Interface Engineering of TiO2 Photoelectrode Coatings Grown by Atomic Layer Deposition on Silicon

Titanium dioxide (TiO2) can protect photoelectrochemical (PEC) devices from corrosion, but the fabrication of high-quality TiO2 coatings providing long-term stability has remained challenging. Here, we compare the influence of Si wafer cleaning and postdeposition annealing temperature on the performance of TiO2/n+-Si photoanodes grown by atomic layer deposition (ALD) using tetrakis(dimethylamido)titanium (TDMAT) and H2O as precursors at a growth temperature of 100 °C. We show that removal of native Si oxide before ALD does not improve the TiO2 coating performance under alkaline PEC water splitting conditions if excessive postdeposition annealing is needed to induce crystallization. The as-deposited TiO2 coatings were amorphous and subject to photocorrosion. However, the TiO2 coatings were found to be stable over a time period of 10 h after heat treatment at 400 °C that induced crystallization of amorphous TiO2 into anatase TiO2. No interfacial Si oxide formed during the ALD growth, but during the heat treatment, the thickness of interfacial Si oxide increased to 1.8 nm for all of the samples. Increasing the ALD growth temperature to 150 °C enabled crystallization at 300 °C, which resulted in reduced growth of interfacial Si oxide followed by a 70 mV improvement in the photocurrent onset potential.

GaAs surface passivation for InAs/GaAs quantum dot based nanophotonic devices

Several passivation techniques are developed and compared in terms of their ability to preserve the optical properties of close-to-surface InAs/GaAs quantum dots (QDs). In particular, the influence of N-passivation by hydrazine chemical treatment, N-passivation by hydrazine followed by atomic layer deposition (ALD) of AlO _x and use of AlN _x deposited by plasma-enhanced ALD are reported. The effectiveness of the passivation is benchmarked by measuring the emission linewidths and decay rates of photo-carriers for the near-surface QDs. All three passivation mechanisms resulted in reducing the oxidation of Ga and As atoms at the GaAs surface and consequently in enhancing the room-temperature photoluminescence (PL) intensity. However, long-term stability of the passivation effect is exhibited only by the hydrazine + AlO _x process and more significantly by the AlN _x method. Moreover, in contrast to the results obtained from hydrazine-based methods, the AlN _x passivation strongly reduces the spectral diffusion of the QD exciton lines caused by charge fluctuations at the GaAs surface. The AlN _x passivation is found to reduce the surface recombination velocity by three orders of magnitude (corresponding to an increase of room-temperature PL signal by ∼1030 times). The reduction of surface recombination velocity is demonstrated on surface-sensitive GaAs (100) and the passivating effect is stable for more than one year. This effective method of passivation, coupled with its stability in time, is extremely promising for practical device applications such as quantum light sources based on InAs/GaAs QDs positioned in small-volume photonic cavities and hence in the proximity of GaAs-air interface.

Diversity of TiO2: Controlling the Molecular and Electronic Structure of Atomic-Layer-Deposited Black TiO2

Visually black, electrically leaky, amorphous titania (am-TiO₂) thin films were grown by atomic layer deposition (ALD) for photocatalytic applications. Broad spectral absorbance in the visible range and exceptional conductivity are attributed to trapped Ti³⁺ in the film. Oxidation of Ti³⁺ upon heat treatment leads to a drop in conductivity, a color change from black to white, and crystallization of am-TiO₂. ALD-grown black TiO₂, without any heat treatment, is subject to dissolution in alkaline photoelectrochemical conditions. The best photocatalytic activity for solar water splitting is obtained for completely crystalline white TiO₂.

