Table of contents

Effective stiffness properties (D) of nanosized structural elements such as plates and beams differ from those predicted by standard continuum mechanics (D_c). These differences (D-D_c)/D_c depend on the size of the structural element. A simple model is constructed to predict this size dependence of the effective properties. The important length scale in the problem is identified to be the ratio of the surface elastic modulus to the elastic modulus of the bulk. In general, the non-dimensional difference in the elastic properties from continuum predictions (D-D_c)/D_c is found to scale as αS/Eh, where α is a constant which depends on the geometry of the structural element considered, S is a surface elastic constant, E is a bulk elastic modulus and h a length defining the size of the structural element. Thus, the quantity S/E is identified as a material length scale for elasticity of nanosized structures. The model is compared with direct atomistic simulations of nanoscale structures using the embedded atom method for FCC Al and the Stillinger-Weber model of Si. Excellent agreement between the simulations and the model is found.

A three-dimensional model of molecular dynamics (MD) is proposed to study the effects of tool geometry and processing resistance on the atomic-scale cutting mechanism. The model includes the utilization of the Morse potential function to simulate the interatomic force between the workpiece and a tool. The results show that the cutting resistance increases with the angle of the pin tool and the depth of cut, and the cutting force is essentially constant over the range of velocities simulated. In addition, the obtained cutting resistance of present MD simulation exhibits an evident relationship to the ratio of the vertical and the horizontal contact area between the tool and the workpiece within the range of a pin angle of 90-150°. Finally, work hardening and stick-slip phenomena during the process are also observed.

A new single-electron circuit using the unique features of single-electron devices is proposed, based on a basic strategy and circuit architecture for achieving large-scale integration. A unit circuit consisting of a single-electron transistor and a capacitor operates as an exclusive-NOR gate by the Coulomb blockade effect, and its transient behaviour is stochastic due to electron-tunnelling events. Using this unit circuit, a stochastic associative processing circuit is proposed, based on a new information-processing principle where the association probability depends on the similarity between the input and reference data. This circuit can be constructed by using a silicon nanocrystal floating-gate structure in which dots are regularly arranged on a gate electrode of a MOSFET. The simulation results of a simple digit pattern association demonstrate the successful stochastic operation. The background-charge effects on the proposed circuit are analysed and simulated, and it is shown that the circuit is much more robust to such effects than the conventional single-electron logic circuits.

The reflection properties of 300 nm periodically structured silicon surfaces with depth varying between 35 and 190 nm, prepared by interference lithography, were examined in the range 200 nm<λ<3000 nm. A decrease in the reflectivity that becomes stronger with increasing structure depth is observed below 1000 nm. This broad-band reduction is caused by diffraction effects at short wavelengths and by the `moth-eye effect' at long wavelengths. The results show a universal behaviour in the optical-path to wavelength ratio dependence of the reflectivity and are in good agreement with the results obtained for the `moth-eye effect' from the effective medium theory.

We demonstrate how to machine a vibrating wire resonator for ultrasonic excitations in gaseous and liquid helium. This novel resonator is designed as a nanoscopic mechanically flexible bridge machined out of a semiconductor/metal hybrid. Quenching of the mechanical resonance around 100 MHz in gaseous and liquid ⁴He at 4.2 K is shown.

Micromechanical cantilevers used in atomic force microscopy are characterized by the geometry, the elastic modulus E and the quality factor Q. The sensor can be regarded as a rectangular bar clamped on one side and free on the other. In contrast to a simple harmonic oscillator a cantilever has different eigenfrequencies ω_n and a mode-dependent spring constant D_n. Using the fluctuation-dissipation theorem we developed a simple model to calculate the thermal noise on each eigenmode for a free cantilever. With this result we can decide whether measuring on higher eigenmodes increases the force sensitivity.

This paper discusses the phase transformation of diamond cubic silicon under nano-indentation with the aid of molecular dynamics analysis using the Tersoff potential. By monitoring the positions of atoms within the model, the microstructural changes as silicon transforms from its diamond cubic structure to other phases were identified. The simulation showed that diamond cubic silicon transforms into a body-centred tetragonal form (β-silicon) upon loading of the indentor. The change of structure is accomplished by the flattening of the tetrahedron structure in diamond cubic silicon. Upon unloading, the body-centred tetragonal form transforms into an amorphous phase accompanied by the loss of long-range order of the silicon atoms. By performing a second indentation on the amorphous zone, it was found that the body-centred-tetragonal-to-amorphous phase transformation could be a reversible process.

The machining characteristics of nano-lithography are studied using atomic force microscopy (AFM). Scribing (scratching) experiments containing reciprocal single line furrows and multiple furrows are conducted to investigate the influence of the working parameters on the machined surface's properties, and upon the machining efficiency. The influence of the working parameters, including the applied load on the cantilever, scribing cycles, scribing speed and scribing feed, on the surface roughness, surface depth and material removal rate can then be accessed. Results indicate that the applied load is more significant than the scribing cycles on the groove depth. However, rougher surfaces are produced at larger loads. In multiple furrows produced with larger applied loads in order to obtain deeper furrows, surface roughness is improved by adjusting the scribing feed to a small value.

A method of contact scanning probe lithography has been developed to enable fabrication of elements with characteristic dimensions of about 50 nm. The method involves deposition of a thin-film two-layer polymer-metal mask coating, mechanical or thermal nonplastic deformation of the top metal layer with a probe microscope, the transfer of the pattern through the polymer by means of dry etching and the formation of various nanoelements through this prepared mask. The method is applicable to any materials relevant to the formation of different nanometre objects - both metal and dielectric - on their surface.

An atomic force microscope which is operated in the oscillating mode is an example of an impact oscillator. The description of such dynamical systems can be reduced to a mathematical mapping, which displays a square-root singularity. A direct consequence of this property is the emergence of an infinite series of period-adding bifurcations. This extremely characteristic phenomenon should be observed in atomic force microscopes. We consider an atomic force microscope in which the tip-substrate forces are modelled by a liquid-bridge interaction. By integrating the dynamical equations we show that the atomic force microscopy (AFM) dynamical behaviour has the same characteristic bifurcation scenario as the square-root map. We point to the remarkable role of the energy that is dissipated upon impact. We finally suggest ways to improve the operation of AFM.