arXiv subjects

Feng Ding

Publications and source records attributed to Feng Ding.

103 records · Page 6Linked to original sources

arXiv2015

Synthesis of large single-crystal hexagonal boron nitride grains on Cu-Ni alloy

Hexagonal boron nitride (h-BN) has attracted significant attention due to its superior properties as well as its potential as an ideal dielectric layer for graphene-based devices. The h-BN films obtained via chemical vapor deposition in earlier reports are always polycrystalline with small grains due to high nucleation density on substrates. Here we report the successful synthesis of large single-crystal h-BN grains on rational designed Cu-Ni alloy foils. It is found that the nucleation density can be greatly reduced to 60 per mm2 by optimizing Ni ratio in substrates. The strategy enables the growth of single-crystal h-BN grains up to 7,500 um2, about 2 orders larger than that in previous reports. This work not only provides valuable information for understanding h-BN nucleation and growth mechanisms, but also gives an effective alternative to exfoliated h-BN as a high-quality dielectric layer for large-scale nano-electronic applications.

cond-mat.mtrl-sci↗

arXiv2015

Silane-Catalyzed Fast Growth of Large Single-Crystalline Graphene on Hexagonal Boron Nitride

The direct growth of high-quality, large single-crystalline domains of graphene on a dielectric substrate is of vital importance for applications in electronics and optoelectronics. Traditionally, graphene domains grown on dielectrics are typically only ~1 nm with a growth rate of ~1 nm/min or less, the main reason is the lack of a catalyst. Here we show that silane, serving as a gaseous catalyst, is able to boost the graphene growth rate to ~1 um/min, thereby promoting graphene domains up to 20 um in size to be synthesized via chemical vapor deposition on hexagonal boron nitride. Hall measurements show that the mobility of the sample reaches 20,000 cm2/Vs at room temperature, which is among the best for CVD-grown graphene. Combining the advantages of both catalytic CVD and the ultra-flat dielectric substrate, gaseous catalyst-assisted CVD paves the way for synthesizing high-quality graphene for device applications while avoiding the transfer process.

cond-mat.mtrl-sci↗

arXiv2015

Wafer-scale CVD Growth of Monolayer Hexagonal Boron Nitride with Large Domain Size by Cu Foil Enclosure Approach

Chemical vapor deposition synthesis of large domain hexagonal boron nitride (h-BN) with uniform thickness on Cu foils is of great challenge, originating from the extremely high nucleation densities and the reverse hydrogen etching competition reaction. We report herein the successful growth of wafer-scale high-quality h-BN monolayer film with the largest single crystalline domain sizes up to 72 micrometer in edge length using a folded Cu enclosure approach. The highly-confined growth space with this facile and unique approach enables the drastic decrease of nucleation centers together with the effective suppression of hydrogen etching reaction. It is revealed, for the first time, that the orientations of as-grown h-BN monolayers are strongly correlated with the crystalline facets of growth substrates, with the Cu (111) being the best substrate for growing high-quality single crystalline h-BN monolayer, consistent with the density functional theory calculations. The present study offers a practical pathway for growing high-quality h-BN films and deepens the fundamental understanding of h-BN growth process.

cond-mat.mtrl-sci↗

arXiv2014

The Kinetics of Chirality Assignment in Catalytic Single Walled Carbon Nanotube Growth

Chirality-selected single-walled carbon nanotubes (SWCNTs) ensure a great potential of building ~1 nm sized electronics. However, the reliable method for chirality-selected SWCNT is still pending. Here we present a theoretical study on the SWCNT's chirality assignment and control during the catalytic growth. This study reveals that the chirality of a SWCNT is determined by the kinetic incorporation of the pentagon formation during SWCNT nucleation. Therefore, chirality is randomly assigned on a liquid catalyst surface. Furthermore, based on the understanding, two potential methods of synthesizing chirality-selected SWCNTs are proposed: i) by using Ta, W, Re, Os, or their alloys as solid catalysts, and ii) by changing the SWCNT's chirality frequently during the growth.

