bluuebunny/crossref_metadata_2025 huggingface dataset:
Teachers' Ability to Estimate Item Difficulty: A Test of the Assumptions in the Angoff Standard Setting Method
Authors: Impara James C. , Plake Barbara S.
Published: September 2005

The Angoff (1971) standard setting method requires expert panelists to (a) conceptualize candidates who possess the qualifications of interest (e.g., the minimally qualified) and (b) estimate actual item performance for these candidates. Past and current research (Bejar, 1983; Shepard, 1994) suggests that estimating item performance is difficult for panelists. If panelists cannot perform this task, the validity of the standard based on these estimates is in question. This study tested the ability of 26 classroom teachers to estimate item performance for two groups of their students on a locally developed district‐wide science test. Teachers were more accurate in estimating the performance of the total group than of the “borderline group,” but in neither case was their accuracy level high. Implications of this finding for the validity of item performance estimates by panelists using the Angoff standard setting method are discussed.
Psychometric Characteristics of Computer‐Adaptive and Self‐Adaptive Vocabulary Tests: The Role of Answer Feedback and Test Anxiety
Authors: Vispoel Walter P.
Published: September 2005

This study focused on the effects of administration mode (computer‐adaptive test [CAT] versus self‐adaptive test [SAT]), item‐by‐item answer feedback (present versus absent), and test anxiety on results obtained from computerized vocabulary tests. Examinees were assigned at random to four testing conditions (CAT with feedback, CAT without feedback, SAT with feedback, SAT without feedback). Examinees completed the Test Anxiety Inventory (Spielberger, 1980) before taking their assigned computerized tests. Results showed that the CATs were more reliable and took less time to complete than the SATs. Administration time for both the CATs and SATs was shorter when feedback was provided than when it was not, and this difference was most pronounced for examinees at medium to high levels of test anxiety. These results replicate prior findings regarding the precision and administrative efficiency of CATs and SATs but point to new possible benefits of including answer feedback on such tests.
Moderating Possibly Irrelevant Multiple Mean Score Differences on a Test of Mathematical Reasoning
Authors: Stocking Martha L. , Jirele Thomas , Lewis Charles , Swanson Len
Published: September 2005

A pool of items from operational tests of mathematical reasoning was constructed to investigate the feasibility of using automated test assembly (ATA) methods to simultaneously moderate possibly irrelevant differences between the performance of women and men, and African American and White test takers. None of the artificial tests exhibited substantial impact moderation, although the estimated mean scaled score differences for the relevant population indicated a modest move in the intended direction: the difference between scaled score means was reduced by about 20% for women and men and about 9% for African American and White test takers. Although many issues in the implementation of this methodology remain to be solved, the consideration of impact in ATA, along with the maintenance of the detailed test plan, appears to be a potential method of moderating possibly irrelevant mean test score differences.
Generating Random Parallel Test Forms Using CTT in a Computer‐Based Environment
Authors: Gibson Wade M. , Weiner John A.
Published: September 2005

This paper describes a procedure for automated test forms assembly based on Classical Test Theory (CTT). The procedure uses stratified random content sampling and test form pre‐equating to ensure both content and psychometric equivalence in generating virtually unlimited parallel forms. The procedure extends the usefulness of CTT in automated test form construction, yielding classical item statistics based on representative sample distributions and pre‐equated test forms with known psychometric characteristics. A rationale for the procedure is presented followed by an example application and discussion of psychometric considerations related to its use.
A Comparison of Item Exposure Control Methods in Computerized Adaptive Testing
Authors: Revuelta Javier , Ponsoda Vicente
Published: September 2005

Two new methods for item exposure control were proposed. In the Progressive method, as the test progresses, the influence of a random component on item selection is reduced and the importance of item information is increasingly more prominent. In the Restricted Maximum Information method, no item is allowed to be exposed in more than a predetermined proportion of tests. Both methods were compared with six other item‐selection methods (Maximum Information, One Parameter, McBride and Martin, Randomesque, Sympson and Hetter, and Random Item Selection) with regard to test precision and item exposure variables. Results showed that the Restricted method was useful to reduce maximum exposure rates and that the Progressive method reduced the number of unused items. Both did well regarding precision. Thus, a combined Progressive‐Restricted method may be useful to control item exposure without a serious decrease in test precision.
Reviewing and Changing Answers on Computer‐adaptive and Self‐adaptive Vocabulary Tests
Authors: Vispoel Walter P.
Published: September 2005

Results obtained from computer‐adaptive and self‐adaptive tests were compared under conditions in which item review was permitted and not permitted. Comparisons of answers before and after review within the “review” condition showed that a small percentage of answers was changed (5.23%), that more answers were changed from wrong to right than from right to wrong (by a ratio of 2.92:1), that most examinees (66.5%) changed answers to at least some questions, that most examinees who changed answers improved their ability estimates by doing so (by a ratio of 2.55 to 1), and that review was particularly beneficial to examineees at high ability levels. Comparisons between the “review” and “no‐review” conditions yielded no significant differences in ability estimates or in estimated measurement error and provided no trustworthy evidence that test anxiety moderated the effects of review on those indexes. Most examinees desired review, but permitting it increased testing time by 41%.
The Effect of Model Misspecification on Classification Decisons Made Using a Computerized Test
Authors: Kalohn John C. , Spray Judith A.
Published: September 2005

