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We used local probe techniques to characterize electron beam (e‐beam) induced changes in thin oxides on silicon. Primary effects of the 1 nm wide, 300 keV e beam included the formation of positive charges trapped in the SiO2, physical restructuring in the oxide, and deposition of carbonaceous compounds. Charges remained stable in thicker oxides (460 nm) and appeared as changes in the contact potential or microwave response with widths down to 100 nm. In thinner oxides (20 nm) the amount of charge was smaller and less stable; below 7 nm no charge was detected. Physical changes in the oxide, evident as a swelling of irradiated areas, accounted for the etching selectivity of these regions.

Silicon based structures were fabricated using scanning tunneling microscope on a Si(111) surface by the localized decomposition of gaseous silane at pressures of 10−5–10−6 Torr. Continuous wires of width 5 nm could be produced while atomically resolved images of the nearby substrate were obtained. We argue that the fabrication process is effected by field‐assisted decomposition of silane on the tip surface, which subsequently migrates to the tunneling region at the tip apex where it field desorbs to the silicon surface.

The orientation of the endohedral La atom in $\mathrm{La}@{\mathrm{C}}_{82}$ adsorbed on Cu(111) has been determined using the normal-incidence x-ray standing wave (NIXSW) technique. The NIXSW measurements were carried out using both the normal 〈111〉 and 70.5\ifmmode^\circ\else\textdegree\fi{} off-normal $〈1\ifmmode\bar\else\textasciimacron\fi{}11〉$ Bragg reflections. The La $〈1\ifmmode\bar\else\textasciimacron\fi{}11〉$ profiles of the $\mathrm{La}@{\mathrm{C}}_{82}$ monolayer and submonolayers are found to be similar to the 〈111〉 profile of the multilayer, while the 〈111〉 profiles of the monolayer and submonolayers are distinctly different with much lower peak height. This indicates significant ordering of the La atoms in the monolayers with respect to height above the Cu surface but little lateral ordering. The results of curve fits to the monolayer profiles show that the La atoms are regionally located at 1.62 (\ifmmode\pm\else\textpm\fi{}0.77) \AA{} above an extended scattering plane from the crystal. Cooling the monolayers to a temperature of 170 K increases ordering of the La atoms with respect to height above the surface. The NIXSW results demonstrate that the endohedral molecules adopt a restricted orientation upon adsorbing on the surface and the La atom resides on either the upper or lower half of the cage. Theoretical calculations show that the most stable La positions are located in the top half of the fullerene cage, which supports the La upper configuration. The results are explained in terms of electrostatic interactions between the endohedral atom, the fullerene cage, and the substrate.

Titanium dioxide has shown its potential application in solar cells, optical waveguides, gas sensors and photochromic devices. One of the hindrances for miniaturization of these devices is the lack of an easy and reliable way of patterning TiO2. In this paper, we describe a simple process of electron beam patterning of TiO2 using a spin-coatable TiO2 resist prepared by reacting titanium n-butoxide with benzoylacetone in isopropyl alcohol. The sensitivity of ~115 nm thick spin-coatable TiO2 resist is ~30 mC cm-2, which is ~107 times higher than sputtered TiOx and crystalline TiO2 films. Exposure to an electron beam results in the gradual removal of organic material from the resist. This makes the exposed resist insoluble in organic solvents such as acetone; thereby providing high resolution negative line patterns as small as 19 nm wide. Heating of the patterned films results in pure TiO2.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The photon-energy dependences of valence-band photoemission spectra have been investigated for monolayer, submonolayer, and multilayer C 6 0 films on Ag(111). The intensity ratios of the highest and next-highest occupied molecular orbitals (the HOMO and NHOMO) of the films are found to oscillate with the same period as the incident photon energy is varied, but the amplitude of the oscillation is smaller with lower film coverage. Since the characteristics of the molecular orbitals of C 6 0 in the monolayers are considerably different from those of the thick film due to the charge-transfer interaction between the metallic surface and the molecule the observation opposes the proposal in which the oscillation is entirely dependent on the nature of the empty and occupied states involved in the photoemission process. The results instead support the photoelectron interference model by Hasegawa et al. [Phys. Rev. B 58, 4927 (1998)]. Variation of the oscillation amplitude with C 6 0 coverage is explained in terms of hybridization of the HOMO and NHOMO with the surface. Depositing C 6 0 onto Ag(111) held at a high temperature produces a single-phase (2√3×2√3) R30° C 6 0 monolayer. Angle-resolved photoemission experiments reveal changes in the relative intensities of the two bands with the azimuth-emission angle, measured with respect to the symmetry axes of the ordered monolayer. The intensity modulation is due to anisotropic scattering of photoelectrons along various molecular axes.

