010084 ◽

2020 ◽

Vol 10 (1) ◽

pp. 84 ◽

Cited By ~ 2

Author(s):

Ilya Okulov ◽

Ivan Soldatov ◽

Ivan Kaban ◽

Baran Sarac ◽

Florian Spieckermann ◽

...

Keyword(s):

Mechanical Properties ◽

Metallic Glass ◽

Heating Rate ◽

Joule Heating ◽

Annealing Time ◽

Volume Fraction ◽

Glassy Material ◽

Flash Annealing ◽

Temperature Equilibrium

Flash Joule-heating was applied to the Cu47.5Zr47.5Al5 metallic glass for designing fully crystalline metastable nanocomposites consisting of the metastable B2 CuZr and low-temperature equilibrium Cu10Zr7 phases. The onset of crystallization was in situ controlled by monitoring resistivity changes in the samples. The effect of heating rate and annealing time on the volume fraction of the crystalline phases and mechanical properties of the nanocomposites was studied in detail. Particularly, an increase of the heating rate and a decrease of the annealing time lead to a lower number of equilibrium Cu10Zr7 precipitates and an increase of tensile ductility. Tailoring of these non-equilibrium microstructures and mechanical properties may not be possible unless one starts with a fully glassy material that opens new perspectives for designing metastable nanomaterials with unique physical properties.

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UV-induced vesicle to micelle transition: a mechanistic study

Polymer Chemistry ◽

10.1039/c9py01259a ◽

2019 ◽

Vol 10 (44) ◽

pp. 6037-6046 ◽

Cited By ~ 3

Author(s):

Craig A. Machado ◽

Roger Tran ◽

Taylor A. Jenkins ◽

Amanda M. Pritzlaff ◽

Michael B. Sims ◽

...

Keyword(s):

Block Copolymer ◽

Volume Fraction ◽

Relative Volume ◽

Mechanistic Study ◽

Relative Volume Fraction ◽

Self Assembled

The morphology of self-assembled block copolymer aggregates is highly dependent on the relative volume fraction of the hydrophobic block.

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Growth of Polycrystalline Silicon films at low Temperature by Remote Plasma CVD

MRS Proceedings ◽

10.1557/proc-283-635 ◽

1992 ◽

Vol 283 ◽

Author(s):

Sung Chul Kim ◽

Kyu Chang Park ◽

Sung Ki Kim ◽

Jung Mok Jun ◽

Jin Jang

Keyword(s):

Substrate Temperature ◽

Polycrystalline Silicon ◽

Volume Fraction ◽

Power Level ◽

Chemical Vapour ◽

Rf Power ◽

Crystalline Volume Fraction ◽

Remote Plasma ◽

Chemical Vapour Deposition Technique ◽

Polycrystalline Silicon Films

ABSTRACTWe studied the growth of polycrystalline silicon by using remote plasma chemical vapour deposition technique. The effects of RF power and the substrate temperature on the structural properties have been investigated. With increasing the RF power, the crystalline volume fraction and the grain size increase up to 100W, but decrease for the further increase in power level. We obtained the poly-Si with the crystalline volume fraction of about 74 at.% at the substrate temperature of 330°C.

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Microcrystalline Silicon for Solar Cells at High Deposition Rates by Hot Wire Cvd

MRS Proceedings ◽

10.1557/proc-715-a26.3 ◽

2002 ◽

Vol 715 ◽

Cited By ~ 21

Author(s):

R. E. I. Schropp ◽

Y. Xu ◽

E. Iwaniczko ◽

G. A. Zaharias ◽

A. H. Mahan

Keyword(s):

