C60:LiF nanocomposite for high power efficiency fluorescent organic light-emitting diodes.

To reduce the driving voltage, and hence enhance the power efficiency of OLEDs, the mobility of the various carrier transport layers needs to be increased. Buckminsterfullerene (C(60)) has been proposed to be one possible alternative conductive electron transport layer (ETL) to enhance the power efficiency in OLEDs, due to its high conductivity and the formation of an ohmic contact with the LiF/Al cathode. The optical properties of a nanocomposite of C(60) with LiF (C(60):LiF) and its potential as an efficient ETL in OLEDs was studied. With proper optimization of the device structure, a more than 50% improvement in the power efficiency, without sacrificing the high EQE, in optimized fluorescent OLEDs with the use of C(60):LiF nanocomposite ETL was achieved.

Note: binding energy scale calibration of electron spectrometers for photoelectron spectroscopy using a single sample.

The feasibility of calibrating the binding energy scale for photoelectron spectroscopy using a single sample without sputter cleaning was investigated. By measuring the Fermi level of a Au film with both monochromatic Al Kα (hν = 1486.7 eV) and He Iα (hν = 21.22 eV), the binding energy scale was simply and accurately calibrated. This method is found to yield binding energy values for the Cu 2p(3/2), Ag 3d(5/2), and Au 4f(7/2) peaks that agree with the standard tabulated values defined in International Organization for Standardization 15472 to within ±0.02 eV.

Chlorinated indium tin oxide electrodes with high work function for organic device compatibility.

In organic light-emitting diodes (OLEDs), a stack of multiple organic layers facilitates charge flow from the low work function [~4.7 electron volts (eV)] of the transparent electrode (tin-doped indium oxide, ITO) to the deep energy levels (~6 eV) of the active light-emitting organic materials. We demonstrate a chlorinated ITO transparent electrode with a work function of >6.1 eV that provides a direct match to the energy levels of the active light-emitting materials in state-of-the art OLEDs. A highly simplified green OLED with a maximum external quantum efficiency (EQE) of 54% and power efficiency of 230 lumens per watt using outcoupling enhancement was demonstrated, as were EQE of 50% and power efficiency of 110 lumens per watt at 10,000 candelas per square meter.

The impact of the Fermi-Dirac distribution on charge injection at metal/organic interfaces.

The Fermi level has historically been assumed to be the only energy-level from which carriers are injected at metal/semiconductor interfaces. In traditional semiconductor device physics, this approximation is reasonable as the thermal distribution of delocalized states in the semiconductor tends to dominate device characteristics. However, in the case of organic semiconductors the weak intermolecular interactions results in highly localized electronic states, such that the thermal distribution of carriers in the metal may also influence device characteristics. In this work we demonstrate that the Fermi-Dirac distribution of carriers in the metal has a much more significant impact on charge injection at metal/organic interfaces than has previously been assumed. An injection model which includes the effect of the Fermi-Dirac electron distribution was proposed. This model has been tested against experimental data and was found to provide a better physical description of charge injection. This finding indicates that the thermal distribution of electronic states in the metal should, in general, be considered in the study of metal/organic interfaces.

Experimental design for the determination of the injection barrier height at metal/organic interfaces using temperature dependent current-voltage measurements.

Determination of the injection barrier height for holes or electrons at metal/organic interfaces is essential to understanding the device physics of organic electronics. Due to the disordered molecular packing of organic semiconductors, careful consideration is required in the design of both the device structure and the experimental measurement technique used to extract the barrier height. We report a methodology for extracting the injection barrier height at metal/organic interfaces from temperature dependent current-voltage measurements. This methodology includes the design of single carrier devices with specific consideration of the intrinsic properties of organic semiconductors, as well as the design of a variable temperature cryostat suited to the measurement of organic electronic device architectures. Experimental results for single carrier hole-only devices using two commonly studied hole transport materials, namely N,N(')-diphenyl-N,N(')-bis-(1-naphthyl)-1-1(')-biphenyl-4,4(')-diamine (alpha-NPD) and 4,4('),4(")-tris(N-3- methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA) are also presented as examples.

Transfer-arm evaporator cell for rapid loading and deposition of organic thin films.

Described herein is a transfer-arm evaporator cell (TAE-cell), which allows for rapid loading of materials into vacuum for low-temperature sublimation deposition of thin films. This design can be incorporated with an existing analysis system for convenient in situ thin film characterization. This evaporator is especially well suited for photoemission characterization of organic semiconductor interfaces. Photoemission is one of the most important techniques for characterizing such, however, it generally requires in situ sample preparation. The ease with which materials can be loaded and evaporated with this design increases the throughput of in situ photoemission characterization, and broadens the research scope of the technique. Here, we describe the design, operation, and performance of the TAE-cell.

Modeling the customer in electronic commerce.

This paper reviews interface design of web pages for e-commerce. Different tasks in e-commerce are contrasted. A systems model is used to illustrate the information flow between three subsystems in e-commerce: store environment, customer, and web technology. A customer makes several decisions: to enter the store, to navigate, to purchase, to pay, and to keep the merchandize. This artificial environment must be designed so that it can support customer decision-making. To retain customers it must be pleasing and fun, and create a task with natural flow. Customers have different needs, competence and motivation, which affect decision-making. It may therefore be important to customize the design of the e-store environment. Future ergonomics research will have to investigate perceptual aspects, such as presentation of merchandize, and cognitive issues, such as product search and navigation, as well as decision making while considering various economic parameters. Five theories on e-commerce research are presented.

