The radio-frequency single-electron transistor (RF-SET): A fast and ultrasensitive electrometer

A new type of electrometer is described that uses a single-electron transistor (SET) and that allows large operating speeds and extremely high charge sensitivity. The SET readout was accomplished by measuring the damping of a 1.7-gigahertz resonant circuit in which the device is embedded, and in some ways is the electrostatic "dual" of the well-known radio-frequency superconducting quantum interference device. The device is more than two orders of magnitude faster than previous single-electron devices, with a constant gain from dc to greater than 100 megahertz. For a still-unoptimized device, a charge sensitivity of 1.2 x 10(-5) e/hertz was obtained at a frequency of 1.1 megahertz, which is about an order of magnitude better than a typical, 1/f-noise-limited SET, and corresponds to an energy sensitivity (in joules per hertz) of about 41 Planck's over 2pi.     

Observation of single-electron charging in double-barrier heterostructures

Incremental single-electron charging of size-quantized states has been observed in the well in submicrometer double-barrier resonant tunneling devices. In order to distinguish between the effects of size quantization and the single-electron charging, the heterostructure material was grown asymmetrical so that one barrier is substantially less transparent than the other. In the voltage polarity such that the emitter barrier is more transparent than the collector barrier, electrons accumulate in the well; incremental electron occupation of the well is accompanied by Coulomb blockade, which leads to sharp steps of the tunneling current. In the opposite voltage polarity the emitter barrier is less transparent than the collector barrier and the tunneling current reflects resonant tunneling through size-quantized well states.     

Geophysicists celebrate two satellites, mourn a third

Searching for a common theme in a gathering as diverse as the spring meeting of the American Geophysical Union (AGU) in Baltimore last month might seem futile. But satellites, both natural and artificial, provided some of the meeting's high points. Researchers reported on the first science results from the Clementine spacecraft's 2-month sojourn orbiting the moon, the revealing color of the small moon that accompanies the asteroid lda, and the planned termination of the Magellan spacecraft orbiting Venus.     

The Kondo effect in the presence of ferromagnetism

We measured Kondo-assisted tunneling via C60 molecules in contact with ferromagnetic nickel electrodes. Kondo correlations persisted despite the presence of ferromagnetism, but the Kondo peak in the differential conductance was split by an amount that decreased (even to zero) as the moments in the two electrodes were turned from parallel to antiparallel alignment. The splitting is too large to be explained by a local magnetic field. However, the voltage, temperature, and magnetic field dependence of the signals agree with predictions for an exchange splitting of the Kondo resonance. The Kondo effect leads to negative values of magnetoresistance, with magnitudes much larger than the Julliere estimate.     

Magnetic clusters on single-walled carbon nanotubes: the Kondo effect in a one-dimensional host

Single-walled carbon nanotubes are ideal systems for investigating fundamental properties and applications of one-dimensional electronic systems. The interaction of magnetic impurities with electrons confined in one dimension has been studied by spatially resolving the local electronic density of states of small cobalt clusters on metallic single-walled nanotubes with a low-temperature scanning tunneling microscope. Spectroscopic measurements performed on and near these clusters exhibit a narrow peak near the Fermi level that has been identified as a Kondo resonance. Using the scanning tunneling microscope to fabricate ultrasmall magnetic nanostructures consisting of small cobalt clusters on short nanotube pieces, spectroscopic studies of this quantum box structure exhibited features characteristic of the bulk Kondo resonance, but also new features due to finite size.     

The Kondo effect in an artificial quantum dot molecule

Double quantum dots provide an ideal model system for studying interactions between localized impurity spins. We report on the transport properties of a series-coupled double quantum dot as electrons are added one by one onto the dots. When the many-body molecular states are formed, we observe a splitting of the Kondo resonance peak in the differential conductance. This splitting reflects the energy difference between the bonding and antibonding states formed by the coherent superposition of the Kondo states of each dot. The occurrence of the Kondo resonance and its magnetic field dependence agree with a simple interpretation of the spin status of a double quantum dot.     

