用分子自组装技术制备的单电子器件的Monte Carlo模拟

用分子自组装技术制备出纳米金单电子器件,并测量了其伏安特性,根据单电子系统的半经典理论,用MonteCarlo法对其结果进行了模拟.结果表明,模拟出的伏安曲线与实测的伏安曲线有较好的一致性,反映了模拟方法用于单电子器件研究的合理性,此外发现,虽然单电子器件两电极间含有众多的纳米粒子,但在低压区,其伏安特性只与少数纳米粒子有关 关键词： 单电子器件 MonteCarlo模拟 分子自组装     

Thermodynamic Enantioface-Binding Selectivities of Monosubstituted Alkenes to a Highly Discriminating Chiral Transition -Metal Lewis Acid; equilibration of diastereoisomeric (cyclopentadienyl)(alkene)(nitrosyl)(triphenylphosphine)rhenium complexes ([Re(η5–C5H5)(CH2 = CHR)(NO) (PPh3)]+BF)

Reactions of monosubstituted alkenes RCH = CH₂ and [Re(η⁵–C₅H₅)(CH₂Cl₂) (NO)(PPh₃)]⁺BF give complexes ([Re(η⁵–C₅H₅))(CH₂?CHR)(NO) (PPh₃)]⁺BF ( 1a–g ) in 63–99% yields as mixtures of (RS,SR)- and (RR,SS)-diastereoisomers ( 1a (R = Me), 66:34; 1b (R = Pr), 63:37; 1c (R = PhCH₂), 70:30; 1d (R = Ph), 75:25; 1e (R = i-Pr), 64:36; 1f (R = t-Bu), 84:16; 1g (R = Me₃Si), 69:31; Scheme 2). These differ in the C?C enantioface bound to the chiral Re fragment. In most cases, the analogous reactions of RCH?CH₂ and [Re(η⁵–C₅H₅) (C₆H₅Cl)(NO)(PPh₃)]⁺ BF give comparable results. When 1a – e , g are heated in PhCl at 95–100°, equilibration to 96:4, 97:3, 97:3, 90:10, > 99:< 1, and > 99:< 1 (RS,SR)/(RR,SS) mixtures occurs (79–99% recoveries; Tables 1 and 2). Thus, thermodynamic enantioface-binding selectivities are much higher than kinetic binding selectivities. This phenomenon is analyzed in detail. A crystal structure of (RS,SR)- 1e (monoclinic, P2₁/c, a = 10.256(1) Å. b = 17.191(1) Å, c = 16.191(1) Å, β = 101.04(1)°, Z = 4) shows that the Re–C(1)–C(2) plane (see Fig.2) is nearly coincident with the Re–P bond (angle 15°), and that the i-Pr group is ‘syn’ to the nitrosyl ligand.     

AlGaN/GaN HEMTs on 4-Inch Silicon Substrates in the Presence of 2.7-μm -Thick Epilayers with the Maximum Off-State Breakdown Voltage of 500 V

We report on the high breakdown performance of AlGaN/GaN high electron mobility transistors （HEMTs） grown on 4-inch silicon substrates. The HEMT structure including three Al-content step-graded AlGaN transition layers has a total thickness of 2.7 μm. The HEMT with a gate width WG of 300 μm acquires a maximum off-state breakdown voltage （BV） of 550 V and a maximum drain current of 527 mA/mm at a gate voltage of 2 V. It is found that BV is improved with the increase of gate-drain distance LGD until it exceeds 8 μm and then BV is tended to saturation. While the maximum drain current drops continuously with the increase of LGD. The HEMT with a WG of 3 mm and a LGD of 8 μm obtains an off-state BV of 500 V. Its maximum leakage current is just 13 μA when the drain voltage is below 400 V. The device exhibits a maximum output current of 1 A with a maximum transconductance of 242 mS.     

Ultraviolet Phototransistors on AlGaN/GaN Heterostructures

We report on the fabrication and characterization of phototransistors based on AIGaN/GaN heterostructure grown over 6H-SiC substrates. The device has two functions： as a high electron mobility transistor （HEMT） and an ultraviolet photodetector at the same time. As an HEMT, its maximum transconductance is 170mS/ram, while the minimum cutoff frequency fT and the maximum oscillation frequency fm are 19 and 35 GHz, respectively. As a photodetector, the device is visible blind, with an ultraviolet/green contrast of three orders of magnitude, and a responsivity as high as 1700 A/W at the wavelength of 362nm.