There is a demand for good theoretical understanding of the response of an atomic force microscope cantilever to the extremely nonlinear impacts received while tapping a sample. A model and numerical simulations are presented in this paper which provide a very pleasing comparison with experimental results. The dependence of the cantilever amplitude and phase upon the sample stiffness, adhesion and damping are investigated using these simulations, and it is found that 'topographic' tapping images are not independent of sample properties, nor will it be trivial to measure materials' properties from the tapping data. The simulation can be applied to other probe microscope configurations as well.
We describe subwavelength surfaces etched into silicon wafers that exhibit antireflection characteristics for visible light. The wafers are fabricated by holographically recording a crossed-grating in a photoresist mask followed by reactive-ion etching to transfer the primary mask onto the silicon substrate. The dependence of reflectivity on the wavelength and angle of incidence is measured. The overall antireflection performance of the corrugated silicon wafers is compared with that of standard thin-film stacks, and is interpreted with the effective medium theory and with simulation results obtained from rigorous computations.
We use a molecular dynamics simulation to investigate the properties and design space of molecular gears fashioned from carbon nanotubes with teeth added via a benzyne reaction known to occur with C-60. Brenner's reactive hydrocarbon potential is used to model interatomic forces within each molecular gear. A Lennard-Jones 6-12 potential or the Buckingham (exp+6) potential plus electrostatic interaction terms are used for intermolecular interactions between gears. A number of gear and gear/shaft configurations are simulated on parallel computers. One gear is powered by forcing the atoms near the end of the nanotube to rotate, and a second gear is allowed to rotate by keeping the atoms near the end of its nanotube constrained to a cylinder. The meshing aromatic gear teeth transfer angular momentum from the powered gear to the driven gear. Results suggest that these gears can operate at up to 50-100 GHz in a vacuum at room temperature. The failure mode involves tooth slip, not bond breaking, so failed gears can be returned to operation by lowering the temperature and/or rotation rate.
Scanning force microscopy (SFM) has been used to perform nanoscale studies of domain structures and switching behaviour of Pb(ZrxTi1-x)O-3 (PZT) thin films. An SFM piezoresponse mode, based on the detection of the piezoelectric vibration of a ferroelectric sample, was shown to be suitable for high resolution imaging of ferroelectric domains in thin films. The lower limit of the piezoresponse mode imaging resolution depends on the radius of the probing lip and is estimated to be of the order of several nanometers. The effect of the film microstructure on the imaging resolution is discussed. The ability of effective control of domains as small as 50 nm by means of SFM has been demonstrated. Ii: is shown that SFM can be used in the investigation of electrical degradation effects in ferroelectric thin films. Formation of regions with unswitchable polarization as a result of fatigue, within grains of submicron size, was experimentally observed.
A phenomenological model for the rotational dynamics of a single laser-powered molecular motor is discussed and tested through molecular dynamics simulations. The motor is used to power carbon nanotube-based gears. For a given laser power density and arrangement of free charges in the body of the gear we have defined an intrinsic frequency of the gear oscillatory rotations. The nanotube rotations are not of an oscillatory nature if the laser field frequency is of the same order of magnitude as the intrinsic frequency of the tube and there is an additional phase match between the two. For the laser-powered gear motor dynamics, the rotational angular momentum of the driven gear tend to stabilize the rotational dynamics of the system, and unidirectional rotations for the entire duration of the simulations are observed.
The fabrication of microcomponents or microstructured surfaces with conventional manufacturing methodssuch as turning, milling or drilling-imposes high demands on the machine behavior. The high requirements in terms of machine characteristics are currently met by only few ultraprecision machine tools. A broad range of materials such as, for example, non-ferrous metals or plastics can be machined, producing real three-dimensional structures with an optical surface quality.
The cantilever in an atomic force microscope (AFM) is forced to vibrations if its sensor tip is in contact with an insonified sample. These vibrations and the motion of the sensor tip depend on the forces between the sensor tip and the sample, the mechanical excitation of the sample surface, and the oscillatory behaviour of the cantilever. In this paper, the transfer of vibrations from a sample to an AFM-cantilever is described theoretically supposing a rectangular-beam cantilever with the sensor tip at its very end and taking into account flexural vibrations only. The calculations include nonlinear effects resulting from the nonlinearity of the tip-sample forces. The comparison with experimental results shows a convincing agreement. The presented theory yields the fundamentals to determine elastic properties and adhesive forces of a sample surface with the lateral resolution of an AFM exploiting AFM-cantilever vibrations enforced by a suitable insonification of the sample.
