Looking Outside the Square: The Growth, Structure, and Resilient Two-Dimensional Surface Electron Gas of Square SnO2 Nanotubes.

Nanotechnology has delivered an amazing range of new materials such as nanowires, tubes, ribbons, belts, cages, flowers, and sheets. However, these are usually circular, cylindrical, or hexagonal in nature, while nanostructures with square geometries are comparatively rare. Here, a highly scalable method is reported for producing vertically aligned Sb-doped SnO2 nanotubes with perfectly-square geometries on Au nanoparticle covered m-plane sapphire using mist chemical vapor deposition. Their inclination can be varied using r- and a-plane sapphire, while unaligned square nanotubes of the same high structural quality can be grown on silicon and quartz. X-ray diffraction measurements and transmission electron microscopy show that they adopt the rutile structure growing in the [001] direction with (110) sidewalls, while synchrotron X-ray photoelectron spectroscopy reveals the presence of an unusually strong and thermally resilient 2D surface electron gas. This is created by donor-like states produced by the hydroxylation of the surface and is sustained at temperatures above 400 °C by the formation of in-plane oxygen vacancies. This persistent high surface electron density is expected to prove useful in gas sensing and catalytic applications of these remarkable structures. To illustrate their device potential, square SnO2 nanotube Schottky diodes and field effect transistors with excellent performance characteristics are fabricated.

Correlation between Objective Measures of Sun Exposure and Self-Reported Sun Protective Behavior and Attitudes in Predominantly Hispanic Youth.

Melanoma incidence is increasing, with poor prognosis cases growing faster in California Hispanics than in non-Hispanic whites. Ultraviolet Radiation (UVR) exposure as a child has been found to disproportionately increase the risk of melanoma. To determine correlates of UVR exposure in this high-risk population, we conducted a study in predominately Hispanic 4th and 5th grade classrooms in Los Angeles County, a high UVR environment, during the spring. To address potential reporting bias, electronic UV dosimeters were utilized to objectively measure the association between UVR exposure and constructs (acculturation, sun protective behavior and knowledge, family interventions) obtained on baseline questionnaires (n = 125). Tanning attitude (wanting to get a tan) was associated with lower median time spent outside (1.73 min versus 22.17, AUC 82.08, Sensitivity 0.78, Specificity 0.73) and standard erythemal dose (SED) on weekends, but positively associated with sun protective knowledge. Sun protective knowledge and family discussion of sunscreen were also inversely associated with objectively measured time outside. Students spent a median 30.61 (IQR 19.88) minutes outside per day (SED 0.30, IQR 0.20), with only 35.70% of it occurring in nonschool hours. We determined the majority of UVR exposure in this population occurs at school, providing valuable guidance for future interventions.

Identifying chemical and physical changes in wide-gap semiconductors using real-time and near ambient-pressure XPS.

Photoelectron spectroscopy is a powerful characterisation tool for semiconductor surfaces and interfaces, providing in principle a correlation between the electronic band structure and surface chemistry along with quantitative parameters such as the electron affinity, interface potential, band bending and band offsets. However, measurements are often limited to ultrahigh vacuum and only the top few atomic layers are probed. The technique is seldom applied as an in situ probe of surface processing; information is usually provided before and after processing in a separate environment, leading to a reduction in reproducibility. Advances in instrumentation, in particular electron detection has enabled these limitations to be addressed, for example allowing measurement at near-ambient pressures and the in situ, real-time monitoring of surface processing and interface formation. A further limitation is the influence of the measurement method through irreversible chemical effects such as radiation damage during X-ray exposure and reversible physical effects such as the charging of low conductivity materials. For wide-gap semiconductors such as oxides and carbon-based materials, these effects can be compounded and severe. Here we show how real-time and near-ambient pressure photoelectron spectroscopy can be applied to identify and quantify these effects, using a gold alloy, gallium oxide and semiconducting diamond as examples. A small binding energy change due to thermal expansion is followed in real-time for the alloy while the two semiconductors show larger temperature-induced changes in binding energy that, although superficially similar, are identified as having different and multiple origins, related to surface oxygen bonding, surface band-bending and a room-temperature surface photovoltage. The latter affects the p-type diamond at temperatures up to 400 °C when exposed to X-ray, UV and synchrotron radiation and under UHV and 1 mbar of O2. Real-time monitoring and near-ambient pressure measurement with different excitation sources has been used to identify the mechanisms behind the observed changes in spectral parameters that are different for each of the three materials. Corrected binding energy values aid the completion of the energy band diagrams for these wide-gap semiconductors and provide protocols for surface processing to engineer key surface and interface parameters.

