The tensile strengths of individual multiwalled carbon nanotubes (MWCNTs) were measured with a "nanostressing stage" located within a scanning electron microscope. The tensile-loading experiment was prepared and observed entirely within the microscope and was recorded on video. The MWCNTs broke in the outermost layer ("sword-in-sheath" failure), and the tensile strength of this layer ranged from 11 to 63 gigapascals for the set of 19 MWCNTs that were loaded. Analysis of the stress-strain curves for individual MWCNTs indicated that the Young's modulus E of the outermost layer varied from 270 to 950 gigapascals. Transmission electron microscopic examination of the broken nanotube fragments revealed a variety of structures, such as a nanotube ribbon, a wave pattern, and partial radial collapse.

Ideal nanowire interconnects for nanoelectronics will be refractory, covalently bonded, and highly conductive, irrespective of crystallographic orientation. Theoretical studies suggest that boron nanotubes should be stable and exhibit higher electrical conductivities than those of carbon nanotubes. We describe CVD growth of elemental boron nanowires, which are found to be dense nanowhiskers rather than nanotubes. Conductivity measurements establish that they are semiconducting, with electrical properties consistent with those of elemental boron. High conductivities should be achievable through doping.

Precise control of thermal evaporation deposition parameters allows the reproducible production of silver and gold island films on glass substrates with tunable surface plasmon resonance wavelengths. Specific combinations of substrate temperature, deposition rate, and film thickness produce films exhibiting surface plasmon resonance wavelengths that can be adjusted from throughout the visible and into the near infrared regions of the electromagnetic spectrum. The effects of deposition parameters on surface plasmon resonance wavelengths are quantified using a so-called “design of experiment” analysis. The analysis produces reliable predictive models for producing Ag and Au films with predetermined surface plasmon resonance wavelengths.

Carbon nanotubes are manipulated in three dimensions inside a scanning electron microscope (SEM). A custom piezoelectric vacuum manipulator achieves positional resolutions comparable to scanning probe microscopes, with the ability to manipulate objects along one rotational and three linear degrees of freedom. This prototypical device can probe, select and handle nanometre-scale objects such as carbon nanotubes in order to explore and correlate their mechanical and electrical properties. Under real-time SEM inspection, carbon nanotubes are stressed while monitoring their conductivity, and nanotubes are attached to commercial atomic force microscope (AFM) tips such that the forces applied to the tubes can be measured from the cantilevers' deflections. The manipulator functions both as a research tool for investigating properties of carbon nanotubes and other nanoscale objects without surface restrictions, and as a rudimentary building device for larger nanotube assemblies. This capability to select and manipulate nanoscale components and to examine directly their suitability as construction materials during various phases of the construction process will play an important role in enabling the technology of assembling mechanical and electronic devices from prefabricated components.

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Rate constants kQ for collisional quenching of A 2Σ+, v′=0, OH and OD have been measured for specific rotational levels N′ of the radical and a wide variety of collision partners. Through measurements of the time-dependent laser-induced fluorescence in a low pressure discharge flow at room temperature, we observe a decrease in kQ with increasing rotational quantum number for most quenchers. The internal levels of the collision pairs appear unimportant from experiments involving deuterium substitution. A comparison of rotationless rates for different colliders [kQ(N=0)] with calculations based on collision complex formation indicate that attractive forces play a role in the quenching process.

Spatial distributions of photoelectrons produced by multiphoton ionization of xenon atoms are recorded by projecting the expanding photoelectron cloud onto a two-dimensional position sensitive detector. The projected image provides a direct view of the squared angular wave functions of the free electrons as well as their energy distribution. The results confirm recent observations that intermediate state resonances with 5/and 4/character establish the dominant ionization paths at low intensity, for short pulse excitation at 640 and 620 nm. At higher intensity more complex superpositions occur with formation of electrons with continuous distributions at low energies.PACS numbers: 32.80.RmPhotoelectrons generated at a point source with a discrete energy travel outward on the surface of a sphere that expands with time. For example, electrons produced at time £=0 with an energy of 1 eV can be found 20 ns later on the surface of a sphere of 25 mm diameter. This sphere can be projected onto a flat screen using an external electric field. A circular image results with a diameter that is proportional to square root the electron energy and a filling pattern that reveals the spatial distribution of the electrons on the surface of the sphere. In this way, the squared angular wave function of the free electrons is accessible to direct observation.We have used this approach to investigate multiphoton ionization of xenon atoms in an intense laser field. Simultaneous visualization of the photoelectron energy and angular distributions facilitates the identification and classification of ionization mechanisms.Recent work on multiphoton ionization of atoms and molecules by intense laser fields has shown that the dynamics of ionization are governed by the modification of the electronic structure of the target by the radiation field [1][2][3][4][5][6][7]. The effective energies of the electronic states are shifted (ac Stark effect) so strongly that the laser, which at low intensity was not resonant with any particular multiphoton transition, becomes resonant with individual intermediate states at specific critical intensities. One result is that the photoelectron energy and angular distributions often reflect the nature of the dominant intermediate states.Consistent with previous experiments, we observe that at moderate intensities the photoelectron energies are discrete, appearing as if they had come from photoionization of the intermediate states, E =hv -IP (intermediate), rather than from the ground state, E=nhv -IP (ground state). This apparent nonconservation of energy results from the fact that photoelectrons do not recover the ponderomotive energy under conditions such that the product of the laser pulse duration and the electron velocity is much smaller than the spatial dimensions of the laser focus [1,2]. Our photoelectron angular distributions show that predominantly the m=0 component of the intermediate state is being ionized. This is likely a result of the larger m =0 to m =0 matrix elements in multiphoton transitions. A...

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