Development of a Traceable Atomic Force Microscope with Interferometer and Compensation Flexure Stage

Entwicklung eines ruckfuhrbaren Rasterkraftmikroskops auf der Basis von Interferometern und einer geregelten Einkorperfuhrung Abstrakt Rastersondenmikroskope, zu denen unter anderem Rastertunnelmikroskope (STM) und Rasterkraftmikroskope (AFM) gezahlt werden, werden an vielen Stellen in der Material- und Oberflachenforschung, der Halbleitertechnologie sowie der Biotechnologie angewendet. Sie sind zudem denkbare Werkzeuge der Nanotechnologien, so beispielsweise der Nanolithographie. Zudem konnen sie der Manipulation von Atomen und zur Nanometrologie dienen. Kommerzielle AFM bestehen unter anderem aus einem Laser, Photoempfanger, Regler, Piezoantriebssystem sowie einem Tastsystem. Dabei kommt den Piezoelementen des Antriebssystems besondere Bedeutung zu. Die von Piezoelementen bekannten Nachteile, wie Nichtlinearitat, Hysterese, Alterung, thermische Drift, Kriechen und Ubersprechen, konnen durchaus 20% der Messabweichungen bei Vorwartssteuerung verursachen. Daher sollten AFM, Metrologiestandards entsprechend, zur Reduzierung der Mesunsicherheit regelmasig ruckfuhrbar kalibriert werden. Das Ziel der vorliegenden Arbeit bestand in der Entwicklung eines ruckfuhrbaren Rasterkraftmikroskops (Traceable Atomic Force Microscope, TAFM) zum Einsatz als staatliches Normal zur ruckfuhrbaren Vermessung von Normalen im Nanometer- Bereich fur die taiwanesische Industrie. Das TAFM wurde als Kombination eines kommerziellen AFM, zwei Laserinterferometern, einer aktiv geregelten dreiachsigen Prazisionsfuhrung, einem Metrologierahmen aus Super-Invar, einer Schwingungsdampfung sowie einer temperaturgeregelten Umhausung konzipiert und aufgebaut. Zur Reduzierung des Abbe-Offsets wurden die Interferometer derart angeordnet, dass sich ihre virtuell verlangerten Messstrahlen im Antastpunkt des Cantilevers und damit direkt auf der Probenoberflache im Messpunkt schneiden. Eine einwandfreie Referenzbewegung des Systems wurde durch die eingesetzten Prazisionsfuhrungen sichergestellt, wahrend die direkte Ruckfuhrbarkeit auf die Definition der Langeneinheit ?Meter" durch den Einsatz von zwei Laser- Interferometern erreicht wurde. Die ermittelte erweiterte Messunsicherheit des TAFM fur die laterale Messung einer Lange von 292 nm betrugt bei einer statistischen Sicherheit von 95% unter Berucksichtigung von 29 Freiheitsgraden 2,5 nm. Da die ermittelte erweiterte Messunsicherheit fur laterale Langenmessungen noch nicht zufriedenstellend und die Ruckfuhrbarkeit in Richtung der Z-Achse nicht gewahrleistet ist, soll das TAFM verbessert werden, um perspektivisch eine Messunsicherheit von 0,5 nm in allen drei Messachsen zu erreichen. Dieses Ziel kann zunachst durch den Einbau eines weiteren Laserinterferometers zur Kalibrierung des Messystems der Z-Achse erreicht werden. Zusatzlich sollte die Umhausung statt auf einem Tisch auf dem schwingungsarmeren Boden platziert werden, was das Rauschen der Interferometer auf weniger als 5 nm reduzieren sollte. Ein verstarkter Metrologierahmen, die Verlagerung der Referenzspiegel vom AFM auf die Prazisionsfuhrung und verkurzte Messkreise, die Konstruktion aller Teile aus dem gleichen Material, ein symmetrischer mechanischer Aufbau und der Einsatz einer aktiven Temperaturregelung mit einer Temperaturstabilitat von 20¡Ó0.1 ¢XC sind weitere wichtige Schritte.Scanning Probe Microscopes (SPMs), generally including such instruments as Scanning Tunneling Microscopes (STMs) and Atomic Force Microscopes (AFMs), have been widely applied to measure engineering surfaces in a variety of fields, such as material sciences, semiconductor industry, and biotechnology. SPMs will also be a potential tool in nanotechnology, for example nanolithography, atom manipulation, and nanometrology. Normally, a commercial AFM consists of a laser, a photo-detector, a controller, a piezo-scanner, and a cantilever tip. The piezo-scanner is critical to the performance of AFMs. The intrinsic properties of piezo-scanners, for instance non-linearity, hysteresis, aging, thermal drift, creep, and coupling effect will result in measurement errors that may reach up to 20 % of the reading. To reduce major measurement errors mentioned above, an AFM should be periodically calibrated with a traceable standard. The goal of my research study was to design a state-of-the-art Traceable Atomic Force Microscope (TAFM) to be used as a primary realization of nanometer scale standards for Taiwan industry. The TAFM was composed of a commercial AFM, two laser interferometers, a 3-axis active compensation flexure stage, a super-Invar metrology frame, a vibration isolator, and a temperature-controlled enclosed box with circulating water. To eliminate the Abbe-offset, the surface-plane of specimens was arranged on the same plane-level to the laser beams emitted by interferometers. The compensation flexure stage was aimed to provide a perfect reference motion mechanism. To achieve the direct traceability to the definition of meter, two interferometers were added to the flexure stage. The TAFM was evaluated to have an expanded uncertainty of 2.5 nm at a confidence level of 95 % and 29 degrees of freedom for a nominal pitch value of 292 nm. Since the expanded uncertainty of pitch measurement is not satisfactory and there is no traceability in the Z direction. The TAFM needs to be improved to meet the requirement of an expanded uncertainty of no more than 0.5 nm at 95 % confidence level at all three axes. The requirement can be achieved by the following improvements: A laser interferometer is added to the flexure stage for Z-height calibration. To reduce the noise of laser interferometer to about 5 nm, the support of the enclosed box is moved from tabletop to the floor. The metrology frame is improved by changing the reference mirrors from AFM to flexure stage, thickening the super-Invar frame, shortening the structure loop and metrology loop, using one material, and realizing a symmetrical mechanism design. The passive temperature control is changed to active temperature control, which will approach an anticipative temperature stability of (20¡Ó0.1) ¢XC in the measuring volume

