In this paper, we present extensive molecular mechanics and molecular dynamics studies on the energy, structure, mechanical and vibrational properties of single-wall carbon nanotubes. In our study we employed an accurate interaction potential derived from quantum mechanics. We explored the stability domains of circular and collapsed cross section structures of armchair (n, n), zigzag (n, 0), and chiral (2n, n) isolated single-walled carbon nanotubes (SWNTs) up to a circular cross section radius of 170 Angstrom. We have found three different stability regions based on circular cross section radius. Below 10 Angstrom radius only the circular cross section tubules are stable. Between 10 and 30 Angstrom both circular and collapsed forms are possible, however, the circular cross section SWNTs are energetically favorable. Beyond 30 ri (crossover radius) the collapsed form becomes favorable for all three types of SWNTs. We report the behavior of the SWNTs with radii close to the crossover radius ((45, 45), (80, 0), (70, 35)) under uniaxial compressive and tensile loads. Using classical thin-plane approximation and variation of strain energy as a function of curvature, we calculated the bending modulus of the SWNTs. The calculated bending moduli are K-(n,K-n) = 963.44 GPa, K-(n,K-0) = 911.64 GPa, and k((2n,n)) = 935.48 GPa. We also calculated the interlayer spacing between the opposite sides of the tubes and found d((n,n)) = 3.38 Angstrom, d((2n,n)) = 3.39 Angstrom, and d((n,0)) = 3.41 Angstrom, Using an enthalpy optimization method, we have determined the crystal structure and Young's modulus of (10,10) armchair, (17, 0) zigzag and (12, 6) chiral forms (which have similar diameter as (10,10)). They all pack in a triangular pattern in two dimensions. Calculated lattice parameters are a((10,10)) = 16.78 Angstrom, a((17,0)) =16.52 Angstrom and a((12,6)) =16.52 Angstrom. Using the second derivatives of potential we calculated Young's modulus along the tube axis and found Y-(10,Y-10) = 640.30 GPa, Y-(17,Y-0) = 648.43 GPa, and Y-(12,Y-6) = 673.94 GPa. Using the optimized structures of (10, 10), (12. 6) and (17, 0), we determined the vibrational modes and frequencies. Here, we report the highest in-plane mode, compression mode, breathing mode, shearing mode and relevant cyclop mode frequencies.
Experimental results that provide new insights into nanomanipulation phenomena are presented. Reliable and accurate positioning of colloidal nanoparticles on a surface is achieved by pushing them with the tip of an atomic force microscope under control of software that compensates for instrument errors. Mechanical pushing operations can be monitored in real time by acquiring simultaneously the cantilever deflection and the feedback signal (cantilever non-contact vibration amplitude). Understanding of the underlying phenomena and real-time monitoring of the operations are important for the design of strategies and control software to manipulate nanoparticles automatically. Manipulation by pushing can be accomplished in a variety of environments and materials. The resulting patterns of nanoparticles have many potential applications, from high-density data storage to single-electron electronics, and prototyping and fabrication of nanoelectromechanical systems.
In this paper we present a method for manipulating nanometer-sized particles on surfaces using a commercial atomic force microscope (AFM). A PC-mouse-based 'click and move' manipulation scheme was implemented without the need for additional software or hardware development. The success of the scheme depends mostly on the choice of tip and cantilever which should be able to operate in both the contact mode and vibrating cantilever mode. Four different tip/cantilever combinations were tested and suitable types were found among those commercially available. The necessary properties are defined. The technique enables the fabrication of various kinds of two-dimensional structures of nanoparticles but may have relevance also to other areas of nanoscience, e.g. biotechnology. We developed the technique in order to study the magnetization of single nanoparticles using a very sensitive Hall micromagnetometer. The AFM is used as a tool to select and position a specific particle in the active region of the magnetometer.
This paper deals with a displacement control method of a piezoelectric actuator (piezo). When voltage is applied to conductive plates which are attached on both ends of a piezo, charges are induced on the conductive plates. This induced charge indicates the deformation of the piezo. Since the relationship between the deformation of the piezo and the induced charge has less hysteresis, the displacement of the piezo can be measured by observing the induced charge. In the case of step response, the displacement of the piezo can be controlled by the feedback of the induced charge as well as by a feedback of the displacement with other measuring instruments. This method can be used at a high driving frequency as the piezo is driven with a voltage source which has a low output impedance.
