Hien V. Nguyen

Flipping the Work Design in an industrial engineering course

Educational practice and the concept of ‘active learning’ have had a significant impact on engineering education. Challenging students with questions and problem-solving activities to learn course material is what we do in engineering courses. However, how do we continue to cover the amount of material we need to cover and still open up class time to include the active learning strategies so necessary in engineering? This paper describes the design and implementation of an instructional strategy called ‘the classroom flip’ or inverted classroom that was put into practice in an industrial engineering course. Initial results from the classroom provide feedback and insight into how this technique might be best utilized to enhance learning in engineering education.

In situ determination of dielectric functions and optical gap of ultrathin amorphous silicon by real time spectroscopic ellipsometry

We have developed techniques to determine the near‐infrared to near‐ultraviolet dielectric function and optical gap of ultrathin amorphous silicon [a‐Si:(H)] using real‐time spectroscopic ellipsometry during preparation and processing. The techniques have been applied to ∼50 A a‐Si:H films prepared by plasma‐enhanced chemical vapor deposition, and to ∼250 A pure a‐Si chemically modified by atomic H exposure. For the latter, the time evolution of the bonded H content can be estimated along with the evolution of the gap.

Preparation of ultrathin microcrystalline silicon layers by atomic hydrogen etching of amorphous silicon and end‐point detection by real time spectroellipsometry

The etching of hydrogenated amorphous silicon (a‐Si:H) in thermally generated atomic hydrogen has been investigated in detail, utilizing real time spectroellipsometry for characterization and end‐point detection. When properly controlled, etching can yield ultrathin microcrystalline Si (μc‐Si:H) films of relatively high density on virtually any substrate material. These films are unique in that their microstructure is established by the crystallization of the near‐surface a‐Si:H, rather than by the nucleation of crystallites on the substrate, as occurs for plasma‐enhanced chemical vapor‐deposited μc‐Si:H films.

Simultaneous real‐time spectroscopic ellipsometry and reflectance for monitoring thin‐film preparation

An expansion of the capabilities of high‐speed, multichannel spectroscopic ellipsometry (SE) is described that involves simultaneous measurement of the reflectance spectrum along with the two spectra in the ellipsometric angles (ψ, Δ). Previously, a novel rotating‐polarizer spectroscopic ellipsometer has been perfected that employs a photodiode array detector for high‐speed acquisition of (ψ, Δ) spectra, designed for real‐time studies of thin‐film growth. For a polarizer angular rotation frequency of ω0, the (ψ, Δ) values at a given photon energy are deduced from the 2ω0 Fourier components of the detector irradiance, normalized by the dc component. A third parameter, the weighted reflectance RA, can be obtained from the dc component and from a calibration based on the known optical properties of the substrate measured prior to film growth. With (ω0/2π)=12.5 Hz, three‐parameter data sets, [ψ(hν), Δ(hν), RA(hν); 1.5≤hν≤4.5 eV], can be acquired with a time resolution as short as 40 ms. Although RA provides c...

Real time spectroscopic ellipsometry characterization of the nucleation of diamond by filament‐assisted chemical vapor deposition

The recently developed technique of real time spectroscopic ellipsometry (SE) has been applied to characterize the nucleation of diamond on c‐Si by W filament‐assisted chemical vapor deposition, leading to improved control over the process. Specifically, techniques are developed which minimize W contamination at the diamond/substrate interface; calibrations are performed which determine the temperature of the top ∼250 A of the substrate under growth conditions; and alterations in gas flow conditions are implemented in response to diamond growth for a reduced induction time. With these procedures in place, real time SE provides the induction time, nucleation density, and mass thickness, and is in quantitative agreement with ex situ scanning electron microscopy.

Real time spectroscopic ellipsometry for characterization of nucleation, growth, and optical functions of thin films

We have exploited the unique capabilities of a rotating-polarizer multichannel spectroscopic ellipsometer in real time studies of the evolution of microstructure and optical functions for various thin film materials. With a 16 ms acquisition time for ∼50 point spectra from 1.3 to 4.3 eV, the precision of the ellipsometer is (0.04°, 0.12°) in (Ψ, Δ) for a Si surface at 2.5 eV. Real time investigations of aluminum prepared by physical vapor deposition and hydrogenated amorphous semiconductors prepared by plasma-enhanced chemical vapor deposition are highlighted here. We focus on capabilities that elude a real time discrete-wavelength approach. For aluminum, this includes determining (i) the optical functions of small Al particles (<50 A diameter) in the nucleation regime for comparison with those of bulk Al, and (ii) an electron mean free path that characterizes the effect of defects on the optical functions of the particles. For the amorphous semiconductors, this includes determining (i) the optical gap from real time measurements, and (ii) the monolayer-scale coalescence behavior that correlates well with the device suitability of the material.