Effect of an interactive educational activity using handheld ultraviolet radiation dosimeters on sun protection knowledge among Australian primary school students.

Ultraviolet radiation (UV) is the main cause of skin cancer, and children are a priority group for reducing UV exposure. We evaluated whether an interactive educational activity using handheld dosimeters improved UV-related knowledge among primary (elementary) school students. We conducted an uncontrolled before-after study among 427 students in grades 3-6 (ages 8-12 years) at five schools in the Greater Sydney region, Australia. Students used UV dosimeters to measure UV exposure, using the UV index scale, at different locations on their school grounds with and without different forms of sun protection, followed by an indoor classroom presentation and discussion. A 10-point anonymous questionnaire was completed by each student before and after the entire session (60-90 min). Before-after responses were compared using a generalised linear mixed model, adjusted for school, grade and gender. Overall, the mean raw scores increased from 6.3 (out of 10) before the intervention to 8.9 after the intervention, and the adjusted difference in scores was 2.6 points (95% confidence interval 2.4-2.8; p < 0.0001). Knowledge improved for all questions, with the greatest improvement for questions related to the UV Index (p < 0.05). The effect of the intervention was similar across different school, grade and gender groups. School and grade had no significant effect on mean survey scores, but girls scored an average 0.2 points higher than boys (95% confidence interval 0.1-0.4; p = 0.01). In conclusion, Australian primary school students had moderate knowledge about UV and sun protection, and knowledge improved significantly after a short interactive educational activity using handheld UV dosimeters.

Influenza virus genotype to phenotype predictions through machine learning: a systematic review.

BACKGROUND: There is great interest in understanding the viral genomic predictors of phenotypic traits that allow influenza A viruses to adapt to or become more virulent in different hosts. Machine learning techniques have demonstrated promise in addressing this critical need for other pathogens because the underlying algorithms are especially well equipped to uncover complex patterns in large datasets and produce generalizable predictions for new data. As the body of research where these techniques are applied for influenza A virus phenotype prediction continues to grow, it is useful to consider the strengths and weaknesses of these approaches to understand what has prevented these models from seeing widespread use by surveillance laboratories and to identify gaps that are underexplored with this technology. METHODS AND RESULTS: We present a systematic review of English literature published through 15 April 2021 of studies employing machine learning methods to generate predictions of influenza A virus phenotypes from genomic or proteomic input. Forty-nine studies were included in this review, spanning the topics of host discrimination, human adaptability, subtype and clade assignment, pandemic lineage assignment, characteristics of infection, and antiviral drug resistance. CONCLUSIONS: Our findings suggest that biases in model design and a dearth of wet laboratory follow-up may explain why these models often go underused. We, therefore, offer guidance to overcome these limitations, aid in improving predictive models of previously studied influenza A virus phenotypes, and extend those models to unexplored phenotypes in the ultimate pursuit of tools to enable the characterization of virus isolates across surveillance laboratories.

Electroreduction of Aryldiazonium Ion at the Polar and Non-Polar Faces of ZnO: Characterisation of the Grafted Films and Their Influence on Near-Surface Band Bending.

ZnO is a strong candidate for transparent electronic devices due to its wide band gap and earth-abundance, yet its practical use is limited by its surface metallicity arising from a surface electron accumulation layer (SEAL). The SEAL forms by hydroxylation of the surface under normal atmospheric conditions, and is present at all crystal faces of ZnO, although with differing hydroxyl structures. Multilayer aryl films grafted from aryldiazonium salts have previously been shown to decrease the downward bending at O-polar ZnO thin films, with Zn-O-C bonds anchoring the aryl films to the substrate. Herein we show that the Zn-polar (0001), O-polar (000 1‾ ), and non-polar m-plane (10 1‾ 0) faces of ZnO single crystals, can also be successfully electrografted with nitrophenyl (NP) films. In all cases, X-ray photoelectron spectroscopy (XPS) measurements reveal that the downward surface band bending decreases after modification. XPS provides strong evidence for Zn-O-C bonding at each face. Electrochemical reduction of NP films on O-polar ZnO single crystals converts the film to a mainly aminophenyl layer, although with negligible further change in band bending. This contrasts with the large upward shifts in band bending caused by X-ray induced reduction.

A Comparison of Solar Ultraviolet Radiation Exposure in Urban Canyons in Venice, Italy and Johannesburg, South Africa.

