Scanning capacitance microscopy registration of buried atomic-precision donor devices.

We show that a scanning capacitance microscope (SCM) can image buried delta-doped donor nanostructures fabricated in Si via a recently developed atomic-precision scanning tunneling microscopy (STM) lithography technique. A critical challenge in completing atomic-precision nanoelectronic devices is to accurately align mesoscopic metal contacts to the STM defined nanostructures. Utilizing the SCMs ability to image buried dopant nanostructures, we have developed a technique by which we are able to position metal electrodes on the surface to form contacts to underlying STM fabricated donor nanostructures with a measured accuracy of 300 nm. Low temperature (T = 4 K) transport measurements confirm successful placement of the contacts to the donor nanostructures.

Transport spectroscopy of low disorder silicon tunnel barriers with and without Sb implants.

We present transport measurements of silicon MOS split gate structures with and without Sb implants. We observe classical point contact (PC) behavior that is free of any pronounced unintentional resonances at liquid He temperatures. The implanted device has resonances superposed on the PC transport indicative of transport through the Sb donors. We fit the differential conductance to a rectangular tunnel barrier model with a linear barrier height dependence on source-drain voltage and non-linear dependence on gate bias. Effects such as Fowler-Nordheim (FN) tunneling and image charge barrier lowering (ICBL) are considered. Barrier heights and widths are estimated for the entire range of relevant biases. The barrier heights at the locations of some of the resonances for the implanted tunnel barrier are between 15-20 meV, which are consistent with transport through shallow partially hybridized Sb donors. The dependence of width and barrier height on gate voltage is found to be linear over a wide range of gate bias in the split gate geometry but deviates considerably when the barrier becomes large and is not described completely by standard 1D models such as FN or ICBL effects.

Lithography and doping in strained Si towards atomically precise device fabrication.

We investigate the ability to introduce strain into atomic-scale silicon device fabrication by performing hydrogen lithography and creating electrically active phosphorus δ-doped silicon on strained silicon-on-insulator (sSOI) substrates. Lithographic patterns were obtained by selectively desorbing hydrogen atoms from a H resist layer adsorbed on a clean, atomically flat sSOI(001) surface with a scanning tunnelling microscope tip operating in ultra-high vacuum. The influence of the tip-to-sample bias on the lithographic process was investigated allowing us to pattern feature-sizes from several microns down to 1.3 nm. In parallel we have investigated the impact of strain on the electrical properties of P:Si δ-doped layers. Despite the presence of strain inducing surface variations in the silicon substrate we still achieve high carrier densities (>1.0 × 10(14) cm(-2)) with mobilities of ∼100 cm(2) V(-1) s(-1). These results open up the possibility of a scanning-probe lithography approach to the fabrication of strained atomic-scale devices in silicon.

Efficient clocked electron transfer on superfluid helium.

Unprecedented transport efficiency is demonstrated for electrons on the surface of micron-scale superfluid helium-filled channels by co-opting silicon processing technology to construct the equivalent of a charge-coupled device. Strong fringing fields lead to undetectably rare transfer failures after over a billion cycles in two dimensions. This extremely efficient transport is measured in 120 channels simultaneously with packets of up to 20 electrons, and down to singly occupied pixels. These results point the way towards the large scale transport of either computational qubits or electron spin qubits used for communications in a hybrid qubit system.

Single ion implantation for single donor devices using Geiger mode detectors.

Electronic devices that are designed to use the properties of single atoms such as donors or defects have become a reality with recent demonstrations of donor spectroscopy, single photon emission sources, and magnetic imaging using defect centers in diamond. Ion implantation, an industry standard for atom placement in materials, requires augmentation for single ion capability including a method for detecting a single ion arrival. Integrating single ion detection techniques with the single donor device construction region allows single ion arrival to be assured. Improving detector sensitivity is linked to improving control over the straggle of the ion as well as providing more flexibility in lay-out integration with the active region of the single donor device construction zone by allowing ion sensing at potentially greater distances. Using a remotely located passively gated single ion Geiger mode avalanche diode (SIGMA) detector we have demonstrated 100% detection efficiency at a distance of >75 microm from the center of the collecting junction. This detection efficiency is achieved with sensitivity to approximately 600 or fewer electron-hole pairs produced by the implanted ion. Ion detectors with this sensitivity and integrated with a thin dielectric, for example a 5 nm gate oxide, using low energy Sb implantation would have an end of range straggle of <2.5 nm. Significant reduction in false count probability is, furthermore, achieved by modifying the ion beam set-up to allow for cryogenic operation of the SIGMA detector. Using a detection window of 230 ns at 1 Hz, the probability of a false count was measured as approximately 10(-1) and 10(-4) for operation temperatures of approximately 300 K and approximately 77 K, respectively. Low temperature operation and reduced false, 'dark', counts are critical to achieving high confidence in single ion arrival. For the device performance in this work, the confidence is calculated as a probability of >98% for counting one and only one ion for a false count probability of 10(-4) at an average ion number per gated window of 0.015.