Acceptance of Tablet PC technology by engineering faculty

This paper considers the results of a two-year project in which Tablet PCs were given to engineering faculty at the Pennsylvania State University. During Phase 1, 34 faculty members received a Tablet PC for use in the classroom. Due to the success of this implementation and demand by other faculty, the project was expanded in the following year to include an additional 30 faculty members in the College of Engineering. During both phases of the project, the participants were asked to complete various assessment tools including scales measuring teaching efficacy, computer skills efficacy, and technology acceptance. A sample of the faculty members participated in interviews intended to gather additional information on their perceptions of the Tablet PC and its benefit in the classroom environment. This paper provides results of the project assessment and its relation to the literature on the diffusion of innovation and the Technology Acceptance Model. Implications of the assessment will be discussed that may be helpful to those who are interested in implementing a similar program for engineering faculty.

Multichannel transmission ellipsometer for characterization of anisotropic optical materials

We have developed a multichannel transmission ellipsometer to characterize the wavelength dependence of the optical characteristics of transparent, anisotropic solids. The source side of the instrument employs a broadband lamp in conjunction with a rotating polarizer. The light transmitted through the sample is analyzed by a stationary polarizer, a grating spectrograph, and a 1024-pixel photodiode array. The photodiode array collects irradiance spectra at several uniformly spaced values of the rotating polarizer angle P, and the irradiance registered at each pixel of the array is Fourier analyzed versus P. From this analysis one can characterize the change in polarization state induced by the sample as a continuous function of wavelength from 400 to 800 nm. The multichannel transmission ellipsometer can be applied in studies of linear and circular birefringence in new materials as well as in assessments of the spectroscopic performance of polarization modifying devices such as retarders. However, we also emphasize the application of the instrument as an educational tool for demonstrating polarization concepts in advanced undergraduate physics and optics laboratories. In this application anisotropies in common optical materials have been characterized, including circular birefringence in quartz and linear birefringence and dichroism in mica. Because high-precision data are collected continuously versus wavelength, the results represent a clear improvement over those obtained at discrete wavelengths.

Real time spectroscopic ellipsometry for characterization of thin film optical properties and microstructural evolution

Abstract A rotating polarizer multichannel ellipsometer was applied in spectroscopic (1.3–4.2 eV) investigations of thin films during deposition. In this review, two examples are selected which demonstrate real time spectroscopic ellipsometry. In the first, we compare results for amorphous silicon and germanium sputtered to approximately 50 A on native oxide-covered c-Si. For these films, the evolution of the effective optical properties with thickness is dominated by changes in void volume fraction and surface roughness which accompany nucleation and growth. Abrupt transitions from cluster to bulk film growth occur at total thicknesses of 10–15 A for materials deposited under optimum conditions of microstructural uniformity. In the second example, corresponding results for aluminum evaporated to opacity onto thermally oxidized c-Si are discussed. In this case, the evolution of the effective optical properties with thickness is strongly influenced by changes in the intrinsic aluminum dielectric function. In particular, we find that the relaxation time for the (200) parallel-band transition increases abruptly with thickness over the 55–60 A range. The enhanced scattering of electrons in the films less than 60 A thick may originate from a disordered or fine-grained film structure, and for thicknesses less than 55 A the (200) parallel-band feature in the aluminum dielectric function at 1.5 eV disappears.

Real time monitoring of filament-assisted chemically vapor deposited diamond by spectroscopic ellipsometry

Abstract Spectroscopic ellipsometry over the range 1.5–4.5 eV was applied as a real time probe of the processes occurring in the initial nucleation of thin film diamond by heated-filament assisted chemical vapor deposition. Using both untreated and diamond-polished c-Si substrates, as well as both carburized and uncarburized tungsten filaments, it was possible to separate and characterize competing phenomena, including the increase in surface temperature induced by filament ignition, the formation of carbide layers, contamination of the substrate by tungsten from the filament, annealing of diamond polishing damage, and, finally, diamond nucleation. An accurate measurement of the true temperature of the substrate surface averaged over the top 500 A can be obtained from the energy position of critical points in the c-Si band structure. For diamond deposition, we operated with an initial excess flow of CH4 to stimulate nucleation. We applied real time feedback and manual control to reduce the CH4 flow in the first monolayers of deposition. The thickness of diamond and an estimate of its nucleation density can be obtained from real time spectra, and the latter was in good agreement with that obtained from scanning electron microscopy.