Many computerized testing algorithms require the fitting of some item response theory (IRT) model to examinees’ responses to facilitate item selection, the determination of test stopping rules, and classification decisions. Some IRT models are thought to be particularly useful for small volume certification programs that wish to make the transition to computerized adaptive testing (CAT). The one‐parameter logistic model (1‐PLM) is usually assumed to require a smaller sample size than the three‐parameter logistic model (3‐PLM) for item parameter calibrations. This study examined the effects of model misspecification on the precision of the decisions made using the sequential probability ratio test (SPRT). For this comparison, the 1‐PLM was used to estimate item parameters, even though the items’ characteristics were represented by a 3‐PLM. Results demonstrated that the 1‐PLM produced considerably more decision errors under simulation conditions similar to a real testing environment, compared to the true model and to a fixed‐form standard reference set of items.
Effects of Coaching on SAT I: Reasoning Test Scores
Authors: Powers Donald E. , Rock Donald A.
Published: September 2005

A College Board‐sponsored survey of a nationally representative sample of 1995–96 SAT takers yielded a data base for more than 4, 000 examinees, about 500 of whom had attended formal coaching programs outside their schools. Several alternative analytical methods were used to estimate the effects of coaching on SAT I: Reasoning Test scores. The various analyses produced slightly different estimates. All of the estimates, however, suggested that the effects of coaching are far less than is claimed by major commercial test preparation companies. The revised SAT does not appear to be any more coachable than its predecessor.
Contextual Explanations of Local Dependence in Item Clusters in a Large Scale Hands‐On Science Performance Assessment
Authors: Ferrara Steven , Huynh Huynh , Michaels Hillary
Published: September 2005

This study provides hypothesized explanations for local item dependence (LID) in a large scale hands‐on science performance assessment. Items within multi‐step item clusters were classified as low or high in LID using contextual analysis procedures described in this and other studies. LID was identified statistically using the average within cluster (AWC) correlation procedure described in previous studies. Levels of LID identified in contextual analyses were compared to levels of LlD identified in correlation analyses. Consistent with other studies, items that appear to elicit locally dependent responses require examinees to answer and explain their answer or to use given or generated information to respond
‘Mental Model’ Comparison of Automated and Human Scoring
Authors: Williamson David M. , Bejar Isaac I. , Hone Anne S.
Published: September 2005

‘Mental models’ used by automated scoring for the simulation divisions of the computerized Architect Registration Examination are contrasted with those used by experienced human graders. Candidate solutions (N = 3613) received both automated and human holistic scores. Quantitative analyses suggest high correspondence between automated and human scores; thereby suggesting similar mental models are implemented. Solutions with discrepancies between automated and human scores were selected for qualitative analysis. The human graders were reconvened to review the human scores and to investigate the source of score discrepancies in light of rationales provided by the automated scoring process. After review, slightly more than half of the score discrepancies were reduced or eliminated. Six sources of discrepancy between original human scores and automated scores were identified: subjective criteria; objective criteria; tolerances/ weighting; details; examinee task interpretation; and unjustified. The tendency of the human graders to be compelled by automated score rationales varied by the nature of original score discrepancy. We determine that, while the automated scores are based on a mental model consistent with that of expert graders, there remain some important differences, both intentional and incidental, which distinguish between human and automated scoring. We conclude that automated scoring has the potential to enhance the validity evidence of scores in addition to improving efficiency.
Identifying the Causes of DIF in Translated Verbal Items
Authors: Allalouf Avi , Hambleton Ronald K. , Sireci Stephen G.
Published: September 2005

Translated tests are being used increasingly for assessing the knowledge and skills of individuals who speak different languages. There is little research exploring why translated items sometimes function differently across languages. If the sources of differential item functioning (DIF) across languages could be predicted, it could have important implications on test development, scoring and equating. This study focuses on two questions: “Is DIF related to item type?”, “What are the causes of DIF?” The data were taken from the Israeli Psychometric Entrance Test in Hebrew (source) and Russian (translated). The results indicated that 34% of the items functioned differentially across languages. The analogy items were the most problematic with 65% showing DIF, mostly in favor of the Russian‐speaking examinees. The sentence completion items were also a problem (45% D1F). The main reasons for DIF were changes in word difficulty, changes in item format, differences in cultural relevance, and changes in content.
Stepwise Analysis of Differential Item Functioning Based on Multiple‐Group Partial Credit Model
Authors: Muraki Eiji
Published: September 2005

