电子器件的第二次变革

本文分析了电子器件发展的两次变革，比较了真空电子器件、微电子器件和纳电子器件的结构与特性，给出了它们在理论、材料和技术上的主要差别。提出了纳电子器件的基础结构是纳米点双隧道结构成的单电子管（ＳＥＴ），纳米功能单元的超高密度集成是纳电子器件的主要特征。

浅谈数字电视发射机技术的发展

经过近十几年的努力,数字电视地面广播所必需的数字电视发射机技术有了飞速的发展。本文简要介绍了国内外近年在数字电视发射机研制方面的进展,讨论了我国今后几年在数字电视发射机研制方面需要解决的若干技术问题。

Fabrication and Characteristics of a Si-Based Single Electron Transistor

Si based single electron transistor (SET) is fabricated successfully on p type SIMOX substrate,based on electron beam (EB) lithography,reactive ion etching (RIE) and thermal oxidation.In particular,using thermal oxidation and etching off the oxide layer,a one dimensional Si quantum wire can be converted into several quantum dots inside quantum wire in connection with the source and drain regions.The differential conductance (d I ds /d V ds ) oscillations and the Coulomb staircases in the source drain current ( I ds ) are shown clearly dependent on the source drain voltage at 5 3K.The I ds V gs (gate voltage) oscillations are observed from the I ds V gs characteristics as a function of V gs at different temperatures and various values of V ds .For a SET whose total capacitance is about 9 16aF,the I ds V gs oscillations can be observed at 77K.

A Model of a Single Electron Transistor of Metallic Tunneling Junctions and Its Validation

Based on the orthodox theory,a model of a single electron transistor （SET） of metallic tunneling junctions is built using the master equation method. Several parameters of the device, such as capacitance, resistance and temperature,are input into the model and thus the I-V curves are attained. These curves are consistent with those from other experiments; therefore, the model is verified. However, there still exists a difference between simulated results and experimental results,mainly comes from the stationary case of the master equation. In other words, precision of simulated results would be increased if the transient case of the master equation is considered. Moreover, the current increases exponentially at higher drain voltages, which is due to the fact that the barrier suppression is caused by the image charge potential.

Detection of Terahertz Photon by GaAs-Based Single Electron Transistor at Low Temperatures

A reproducible terahertz （THz） photocurrent was observed at low temperatures in a Schottky wrap gate single electron transistor with a normal-incident of a CH3OH gas laser with the frequency 2.54THz. The change of source-drain current induced by THz photons shows that a satellite peak is generated beside the resonance peak. THz photon energy can be characterized by the difference of gate voltage positions between the resonance peak and satellite peak. This indicates that the satellite peak exactly results from the THz photon-assisted tunneling. Both experimental results and theoretical analysis show that a narrow spacing of double barriers is more effective for the enhancement of THz response.

A Monolithic Integrated Logic Circuit of Resonant Tunneling Diodes and a HEMT

A technology for the monolithic integration of resonant tunneling diodes （RTDs） and high electron mobility transistors （HEMTs） is developed. Molecular beam epitaxy is used to grow an RTD on a HEMT structure on GaAs substrate. The RTD has a room temperature peak-to-valley ratio of 5.2 ： 1 with a peak current density of 22. 5kA/cm^2. The HEMT has a 1μm gate length with a - 1V threshold voltage. A logic circuit called a monostable-to-bistable transition logic element （MOBILE） circuit is developed. The experimental result confirms that the fabricated logic circuit operates successfully with frequency operations of up to 2GHz.

Strong shape-dependence of Morin transition in α-Fe2O3 single-crystalline nanostructures

Single-crystalline hematite （α-Fe2O3） nanorings （short nanotubes） and nanotubes were synthesized by a hydrothermal method. High-resolution transmission electron microscopy and selected-area electron diffraction confirm that the axial directions of both the nanorings and nanotubes are parallel to the crystalline c-axis. Intriguingly, the Morin transition occurs at about 210 K in the short nanotubes with a mean tube length of about 115 nm and a mean outer diameter of about 169 nm. However, it does not occur in the nanotubes with a mean tube length of about 317 nm and a mean outer diameter of about 148 nm. Detailed analysis of magnetization data, X-ray diffraction patterns, and room-temperature M6ssbauer spectra demonstrates that this very strong shape-dependence of Morin transition is intrinsic to hematite. We explain this intriguing shape- dependence quantitatively, in terms of the opposite signs of the surface mag- netic anisotropy constants of the surface planes parallel and perpendicular to the c-axis.

