Comparison of etch characteristics of KOH, TMAH and EDP for bulk micromachining of silicon (110)

Bulk micromachining in Si (110) wafer is an essential process for fabricating vertical microstructures by wet chemical etching. We compared the anisotropic etching properties of potassium hydroxide (KOH), tetra-methyl ammonium hydroxide (TMAH) and ethylene di-amine pyro-catechol (EDP) solutions. A series of etching experiments have been carried out using different etchant concentration and temperatures. Etching at elevated temperatures was found to improve the surface quality as well as shorten the etching time in all the etchants. At 120°C, we get a smooth surface (Ra?=?21.2?nm) with an etching rate 12.2???m/min in 40wt% KOH solution. At 125°C, EDP solution (88wt%) was found to produce smoothest surface (Ra?=?9.4?nm) with an etch rate of 1.8???m/min. In TMAH solution (25wt%), the best surface roughness was found to be 35.6?nm (Ra) at 90°C with an etch rate of 1.18???m/min. The activation energy and pre-exponential factor in Arrhenius relation are also estimated from the corresponding etch rate data.     

Direct bonding of PFTF sheets assisted by shynchrotron radiation induced surface modification

Characteristics of the microfabrication and modification of polytetrafluoroethylene (PTFE) using X-ray photo decomposition desorption and ablation are studied in the highest energy region (2 keV to over 12 keV). We have discussed that the PTFE polymer takes liquid state due to irradiation of high-energy photons with high-penetration depth, and this leads to the dominant decomposition, photo-induced ablation of PTFE and following generation of the volatile fragments including PTFE polymer itself. Furthermore, we found that melting point of the surface bulk layer of PTFE drastically decreased due to the irradiation of SR. The result of the differential thermal analysis of the SR-irradiated PTFE sheet shows the decay of the weight of PTFE sheet induced by thermal desorption starts at 155°C. This suggests that the apparent melting point of PTFE of which surface is modified by SR irradiation decreases drastically from original melting point. We finally successfully demonstrated that the two PTFE sheets could be bonded directly at low temperature less than 200°C without bonding reagent.     

Comparison of etch characteristics of KOH,TMAH and EDP for bulk micromachining of silicon (110)

Bulk micromachining in Si (110) wafer is an essential process for fabricating vertical microstructures by wet chemical etching. We compared the anisotropic etching properties of potassium hydroxide (KOH), tetra-methyl ammonium hydroxide (TMAH) and ethylene di-amine pyro-catechol (EDP) solutions. A series of etching experiments have been carried out using different etchant concentration and temperatures. Etching at elevated temperatures was found to improve the surface quality as well as shorten the etching time in all the etchants. At 120°C, we get a smooth surface (Ra = 21.2 nm) with an etching rate 12.2 μm/min in 40wt% KOH solution. At 125°C, EDP solution (88wt%) was found to produce smoothest surface (Ra = 9.4 nm) with an etch rate of 1.8 μm/min. In TMAH solution (25wt%), the best surface roughness was found to be 35.6 nm (Ra) at 90°C with an etch rate of 1.18 μm/min. The activation energy and pre-exponential factor in Arrhenius relation are also estimated from the corresponding etch rate data.

     

Measured Emissivity of Soils in the Southeast United States

The thermal emissivities of exposed soil surfaces for the major soil subgroups of Alabama, Georgia, and Florida were determined. It was found that brightness temperature sensed by narrow-band infrared radiometers (10.4–12.6 μm), as used on SMS-GOES spacecraft would not deviate from thermodynamic temperatures by more than -2°C as a result of surface emissivity. Emissivity effects on the brightness temperature determined with broad-band radiometers (5–15 μm), however, could be as great as -6°C.     