A novel kind of micromachined fiber-optic pressure sensor is developed. This paper describes our progress in the development of the novel, MEMS based, high-sensitivity, high-resolution, high-temperature and fast-response optical fiber pressure sensor for pressure measurement in unsteady and turbulent flow fields system. The development process includes design, simulation, fabrication and package of the sensor is demonstrated The pressure sensor is fabricated by deep reactive ion etching (RIE) technology. The finished device has a sensing element with a size of 100 /spl mu/m in diameter. It has been expected - through ANSYS simulation, to show good sensitivity, wide measuring scale, as well as high frequency response. The fiber optic pressure sensor measurement system is based upon the interferometric response of an extrinsic cavity formed between the interrogation fiber and a reflective silicon diaphragm. We discussed the design trade offs, optical interrogation and temperature sensitivity of such a configuration, and demonstrate the success of the design in small-scale shock tube experiments. We then describe the application of the sensor in a full-scale turbine test facility in which pressure signals with frequency components exceeding 50 kHz were obtained.

WHEN a material absorbs a photon, a fraction of the energy may be transformed into heat. A measurement of photothermal heating as a function of wavelength can provide an absorption spectrum of the material. We have recently1,2 developed a micromechanical sensor capable of detecting heat changes of the order of picojoules (10-12 J). The instrument incorporates a bilayer cantilever of micrometre dimensions which bends in response to heating. Here we show that this device can be used for photothermal spectroscopy with a power sensitivity of 100 pW—two orders of magnitude better than the sensitivity of conventional photothermal deflection spectroscopy3. The small size of the sensor allows picogram quanti-ties of material to be studied, opening up the possibility of spectro-scopic studies on individual cells and bacteria. Being based on silicon technology, the sensor should be compatible with micro-electronic circuitry.

Two ac techniques for imaging under liquids using atomic force microscopy are investigated. In the first method, the sample is oscillated with a sinusoidal displacement, whereas in the second method, the cantilever is oscillated with a sinusoidal magnetic force. Both techniques are successful for topographic imaging under liquids with the tip in repulsive contact with the sample. Of the two methods, the cantilever driven technique is found to be less noisy. In addition to topographic imaging, noncontact magnetic force imaging under liquid is demonstrated.

Bent by oxidation! A polyaniline (PAn, blue) coated cantilever acts as an electro-driven microdevice. Reversible oxidation/reduction of the PAn results in reversible deflection of the cantilever originating from the electrostatic repulsion of the charged polymer chains of PAn2+ (green).

The possibility of achieving nanometer-scale sensitivity in a surface-enhanced Raman (SERS) experiment while using larger-sized probes (0.1--1 \ensuremath{\mu}m) is investigated. The application targeted is carbon film transformation under high-energy beam irradiation, and, primarily, the transformation of amorphous carbon into nanocrystalline graphite. The carbon film covers nanometer-size Ag particles which enhance the signal from zones of material adjacent to them. This geometry gives access to the film/substrate interface, and in this way it complements scanning near-field techniques which have similar spatial sensitivity but are mainly surface sensitive. The SERS effect has been studied as a function of the Ag nanoparticle size, carbon film thickness, and excitation wavelength. A selective enhancement of the Raman cross section of the D band of amorphous carbons was observed. The dielectric properties of the carbon film, when used as an overlayer, strongly affect the SERS enhancement, so that changes in the dielectric function upon irradiation can be used to produce local enhancement contrast, and to establish an identification procedure for material transformation.

