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School of Materials Science and Engineering

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College of Engineering

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Now showing 1 - 10 of 100

Temperature driven in-situ phase transformation of PbWO₄ nanobelts

(Georgia Institute of Technology, 2011-06-23) Wang, Xue ; Ding, Yong ; Wang, Z. L. (Zhong Lin) ; Hu, Chenguo

Monoclinic raspite PbWO₄ nanobelts were synthesized by a facile composite-salt-mediated method. By in situ heating to above 538 °C inside the chamber of a transmission electron microscope, the raspite nanobelts transformed irreversibly to tetragonal scheelite phase. By analyzing the experimental data, three possible topotactic transformation relationships between raspite and scheelite phases have been proposed. With further increasing the temperature up to 618 °C, part of the PbWO₄ nanobelts reduced to tetragonal WO₃ nanorods owing to the evaporation of Pb.
In vitro Biomimetic Construction of Hydroxyapatite–Porcine Acellular Dermal Matrix Composite Scaffold for MC3T3-E1 Preosteoblast Culture

(Georgia Institute of Technology, 2011-02-26) Zhao, Hongshi ; Wang, Guancong ; Hu, Shunpeng ; Cui, Jingjie ; Ren, Na ; Liu, Duo ; Liu, Hong ; Cao, Chengbo ; Wang, Jiyang ; Wang, Z. L. (Zhong Lin)

The application of porous hydroxyapatite–collagen (HAp-Collagen) as a bone tissue engineering scaffold is hindered by two main problems: its high cost and low initial strength. As a native 3-dimenssional collagen framework, purified porcine acellular dermal matrix (PADM) has been successfully used as a skin tissue engineering scaffold. Here we report its application as a matrix for the preparation of HAp to produce a bone tissue scaffold through a biomimetic chemical process. The HAp-PADMscaffold has two-level pore structure, with large channels (*100 mm in diameter) inherited from the purified PADM microstructure and small pores (<100 nm in diameter) formed by self-assembled HAp on the channel surfaces. The obtained HAp-PADM scaffold (S15D) has a compressive elastic modulus as high as 600 kPa. The presence of HAp in sample S15D reduces the degradation rate of PADM in collagenase solution at 378C. After 7 day culture of MC3T3-E1 pre-osteroblasts, MTT data show no statistically significant difference on pure PADM framework and HAp-PADM scaffold ( p>0.05). Because of its high strength and nontoxicity, its simple preparation method, and designable and tailorable properties, the HAp- PADM scaffold is expected to have great potential applications in medical treatment of bone defects.
Tracking the catalyzed growth process of nanowires by in situ x-ray diffraction

(Georgia Institute of Technology, 2010-07-06) Kirkham, Melanie ; Wang, Z. L. (Zhong Lin) ; Snyder, Robert L.

Quasi-one-dimensional nanostructures of silicon, oxides, and other materials show great promise for a variety of applications. These nanostructures are commonly grown using metal catalyst nanoparticles. This paper investigates the growth mechanism of Au-catalyzed Si nanowires through in situ x-ray diffraction, and the results are compared to previously studied Au-catalyzed ZnO nanorods. The Si nanowires were found to grow from molten catalyst particles, however, the ZnO nanorods were found to grow from solid catalyst particles through a surface diffusion process. From this comparison, the relative bonding types of the catalyst and source material are determined to have a significant effect on the growth mechanism.
Growth direction and morphology of ZnO nanobelts revealed by combining in situ atomic force microscopy and polarized Raman spectroscopy

(Georgia Institute of Technology, 2010-01-14) Lucas, Marcel ; Wang, Z. L. (Zhong Lin) ; Riedo, Elisa

Control over the morphology and structure of nanostructures is essential for their technological applications, since their physical properties depend significantly on their dimensions, crystallographic structure, and growth direction. A combination of polarized Raman (PR) spectroscopy and atomic force microscopy (AFM) is used to characterize the growth direction, the presence of point defects and the morphology of individual ZnO nanobelts. PR-AFM data reveal two growth modes during the synthesis of ZnO nanobelts by physical vapor deposition. In the thermodynamics-controlled growth mode, nanobelts grow along a direction close to [0001], their morphology is growth-direction dependent, and they exhibit no point defects. In the kinetics-controlled growth mode, nanobelts grow along directions almost perpendicular to [0001], and they exhibit point defects.
Large enhancement in photon detection sensitivity via Schottky-gated CdS nanowire nanosensors

(Georgia Institute of Technology, 2010-01-06) Wei, Te-Yu ; Huang, Chi-Te ; Hansen, Benjamin J. ; Lin, Yi-Feng ; Chen, Lih-Juann ; Lu, Shih-Yuan ; Wang, Z. L. (Zhong Lin)