cond-mat.mes-hall↗

arXiv2012

Direct observation of silver nanoparticle-ubiquitin corona formation

Upon entering physiological environments, nanoparticles readily assume the form of a nanoparticle-protein corona that dictates their biological identity. Understanding the structure and dynamics of nanoparticle-protein corona is essential for predicting the fate, transport, and toxicity of nanomaterials in living systems and for enabling the vast applications of nanomedicine. We combined multiscale molecular dynamics simulations and complementary experiments to characterize the silver nanoparticle-ubiquitin corona formation. Specifically, ubiquitins competed with citrates for the nanoparticle surface and bound to the particle in a specific manner. Under a high protein/nanoparticle stoichiometry, ubiquitions formed a multi-layer corona on the particle surface. The binding exhibited an unusual stretched-exponential behavior, suggesting a rich kinetics originated from protein-protein, protein-citrate, and protein-nanoparticle interactions. Furthermore, the binding destabilized the α-helices while increasing the β-sheets of the proteins. Our results revealed the structural and dynamic complexities of nanoparticle-protein corona formation and shed light on the origin of nanotoxicity.

physics.bio-ph↗

arXiv2011

Graphene Nucleation on Transition Metal Surface: Structure Transformation and Role of the Metal Step Edge

The nucleation of graphene on a transition metal (TM) surface, either on a terrace or near a step edge, is systematically explored using density functional theory (DFT) calculations and applying the two-dimensional (2D) crystal nucleation theory. Careful optimization of the supported carbon clusters, CN (with size N ranging from 1 to 24), on the Ni(111) surface indicates a ground state structure transformation from a one-dimensional (1D) C chain to a two-dimensional (2D) sp2 C network at N ~ 10-12. Furthermore, the crucial parameters controlling graphene growth on the metal surface, nucleation barrier, nucleus size, and the nucleation rate on a terrace or near a step edge, are calculated. In agreement with numerous experimental observations, our analysis shows that graphene nucleation near a metal step edge is superior to that on a terrace. Based on our analysis, we propose the use of seeded graphene to synthesize high-quality graphene in large area.

cond-mat.mtrl-sci↗

arXiv2006

Dependence of SWNT Growth Mechanism on Temperature and Catalyst Particle Size: Bulk versus Surface Diffusion

MD simulations reveal that many aspects of SWNT nucleation and growth from solid and liquid metal particles are similar. In both cases graphitic islands lift off the cluster surface to form caps that grow into SWNTs. However, in contrast to liquid particles, where C atoms primarily diffuse into the bulk of the cluster before adding to the growing SWNT, incorporation of C into SWNTs on solid particles occurs predominantly via surface diffusion.

cond-mat.mtrl-sci↗

arXiv2006

Molecular Dynamics Study of Bamboo-like Carbon Nanotube Nucleation

MD simulations based on an empirical potential energy surface were used to study the nucleation of bamboo-like carbon nanotubes (BCNTs). The simulations reveal that inner walls of the bamboo structure start to nucleate at the junction between the outer nanotube wall and the catalyst particle. In agreement with experimental results, the simulations show that BCNTs nucleate at higher dissolved carbon concentrations (i.e., feedstock pressures) than those where non-bamboolike carbon nanotubes are nucleated.

cond-mat.mtrl-sci↗

arXiv2006

The role of the catalytic particle temperature gradient for SWNT growth from small particles

The Vapour-Liquid-Solid (VLS) model, which often includes a temperature gradient (TG) across the catalytic metal particle, is often used to describe the nucleation and growth of carbon nanostructures. Although the TG may be important for the growth of carbon species from large metal particles, molecular dynamics simulations show that it is not required for single-walled carbon nanotube growth from small catalytic particles.