Recent studies of potential components for nanomachines reveal that for a wide variety of structures. the rigidity of the structure is a key element in its proper performance. Vibrational analysis is an ideal way to study structural rigidity, but standard methods of molecular Vibrational analysis are computationally prohibitive for nanostructures with large numbers of atoms. Herein, the Vibration of nanotubes is used to demonstrate that continuum methods of Vibrational analysis have potential utility in the engineering of nanostructures.
A nanosieve with a very uniform pore size of 260 nm and a pore-to-pore spacing of 510 nm has been fabricated using multiple exposure interference lithography and (silicon) micromachining technology. The nanosieve filter consists of a 0.1 mu m thick silicon nitride membrane perforated with submicron diameter pores and a macroperforated inorganic silicon support. The calculated clean water flux is at least one to two orders higher than that of conventional inorganic membranes.
In this paper, we present techniques for the direct and controlled manipulation of nanoscale three-dimensional (3D) features using the non-contact atomic force microscope (NC-AFM). A systematic examination of the nature of NC-AFM images of such 3D features leads us to propose two distinct protocols for nanomanipulation. The first protocol consists of switching off the NC-AFM feedback loop just as the tip approaches a nanofeature of interest. This results in tip-nanofeature contact and causes the feature to be 'pushed' along the surface as the tip continues to move laterally. The second protocol exploits a peculiar feature of the NC-AFM which produces reversal of contrast of nanofeatures from positive to negative in NC-AFM images, due to a feedback instability The contrast reversal, which is likely to be universal to NC-AFM, occurs with changes in imaging conditions and potentially leads to tip-sample contact, thereby allowing manipulation. This second technique has the advantage of easier identification of the manipulation regime and the potential for manipulating features that are only a few nm in size. We demonstrate the viability of these two protocols by directly manipulating gold particles of diameters 5 and 15 nm into predetermined patterns on a mica surface. We also illustrate a simple, generic approach that is useful for obtaining detailed information on the mechanism of any manipulation based on the scanning probe microscope.
Atomic force microscopies were used to quantitatively study and map the surface elastic properties of polymers and polypropylene/ethylene-propylene copolymer blends (PP/EP). Force curve and force modulation measurements were realized on polymers with moduli ranging from 10 to 3000 MPa. Both types of measurements enable us to classify polymers as a function of their rigidity. For rigid polymers, the results are in quantitative agreement with the predictions of a simple elastic model. The influence of a thin polymer layer on the surface elastic properties was also investigated. Force modulation responses are influenced by the subsurface elastic properties down to depths that may reach hundreds of nanometres. Force modulation microscopy was performed on the surface of physical blend compression-moulded plates and of 'reactor blend' injection-moulded plates. Images reveal soft regions embedded in a rigid matrix. For the physical blend, the force modulation measurements indicate that the rigidity on the EP nodules is close to that measured on pure EP, suggesting that the nodules are present at the outermost surface. Conversely, for the 'reactor blend', the EP nodules have an intermediary rigidity between those measured on bulk EP nodules and on pure PP, suggesting that EP nodules are under a skin of PP.
Recently, we have invested a great deal of effort to construct molecular building blocks from unusual DNA motifs. DNA is an extremely favorable construction medium. The sticky-ended association of DNA molecules occurs with high specificity, and it results in the formation of B-DNA, whose structure is well known. The use of stable-branched DNA molecules permits one to make stick-figures. We have used this strategy to construct a covalently closed DNA molecule whose helix axes have the connectivity of a cube, and a second molecule, whose helix axes have the connectivity of a truncated octahedron, In addition to branching topology, DNA also yields control of linking topology, because double helical half-turns of B-DNA or Z-DNA can be equated, respectively, with negative or positive crossings in topological objects. Consequently, we have been able to use DNA to make trefoil knots of both signs and figure of 8 knots. By making RNA knots, we have discovered the existence of an RNA topoisomerase. DNA-based topological control has also led to the construction of Borromean rings, which could be used in DNA-based computing applications. The key feature previously lacking in DNA construction has been a rigid molecule. We have discovered that DNA double crossover molecules can provide this capability. We have incorporated these components in DNA assemblies that use this rigidity to achieve control on the geometrical level, as well as on the topological level. Some of these involve double crossover molecules, and others involve double crossovers associated with geometrical figures, such as triangles and deltahedra.