Long-term drift of Si-MOS quantum dots with intentional donor implants.

Charge noise can be detrimental to the operation of quantum dot (QD) based semiconductor qubits. We study the low-frequency charge noise by charge offset drift measurements for Si-MOS devices with intentionally implanted donors near the QDs. We show that the MOS system exhibits non-equilibrium drift characteristics, in the form of transients and discrete jumps, that are not dependent on the properties of the donor implants. The equilibrium charge noise indicates a 1/f noise dependence, and a noise strength as low as [Formula: see text], comparable to that reported in more model GaAs and Si/SiGe systems (which have also not been implanted). We demonstrate that implanted qubits, therefore, can be fabricated without detrimental effects on long-term drift or 1/f noise for devices with less than 50 implanted donors near the qubit.

Single-Shot Readout Performance of Two Heterojunction-Bipolar-Transistor Amplification Circuits at Millikelvin Temperatures.

High-fidelity single-shot readout of spin qubits requires distinguishing states much faster than the T1 time of the spin state. One approach to improving readout fidelity and bandwidth (BW) is cryogenic amplification, where the signal from the qubit is amplified before noise sources are introduced and room-temperature amplifiers can operate at lower gain and higher BW. We compare the performance of two cryogenic amplification circuits: a current-biased heterojunction bipolar transistor circuit (CB-HBT), and an AC-coupled HBT circuit (AC-HBT). Both circuits are mounted on the mixing-chamber stage of a dilution refrigerator and are connected to silicon metal oxide semiconductor (Si-MOS) quantum dot devices on a printed circuit board (PCB). The power dissipated by the CB-HBT ranges from 0.1 to 1 µW whereas the power of the AC-HBT ranges from 1 to 20 µW. Referred to the input, the noise spectral density is low for both circuits, in the 15 to 30 fA/[Formula: see text] range. The charge sensitivity for the CB-HBT and AC-HBT is 330 µe/[Formula: see text] and 400 µe/[Formula: see text], respectively. For the single-shot readout performed, less than 10 µs is required for both circuits to achieve bit error rates below 10-3, which is a putative threshold for quantum error correction.

Ion implantation for deterministic single atom devices.

We demonstrate a capability of deterministic doping at the single atom level using a combination of direct write focused ion beam and solid-state ion detectors. The focused ion beam system can position a single ion to within 35 nm of a targeted location and the detection system is sensitive to single low energy heavy ions. This platform can be used to deterministically fabricate single atom devices in materials where the nanostructure and ion detectors can be integrated, including donor-based qubits in Si and color centers in diamond.

Private health insurance plans in 1977: coverage, enrollment, and financial experience.

The private health insurance industry collected $47.1 billion in premiums in 1977 and returned $41.6 billion in benefits to their subscribers. Premiums rose 16.3 percent as a direct consequence of rapid claims growth in 1976. After operating expenses were deducted, the industry showed a small, $.4 billion underwriting loss. About 78 percent of the population were insured for hospital care, and about 76 percent for surgical services. Smaller percentages had coverage for other types of care. An estimated 61.8 percent of the aged bought private hospital insurance, and 47.1 percent bought surgical insurance, mostly to supplement Medicare benefits. About 12 percent of persons under age 65 had no protection against the cost of hospital care either through private insurance or a public program such as Medicare or Medicaid.

Private health insurance plans in 1978 and 1979: a review of coverage, enrollment, and financial experience.