cond-mat.mtrl-sci↗

arXiv2006

Molecular Dynamics Study of the Catalyst Particle Size Dependence on Carbon Nanotube Growth

The molecular dynamics method, based on an empirical potential energy surface, was used to study the effect of catalyst particle size on the growth mechanism and structure of single-walled carbon nanotubes (SWNTs). The temperature for nanotube nucleation (800-1100 K), which occurs on the surface of the cluster, is similar to that used in catalyst chemical vapor deposition experiments, and the growth mechanism, which is described within the vapor-liquid-solid model, is the same for all cluster sizes studied here (iron clusters containing between 10 and 200 atoms were simulated). Large catalyst particles, that contain at least 20 iron atoms, nucleate SWNTs and have a far better tubular structure than SWNTs nucleated from smaller clusters. In addition, the SWNTs that grow from the larger clusters have diameters that are similar to the cluster diameter, whereas the smaller clusters, which have diameters less than 0.5 nm, nucleate nanotubes that are approximately 0.6-0.7 nm in diameter. This is in agreement with the experimental observations that SWNT diameters are similar to the catalyst particle diameter, and that the narrowest free-standing SWNT is 0.6-0.7 nm.

cond-mat.mtrl-sci↗

arXiv2006

Theoretical study of position-dependent defect formation in a single-walled carbon nanotube: Stability towards an open end

Point defects, including atom vacancy, add atom and Stone-Wale defect, close to a (5, 5) single-walled carbon nanotube (SWNT) end were studied by DFT, semi-empirical PM3 method and empirical Brenner Potential. It is found that closer to the SWNT opening end more stable these defects are. Based on these calculations, a model about fixing defects on a growing SWNT by defects diffusing to the SWNT opening end was proposed. Furthermore, calculations also show that, similar to the DFT calculation, semi-empirical PM3 method is accurate enough for studying defect formation in SWNT. In contrast, the results based on the empirical Brenner potential show large errors and sometimes even not correct in quality.

cond-mat.mtrl-sci↗

arXiv2004

Folding Trp-cage to NMR resolution native structure using a coarse-grained model

We develop a coarse-grained protein model with a simplified amino acid interaction potential. We perform discrete molecular dynamics folding simulations of a small 20 residue protein - Trp-cage - from a fully extended conformation. We demonstrate the ability of the Trp-cage model to consistently reach conformations within 2angstrom backbone root-mean-square distance (RMSD) from the corresponding NMR structures. The minimum RMSD of Trp-cage conformations in the simulation can be smaller than 1.00angstrom. Our findings suggest that, at least for the case of Trp-cage, a detailed all-atom protein model with a physical molecular mechanics force field is not necessary to reach the native state of a protein. Our results also suggest that the success folding Trp-cage in our simulations and in the reported all-atom molecular mechanics simulations studies may be mainly due to the special stabilizing features specific to this miniprotein.

physics.bio-ph↗

arXiv2003

Folding of Cu, Zn superoxide dismutase and Familial Amyotrophic Lateral Sclerosis

Cu,Zn superoxide dismutase (SOD1) has been implicated in the familial form of the neurodegenerative disease Amyotrophic Lateral Sclerosis (ALS). It has been suggested that mutant mediated SOD1 misfolding/aggregation is an integral part of the pathology of ALS. We study the folding thermodynamics and kinetics of SOD1 using a hybrid molecular dynamics approach. We reproduce the experimentally observed SOD1 folding thermodynamics and find that the residues which contribute the most to SOD1 thermal stability are also crucial for apparent two-state folding kinetics. Surprisingly, we find that these residues are located on the surface of the protein and not in the hydrophobic core. Mutations in some of the identified residues are found in patients with the disease. We argue that the identified residues may play an important role in aggregation. To further characterize the folding of SOD1, we study the role of cysteine residues in folding and find that non-native disulfide bond formation may significantly alter SOD1 folding dynamics and aggregation propensity.

physics.bio-ph↗