Showing papers in "Nanotechnology in 2002"
TL;DR: In this paper, the equilibrium position, adsorption energy, charge transfer, and electronic band structures of single-walled carbon nanotubes (SWNTs) and bundles were obtained for different kinds of SWNTs.
Abstract: We studied various gas molecules (NO2, O2, NH3, N2, CO2, CH4, H2O, H2, Ar) on single-walled carbon nanotubes (SWNTs) and bundles using first principles methods. The equilibrium position, adsorption energy, charge transfer, and electronic band structures are obtained for different kinds of SWNTs. Most molecules adsorb weakly on SWNTs and can be either charge donors or acceptors to the nanotubes. We find that the gas adsorption on the bundle interstitial and groove sites is stronger than that on individual nanotubes. The electronic properties of SWNTs are sensitive to the adsorption of certain gases such as NO2 and O2. Charge transfer and gas-induced charge fluctuation might significantly affect the transport properties of SWNTs. Our theoretical results are consistent with recent experiments.
1,107 citations
TL;DR: In this article, the authors exploit the unique properties of single-walled carbon nanotubes (SWNT) to achieve direct electron transfer with the redox active centres of adsorbed oxidoreductase enzymes.
Abstract: In this report, exploitation of the unique properties of single-walled carbon nanotubes (SWNT) leads to the achievement of direct electron transfer with the redox active centres of adsorbed oxidoreductase enzymes. Flavin adenine dinucleotide (FAD), the redox active prosthetic group of flavoenzymes that catalyses important biological redox reactions and the flavoenzyme glucose oxidase (GOx), were both found to spontaneously adsorb onto carbon nanotube bundles. Both FAD and GOx were found to spontaneously adsorb to unannealed carbon nanotubes that were cast onto glassy carbon electrodes and to display quasi-reversible one-electron transfer. Similarly, GOx was found to spontaneously adsorb to annealed, single-walled carbon nanotube paper and to display quasi-reversible one-electron transfer. In particular, GOx immobilized in this way was shown, in the presence of glucose, to maintain its substrate-specific enzyme activity. It is believed that the tubular fibrils become positioned within tunnelling distance of the cofactors with little consequence to denaturation. The combination of SWNT with redox active enzymes would appear to offer an excellent and convenient platform for a fundamental understanding of biological redox reactions as well as the development of reagentless biosensors and nanobiosensors.
584 citations
TL;DR: In this paper, the pull-in voltage characteristics of double-wall carbon nanotubes suspended over a graphitic ground electrode were studied and parametrized continuum models for three coupled energy domains: the elastostatic energy domain, the electrostatic energy domain and the van der Waals energy domain.
Abstract: We study the pull-in voltage characteristics of several nanotube electromechanical switches, such as double-wall carbon nanotubes suspended over a graphitic ground electrode. We propose parametrized continuum models for three coupled energy domains: the elastostatic energy domain, the electrostatic energy domain and the van der Waals energy domain. We compare the accuracy of the continuum models with atomistic simulations. Numerical simulations based on continuum models closely match the experimental data reported for carbon-nanotube-based nanotweezers. An analytical expression, based on a lumped model, is derived to compute the pull-in voltage of cantilever and fixed-fixed switches. We investigate the significance of van der Waals interactions in the design of nanoelectromechanical switches.
505 citations
TL;DR: In this paper, the spring constant of a V-shaped cantilever was determined using the thermal fluctuation method and a comparison between this method and those of Sader-Neumeister and Ducker has been established.