The private health insurance industry collected $55.9 billion in premiums in 1979 and returned $50.2 billion in benefits to its subscribers. Premiums rose 12.4 percent, slightly faster than in 1978 when premiums rose 11.4 percent, to $49.7 billion. Benefits rose 11.4 percent in 1979, down from the 12.6 rate in 1978. After operating expenses were deducted, the industry showed underwriting losses of $1.4 billion in 1979 and $1.5 billion in 1978. About 78 percent of the population was insured for hospital care, 76 percent for x-ray and laboratory examinations, and about 76 percent for surgical services in 1979. Smaller percentages had coverage for other types of care. An estimated 64 percent of the aged bought private hospital insurance, and about 43 percent bought surgical insurance, mostly to supplement Medicare benefits. An estimated 12 percent of persons under age 65 had no protection against the cost of hospital care either through private insurance or a public program such as Medicare or Medicaid.

Managed care programs: an employer perspective.

Throughout the 1980s, employers made many health care benefit plan modifications that were directed toward containing costs. This chapter discusses potential managed care program changes that may occur in the coming years. Specifically reviewed are partnerships between employers and managed care entities; possible features of the next generation of managed are plans; and dimensions of a cost-benefit analysis that employers could use to gauge the cost-effectiveness of future plan changes.

Cellular electrophysiological effects of the class III antiarrhythmic agents sematilide and clofilium on rabbit atrial tissues.

Sematilide (N-[2-(diethylamino)ethyl]-4- [(methylsulfonyl)amino]benzamide HCl) is a new class III antiarrhythmic agent that has been shown to be effective in preventing reentrant ventricular arrhythmias in experimental animals and humans. In this study, we examined the in vitro effects of sematilide (1-100 microM) on isolated sinoatrial (SA) node, atrioventricular (AV) node, and atrial muscle. These results were then compared to another class III agent, clofilium (1-30 microM). In SA nodal tissue, sematilide increased the action potential duration (APD) and spontaneous cycle length (SCL) in a concentration-dependent manner (EC20% = 15 +/- 3 and 54 +/- 13 microM, respectively). In addition, there was a slight reduction in maximum diastolic potential at 100 microM. Clofilium had similar class III effects, but was approximately 3 to 18 times more potent (EC20% = 6 +/- 2 and 3 +/- 1 microM for the APD and SCL, respectively). Neither agent had a significant effect on the slope of phase 4 nor on other action potential parameters. Results in AV nodal preparations were similar. Both sematilide and clofilium increased the APD and SCL in a concentration-dependent manner, with clofilium being approximately four to six times more potent than sematilide (EC20% for the APD and SCL for sematilide = 12 +/- 4 and 12 +/- 8 microM, respectively, and for clofilium = 2 +/- 1 and 3 +/- 2 microM, respectively). No significant effects were observed on other action potential parameters. Sematilide and clofilium increased the APD and effective refractory period (ERP) in atrial trabeculae in a concentration-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Terbutaline in the treatment of chronic urticaria.

Eighteen patients with chronic urticaria were evaluated concerning the benefit of oral sympathomimetic therapy. No significant differences could be found between the sympathomimetic agent (terbutaline) and a placebo in the various clinical parameters evaluated. The authors conclude that the efficacy of this drug is doubtful in the treatment of chronic urticaria.

Use of a twelve-hour theophylline preparation in chronic adult asthmatics.

Twenty-one adult chronic asthmatic patients were studied while taking a 12-hour sustained-action theophylline tablet. Pulmonary function testing and serum theophylline levels were monitored for 12 weeks, including testing every two hours over one dosing interval on the final day of the study. Results indicate the preparation tested produced sustained stable theophylline levels for a full 12 hours, with pulmonary function also remaining elevated and stable during this period. There was minimal toxicity reported over the 12-week period and no evidence of tolerance.

Bioavailability and multiple dose characteristics of a new sustained release theophylline tablet.

Bioavailability and theophylline level variability were compared between a standard theophylline elixir and a new sustained release theophylline tablet. The results demonstrate a good bioavailability and a reduced dosage interval with less theophylline level variability for the sustained release tablet, administered every 12 hours, than with the immediate release product, every six hours.

The use of ketotifen in the prophylaxis of seasonal allergic asthma.