Adaptation and sensitivity to postural change in sitting.

We used 3 psychophysics methods to determine perceptible changes in seat height, seat pan angle, and backrest angle using an experimental chair. In the method of adjustment, the chosen chair settings were affected by the initial setting. For example, a high initial setting of the seat height led to a high selected setting and a low setting led to a low value. The difference between settings was referred to as not noticeable difference (NND). The method of limits was used to determine acceptable chair settings using verbal limits such as "too high" and "too low." Using the method of constant stimuli, just noticeable differences (JNDs) were determined for chair height (1.5 cm), seat pan angle (1.2 degrees) and backrest angle (1.7 degrees). The corresponding values for NNDs and verbal limits were about twice as large: chair height (2.5 cm), seat pan angle (4 degrees) and backrest angle (3 degrees). NNDs and verbal limits are unobtrusive measures that are considered more valid than JNDs, which exaggerate the need for adjustability. The results have practical implications for the design of office chairs.

Field studies of comfort and discomfort in sitting.

A previous study defined sitting comfort and discomfort as independent entities associated with different factors: discomfort is related to biomechanics and fatigue factors, and comfort to a sense of well-being and aesthetics. In this study a checklist for evaluation of chair comfort and discomfort was analysed in two field studies. In the first study two groups of subjects, ten secretaries and ten managers, evaluated two groups of ten chairs. Subjects assessed each chair three times during a workday using three different types of scales. The results of a factor analysis reconfirmed the factor structure of comfort and discomfort. Analysis of variance demonstrated that discomfort was related to fatigue accumulated during the workday, but it was not related to chair design. There was no significant Chair x Time period interaction, which implies that the rank order of preference among a set of chairs was established during the first assessment and did not change during the day. In a second field study 37 secretaries used three different formats of a Chair Evaluation Checklist with 14 items. The results of a factor analysis again confirmed the factor structure of comfort and discomfort. Analyses of variance demonstrated that subjects can evaluate comfort and discomfort simultaneously without any halo-effect. The results have methodological implications for measurement of comfort and discomfort. The findings for comfort, as defined, carry an important message that aesthetic design matters. This could provide a unifying focus for ergonomists and designers.

Effects of two types of chairs on stature change and comfort for individuals with healthy and herniated discs.

The objective of this study was to determine if stature change and perceived comfort are significantly different for individuals with either healthy or herniated discs when seated in a conventional chair or a sit-stand chair. Sixteen subjects were studied (5 young/healthy, 6 old/healthy, 5 old/herniated). Subjects performed a search task on a computer screen during two 2 h sessions for two consecutive days, with a different chair each day. Changes in stature were measured with a stadiometer. General comfort and body parts discomfort rating scales were administered every 30 min. The main findings were: (1) for all subjects, the sit-stand chair produces less height loss than the conventional chair; and (2) for both chairs, subjects with herniated discs lost more height than subjects with healthy discs. A positive correlation was observed for height loss and age with the sit-stand chair. Subjects with herniated discs felt relatively more uncomfortable in the conventional chair and more comfortable in the sit-stand chair compared to subjects with healthy discs. Both old healthy and young healthy subjects felt more comfortable in the conventional chair in comparison to the sit-stand chair. But, old healthy subjects had a relatively greater perception of comfort in the conventional chair compared with the younger subjects.

Planning and implementation of microscope work.

In modern electronics manufacturing, many of the assembly operations require the use of microscopes. This paper presents measures and suggestions that could help in relieving visual and postural fatigue in microscope work. These measures include the ergonomic design of microscope workstations as well as of microscopes themselves, process changes to minimise use of the microscope, replacement of microscope workstations with television systems, and a training programme for inexperienced operators. The main emphasis in implementing these recommendations was the ergonomic design of microscope workstations; several examples are given.

Effect of work-rest schedules on spinal shrinkage in the sedentary worker.

The relationship between duration and frequency of rest intervals and spinal shrinkage was investigated. The objective was to determine whether the amount of spinal shrinkage can be significantly reduced by rest breaks during which the individual is either walking or standing rather than sitting. Seven subjects were studied during 4-h sessions for four consecutive days. During each session the subject sat and typed for a total of 3 h 20 min. Forty minutes of rest breaks were dispersed throughout the 4-h period. One condition was administered during each day with either eight breaks of 5 min, four breaks of 10 min, two breaks of 20 min or a single break of 40 min at the end of the work session. Using a stadiometer, changes in stature were measured with an accuracy of about 0.2 mm. Measurements were taken at the beginning of each work period and before and after each rest break. For the conditions with rest breaks of 20 or 40 min, there was significantly less shrinkage at the end of the 4-h work session.

An overview of standards and guidelines for visual display terminals.

This paper provides a discussion of several standards and guidelines for design of visual display terminal (VDT) workplaces. The material represents products of government agencies, commercial standards organisations and of labour unions. Seven documents are reviewed: US MIL STD 1472-C, German DIN 66234, British HSE, Swedish ISO Proposal, British APEX, US NYCOSH, and Australian ACTU-VTHC. There is considerable disagreement in the specification of design parameters in these standards. The issues are discussed in terms of their importance and the availability of supporting ergonomics research. There are several types of VDT tasks and the number and variety of applications are growing rapidly. Due to these factors and the development of new display technologies, different recommendations may be appropriate depending upon the task and the technology. Research and careful deliberation will be required to deal with this development.