Milo Koretsky

Enhancement of Student Learning in Experimental Design Using a Virtual Laboratory

This paper describes the instructional design, implementation, and assessment of a virtual laboratory based on a numerical simulation of a chemical vapor deposition (CVD) process, the virtual CVD laboratory. The virtual CVD laboratory provides a capstone experience in which students synthesize engineering science and statistics principles and have the opportunity to apply experimental design in the context similar to that of a practicing engineer in industry with a wider design space than is typically seen in the undergraduate laboratory. The simulation of the reactor is based on fundamental principles of mass transfer and chemical reaction, obscured by added ldquonoise.rdquo The software application contains a 3-D student client that simulates a cleanroom environment, an instructor Web interface with integrated assessment tools, and a database server. As opposed to being constructed as a direct one-to-one replacement, this virtual laboratory is intended to complement the physical laboratories in the curriculum so that certain specific elements of student learning can be enhanced. Implementation in four classes is described. Assessment demonstrates students are using an iterative experimental design process reflective of practicing engineers and correlates success in this project to higher order thinking skills. Student surveys indicate that students perceived the virtual CVD laboratory as the most effective learning medium used, even above physical laboratories.

Effect of Moisture on the Spatial Uniformity of Cathodic Protection of Steel in Reinforced Concrete

Abstract A numerical model for the cathodic protection (CP) of steel in reinforced concrete was developed. Parameters were set to represent a three-dimensional section of a bridge beam exposed to the atmosphere and coated with a thermally sprayed zinc anode. Both the diffusion of oxygen and the conduction of charge within the concrete were considered explicitly through a two-dimensional finite element model. The diffusivity and conductivity were represented as functions of concrete moisture content. Electrochemical reactions considered at the rebar-concrete interface included the reduction of oxygen, the oxidation of iron, and the evolution of hydrogen in a constant-potential CP circuit. Reaction-kinetic parameters for actively corroding steel (not passivated steel) were used. Reactions at the zinc-concrete interface were not considered explicitly. The effectiveness of protection was found to vary significantly with both concrete moisture content and position on the rebar. For spatially uniform pore satur...

Effect of chloride on the photoluminescence of ZnS:Mn thin films

ZnS:Mn thin films at various substrate temperature are grown by halide transport chemical vapor deposition. These films show blue and red photoluminescence (PL) in addition to the typical yellow-orange emission. The manganese crystal environment is characterized by electron spin resonance (ESR) spectroscopy. A computer simulation of the ESR spectra is used to quantify the number of isolated manganese and the number of clustered manganese in the crystal lattice. These data reveal that the red emission occurs in films with low manganese concentration, and, therefore, occurs from a mechanism different than those previously posed. The activation energy for Mn incorporation is measured to be Ea=137 kJ/mol. From these data, a Mn–Cl defect pair is proposed as the red emission center. Self-activated blue emission in intentionally Cl-doped ZnS films is also demonstrated. Thus both red and blue PL in ZnS thin films result from chloride impurities.

The Effect of Processing Conditions on Crystal Orientation and Structure in ZnS:Mn Thin Films

Hexagonal and cubic thin-film ZnS:Mn electroluminescent phosphors are grown by halide transport chemical vapor deposition. Processing conditions, most notably introduction of a H 2 S ambient, lead to a change in the preferred orientation and phase of the polycrystalline thin film. In addition to the commonly reported growth along the closest packed plane [(111) for cubic crystal structure or (002) for hexagonal], thin films have been grown along the less dense cubic (311) direction. When grown in the (311) direction, the conduction charge of ZnS:Mn alternating-current, thin-film electroluminescent devices increases from 2.3 to 5.0 μC/cm 2 .