This double-blind parallel group study evaluated ketotifen 1 mg bid versus placebo in the treatment of 30 adult seasonally allergic asthmatics during the course of the spring pollen season. Those individuals on placebo had a fall in FEV1 through the pollen season, those on Ketotifen generally did not, and some individuals, in fact, showed improvement. Those patients receiving ketotifen had fewer allergic symptoms, better exercise tolerance, and in general had a better spring. This study demonstrated that ketotifen may have some benefit in the treatment of adult allergic asthma.

Electrophysiologic activity and antiarrhythmic efficacy of CK-3579, a new class III antiarrhythmic agent with beta-adrenergic blocking properties.

CK-3579 (N-[4-[2-hydroxy-3-[[2-[4-(1H-inidazol-1- yl)phenoxy]ethyl]amino]propoxy]phenyl]methanesulfonamide, HCL-[RS]), is a new class III antiarrhythmic agent with beta-adrenoceptor blocking properties shown to be effective in preventing ventricular arrhythmias in experimental animals. We examined the beta 1- and beta 2-adrenoceptor binding properties, cellular electrophysiology, and antiarrhythmic efficacy of CK-3579 and the two enantiomers CK-4000 (S) and CK-4001 (R). Both CK-3579 and CK-4000 were equipotent in displacing [3H]dihydroalprenolol from cardiac membranes (IC50 = 2.4 +/- 0.3 and 1.7 +/- 0.4 microM, respectively) and were approximately 23-59 times more selective for the heart receptor than the lung receptor. The IC50 for CK-4001 at the beta 1-adrenoceptor was 38.1 +/- 8 microM and > 100 microM at the beta 2-adrenoceptor. In isolated canine Purkinje fibers and ventricular muscle preparations, all three compounds increased action potential duration at 95% repolarization (APD95) with equal potency, having an average EC20 of approximately 1 microM in Purkinje fiber and 2 microM in ventricular muscle. No significant effects were observed on any other action potential (AP) parameters. In Purkinje fibers with APs shortened by isoproterenol, the class III activity of CK-4000 was significantly greater than that of CK-4001. CK-4000 inhibits the potassium delayed rectifier current Ik in a concentration-dependent manner in isolated feline ventricular myocytes. The IC50 for inhibition of fully activated current was 0.4 +/- 0.2 microM. Steady-state currents negative to -20 mV were unchanged by CK-4000, but the "hump" in the outward current between -20 and +30 mV was flattened.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of nebulized terbutaline (TERB) and subcutaneous epinephrine (EPI) in the treatment of acute asthma.

The purpose of this study was to compare nebulized terbutaline 5 mg vs. subcutaneous epinephrine (1/1000, 0.3 cc) in the treatment of acute exacerbations of asthma in adult patients. Patients with a known diagnosis of asthma, who presented to the investigators in acute respiratory distress, without any previous adrenergic agents for six hours, were the subjects for this study. There were 33 patients enrolled in the study between 16 and 64 years of age. The results indicate both treatment groups gave significant increases in pulmonary function at all times when compared to baseline (p less than 0.001). Nebulized terbutaline and subcutaneous epinephrine appeared equally effective in the treatment of acute exacerbations of asthma, without significant differences in bronchodilator effectiveness or side effects.

Interaction between cellular voltage-sensitive conductance and network parameters in a model of neocortex can generate epileptiform bursting.

We examined the effects of both intrinsic neuronal membrane properties and network parameters on oscillatory activity in a model of neocortex. A scalable network model with six different cell types was built with the pGENESIS neural simulator. The neocortical network consisted of two types of pyramidal cells and four types of inhibitory interneurons. All cell types contained both fast sodium and delayed rectifier potassium channels for generation of action potentials. A subset of the pyramidal neurons contained an additional slow inactivating (persistent) sodium current (NaP). The neurons with the NaP current showed spontaneous bursting activity in the absence of external stimulation. The model also included a routine to calculate a simulated electroencephalogram (EEG) trace from the population activity. This revealed emergent network behavior which ranged from desynchronized activity to different types of seizure-like bursting patterns. At settings with weaker excitatory network effects, the propensity to generate seizure-like behavior increased. Strong excitatory network connectivity destroyed oscillatory behavior, whereas weak connectivity enhanced the relative importance of the spontaneously bursting cells. Our findings are in contradiction with the general opinion that strong excitatory synaptic and/or insufficient inhibition effects are associated with seizure initiation, but are in agreement with previously reported behavior in neocortex.