Solar Cells ◽

Substrate Temperature ◽

Volume Fraction ◽

Silicon Layer ◽

Hot Wire ◽

Crystalline Volume Fraction ◽

Microcrystalline Silicon ◽

Deposition Rates ◽

Deposition Parameters ◽

Si Films

AbstractWe have explored which deposition parameters in Hot Wire CVD have the largest impact on the quality of microcrystalline silicon (μc-Si) made at deposition rates (Rd) < 10 Å/s for use in thin film solar cells. Among all parameters, the filament temperature (Tfil) appears to be crucial for making device quality films. Using two filaments and a filament-substrate spacing of 3.2 cm, μc-Si films, using seed layers, can be deposited at high Tfil (∼2000°C) with a crystalline volume fraction < 70-80 % at Rd's < 30 Å/s. Although the photoresponse of these layers is high (< 100), they appear not to be suitable for incorporation into solar cells, due to their porous nature. n-i-p cells fabricated on stainless steel with these i-layers suffer from large resistive effects or barriers, most likely due to the oxidation of interconnected pores in the silicon layer. The porosity is evident from FTIR measurements showing a large oxygen concentration at ∼1050 cm-1, and is correlated with the 2100 cm-1 signature of most of the Si-H stretching bonds. Using a Tfil of 1750°C, however, the films are more compact, as seen from the absence of the 2100 cm-1 SiH mode and the disappearance of the FTIR Si-O signal, while the high crystalline volume fraction (< 70-80 %) is maintained. Using this Tfil and a substrate temperature of 400°C, we obtain an efficiency of 4.9 % for cells with a Ag/ZnO back reflector, with an i-layer thickness of only ∼0.7 μm. High values for the quantum efficiency extend to very long wavelengths, with values of 33 % at 800 nm and 15 % at 900 nm, which are unequalled by a-SiGe:H alloys. Further, by varying the substrate temperature to enable deposition near the microcrystalline to amorphous transition (‘edge’) and incorporating variations in H2 dilution during deposition of the bulk, efficiencies of 6.0 % have been obtained. The Rd's of these i-layers are 8-10 Å/s, and are the highest to date obtained with HWCVD for microcrystalline layers used in cells with efficiencies of ∼6 %.

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Substrate temperature dependence of electrical conduction in nanocrystalline CdTe:TiO2 sputtered films

Pure and Applied Chemistry ◽

10.1351/pac200274091739 ◽

2002 ◽

Vol 74 (9) ◽

pp. 1739-1749 ◽

Cited By ~ 3

Author(s):

S. N. Sharma ◽

S. M. Shivaprasad ◽

Sandeep Kohli ◽

A. C. Rastogi

Keyword(s):

Substrate Temperature ◽

Electrical Conduction ◽

Volume Fraction ◽

High Volume ◽

Rf Magnetron Sputtering ◽

Electrical Percolation ◽

Sputtered Films ◽

Cdte Nanoparticles ◽

3D Network ◽

Type Conduction

TiO2 thin films with high volume fraction (∼5070 %) of CdTe nanoparticles were prepared by radio frequency (rf) magnetron sputtering from a composite TiO2:CdTe target. With increase in substrate temperature Ts from room temperature (RT ∼300 K) to 373 K, a transition from an ordered structure exhibiting metallic-type conduction to a disordered structure exhibiting nonmetallic-type conduction was observed for annealed nanocrystalline CdTe:TiO2 films. The annealed RT-deposited films showed a large coalescence of distinct islands (size ∼0.30.7 µm) mainly of Cd and CdTe, and as result, a 3D network was realized. For metallic regime films, electrical conduction is essentially due to electrical percolation through Cd/CdTe crystallites embedded in an amorphous TiO2 matrix. However, the annealed high Ts films consisted of noncoalescent, small islands (size ∼0.150.3 µm) of Cd and CdTe embedded in amorphous TiO2 matrix. Here, the conduction is essentially by hopping mechanism via thermally activated tunneling.

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Influence of Direct Current Magnetron Sputtering Parameters on Electrical Properties of Copper Films

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.37-38.540 ◽

2010 ◽

Vol 37-38 ◽

pp. 540-543

Author(s):

Yin Qun Hua ◽

Rui Fang Chen ◽

Zhong Xiu Niu ◽

Jie Yu

Keyword(s):

Magnetron Sputtering ◽

Substrate Temperature ◽

Zone Model ◽

Temperature Structure ◽

Working Pressure ◽

Cu Films ◽

Film Resistivity ◽

Sputtering Power ◽

Cu Film ◽

Rate Of Increase

Cu thin films were prepared by DC magnetron sputtering on Si substrate, and the resistivities change by adjusting its sputtering parameters. It is found that the changes of the sputtering power and substrate temperature and working pressure can affect significantly the Cu film resistivity (ρ). The Cu films resistivity decreases with the increasing of sputtering power. As the substrate temperature “structure zone model” effect, the Cu film resistivity decreases when the substrate temperature was less than 150°C. The resistivities (ρ) begin to increase gradually at various temperatures ranging from 150°C to 300°C, but the rate of increase is not significant. The resistivity abnormal increases when the substrate temperature was 400°C. The Cu films resistivity increases with argon working gas pressure ranging from 0.15 Pa to 2 Pa.