Improved Stability of Atomic Layer Deposited Amorphous TiO2 Photoelectrode Coatings by Thermally Induced Oxygen Defects

Amorphous titanium dioxide (a-TiO₂) combined with an electrocatalyst has shown to be a promising coating for stabilizing traditional semiconductor materials used in artificial photosynthesis for efficient photoelectrochemical solar-to-fuel energy conversion. In this study we report a detailed analysis of two methods of modifying an undoped thin film of atomic layer deposited (ALD) a-TiO₂ without an electrocatalyst to affect its performance in water splitting reaction as a protective photoelectrode coating. The methods are high-temperature annealing in ultrahigh vacuum and atomic hydrogen exposure. A key feature in both methods is that they preserve the amorphous structure of the film. Special attention is paid to the changes in the molecular and electronic structure of a-TiO₂ induced by these treatments. On the basis of the photoelectrochemical results, the a-TiO₂ is susceptible to photocorrosion but significant improvement in stability is achieved after heat treatment in vacuum at temperatures above 500 °C. On the other hand, the hydrogen treatment does not increase the stability despite the ostensibly similar reduction of a-TiO₂. The surface analysis allows us to interpret the improved stability to the thermally induced formation of O^- species within a-TiO₂ that are essentially electronic defects in the anionic framework.

Tailored Fabrication of Transferable and Hollow Weblike Titanium Dioxide Structures

The preparation of weblike titanium dioxide thin films by atomic layer deposition on cellulose biotemplates is reported. The method produces a TiO₂ web, which is flexible and transferable from the deposition substrate to that of the end application. Removal of the cellulose template by calcination converts the amorphous titania to crystalline anatase and gives the structure a hollow morphology. The TiO₂ webs are thoroughly characterized using electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy to give new insight into manufacturing of porous titanium dioxide structures by means of template-based methods. Functionality and integrity of the TiO₂ hollow weblike thin films were successfully confirmed by applying them as electrodes in dye-sensitized solar cells.

Color Bricks: Building Highly Organized and Strongly Absorbing Multicomponent Arrays of Terpyridyl Perylenes on Metal Oxide Surfaces

Terpyridine-substituted perylenes containing cyclic anhydrides in the peri position were synthesized. The anhydride group served as an anchor for assembly of the terpyridyl-crowned chromophores as monomolecular layers on metal oxide surfaces. Further coordination with Zn(2+) ions allowed for layer-by-layer formation of supramolecular assemblies of perylene imides on the solid substrates. With properly selected anchor and linker molecules it was possible to build high quality structures of greater than ten successive layers by a simple and straightforward procedure. The prepared films were stable and had a broad spectral coverage and high absorbance. To demonstrate their potential use, the synthesized dyes were employed in solid-state dye-sensitized solar cells, and electron injection from the perylene antennas to titanium dioxide was observed.

Intersubject consistency of cortical MEG signals during movie viewing

According to recent functional magnetic resonance imaging (fMRI) studies, spectators of a movie may share similar spatiotemporal patterns of brain activity. We aimed to extend these findings of intersubject correlation to temporally accurate single-trial magnetoencephalography (MEG). A silent 15-min black-and-white movie was shown to eight subjects twice. We adopted a spatial filtering model and estimated its parameter values by using multi-set canonical correlation analysis (M-CCA) so that the intersubject correlation was maximized. The procedure resulted in multiple (mutually uncorrelated) time-courses with statistically significant intersubject correlations at frequencies below 10 Hz; the maximum correlation was 0.28 ± 0.075 in the ≤1 Hz band. Moreover, the 24-Hz frame rate elicited steady-state responses with statistically significant intersubject correlations up to 0.29 ± 0.12. To assess the brain origin of the across-subjects correlated signals, the time-courses were correlated with minimum-norm source current estimates (MNEs) projected to the cortex. The time series implied across-subjects synchronous activity in the early visual, posterior and inferior parietal, lateral temporo-occipital, and motor cortices, and in the superior temporal sulcus (STS) bilaterally. These findings demonstrate the capability of the proposed methodology to uncover cortical MEG signatures from single-trial signals that are consistent across spectators of a movie.

Understanding and coping with the new HCFA physician incentives stop-loss insurance rules

The imposition of physician incentive regulations by the Health Care Financing Administration for Medicare risk and Medicaid managed care contracts has created disclosure and stop-loss reinsurance issues for both physician groups and their contracting health maintenance organizations. This article summarizes the key points of the stop-loss requirements of the new rules, describes the current types of stop-loss reinsurance purchased prior to the effective date of the regulations, and the practical problems of conforming current physician group contracting practices to these rules. The article also provides several suggested steps that physician groups should take to manage the changes required.

