Search Results - (Author, Cooperation:D. J. Thomson)

2015-11-14

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

1089-7550

AIP Digital Archive

Physics

We report a study of tip artifacts in atomic force microscope (AFM) images of thin film surfaces. Specifically, a troublesome artifact that occurs when an AFM tip images surface features with a radius of curvature less than the apex of the tip. These artifacts are not easily detected, since the affected AFM images are similar to those expected for a thin film with a columnar microstructure. In a study of 23 thin films, we found that for a significant fraction, the AFM image was affected by this type of tip artifact. In the worst cases, the AFM images consisted almost entirely of images of the AFM tip. We discuss a simple technique to determine the extent of these tip artifacts.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Carrier profiling of a 400 nm complementary metal–oxide–semiconductor device has been accomplished by combining metal–semiconductor capacitance–voltage profiling techniques with two-dimensional scanning probe microscopy. When a metal probe is brought into contact with a semiconductor, a space-charged depletion region and therefore a capacitor is formed at the junction. By applying a small ac voltage, the voltage derivative of the contact capacitance can be measured with a lock-in amplifier. The amplitude of the derivative signal is a function of the carrier concentration, and the sign gives the type of carrier. The present work concentrates on the two dimensional (2D) carrier profiling of a 400 nm metal–oxide–semiconductor field effect transistor. The results demonstrate that this technique is capable of quantitative 2D characterization of semiconductor devices. © 2000 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A high-resolution noncontact scanned probe technique has been developed for sampling the internal signals of an operating integrated circuit. The signal waveform is extracted by sensing the localized electrostatic force between a small probe and point on the circuit being measured. A heterodyne approach is used to enable the sampled measurement of high-frequency digital or analog waveforms. In conjunction with a nulling method, the technique is capable of accurate signal measurement without complex calibration or probe positioning, and can be performed over passivated structures. Measurement of digital and analog signals is demonstrated with a voltage accuracy of less than 100 mV.

Electronic Resource

1365-2494

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Forage diets were prepared from ryegrass (non oestrogenic control) and from red clover as pellets or as unwilted silage. Each diet was fed to separate groups of 20 Border Leicester × Cheviot ewes for three weeks prior to the introduction of the ram, and for two cycles after mating. Subsequently, all three groups of ewes were fed in a similar manner until lambing and the reproductive performance of the ewes was measured. The control diet was prepared by barn drying a primary growth crop of perennial ryegrass, Lolium perenne cv S23. Tetraploid red clover, Trifolium pratense cv. Hungarpoly, was harvested as a first regrowth crop and the pelleted diet prepared by high temperature drying, grinding (2 mm screen) and pelleting. The silage was prepared without wilting. The level of formononetin in the red-clover silage was three times that in the dried red-clover pellets.Compared with the control grass diet, the feeding of red clover in either form significantly reduced (P〈0·001) the number of lambs born. The incidence of barrenness was higher (P〈0·001) for ewes fed red-clover silage compared with red-clover pellets and the control diet. The rate of twinning was significantly (P〈0·001) higher for the ewes fed the control grass diet than for either of the red-clover diets. The resultant lambing percentages were 190,165, and 100% for the control grass, red-clover pellet and red-clover silage treatments. In flock management, both the grazing of red clover and the feeding of red-clover pellets or silage, prior to and during mating, should be avoided.

Electronic Resource

1365-2494

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

With its potential for high yields and high animal output, lucerne appears to be an underexploited crop in British agriculture. In this paper an attempt is made to assess the prospects for expansion of the area of lucerne in Britain from an economic viewpoint, concentrating on lucerne as a conservation crop. Under good management lucerne is shown to have lower production costs than grass and its inclusion in the diet of dairy cows, but not beef cattle, could significantly lower winter feed costs. However, under apparently similar growing conditions, lucerne yields on different farms vary significantly, ranging from 9 to 13 t dry matter ha−1 a−1. At the lower yields, the economic attraction of growing and feeding lucerne in place of grass is small. Moreover, since potential lucerne production is concentrated in the south and east of Britain, lucerne competes with other arable crops. For lucerne to offer a gross margin per unit area comparable with these, the price for conserved lucerne would have to be set at a level at which dairy farmers would derive little economic advantage from feeding it. Thus, although lucerne is a forage crop with some potential, at present it is likely to offer economic possibilities only where producers can combine high yields with on-farm utilization of the crop.