Bock, Muraki, and Pfeiffenberger (1988) proposed a dichotomous item response theory (IRT) model for the detection of differential item functioning (DIF), and they estimated the IRT parameters and the means and standard deviations of the multiple latent trait distributions. This IRT DIF detection method is extended to the partial credit model (Masters, 1982; Muraki, 1993) and presented as one of the multiple‐group IRT models. Uniform and non‐uniform DIF items and heterogeneous latent trait distributions were used to generate polytomous responses of multiple groups. The DIF method was applied to this simulated data using a stepwise procedure. The standardized DIF measures for slope and item location parameters successfully detected the non‐uniform and uniform DIF items as well as recovered the means and standard deviations of the latent trait distributions.This stepwise DIF analysis based on the multiple‐group partial credit model was then applied to the National Assessment of Educational Progress (NAEP) writing trend data.
Alternative Displays for Communicating NAEP Results: A Redesign and Validity Study
Authors: Wainer Howard , Hambleton Ronald K. , Meara Kevin
Published: September 2005

Five diswlays, chosen from the NAEP 1994 Reading: A First Look, were redesigned. The redesign was informed by the principles developed and enunciated in Wainer's 1997 popular text Visual Revelations. After the redesign was completed a survey of educational policymakers was done in which substantive questions were asked about the content of the various displays. Each redesign was paired with the original and were assigned randomly to one of two survey forms. We found that, on average, the redesigns yielded both more accurate and faster answers to the questions asked. The more difficult the question the greater the disparity between the original format and the redesigned one.
Limiting Answer Review and Change on Computerized Adaptive Vocabulary Tests: Psychometric and Attitudinal Results
Authors: Vispoel Walter P. , Hendrickson Amy B. , Bleiler Timothy
Published: September 2005

Previous simulation studies of computerized adaptive tests (CATs) have revealed that the validity and precision of proficiency estimates can be maintained when review opportunities are limited to items within successive blocks. Our purpose in this study was to evaluate the effectiveness of CATs with such restricted review options in a live testing setting. Vocabulary CATs were compared under four conditions: (a) no item review allowed, (b) review allowed only within successive 5‐item blocks, (c) review allowed only within successive lO‐item blocks, and (d) review allowed only after answering all 40 items. Results revealed no trust‐worthy differences among conditions in vocabulary proficiency estimates, measurement error, or testing time. Within each review condition, ability estimates and number correct scores increased slightly after review, more answers were changed from wrong to right than from right to wrong, most examinees who changed answers improved proficiency estimates by doing so, and nearly all examinees indicated that they had an adequate opportunity to review their previous answers. These results suggest that restricting review opportunities on CATs may provide a viable way to satisfy examinee desires, maintain validity and measurement precision, and keep testing time at acceptable levels.
Effects of Response Format on Difficulty of SAT‐Mathematics Items: It's Not the Strategy
Authors: Katz Irvin R. , Bennett Randy Elliot , Berger Aliza E.
Published: September 2005

Problem‐solving strategy is frequently cited as mediating the effects of response format (multiple‐choice, constructed response) on item difficulty, yet there are few direct investigations of examinee solution procedures. Fifty‐five high school students solved parallel constructed response and multiple‐choice items that differed only in the presence of response options. Student performance was videotaped to assess solution strategies. Strategies were categorized as “traditional”–those associated with constructed response problem solving (e.g., writing and solving algebraic equations)–or “nontraditional”–those associated with multiple‐choice problem solving (e.g., estimating a potential solution). Surprisingly, participants sometimes adopted nontraditional strategies to solve constructed response items. Furthermore, differences in difficulty between response formats did not correspond to differences in strategy choice: some items showed a format effect on strategy but no effect on difficulty; other items showed the reverse. We interpret these results in light of the relative comprehension challenges posed by the two groups of items.
A Comparison of Methods of Estimating Conditional Standard Errors of Measurement for Testlet‐Based Test Scores Using Simulation Techniques
Authors: Lee Guemin
Published: September 2005

The primary purpose of this study was to investigate the appropriateness and implication of incorporating a testlet definition into the estimation of procedures of the conditional standard error of measurement (SEM) for tests composed of testlets. Another purpose was to investigate the bias in estimates of the conditional SEM when using item‐based methods instead of testlet‐based methods. Several item‐based and testlet‐based estimation methods were proposed and compared. In general, item‐based estimation methods underestimated the conditional SEM for tests composed for testlets, and the magnitude of this negative bias increased as the degree of conditional dependence among items within testlets increased. However, an item‐based method using a generalizability theory model provided good estimates of the conditional SEM under mild violation of the assumptions for measurement modeling. Under moderate or somewhat severe violation, testlet‐based methods with item response models provided good estimates.
Some Paths Toward Making Praxis Scores More Useful
Authors: Wainer Howard , Sheehan Kathleen M. , Wang Xiaohui
Published: September 2005

