Strategies for Controlled Placement of Nanoscale Building Blocks

The capability of placing individual nanoscale building blocks on exact substrate locations in a controlled manner is one of the key requirements to realize future electronic, optical, and magnetic devices and sensors that are composed of such blocks. This article reviews some important advances in the strategies for controlled placement of nanoscale building blocks. In particular, we will overview template assisted placement that utilizes physical, molecular, or electrostatic templates, DNA-programmed assembly, placement using dielectrophoresis, approaches for non-close-packed assembly of spherical particles, and recent development of focused placement schemes including electrostatic funneling, focused placement via molecular gradient patterns, electrodynamic focusing of charged aerosols, and others

Direct observation of rotational cooling in thermal desorption: No/Pd(111)

The rotational energy distribution of nitric oxide desorbed from a Pd(111) surface has been determined directly at high surface temperature by means of laser heating of the substrate. For a surface temperature of Ts = 1100 ± 100 K, the rotational energy distribution of the desorbed NO could be described as thermal, but with a significantly lower temperature of Tr = 640 ± 40 K. © 1990

Desorption of NO/Pd(111) induced by subpicosecond laser pulses: internal energy distributions

Results are presented on the desorption of nitric oxide (NO) from a Pd(111) surface under exposure to visible laser radiation in a 200-fs pulse. The desorption process for this prototype system of a diatomic molecule chemisorbed on a nonreactive metal surface has been investigated by measuring the yield and energy distribution of the desorbed molecules. The salient features of the experiment are described, with emphasis on the internal energy distributions of the desorbed NO molecules. A rotational energy distribution for desorbed NO molecules in the ground vibrational and electronic states is shown and discussed

Vibrationally assisted electronic desorption: Femtosecond surface chemistry of O2/Pd(111)

The process of desorption for the system of O2/Pd(111) under excitation by 100 fs pulses of visible light has been examined. Molecular desorption is found to occur with high efficiency and a nonlinear dependence on laser fluence. Direct time-domain measurements using a two-pulse correlation scheme reveal a dominant subpicosecond response together with a weaker, but significant correlation persisting for tens of picoseconds. These results imply a desorption pro-cess driven by the high electron temperatures produced by the femtosecond laser radiation. The slower component of the correlation response is interpreted as an enhancement of the desorption rate by adsorbate vibrational excitation. © 1994 American Institute of Physics

Vibrational distributions in desorption induced by femtosecond laser pulses: coupling of adsorbate vibration to substrate electronic excitation

Quantum-state distributions are reported for nitric oxide (NO) molecules desorbed from a Pd(111) surface at a base temperature of 140 K by laser pulses of 400 fs duration. Significant vibrational populations are observed in the V; = 0, 1, and 2 levels. For a femtosecond laser fluence capable of producing substrate electronic temperatures of ∼ 4500 K, the vibrational distribution of the desorbed NO molecules is roughly thermal with an average degree of vibrational excitation corresponding to a temperature of 2900 K. These measurements can be regarded as the reverse of the usual vibrational relaxation measurement in that here energy flows from the substrate to the adsorbate vibration. The high degree of excitation of the NO intramolecular vibration can be attributed directly to efficient coupling to the electron-hole pairs generated in the Pd substrate by the femtosecond laser pulse. The process is modeled by calculating electronic and lattice temperatures for the Pd substrate and then incorporating the electron temperature profile into a master equation for the NO vibrational populations. The analysis permits an effective coupling constant of ∼ 15 cm-1 to be inferred for the interaction between the substrate electronic excitation and the intramolecular vibration. © 1993

Ambipolar Tetraphenylpyrene (TPPy) Single-Crystal Field-Effect Transistor with Symmetric and Asymmetric Electrodes

An ambipolar field-effect transistor (FET) based on a 1,3,6, 8-tetraphenylpyrene (TPPy) single-crystal, a high photoluminescent material, has been successfully fabricated using symmetric and asymmetric electrodes. Several kinds of metal electrodes have been employed to investigate the charge injection characteristics in the single-crystal FET. Hole and electron mobilities of 0.34 and 7.7 × 10−2cm2 V−1 s−1 were achieved by using Au and Ca electrodes, respectively. The ambipolar characteristic of this device gives a prospect for further development in light-emitting FET operation