The combination of electron beam lithography using the scanning electron microscope (SEM) and direct nanofabrication with the scanning tunneling microscope (STM) has been used to fabricate a nanometer size link between two prefabricated nanometer size wires. The wires were fabricated by electron beam lithography using a high resolution SEM. This sample was then transferred to a combined SEM and STM instrument which is used to locate the wires, position them beneath the STM tip, and fabricate the link using the technique of tip bias pulsing with the STM.

The authors have developed a novel piezoelectric-based linear inertial slider to achieve remote micropositioning in any orientation. It is particularly suitable for SPM in cryogenic and ultra-high vacuum environments and the simple, coaxial design results in a rigid structure. Speeds of up to 2 mm s-1 have been achieved vertically against gravity, and the ability to lift up to 100 g has been demonstrated. A computer simulation for the system has been developed and used to investigate the effects of different driving waveforms. In particular an exponential ramp was shown to be most effective, this was corroborated by experimental results.

Using a modified atomic force microscope (AFM) with a conducting cantilever, we have investigated the dielectric strength of SiO2 gate oxide films. This has been achieved by spatially resolving the prebreakdown tunneling current flowing between the silicon substrate and tip. During AFM imaging a voltage ramp was applied to the tip at each image point so as to determine the local threshold voltage required to generate a small tunneling current in the oxide, without causing an irreversible electrical breakdown. For an oxide 12‐nm thick this voltage was found to vary by more than a factor of 2.7 over an area of 0.14 μm2, with a maximum value of 40.5 V. This suggests that the breakdown strength of conventional metal‐oxide‐silicon capacitors may not be limited by the intrinsic dielectric strength of the oxide, but by imperfections or nonuniformities in the Si/SiO2 structure. By preventing irreversible oxide breakdown during scanning, we can image the dielectric properties of oxide films with a lateral resoluti...

A high performance ferroelectric non-volatile memory device based on a top-gate ZnO nanowire (NW) transistor fabricated on a glass substrate is demonstrated. The ZnO NW channel was spin-coated with a poly (vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) layer acting as a top-gate dielectric without buffer layer. Electrical conductance modulation and memory hysteresis are achieved by a gate electric field induced reversible electrical polarization switching of the P(VDF-TrFE) thin film. Furthermore, the fabricated device exhibits a memory window of ∼16.5 V, a high drain current on/off ratio of ∼105, a gate leakage current below ∼300 pA, and excellent retention characteristics for over 104 s.

We report the self-assembly of single crystals of single-walled carbon nanotubes (SWCNTs) using thermolysis of nano-patterned precursors. The synthesis of these perfectly ordered, single crystals of SWCNTs results in extended structures with dimension on the micrometer scale. Each crystal is composed of an ordered array of tubes with identical diameters and chirality, although these properties vary between crystals. The results show that SWCNTs can be produced as a perfect bulk material on the micrometer scale and point toward the synthesis of bulk macroscopic crystalline material.

The ohmic conductivity of the sol-gel derived Pb1+y(Zr0.3Ti0.7)O3 thin films (with the excess lead y=0.0 to 0.4) are investigated using low frequency small signal alternate current (AC) and direct current (DC) methods. Its temperature dependence shows two activation energies of 0.26 and 0.12 eV depending on temperature range and excess Pb levels. The former is associated with Pb3+ acceptor centers, while the latter could be due to a different defect level yet to be identified., Comment: 13 pages, 3 figures, PostScript. Submitted to Applied Physics Letters

An atomic force microscope is used to investigate the lubrication properties of a simple surfactant (n‐dodecanol) on mica at 24 °C. The liquid becomes strongly layered as it is confined between the tip and the mica and a bilayer structure was often observed. The lubrication properties of the adsorbed molecules are clearly evident in the very low friction forces observed at appreciable applied loads (∼100 MPa). It is only when the last layer of molecules is removed that a significant friction signal is observed. It appears that the tip‐mica interaction is dominated by adhesive forces and hence the measured friction and normal forces are strongly influenced by the effective contact area of the tip.