The possibility of SPM-based data storage is described regarding both its recording density and readout speed for ultrahigh density data storage. We consider their gap control to achieve high-speed readout, Suitable SPM-based storages are selected and their details are studied. as a result, scanning near-field optical microscope (SNOM)- and atomic force microscope (AFM)-based storages are expected to be candidates for future storage. SNOM-based storage is for 100 Gb in(-2). AFM-based storage is for 1 Tb in(-2). Using new force modulation AFM pit recording, an ultrahigh recording density of 1.2 Tb in(-2) and a readout speed of 1.25 Mb s(-1) are demonstrated.
The gelation system of a 1:1 mixture of cholesterol-containing isocyanuric acid (1) and cholesterol-containing 2,4,6-triaminopyrimidine (2) in organic fluids was investigated to understand the gelation mechanism. A series of gelation tests have shown that the gelation is remarkably dependent upon the cooling rate of the mixture solution as well as the nature of solvents and concentrations. The investigation using FT-IR revealed that the mismatched hydrogen-bonding interaction between (1) and (2) is responsible for the gelation and well defined hydrogen-bonding interaction such as a 'molecular tape' rather results in coprecipitation. It was confirmed by the gelation test of two-faced (1) and (2) with the complementary single-faced compounds that the gel is constructed by the three-dimensional network through an irregular hydrogen-bonding interaction.
Future nanotechnology applications are likely to involve reactive or non-reactive species carried along a fluid stream. We have performed several molecular dynamics simulations of a buckyball, C-60, cage or idealized atom in a helium fluid flowing axially inside a carbon nanotube. The fluid was started at some initial velocity and both the fluid and buckyball allowed to recycle axially via minimum image boundary conditions. A buckyball introduced into the feedstream (started at zero velocity) usually reached fluid velocity within 5 ps. Leakage rates of helium past the C-60 depended on the nanotube diameter and fluid velocity. These leakage rates and other important features of the dynamics changed significantly when C-60 was modelled as an idealized atom or when the nanotube was held rigid, suggesting that simulations of fluid dynamics inside nanomachines should be fully dynamic and atomistic.
Various types of molecular bearings, gears, joints, etc have recently been proposed and studied in the growing nanotechnology literature using classical molecular dynamics. In a previous study, we reported simulations for several model graphite bearings using fully atomistic molecular dynamics simulations. It was subsequently found that various predictions based on simulations of this type do not agree with those of a more correct quantum approach owing to leakage of the quantum zero-point vibrational energy in the molecular dynamics simulations. In this study we use the tools of rigid-body dynamics to address the zero-point energy problem. The results of these simulations are striking in the sense that under certain conditions the bearing is found to be frictionless, as previously alluded to by Feynman. A frictionless bearing will undergo 'superrotation', a classical dynamical behavior reminiscent of superfluidity. States which are chaotic in nature may not have this new characteristic, an issue we investigate with maps of phase space.
An organosilane monolayer consisting of trimethylsilyl ([-Si(CH3)(3)], TMS) STOUPS prepared on the native oxide of a silicon substrate effectively served as a resist material for AFM-based nanolithography. The patterning of this resist was performed through its electrochemical degradation locally induced around the contact point of a conductive AFM probe while biasing the sample substrate positively, In the region where the probe passed, the monolayer resist was degraded and the underlying silicon oxide surface was selectively uncovered. The number of electrons injected into the probe-scanned region was controlled by conducting the AFM lithography in constant current mode. By means of this constant current AFM lithography a sufficient amount of electrons could be injected even at high probe-scan rates faster than 1000 mu m s(-1). II was demonstrated that the TMS monolayer resist was sensitive enough to allow line drawing at a probe scan rate of 5000 mu m s(-1).