A microfluidic gel valve device using reversible sol–gel transition of methyl cellulose for biomedical application

We have fabricated a microfluidic gel valve device that used reversible sol–gel transition of methyl cellulose (MC). A microheater and a microtemperature sensor were implemented in each microchannel in the gel valve device. Before evaluating the performance of the gel valve device, various properties of the MC solution were investigated using viscometer, spectrophotometer, and NMR. Gelation temperature was increased as the MC concentration was increased. Clear gel, an intermediate state between clear sol and turbid gel, was found at the temperature range from 30–40°C to 50–60°C. Temperature at each microchannel of the device was measured and the effect of the temperature difference on the valve operation was elucidated. In order to have normal operation of the gel valve, it was important to keep the temperature of the heated microchannel around 60°C while keeping the temperature of the flowing microchannel below 35°C. The temperature difference between two microchannels was about 23 K when fan forced cooling (FFC) method was used. For normal performance of the gel valve device, a temporary pause of fluid flow for at least 5 s was required to complete the local gelation in the microchannel. Stable gel valve performance was obtained at the flow rates larger than 5 μl/min. The gel valve device showed no leakage up to 2.07×10⁴ Pa.     

Intercomparison of methods for estimating land surface temperature from a Landsat-5 TM image in an arid region with low water vapour in the atmosphere

This study compares the methods for retrieving the land surface temperature (LST) (T _s) from Landsat-5 TM (Thematic Mapper) data, including the radiative transfer equation (RTE) method, the mono-window algorithm (MWA) and the generalized single-channel (GSC) method in an arid region with low atmospheric water vapour content. In addition, T _s calculated without atmospheric correction of TM band 6 is also assessed. The intercomparison is divided into two parts. The first part is applying the methods at the Biandukou site (100° 58′ E, 38° 16′ N, elevation?=?2690 m) and the second part is applying them at Binggou (100° 13′ E, 38° 42′ N, elevation?=?3400 m) and Arou (100° 27′ E, 38° 36′ N, elevation?=?2960 m) sites. Results demonstrate that these methods provide acceptable accuracies at the Biandukou site. At this site, GSC generates nearly the same accuracy as RTE; MWA estimations are slightly less accurate than RTE and GSC; estimations without atmospheric correction of TM band 6 exhibit the largest errors. On the other hand, MWA is a good choice for retrieving the LST at Binggou and Arou sites. In cases where the meteorological parameters are unavailable, it is an alternative option to calculate T _s directly from TM band 6 image without atmospheric correction at these two sites.     

Multitemporal analysis of land surface temperature using NOAA-AVHRR: preliminary relationships between climatic anomalies and forest fires

Advanced Very High Resolution Radiometer (AVHRR) National Oceanic and Atmospheric Administration (NOAA)-14 imagery was used to analyse changes in land surface temperature in an area of Central Mexico during the course of each dry season (November–April) for the period 1996–2000. Daily surface temperature was obtained by the split-window method and cloud-free monthly composites were subsequently built. This value was related to maximum air temperatures recorded at meteorological stations and to forest fires detected from night-time images. During 1996–1997 and 1997–1998 (El Niño) dry seasons, monthly surface temperature ranged from 35°C to 46°C and from 33°C to 51°C, respectively; during 1998–1999 (La Niña) and 1999–2000 it was lower, ranging from 28°C to 47°C, and from 28°C to 41°C, respectively. At the end of El Niño, land surface temperatures higher than 50°C were registered, and 730 forest fires were detected, suggesting that this temperature increment also contributed to the vulnerability of vegetation to fire. It is concluded that land surface temperature during the first four months of the dry season can be used as a variable for modelling the probability of forest fire occurrence, in combination with other environmental variables. Similarities between land surface temperature and maximum air temperature suggest the potential use of NOAA-AVHRR imagery for evaluating El Niño/La Niña effects on the continental surface.     

Annealing temperature effect on structural,optical, morphological and electrical properties of CdS/Si(100) nanostructures

CdS nanostructures have grown on p-type silicon (Si) (100) substrates using sol–gel method. The crystalline quality, surface morphology, optical and electrical properties of the deposited CdS nanostructures have been characterized and analyzed using atomic force microscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, differential thermal analysis, UV–vis spectroscopy and electrical characterization, respectively. The effect of annealing temperature in the range 200–600 °C on the structural, morphological, optical and electrical properties has been elaborated. The XRD analysis shows that the crystalline quality can be improved by increasing the temperature to 400 °C, but further increase to 600 °C leads to degradation of crystalline quality. The bulk modulus is calculated and showed good agreement with experimental and theoretical results. The optical properties of absorption, reflection, energy band gap and extinction coefficient are obtained by UV–vis spectroscopy. The calculated refractive index and optical dielectric constant have shown good agreement with other results. The electrical and thermal properties are studied for antireflection coating applications.     