In this study we describe an analytic method for aiding in the generation of subscales that characterize the deep structure of tests. In addition we also derive a procedure for estimating scores for these scales that are much more statistically stable than subscores computed solely from the items that are contained on that scale. These scores achieve their stability through augmentation with information from other related information on the test. These methods were used to complement each other on a data set obtained from a Praxis administration. We found that the deep structure of the test yielded ten subscales and that, because the test was essentially unidimensional, ten subscores could be computed, all with very high reliability. This result was contrasted with the calculation of six traditional subscales based on surface features of the items. These subscales also yielded augmented subscores of high reliability.
Psychometric Properties of Scale Scores and Performance Levels for Performance Assessments Using Polytomous IRT
Authors: Wang Tianyou , Kolen Michael J. , Harris Deborah J.
Published: September 2005

With a focus on performance assessments, this paper describes procedures for calculating conditional standard error of measurement (CSEM) and reliability of scale scores and classification consistency of performance levels. Scale scores that are transformations of total raw scores are the focus of these procedures, although other types of raw scores are considered as well. Polytomous IRT models provide the psychometric foundation for the procedures that are described. The procedures are applied using test data from ACT's Work Keys Writing Assessment to demonstrate their usefulness. Two polytomous IRT models were compared, as were two different procedures for calculating scores. One simulation study was done using one of the models to evaluate the accuracy of the proposed procedures. The results suggest that the procedures provide quite stable estimates and have the potential to be useful in a variety of performance assessment situations.
The Generalizability of Scores for a Performance Assessment Scored with a Computer‐Automated Scoring System
Authors: Clauser Brian E. , Harik Polina , Clyman Stephen G.
Published: September 2005

When performance assessments are delivered and scored by computer, the costs of scoring may be substantially lower than those of scoring the same assessment based on expert review of the individual performances. Computerized scoring algorithms also ensure that the scoring rules are implemented precisely and uniformly. Such computerized algorithms represent an effort to encode the scoring policies of experts. This raises the question, would a different group of experts have produced a meaningfully different algorithm? The research reported in this paper uses generalizability theory to assess the impact of using independent, randomly equivalent groups of experts to develop the scoring algorithms for a set of computer‐simulation tasks designed to measure physicians’ patient management skills. The results suggest that the impact of this “expert group” effect may be significant but that it can be controlled with appropriate test development strategies. The appendix presents multivariate generalizability analysis to examine the stability of the assessed proficiency across scores representing the scoring policies of different groups of experts.
An Expected Response Function Approach to Graphical Differential Item Functioning
Authors: Scrams David J. , McLeod Lori D.
Published: September 2005

In this paper a new approach to graphical differential item functioning (DIF) is offered. The methodology is based on a sampling‐theory approach to expected response functions (Lewis, 1985; Mislevy, Wingersky, & Sheehan, 1994). Essentially error in item calibrations is modeled explicitly, and repeated samples are taken from the posterior distributions of the item parameters. Sampled parameter values are used to estimate the posterior distribution of the difference in item characteristic curves (ICCs)for two groups. A point‐wise expectation is taken as an estimate of the true difference between the ICCs, and the sampled‐difference functions indicate uncertainty in the estimate. Tbe approach is applied to a set of pretest items, and the results are compared to traditional Mantel‐Haenszel DIF statistics. The expected‐response‐function approach is contrasted with Pashley's (1992) graphical DIF approach.
Population Invariance and the Equatability of Tests: Basic Theory and The Linear Case
Authors: Dorans Neil J. , Holland Paul W.
Published: September 2005

How does the fact that two tests should not be equated manifest itself? This paper addresses this question through the study of the degree to which equating functions fail to exhibit population invariance across subpopulations. Equating fimctions are supposed to be population invariant by definition. But, when two tests are not equatable, it is possible that the linking functions, used to connect the scores of one to the scores of the other, are not invariant across different populations of examinees. While no acceptable equating function is ever completely population invariant, in the situations where equating is usually performed we believe that the dependence of the equating function on the population used to compute it is usually small enough to be ignored. We introduce two root‐mean‐square difference measures of the degree to which the functions used to link two tests computed on different subpopulations differ from the linking function computed for the whole population. We also introduce the system of “parallel‐linear” linking functions for multiple subpopulations and show that, for this system, our measure of population invariance can be computed easily from the standardized mean differences between the scores of the subpopulations on the two tests. For the parallel‐linear case, we develop a correlation‐based upper bound on our measure that holds for all systems of subpopulations. We illustrate these ideas using data from the SAT I and from a concordance study of several combinations of ACT and SAT I scores, In the appendices, we give some theoretical results bearing on the other equating “requirements” of “same construct,”“same reliability” and one aspect of Lord's concept of equity.
Performance of a Proposed Method for the Linking of Mixed Format Tests With Constructed Response and Multiple Choice Items
Authors: Tate Richard
Published: September 2005