Urban environments can have high-risk spaces that can provide excess personal sun exposure, such as urban or street canyons, and the spaces between buildings, among others. In these urban spaces, sun exposure can be high or low depending on several factors. Polysulphone film (PSF) was used to assess possible daily solar ultraviolet radiation (UVR) exposure in urban canyons in Venice, Italy and, for the first time in Africa, in Johannesburg, South Africa. The photodegradation of PSF upon solar exposure was monitored at a wavelength of 330 nm by ultraviolet-visible spectrophotometry, and the resultant change was converted to standard erythemal dose (SED) units (1 SED = 100 J m-2 ). Mean daily ambient solar UVR exposure measured for Venice and Johannesburg ranged between 20-28 SED and 33-43 SED, respectively. Canyon-located PSF exposures were lower in Venice (1-9 SED) than those in Johannesburg (9-39 SED), depending mainly on the sky view factor and orientation to the sun. There was large variation in solar UVR exposure levels in different urban canyons. These preliminary results should be bolstered with additional studies for a better understanding of excess personal exposure risk in urban areas, especially in Africa.

Characterization of personal solar ultraviolet radiation exposure using detrended fluctuation analysis.

Studies of personal solar ultraviolet radiation (pUVR) exposure are important to identify populations at-risk of excess and insufficient exposure given the negative and positive health impacts, respectively, of time spent in the sun. Electronic UVR dosimeters measure personal solar UVR exposure at high frequency intervals generating large datasets. Sophisticated methods are needed to analyze these data. Previously, wavelet transform (WT) analysis was applied to high-frequency personal recordings collected by electronic UVR dosimeters. Those findings showed scaling behavior in the datasets that changed from uncorrelated to long-range correlated with increasing duration of time spent in the sun. We hypothesized that the WT slope would be influenced by the duration of time that a person spends in continuum outside. In this study, we address this hypothesis by using an experimental study approach. We aimed to corroborate this hypothesis and to characterize the extent and nature of influence time a person spends outside has on the shape of statistical functions that we used to analyze individual UVR exposure patterns. Detrended fluctuation analysis (DFA) was applied to personal sun exposure data. We analyzed sun exposure recordings from skiers (on snow) and hikers in Europe, golfers in New Zealand and outdoor workers in South Africa. Results confirmed validity of the DFA superposition rule for assessment of pUVR data and showed that pUVR scaling is determined by personal patterns of exposure on lower scales. We also showed that this dominance ends at the range of time scales comparable to the maximal duration of continuous exposure to solar UVR during the day; in this way the superposition rule can be used to quantify behavioral patterns, particularly accurate if it is determined on WT curves. These findings confirm a novel way in which large datasets of personal UVR data may be analyzed to inform messaging regarding safe sun exposure for human health.

The effect of covalently bonded aryl layers on the band bending and electron density of SnO2 surfaces probed by synchrotron X-ray photoelectron spectroscopy.

Tin(iv) dioxide (SnO2) is a technologically important transparent conducting oxide with high chemical stability. In air, the SnO2 surface is terminated with hydroxyl groups which cause the electronic bands to bend downward at the surface capturing a two-dimensional surface electron accumulation layer (SEAL). The SEAL promotes adsorption at the surface, giving environmentally-sensitive electronic properties; this sensitivity is a barrier to some potential applications of the material. This work investigates surface modification of SnO2via reaction with an aryldiazonium salt as a route to controlling the surface band bending. We compare the surface layers formed by reaction at open-circuit potential and under potential control of 4-(trifluoromethyl)benzene diazonium ions with moderately- and highly-doped (101) SnO2 thin films grown by plasma-assisted molecular beam epitaxy. Atomic force microscopy and synchrotron X-ray photoelectron spectroscopy (XPS) measurements demonstrate that both reaction conditions lead to covalently-attached 4-(trifluoromethyl)phenyl groups, with grafting at open-circuit potential giving thinner layers (<2 nm) and fewer direct bonds to the surface than electrografting (layer thickness >3 nm). Valence band investigations show that for all samples the 4-(trifluoromethyl)phenyl layers decrease the surface downward band bending with the greatest effect observed for the electrografted sample. In the latter case, a +0.29 eV shift in band bending relative to that of the unmodified material indicates the success in turning the surface electron accumulation layer into a depletion layer.

Prevalence of sun protection behaviors in Hispanic youth residing in a high ultraviolet light environment.

