The onset of superfluidity in4He films adsorbed in aerogel glass

We have completed a systematic study of the superfluid density of ⁴ He films adsorbed in 91% porosity aerogel glass. We have concentrated on the low-coverage regime (T_c<200 mK) in an attempt to address recent theoretical work on the onset of superfluidity in dirty boson systems. Our data are not in agreement with the predictions of a scaling theory of the onset transition developed by Fisher et al. ¹ We discuss the extent of this disagreement and the limitations of other models of the onset transition.     

Assessment of on-chip wire-length distribution models

Ultralarge-scale integrated (ULSI) chip design data is needed for an assessment of existing on-chip wirelength distribution models. Data extracted from modern chips such as high-performance microprocessors provide information about actual wire length requirements in ULSI chip designs. These requirements are compared with wirelength estimates obtained by evaluating existing models as functions of Rent's parameters that are extracted from the designs. This brief assesses the extent to which existing models estimate wirelength requirements in 100 ASIC-like control logic designs in the 1.3-GHz POWER4 microprocessor. For each design, physical design characteristics and wirelength requirements are measured and compared with model estimates. Lack of agreement between the data and models is observed for most designs, and possible reasons for the lack of agreement are discussed.     

Status and Direction of Communication Technologies - SiGe BiCMOS and RFCMOS

We present the status and direction of silicon semiconductor technologies targeted for applications such as wireless, networking, instrumentation, and storage markets. Various technological aspects for multiple branches of RF foundry technologies that are based on the standard foundry compatible CMOS node are discussed - SiGe BiCMOS HP ("high performance") tailored to high-frequency applications, SiGe BiCMOS WL ("cost performance") tailored to wireless/storage applications, and RF-CMOS optimized for low-cost consumer applications. Future opportunities and challenges for advancement in RF technologies are described in light of CMOS and SiGe heterojunction bipolar transistor scaling. In addition, we discuss the maturity of SiGe BiCMOS by looking at the levels of integration and manufacturability.     

Iodine-atom laser emission in 2-2-2 trifluoroethyliodide

Lasing at 1.3 μ upon flash photolysis of 2-2-2 tri-fluoroethyliodide, CF3CH2I, has been observed on the²P_{1/2}-²P_{3/2}magnetic dipole allowed transition of atomic iodine. Using an 800-J flash, a maximum peak power output of approximately 108 W for 10-μs duration at half-maximum intensity was obtained with a pressure of 17 torr CF3CH2I.     

Atomic force microscopy studies of fracture surfaces of composition B energetic materials

The characteristics of trinitrotoluene (TNT) crystals in composition B have been studied using atomic force microscopy (AFM). The size of TNT crystals has been examined by analyzing the surface structure that is exhibited after mechanical failure of the composition B. The mechanical failure occurs when the material is subjected to high acceleration (high g) in an ultracentrifuge and the shear or tensile strength is exceeded. The AFM examination of the topography of the composition B fracture surface reveals fracture across columnar grains of the TNT. The width of the columnar TNT grains ranges in size from ∼1 to ∼2 μm. Their height ranges in size from ∼50 to ∼300 nm. Flat TNT columns alternate with TNT columns containing river patterns that identify the direction of crack growth. Steps in the river patterns are a few nanometers in depth. The TNT constituent fracture surface morphology is shown to occur on such fine scale, beginning from adjacent columnar crystals only 1 to 2 μm in width and including river marking step heights of only a few nanometers, that AFM-type resolution is required even to begin to make clear what has happened. This article is based on a presentation given in the symposium “Dynamic Deformation: Constitutive Modeling, Grain Size, and Other Effects: In Honor of Prof. Ronald W. Armstrong,” March 2–6, 2003, at the 2003 TMS/ASM Annual Meeting, San Diego, California, under the auspices of the TMS/ASM Joint Mechanical Behavior of Materials Committee.     

Si/Si1-x-yGexCy/Si heterojunctionbipolar transistors

We report the first Si/Si_1-x-yGe_xC_y /Si n-p-n heterojunction bipolar transistors and the first electrical bandgap measurements of strained Si_1-x-yGe_x C_y on Si (100) substrates. The carbon compositions were measured by the shift between the Si_1-x-yGe_xC_y and Si_1-xGe_x X-ray diffraction peaks. The temperature dependence of the HBT collector current demonstrates that carbon causes a shift in bandgap of +26 meV/%C for germanium fractions of x=0.2 and x=0.25. These results show that carbon reduces the strain in Si_1-x Ge_x at a faster rate than it increases the bandgap (compared to reducing x in Si_1-xGe_x), so that a Si _1-x-yGe_xC_y film will have less strain than a Si_1-xGe_x film with the same bandgap     

Low-Power Portable Geophysical Data Acquisition System And Its Use in Geomagnetic Measurements

A low-power portable data acquisition system presently in use for geomagnetic measurements is described. The system is composed of a data-processing system containing a low-power microprocessor, a 9-track digital tape recorder, and a rechargeable battery pack. The magnetometer is a low-power three axis fluxgate design. Under program control the data processing system keeps track of time of day and date, samples three analog magnetometer outputs at intervals of either 0.4 or 2 s, digitizes the data to 15-bit resolution, and, depending upon relative magnetic activity, decides upon data compression to increase the tape storage capacity. It also monitors and records internal voltages and provides self-checking functions which may be monitored through a visual readout on the control panel. The system is mounted in a rugged, weather-tight carrying case suitable for use outdoors with minimal protection. The system, including magnetometer, uses 1.6-W power and can store 5.7 Mbytes of data.