The Schottky contact based photon detection was demonstrated using CdS (visible light responsive), silicon (indirect n-type oxygen-non-adsorbing), and CuO (indirect p-type oxygen-adsorbing) nanowire nanosensors. With changing one of the two nanowire-electrode contacts from ohmic to Schottky, detection sensitivities as high as 105% were achieved by the CdS nanowire nanosensor operated at the reverse bias mode of −8 V, which was 58 times higher than that of the corresponding ohmic contact device. The reset time was also significantly reduced. In addition, originally light nonresponsive silicon and CuO nanowires became light responsive when fabricated as a Schottky contact device. These improvements in photon detection can be attributed to the Schottky gating effect realized in the present nanosensor system by introducing a Schottky contact.
Depth resolved luminescence from oriented ZnO nanowires

(Georgia Institute of Technology, 2009-12-14) Rosenberg, R. A. ; Haija, M. Abu ; Vijayalakshmi, K. ; Zhou, Jun ; Xu, Sheng ; Wang, Z. L. (Zhong Lin)

We have utilized the limited penetration depth of x-rays to study the near-surface properties of vertically aligned ZnO nanowires. For an energy of 600 eV the penetration depth varies between 3 and 132 nm as the incidence angle changes from 2° to 33°. Thus, by obtaining optical luminescence spectra as a function of incidence angle, it is possible to probe the near-surface region with nanometer-scale resolution. We will present angle dependent optical luminescence data from oriented ZnO nanowires. By fitting the results to a simple model, we extract a depth for the surface defect regions of ~14 nm.
Structural colors from Morpho peleides butterfly wing scales

(Georgia Institute of Technology, 2009-10-12) Ding, Yong ; Xu, Sheng ; Wang, Z. L. (Zhong Lin)

A male Morpho peleides butterfly wing is decorated by two types of scales, cover and ground scales. We have studied the optical properties of each type of scales in conjunction with the structural information provided by cross-sectional transmission electron microscopy and computer simulation. The shining blue color is mainly from the Bragg reflection of the one-dimensional photonic structure, e.g., the shelf structure packed regularly in each ridges on cover scales. A thin-film-like interference effect from the base plate of the cover scale enhances such blue color and further gives extra reflection peaks in the infrared and ultraviolet regions. The analogy in the spectra acquired from the original wing and that from the cover scales suggests that the cover scales take a dominant role in its structural color. This study provides insight of using the biotemplates for fabricating smart photonic structures.
Combined polarized Raman and atomic force microscopy: In situ study of point defects and mechanical properties in individual ZnO nanobelts

(Georgia Institute of Technology, 2009-08-04) Lucas, Marcel ; Wang, Z. L. (Zhong Lin) ; Riedo, Elisa

We present a method, polarized Raman (PR) spectroscopy combined with atomic force microscopy (AFM), to characterize in situ and nondestructively the structure and the physical properties of individual nanostructures. PR-AFM applied to individual ZnO nanobelts reveals the interplay between growth direction, point defects, morphology, and mechanical properties of these nanostructures. In particular, we find that the presence of point defects can decrease the elastic modulus of the nanobelts by one order of magnitude. More generally, PR-AFM can be extended to different types of nanostructures, which can be in as-fabricated devices.
Erratum: Effects of piezoelectric potential on the transport characteristics of metal-ZnO nanowire-metal field effect transistor

(Georgia Institute of Technology, 2009-08-03) Gao, Zhiyuan ; Zhou, Jun ; Gu, Yudong ; Fei, Peng ; Hao, Yue ; Bao, Gang ; Wang, Z. L. (Zhong Lin)
Effects of piezoelectric potential on the transport characteristics of metal-ZnO nanowire-metal field effect transistor

(Georgia Institute of Technology, 2009-06-05) Gao, Zhiyuan ; Zhou, Jun ; Gu, Yudong ; Fei, Peng ; Hao, Yue ; Bao, Gang ; Wang, Z. L. (Zhong Lin)

We have investigated the effects of piezoelectric potential in a ZnO nanowire on the transport characteristics of the nanowire based field effect transistor through numerical calculations and experimental observations. Under different straining conditions including stretching, compressing, twisting, and their combination, a piezoelectric potential is created throughout the nanowire to modulate/alternate the transport property of the metal-ZnO nanowire contacts, resulting in a switch between symmetric and asymmetric contacts at the two ends, or even turning an Ohmic contact type into a diode. The commonly observed natural rectifying behavior of the as-fabricated ZnO nanowire can be attributed to the strain that was unpurposely created in the nanowire during device fabrication and material handling. This work provides further evidence on piezopotential governed electronic transport and devices, e.g., piezotronics.