The error associated with a proposed linking method for tests consisting of both constructed response and multiple choice items was investigated in a simulation study. Study factors that were varied included the relative proportion of constructed response items in the test, the size of the year‐to‐year change in the ability metric, the number of anchor items, the number of linking papers to be reassessed, and the presence of guessing. The results supported the use of the proposed linking method, In addition, simulations were used to illustrate possible linking bias resulting from (a) the use of the traditional linking method and (b) the use of only multiple choice anchor items in the presence of test multidimensionality.
Consistency of Angoff‐Based Predictions of Item Performance: Evidence of Technical Quality of Results From the Angoff Standard Setting Method
Authors: Plake Barbara S. , Impara James C. , Irwin Patrick M.
Published: September 2005

Judgmental standard‐setting methods, such as the Angoff(1971) method, use item performance estimates as the basis for determining the minimum passing score (MPS). Therefore, the accuracy, of these item peformance estimates is crucial to the validity of the resulting MPS. Recent researchers (Shepard, 1995; Impara & Plake, 1998; National Research Council. 1999) have called into question the ability of judges to make accurate item performance estimates for target subgroups of candidates, such as minimally competent candidates. The propose of this study was to examine the intra‐ and inter‐rater consistency of item performance estimates from an Angoff standard setting. Results provide evidence that item pelformance estimates were consistent within and across panels within and across years. Factors that might have influenced this high degree of reliability, in the item performance estimates in a standard setting study are discussed.
Experimental Studies on Active Vibration Control of a Beam Using Hybrid Active∕Passive Constrained Layer Damping Treatments
Authors: Langote Pankaj K. , Seshu P.
Published: September 2005

Hybrid damping designs with active piezoelectric materials and passive viscoelastic materials (VEMs) combine the advantages of both active and passive constrained layer damping treatments. In this study, experiments have been conducted on nine systems viz., bare beam, active damping (AD), passive constrained layer damping (PCLD—three variants) and hybrid active∕passive constrained layer damping (Hybrid AD∕PCLD—four variants). Based on the time domain analysis of these systems, it is shown that the “best” performance is obtained using a hybrid damping configuration wherein the VEM and the piezoelectric layers are acting separately.
An Adaptive Semiactive Control Algorithm for Magnetorheological Suspension Systems
Authors: Song Xubin , Ahmadian Mehdi , Southward Steve , Miller Lane R.
Published: September 2005

In this paper, we will present a nonlinear-model-based adaptive semiactive control algorithm developed for magnetorheological (MR) suspension systems exposed to broadband nonstationary random vibration sources that are assumed to be unknown or not measurable. If there exist unknown and∕or varying parameters of the dynamic system such as mass and stiffness, then the adaptive algorithm can include on-line system identification such as a recursive least-squares method. Based on a nonparametric MR damper model, the adaptive system stability is proved by converting the hysteresis inherent with MR dampers to a memoryless nonlinearity with sector conditions. The convergence of the adaptive system, however, is investigated through a linearization approach including further numerical illustration of specific cases. Finally the simulation results for a magnetorheological seat suspension system with the suggested adaptive control are presented. The results are compared with low-damping and high-damping cases, and such comparison further shows the effectiveness of the proposed nonlinear model-based adaptive control algorithm for damping tuning.
Tunable Microelectromechanical Filters that Exploit Parametric Resonance
Authors: Rhoads Jeffrey F. , Shaw Steven W. , Turner Kimberly L. , Baskaran Rajashree
Published: September 2005

Background: This paper describes an analytical study of a bandpass filter that is based on the dynamic response of electrostatically-driven MEMS oscillators. Method of Approach: Unlike most mechanical and electrical filters that rely on direct linear resonance for filtering, the MEM filter presented in this work employs parametric resonance. Results: While the use of parametric resonance improves some filtering characteristics, the introduction of parametric instabilities into the system does present some complications with regard to filtering. Conclusions: The aforementioned complications can be largely overcome by implementing a pair of MEM oscillators with tuning schemes and some processing logic to produce a highly effective bandpass filter.
Patch Transfer Functions as a Tool to Couple Linear Acoustic Problems
Authors: Ouisse Morvan , Maxit Laurent , Cacciolati Christian , Guyader Jean-Louis
Published: September 2005

A method to couple acoustic linear problems is presented in this paper. It allows one to consider several acoustic subsystems, coupled through surfaces divided in elementary areas called patches. These subsystems have to be studied independently with any available method, in order to build a database of transfer functions called patch transfer functions, which are defined using mean values on patches, and rigid boundary conditions on the coupling area. A final assembly, using continuity relations, leads to a very quick resolution of the problem. The basic equations are developed, and the acoustic behavior of a cavity separated in two parts is presented, in order to show the ability of the method to study a strong-coupling case. Optimal meshing size of the coupling area is then discussed, some comparisons with experiments are shown, and finally a complex automotive industrial case is presented.
Vacuum and the electron tube industry
Authors: Redhead P. A.
Published: September 2005