Solvation force interactions in a liquid near a solid wall (graphite) were investigated using an atomic force microscope. The general features of the data show the distinctive oscillatory force curve associated with solvation forces, with a mean periodicity approximately equal to the minimum dimensions of the molecules. Moreover, the graphite surface can still be imaged with atomic resolution; which suggests that the technique can be used for the detailed study of short range forces over specific parts of various surfaces.

An analysis of polycrystalline Au thin-film interconnects of widths ranging from 850 to 25 nm, and lengths ranging from 1 μm to 20 nm which have been electrically stressed to the point of failure is presented. A new method for testing failure of interconnects is proposed, based on a quantity we call the failure current density. The mean time to failure for fixed current density and also the failure current density are seen to decrease with decreasing wire width contrary to expectations. The failure current density for a given wire width increases as the length decreases. An analysis of the temperature and stress profiles based on calculations of a simple model is presented which shows that the length dependence is due to thermal stresses rather than electromigration, and the width dependence is due to enhanced electromigration due to surface diffusion.

In this article, we describe nanometer scale characterization of piezoelectric thin films of Lead–Zirconate–Titanate (PZT). Using the electric field from a biased conducting atomic-force microscopy (AFM) tip, we show that it is possible to form and subsequently image ferroelectric domains. Using a sphere-plane model for the tip-sample system we calculate the distribution of electric potential, field and polarization charge, and find good agreement with the experimental values. We also discuss the effects of surface contaminants on domain formation.

The use of surface stress-based sensors as bio-chemical sensors was investigated. In principle, adsorption of bio-chemical species on a functionalised surface of a microfabricated cantilever will cause surface stress and consequently the cantilever bends. Two applications are presented: first lipoproteins and their oxidised form which are responsible for cholesterol accumulation in arteries were differentiated by measuring the surface stress involved in their adsorption on a sugar (heparin); secondly, the surface stress resulting from surface induced conformational changes in protein was monitored. That provided experimental evidence of long time-scale surface processes.

Thin films of hydrogenated amorphous silicon (a-Si:H) have been deposited by plasma-enhanced chemical vapour deposition (PECVD), and the resulting topography measured in-situ on a nanometre scale using a scanning tunnelling microscope (STM). An island structure is observed on the surface of device quality a-Si:H, which can be quantitatively analysed using a one dimensional Fourier transform of the topography. Results suggest that deposition is limited by the creation of dangling bonds on the a-Si:H surface and not by the surface transport of SiH 3 radicals at the deposition temperature (598 K). Island nucleation takes place through the abstraction of hydrogen atoms from the a-Si:H surface by plasma etching and the subsequent attachment of an SiH 3 radicals to the available sites. A thermally activated hydrogen effusion process around the edge of each island, where the step edge causes a high local hydrogen concentration, then creates further dangling bonds which allow the islands to grow. A simulation has been constructed, which confirms this two stage mechanism.

An introduction to experimental aspects of atomic force microscopy specific to the liquid-solid interface is given. Emphasis is given to the measurement of forces (e.g. normal, friction, material compliance, the liquid hydrodynamics) acting on the tip in liquids. Specific examples which are discussed include solvation forces and their relation to local lubrication, and the measurement of single asperity contacts in simple liquids. Some general problems which remain outstanding are highlighted.