Scanned probe imaging of single-electron charge states in nanotube quantum dots

An atomic force microscope was used to study single-electron motion in nanotube quantum dots. By applying a voltage to the microscope tip, the number of electrons occupying the quantum dot could be changed, causing Coulomb oscillations in the nanotube conductance. Spatial maps of these oscillations were used to locate individual dots and to study the electrostatic coupling between the dot and the tip. The electrostatic forces associated with single electrons hopping on and off the quantum dot were also measured. These forces changed the amplitude, frequency, and quality factor of the cantilever oscillation, demonstrating how single-electron motion can interact with a mechanical oscillator.     

Observations of nuclear reactors on satellites with a balloon-borne gamma-ray telescope

Gamma rays at energies of 0.3 to 8 megaelectron volts (MeV) were detected on 15 April 1988 from four nuclear-powered satellites including Cosmos 1900 and Cosmos 1932 as they flew over a double Compton gamma-ray telescope. The observations occurred as the telescope, flown from a balloon at an altitude of 35 kilometers from Alice Springs, Australia, searched for celestial gamma-ray sources. The four transient signals were detected in 30 hours of data. Their time profiles show maxima with durations of (21 +/- 1) and (27 +/- 1) seconds (half-width at half maximum) for the lower two satellites and (85 +/- 5) and (113 +/- 7) seconds for the remaining two. Their durations place the origin of the two shorter signals at orbital radii of 260(+40)(-60) and 260 +/- 60 km above the earth and the two longer at 800(+100)(-300) and 800(+250)(-300) kilometers. Their luminosities for energies >0.3 MeV are then (6.1 +/- 1.5) x 10(15), (3.9 +/- 1.0) x 10(15), (1.10 +/- 0.28) x 10(16), and (1.30 +/- 0.32) x 10(16) photons per second. The imaging of the strongest signal indicates a southeastern direction passing nearly overhead. The energy spectrum can be fit to an exponential with index 2.4 +/- 1.4. These transient events add to the already large backgrounds for celestial gamma ray sources.     

Thin-film transistor fabricated in single-crystalline transparent oxide semiconductor

We report the fabrication of transparent field-effect transistors using a single-crystalline thin-film transparent oxide semiconductor, InGaO3(ZnO)5, as an electron channel and amorphous hafnium oxide as a gate insulator. The device exhibits an on-to-off current ratio of approximately 106 and a field-effect mobility of approximately 80 square centimeters per volt per second at room temperature, with operation insensitive to visible light irradiation. The result provides a step toward the realization of transparent electronics for next-generation optoelectronics.     

扩展动力学平均场理论中近藤晶格模型的Luttinger Ward 泛函方法

提出了一种新的基于 Luttinger Ward 泛函的图解赝粒子方法来处理具有 RKKY 相互作用的重费米子体系的近藤晶格模型。采用此新方法,近藤晶格模型的光导结果被给出,并与已有研究结果较好相符。     

A neuron-silicon junction: a Retzius cell of the leech on an insulated-gate field-effect transistor

An identified neuron of the leech, a Retzius cell, has been attached to the open gate of a p-channel field-effect transistor. Action potentials, spontaneous or stimulated, modulate directly the source-drain current in silicon. The electronic signals match the shape of the action potential. The average voltage on the gate was up to 25 percent of the intracellular voltage change. Occasionally weak signals that resemble the first derivative of the action potential were observed. The junctions can be described by a model that includes capacitive coupling of the plasma membrane and the gate oxide and that accounts for variable resistance of the seal.     

星载雷达在多云多雨地区水稻遥感监测中的应用

综述了星载雷达在水稻遥感监测中的应用与研究.从水稻制图、水稻参数反演和水稻估产3个方面探讨了雷达遥感在水稻监测中应用的可行性和有效性,并针对当前研究的瓶颈,对多参数雷达数据在水稻遥感监测中的优势进行了分析和讨论.     

Elastomeric transistor stamps: reversible probing of charge transport in organic crystals

We introduce a method to fabricate high-performance field-effect transistors on the surface of freestanding organic single crystals. The transistors are constructed by laminating a monolithic elastomeric transistor stamp against the surface of a crystal. This method, which eliminates exposure of the fragile organic surface to the hazards of conventional processing, enables fabrication of rubrene transistors with charge carrier mobilities as high as approximately 15 cm2/V.s and subthreshold slopes as low as 2nF.V/decade.cm2. Multiple relamination of the transistor stamp against the same crystal does not affect the transistor characteristics; we exploit this reversibility to reveal anisotropic charge transport at the basal plane of rubrene.