The electron tube industry started with the patenting of the thermionic diode by John Ambrose Fleming in 1904. The vacuum technology used by the infant tube industry was copied from the existing incandescent lamp industry. The growing demands for electron tubes for the military in the first world war led to major improvements in pumps and processing methods. By the 1920s, mass production methods were developing to satisfy the demands for receiving tubes by the burgeoning radio industry. Further expansion in the 1930s and 1940s resulted in improvements in automatic equipment for pumping vacuum tubes leading to the massive production rates of electron tubes in the second world war and the following two decades. The demand for radar during the war resulted in the development of techniques for large-scale production of microwave tubes and CRTs, the latter technology being put to good use later in TV picture tube production. The commercial introduction of the transistor ended the massive demand for receiving tubes. This review concentrates on the vacuum technology developed for receiving tube production.
Effects of surface chemistry on ALD Ta3N5 barrier formation on low-k dielectrics
Authors: Liu J. , Bao J. , Scharnberg M. , Kim W. C. , Ho P. S. , Laxman R.
Published: September 2005

In situ x-ray photoelectron spectroscopy (XPS) was employed to study the effects of the substrate surface chemistry on atomic layer deposition (ALD) of Ta-based barrier layers on various low k surfaces. The initial chemisorption was found to be through formation of Ta–O bonding on organosilicates (OSG) and charge transfer complexes on aromatic SiLK™. ALD process nucleated very slowly on the OSG low-k films, in distinct contrast with its ready nucleation on SiLK™ films. The evolution of the low-k surface chemistry revealed an initial transient growth region controlled mainly by the substrate surface chemistry. Pretreatment of the low-k surfaces with nitrogen and hydrogen radical beams, particularly with nitrogen radicals, was observed to enhance significantly the chemisorption of the TaCl5 precursor on the OSG surfaces. The enhancement was attributed to dissociation of weakly bonded methyl groups from the low-k surface followed by nitridation with the nitrogen radicals. In the subsequent linear growth region, atomic hydrogen species was able to reduce the chlorine content under appropriate temperature and with sufficient purge. The role of the atomic hydrogen in this process enhancement is discussed.
Atomic layer deposition of nickel oxide films using Ni(dmamp)2 and water
Authors: Yang Taek Seung , Cho Wontae , Kim Minchan , An Ki-Seok , Chung Taek-Mo , Kim Chang Gyoun , Kim Yunsoo
Published: September 2005

A precursor originally synthesized for the chemical vapor deposition of metallic nickel, Ni(dmamp)2 (dmamp=1-dimethylamino-2-methyl-2-propanolate, -OCMe2CH2NMe2), has been adopted as a nickel source for the atomic layer deposition of nickel oxide (NiO) using water (H2O) as the oxygen source. The precursor is a solid at room temperature, but readily sublimes at 90 °C. The self-limiting atomic layer deposition (ALD) process by alternate surface reactions of Ni(dmamp)2 and H2O was confirmed from thickness measurements of the NiO films grown with varying Ni(dmamp)2 supply times and numbers of the Ni(dmamp)2-H2O ALD cycles. The ALD temperature window for this precursor was found to be between 90 and 150 °C. Under optimal reaction conditions, the growth rate of the NiO films was ∼0.8Å∕cycle. The NiO films deposited on Si(001) at 120 °C were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The x-ray diffraction patterns showed no distinct peaks for NiO, indicating that the films deposited at this temperature were amorphous. X-ray photoelectron spectroscopy analysis showed the films to be stoichiometric with no detectable amount of carbon impurities. For a film with the thickness of 810 Å (with 1000 ALD cycles) the root-mean-square surface roughness was only ∼4Å as measured by atomic force microscopy. To elucidate the ALD mechanism of the Ni precursor with water, a quadrupole mass analyzer was employed with D2O as the oxygen source in lieu of H2O. Interestingly, unlike the usual ALD fashion, the Ni(dmamp)2 precursor does not seem to decompose but only coordinatively bond to the OH-terminated surface when it was introduced. Next, the Ni(dmamp)2-surface species decompose to produce a hydroxylated nickel oxide surface and the alcohol dmampH when water was supplied.
Thin-film photovoltaics
Authors: Dhere Neelkanth G. , Dhere Ramesh G.
Published: September 2005

CdTe and CuIn1−xGaxSe2−ySy (CIGSS) are ideal candidates for thin-film solar cells. Present photovoltaic (PV) conversion efficiencies of champion thin-film solar cells are: CuIn1−xGaxSe2 (CIGS) 19.5%, CdTe 16.5%, and a-Si:H 12.4%. Thin-film PV modules could spearhead production growth of photovoltaics in the United States because of their added production capacity. For this purpose, module efficiencies must be improved to the 13%–15% range. Obtaining Ohmic contacts is difficult, especially for CdTe, because of the inherently low p-type doping level. Therefore, increasing the p-type doping level is important. Growth of CIGSS film must be controlled carefully as it transitions from Cu-rich to In-rich composition. Other issues for CIGSS cells are minimizing indium consumption, and increasing process throughput of selenization∕sulfurization and transparent conducting oxide deposition. Development of all-dry processing for CdS deposition would be beneficial for both cells. This paper discusses basic devices and related issues.
In situ examination of tin oxide atomic layer deposition using quartz crystal microbalance and Fourier transform infrared techniques
Authors: Du X. , Du Y. , George S. M.
Published: September 2005