College and university dining service administrators\u27 intention to adopt sustainable practices: An application of the theory of planned behavior

The purpose of this study was to identify sustainable practices existing in college and university dining services (CUDS) and to explore the influence of attitude, subjective norm (social pressures), perceived behavior control and personal norm on college and university dining service administrators\u27 (CUDSAs) intention to implement sustainable practices in their operations using the theory of planned behavior model. Data were collected with a web-based questionnaire sent to 535 CUDSAs in the United States listed in the National Association of College & University Food Services (NACUFS) directory. Thirteen e-mails were returned as undeliverable. A total of 138 CUDSAs responded, resulting in a 26.4% response rate. Sustainable practices perceived to occur most frequently in CUDS were recycling fat, oil and grease; recycling cardboard; using recycled paper products and recycling aluminum. The least common practices were serving locally grown food and composting. Structural equation modeling was used to test hypotheses. Findings revealed that subjective norm had the most positive influence on CUDSAs\u27 intention to adopt sustainable practices, followed by attitude toward sustainable practices and personal norm. There was no significant relationship between perceived behavioral control and behavioral intention, suggesting that implementing sustainable practices was largely under volitional control. Including the personal norm construct in the TPB model reduced unexplained variance in the model by 33.48%, suggesting that personal norm had an effect on CUDSAs\u27 behavioral intention

A Deterministic Equivalent for the Analysis of Non-Gaussian Correlated MIMO Multiple Access Channels

Large dimensional random matrix theory (RMT) has provided an efficient analytical tool to understand multiple-input multiple-output (MIMO) channels and to aid the design of MIMO wireless communication systems. However, previous studies based on large dimensional RMT rely on the assumption that the transmit correlation matrix is diagonal or the propagation channel matrix is Gaussian. There is an increasing interest in the channels where the transmit correlation matrices are generally nonnegative definite and the channel entries are non-Gaussian. This class of channel models appears in several applications in MIMO multiple access systems, such as small cell networks (SCNs). To address these problems, we use the generalized Lindeberg principle to show that the Stieltjes transforms of this class of random matrices with Gaussian or non-Gaussian independent entries coincide in the large dimensional regime. This result permits to derive the deterministic equivalents (e.g., the Stieltjes transform and the ergodic mutual information) for non-Gaussian MIMO channels from the known results developed for Gaussian MIMO channels, and is of great importance in characterizing the spectral efficiency of SCNs.Comment: This paper is the revision of the original manuscript titled "A Deterministic Equivalent for the Analysis of Small Cell Networks". We have revised the original manuscript and reworked on the organization to improve the presentation as well as readabilit

Bank Loan Covenants and Accrual Quality

We examine whether financial covenants in loan contracts motivate banks to monitor borrowers’ financial reporting practices and result in a higher quality of reported accruals. We document that, relative to loans without financial covenants, loans with financial covenants lead to a significant improvement in accrual quality measured by the extent to which accruals can be mapped into cash flows. The effect of loan covenants on accrual quality is stronger when external monitoring by non-bank stakeholders (i.e., institutional investors and financial analysts) is weaker. Furthermore, initiations of bank loans with financial covenants are related to subsequent improvements in analysts’ information environment. The evidence supports the view that bank monitoring improves accounting quality

Perceived threats of vision impairment and its effect on consumption pattern of dietary supplement of lutein and zeaxanthin

Purpose: To explore perceived threats of vision impairment as well as the perceived benefits and barriers of lutein-containing supplements using a health belief model (HBM), and also to assess how these may affect dietary supplement consumption behaviours. Methods: A structured questionnaire was developed on HBM through a focus group interview to gather information from 1,075 drugstore customers in Taiwan. Respondents were 55.16 % female, 64.47 % married, 53.12 % aged between 31 and 50 years, and 91 % with at least a high school education. Results: Perceived severity was much higher that perceived susceptibility. Susceptibility was the most stable construct. Occupation, residence area, and workplace were the top three factors differentiating the variance in HBM constructs. Perceived benefits appeared as the most powerful predictor, followed by perceived barriers. HBM predictors jointly explained 21.9 % of the variance in lutein- and zeaxanthintaking behaviour. Moderating effects of health-related information were not significant. Conclusion: HBM is useful to understand this behaviour. Consumer behaviour is mainly affected by perceived benefits, and not the threat of vision impairment. Since people ignore the possibility of suffering severe vision impairment, more health education is required