Successful training strategies to implement a workplace hazardous materials information system. An evaluation study at 80 plants

According to recent regulations, Canadian companies must establish a Workplace Hazardous Materials Information System (WHMIS). Employee training is an essential facet of the system. The study looked at various training strategies and evaluated employees' comprehension about WHMIS and the quality of the WHMIS system at 80 manufacturing plants in the province of Québec in Canada. Comprehension was best when external experts trained all employees. It was lower when internal instructors were trained to teach WHMIS to other employees of the plant. Other components of WHMIS, such as labels and material safety data sheets, were of better quality in the plants having opted for training internal instructors. WHMIS was better in the plants that were initially good in occupational health and safety than in the marginal plants.

Efficacy of training procedures in implementing a legislated safety programme

This study examines the effect of training procedures, as measured by the results of a test, on the level of assimilation of a new safety programme in 80 Quebec companies. The Workplace Hazardous Materials Information System (WHMIS) was introduced in the province in 1989. The bipartite safety association representing the manufacturers of transportation equipment and machinery offered two types of WHMIS training services to their members: (a) 4 h employee training courses, and (b) two-day trainer training courses. Companies were free to choose from these and other services to comply with the WHMIS training requirements. A test was issued to a stratified sample of 862 employees approximately one year after the training. On average, the scores were best in plants having employees trained directly by experts from the safety association (type a). The training of internal trainers for companies produced slightly inferior learning results (type b).

Organizational factors influencing serious occupational accidents

The aim of this article is to examine organizational factors influencing serious occupational accidents. The study was part of a larger project investigating 99 serious occupational accidents in southern Finland. A workplace analysis and an accident analysis were done at accident sites. In connection with this investigation, 73 victims, 91 foremen, and 83 co-workers were interviewed with a structured questionnaire. The results showed that the need to save time, tight schedules, and a lack of caution had a greater influence on accidents than did the foremen, co-workers, customers, professional pride, curiosity, or the wage system. Big companies had the lowest risk of serious occupational accidents. Accident risk was significantly greater for subcontractors than for main contractors.

Food preferences in human obesity: carbohydrates versus fats

A large clinical sample of obese men and women were asked for a self-generated list of ten favorite foods. The lists were characterized by frequent instances of foods that are major nutrient sources of fat in the American diet. While obese men listed mainly protein/fat sources (meat dishes) among their favorite foods, obese women tended to list predominantly carbohydrate/fat sources (doughnuts, cookies, cake) and foods that were sweet. There was no evidence that selective preferences for a single macronutrient, carbohydrate, were a standard feature of human obesity. Rather, preferences for major nutrient sources of fat as opposed to carbohydrate may be a primary characteristic of human obesity syndromes.

Long-term development of occupational accidents in Finland

In Finland the number of occupational accidents has been increasing throughout the 1900s. This increasing long-term development is related to the improved insurance coverage of workers. The severity of accidents has decreased during the past three decades. Accident curves show variations related to fluctuations in the national economy. The occurrence of accidents seems to be very sensitive to economic determinants. The structural changes of work brought about by automation should lead to a decrease in the occurrence of accidents. With the exception of economic factors and structural changes in the labor force, no signs of any major decrease in the occurrence of accidents have been detected.

Load on back in concrete reinforcement work

The demands of work on the back of concrete reinforcement workers was determined through 4,327 observations of the various work postures and the weights lifted. Static loads from forward-leaning and bent-double postures were found to be common. In the preparation of intermediate and thick rods, forward-leaning was required for more than a third of the total work time, while one central assembly task required work in the bent-double posture for 58% of the total work time. The dynamic loads were of less importance, even though weights over 30 kg were lifted about 15% of the time in the preparation tasks and momentary forces approaching 1,000 N were occasionally needed. The bent-double posture, combined with or quickly followed by additional strain from, for example, weight lifting or slipping, was considered the most probable cause for possible signs of accelerated lumbar disc degeneration, while also the forward-leaning postures could be responsible for reversible low-back symptoms.