The use of Conducting Probe Atomic Force Microscopy to give nm scale electronic characterisation of surfaces is reviewed. Local conductance, Kelvin Probe work function measurements, Fowler-Nordheim tunnelling and local C-V characterisation techniques are outlined. The principle results of these and their applications to the semiconductor surface and thin film characterisation are discussed. We present tunnelling data from silicon through varying oxide thickness using conducting AFM and scanning Kelvin Probe measurements from sub micron MOS capacitors. The F-N tunnelling technique has also been used on epitaxial silicon surfaces with atomically flat topography.The inherent problems associated with quantitative, reproducible measurements are outlined, and the potential applications of the measurements to surface and thin film technology are discussed.

Preface. Towards Molecular and Supramolecular Devices J. A. Preece, J. F. Stoddart. Nanoscale Fabrication W. M. Tolles. Microminiaturization in Laser Surgery and in vivo Intradiscal Pressure Measurements in Intervertebral Discs H. S. Ranu. Self Replicating Systems and Low Cost Manufacturing R. C. Merkle. The Use of Actuation Principles for Micro Robots U. Rembold, S. Fatikow, Th. Dorsam, B. Magnussen. Biophysical Approach to Nanometre Engineering's Limits E. Wallich. IDEAS - Intelligent Design Environment for Algorithms and Systems T. Beth, J. Muller-Quade, A. Nuckel. Electron-Nucleus Interaction in a Finite Atomic Line Modulated by a Focused Electric Field C. Joachim, J. K. Heully, M. Devel, C. Girard. Electromagnetic Radiation in Nanostructures J. B. Pendry. Using Atom Optics to Fabricate Nanostructures R. J. Celotta, J. J. McClelland, R. E. Scholten, R. Gupta. Limits to Squeezing of Quantum Fluctuations A. Orlowski. Micromechanical Calorimeter with pico-Joule Sensitivity E. Meyer, J. K. Gimzewski, Ch. Gerber, R. R. Schlittler. The Point-Contact Thermometer and its Application in the Study of Hydrodynamic Electron Flow L. W. Molenkamp, M. J. M. de Jong. Noise in Scanning Tunnelling Microscopy B. Koslowski, C. Baur, K. Dransfield. A Nanosensor for Admittance Spectroscopy L. Montelius, J. O. Tegenfeldt, T. G. I. Ling. Nanodeformation - Solid or Liquid? J. B. Pethica. Theory of Conduction through Quantum Necks J. A. Torres, J. J. Saenz. A Scanning Force and Friction Microscope Ph. Niedermann, J. Burger, M. Binggeli, R. Christoph, H. E. Hintermann, O. Marti. Electrical Properties of Nanometer-Sized Metal-Semiconductor Point Contacts Y. Hasegawa, I.-W. Lyo,Ph. Avouris. Study of Contact in the Fabrication of Gold Nanostructures by Scanning Tunnelling Microscopy A. M. Baro, J. Gomez-Herrero, J. I. Pascual, J. Mendez, N. Garcia. Fabrication of Nanoscale Gold Contacts with the STM: Possible Applications C. van Haesendonck, L. Stockman, G. Neuttiens, Y. Bruynseraede. Suppression of Electron Tunnelling through Liquid Crystal Molecules due to Infrared Irradiation H. Nejoh, V. A. Tkachenko, M. Tsukada, M. Aono: Influence of Thickness Fluctuations on Exchange Coupling in Fe/Cr/Fe Structures J. A. Stroscio, D. T. Pierce, J. Unguris, R. J. Celotta. 1-->3 Dimensional Structures on a Uni-Directional Substrate P. W. Murray, F. M. Leibsle, C. A. Muryn, H. J. Fischer, C. F. J. Flipse, G. Thornton, J. K. Gimzewski, R. R. Schlittler. S-Layers as Molecular Patterning Structures D. Pum, M. Sara, U. B. Sleytr. Formation of Sub-Micrometer Structures in Soft Functionalized Langmuir--Blodgett Films by Atomic Force Microscopy N. B. Larsen, T. Bjornholm, J. Garnaes, J. Larsen, K. Schaumberg. Individual Molecules on GaAs(001)-(2x4) and Si(001)-(2x1): Images, Statistics, and Modelling C. M. Goringe, A. R. Avery, A. J. Mayne, M. O. Schweitzer, W. Widdra, A. J. Fischer, T. S. Jones, G. A. D. Briggs, W. H. Weinberg, C. W. Smith. Extended Abstracts of Invited Papers: Molecular Manufacturing K. E. Drexler. Self-Assembly: Whither and Thither Molecular Machines J. A. Preece, J. F. Stoddart. Nanostructured Sensors for Molecular Recognition W. Gopel. Micromechanisms H. Guckel. Limits to Mechanical Positioning and Displacement E. C. Teague. Is Quantum Mechanics Useful? R. L

