scholarly journals Influence of the Total Gas Flow at Different Reaction Times for CVD-Graphene Synthesis on Polycrystalline Nickel

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
M. P. Lavin-Lopez ◽  
J. L. Valverde ◽  
L. Sanchez-Silva ◽  
A. Romero
Keyword(s):  
Reaction Time ◽  
Gas Flow ◽  
Reaction Times ◽  
Monolayer Graphene ◽  
Graphene Monolayer ◽  
Multilayer Graphene ◽  
Reaction Step ◽  
Polycrystalline Nickel ◽  
Cvd Graphene ◽  
Graphene Synthesis

Optimization of the total gas flow (CH4+H2) during the reaction step for different reaction times for CVD-graphene synthesis on polycrystalline nickel foil using an atmospheric pressure set-up is reported. Athickness valuerelated to number of graphene layers in each of the synthesized samples was determined using an Excel-VBA application. This method assigned athickness valuebetween 1 and 1000 and provided information on the percentage of each type of graphene (monolayer, bilayer, and multilayer) deposited onto the polycrystalline nickel sheet. The influence of the total gas flow during the reaction step and the reaction time was studied in detail. Optical microscopy showed that samples were covered with different types of graphene, such as multilayer, few-layer, bilayer, and monolayer graphene. The synthesis variables were optimized according to thethickness valueand the results were verified by Raman spectroscopy. The best conditions were obtained with a reaction temperature of 980°C, a CH4/H2flow rate ratio of 0.07 v/v, a reaction time of 1 minute, and a total gas flow of 80 NmL/min. In the sample obtained under the optimized conditions, 80% of the area was covered with monolayer graphene and less than 1% with multilayer graphene.

Plasmon spectrum of graphene monolayer on substrate

2019 ◽  
Vol 33 (09) ◽  
pp. 1950102
Author(s):  
I. N. Askerzade ◽  
R. T. Askerbeyli
Keyword(s):  
Substrate Material ◽  
Plasmon Mode ◽  
Monolayer Graphene ◽  
Graphene Monolayer ◽  
Multilayer Graphene ◽  
Linear Dispersion ◽  
Long Wavelength ◽  
Theoretical Considerations ◽  
Plasmon Spectrum ◽  
Good Agreement

Plasmon modes in monolayer graphene on substrate are analyzed taking into account the thickness of graphene and substrate material layer in the evaluation of Coulomb potential. It is shown that plasmon mode in graphene monolayer has linear dispersion in contrast to multilayer graphene in long-wavelength limit. The slope of plasmon spectrum is determined by the thickness and dielectric constant of substrate. Obtained results are in good agreement with experimental data and other theoretical considerations.

Thickness control of graphene deposited over polycrystalline nickel

2015 ◽  
Vol 39 (6) ◽  
pp. 4414-4423 ◽  
Author(s):  
Ma Prado Lavin-Lopez ◽  
Jose Luis Valverde ◽  
Ma Inmaculada Ruiz-Enrique ◽  
Luz Sanchez-Silva ◽  
Amaya Romero
Keyword(s):  
Monolayer Graphene ◽  
Polycrystalline Nickel ◽  
Inexpensive Method ◽  
Thickness Control ◽  
Cvd Graphene

77% of a polycrystalline nickel sheet has been covered with monolayer graphene, demonstrating an inexpensive method to synthesize CVD-graphene.

Turbostratic multilayer graphene synthesis on CVD graphene template toward improving electrical performance

2019 ◽  
Vol 58 (SI) ◽  
pp. SIIB04 ◽  
Author(s):  
Chaopeng Wei ◽  
Ryota Negishi ◽  
Yui Ogawa ◽  
Masashi Akabori ◽  
Yoshitaka Taniyasu ◽  
...  
Keyword(s):  
Electrical Performance ◽  
Multilayer Graphene ◽  
Cvd Graphene ◽  
Graphene Synthesis

scholarly journals Highly uniform monolayer graphene synthesis via a facile pretreatment of copper catalyst substrates using an ammonium persulfate solution

