Carbon nanotubes as schottky barrier transistors

We show that carbon nanotube transistors operate as unconventional "Schottky barrier transistors," in which transistor action occurs primarily by varying the contact resistance rather than the channel conductance. Transistor characteristics are calculated for both idealized and realistic geometries, and scaling behavior is demonstrated. Our results explain a variety of experimental observations, including the quite different effects of doping and adsorbed gases. The electrode geometry is shown to be crucial for good device performance.     

Electrical transport and noise in semiconducting carbon nanotubes

We investigate electrical transport and noise in semiconducting carbon nanotubes. By studying carbon nanotube devices with various diameters and contact metals, we show that the ON-currents of CNFETs are governed by the heights of the Schottky barriers at the metal/nanotube interfaces. The current fluctuations are dominated by 1/f noise at low-frequencies and correlate with the number of transport carriers in the device regardless of contact metal.     

Some aspects of the infrared multiple photon dissociation of ammonia

The infrared multiple photon dissociation of NH₃ by a CO₂ laser is investigated through laser-induced fluorescence and chemiluminescence techniques. A linear dependence of the fractional dissociation yield on pulse energy is found, the dependence exemplifying two distinct thresholds. Significant collisional enhancement of the fractional yield is observed. The results are discussed in terms of the existence of bottlenecks in the laser up-pumping process.     

EXCITED STATE INTERACTIONS OF 7-AZAINDOLE WITH ALCOHOL AND WATER

Abstract— The fluorescence spectrum of 7-azaindole in alcohol is composed of two fluorescence bands. Effects of pH, temperature and solvent deuteration on the fluorescence spectra and quantum yields of 7-azaindole and other model compounds in ethanol and in water are reported. The long wavelength band arises from a tautomeric species formed in an adiabatic photoreaction involving double proton transfer between one molecule of 7-azaindole and one molecule of alcohol.
The fluorescence spectrum of 7-azaindole in water is composed of only one band, but the emission is weak and shows a large solvent isotope effect. The possibility of a double proton transfer reaction between 7-azaindole and water is discussed.     

Field-modulated carrier transport in carbon nanotube transistors

We have investigated the electrical transport properties of carbon nanotube field-effect transistors as a function of channel length, gate dielectric film thickness, and dielectric material. Our experiments show that the bulk properties of the semiconducting carbon nanotubes do not limit the current flow through the metal/nanotube/metal system. Instead, our results can be understood in the framework of gate and source-drain field induced modulation of the nanotube band structure at the source contact. The existence of one-dimensional Schottky barriers at the metal/nanotube interface determines the device performance and results in an unexpected scaling behavior.     

Influence of the heterocyclic side ring on orientation during nitrations of 1,2-alkylenedioxy-annelated benzenes and their mononitro derivatives

Nitration of 1,2-alkylenedioxybenzenes 1 furnished the respective nitro derivatives 3 and 4 in the relative ratios: 4a:3a /100:trace, 4b:3b /98:2.4, 4c:3c /86:14, 4e:3e /91:9 and 4f:3f /99:1.3. Nitration of 4 gave 5a:6a:8a /0:0:100, 5b:6b:8b /7.7:3.2:89, 5c:6c:8c /23:12:65, 5d:6d:8d /14:74:12, 5e:6e:8e /27:18:55 and 5f:6f:8f /23:7.0:70. Nitration of the isomeric 3 afforded the dinitro products 5, 6 and 7 in the following relative ratios: 5a:6a:7a /92:8:0, 5b:6b:7b /80:20:0, 5c:6c:7c /69:20:1 1, 5d:6d:7d /45:19:36, 5e:6e:7e /37:57:5.9 and 5f:6f:7f /64:36:0. Nitration of 3-nitro-1,2-dimethoxybenzene ( 9 ) furnished: 10:11 /63:37. Orientation as a function of the heterocyclic ring-size is discussed.     

Transformations on 2,3,4,5-tetrahydrobenzo[b][1,4]-dioxocin leading to substituted ortho-nitroaryl azides,benzofuroxans, benzofurazans and related compounds

Nitration of the acetamido-nitrobenzodioxocins 10 , prepared from the corresponding amino derivatives 9 , led to the acetamido-dinitrobenzodioxocins 11 , hydrolysis of which furnished the corresponding amines 13 . Preparation of the dinitroazides 18 and acetamido-nitroazides 21 as precursors to substituted dioxocino-annelated benzofuroxans is described. Thermolysis of the dinitro-azido derivatives 18a,c,e and/or direct nitration of the unsubstituted benzofuroxans 1a, 2a afforded the isomeric nitrobenzofuroxans 1b, 2b,c . Thermolysis of the acetamido-nitroazides 21 gave the acetamidobenzofuroxans 1d, 2d,e . All benzofuroxans were deoxygenated to the corresponding benzofurazans 3b,d, 4b-e . Some aspects of electrophilic and nucleophilic aromatic substitution are discussed.