Exponential increases in semiconductor device density have been accompanied by exponential increases in tooling costs for successive generations. Atomically precise devices (APDs) present a comparatively cheap opportunity to assess future device technologies without the investment required to reach manufacturing scales. However, APDs are not easily integrated into standard workflows and require re-development of common device elements to be compatible with the atomically precise components. APDs prepared in a scanning tunneling microscope (STM) via H desorption lithography [1], [2] produce atomically abrupt dopant profiles, but require a bare silicon surface to start the process and restrict the post-processing thermal budget to ~ 350 o C to prevent dopant diffusion. This prohibits including surface dielectrics in advance of dopant incorporation and permits only deposited oxides in post-processing. Here, we demonstrate for the first time a surface gate incorporating widely available atomic layer deposition (ALD) Al 2 O 3 oxide with APDs made using H lithography and P doping. Fig. 1 shows a schematic (a), an STM image (b) and an optical image (c) of a single electron transistor (SET) processed using previously described methods for P incorporation and Si cap growth at low temperature (LT) [3]. The ALD gate oxide was deposited at 250°C, followed by electron beam lithography to define the metal gate, and photolithography for contact vias and metal fan-out. The SET, though an unconventional device, provides a straightforward path to analyzing energy scales and electrostatics.

Ferroelectricity in doped and alloyed hafnia thin films has been demonstrated using several different electrodes, with TiN and TaN being most prominent. In this work, we demonstrate ferroelectric Hf0.58Zr0.42O2 thin films with superconducting NbN electrodes at cryogenic temperatures. Demonstration of polarization—electric field [P(E)] response at liquid helium cryogenic temperatures, 4 K, suggests that the polarization is switchable over a wide temperature range after an initial 600 °C anneal. Further, room temperature P(E) and capacitance measurements demonstrate an expected polarization response with wake-up required to reach the steady state. Wake-up cycling at 4 K is observed to have no effect upon the ferroelectric phase suggesting an oxygen vacancy mobility freeze out whereas wake-up cycling at 294 K demonstrates close to a 3× increase in remanent polarization. This integration of a ferroelectric Hf0.58Zr0.42O2 thin film with NbN demonstrates the suitability of a highly scalable ferroelectric in applications for cryogenic technologies.

Phase transitions of amorphous alumina (a-alumina) nanotubes grown by atomic layer deposition and templated by carbon nanotubes were investigated with thermal annealing, transmitted Kikuchi electron diffraction, electron-irradiation-induced crystallization, X-ray diffraction, and X-ray photoelectron spectroscopy. The resulting, engineered alumina nanotube arrays demonstrate a large range of tunable phases that are vital for understanding how alumina nanotube arrays can be applied for uses within biotechnology, catalysis, and other academic and industrial uses.

Educating students with emotional and behavioral disorders (EBD) continues to be a challenge for many general and special education professionals. Students with EBD can exhibit behaviors such as chronic classroom disruption, aggression, and general maladaptive behavior toward peers and adults. Some students exhibit depression, obsessive/compulsive behavior, and excessive fears and phobias that merit special education programming. Estimates of those served for EBD are approximately 1% of the school population. The causes can include student biological factors and environmental influences such as family, school, and culture. Educators and researchers are focusing on preventing problematic behaviors and special educators are developing powerful intervention strategies to reduce these behaviors and replace them with more constructive ones.

Al2O3–Ta2O5 nanolaminate films were prepared via atomic layer deposition (ALD) on silicon with a single overall composition and thickness, but with a varying number of Al2O3/Ta2O5 bilayers. The composition of the films was roughly 57% Al2O3 and 43% Ta2O5 and the total film thickness was held at ∼58nm, while the number of bilayers was varied from 3 to 192 by changing the target bilayer thickness from ∼19.2nm to ∼0.3nm. Varying the number of bilayers was found to impact electrical properties. Although, almost all laminate films exhibited leakage, breakdown, hysteresis, and overall dielectric constant intermediate between pure Al2O3 and Ta2O5 films, laminates with few bilayers exhibited leakage current density lower than Al2O3 over the range of ∼3.5–4.5MV/cm. Select samples annealed at temperatures from 400 to 900°C were compared with as-deposited laminates. Annealing the laminate films at low temperatures improved leakage and breakdown while higher temperature anneals degraded both leakage and breakdown but improved the effective dielectric constant. A figure of merit was used to evaluate the overall ability of the various films to store charge. It was found that the few bilayer laminates were ranked higher than the many bilayer laminates as well as above both the pure Ta2O5 and pure Al2O3 films. These results indicate that even for a fixed overall composition, the electrical properties of a nanolaminate can be adjusted by varying the number of bilayers.

Relative seismic quiescence within a region which has already been diagnosed as having entered a “Time of Increased Probability” (TIP) for the occurrence of a strong earthquake can be used to refine the locality in which the earthquake may be expected to occur. A simple algorithm with parameters fitted from the data in Northern California preceding the 1980 magnitude 7.0 earthquake offshore from Eureka depicts relative quiescence within the region of a TTP. The procedure was tested, without readaptation of parameters, on 17 other strong earthquake occurrences in North America, Japan, and Eurasia, most of which were in regions for which a TIP had been previously diagnosed. The localization algorithm successfully outlined a region within which the subsequent earthquake occurred for 16 of these 17 strong earthquakes. The area of prediction in each case was reduced significantly, ranging between 7% and 25% of the total area covered by the TIP.