RSC Advances ◽  
2019 ◽  
Vol 9 (36) ◽  
pp. 20871-20878 ◽  
Author(s):  
Hyunhak Jeong ◽  
Wang-Taek Hwang ◽  
Younggul Song ◽  
Jae-Keun Kim ◽  
Youngrok Kim ◽  
...  
Keyword(s):  
Copper Catalyst ◽  
Ammonium Persulfate ◽  
Monolayer Graphene ◽  
Large Area ◽  
Graphene Growth ◽  
Cvd Graphene ◽  
Graphene Synthesis ◽  
Highly Uniform

A facile method for preparing a pretreated copper catalyst substrate for highly uniform, large-area CVD graphene growth is proposed.

Role of inert gas in the Cvd-graphene synthesis over polycrystalline nickel foils

2019 ◽  
Vol 222 ◽  
pp. 173-180 ◽  
Author(s):  
M.P. Lavin-Lopez ◽  
J.L. Valverde ◽  
S. Ordoñez-Lozoya ◽  
A. Paton-Carrero ◽  
A. Romero
Keyword(s):  
Inert Gas ◽  
Polycrystalline Nickel ◽  
Cvd Graphene ◽  
Graphene Synthesis

Modeling Within-Person Variance in Reaction Time Data of Older Adults

GeroPsych ◽  
2011 ◽  
Vol 24 (4) ◽  
pp. 169-176 ◽  
Author(s):  
Philippe Rast ◽  
Daniel Zimprich
Keyword(s):  
Reaction Time ◽  
Cognitive Aging ◽  
Reaction Times ◽  
Reaction Time Task ◽  
Reaction Time Data ◽  
Scale Model ◽  
Time Data ◽  
Time Task ◽  
The Mean ◽  
Second Wave

In order to model within-person (WP) variance in a reaction time task, we applied a mixed location scale model using 335 participants from the second wave of the Zurich Longitudinal Study on Cognitive Aging. The age of the respondents and the performance in another reaction time task were used to explain individual differences in the WP variance. To account for larger variances due to slower reaction times, we also used the average of the predicted individual reaction time (RT) as a predictor for the WP variability. Here, the WP variability was a function of the mean. At the same time, older participants were more variable and those with better performance in another RT task were more consistent in their responses.

The Level of Reaction Time Determines the ERP Correlates of Auditory Negative Priming

2006 ◽  
Vol 20 (3) ◽  
pp. 186-194 ◽  
Author(s):  
Susanne Mayr ◽  
Michael Niedeggen ◽  
Axel Buchner ◽  
Guido Orgs
Keyword(s):  
Reaction Time ◽  
Negative Priming ◽  
Effect Size ◽  
Priming Effect ◽  
Reaction Times ◽  
Negative Priming Effect ◽  
Episodic Retrieval ◽  
Time Level ◽  
Fast Reactions ◽  
Priming Condition

Responding to a stimulus that had to be ignored previously is usually slowed-down (negative priming effect). This study investigates the reaction time and ERP effects of the negative priming phenomenon in the auditory domain. Thirty participants had to categorize sounds as musical instruments or animal voices. Reaction times were slowed-down in the negative priming condition relative to two control conditions. This effect was stronger for slow reactions (above intraindividual median) than for fast reactions (below intraindividual median). ERP analysis revealed a parietally located negativity of the negative priming condition compared to the control conditions between 550-730 ms poststimulus. This replicates the findings of Mayr, Niedeggen, Buchner, and Pietrowsky (2003) . The ERP correlate was more pronounced for slow trials (above intraindividual median) than for fast trials (below intraindividual median). The dependency of the negative priming effect size on the reaction time level found in the reaction time analysis as well as in the ERP analysis is consistent with both the inhibition as well as the episodic retrieval account of negative priming. A methodological artifact explanation of this effect-size dependency is discussed and discarded.