Conductivity measurements were performed on bundles of single-walled carbon nanotubes with the aid of a scanning tunneling microscope (STM). Semimetallic current-voltage (I-V) characteristics generally indicated the bundles to be electronically similar to graphite. However, by moving the STM tip along the length of the nanotubes, sharp deviations in the I-V characteristics could also be observed. Well-defined positions were found at which the nanotube transport current changed abruptly from a graphitic response to one that is highly nonlinear and asymmetric, including near-perfect rectification. This abrupt change in the nanotube transport suggests that the STM tip had passed a region of the nanotube which acts less like a wire than it does a Schottky barrier or other heterojunction. Similar on-tube nanodevices have been theoretically predicted for point defects in individual carbon nanotubes and are consistent with our observations.
Significant progress in the examination or manipulation of submicrometre particles and large molecules is likely to be dependent upon a suitable method in locating and orienting them onto working substrates. Ideally this would be a general purpose tool that allowed local programming to attract selectively species of interest. Charge writing onto electrets with a scanning-probe microscope offers one possible method. Here the use of this technique for memory applications (the only significant body of research) is examined in order to judge the feasibility of using it with different operational parameters for 'electrostatic clamping'. Until recently it was not regarded as practicable, but new materials developments, especially oxide-nitride-oxide-silicon electrets, show considerably more promise. A clear answer to our question cannot yet be given, but further investigations are suggested and recommended.
Several molecular dynamics simulations are performed, in order to clarify the atomic-scale stick-slip phenomenon which is commonly observed in the surface measurement using an atomic fine microscope (AFM). In the molecular dynamics simulations, a specimen and a slider are assumed to consist of monocrystalline copper and rigid diamond, respectively, and a Morse potential is postulated between a pair of atoms. Atomic behavior in a plane corresponding to the (111) crystal plane is simulated, dealing with a planar strain problem where the effect of the three-dimensional interatomic force and the spring constant of the AFM cantilever are also taken into consideration. Influence of the cantilever stiffness and dynamics of the specimen surface atoms on the atomic-scale stick-slip phenomenon are investigated. The simulation confirms that the atomic-scale stick-slip phenomenon can be expressed by a molecular dynamics simulation and that the stick-slip phenomenon of the surface atoms of the specimen affects the stick-slip phenomenon of the spring force. These results indicate that molecular dynamics simulation has an advantage in deciding the spring constant of cantilevers.
A prerolling behavior called 'nonlinear spring behavior' (NSB) is exhibited in rolling elements, such as linear roller guideways, ball screws and ball bearings, before they begin to roll. Devices using these elements vibrate easily at small displacements due to NSB. The frequency response caused by NSB is different from those caused by rolling in the large displacement area. In this paper a study is carried out to characterize NSB and to explain its influence on frequency response using the case studies of a linear ball guideway, a DC servomotor, and a practical positioning device.
Over the past two years at the Materials and Process Simulation Center, we have been developing simulation approaches for studying the molecular nanomachine designs pioneered by Drexler and Merkle. These nanomachine designs, such as planetary gears and neon pump, are described with atomistic details and involve up to 10 000 atoms. With the Dreiding and universal force fields, we have optimized the structures of the two planetary gear designs and the neon pump. At the Fourth Foresight conference, we reported rotational impulse dynamics studies of the first and second generation designs of planetary gears undergoing very high-frequency rotational motions. We will explore stability of these designs in the lower frequency regimes which require long time simulations. We will report the molecular mechanics and molecular dynamics simulations performed on these model systems. We explore the following modes in these studies: (1) impulse mode; (2) constant angular velocity-perpetual rotation; (3) constant torque-acceleration from rest.