The physical and statistical properties of backscattered signals in medical ultrasonic imaging are reviewed in terms of: 1) the radiofrequency signal; 2) the envelope (video or magnitude) signal; and 3) the density of samples in simple and in compounded images. I INTRODUCTION There is a wealth of physical information in backscattered signals in medical ultrasound. This information is contained in the radiofrequency spectrum--which is not typically displayed to the viewer--as well as in the higher statistical moments of the envelope or video signal--which are not readily accessed by the human viewer of typical B-scans. This information may be extracted from the detected backscattered signals by straightforward signal processing techniques at low resolution. II THE RADIOFREQUENCY SIGNAL In the weak scattering regime of medical ultrasonic imaging (1), (2) the Born approximation is valid and yields the frequency dependence of back-scattered radiofrequency signals from a diffuse cloud of similar scatterers. The result in the acoustic application (3) is similar to that found in electro-magnetic wave scattering and the frequency dependence of the backscattered intensity is given by I cc f4 F 2 (1) where the frequency to the fourth power is the dependence associated with Rayleigh scattering, and I F I 2 is the square of the scattering form factor: the Fourier transform of the distribution of the scattering potential, here the change in compressibility or acoustic impedance of the medium. F I 2 has the form of a low pass filter. Some examples of Eq.(1) are given in Figure la for Gaussian form factors with diameters (four standard deviations) as shown, and in reference (4) this simplified treatment is shown to agree well with an exact calculation after the method of Faran when the product of the wave number k and particle radius a is less than unity. In Figure lb the same curves are presented after spatial attenuation by a factor exp(-,2.cx(2x) f), a reasonable approximation to the round trip attenuation at a depth x and at fre-quency f. The attenuation has appreciable effect only at the higher frequencies, as in many other applications.

In order to design improved spatial compounding ultra- sound scanning systems it is necessary to determine the correlation of speckle patterns as a function of aperture translation. We have con- ducted experiments measuring the speckle correlation with lateral ap- erture translation for linear phased array pulse-echo ultrasonic im- aging systems. Results are presented for variable frequency, range, transducer length, focus error, and reflecting material. Tests were con- ducted on two commercially availahle and one research imaging sys- tem. The measured rates of correlation coefficient decrease are inde- pendent of frequency, reflecting material, and target range when the target is in the focal zone. The experimentally determined correlations are used to derive the optimal spatial separation of images for speckle reduction.

Determination of in situ ultrasound exposures in experimental animals and patients is necessary to assess any potential hazard of ultrasound implied by reported biological effects in animals. A layered model was used to calculate total attenuation of ultrasound pulses as they passed through tissue layers to an organ site, thus enabling calculation of in situ intensities from free-field transducer emissions. The model assumes plane homogeneous layers of tissue of known thickness, attenuation and acoustic impedance. Calculations based on the model, compared with in situ measurements in a human cadaver specimen, were accurate to within ∼ ± 3 dB. We then calculated in situ clinical exposures using published obstetric B-scans. Total attenuation to the fetus averaged ∼ 11 dB at 3.5 MHz.

This paper describes the design and construction of a simple multi-element transducer array capable of converting an A-scan unit to a real-time, hand-held section scanner.Elements are connected in groups of four to give a finer stepping interval than is possible with discrete transducers.Application of the array as an inexpensive alternative to conventional B-scanners is discussed, in addition to its more obvious application as a non-invasive method of imaging the moving heart.

The principles and techniques of real-time imaging with phased array ultrasound scanners are reviewed. Topics include 1) the geometric optics of beam steering and focusing with a linear array in the transmit and receive modes; 2) limitations on image data acquisition due to ultrasound propagation velocity; 3) optical diffraction theory for linear arrays including effects of amplitude grating lobes. Limitations on the image quality of phased array imaging systems are also discussed, including 1) nonideal response of array transducers; 2) target ambiguities caused by phase error grating lobes; 3) refraction errors; 4) delay line design. Finally, an analysis is presented of current techniques for improving ultrasound image quality using phased array methods including phase compensation, spatial compounding, frequency compounding, and parallel processing.

Cytoplasmic free [Ca2+], [Ca2+]i, was measured in human platelets using the intracellularly‐trapped, fluorescent indicator quin2. Basal [Ca2+]i with the Ca2+‐ionophore ionomycin revealed apparent thresholds for shape‐change, 5‐HT release and aggregation of approx. 0.5μM, 0.8μM and 2 μM. Thrombin raised [Ca2+]i to 3 μM fast enough for the Ca2+ to have triggered the cell activation. However, thrombin released more 5‐HT than ionomycin could, and in Ca2+‐free medium thrombin evoked shape‐change and secretion even when [Ca2+]i remained near basal levels throughout, suggesting the existence of alternative triggers for shape‐change and secretory exocytosis.

Keywords BRITISH RAILWAYS BOARD, BRITISH AIRPORTS AUTHORITY TRANSPORTATION, PROJECTS, LINK, PLANNING, AIRPORTS, RECLAMATION, RAILWAYS, ROADS, PORTS, LAND, TERMINALS MAPLIN, ESSEX, KINGS CROSS, LONDON UK... Show All