Abstract: Knowledge of the interaction forces between surfaces gained using an atomic force microscope?(AFM) is crucial in a variety of industrial and scientific applications and necessitates a precise knowledge of the cantilever spring constant. Many methods have been devised to experimentally determine the spring constants of AFM cantilevers. The thermal fluctuation method is elegant but requires a theoretical model of the bending modes. For a rectangular cantilever, this model is available (Butt and Jaschke). Detailed thermal fluctuation measurements of a series of AFM cantilever beams have been performed in order to test the validity and accuracy of the recent theoretical models. The spring constant of rectangular cantilevers can also be determined easily with the method of Sader and White. We found very good agreement between the two methods. In the case of the V-shaped cantilever, we have shown that the thermal fluctuation method is a valid and accurate approach to the evaluation of the spring constant. A comparison between this method and those of Sader-Neumeister and of Ducker has been established. In some cases, we found disagreement between these two methods; the effect of non-conservation of material properties over all cantilevers from a single chip is qualitatively invoked.
366 citations
TL;DR: In this article, a metal probe and molecular monolayers have been characterized using conducting atomic force microscopy in an inert environment and in a voltage range that yields reversible currentvoltage data.
Abstract: Electrical contacts between a metal probe and molecular monolayers have been characterized using conducting atomic force microscopy in an inert environment and in a voltage range that yields reversible current-voltage data. The current through alkanethiol monolayers depends on the contact force in a way that is accounted for by the change of chain-to-chain tunnelling with film thickness. The electronic decay constant, βN, was obtained from measurements as a function of chain length at constant force and bias, yielding βN = 0.8±0.2 per methylene over a ±3 V range. Current-voltage curves are difficult to reconcile with this almost constant value. Very different results are obtained when a gold tip contacts a 1,8-octanedithiol film. Notably, the current-voltage curves are often independent of contact force. Thus the contact may play a critical role both in the nature of charge transport and the shape of the current-voltage curve.
276 citations
TL;DR: In this paper, a self-aligned fabrication process was used to ensure that the carbon nanotubes were always centred with respect to the gate apertures (2 µm diameter) over the entire device.
Abstract: We report on the fabrication of field emission microcathodes which use carbon nanotubes as the field emission source. The devices incorporated an integrated gate electrode in order to achieve truly low-voltage field emission. A single-mask, self-aligned technique was used to pattern the gate, insulator and catalyst for nanotube growth. Vertically-aligned carbon nanotubes were then grown inside the gated structure by plasma-enhanced chemical vapour deposition. Our self-aligned fabrication process ensured that the nanotubes were always centred with respect to the gate apertures (2 µm diameter) over the entire device. In order to obtain reproducible emission characteristics and to avoid degradation of the device, it was necessary to operate the gate in a pulsed voltage mode with a low duty cycle. The field emission device exhibited an initial turn-on voltage of 9 V. After the first measurements, the turn-on voltage shifted to 15 V, and a peak current density of 0.6 mA cm-2 at 40 V was achieved, using a duty cycle of 0.5%.
262 citations
TL;DR: In this article, a novel chemical functionalization method for multiwalled carbon nanotubes (MWNTs), through an oxidation and silanization process, is presented, which allows us to have different organo-functional groups attached to the MWNTs, which improves their chemical compatibility with specific polymers for producing new nanotube-based composites.
Abstract: A novel chemical functionalization method for multiwalled carbon nanotubes (MWNTs), through an oxidation and silanization process, is presented. The method allows us to have different organo-functional groups attached to the MWNTs, which improves their chemical compatibility with specific polymers for producing new nanotube-based composites. The corresponding moieties were characterized by infrared, Raman and energy dispersion spectroscopies.
236 citations
TL;DR: In this paper, amino-terminated DNA strands were used to functionalize the open ends and defect sites of single-walled carbon nanotubes, an important first step in realizing a DNA-guided self-assembly process for carbon-nanotubes.
Abstract: We present here the use of amino-terminated DNA strands in functionalizing the open ends and defect sites of oxidatively prepared single-walled carbon nanotubes, an important first step in realizing a DNA-guided self-assembly process for carbon nanotubes.
236 citations
TL;DR: In this article, the crystalline phase and morphology of alumina-borate fibres were largely influenced by the calcination temperature, and they were characterized by SEM, XRD and FT-IR.