We demonstrate that surface stresses in epitaxially grown VO₂ nanowires (NWs) have a strong effect on the appearance and stability of intermediate insulating M₂ phases, as well as the spatial distribution of insulating and metallic domains during structural phase transitions. During the transition from an insulating M1 phase to a metallic R phase, the coexistence of insulating M₁ and M₂ phases with the absence of a metallic R phase was observed at atmospheric pressure. In addition, we show that, for a VO₂ NW without the presence of an epitaxial interface, surface stresses dominantly lead to spatially inhomogeneous phase transitions between insulating and metallic phases. In contrast, for a VO₂ NW with the presence of an epitaxial interface, the strong epitaxial interface interaction leads to additional stresses resulting in uniformly alternating insulating and metallic domains along the NW length.

A method has been developed to synthesise zinc oxide nanowire arrays that demonstrate superior device performance compared to conventional ZnO nanowires within dye sensitised solar cells (DSSCs). This simple yet effective methodology has produced nanowires with triple device performance when compared to conventional ZnO nanowire DSSCs. We have fully characterised the morphology and physical properties of these wires and have demonstrated that the device improvements are due to a reduction in the recombination centres associated with the ZnO crystal.

A variable temperature scanning tunnelling microscope (STM) in UHV has been used to investigate the growth, morphology and surface atomic structure of ultrathin titanium suicide films on Si(100) and Si(111) substrates. Three stages of suicide growth have been identified based on microstructural considerations. They occur over similar temperature ranges for both substrates and may be summarised as: agglomeration and the formation of disordered islands, crystallite formation, and crystallite growth. Additionally, island burial is found for Si(100) substrates (950°C), and preferential crystallite growth is observed for high temperature processing (1200°C) of titanium silicide on Si(111). Methods for STM crystallography have been developed and used to identify possible epitaxial silicide/silicon relationships based on morphological considerations. Atomic resolution images of titanium silicide crystallites have identified a 2×2 silicon termination of a C54-TiSi2(111) surface, a 2×2 silicon terminated C54-TiSi2(010) surface, and a reconstructed C54-TiSi2(311) surface. It has been concluded that unambiguous identification of epitaxial relationships requires images of the atomic structure of the silicide crystallite surfaces in addition to morphological information.

Self-assembly processes resulting in linear structures are often observed in molecular biology, and include the formation of functional filaments such as actin and tubulin, as well as generally dysfunctional ones such as amyloid aggregates. Although the basic kinetic equations describing these phenomena are well-established, it has proved to be challenging, due to their non-linear nature, to derive solutions to these equations except for special cases. The availability of general analytical solutions provides a route for determining the rates of molecular level processes from the analysis of macroscopic experimental measurements of the growth kinetics, in addition to the phenomenological parameters, such as lag times and maximal growth rates that are already obtainable from standard fitting procedures. We describe here an analytical approach based on fixed-point analysis, which provides self-consistent solutions for the growth of filamentous structures that can, in addition to elongation, undergo internal fracturing and monomer-dependent nucleation as mechanisms for generating new free ends acting as growth sites. Our results generalise the analytical expression for sigmoidal growth kinetics from the Oosawa theory for nucleated polymerisation to the case of fragmenting filaments. We determine the corresponding growth laws in closed form and derive from first principles a number of relationships which have been empirically established for the kinetics of the self-assembly of amyloid fibrils.