Electronic Resource

1365-2494

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

In view of the revived interest in sainfoin, an economic assessment of the prospects for an expansion of its area in Britain has been attempted. It is estimated that potentially it could be grown on 950 × 103 ha of the agricultural area of England and Wales, though it is unlikely in the near future that it would exceed 20 × 103 ha, even if economic conditions were favourable. Comparison of the energy and protein yields of sainfoin, red clover and lucerne under conservation management indicates that one of the attractions of sainfoin is its high protein content. However, an assessment of the costs of production and utilization of sainfoin indicate that, for it to be a more widely used legume, sustainable dry matter (DM) yields would need to be increased by 35% to about 11.5 × 103 kg DM ha−1. At the same time, although growing sainfoin as a mixture with grass appears to improve the economic attractiveness of the crop, silage production costs (kg DM)−1 are still about 15% lower on pure grass swards. However, trials in the UK, Canada and Rumania have shown that, compared to current UK levels, sainfoin yields can be significantly increased.

Electronic Resource

1365-2494

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Two experiments were conducted to measure the voluntary intake and digestibility of (a) primary growth and (b) regrowth of diploid (S22) and tetraploid (Tetila tetrone) varieties of Italian rye-grass (Lolium muitifiorum): Sl00 white clover (Trifolium repens) was included as an additional treatment in the second experiment with the re-growth herbage diets. Mature adult wether sheep, housed indoors in digesdhility crates, were fed individually on fresh herbage cut daily from late April to early June (primary growth) and in early Septemher (regrowth). The yield, digestihility, nitrogen and soluble–carhohydrate contents of the two ryegrass varieties were similar during the primary growth stage. Intake-digestibility relationships for the graces were positive, linear and different (P=0.05). The voluntary intake of diploid ryegrass was approximately 14% higher than that of tetraploid ryegrass of the same digestibility. With regrowth herbage the digestibility and voluntary intake of white clover was higher than both the Italian ryegrasses. The digestihility of the regrowth tetraploid was 6% units higher than the diploid variety, but there was no difference in the voluntary intake of digestible organic matter between the varieties at the regrowth stage. The intake of regrowth herbage was higher thaa that of primary growth herhage of similar digestihility.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have directly imaged n-alkane layers adsorbed at the liquid/graphite interface using a scanning tunneling microscope. The layers possessed a high degree of two-dimensional ordering. The adsorbate was observed to enhance the tunneling current, and the atomic structure of the images was dominated by features associated with the substrate. These systems are excellent vehicles for studies concerning the imaging mechanism of adsorbed organic layers because of their stability and simplicity.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Silicon dioxide films were deposited on crystalline silicon substrates by electron cyclotron resonant (ECR) microwave plasma-enhanced chemical vapor deposition (PECVD). Films were grown on Si〈100〉 substrates at temperatures of 140–600 °C, flow rates of 0.5–10 sccm SiH4, 10–30 sccm O2, and at a pressure of 10−3 Torr. Infrared absorption spectroscopy of the samples indicated no detectable SiH, OH, or SiOH groups. Neither an afterglow chemistry nor He dilution was required to eliminate H impurities as was previously reported for silicon oxide films deposited from rf plasmas. This suggests that significant differences exist between rf and ECR microwave plasma chemistries. We have found that the stoichiometry and index of refraction was not sensitive to oxidant ratio for a wide range of conditions in contrast to other studies. Stoichiometric SiO2 films, with good physical properties, were grown for a much wider range of oxidant ratios relative to those which are characteristic of the rf PECVD technique. In addition, films grown under optimal conditions had infrared absorption spectra nearly identical to those of thermally grown oxides and index of refraction of 1.456, as measured by ellipsometry. We concluded that by using an ECR microwave plasma, SiO2 films with optical and bonding properties comparable to oxides thermally grown at 1000 °C in dry oxygen can be deposited at a low temperature (350 °C) and a low pressure (10−3 Torr) in a O2/SiH4 reactant gas mixture without the need for a carrier gas.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The behavior of electron-cyclotron resonant (ECR) and non-ECR H2 plasmas generated in a microwave plasma chemical-vapor deposition reactor have been studied as a function of magnetic field strength and absorbed microwave power. Plasma diagnostics were performed with a planar electrostatic probe, microwave power measurements, and visual inspection. The probe measurements were concerned with the plasma impingent on a sample table placed downstream from the active core of the plasma. ECR plasmas were found to be more efficient, stable, uniform, and dense than plasmas not generated by ECR. All properties of the ECR plasmas measured by the downstream probe showed a gentle monotonic increase with the magnetic field strength. This was attributed to a reduction in the spacing between the probe and the resonant zone. In the ECR plasmas the average electron temperature was 3 eV and the average density was 1016 m−3. The degree of ionization was on the order of 5×10−4.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A new technique for the two-dimensional delineation of P-N junctions is presented using a scanning resistance microscope (SRM). The SRM uses a conducting probe to perform localized resistance measurements over a surface. These measurements are used to delineate between regions of different doping type and concentration. By using contact forces of 10−4 N, the contact area is estimated to be 30 nm. Experiments have shown the SRM capable of junction delineation with a lateral spacial resolution of less than 35 nm. In addition, during resistance measurements the SRM performs simultaneous surface topography measurements.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We describe a technique that enables us to obtain a stroboscopic image of surface polarization associated with a surface acoustic wave. The surface polarization has been imaged as it travels across the exposed substrate of a surface acoustic wave filter operating at 434 MHz. The high-frequency polarization signals were recovered using a heterodyne electrostatic force scanning probe microscopy technique. © 2001 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