Abstract: Alumina-borate/PVA composite fibres were prepared using sol–gel processing and an electrospinning technique. After calcination of the thin fibres, ultra-fine fibres of alumina-borate oxide with a diameter of about 550 nm could be prepared. The fibres were characterized by SEM, XRD and FT-IR. The results showed that the crystalline phase and morphology of alumina-borate fibres were largely influenced by the calcination temperature.
218 citations
TL;DR: In this article, the authors examine and compare four fault-tolerant techniques: R-fold multiple redundancy, cascaded triple modular redundancy, von Neumann's multiplexing method, and a reconfigurable computer technique.
Abstract: The proposed nanometre-sized electronic devices are generally expected to show an increased probability of errors both in manufacturing and in service. Hence, there is a need to use fault-tolerant techniques in order to make reliable information processing systems out of those devices. Here we examine and compare four fault-tolerant techniques: R-fold multiple redundancy; cascaded triple modular redundancy; von Neumann's multiplexing method; and a reconfigurable computer technique. It is shown that the reconfiguration technique is the most effective technique, able to cope with manufacturing defect rates of the order of 0.01-0.1, but the technique requires enormous amounts of redundancy, of the order of 103-105. However, in the case of transient errors, multiple modular redundancy and multiplexing are the only feasible options.
193 citations
TL;DR: The idea of nature as engineer is an old one, but the realization that this metaphor can be extended (should we say retracted?) to the molecular scale has become common currency only over the past two decades or so as mentioned in this paper.
Abstract: The idea of nature as engineer is an old one, but the realization that this metaphor can be extended (should we say retracted?) to the molecular scale has become common currency only over the past two decades or so. Two reasons for this are perhaps paramount. First, the picture of the cell has been transformed from that of a 'wet chemical' melange—'a vessel, filled with a homogeneous solution, in which all chemical processes take place', as Franz Hofmeister put it in 1901—into an image of a sort of fluid factory, a production plant in which molecular machinery works in near-fantastic orchestration to generate complex products from raw materials. This mechanism is self-assembling, self-repairing and self-replicating. The concept of proteins and nucleic acids as 'molecular machines' is now a mainstream one in cell biology. Second, technological advances have made us accustomed to the idea that engineering can be conducted at scales too small to see with the naked eye, yet employing principles—mechanical, electrical, hydraulic, optical, tribological—familiar from the macroscopic world. Molecular electronics and computing, microelectromechanical devices and nanotechnology, are now mainstream concepts, and are validated by at least some degree of physical realization. In this article I shall briefly review some of nature's principles and practices at the molecular, supramolecular and submicrometre scales, and attempt to illustrate how these can be adapted for developing synthetic chemical and materials systems sharing the kind of superior properties and special functions that natural systems exhibit.
TL;DR: In this paper, the authors discuss applications of surface plasmons enhanced transmission in near-field scanning optical microscopy and in high-density optical data storage, where the metal surface surrounding the subwavelength hole is corrugated.
Abstract: The transmission of light through an aperture in a metal film is extremely small when the aperture diameter is much smaller than the optical wavelength. But when the metal surface surrounding the subwavelength hole is corrugated, the incident light can couple to surface plasmons (SP), excitation modes on the metal surface. A resonant interaction leads to an enhanced transmission at wavelengths determined by the corrugation pitch. We discuss applications of the SP enhanced transmission in near-field scanning optical microscopy and in high-density optical data storage.
TL;DR: In this article, the effect of synthetic conditions, such as the molar ratio of D-CSA to aniline (An), the concentration of D -CSA in the polymerization media, the reaction temperature and time, on the morphology and size as well as the electrical properties of the PANI-(CSA) was investigated.
Abstract: Conducting nanotubes of polyaniline (PANI) about 80–180 nm in diameter were synthesized by a chemical template-free method in the presence of D-10-camphorsulfonic acid (D-CSA) as the dopant, and ammonium persulfate ((NH4)2S2O8) as the oxidant. The effect of synthetic conditions, such as the molar ratio of D-CSA to aniline (An), the concentration of D-CSA in the polymerization media, the reaction temperature and time, on the morphology and size as well as the electrical properties of the PANI–(D-CSA) was investigated. It was found that the above synthetic conditions, especially the molar ratio of D-CSA to An, strongly affected the morphology and formation probability of the resulting PANI. The micelles formed by D-CSA and anilinium cations act as the templates in the formation of PANI–(D-CSA) nanotubes.