Zinc oxide-titanium dioxide core-shell nanowire dye-sensitised solar cells have been synthesised, making use of a recently developed organic dye and iodide-based electrolyte. We have been able to demonstrate a cell efficiency of 2.53% under AM1.5 for our system. Compared to other cells based on vertically aligned, hydrothermally grown ZnO nanowires, and systems of comparable architecture, our device demonstrates one of the highest cell efficiencies to date and is due to the precise control of the semiconductor's growth and the high performance of the incorporated dye. We have carried out complete morphological analysis and have been able to fully characterise the device.

Light, emission arising from an electron making a transition between two energy levels provides one of the most important sources of information on the electronic structure of matter. In optical microscopy and spectroscopy, the spatial resolution achievable is generally limited by the wavelength of the photons involved. Two approaches developed to overcome this limitation are near-field optic probes to spatially confine the electromagnetic fields used and the use of sub-nm sized electron excitation probes. The latter approach, developed by us using the STM, has similarities and differences with the former approach which forms the main part of the present workshop. We discuss the technique with examples of optical spectroscopy and, comparisons of topography and photon maps for metal, semiconductor and adsorbate systems.

Herein we report a low-threshold organic laser device based on semiconducting poly(9,9′-dioctylfluoren-2,7-diyl-alt-benzothiadiazole) (F8BT) encapsulated in a mechanically stretchable polydimethylsiloxane (PDMS) matrix. We take advantage of the natural flexibility of PDMS to alter the periodicity of the distributed feedback grating which in turn tunes the gain wavelength at which the resonant feedback is obtained. This way, we demonstrate that low-threshold lasing [6.1 μJ cm−2 (5.3 nJ)] is maintained over a large stretching range of 0%–7% which translates into a tuning range of about 20 nm.

Functionalized single-walled carbon nanotubes (SWNTs) are currently being investigated for a variety of applications, including contrast agents for medical imaging1. However before they can be used commercially it is necessary to assess whether they enter cells, the site they target within the cell and whether they cause any cytotoxicity. Here we characterize uptake of unlabelled, acid-treated, COO− functionalized SWNTs by human monocyte derived macrophage cells using both low-loss and energy loss spectroscopy and compare our findings to previous work on unpurified SWNTs. The acid-treated SWNTs were less aggregated within cells than unpurified SWNTs. Acid treatment was found to affect the distribution of intracellular SWNTs. Bundles, and also individual acid treated SWNTs, were found frequently inside lysosomes, cytoplasm and also inserting into the plasma membrane whereas unpurified non-functionalised SWNTs entered lysosomes and occasionally the nucleus.

We have investigated the effect on a silicon surface of both wet chemical and cluster-tool UV/ozone cleaning, prior to UHV processing to fabricate MOS test structures. The physical and chemical condition of the Si surface has been examined by Scanning Tunnelling and Atomic Force Microscopy (STM, AFM) and Medium Energy Ion Scattering (MEIS). After MOS fabrication some of the structures were examined by Cross-sectional Transmission Electron Microscopy (TEM). The electrical performance of the MOS test sets were characterized by breakdown voltage measurements.We have found correlations between the electrical performance of the MOS devices, the structure of the Si surface prior to oxidation, and the details of the UHV fabrication technique. In particular any MOS device fabricated on a Si surface thermally cleaned in UHV prior to oxidation has a poor breakdown strength. We have found that this is the result of the formation of silicon carbide on the Si surface at high temperature and the subsequent local disruption of the oxidation step of MOS fabrication by the SiC. A UHV cleaning procedure has been developed to avoid this C contamination problem.

