Alper Buldum

Gas molecule adsorption in carbon nanotubes and nanotube bundles

We studied various gas molecules (NO2, O2, NH3, N2, CO2, CH4, H2O, H2, Ar) on single-walled carbon nanotubes (SWNTs) and bundles using first principles methods. The equilibrium position, adsorption energy, charge transfer, and electronic band structures are obtained for different kinds of SWNTs. Most molecules adsorb weakly on SWNTs and can be either charge donors or acceptors to the nanotubes. We find that the gas adsorption on the bundle interstitial and groove sites is stronger than that on individual nanotubes. The electronic properties of SWNTs are sensitive to the adsorption of certain gases such as NO2 and O2. Charge transfer and gas-induced charge fluctuation might significantly affect the transport properties of SWNTs. Our theoretical results are consistent with recent experiments.

First-Principles Study of Li-Intercalated Carbon Nanotube Ropes

We studied Li-intercalated carbon nanotube ropes by first-principles methods. Results show charge transfer between Li and C and small structural deformation due to intercalation. Both the interior of the nanotube and the interstitial space are susceptible for intercalation. The Li intercalation potential of a single-walled nanotube rope is comparable to that of graphite and almost independent of the Li density up to around LiC2, as observed in recent experiments. This density is significantly higher than that of Li-intercalated graphite, making the nanorope a promising candidate for the anode material in battery applications.

Contact resistance between carbon nanotubes

Fascinating properties of nanotubes arise when they form intermolecular junctions. In this rapid communication, we demonstrate that such nanotube junctions have atomic scale characteristics and the contact resistance between the tubes depends strongly on atomic structure in the contact region. Our calculations show that the optimal electronic transport between nanotubes occurs when the tubes are in atomic scale registry. The contact resistance can vary several orders of magnitude with atomic scale movements. Phenomena such as the negative differential resistance and nonlinear variation of resistance are found. These properties may lead to new device applications.

Atomic Scale Sliding and Rolling of Carbon Nanotubes

A carbon nanotube is an ideal object for understanding the atomic scale aspects of interface interaction and friction. Using molecular statics and dynamics methods different types of motion of nanotubes on a graphite surface are investigated. We found that each nanotube has unique equilibrium orientations with sharp potential energy minima. This leads to atomic scale locking of the nanotube. The effective contact area and the total interaction energy scale with the square root of the radius. Sliding and rolling of nanotubes have different characters. The potential energy barriers for sliding nanotubes are higher than that for perfect rolling. When the nanotube is pushed, we observe a combination of atomic scale spinning and sliding motion. The result is rolling with the friction force comparable to sliding.

Atomistic calculation of elastic moduli in strained silicon

Strained silicon is becoming a new technology in silicon industry where the novel strain-induced features are utilized. In this paper we present a molecular dynamic prediction for the elastic stiffnesses C11, C12 and C44 in strained silicon as functions of the volumetric strain level. Our approach combines basic continuum mechanics with the classical molecular dynamic approach, supplemented with the Stillinger–Weber potential. Using our approach, the bulk modulus, effective elastic stiffnesses C11, C12 and C44 of the strained silicon, including also the effective Youngs modulus and Poissons ratio, are all calculated and presented in terms of figures and formulae. In general, our simulation indicates that the bulk moduli, C11 and C12, increase with increasing volumetric strain whilst C44 is almost independent of the volumetric strain. The difference between strained moduli and those at zero strain can be very large, and therefore use of standard free-strained moduli should be cautious.

Quantum effects in electrical and thermal transport through nanowires

Nanowires, point contacts and metallic single-wall carbon nanotubes are one-dimensional nanostructures which display important size-dependent quantum effects. Quantization due to the transverse confinement and resultant finite level spacing of electronic and phononic states are responsible for some novel effects. Many studies have revealed fundamental and technologically important properties, which are being explored for fabricating future nanodevices. Various simulation studies based on the classical molecular dynamics method and combined force and current measurements have shown the relationship between atomic structure and transport properties. The atomic, electronic and transport properties of these nanostructures have been an area of active research. This brief review presents some quantum effects in the electronic and phononic transport through nanowires.

Structure of aluminum atomic chains

First-principles density-functional calculations reveal that aluminum can form planar chains in zigzag and ladder structures. The most stable one has equilateral triangular geometry with four nearest neighbors; the other stable zigzag structure has wide bond angle and allows for two nearest neighbors. An intermediary structure has the ladder geometry and is formed by two strands. While all these planar geometries are more favored energetically than the linear chain, the binding becomes even stronger in nonplanar geometries. We found that by going from bulk to a chain the character of bonding changes and acquires directionality. The conductance of zigzag and linear chains is

First-principles study of graphene-lithium structures for battery applications

{4e}^{2}/h

Quantum interference effects in electronic transport through nanotube contacts

under ideal ballistic conditions.

Atomic-scale study of friction and energy dissipation

In order to identify the best and most promising graphene-lithium structures for battery applications, we performed a systematic study of different multilayer graphene-lithium structures using first-principles density-functional theory. The most promising structure identified is a few layer compound which contains a single graphene layer and four lithium layers. In this structure, lithium density is six times higher than that of intercalated graphite, and high lithium density observed in recent experiments can be due to this structure. In addition, we show that electron density distribution around the positive Li ions is very important to design new advanced materials for battery applications.