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Nanostructures from POSS-Grafted Block Copolymer Precursors

MRS Proceedings ◽

10.1557/proc-661-kk10.8 ◽

2000 ◽

Vol 661 ◽

Cited By ~ 1

Author(s):

Seung B. Chun ◽

Patrick T. Mather

Keyword(s):

Block Copolymer ◽

Diblock Copolymers ◽

Volume Fraction ◽

Organic Hybrid ◽

Hybrid Copolymer ◽

The Matrix ◽

Nanoporous Surface ◽

Vinyl Group ◽

Oligomeric Silsesquioxane ◽

Microdomain Structure

ABSTRACTA new method to prepare novel nanocomposites has been studied in which a polyhedral oligomeric silsesquioxane (POSS) monomer is grafted to a polyisoprene-block-polystyrene copolymer to yield an inorganic-organic hybrid copolymer (POSS-g-PI-block-PS). PS-block-PI copolymers (SI) were synthesized via anionic polymerization in tetrahydrofuran (THF) as solvent. The polyisoprene block of the SI diblock copolymers in this study featured a very high vinyl group fraction (65 mole % of 3,4- addition and 35 mole % of 1,2-addition) available to react with hydride-substituted POSS (isobutyldimethyl silane-POSS) to form a grafted block copolymer. Due to the immiscibility between POSS-grafted PI block and PS block, the grafted block copolymer developed a microdomain structure. The volume fraction of PS block in the grafted block copolymer was varied in the range of 0.45 to 0.37 in order to yield cylindrical PS microdomains in the matrix of POSS-grafted PI. After exposure to an oxygen plasma, it is expected that preferential erosion of the grafted block copolymer will occur for the organic potion (PS microdomains) thus leaving a well-defined nanoporous surface structure for nonlithographic functionalization of coated substrates.

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Effect of the Substrate Temperature on the Transition from Amorphous to Microcrystalline Silicon with High Hydrogen Dilution

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.773.520 ◽

2013 ◽

Vol 773 ◽

pp. 520-523

Author(s):

Ming Liang Zhang ◽

Hui Dong Yang ◽

Kai Zhao Yang

Keyword(s):

Substrate Temperature ◽

Volume Fraction ◽

Chemical Vapor ◽

Silicon Films ◽

Microcrystalline Silicon ◽

High Hydrogen ◽

Hydrogenated Silicon ◽

Glass Substrates ◽

Amorphous Hydrogenated Silicon ◽

The Stability

Transition films of amorphous hydrogenated silicon (a-Si:H) to microcrystalline silicon (μc-Si:H) have attracted much attention due to the stability, high overall quality for solar cells configuration. Hydrogenated amorphous and microcrystalline silicon films were deposited on glass substrates by a conventional plasma enhanced chemical vapor deposition (PEVCD) varying the substrate temperature from 275 to 350 °C. A silane concentration of 4% and a total flow rate of 100 sccm were used at a gas pressure of 267 Pa. The film thicknesses of the prepared samples were between 700 and 900 nm estimated from the optical transmission spectra. The deposition rates were between 0.2 and 0.3 nm/s. The phase composition of the deposited silicon films were investigated by Raman spectroscopy. The transition from amorphous to microcrystalline silicon was found at the higher temperatures. The crystallization process of the amorphous silicon can be affected by the substrate temperature. A narrow structural transition region was observed from the changes of the crystalline volume fraction. The dark electrical conductivity of the silicon films increased as the substrate temperature increasing.

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A computational study of soot formation and flame structure of coflow laminar methane/air diffusion flames under microgravity and normal gravity

10.32920/ryerson.14637570.v1 ◽

2021 ◽

Author(s):

Armin Veshkini ◽

Seth B. Dworkin

Keyword(s):

Normal Gravity ◽

Volume Fraction ◽

Diffusion Flames ◽

Soot Formation ◽

Numerical Study ◽

Computational Study ◽

Flame Structure ◽

Chemical Kinetic ◽

Surface Growth ◽

Rate Of Increase

A numerical study is conducted of methane-air coflow diffusion flames at microgravity (μg) and normal gravity (lg), and comparisons are made with experimental data in the literature. The model employed uses a detailed gas phase chemical kinetic mechanism that includes PAH formation and growth, and is coupled to a sectional soot particle dynamics model. The model is able to accurately predict the trends observed experimentally with reduction of gravity without any tuning of the model for different flames. The microgravity sooting flames were found to have lower temperatures and higher volume fraction than their normal gravity counterparts. In the absence of gravity, the flame radii increase due to elimination of buoyance forces and reduction of flow velocity, which is consistent with experimental observations. Soot formation along the wings is seen to be surface growth dominated, while PAH condensation plays a more major role on centerline soot formation. Surface growth and PAH growth increase in microgravity primarily due to increases in the residence time inside the flame. The rate of increase of surface growth is more significant compared to PAH growth, which causes soot distribution to shift from the centerline of the flame to the wings in microgravity. Keywords: laminar diffusion flame,methane-air,microgravity, soot formation, numerical modelling

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