Although rates of late-stage melanoma are rising in Hispanics, particularly those living in high ultraviolet light environments, little is known about the prevalence of sun protective behaviors in Hispanic children. We analyzed baseline data including frequency of sunburn, sun protective behaviors, level of U.S. acculturation, and skin phototype from a cross-sectional survey of 2003 Hispanic elementary school children in Los Angeles, California, who participated in a skin cancer prevention intervention. Although the Hispanic children reported frequently engaging in some sun protective behaviors, they also had a high rate of sunburn (59%) that exceeded previous national estimates for non-Hispanic white children (43%). Fewer U.S.-acculturated children reported more frequent shade-seeking at home (P = .02), along with less shade-seeking at school (P = .001) and more sunscreen use at school (P = .02). The surprisingly high rate of sunburn in Hispanic children suggests that the way in which they are practicing sun protection is not preventing sunburns. Sun safety interventions should be targeted toward Hispanic youth to provide them with practical methods of effective sun protection, in addition to education on the risks of high sun exposure.

Surface sensitivity of four-probe STM resistivity measurements of bulk ZnO correlated to XPS.

Multi-probe instruments based on scanning tunnelling microscopy (STM) are becoming increasingly common for their ability to perform nano- to atomic-scale investigations of nanostructures, surfaces and in situ reactions. A common configuration is the four-probe STM often coupled with in situ scanning electron microscopy (SEM) that allows precise positioning of the probes onto surfaces and nanostructures enabling electrical and scanning experiments to be performed on highly localised regions of the sample. In this paper, we assess the sensitivity of four-probe STM for in-line resistivity measurements of the bulk ZnO surface. The measurements allow comparisons to established models that are used to relate light plasma treatments (O and H) of the surfaces to the resistivity measurements. The results are correlated to x-ray photoelectron spectroscopy (XPS) and show that four-probe STM can detect changes in surface and bulk conduction mechanisms that are beyond conventional monochromatic XPS.

Sun exposure and 25-hydroxyvitamin D3 levels in a community sample: Quantifying the association with electronic dosimeters.

There is uncertainty about the amount of sun exposure required to increase low blood 25-hydroxyvitamin D (25(OH)D3) levels, a possible disease risk factor. The study aimed to quantify the association between sun exposure and serum 25(OH)D3 concentrations in a multiethnic community sample (n=502) living in Auckland (37°S) and Dunedin (46°S), New Zealand, aged 18-85 years. They wore electronic ultraviolet dosimeters between March and November (autumn, winter and spring) for 8 weeks to record their sun exposure. This was converted to standard erythemal doses (SEDs), corrected for clothing to generate equivalent full-body exposures, SEDEFB. Blood samples were collected at the end of weeks 4 and 8 to measure 25(OH)D3. Median weekly SEDEFB was 0.33 during weeks 1-4 and 0.34 during weeks 5-8. Weekly exposures <0.5 SEDEFB during weeks 5-8 were associated with decreasing 25(OH)D3 concentrations at the end of week 8. There was a non-linear association between sun exposure and 25(OH)D3, with most of the increase in 25(OH)D3 being at exposures <2 SEDEFB per week. This finding suggests that vitamin D status is increased by regular small sun exposures (<2 SEDEFB per week), and that greater exposures result in only small additional increases in 25(OH)D3.

Correlates of sun protection behaviors among Hispanic children residing in a high UVR environment.

BACKGROUND/PURPOSE: Rates of melanoma are rising in Hispanics in the United States. Excessive sun exposure in childhood increases the risk of melanoma in adulthood, and little is known about the factors motivating sun protection behaviors among Hispanic youth. METHODS: Correlates of sun protection were examined among Hispanic children residing in Los Angeles, California (N = 1891). Associations between multiple constructs (psychosocial, familial, and cultural) and sun protection outcomes (use of sunscreen, protective clothing, and shade seeking/sun avoidance) were examined. RESULTS: Family variables were associated with more frequent sun protection among Hispanic children across outcomes, as were perceived peer norms, perceived self-efficacy, and fewer sun protection barriers. Skin cancer risk factors such as lighter skin and sunburn experience, and level of acculturation were not associated with greater sun protection. CONCLUSION: Family sun protection habits are instrumental to Hispanic children's sun safe behaviors, and interventions that engage the family may be most effective. Increasing risk communication to high-risk subgroups of Hispanic children (those with lighter, more sun reactive skin) is important when developing intervention strategies. However, there is overlap between Hispanic children's sun protection correlates and those observed among non-Hispanic white children, suggesting that interventions to improve sun protection may generalize across cultural contexts.