Structural and electronic properties of chiral single-wall copper nanotubes

The structural,energetic and electronic properties of chiral(n,m)(3≤n≤6,n/2≤m≤n)single-wall copper nanotubes(CuNTs)have been investigated by using projector-augmented wave method based on density-functional theory.The(4,3)CuNT is energetically stable and should be observed experimentally in both free-standing and tip-suspended conditions,whereas the(5,5)and(6,4)CuNTs should be observed in free-standing and tip-suspended conditions,respectively.The number of conductance channels in the CuNTs does not always correspond to the number of atomic strands comprising the nanotube.Charge density contours show that there is an enhanced interatomic interaction in CuNTs compared with Cu bulk.Current transporting states display different periods and chirality,the combined effects of which lead to weaker chiral currents on CuNTs.

Observation of Coulomb blockade and ballistic tunneling in graphene single electron transistor

A square graphene single electron transistor （SET） was defined with two side gates, and its transport was studied at low temperature at T = 2 K. At zero magnetic field, Coulomb blockade oscillations were clearly observed near the Dirac point of this device. At high magnetic field, in the quantum Hall regime, we observed ballistic tunneling of the carders through the graphene SET, contrary to the Coulomb blockades observed while approaching the vicinity of the Dirac point.

Two-dimensional organic single-crystalline p-n junctions for ambipolar field transistors

Two-dimensional single-crystalline p-n junctions of organic semiconductors(pn-2 DCOSs) show great potential in organic logic circuits due to their single crystal nature and excellent ambipolar charge transport. However,there are only few reports on pn-2 DCOSs because it is difficult to obtain such highly ordered structure in p-n junction.Herein, a novel and effective solution processing method of secondary transfer technology based on the facile drop casting is used to fabricate devices of pn-2 DCOSs based on C8-BTBT(p-type) and TFT-CN(n-type) successfully. The high-performance ambipolar field transistors based on such ultrathin pn-2 DCOSs with several molecular layers thickness show wellbalanced ambipolar charge transport behaviors with hole mobility as high as 0.43 cm^2 V^-1 s^-1 and electron mobility up to 0.11 cm^2 V^-1 s(^-1), respectively. This work is essential for studying the intrinsic properties of organic p-n junctions and achieving high performance in organic complementary circuits.

Electronics and Structural Properties of Single-Walled Carbon Nanotubes Interacting with a Glucose Molecule: ab initio Calculations

The adsorption of glucose molecule on single-walled carbon nanotubes(SWCNTs)is investigated by density functional theory calculations.Adsorption energies and equilibrium distances are evaluated,and glucose binding to the typical semiconducting and metallic nanotubes with various diameters and chirality are compared.We also investigated the role of the structural defects on the adsorption capability of the SWCNTs.We could observe larger adsorption energies for the larger diameters semiconducting CNTs,while the story is paradoxical for the metallic CNTs.The obtained results reveal that the adsorption energy is significantly higher for nanotubes with higher chiral angles.Finally,the adsorption energies are calculated for defected nanotubes for various configurations such as glucose molecule approaching to the pentagon,hexagon,and heptagon sites in the tube surface.We find that the respected defects have a minor contribution to the adsorption mechanism of the glucose on SWNTs.The calculation of electron transfers and the density of states supports that the electronic properties of SWCNTs do not change significantly after the gluycose molecular adsorption.Consequently,one can predict that presence of glucose would neither modify the electronic structure of the SWCNTs nor direct to a change in the conductivity of the intrinsic nanotubes.

Stable single-photon detection based on Si-avalanche photodiode in a large temperature variation range

In this paper, we present a stable single-photon detection method based on Si-avalanche photodiode(Si-APD) operating in Geiger mode with a large temperature variation range. By accurate temperature sensing and direct current(DC) bias voltage compensation, the single-photon detector can work stably in Geiger mode from-40 °C to 35 °C with an almost constant avalanche gain. It provides a solution for single-photon detection at outdoor operation in all-weather conditions.

Negative differential resistance in a molecular junction of carbon nanotube and benzene

We propose a novel molecular junction with single-walled carbon nanotubes as electrodes bridged by a benzene molecule, in which the electrodes are saturated by different terminations (C-, H- and N-). It is found that the different terminations at the carbon nanotube ends strongly affect the electronic transport properties of the junction. The current-voltage (I-V) curve of the N-terminated carbon nanotube junction shows a more striking nonlinear feature than that of the C- and H-terminated junctions at small bias. Moreover, the negative differential resistance behaviors can be observed significantly in the N-terminated carbon nanotube junction, whereas not in the other two cases.