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Gwo-Ching Wang

Bio: Gwo-Ching Wang is an academic researcher from Rensselaer Polytechnic Institute. The author has contributed to research in topics: Thin film & Reflection high-energy electron diffraction. The author has an hindex of 53, co-authored 344 publications receiving 9873 citations. Previous affiliations of Gwo-Ching Wang include National Institute of Standards and Technology & Oak Ridge National Laboratory.


Papers
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Journal ArticleDOI
TL;DR: Using a pump-probe method with a 150 fs laser at the wavelength of 1.55 μm, this article demonstrated that single-walled carbon nanotubes (SWNT) have an exciton decay time of less than 1 ps and a high third-order polarizability, which is reasonably interpreted as due to their azimuthal symmetry.
Abstract: Using a pump–probe method with a 150 fs laser at the wavelength of 1.55 μm, we have experimentally demonstrated that single-walled carbon nanotubes (SWNT) have an exciton decay time of less than 1 ps and a high third-order polarizability, which is reasonably interpreted as due to their azimuthal symmetry. These experimental results reveal that a SWNT polymer composite may be a candidate material for high-quality subpicosecond all-optical switches.

438 citations

Journal ArticleDOI
TL;DR: In this paper, the design, construction, operation, and performance of a spin polarized electron source utilizing photoemission from negative electron affinity (NEA) GaAs are presented in detail.
Abstract: The design, construction, operation, and performance of a spin polarized electron source utilizing photoemission from negative electron affinity (NEA) GaAs are presented in detail. A polarization of 43±2% is produced using NEA GaAs (100). The polarization can be easily modulated without affecting other characteristics of the electron beam. The electron beam intensity depends on the intensity of the exciting radiation at 1.6 eV; beam currents of 20 μA/mW are obtained. The source is electron optically bright; the emittance phase space (energy‐area‐solid angle product) is 0.043 eV mm2 sr. The light optics, electron optics, and cathode preparation including the GaAs cleaning and activation to NEA are discussed in depth. The origin of the spin polarization in the photoexcitation process is reviewed and new equations describing the depolarization of photoelectrons in the emission process are derived. Quantum yield and polarization measurements for both NEA and positive electron affinity surfaces are reported. T...

392 citations

Book ChapterDOI
01 Jan 2001
TL;DR: In this paper, the authors focus on the basic principles of real and diffraction techniques for quantitative characterization of the rough surfaces and apply them to a wide variety of rough surfaces (e.g., self-affine, mounded, anisotropic, and two-level surfaces).
Abstract: The structure of a growth or an etch front on a surface is not only a subject of great interest from the practical point of view but also is of fundamental scientific interest. Very often surfaces are created under non-equilibrium conditions such that the morphology is not always smooth. In addition to a detailed description of the characteristics of random rough surfaces, "Experimental Methods in the Physical Sciences, Volume 37", "Characterization of Amorphous and Crystalline Rough Surface-Principles and Applications" will focus on the basic principles of real and diffraction techniques for quantitative characterization of the rough surfaces. The book thus includes the latest development on the characterization and measurements of a wide variety of rough surfaces. The complementary nature of the real space and diffraction techniques is fully displayed. It includes an accessible description of quantitative characterization of random rough surfaces and growth/etch fronts. It has a detailed description of the principles, experimentation, and limitations of advanced real-space imaging techniques (such as atomic force microscopy) and diffraction techniques (such as light scattering, X-ray diffraction, and electron diffraction). It has characterization of a variety of rough surfaces (e.g., self-affine, mounded, anisotropic, and two-level surfaces) accompanied by quantitative examples to illustrate the essence of the principles. It is an insightful description of how rough surfaces are formed. There is presentation of the most recent examples of the applications of rough surfaces in various areas.

325 citations

Journal ArticleDOI
TL;DR: In this paper, a method to fabricate nano-column arrays with different shapes and in-plane orientations by glancing angle deposition was reported, which has potential application to produce 3D lattice.
Abstract: In this letter, we report a method to fabricate nano-column arrays with different shapes and in-plane orientations by glancing angle deposition. By changing the rate of the rotation during each revolution, we can fabricate nano-columns with circular, elliptical, triangle, rectangular, and pentagon shapes. Depending on the nucleation sites, we can even fabricate flowerlike nano-columns. This method has potential application to produce 3-D lattice.

234 citations

Proceedings ArticleDOI
27 Oct 2003
TL;DR: In this paper, the current status of the glancing angle deposition technology, its potential applications, and its future challenges are discussed, as well as the future challenges of this technique.
Abstract: Three-dimensional nanostructures can be fabricated by the glancing angle deposition technique. By rotating the substrate in both polar and azimuthal directions, one can fabricate desired nanostructures, such as nano-rod arrays with different shapes, nano-spring arrays, and even multilayer nanostructures. This method offers a fully three-dimensional control of the nanostructure with additional capability of self-alignment. There is almost no limitation on materials that can be fabricated into desired nanostructures. In this presentation, we will discuss the current status of the glancing angle deposition technology, its potential applications, and its future challenges.