TL;DR: In this article, the development of a nanoplotter that consists of an array of micro-fabricated probes for parallel dip-pen nanolithography is described. But the nanoplotster is not suitable for writing and imaging capabilities, but is challenged with respect to tip sharpness.
Abstract: We report on the development of a nanoplotter that consists of an array of microfabricated probes for parallel dip-pen nanolithography. Two types of device have been developed by using microelectromechanical systems micromachining technology. The first consists of 32 silicon nitride cantilevers separated by 100 µm, while the second consists of eight boron-doped silicon tips separated by 310 µm. The former offers writing and imaging capabilities, but is challenged with respect to tip sharpness. The latter offers smaller linewidths and increased imaging capabilities at the expense of probe density. Parallel generation of nanoscopic monolayer patterns with a minimum linewidth of 60 nm has been demonstrated using an eight-pen microfabricated probe array.
TL;DR: In this article, two polymer-montmorillonite (MMT) nanocomposites have been synthesized by in situ intercalative polymerization, where styrene monomer is intercalated into the interlayer space of organically modified MMT, a layered clay mineral.
Abstract: Two polymer-montmorillonite (MMT) nanocomposites have been synthesized by in situ intercalative polymerization. The styrene monomer is intercalated into the interlayer space of organically modified MMT, a layered clay mineral. Upon the intercalation, the complex is subsequently polymerized in the confinement environment of the interlayer space with a free radical initiator, 2,2-azobis isobutyronitrile. The aniline monomer is also intercalated and then polymerized within the interlayer space of sodium- and copper-MMT initiated by ammonium peroxodisulphate and interlayer copper cations respectively. X-ray diffraction indicates that the MMT layers are completely dispersed in the polystyrene matrix and an exfoliated structure has been obtained. The resulting polyaniline-MMT nanocomposites show a highly ordered structure of a single polyaniline layer stacked with the MMT layers. Fourier transform infrared spectra further confirm the intercalation and formation of both polymer-MMT nanocomposites.
TL;DR: In this article, electron beam lithography and focused ion beam (FIB) were combined to make low-resistance ohmic contacts to individual bismuth nanowires.
Abstract: Techniques are presented for making ohmic contacts to nanowires with a thick oxide coating. Although experiments were carried out on Bi nanowires, the techniques described in this paper are generally applicable to other nanowire systems. Metal electrodes are patterned to individual Bi nanowires using, electron beam lithography. Imaging the chemical reaction on the atomic scale with in situ high-resolution transmission electron microscopy shows that annealing in H-2 or NH3 can reduce the nanowires' oxide coating completely. The high temperatures required for this annealing, however, are not compatible with the lithographic techniques. Low-resistance ohmic contacts to individual bismuth nanowires are achieved using a focused ion beam (FIB) to first sputter away the oxide layer and then deposit Pt contacts. By combining electron beam lithography and FIB techniques, ohmic contacts stable from 2 to 400 K are successfully made to the nanowires. A method for preventing the burnout of nanowires from electrostatic discharge is also developed.
TL;DR: In this paper, an electronic nose using polymer layers as partially selective cantilever coatings was built to recognize chemical vapours and odours by evaluating the cantilevers' bending pattern.
Abstract: Atomic force microscopy (AFM) is a technique to image surfaces with unprecedented vertical and lateral resolution. Many related techniques have been derived from AFM, taking advantage of local interactions between a tip on a cantilever and a surface. However, cantilevers can also be used for sensing applications. These so-called nanosensors feature extreme sensitivity for the detection of chemical vapours or adsorption of molecules. Upon adsorption to the cantilever surface, the molecules cause the cantilever to bend. Thus physical, chemical or biochemical processes are directly transduced into nanomechanical motion. We show that measurement of the deflection of a single cantilever might be misleading. Reliable information can only be obtained by using a sensor cantilever and at least one reference cantilever integrated into an array. We have built an electronic nose using polymer layers as partially selective cantilever coatings to recognize chemical vapours and odours by evaluating the cantilevers' bending pattern. Major applications lie in the fields of process and quality control, biosensing, medical diagnostics, molecular recognition and proteomics.