Force modulation microscopy via sample displacement has been used to image the elastic characteristics of a stiff material-a nickel-based superalloy in which the two phases have close Young's moduli. The experimental operating conditions for obtaining good images are such that the hypothesis of a linear tip-sample interaction is difficult to satisfy when stiff samples are involved, more difficult for a given static load than with compliant materials. To limit the undesirable effects of friction, the cantilever deflection amplitude must be kept small and the modulation frequency must be chosen outside a resonance of the system, but high enough to generate a strong dynamic load able to sufficiently indent the sample. A semiquantitative approach of the elasticity measurement taking into account the nonlinearity of the tip-sample interaction is proposed and described. The semiquantitative term is understood here as the possibility of measuring the elastic modulus of one of the constituents of a material relative to another constituent, the Young's modulus of which is known and used as a reference.
A new scanning method, 'touch and lift', aimed to improve the simultaneous acquisition of topography and force-distance curves on each point of the scanned surface, is presented. This method does not damage the sample or the cantilever and enables us to collect a lot of data in a relatively short time. Its most important feature is that data are directly organized in 'force-slices', i.e. images giving immediate qualitative information on the physico-chemical structure of the sample. We present and discuss such images for two samples: a fluorescein isothyocyanate grating on silicon in air and a peroxidase grating on silicon in water, measuring the spatial variation of stiffness, attractive forces and adhesion in both cases.
Energy levels are calculated for three-dimensional (3D) quantum-confinement structures with finite potential barriers. GaAs/Ga0.63Al0.37As, Ga0.47In0.53As/InP and Ga0.47In0.53As/Al0.48In0.52As systems are considered. Analytic results are presented for spherical structures including the effects of nonparabolicity. A numerical method is also presented for the calculation of the energy levels in a 3D quantum-confinement structure in the shape of a cube or a parallelopiped. The method is applied for calculating the energy shift in a cylindrical dot of the GaAs/Ga0.63Al0.37As system.
Positional control is fundamental to most manufacturing processes as well as a wide range of other applications. Many types of positional devices have been proposed and used, ranging from robotic arms to Stewart platforms. This paper discusses a new family of six degrees of freedom positional control devices which generally combine simple designs, high stiffness and strength, and a wider range of motion. Stiffness is particularly advantageous in very small (submicron) positional devices as thermal motion is a significant source of positional uncertainty. The stiffness and thermally induced positional uncertainty of three designs-a robotic arm, a Stewart platform, and one member of the new family-are analysed and compared. The Stewart platform provides the greatest stiffness for a given structural mass but has the most restrictive range of motion. The robotic arm is least stiff. The new proposal combines greater stiffness than the robotic arm with a significantly greater range of motion than the Stewart platform.
Molecular manufacturing should let us synthesize most arrangements of atoms that are consistent with physical law. Assemblers have been proposed as a means of accomplishing this objective. They would be able to build a wide range of useful products as well as copies of themselves. A simpler though less general proposal is a hydrocarbon assembler, restricted to manufacturing relatively stiff hydrocarbons. The design and analysis of such an assembler should be substantially simpler than that of a more general assembler. In this paper, we consider the 'intermediary metabolism' of a hydrocarbon assembler, i.e. the set of reactions that permit processing of the feedstock molecules and their conversion into molecular tools (positionally controlled carbenes, radicals, and other reactive species). The specific feedstock molecule analyzed is butadiyne (a linear molecule, C4H2, also known as diacetylene; not to be confused with the more common but chemically distinct nonlinear molecule butadiene: C4H6).
In this article it is argued that classical molecular dynamics studies of nanomachines may not give an accurate representation of their performance. Fortunately a new method, internal coordinate quantum Monte Carte, an improved technique for computing quantum mechanical ground-state energies and wavefunctions, has the potential capability to model these systems. Some relevant examples demonstrate that the quantum ground state for many-body systems similar to those of interest in nanotechnology has a qualitatively different structure than that obtained from a molecular dynamics calculation which exhibited chaos and gross instabilities at energies of only a fraction of the ground-state energy. This result casts uncertainty on the reliability of using the molecular dynamics method to calculate the structure or any other dynamical quantity relevant to nanotechnology.
We investigate the possibility of storing data using H and F on a polymer to signify 0 and 1 bits. A probe is used to differentiate between the H and F atoms. We show that the difference between the B-F and B-H interaction energies for either the C5H5B or C3H3N2B probes is only slightly larger than the variation in B-F interaction energy with type of neighbouring data atom. Pyridine (C5H5N) and (CH3)(3)PO have a much larger difference in the H and F interaction energies. (CH3)(3)PO may be better suited as a surface probe, because the interaction with neighbouring data sites should be smaller.