The Effect of Retest Practice on the Speed-Ability Relationship

2004 ◽  
Vol 9 (1) ◽  
pp. 24-31 ◽  
Author(s):  
Sybille Rockstroh ◽  
Karl Schweizer
Keyword(s):  
Reaction Time ◽  
Skill Acquisition ◽  
Reaction Times ◽  
Cognitive Tasks ◽  
General Intelligence ◽  
Attention Switching ◽  
Letter Comparison ◽  
Sternberg Paradigm ◽  
The Relationship ◽  
Elementary Cognitive Tasks

Effects of four retest-practice sessions separated by 2 h intervals on the relationship between general intelligence and four reaction time tasks (two memory tests: Sternberg's memory scanning, Posner's letter comparison; and two attention tests: continuous attention, attention switching) were examined in a sample of 83 male participants. Reaction times on all tasks were shortened significantly. The effects were most pronounced with respect to the Posner paradigm and smallest with respect to the Sternberg paradigm. The relationship to general intelligence changed after practice for two reaction time tasks. It increased to significance for continuous attention and decreased for the Posner paradigm. These results indicate that the relationship between psychometric intelligence and elementary cognitive tasks depends on the ability of skill acquisition. In the search for the cognitive roots of intelligence the concept of learning seems to be of importance.

How Useful is the Power Law of Practice for Recognizing Practice in Concentration Tests?

2007 ◽  
Vol 23 (3) ◽  
pp. 157-165 ◽  
Author(s):  
Carmen Hagemeister
Keyword(s):  
Logistic Regression ◽  
Reaction Time ◽  
Power Law ◽  
Error Rate ◽  
Reaction Times ◽  
Practice Effect ◽  
Practice Effects ◽  
Rate Decrease ◽  
Small Practice

Abstract. When concentration tests are completed repeatedly, reaction time and error rate decrease considerably, but the underlying ability does not improve. In order to overcome this validity problem this study aimed to test if the practice effect between tests and within tests can be useful in determining whether persons have already completed this test. The power law of practice postulates that practice effects are greater in unpracticed than in practiced persons. Two experiments were carried out in which the participants completed the same tests at the beginning and at the end of two test sessions set about 3 days apart. In both experiments, the logistic regression could indeed classify persons according to previous practice through the practice effect between the tests at the beginning and at the end of the session, and, less well but still significantly, through the practice effect within the first test of the session. Further analyses showed that the practice effects correlated more highly with the initial performance than was to be expected for mathematical reasons; typically persons with long reaction times have larger practice effects. Thus, small practice effects alone do not allow one to conclude that a person has worked on the test before.

Porous Gel Coatings Obtained by Phase Separation in ORMOSIL System

2000 ◽  
Vol 628 ◽  
Author(s):  
Kazuki Nakanishi ◽  
Souichi Kumon ◽  
Kazuyuki Hirao ◽  
Hiroshi Jinnai
Keyword(s):  
Phase Separation ◽  
Reaction Time ◽  
Volume Fraction ◽  
Sol Gel ◽  
Reaction Times ◽  
Dip Coating ◽  
Coating Solution ◽  
Coating Method ◽  
Gel Phase ◽  
Dip Coating Method

ABSTRACTMacroporous silicate thick films were prepared by a sol-gel dip-coating method accompanied by the phase separation using methyl-trimethoxysilane (MTMS), nitric acid and dimethylformamide (DMF) as starting components. The morphology of the film varied to a large extent depending on the time elapsed after the hydrolysis until the dipping of the coating solution. On a glass substrate, the films prepared by early dipping had inhomogeneous submicrometer-sized pores on the surface of the film. At increased reaction times, relatively narrow sized isolated macropores were observed and their size gradually decreased with the increase of reaction time. On a polyester substrate, in contrast, micrometer-sized isolated spherical gel domains were homogeneously deposited by earlier dippings. With an increase of reaction time, the volume fraction of the gel phase increased, then the morphology of the coating transformed into co-continuous gel domains and macropores, and finally inverted into the continuous gel domains with isolated macropores. The overall morphological variation with the reaction time was explained in terms of the phase separation and the structure freezing by the forced gelation, both of which were induced by the evaporation of methanol during the dipping operation.

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