Trimming implicit surfaces

Algorithms for trimming implicit surfaces yielding surface sheets and stripes are presented. These two-dimensional manifolds with boundaries result from set-theoretic operations on an implicit surface and a solid or another implicit surface. The algorithms generate adaptive polygonal approximation of the trimmed surfaces by extending our original implicit surface polygonization algorithm. The presented applications include modeling several spiral shaped surface sheets and stripes (based on M. Eschers artworks) and extraction of ridges on implicit surfaces. Another promising application of the presented algorithms is modeling heterogeneous objects as implicit complexes.     

Effects of ITO film annealing temperature on hybrid solar cell performance

The effects of indium tin oxide (ITO) film annealing temperature on the performance of organic solar cells are investigated. The roughness of the ITO film surface morphology increased with increasing annealing temperature. The optical penetration and rate of exciton generation both increased with increasing ITO film annealing temperature, enhancing the short-circuit current density. The maximum efficiency (2.62 %) was obtained with an annealing temperature of about 500 °C. The incident-photon-to-current efficiency value for a hybrid photovoltaic device with an ITO film annealed temperature at 500 °C was 45 % at 475 nm.     

A comparison of surface temperature derived from HCMM infrared measurements with field data

HCMM surface temperatures were compared to field data obtained in the Mississippi River in the vicinity of St. Louis, Missouri, and in the oceans in the vicinity of the Nantucket Shoals and in the eastern Gulf of Mexico. It was found that, on the average, the difference between the HCMM surface temperature corrected for atmospheric attenuation and the in situ temperature at the same location was ?4.6°C. Previous calibration results (Barnes and Price, 1980) indicated that the difference was +5.2°C. That calibration study used data collected in the first few months after HCMM was launched, suggesting that there was a calibration problem at that time. As a result of that study, the HCMM data were adjusted so that they were 5.2°C lower. The results of this study, which used data collected after 1 June 1978, suggest that the adjustment was no longer necessary and that 5.2°C must now be added to the HCMM surface temperatures to obtain the correct value. Calibrated and atmospherically corrected HCMM surface temperature data were compared with the ocean surface data. Fifty-seven data pairs were compared over the temperature range from 10°C to 25°C. The RMSD was ±1.0°C, and the linear correlation coefficient was 0.97.     

Reducing heat stress under thermal insulation in protective clothing: microclimate cooling by a ‘physiological’ method

Heat stress caused by protective clothing limits work time. Performance improvement of a microclimate cooling method that enhances evaporative and to a minor extent convective heat loss was tested. Ten male volunteers in protective overalls completed a work-rest schedule (130 min; treadmill: 3 × 30 min, 3 km/h, 5% incline) with or without an additional air-diffusing garment (climatic chamber: 25°C, 50% RH, 0.2 m/s wind). Heat loss was supported by ventilating the garment with dry air (600 l/min, ?5% RH, 25°C). Ventilation leads (M ± SD, n = 10, ventilated vs. non-ventilated) to substantial strain reduction (max. HR: 123 ± 12 b/min vs. 149 ± 24 b/min) by thermal relief (max. core temperature: 37.8 ± 0.3°C vs. 38.4 ± 0.4°C, max. mean skin temperature: 34.7 ± 0.8°C vs. 37.1 ± 0.3°C) and offers essential extensions in performance and work time under thermal insulation.     