Tuning the Band Bending and Controlling the Surface Reactivity at Polar and Nonpolar Surfaces of ZnO through Phosphonic Acid Binding.

ZnO is a prime candidate for future use in transparent electronics; however, development of practical materials requires attention to factors including control of its unusual surface band bending and surface reactivity. In this work, we have modified the O-polar (0001̅), Zn-polar (0001), and m-plane (101̅0) surfaces of ZnO with phosphonic acid (PA) derivatives and measured the effect on the surface band bending and surface sensitivity to atmospheric oxygen. Core level and valence band synchrotron X-ray photoemission spectroscopy was used to measure the surface band bending introduced by PA modifiers with substituents of opposite polarity dipole moment: octadecylphosphonic acid (ODPA) and 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctylphosphonic acid (F13OPA). Both PAs act as surface electron donors, increasing the downward band bending and the strength of the two-dimensional surface electron accumulation layer on all of the ZnO surfaces investigated. On the O-polar (0001̅) and m-plane (101̅0) surfaces, the ODPA modifier produced the largest increase in downward band bending relative to the hydroxyl-terminated unmodified surface of 0.55 and 0.35 eV, respectively. On the Zn-polar (0001) face, the F13OPA modifier gave the largest increase (by 0.50 eV) producing a total downward band bending of 1.00 eV, representing ∼30% of the ZnO band gap. Ultraviolet (UV) photoinduced surface wettability and photoconductivity measurements demonstrated that the PA modifiers are effective at decreasing the sensitivity of the surface toward atmospheric oxygen. Modification with PA derivatives produced a large increase in the persistence of UV-induced photoconductivity and a large reduction in UV-induced changes in surface wettability.

Novel approach to analysing large data sets of personal sun exposure measurements.

Personal sun exposure measurements provide important information to guide the development of sun awareness and disease prevention campaigns. We assess the scaling properties of personal ultraviolet radiation (pUVR) sun exposure measurements using the wavelet transform (WT) spectral analysis to process long-range, high-frequency personal recordings collected by electronic UVR dosimeters designed to measure erythemal UVR exposure. We analysed the sun exposure recordings of school children, farmers, marathon runners and outdoor workers in South Africa, and construction workers and work site supervisors in New Zealand. We found scaling behaviour in all the analysed pUVR data sets. We found that the observed scaling changes from uncorrelated to long-range correlated with increasing duration of sun exposure. Peaks in the WT spectra that we found suggest the existence of characteristic times in sun exposure behaviour that were to some extent universal across our data set. Our study also showed that WT measures enable group classification, as well as distinction between individual UVR exposures, otherwise unattainable by conventional statistical methods.

Patterns of sun protective behaviors among Hispanic children in a skin cancer prevention intervention.

BACKGROUND: Invasive melanoma is becoming more common in U.S. Hispanics, yet little is known about the sun protection behaviors in this population, particularly children and adolescents who incur high ultraviolet (UV) exposures. METHODS: We used latent class analysis to examine patterns of sun protective behaviors in a cross-sectional survey of Hispanic elementary students participating in a sun safety intervention in Los Angeles from 2013- to 2014 (N=972). Five behavior indicators in two environments (school and home) representing multiple methods of sun protection were selected for the model. RESULTS: Results suggested a four-class model best fit the data. Classes were labeled in order of increasing risk as multiple protective behaviors (28%), clothing and shade (32%), pants only (15%), and low/inconsistent protective behaviors (25%). Children who reported high parental engagement with sun protection were significantly more likely to be classified in high overall protective categories (odds ratio (OR)=4.77). Girls were more likely than boys to be classified in the highest protecting class (OR=3.46), but were also more likely to be in the "pants only" class (OR=2.65). Sensitivity to sunburn was associated with less likelihood of being in the "clothing and shade" class (OR=0.53). CONCLUSION: The differences among these classes and their predictors reveal the heterogeneity and complexity of Hispanic children's sun protective behaviors. These findings have implications for the design and delivery of future sun protection interventions targeting Hispanic children, as strategies tailored to specific subgroups may be more effective in achieving meaningful behavioral changes.

Small doses from artificial UV sources elucidate the photo-production of vitamin D.