TL;DR: In this paper, the authors used electrospun fibres of polyvinyl alcohol/silica composite as a precursor to obtain amorphous silica nanofibres with diameters of 200-400 nm.
Abstract: For the first time, silica nanofibres with diameters of 200–400 nm were prepared by using electrospun fibres of polyvinylalcohol/silica composite as precursor. The products were characterized by the scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), and x-ray diffractometry (XRD) methods. The results showed that the crystalline phase and morphology of silica fibres were substantially influenced by the calcination temperature. The amorphous silica nanofibres could be obtained at 550oC.
TL;DR: In this article, self-assembled polypyrrole (PPy) micro/nanotubes, whose diameters and room temperature conductivities were within the ranges of 50-2000 nm and 2-40 S cm−1, were successfully synthesized by a chemical and electrochemical method in the presence of β-naphthalene sulfonic acid or p-toluenesulfonate acid as the dopant.
Abstract: Self-assembled polypyrrole (PPy) micro/nanotubes, whose diameters and room temperature conductivities were within the ranges of 50–2000 nm and 2–40 S cm−1 respectively, were successfully synthesized by a chemical and electrochemical method in the presence of β-naphthalene sulfonic acid or p-toluenesulfonate acid as the dopant. By changing the polymerization method and conditions as well as dopant structures, one can control the morphology, size and electrical properties of the doped PPy. It was proposed that dopant micelles or pyrrole/dopant clusters act as templates in the formation of the micro/nanotubes.
TL;DR: In this paper, the electrical and optical response of thin films of surface functionalized nanoparticles upon exposure to various chemical vapours has been studied and it was found that the electrical response to chemical vapour adsorbed on the various nanoparticle films varied markedly and was determined by the surface functional groups.
Abstract: The electrical and optical response of thin films of surface functionalized nanoparticles upon exposure to various chemical vapours has been studied. It was found that the electrical response to chemical vapours adsorbed on the various nanoparticle films varied markedly and was determined by the surface functional groups. Ellipsometric studies revealed that the film thickness increased during exposure to the chemical vapours. These thickness changes of the films correlate with the changes in electrical conductivity. Two physical effects are believed to play a role in determining these conductivity changes. Under high partial pressure, the change in nanoparticle core-core separation is the main contribution to the change in conductivity and generally leads to a reduction in the conductivity. However, for relatively low partial pressures the adsorption of vapour molecules leads to permittivity changes that tend to increase the conductivity.
TL;DR: Using a surfactant-mediated method, tin dioxide nanoparticles with a high surface area were generated within the template of the cationic surfactants (cetyltrimethylammonium bromide) micelle assembly from the hydrous metal chloride.
Abstract: Using a surfactant-mediated method, tin dioxide nanoparticles with a high surface area were generated within the template of the cationic surfactant (cetyltrimethylammonium bromide) micelle assembly from the hydrous metal chloride (SnCl4 ? 5H2O). The as-synthesized product was amorphous and transformed into crystalline calcined at 500?C for 2 h, and exhibited a higher Brunauer?Emmet?Teller surface area of 69.2 m2 g?1. The resulting particles were highly crystalline and largely monodisperse oxide particles in the nanometre range (15?25 nm). Thermogravimetric analysis, x-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy were used to characterize the final products.
TL;DR: The hardness and Young's modulus of barrier-type, amorphous anodic oxides have been determined by nanoindentation as discussed by the authors, using shallow indents, of 55 nm depth, with alumina, tantala and alumina/tantala ''mixed oxide'' films of about 500 nm thickness.