The atomic layer deposition (ALD) of tin oxide thin films has been examined using in situ quartz crystal microbalance (QCM) and Fourier transform infrared (FTIR) techniques. The SnOx films were deposited using sequential exposures of SnCl4 and H2O2 at temperatures from 150 to 430 °C. The linear growth of the tin oxide ALD films was observed by both the mass gain during QCM measurements and the background infrared absorbance increase during FTIR investigations. The FTIR spectra revealed the loss and gain of the O–H stretching vibrations of the hydroxyl group for the SnCl4 and H2O2 exposures, respectively. The background infrared absorbance also oscillated after each SnCl4 and H2O2 exposure. The background absorbance increased after SnCl4 exposure and decreased after H2O2 exposure. QCM measurements were consistent with a tin oxide ALD growth rate of ∼60ngcm−2 per cycle. This mass change corresponds to a growth rate of ∼0.7Å∕cycle at 325 °C assuming a SnO2 density of 6.9gcm−3. Additional ex situ surface analysis using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) revealed that the SnOx films grown at 325 °C were defined by x<2. Atomic force microscope (AFM) results also showed that the SnOxALD films deposited on Si(100) wafers have a very rough surface. Understanding and controlling the growth of tin oxide ALD films should be useful to enhance the sensitivity of SnOx gas sensors.
Effect of stress and density on the electrical and physical properties of MgO protecting layer for alternating current-plasma display panels
Authors: Lee Mi Jung , Park Sun Young , Kim Soo Gil , Kim Hyeong Joon , Moon Sung Hwan , Kim Jong Kuk
Published: September 2005

The stress state of MgO thin films, which are used as the dielectric protective layer in alternating current plasma display panels (ac-PDP), was measured by a laser scanning method, in which the bending curvature of a substrate was detected. MgO films were deposited by e-beam evaporation on glass substrates with a dielectric layer at various deposition conditions. The substrate temperatures ranged from room temperature to 300°C. The compressive stresses of the MgO films increased with increasing substrate temperature due to an increase in the intrinsic stress of MgO film. The discharge properties of the ac-PDP, specifically firing voltage (Vf), and sustaining voltage (Vs), were improved in a real panel with the strongly compressively stressed MgO film. Other properties of the MgO films were evaluated using atomic force microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy. Strong compressive stress was caused by the dense microstructure of the film, mainly depending on the deposition temperature. The improved discharge properties of a MgO thin film were affected not by the crystallographic orientation or surface roughness of film but by the high compressive stress of film arising from its high density. In addition the more compressively stressed and denser MgO films showed better physical stability without a crack by thermal stress in the thermal budget of a manufacturing process for ac-PDPs.
Enlargement of grain in poly-Si by adding Au in Ni-mediated crystallization of amorphous Si using a SiNx cap layer
Authors: Kim Kyung Ho , Oh Jae Hwan , Kim Eun Hyun , Jang Jin , Kang Jeon Yeon , Oh Kyu Hwan
Published: September 2005

We have studied the effect of Au addition on Ni-mediated crystallization of amorphous silicon(a-Si) using a silicon–nitride (SiNx) cap layer. The Ni and Au particles were sputtered on the SiNx∕a-Si and then the samples were heated for crystallization at a temperature of 550 °C. We achieved disk-shaped grains and found that the grain size increased with increasing Au density when the Ni density was fixed at 2.45×1014∕cm2. We achieved a grain size of ∼45μm, however the a-Si could not be crystallized when Au density is higher than Ni density.
Electrochemical characterization of plasma polymer coatings in corrosion protection of aluminum alloys
Authors: Chan Yenfong , Yu Qingsong
Published: September 2005

Low-temperature plasma polymerization is a promising pretreatment technique to create environmentally friendly coating systems for corrosion protection of aluminum alloys. In this study, the pretreatment effects of plasma treatment and plasma polymerization on corrosion properties of alclad aluminum alloy 2024-T3 ([2A]) were investigated using electrochemical characterization techniques, including cyclic polarization (CP) and electrochemical impedance spectroscopy (EIS). The [2A] panels were coated with an ultrathin layer (∼50nm) of plasma polymers in a direct current (dc) glow discharge of trimethylsilane or its mixtures with one of two diatomic gases (O2 and N2). The CP measurement results showed that the plasma polymer coated [2A] panels exhibited more negative corrosion potentials (Ecorr), smaller corrosion currents (Icorr), and no surface passivation when compared with uncoated [2A] control panels. The lower values of Icorr imply a higher corrosion resistance on the plasma polymer coated [2A]. When investigated using EIS, these plasma polymer coated [2A] panels exhibited higher impedance (∣Z∣) at lower frequency when first immersed in electrolyte solution, yet degraded quickly to a similar level as uncoated controls within 1day of immersion. These results illustrated that thin plasma polymer films provided a certain but very limited corrosion resistance to [2A] substrate; their dominant role in plasma interface engineered coating systems still relied mostly on their adhesion enhancement at metal∕paint interface as observed in our previous studies.
Sb-induced reconstruction of the Si(112) surface
Authors: Cho E. S. , Kim M. K. , Hur H. , Park J. W. , Baik J. Y. , Kim N. H. , Park C. Y. , An K. S.
Published: September 2005