This paper describes four significant breakthroughs in the syntheses and testing of molecular scale electronic devices. The 16-mer of oligo(2-dodecylphenylene ethynylene) was prepared on Merrifields resin using the iterative divergent/convergent approach which significantly streamlines the preparation of this molecular scale wire. The formation of self-assembled monolayers and multilayers on gold surfaces of rigid rod conjugated oligomers that have thiol, alpha, omega-dithiol, thioacetyl, or alpha, omega-dithioacelyl end groups have been studied. The direct observation of charge transport through molecules of benzene-1, 4-dithiol, which have been self-assembled onto two facing gold electrodes, has been achieved. Finally, we report initial studies into what effect varying the molecular alligator clip has on the molecule scale wire's conductivity.
It is well established that the dispersion of nanosized metal particles in a polymer matrix can induce nonlinear optical properties, yet very little is known about the effect of semiconducting transition metal oxide nanoparticles on luminescence properties of conjugated polymers. In this paper, we report the synthesis of a nanostructured TiO2/poly(p-phenylenevinylene) (PPV) system and show by diffuse reflectance infrared Fourier transform spectrometry that a stable conjugated nanocomposite is obtained. Investigation of the photoluminescence (PL) properties reveals both a broadening and a blueshift of the emission spectra. Adsorption of oxygen is found to be stronger on the nanocomposite than on PPV and to reversibly quench the PL emission, thus suggesting enhanced gas sensing properties. A tentative mechanism explaining the role of n-TiO2 is briefly discussed.
Although a complete nanotechnology does not yet exist, we can already foresee some new directions in theoretical computer science that will be required to help us design maximally efficient computers using nanoscale components. In particular, we can devise novel theoretical models of computation that are intended to faithfully reflect the computational capabilities of physics at the nanoscale, in order to serve as a basis for the most powerful possible future nanocomputer architectures. In this paper we present arguments that a reversible 3D mesh of processors is an optimal physically realistic model for scalable computers. We show that any physical architecture based on irreversible logic devices would be asymptotically slower than realizations of our model, and we argue that no physical realization of computation aside from quantum computation could be asymptotically faster. We also calculate, using parameters from a variety of different existing and hypothetical technologies, how large a reversible computer would need to be in order to be faster than an irreversible machine. We find that using current technology, a reversible machine containing only a few hundred layers of circuits could outperform any existing machine, and that a reversible computer based on nanotechnology would only need to be a few microns across in order to outperform any possible irreversible technology. We argue that a silicon implementation of the reversible 3D mesh could be valuable today for speeding up certain scientific and engineering computations, and propose that the model should become a focus of future study in the theory of parallel algorithms for a wide range of problems.
The nanoscopic ferroelectric domains could be formed in P(VDF/TrFE) thin films by applying electric pulses with a conductive atomic force microscope, and detected by using piezoelectric response, revealing that the directions of electric dipoles in organic molecules can be controlled in nanoscale. By changing the polarity of the applied pulses, temporally stable binary information could be 'written' in these films. Moreover, the possibilities of the molecular manipulation and the creation of high-density molecular memory devices utilizing the electric interaction between the polar molecules and the scanning probe microscopy tips are discussed.
Langmuir-Schaefer (LS) films of poly(o-anisidine) (POAS) were fabricated and characterized by means of Brewster-angle microscopy, ellipsometry and electrochemical techniques. The studied optical, cyclic voltammetric and ellipsometric properties of films underlined a regular deposition up to at least 40 monolayers of POAS conducting polymer. The development of surface irregularities beyond 40 monolayers in LS films showed an electrochemical kinetic similar to electrodeposited films. More importantly, the electrochemical kinetic in a small number of monolayers was indicative of the fast transfer process of the electrons. The nature of anions caused meaningful changes in the redox properties of POAS LS films. The electrochromic switching response lime and diffusion coefficient of the LS films were estimated through electrochemical surveying. Later, POAS LS films were used as a sensing element for a survey of 0.1 ppm of acid in water through conductimetric measurement.
Recent advances in fullerene science and technology suggest that it may be possible, in the distant future, to design and build atomically precise programmable machines composed largely of functionalized fullerenes. Large numbers of such machines with appropriate interconnections could conceivably create a material able to react to the environment and repair itself. This paper reviews some of the experimental and theoretical work relating to these materials, sometimes called machine phase, including the fullerene gears and high-density memory recently designed and simulated in our laboratory.