Approximating the average daily surface albedo with respect to soil roughness and latitude

The present study explores the diurnal variations in blue-sky albedo (α) of soils under clear sky conditions with respect to surface roughness. Three roughness levels of ploughed and unploughed soil surfaces, developed from the same loessial material, were examined. The relation between α of the surfaces and the solar zenith angle, determined during the experiment, enabled us to predict the diurnal α variation of the surfaces throughout the year at a given latitude, between 75° S and 75° N. The optimal time (T _O) for measuring the soil albedo by an instantaneous observation was considered as the best represented time for the daily averaged value within an error lower than ±2%. It was found that the T _O, falling at different times depending on the soil surface roughness, limits the possibilities of data achievement by remote-sensing satellites along one of their sun-synchronous orbits.     

Using trunk posture to monitor heat strain at work

Abstract

This study aimed to determine if trunk posture during walking is related to increases in rectal temperature (T_re). 24 males treadmill walked in one of four conditions (1): 30?min at 3.0?mph and 0% grade, 20?°C and 50% relative humidity (RH), wearing healthcare worker (HCW) PPE; (2): 30?min at 3.0?mph and 0% grade, 27.5?°C and 60% RH, HCW PPE; (3): 30?min at 3.0?mph and 0% grade, 32.5?°C and 70% RH, HCW PPE; and (4): 40?min at 40% VO₂max, 30?°C and 70% RH, wearing firefighter PPE. Trunk posture (Zephyr BioHarness 3) and T_re were measured continuously. T_re was positively related to trunk posture, controlling for covariates (B?=?3.49, p?<?.001). BMI and age moderated this relationship (T_re×age, B?=?0.76, p?<?.001; T_re*BMI, B?=??1.85, p?<?.001). Trunk posture measurement may be useful in monitoring fall potential and magnitude of heat stress of workers in hot environments.

Practitioner Summary: Occupational hyperthermia increases worker risk for heat illness and injury but is difficult to monitor in the field. This investigation shows that trunk posture is independently and positively related to core temperature. Non-invasive measurement or visual inspection of trunk posture could provide novel insight on individual heat strain level.     

Hydrophobic direct bonding of silicon reconstructed surfaces

The bonding of hydrophobic, reconstructed (001) Si surfaces obtained with high temperature H₂ processes has been studied with atomic force microscopy, low energy electron diffraction spectroscopy, X-ray reflectivity and bonding energy measurements. Surface reconstruction is shown to strongly affect bonding mechanisms. As a consequence, bonding energies of such surfaces are significantly higher, in the room temperature ?500 °C range, than those of “HF-last” surfaces.     

Electrowetting on non‐fluorinated hydrophobic surfaces

Fluorinated polymers, the most extensively used hydrophobic surface materials for electrowetting (EW) devices, are expensive and have potential risks to health and environment. In this paper, EW devices fabricated with non‐fluorinated hydrophobic surfaces are demonstrated by using a polysiloxane‐modified polyacrylate (BYK® Silclean® 3700, Louisville, KY). Water contact angle, which is the most critical parameter of EW devices, changes from ~165° to ~95° with a negligible hysteresis (~3°) when a 42 V AC voltage is applied. EW array display prototypes were constructed on the non‐fluorinated surface and can be switched reversibly by applying a low voltage difference. These results indicate the promise of this BYK® Silclean® hydrophobic surface for EW devices in electronic readers and other mobile devices.     

The effects of a sloped ground surface on trunk kinematics and L5/S1 moment during lifting

There are many work environments that require workers to perform manual materials handling tasks on ground surfaces that are not perfectly flat (e.g. in agriculture, construction, and maritime workplaces). These sloped ground surfaces may have an impact on the lifting strategy/technique employed by the lifter, which may, in turn, alter the biomechanical loading of the spine. Describing the changes in kinematics and kinetics of the torso is the first step in assessing the impact of these changes and is the focus of the current research. Subjects' whole-body motions were recorded as they lifted a 10 kg box while standing on two inclined surfaces (facing an upward slope: 10° and 20°), two declined surfaces (facing a downward slope: ? 10° and ? 20°), and a flat surface (0°) using three lifting techniques (leg lift, back lift and freestyle lift). These data were then used in a two-dimensional, five-segment dynamic biomechanical model (top-down) to evaluate the effect of these slopes on the net moment about the L5/S1 joint. The results of this study showed an interesting interaction effect wherein the net L5/S1 moment was relatively insensitive to changes in slope angle under the back lift condition, but showed a significant effect during the leg lift and freestyle lifting conditions. The results show that under the freestyle lifting condition the peak L5/S1 moment was significantly higher for the inclined surfaces as compared to the flat surfaces (6.8% greater) or declined surfaces (10.0% greater). Subsequent component analysis revealed that both trunk flexion angle and angular trunk acceleration were driving this response. Collectively, the results of this study indicate that ground slope angle does influence the lifting kinematics and kinetics and therefore needs to be considered when evaluating risk of low back injury in these working conditions.     

