David Z. Chen

Duke University | DU · Department of Physics

The atomic-level structures of liquids and glasses are amorphous, lacking long-range order. We characterize the atomic structures by integrating radial distribution functions (RDF) from molecular dynamics (MD) simulations for several metallic liquids and glasses: Cu_(46)Zr_(54), Ni_(80)Al_(20), Ni_(33.3)Zr_(66.7), and Pd_(82)Si_(18). Resulting cumu...

The atomic-level structures of liquids and glasses are similar, obscuring any structural basis for the glass transition. To delineate structural differences between them, we characterized the atomic structures using the integrated radial distribution functions (RDF) from molecular dynamics (MD) simulations for several metallic liquids and glasses:...

Metallic glasses are metallic alloys that exhibit exotic material properties. They may have fractal structures at the atomic level, but a physical mechanism for their organization without ordering has not been identified. We demonstrated a crossover between fractal short-range (<2 atomic diameters) and homogeneous long-range structures using in sit...

To harness 'Smaller is more ductile' behavior emergent at nanoscale and to proliferate it onto materials with macroscale dimensions, we produced hollow-tube Cu60Zr40 metallic glass nanolattices with the layer thicknesses of 120, 60 and 20 nm. They exhibit unique transitions in deformation mode with tube-wall thickness and temperature. Molecular dyn...

The interfacial shear strength between Si microwires and a Nafion membrane has been tailored through surface functionalization of the Si. Acidic (-COOH terminated) or basic (-NH2-terminated) surface-bound functionality was introduced by hydrosilylation reactions to probe the interactions between the functionalized Si microwires and hydrophilic, ion...

In-situ nano-tensile experiments on 70 nm-diameter free-standing electroplated NiP metallic glass nanostructures reveal tensile true strains of similar to 18%, an amount comparable to compositionally identical 100 nm-diameter focused ion beam samples and similar to 3 times greater than 100 nm-diameter electroplated samples. Simultaneous in-situ obs...

Emergence of size-dependent mechanical strength in nano-sized materials is now well established, but no fundamental understanding of fracture toughness or flaw sensitivity in nanostructures exists. We report the fabrication and in-situ fracture testing of ~70 nm-diameter Ni-P metallic glass samples with a structural flaw. Failure occurs at the stru...

We report tensile experiments on Ni80P20 metallic glass samples fabricated via a templated electroplating (EP) process and via focused ion beam (FIB) milling, which differed only in their surface energy states: Ga-ion-irradiated and as-electroplated. Molecular Dynamics (MD) simulations on similar Ni80Al20 systems corroborate the experimental result...

This study summarizes our current research in using different types of nanographene platelets (NGPs) to create polymer–graphene nanocomposites for selective laser sintering manufacturing application. This article describes five NGPs that were available to our research group. Morphological characterization of their microstructures was examined using...

In this paper, we evaluate of the adsorption/ desorption of ammonia molecules on a graphene surface by studying the Fermi level shift. Based on a physically plausible model, the adsorption and desorption rates of ammonia molecules on graphene have been extracted from the measured Fermi level shift as a function of exposure time. An electric field-i...

Graphite oxide was exfoliated and dispersed in propylene carbonate (PC) by bath sonication. Heating the graphene oxide suspensions at 150 degrees C significantly reduced the graphene oxide platelets; paper samples comprising such reduced graphene oxide platelets had an electrical conductivity of 5230 S/m. By adding tetraethylammonium tetrafluorobor...

Nano-graphene platelets (NGPs) were added to polyamide 11 (PA11) powder in 1%, 3%, and 5% weight loading in an attempt to create electrostatic dissipative polymer nanocomposites (PNC) using SLS, a rapid manufacturing process. Powder-powder mixing techniques were explored as a potential replacement for twin-screw extrusion for dispersing nano-graphe...

Graphene, a two-dimensional monolayer of sp(2)-bonded carbon atoms, has been attracting great interest due to its unique transport properties. One of the promising applications of graphene is as a transparent conductive electrode owing to its high optical transmittance and conductivity. In this paper, we report on an improved transfer process of la...