We show that graphene chemical vapor deposition growth on copper foil using methane as a carbon source is strongly affected by hydrogen, which appears to serve a dual role: an activator of the ...surface bound carbon that is necessary for monolayer growth and an etching reagent that controls the size and morphology of the graphene domains. The resulting growth rate for a fixed methane partial pressure has a maximum at hydrogen partial pressures 200–400 times that of methane. The morphology and size of the graphene domains, as well as the number of layers, change with hydrogen pressure from irregularly shaped incomplete bilayers to well-defined perfect single layer hexagons. Raman spectra suggest the zigzag termination in the hexagons as more stable than the armchair edges.
We present a comprehensive study of the parameter space for single layer graphene growth by chemical vapor deposition on Cu. The temperature is the most widely recognized control parameter in single ...layer graphene growth. We show that the methane-to-hydrogen ratio and the growth pressure also are critical parameters that affect the structural perfection and the cleanliness of graphene. The optimal conditions for suppressing double and multilayer graphene growth occur near 1000
°C, 1:20 methane-to-hydrogen ratio, and a total pressure in the range from 0.5 to 1
Torr. Raman mapping of a 40
×
30
μm
2 area shows single layer domains with 5–10
μm linear dimensions. Atomic resolution imaging of suspended graphene by aberration corrected scanning transmission electron microscopy shows that the single layer graphene consists of areas of 10–15
nm linear dimensions and smaller patches of residual contamination that was undetected by other characterization methods.
In this paper we discuss the effect of background pressure and synthesis temperature on the graphene crystal sizes in chemical vapor deposition (CVD) on copper catalyst. For the first time, we ...quantitatively demonstrate a fundamental role of the background pressure and provide the activation energy for graphene nucleation in atmospheric pressure CVD (9 eV), which is substantially higher than for the low pressure CVD (4 eV). We attribute the difference to a greater importance of copper sublimation in the low pressure CVD, where severe copper evaporation likely dictates the desorption rate of active carbon from the surface. At atmospheric pressure, where copper evaporation is suppressed, the activation energy is assigned to the desorption energy of carbon clusters instead. The highest possible temperature, close to the melting point of copper, should be used for large single crystal graphene synthesis. Using these conditions, we have synthesized graphene single crystals with sizes over 0.5 mm. Single crystal nature of synthesized graphene was confirmed by low-energy electron diffraction. We also demonstrate that CVD of graphene at temperatures below 1000 °C shows higher nucleation density on (111) than on (100) and (101) copper surfaces, but there is no identifiable preference at higher temperatures.
In this work we explore the kinetics of single-crystal graphene growth as a function of nucleation density. In addition to the standard methods for suppressing nucleation of graphene by pretreatment ...of Cu foils using oxidation, annealing, and reduction of the Cu foils prior to growth, we introduce a new method that further reduces the graphene nucleation density by interacting directly with the growth process at the onset of nucleation. The successive application of these two methods results in roughly 3 orders of magnitude reduction in graphene nucleation density. We use a kinetic model to show that at vanishingly low nucleation densities carbon incorporation occurs by a cooperative island growth mechanism that favors the formation of substrate-size single-crystal graphene. The model reveals that the cooperative growth of millimeter-size single-crystal graphene grains occurs by roughly 3 orders of magnitude increase in the reactive sticking probability of methane compared to that in random island nucleation.
This paper investigates the cross‐cultural validity of the Wong and Law Emotional Intelligence Scale. Two samples of university students were recruited: 504 from a Nepali university and 260 from a UK ...university. In relation to culture, structural equation modelling analyses provided support for the scale's configural invariance and the configural, metric, and scalar invariance of two if its subscales. Evidence for measurement invariance was also found in relation to gender in both samples. Tentative analyses suggested that the correlation between self and other emotion appraisal was stronger among UK participants and that UK participants scored higher on the Other Emotion Appraisal subscale. No gender differences on emotional intelligence were found in the Nepali sample, while among UK students, males scored higher on Regulation of Emotion and lower on Other Emotion Appraisal than females. In the Nepali sample, science students scored lower on various aspects of emotional intelligence than humanities students.
This journal brings together current research on emotional intelligence, an important factor in the development of emotional competency and cognition. The contributions are multipurpose and deal with ...coherent findings. As such, they represent a useful resource for teachers, researchers and students of social sciences, gender studies, and adolescent psychology, and for mental health workers.The contributors represent erudite and distinguished scholars from a variety of fields and from across the world. This allows for a multifaceted dialogue between cultural contexts, empirical studies and lucid experiences.
This journal brings together current research on emotional intelligence, an important factor in the development of emotional competency and cognition. The contributions are multipurpose and deal with ...coherent findings. As such, they represent a useful resource for teachers, researchers and students of social sciences, gender studies, and adolescent psychology, and for mental health workers.
Prototypes of in-house developed boron-coated straw (BCS) detectors have been tested in the thermal and cold neutron energy ranges. Their neutron detection performance has been benchmarked against ...the industry standard (detector tubes filled with 3He gas). The tests show that the BCS detectors perform near their theoretical limit regarding the detection efficiency, which is adequate for scientific instruments in the cold neutron energy range. Finally, the BCS detectors perform on par with 3He tubes in terms of signal to noise and timing resolution, and superior regarding longitudinal spatial resolution.
Prototypes of in-house developed boron-coated straw (BCS) detectors have been tested in the thermal and cold neutron energy ranges. Their neutron detection performance has been benchmarked against ...the industry standard (detector tubes filled with 3He gas). The tests show that the BCS detectors perform near their theoretical limit regarding the detection efficiency, which is adequate for scientific instruments in the cold neutron energy range. The BCS detectors perform on par with 3He tubes in terms of signal to noise and timing resolution, and superior regarding longitudinal spatial resolution.
We present a comprehensive study of the parameter space for biasing the Ir(100) surface to determine the optimal conditions for high density heteroepitaxial diamond nucleation. The nucleation density ...was determined in a bias voltage range from 0 to 225V, and methane concentration range from 0 to 10% using scanning electron microscopy imaging. These data show that high density nucleation exceeding 1011cm−2 occurs only in a narrow bias voltage range from 125 to 175V and a narrow methane concentration range from 1.5 to 3%. At bias voltages and methane concentrations outside of these windows epitaxial diamond nucleation densities fall abruptly to near zero. Using the conditions for high density epitaxial diamond nucleation 80nm thick featureless continuous diamond films grow already after 20min. In several microns thick films the misfit dislocations are confined within a narrow band of 1μm near the diamond–Ir interface showing low residual stress according to x-ray diffraction measurements.
► A new design for the biasing stage using no bias ring. ► High nucleation density with this new stage configuration. ► Narrow processing window in bias voltage and methane concentration. ► Implications of the narrow processing windows for nucleation and growth mechanisms of diamond.
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