234 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the surface chemistry of the trimethylaluminum/water ALD process is reviewed, with an aim to combine the information obtained in different types of investigations, such as growth experiments on flat substrates and reaction chemistry investigation on high-surface-area materials.
Abstract: Atomic layer deposition(ALD), a chemical vapor deposition technique based on sequential self-terminating gas–solid reactions, has for about four decades been applied for manufacturing conformal inorganic material layers with thickness down to the nanometer range. Despite the numerous successful applications of material growth by ALD, many physicochemical processes that control ALD growth are not yet sufficiently understood. To increase understanding of ALD processes, overviews are needed not only of the existing ALD processes and their applications, but also of the knowledge of the surface chemistry of specific ALD processes. This work aims to start the overviews on specific ALD processes by reviewing the experimental information available on the surface chemistry of the trimethylaluminum/water process. This process is generally known as a rather ideal ALD process, and plenty of information is available on its surface chemistry. This in-depth summary of the surface chemistry of one representative ALD process aims also to provide a view on the current status of understanding the surface chemistry of ALD, in general. The review starts by describing the basic characteristics of ALD, discussing the history of ALD—including the question who made the first ALD experiments—and giving an overview of the two-reactant ALD processes investigated to date. Second, the basic concepts related to the surface chemistry of ALD are described from a generic viewpoint applicable to all ALD processes based on compound reactants. This description includes physicochemical requirements for self-terminating reactions,reaction kinetics, typical chemisorption mechanisms, factors causing saturation, reasons for growth of less than a monolayer per cycle, effect of the temperature and number of cycles on the growth per cycle (GPC), and the growth mode. A comparison is made of three models available for estimating the sterically allowed value of GPC in ALD. Third, the experimental information on the surface chemistry in the trimethylaluminum/water ALD process are reviewed using the concepts developed in the second part of this review. The results are reviewed critically, with an aim to combine the information obtained in different types of investigations, such as growth experiments on flat substrates and reaction chemistry investigation on high-surface-area materials. Although the surface chemistry of the trimethylaluminum/water ALD process is rather well understood, systematic investigations of the reaction kinetics and the growth mode on different substrates are still missing. The last part of the review is devoted to discussing issues which may hamper surface chemistry investigations of ALD, such as problematic historical assumptions, nonstandard terminology, and the effect of experimental conditions on the surface chemistry of ALD. I hope that this review can help the newcomer get acquainted with the exciting and challenging field of surface chemistry of ALD and can serve as a useful guide for the specialist towards the fifth decade of ALD research.

2,212 citations

Journal ArticleDOI
TL;DR: In this article, the authors review recent progress and advances that have been made on: (a) dispersion of CNTs in a polymer matrix, including optimum blending, in situ polymerization and chemical functionalization; and (b) alignment of CNNs in the matrix enhanced by ex situ techniques, force and magnetic fields, electrospinning and liquid crystalline phase-induced methods.
Abstract: Polymer/carbon nanotube (CNT) composites are expected to have good processability characteristics of the polymer and excellent functional properties of the CNTs. The critical challenge, however, is how to enhance dispersion and alignment of CNTs in the matrix. Here, we review recent progress and advances that have been made on: (a) dispersion of CNTs in a polymer matrix, including optimum blending, in situ polymerization and chemical functionalization; and (b) alignment of CNTs in the matrix enhanced by ex situ techniques, force and magnetic fields, electrospinning and liquid crystalline phase-induced methods. In addition, discussions on mechanical, thermal, electrical, electrochemical, optical and super-hydrophobic properties; and applications of polymer/CNT composites are included. Enhanced dispersion and alignment of CNTs in the polymer matrix will promote and extend the applications and developments of polymer/CNT nanocomposites.

1,848 citations

Journal ArticleDOI
TL;DR: In this paper, the synthesis of novel 3D flower-like iron oxide nanostructures by an ethylene glycol (EG)-mediated self-assembly process is reported, which can be used to further understand the mechanism of self-organization and expand the applications of IR nanomaterials.
Abstract: 3D nanostructures have attracted much attention because of their unique properties and potential applications. The simplest synthetic route to 3D nanostructures is probably selfassembly, in which ordered aggregates are formed in a spontaneous process. However, it is still a big challenge to develop simple and reliable synthetic methods for hierarchically selfassembled architectures with designed chemical components and controlled morphologies, which strongly affect the properties of nanomaterials. Iron oxides have been extensively studied in diverse fields including catalysis, environment protection, sensors, magnetic storage media, and clinical diagnosis and treatment. Various iron oxide structures, such as nanocrystals, particles, cubes, spindles, rods, wires, tubes, and flakes, have been successfully fabricated by a variety of methods. However, the self-assembly of these low-dimensional building blocks into complex 3D ordered nanostructures is still considerably more difficult. In order to further understand the mechanism of self-organization and expand the applications of iron oxide nanomaterials, self-assembled iron oxide 3D nanostructures need to be explored in more detail. Herein, we report the synthesis of novel 3D flowerlike iron oxide nanostructures by an ethylene glycol (EG)-mediated self-assembly process. Such a method has been adopted previously for the preparation of V2O5 hollow microspheres, [7]

1,508 citations

Journal ArticleDOI
TL;DR: Transparent conductors (TCs) have a multitude of applications for solar energy utilization and for energy savings, especially in buildings as discussed by the authors, which leads naturally to considerations of spectral selectivity, angular selectivity, and temporal variability of TCs, as covered in three subsequent sections.

1,471 citations