To clarify the relation between UV exposure and vitamin D status, 201 volunteers wore personal electronic UV dosimeters during daylight hours, to record their UV exposure over a 10 week period when ambient UV levels were significantly less than the summer maxima. Blood samples to determine serum 25-hydroxyvitamin D3 [25(OH)D3] levels were taken at the end of week 4 and week 8. Participants were then given a single full-body exposure of approximately 2 SED from one of four artificial UV sources with different spectral outputs and a further blood sample taken at study completion, nominally week 10. The artificial UV exposure reversed the mean seasonal decline in 25(OH)D3. Increases in 25(OH)D3 from week 8 to week 10 were related to total UV exposure, including the ambient sun exposures. These exposures were weighted by the erythemal action spectrum and separately for three different action spectra for pre-vitamin D production. For the erythema weighting function, 25(OH)D3 increased 1.78 ± 0.25 nmol per litre per SED, a value consistent with other studies. Any differences due to age, BMI, gender, and skin reflectance were not statistically significant. Ethnicity differences were the only significant factor, with Asians producing the least vitamin D, and Maori the most. There was no statistically significant improvement in consistency between sources for any of the three pre-vitamin weightings compared with that for erythema. Further work is needed to verify which vitamin D action spectrum is most appropriate. Nevertheless, these small doses of UV from artificial sources were helpful in quantifying the relationship between UV exposure and vitamin D status among the New Zealand population.

Validation of brief questionnaire measures of sun exposure and skin pigmentation against detailed and objective measures including vitamin D status.

Self-reported sun exposure is commonly used in research, but how well this represents actual sun exposure is poorly understood. From February to July 2011, a volunteer sample (n = 47) of older adults (≥45 years) in Canberra, Australia, answered brief questions on time outdoors (weekdays and weekends) and natural skin color. They subsequently maintained a sun diary and wore an ultraviolet radiation (UVR) digital dosimeter for 7 days. Melanin density was estimated using reflectance spectrophotometry; lifetime sun damage was assessed using silicone casts of the back of the hand; and serum 25-hydroxyvitamin D (25(OH)D) concentration was assayed. Questionnaire-reported time outdoors correlated significantly with diary-recorded time outdoors (Spearman correlation r(s) = 0.66; 95% CI 0.46, 0.80; P < 0.001) and UVR dosimeter dose (r(s ) = 0.46; 95% CI 0.18, 0.68; P = 0.003), but not 25(OH)D concentration (r(s) = 0.24; 95% CI -0.05, 0.50; P = 0.10). Questionnaire-reported untanned skin color correlated significantly with measured melanin density at the inner upper arm (r(s) = 0.49; 95% CI 0.24, 0.68; P < 0.001). In a multiple linear regression model, statistically significant predictors of 25(OH)D concentration were self-reported frequency of physical activity, skin color and recent osteoporosis treatment (R(2) = 0.54). In this study, brief questionnaire items provided valid rankings of sun exposure and skin color, and enabled the development of a predictive model for 25(OH)D concentration.

The presence of a (1 × 1) oxygen overlayer on ZnO(0001) surfaces and at Schottky interfaces.

The atomic surface and interface structures of uncoated and metal-coated epi-polished ZnO(0001) Zn-polar wafers were investigated via surface x-ray diffraction. All uncoated samples showed the presence of a fully occupied (1 × 1) overlayer of oxygen atoms located at the on-top position above the terminating Zn atom, a structure predicted to be unstable by several density functional theory calculations. The same oxygen overlayer was clearly seen at the interface of ZnO with both elemental and oxidized metal Schottky contact layers. No significant atomic relaxations were observed at surfaces and interfaces processed under typical device fabrication conditions.

A critical assessment of two types of personal UV dosimeters.

Doses of erythemally weighted irradiances derived from polysulphone (PS) and electronic ultraviolet (EUV) dosimeters have been compared with measurements obtained using a reference spectroradiometer. PS dosimeters showed mean absolute deviations of 26% with a maximum deviation of 44%, the calibrated EUV dosimeters showed mean absolute deviations of 15% (maximum 33%) around noon during several test days in the northern hemisphere autumn. In the case of EUV dosimeters, measurements with various cut-off filters showed that part of the deviation from the CIE erythema action spectrum was due to a small, but significant sensitivity to visible radiation that varies between devices and which may be avoided by careful preselection. Usually the method of calibrating UV sensors by direct comparison to a reference instrument leads to reliable results. However, in some circumstances the quality of measurements made with simple sensors may be over-estimated. In the extreme case, a simple pyranometer can be used as a UV instrument, providing acceptable results for cloudless skies, but very poor results under cloudy conditions. It is concluded that while UV dosimeters are useful for their design purpose, namely to estimate personal UV exposures, they should not be regarded as an inexpensive replacement for meteorological grade instruments.