We describe a sensor for use in a scanning capacitance microscope (SCM) that is capable of "zeptofarad" (10−21 F) capacitance measurement resolution in a 1 Hz bandwidth with a peak-to-peak sense voltage on the probe tip of no more than 300 mV. This sensitivity is based on experimental data and simulation results that are in excellent agreement. The complete sensor incorporates an oscillator (phase locked to a 10 MHz crystal oscillator), a coupled transmission line resonator, an amplifier, and a peak detector. The resonator is fabricated from copper-clad, low-loss dielectric material and its size is such that it is easily incorporated with a scanning probe microscope. The sensor's use in the SCM enables capacitance resolution that has not previously been possible while retaining the instrumental advantages of imaging at low sense voltages. The performance of this sensor is discussed and compared to alternative scanning capacitance microscopy methodologies. © 2001 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Silicon dioxide films have been fabricated at growth temperatures ranging from 25 to 330 °C from an electron cyclotron resonant microwave plasma. Films were deposited from a SiH4/Ar/N2O reactant gas mixture. The minimum temperature required to fabricate high-electrical-quality silicon dioxide films is between 255 and 290 °C. In metal-oxide-semiconductor devices, electron injection field strengths and breakdown field strengths were as high as 5 and 8 MV/cm, respectively, for oxides grown above this temperature range. Films grown at temperatures slightly below the 255–290 °C range have much poorer electrical integrity. A concomitant increase in the refractive index was observed with the improvement in the electrical integrity of these films. The refractive index increased with increasing growth temperature and was in the range of 1.44–1.47. In the 255–290 °C temperature range, the refractive index of the silicon dioxide films reached approximately 1.46–1.47, and saturates thereafter. Infrared spectroscopy indicated a hydrogen content in these films of approximately 4 at. %. The hydrogen was bonded as SiOH, while no SiH impurity groups were detected. The dependence of the deposition rate on the substrate temperature was dependent on the location of the substrate. For films grown on substrates in contact with the plasma, the deposition rate was found to decrease with increasing substrate temperature. In contrast, for films grown on substrates located in the plasma afterglow, the deposition rate increased with increasing substrate temperature.