A simple model for the etching of photoresist with plasma‐generated reactants

The neutral heterogeneous chemistry between reactive species formed in a glow discharge plasma and a polymer surface is investigated. Oxygen and fluorine atom concentrations in an O2/CF4 plasma afterglow are measured by gas phase electron resonance spectroscopy. These atom concentrations are correlated to etch rate data via a simple heterogeneous model which divides the etching process into three steps: initiation, etching, and passivation. The model predicts etch rate data well using measured atom concentrations. When the substrate temperature is changed, the etching step is affected most, presumably limited by product desorption. Dilution of the discharge with argon enhances the etch rate in two ways. First, the homogeneous chemistry is altered, most notably affecting the fluorine atom concentration. The homogeneous effects are taken into account through measured atom concentrations. Second, the argon metastables play a role in the heterogeneous chemistry, enhancing the etching step. From an estimation ...

Surface Kinetics of Polyphenylene Oxide Etching in a CF 4 / O 2 / Ar Downstream Microwave Plasma

A downstream microwave plasma etcher with in situ diagnostics has been constructed to elucidate the chemical mechanisms in plasma etching of polyphenylene oxide (PPO). CF 4 /O 2 /Ar reactant gases are used. Stable reaction products are investigated with mass spectrometry while reactive-free radical information is obtained using optical emission spectroscopy. Additionally, the weight loss of PPO is measured to determine average etch rate. A linear correlation between weight loss measurements of PPO laminates and integration of CO and CO 2 formation measured by mass spectrometry suggests that real-time monitoring of polymer etching can be achieved. Etching dynamics are studied with gas compositions of CF 4 varied from 6.6 to 30%. The etch process exhibits a dynamic reduction in rate with CF 4 ≥ 20%. C 1s spectra of X-ray photoelectron spectroscopy show an increase in fluorination of the etched surface with CF 4 %. A kinetic model based on the dynamic change of the number of carbon sites that are fluorinated is proposed.

Anomalous etch rates of photoresist with argon dilution of CF4/O2 plasma afterglows

It is shown that the downstream etching of a photoresist with CF4/O2 mixtures can be enhanced by a factor of at least 2 with addition of argon to the gas mixture. Analysis of the oxygen and fluorine atom densities with gas‐phase magnetic resonance downstream of the discharge suggests that argon metastables alter the homogeneous chemistry for fluorine atom production as well as the heterogeneous chemistry of photoresist chain scission.

Written justifications to multiple-choice concept questions during active learning in class

ABSTRACT Increasingly, instructors of large, introductory STEM courses are having students actively engage during class by answering multiple-choice concept questions individually and in groups. This study investigates the use of a technology-based tool that allows students to answer such questions during class. The tool also allows the instructor to prompt students to provide written responses to justify the selection of the multiple-choice answer that they have chosen. We hypothesize that prompting students to explain and elaborate on their answer choices leads to greater focus and use of normative scientific reasoning processes, and will allow them to answer questions correctly more often. The study contains two parts. First, a crossover quasi-experimental design is employed to determine the influence of asking students to individually provide written explanations (treatment condition) of their answer choices to 39 concept questions as compared to students who do not. Second, we analyze a subset of the questions to see whether students identify the salient concepts and use appropriate reasoning in their explanations. Results show that soliciting written explanations can have a significant influence on answer choice and, when it does, that influence is usually positive. However, students are not always able to articulate the correct reason for their answer.

Terahertz spectroscopy of Ni–Ti alloy thin films

We investigate the carrier dynamics in nickel–titanium (Ni–Ti) alloy thin films using terahertz transmission spectroscopy. Analyzing the power transmission data and the transmitted waveforms, we obtained the alloy resistivity as a function of Ti concentration. Sharp changes in the resistivity were observed at the Ti fractions of 22%, 44%, and 62%, indicating that structural disorder is greatly enhanced when the alloy undergoes a phase transition.

Productively engaging student teams in engineering: The interplay between doing and thinking

A comparative case study examined two teams for instances of Productive Disciplinary Engagement (PDE) as they completed a complex, virtual process development project. Discourse from team meetings was analyzed to interpret how engagement unfolds, specifically classifying engagement in two dimensions: School vs. Engineering World, and task co-production vs. knowledge co-construction. Teams were found to move back and forth between School World and Engineering World as different aspects of the learning system become salient and instances of PDE were triggered when teams experienced productive frictions from interlocking components of the learning system.