We have investigated the Sb-induced reconstruction of the Si(112) surface using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Upon Sb adsorption on the clean reconstructed Si(112) surface at 300°C, the Si(112)-(111)1×1-Sb surface was obtained. The present STM study gathered the following findings: The Sb-adsorbed Si(112) surface is composed of saw toothlike nanofacets, which are composed of the (557) plane and the (111) plane. The (557) plane consists of about five (111) planes with five times the width of bulk-terminated (111)1×1 unit cell and (001) plane. It is also about 8.5Å in height and tilted at a 9.9° angle with respect to the basal plane (112). Based on observation, it appears that the Sb atoms on the (111) planes substitute for the topmost Si atoms on the ideal Si(111)1×1 surface. Based on the STM results, we suggest a structural model and discuss the reconstructing mechanism of nanofacets induced by Sb adsorption.
Clean wurtzite InN surfaces prepared with atomic hydrogen
Authors: Piper L. F. J. , Veal T. D. , Walker M. , Mahboob I. , McConville C. F. , Lu Hai , Schaff W. J.
Published: September 2005

Conventional methods of surface preparation for III–V semiconductors, such as thermal annealing and sputtering, are severely limited for InN, resulting in In-enrichment and the introduction of donorlike defects. This is explained in terms of the unusually low Γ-point conduction band minimum of InN with respect to its Fermi stabilization energy. Here, low energy atomic hydrogen irradiation is used to produce clean wurtzite InN surfaces without such detrimental effects. A combination of x-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy was used to confirm the removal of atmospheric contaminants. Low energy electron diffraction revealed a (1×1) surface reconstruction after cleaning. Finally, XPS revealed In∕N intensity ratios consistent with a predominantly In polarity InN film terminated by In-adlayers in analogy with c-plane GaN{0001}-(1×1) surfaces.
Removal characteristics of hillock on SnO2 thin film by chemical mechanical polishing process
Authors: Seo Yong-Jin , Kim Nam-Hoon , Chang Eui-Goo , Park Jinseong , Choi Gwon-Woo , Lee Woo-Sun
Published: September 2005

SnO 2 is one of the most suitable materials for gas sensors. The microstructure and surface morphology of SnO2 films must be controlled because the electrical and optical properties of SnO2 films depend on these characteristics. We investigated the effects of chemical mechanical polishing (CMP) on the variation of morphology of SnO2 films prepared by rf sputtering system. The commercially developed ceria-based oxide slurry, silica-based oxide slurry, and alumina-based tungsten slurry were used as CMP slurry. Nonuniformities of all slurries coincided with stability standards of less than 5%. Silica slurry had the highest removal rate among three different slurries. In addition, the particle size analysis showed that silica slurry had an abrasive with the largest average particle size of the three. Based on the atomic force microscopy analysis of thin film topographies and root mean square values, silica slurry has excellent properties that allow the application of SnO2 thin films as gas sensor materials.
Plasma-assisted atomic layer deposition of TiN monitored by in situ spectroscopic ellipsometry
Authors: Heil S. B. S. , Langereis E. , Kemmeren A. , Roozeboom F. , van de Sanden M. C. M. , Kessels W. M. M.
Published: September 2005

In situ spectroscopic ellipsometry has been employed to determine the properties of titanium nitride (TiN) films during plasma-assisted atomic layer deposition by alternating TiCl4 precursor dosing and H2–N2 plasma exposure. Besides monitoring the film thickness when optimizing the half reactions, it is shown that spectroscopic ellipsometry is a very valuable tool for in situ studies of (air-sensitive) film properties such as resistivity, and for investigating the nucleation phase during initial film growth.
Luminescence characteristics of Eu-doped GdVO4 thin films grown by pulsed-laser deposition
Authors: Yi S. S. , Bae J. S. , Shim K. S. , Moon B. K. , Jeong J. H. , Chung S. T. , Kim J. H.
Published: September 2005

GdVO 4 :Eu3+ thin films were grown on Al2O3 (0001) substrates using pulsed-laser deposition. The crystallinity, surface morphology, and photoluminescence of the films were highly dependent on the deposition conditions, especially oxygen pressure and substrate temperature. The photoluminescence of GdVO4:Eu3+ films grown under optimized conditions indicated that Al2O3 (0001) is a promising substrate for the growth of high-quality GdVO4:Eu3+ phosphor films. In particular, the surface morphology and photoluminescence of GdVO4:Eu3+ films show very similar behavior as a function of oxygen pressure and substrate temperature. The emitted radiation was dominated by the red-emission peak at 620 nm and this phosphor is promising for flat-panel-display applications.