CiteULike: dchen's atlanta

Size Dependence of Young's Modulus in ZnO Nanowires

CQ Chen — 2008-03-18T16:20:22-00:00

Physical Review Letters, Vol. 96, No. 7. (2006)

We report a size dependence of Young's modulus in [0001] oriented ZnO nanowires (NWs) with diameters ranging from 17 to 550 nm for the first time. The measured modulus for NWs with diameters smaller than about 120 nm is increasing dramatically with the decreasing diameters, and is significantly higher than that of the larger ones whose modulus tends to that of bulk ZnO. A core-shell composite NW model in terms of the surface stiffening effect correlated with significant bond length contractions occurred near the 100 free surfaces (which extend several layers deep into the bulk and fade off slowly) is proposed to explore the origin of the size dependence, and present experimental result is well explained. Furthermore, it is possible to estimate the size-related elastic properties of GaN nanotubes and relative nanostructures by using this model.

Dual-mode mechanical resonance of individual ZnO nanobelts

XD Bai — 2008-07-24T18:38:23-00:00

Applied Physics Letters, Vol. 82, No. 26. (2003), pp. 4806-4808.

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Novel Phase Transformation in ZnO Nanowires under Tensile Loading

Ambarish Kulkarni — 2008-07-24T18:34:11-00:00

Physical Review Letters, Vol. 97, No. 10. (2006)

We predict a previously unknown phase transformation from wurtzite to a graphitelike (P63/mmc) hexagonal structure in [010]-oriented ZnO nanowires under uniaxial tensile loading. Molecular dynamics simulations and first principles calculations show that this structure corresponds to a distinct minimum on the enthalpy surfaces of ZnO for such loading conditions. This transformation is reversible with a low level of hysteretic dissipation of 0.16 J/m3 and, along with elastic stretching, endows the nanowires with the ability to recover pseudoelastic strains up to 15%.

Strength and Breaking Mechanism of Multiwalled Carbon Nanotubes Under Tensile Load

Min-Feng Yu — 2007-10-23T14:26:33-00:00

Science, Vol. 287, No. 5453. (28 January 2000), pp. 637-640.

10.1126/science.287.5453.637

Nanomechanics from atomic resolution to molecular recognition based on atomic force microscopy technology

HP Lang — 2008-07-24T18:27:23-00:00

Nanotechnology, Vol. 13, No. 5. (2002), pp. R29-R36.

Atomic force microscopy (AFM) is a technique to image surfaces with unprecedented vertical and lateral resolution. Many related techniques have been derived from AFM, taking advantage of local interactions between a tip on a cantilever and a surface. However, cantilevers can also be used for sensing applications. These so-called nanosensors feature extreme sensitivity for the detection of chemical vapours or adsorption of molecules. Upon adsorption to the cantilever surface, the molecules cause the cantilever to bend. Thus physical, chemical or biochemical processes are directly transduced into nanomechanical motion. We show that measurement of the deflection of a single cantilever might be misleading. Reliable information can only be obtained by using a sensor cantilever and at least one reference cantilever integrated into an array. We have built an electronic nose using polymer layers as partially selective cantilever coatings to recognize chemical vapours and odours by evaluating the cantilevers' bending pattern. Major applications lie in the fields of process and quality control, biosensing, medical diagnostics, molecular recognition and proteomics.

Direct-Current Nanogenerator Driven by Ultrasonic Waves

Xudong Wang — 2007-07-25T03:43:40-00:00

Science, Vol. 316, No. 5821. (6 April 2007), pp. 102-105.

We have developed a nanowire nanogenerator that is driven by an ultrasonic wave to produce continuous direct-current output. The nanogenerator was fabricated with vertically aligned zinc oxide nanowire arrays that were placed beneath a zigzag metal electrode with a small gap. The wave drives the electrode up and down to bend and/or vibrate the nanowires. A piezoelectric-semiconducting coupling process converts mechanical energy into electricity. The zigzag electrode acts as an array of parallel integrated metal tips that simultaneously and continuously create, collect, and output electricity from all of the nanowires. The approach presents an adaptable, mobile, and cost-effective technology for harvesting energy from the environment, and it offers a potential solution for powering nanodevices and nanosystems. 10.1126/science.1139366

Scaling and dynamics of sphere and disk impact into granular media

Daniel Goldman — 2008-04-14T00:46:54-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 77, No. 2. (2008)

Direct measurements of the acceleration of spheres and disks impacting granular media reveal simple power law scalings along with complex dynamics which bear the signatures of both fluid and solid behavior. The penetration depth scales linearly with impact velocity while the collision duration is constant for sufficiently large impact velocity. Both quantities exhibit power law dependence on sphere diameter and density, and gravitational acceleration. The acceleration during impact is characterized by two jumps: a rapid, velocity-dependent increase upon initial contact and a similarly sharp depth-dependent decrease as the impacting object comes to rest. Examination of the measured forces on the sphere in the vicinity of these features leads to an experimentally based granular force model for collision. We discuss our findings in the context of recently proposed phenomenological models that capture qualitative dynamical features of impact but fail both quantitatively and in their inability to capture significant acceleration fluctuations that occur during penetration and which depend on the impacted material.

Novel Defect Structures in Nematic Liquid Crystal Shells

Fernández-Nieves — 2008-04-17T19:44:27-00:00

Physical Review Letters, Vol. 99 (2007)

Absolute Instability of a Liquid Jet in a Coflowing Stream

Andrew Utada — 2008-04-17T18:57:14-00:00

Physical Review Letters, Vol. 100, No. 1. (2008)

Cylindrical liquid jets are inherently unstable and eventually break into drops due to the Rayleigh-Plateau instability, characterized by the growth of disturbances that are either convective or absolute in nature. Convective instabilities grow in amplitude as they are swept along by the flow, while absolute instabilities are disturbances that grow at a fixed spatial location. Liquid jets are nearly always convectively unstable. Here we show that two-phase jets can breakup due to an absolute instability that depends on the capillary number of the outer liquid, provided the Weber number of the inner liquid is >O(1). We verify our experimental observations with a linear stability analysis.