Abstract: The hardness and Young's modulus of barrier-type, amorphous anodic oxides have been determined by nanoindentation The procedure used shallow indents, of 55 nm depth, with alumina, tantala and alumina/tantala `mixed oxide' films of about 500 nm thickness The results revealed respective hardnesses of approximately 70, 53 and 65 GPa, and respective Young's moduli of approximately 122, 140 and 130 GPa Thus, the hardness and Young's modulus followed opposite trends, with alumina having the highest hardness and lowest modulus, and the `mixed oxide' having intermediate properties The hardness and Young's modulus of amorphous alumina are factors of about 31-37 times lower than those of crystalline aluminas
TL;DR: In this paper, the authors explored the limits of pushing storage density to the atomic scale with a memory that stores a bit by the presence or absence of one silicon atom, which can be initialized and reformatted by controlled deposition of silicon.
Abstract: The limits of pushing storage density to the atomic scale are explored with a memory that stores a bit by the presence or absence of one silicon atom. These atoms are positioned at lattice sites along self-assembled tracks with a pitch of five atom rows. The memory can be initialized and reformatted by controlled deposition of silicon. The writing process involves the transfer of Si atoms to the tip of a scanning tunnelling microscope. The constraints on speed and reliability are compared with data storage in magnetic hard disks and DNA.
TL;DR: In this article, the red-emitting nanophosphor Eu:Y2O3 was synthesized using the microemulsions method, which was composed of petroleum ether (60-80??C), nonionic surfactants NP5/NP9, aqueous yttrium nitrate/europium nitrate and ammonium hydroxide solution.
Abstract: The red-emitting nanophosphor Eu:Y2O3 was synthesized using the the microemulsions method. The microemulsion system was composed of petroleum ether (60-80??C), nonionic surfactants NP5/NP9, aqueous yttrium nitrate/europium nitrate and ammonium hydroxide solution. The nanoparticles were studied by thermal analysis, x-ray diffraction, transmission electronic microscopy, scanning electron microscopy and photoluminescence. The size of the nanoparticles was in the range 10-100?nm, and showed a narrow size distribution, high crystallinity and special luminescent properties. Compared with the phosphors prepared by the conventional method, the quenching concentration of Eu was raised remarkably. For this type of nanophosphor, quenching starts at a Eu concentration of 10% (mol%), while a value of 6-8% was obtained for the conventional one (Tao?Y 1996 Mater. Lett. 28 137-40). Based on this study, we have successfully prepared some promising nanophosphors.
TL;DR: In this paper, a single GaN nanowire was fabricated by chemical vapour deposition and several Schottky-junction diodes were fabricated and their electrical transport properties were studied.
Abstract: On a single GaN nanowire, obtained by chemical vapour deposition, several Schottky-junction diodes were fabricated and their electrical transport properties were studied. Alternately attached metal electrodes of Al and Ti/Au formed a Schottky barrier junction (for Al) or an ohmic contact (for Ti/Au), resulting in several diodes on a single nanowire. The current–voltage measurements exhibited clear rectifying behaviour and no reverse-bias breakdown was observed up to the measured voltage, −5 V. The forward-bias threshold voltage was observed to decrease linearly with temperature, from 0.4 V at 280 K to 1 V at 10 K.
TL;DR: In this article, a diamond mould was pressed into polymethylmethacrylate (PMMA) and oxygen gas reactive ion etching (RIE) to fabricate fine patterns in a diamond mold.
Abstract: Electron beam (EB) lithography using polymethylmethacrylate (PMMA) and oxygen gas reactive ion etching (RIE) were used to fabricate fine patterns in a diamond mould. To prevent charge-up during EB lithography, thin conductive polymer was spin-coated over the PMMA resist, yielding dented line patterns 2 μ m wide and 270 nm deep. The diamond mould was pressed into PMMA on a silicon substrate heated to 130, 150 and 170oC at 43.6, 65.4 and 87.2 MPa. All transferred PMMA convex line patterns were 2 μ m wide. Imprinted pattern depth increased with rising temperature and pressure. PMMA patterns on diamond were transferred by the diamond mould at 150oC and 65.4 MPa, yielding convex line patterns 2 μ m wide and 200 nm high. Direct aluminium and copper patterns were obtained using the diamond mould at room temperature and 130.8 MPa. The diamond mould is thus useful for replicating patterns on PMMA and metals.