Electronic Resource

1365-2494

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

The effect of artificial dehydration and processing of red clover on nutrient digestion and absorption has been studied with sheep. A total of three diets were fed, each at an intake of 900 g DM d-1; comprising frozen (to represent fresh control), wafered and pelleted red clover.Dehydration caused small depressions in energy and N digestibility. Grinding and pelleting had no further effect, although both treatments reduced the amount of energy digestion occurring in the rumen, frozen 63, dried 60, pelleted 48 MJ per 100 MJ digestible energy. Digestion of energy in the caecum and colon was increased on both dried diets, and in the small intestine on the pelleted diet.Almost 40% of the extra duodenal energy on the pelleted diet was due to increased cellulose flow, with only 79% of digestible cellulose being digested in the rumen compared with 96% on the other two diets. There was an associated decrease in ruminal volatile fatty acid production of approx. 20%. Approximately half of the extra energy was due to an elevated flow of protein on the pelleted diet, but this increase was not reflected in amino acid absorption due to a reduced efficiency with the dried diets (frozen 72%, dried diets 54%).The results demonstrate that dehydration and processing of red clover can markedly influence nutrient digestion and supply and thus offer attractive means of improving the nutritive value.

Electronic Resource

1420-9136

Tsunami ; geopotential ; geomagnetism

Springer Online Journal Archives 1860-2000

Geosciences

Physics

Abstract The movement of the seawater across the earth's magnetic field produces a large-scale motional electric field. Using the Point Arena, California, to Hanauma Bay, Hawaii, unpowered HAW-1 cable, we have studied the geopotential across this distance to look for possible tsunami-induced fields that might have been produced following the April 1992 Cape Mendocino earthquake. We have used a ten-day interval prior to and including the earthquake as a reference for geopotential signals and for geomagnetic activity. We have also used geomagnetic data from Point Arena, Honolulu and Boulder as reference data. The results of the analyses show that there are tsunami-related effects in the cable geopotential data. These are (a) larger voltage prediction errors (residuals) for the interval following the main shock; (b) enhanced (compared to the 10d reference interval) geopotential spectral power following the main shock: two enhancements are larger than geomagnetically-induced spectral power enhancements in the same time interval; and (c) strong evidence for an ∼30 min “echo” in the cable geopotential signal following the main shock.

Electronic Resource

1573-1472

Springer Online Journal Archives 1860-2000

Geosciences

Physics

Abstract Recent papers by Wilson et al. (1981b) and Legg and Raupach (1982) give methods for the calculation of particle trajectories in turbulence with a gradient in vertical velocity variance Σ 2 w. However the two methods seem contradictory. This paper demonstrates that in systems in which l(dΣ w /dz) (where / is the length scale) varies only slowly with height z, the two methods give similar predictions, and indicates why this is the case. For a particular system in which the restriction on l(dΣ w /dz) is not satisfied, it is shown that neither method is correct but that a simple modification of the method of Wilson et al. (1981b) gives reasonable predictions.

Electronic Resource

1573-1472

Springer Online Journal Archives 1860-2000

Geosciences

Physics

Abstract This paper compares three schemes which use standard meteorological observations to estimate values of the surface sensible heat flux. All three schemes have been designed to be applicable to mid-latitude, grass covered surfaces. The estimates are compared with heat flux data measured by a sonic anemometer situated at Cardington in the UK. Consideration is also given to the problem of predicting the surface sensible heat flux when could information is not available, as is the case for automatic weather stations. Provided incoming solar radiation is available, the predictions are not substantially worse.

Electronic Resource