Comparison of polar and geostationary satellite infrared observations of sea surface temperatures in the Gulf of Maine

A comparison is made between the polar orbiting (NOAA) and the geostationary (GOES) satellite infrared observations of sea surface temperatures in the Gulf of Maine between 23 May and 6 June 1978. Color image enhancement is used to demonstrate that both satellites are capable of detecting the large-scale surface patterns associated with the Gulf Stream and sea surface temperature fronts in the vicinity of Georges Bank and Nova Scotia. The main difference between the range of surface temperatures detected by the two satellites is due to their different spacial resolution: 1 km for the NOAA and 8 km for the GOES. The equivalent blackbody temperatures recorded by the GOES are 2–3°C lower than those obtained by the NOAA satellite because of a GOES calibration offset. The comparison of the NOAA data with ship observations off Nantucket indicates that, at sea surface temperatures of 6–7°C, the NOAA Satellite and ship observations agree within 1°C. A similar comparison in the Gulf Stream at sea surface temperatures of 23–27°C, indicates that the NOAA measurements are 2–3°C lower than in situ observations. Coastal radiosonde profiles are used to estimate the correction for atmospheric attenuation of the infrared radiation. A comparison of Maul and Sidran (1973) and Weinreb and Neuendorffer (1973) models for attenuation of infrared by atmospheric water vapor shows significant differences. It was not possible to resolve the discrepancy between the models because of measurement uncertainties.     

EO characteristics for a photoaligned VA‐1/4 π cell on a photopolymer layer

The generation of a liquid‐crystal (LC) tilt angle on a copolymer with chalconyl and cholesteryl moiety characteristics was performed, and the electro‐optical (EO) performance of the photoaligned vertical‐alignment (VA) 1/4 π cell by polarized UV exposure on a homeotropic photopolymer surfaces was studied. The LC tilt angles decreased as UV exposure time increased on the copolymer surfaces. A tilt angle of 87° in NLC was observed with an UV exposure of 3 min on the photoalignment‐2 surface. The LC tilt angle is attributed to increased chalcone moiety with increasing UV exposure time. Excellent voltage‐transmittance (V‐T) curves of the photoaligned VA 1/4 π cell by polarized UV exposure on the photopolymer surface for 3 min containing a cholesteryl moiety of 8% were obtained. The V‐T and response‐time characteristics can be improved by the presence of a cholesteryl moiety in the photopolymer.     

On-chip CO<Subscript>2</Subscript> incubation for pocket-sized microfluidic cell culture

We have developed an on-chip CO₂ incubation system based on mass/heat transfer from aqueous solutions of bicarbonate source to cell culture media through a permeable poly(dimethylsiloxane) (PDMS) wall. Heating a carbonate-buffered bicarbonate solution successfully regulated CO₂ generation without any feedback control. Because a microfluidic cell culture chip with the incubation system does not require an external chamber or gas supply, the entire microfluidic cell culture setup becomes pocket sized. Using 5 ml of 0.8 M sodium bicarbonate with 65 mM sodium carbonate as the water jacket, the chip maintained the temperature, osmolality, and pH of 750 μl cell culture medium within physiological levels when the chip was placed on a 37°C surface. The osmolality shift and pCO₂ of the media reservoir stabilized within <5 mmol/kg and 5.0 ± 1.0% over at least 9 days. The incubation capabilities were demonstrated through microfluidic culture of COS-7 epithelial cells under an inverted microscope for 17 days.