1,720,963 research outputs found
Formation of Twinned Graphene Polycrystals
No full textLiquid metals have been widely used as substrates to grow graphene and other 2D materials. On a homogeneous and isotropic liquid surface, a polycrystalline 2D material is formed by coalescence of many randomly nucleated single-crystal islands, and as a result, the domains in a polycrystal are expected to be randomly aligned. Here, we report the unexpected finding that only 30 degrees-twinned graphene polycrystals are grown on a liquid Cu surface. Atomic simulations confirm that the unique domain alignment in graphene polycrystals is due to the free rotation of graphene islands on the liquid Cu surface and the highly stable 30 degrees-grain boundaries in graphene. In-depth analysis predicts 30 types of possible 30 degrees-twinned graphene polycrystals and 27 of them are observed. The revealed formation mechanism of graphene polycrystals on a liquid Cu surface deepens our fundamental understanding on polycrystal growth and could serve as a guideline for the controlled synthesis of 2D materials
Etching of two-dimensional materials
No full textEtching is one of the key steps in materials processing in the semiconducting industry and recent progress in this field has shown that etching can be used to create various structures of two-dimensional (2D) materials, and can be viewed as a complementary technique to growth. Besides, etching has many other applications in 2D materials synthesis, processing and characterization, such as helping to understand the growth mechanism in-depth, identifying point and line defects in a 2D material, improving the quality of 2D materials by combining the growth process, and for fabricating 2D heterojunctions. Here, we review the current progress on the etching of graphene and other 2D materials; the content of this review includes: (i) etching of single-crystalline 2D materials; (ii) etching of multilayer 2D materials; (iii) etching of polycrystalline 2D materials; (iv) experimental factors, such as partial pressure of etchants, etchant species, and substrate, that affect 2D materials etching; (v) applications of etching in graphene and other 2D materials synthesis, characterization and processing and (vi) the challenges and opportunities in 2D materials etching
The wrinkle formation in graphene on transition metal substrate: a molecular dynamics study
Full text linkTo explore the mechanism of the wrinkle formation in graphene on transition metal substrate, a molecular dynamics (MD) simulation package that allows us to simulate systems of millions of atoms was developed. Via the MD simulation, we reveal the detailed kinetics of wrinkles formation on a Cu substrate under compressive strain, from nucleation to one-dimensional propagation and then the splitting of a large wrinkle to a few smaller ones, which is in good conformity with experimental observation. Further study reveals that both friction and the adhesion between graphene and Cu substrate are critical for the wrinkle formation and wrinkles can be easily formed with a lower frictional force and/or a smaller adhesion. Finally, we have shown that impurities in graphene or substrates can greatly facilitate the nucleation of wrinkles. The systematic exploration of the wrinkle formation in graphene on a substrate is expected to facilitate the experimental designs for the controllable synthesis of high-quality graphene
Achievements and Challenges of Graphene Chemical Vapor Deposition Growth
No full textGraphene, since the first successful exfoliation of graphite, has continuously attracted attention due to its remarkable properties and applications. Recently, the research focus on graphene synthesis has been directed to the controllable synthesis of large-area and high-quality graphene. In the last decade, there has been great progress in the chemical vapor deposition (CVD) growth of graphene. Theoretical investigations have led to an enhanced understanding of puzzles on hydrocarbon species stability, key reaction pathways, the role of hydrogen gas, the morphology of graphene islands, and the alignment of graphene on substrates. Experimentally, high-quality graphene is epitaxially grown on both insulating and metal substrates. Progress has also been reported on low-temperature graphene growth and on controlling the thickness and stacking of graphene layers. In this review, the authors summarize the previous theoretical and experimental studies on graphene CVD growth and discuss the future challenges on the growth of graphene i) on insulating substrates, ii) at low temperature, iii) with controllable thickness, and iv) with selected stacking twist angles. The authors assert that the key to the continuous advancement of graphene growth is the synergy of experimental and theoretical investigations
Growth of high-density single-wall carbon nanotubes with a uniform structure using a CoRu catalyst
No full textThe inefficient production of structurally uniform single-wall carbon nanotubes (SWCNTs) is an obstacle to their practical use in high-performance electronic devices. We have synthesized SWCNTs with a narrow diameter distribution (1.35 ± 0.25 nm) using a CoRu catalyst. Monodispersed nanoparticles with a narrow size distribution (2.4 ± 0.6 nm) and different compositions were prepared and used as catalysts for SWCNT growth. A furnace with an 80 cm-long uniform temperature zone (±10 °C) was designed and used to study the effect of catalyst composition on the growth of SWCNTs under the same conditions. By optimizing the composition of the bimetallic CoRu catalyst, SWCNTs with a uniform structure were efficiently synthesized. In addition, the effect of the growth conditions of temperature and carbon feed rate was investigated, and it was found that with an increase in yield, the structural uniformity of SWCNTs usually became worse. Both catalysts with elements in the suitable proportions and appropriate growth conditions are critical to achieving the high-efficiency structure-controlled growth of SWCNTs. © 2023 Elsevier Ltd11Nsciescopu
Spiral Growth of Adlayer Graphene
No full textThe morphology of as-grown graphene in chemical vapor deposition (CVD) experiments is sensitive to the reaction environment. Understanding the mechanism of formation of different graphene morphologies is essential to achieve controlled graphene CVD growth. Here the growth and formation mechanism of adlayer graphene spirals are reported. An adlayer graphene spiral is formed by fast propagation of the tips of spiral arms along the edge of the first graphene layer. The driving force to form spirals is the limited availability of carbon diffusing from the Cu surface through the edge of the first graphene layer. In addition, it is found that graphene onions are formed by overlapping graphene spirals with clockwise and anticlockwise arms. Based on these features, a kinetic Monte Carlo (kMC) method is demonstrated using which all the observed graphene spiral structures are successfully reproduced at the atomic level. This study thus unravels the hither-to unresolved mechanism of graphene onion growth and paves the way to the controllable growth of few-layer graphene by increasing the carbon supply at the edge of the first layer graphene.clos
Growth and Selective Etching of Twinned Graphene on Liquid Copper Surface
No full text© 2021 Wiley-VCH GmbH Although grain boundaries (GBs) in two-dimensional (2D) materials have been extensively observed and characterized, their formation mechanism still remains unexplained. Here a general model has reported to elucidate the mechanism of formation of GBs during 2D materials growth. Based on our model, a general method is put forward to synthesize twinned 2D materials on a liquid substrate. Using graphene growth on liquid Cu surface as an example, the growth of twinned graphene has been demonstrated successfully, in which all the GBs are ultra-long straight twin boundaries. Furthermore, well-defined twin boundaries (TBs) are found in graphene that can be selectively etched by hydrogen gas due to the preferential adsorption of hydrogen atoms at high-energy twins. This study thus reveals the formation mechanism of GBs in 2D materials during growth and paves the way to grow various 2D nanostructures with controlled GBs.11Nsciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