TL;DR: A nanofabricated electrochemical detector array is discussed that reveals the spatio-temporal dynamics of exocytosis in single chromaffin cells and may be applicable to study the correlation of exocytes with signalling events that could be simultaneously monitored by fluorescence microscopy.
Abstract: Nanobiotechnology is a field that utilizes the techniques of nano- and microfabrication to study biosystems or to use biological material and principles to build new devices. As an example we discuss the development of a nanofabricated electrochemical detector array that reveals the spatio-temporal dynamics of exocytosis in single chromaffin cells. In a quantal release event a single vesicle fuses with the plasma membrane releasing its contents through the fusion pore. The time-resolved amperometric currents measured by the individual electrodes detecting different fractions of the released molecules allow determination of the time course as well as localization of quantal events. Such a device may be applicable to study the correlation of exocytotic events with signalling events that could be simultaneously monitored by fluorescence microscopy.
TL;DR: In this article, single-walled carbon nanotubes (SWNTs) are grown from a methane feedstock by thermal chemical vapour deposition (CVD) and an ethylene-hydrogen plasma generated in an inductively coupled plasma reactor.
Abstract: Single-walled carbon nanotubes (SWNTs) are grown from a methane feedstock by thermal chemical vapour deposition (CVD). An ethylene-hydrogen plasma generated in an inductively coupled plasma reactor primarily yields multi-walled carbon nanotubes and thicker fibres. In both cases, an iron catalyst layer and an aluminium underlayer are deposited by ion beam sputtering onto silicon wafers for the growth of carbon nanotubes (CNTs). The plasma process provides well-aligned multi-walled nanofibres useful for fabrication of electrodes and sensors and further tip functionalization whereas thermal CVD produces a mat of SWNT ropes. In addition, CNTs grown at the tips of silicon cantilevers are demonstrated to be ideal for high-resolution imaging of biological samples and simulated Mars dust grains using atomic force microscopy.
TL;DR: In this article, the design of a monomolecular barrow 1.6 nm×1.5 nm in dimension made of a central board, two rear legs and two front wheels is discussed.
Abstract: The design of a monomolecular barrow 1.6 nm×1.5 nm in dimension made of a central board, two rear legs and two front wheels, is discussed. This barrow is guided and driven by the tip apex of an STM which manipulates it from the rear legs. The central board has been chosen in such a way that the rotation of the front wheels can be deduced from the surface tunnelling current intensity measured during a sequence of manipulations of the barrow. Our calculations show that in UHV and without friction, the front wheels of the barrow that we designed will not rotate. This led us to design a new barrow including two ratchet molecular groups to compensate for the absence of friction.
TL;DR: In this paper, the authors demonstrate a high yield production scheme to fabricate sub-5 nm co-planar metal-insulator-metal junctions using an AFM equipped with a carbon nanotube tip.
Abstract: We demonstrate a high yield production scheme to fabricate sub-5 nm co-planar metal–insulator–metal junctions. This involves determining the relationship between the actual gap between the metallic junctions for a given designed gap, and the use of weak developers with ultrasonic agitation to process the exposed resist. This results in an improved process to achieve narrow inter-electrode gaps. The gaps were imaged using an AFM equipped with a carbon nanotube tip to achieve a high degree of accuracy in measurement. The smallest gap unambiguously measured was ~ 2 nm. Gaps with ≤ 5 nm spacing were produced with a very high yield of about 75% for a designed inter-electrode distance of 0 nm. The leakage resistance of the gaps was found to be of the order of 1012 Ω. The entire junction structure was designed to be co-planar to better than 1 nm over 1 μ m2.