We have made a detailed atomic study of the early stages of oxidation of silicon at room temperature. On the reconstructed 111 surface the reaction occurs rapidly with a sticking coefficient of ~0.02. Three types of defect or reacted site are found on the surface; the number density of the two commonest defects increasing linearly with oxygen dose. The commoner of the two defect types exhibits image contrast consistent with a depletion in electron density from empty (anti-bonding) to filled (bonding) states which we believe is due to the reaction of the oxygen in the layer immediately below the adatoms. Tunnelling spectroscopy at such sites on the surface shows the quenching of the adatom states and the appearance of a peak in the density of states at -0.8 eV. The other common defect appears in the filled state image exhibiting weaker contrast than the first type and indicating an enhancement in the filled state density. Both defect types preferentially react in the faulted half of the unit cell with an 88% probability. The third type of defect, with only a weak dependence on oxygen dose, occurs at the corner of the unit cell and produces a large change in the electron barrier height consistent with uncompensated charge or an electron trap.

Au nanoparticles stabilized by poly(methyl methacrylate) (PMMA) were used as a catalyst to grow vertically aligned ZnO nanowires (NWs). The density of ZnO NWs with very uniform diameter was controlled by changing the concentration of Au-PMMA nanoparticles (NPs). The density was in direct proportion to the concentration of Au-PMMA NPs. Furthermore, the growth process of ZnO NWs using Au-PMMA NPs was systematically investigated through comparison with that using Au thin film as a catalyst. Au-PMMA NPs induced polyhedral-shaped bases of ZnO NWs separated from each other, while Au thin film formed a continuous network of bases of ZnO NWs. This approach provides a facile and cost-effective catalyst density control method, allowing us to grow high-quality vertically aligned ZnO NWs suitable for many viable applications.

Carbon-based nanoparticles have attracted significant attention due to their unique physical, chemical, and electrical properties. Numerous studies have been published on carbon nanoparticle toxicity; however, the results remain contradictory. An ideal approach is to combine a cell viability assay with nanometer scale imaging to elucidate the detailed physiological and structural effects of cellular exposure to nanoparticles. We have developed and applied a combination of advanced microscopy techniques to image carbon nanoparticles within cells. Specifically, we have used EFTEM, HAADF-STEM, and tomography and confocal microscopy to generate 3-D images enabling determination of nanoparticle spatial distribution in a cell. With these techniques, we can differentiate between the carbon nanoparticles and the cell in both stained and unstained sections. We found carbon nanoparticles (C60, single-walled carbon nanotubes (SWNT), and multi-walled carbon nanotubes (MWNT)) within the cytoplasm, lysosomes, and nucleus of human monocyte-derived macrophage cells (HMM). C60 aggregated along the plasma and nuclear membrane while MWNTs and SWNTs were seen penetrating the plasma and nuclear membranes. Both the Neutral Red (NR) assay and ultra-stuctural analysis showed an increase in cell death after exposure to MWNTs and SWNTs. SWNTs were more toxic than MWNTs. For both MWNTs and SWNTs, we correlated uptake of the nanoparticles with a significant increase in necrosis. In conclusion, high resolution imaging studies provide us with significant insight into the localised interactions between carbon nanoparticles and cells. Viability assays alone only provide a broad toxicological picture of nanoparticle effects on cells whereas the high resolution images associate the spatial distributions of the nanoparticles within the cell with increased incidence of necrosis. This combined approach will enable us to probe the mechanisms of particle uptake and subsequent chemical changes within the cell, essential for identifying the toxicological profiles of carbon nanoparticles.

Dielectrophoresis of non-spherical particles is attracting attention, particularly for the aligned deposition of nanowires and nanotubes. The orientation and translation of ellipsoids are studied theoretically, and it is found that the orientation plays a significant role in determining the particle trajectory. A new equation for dielectrophoresis is presented which allows for orientation to be taken into account. Numerical simulation of particle motion is performed to demonstrate these effects.

The transient behavior of a trapped electron in the TiO2 sol-gel based gate dielectric layer of a silicon-on-insulator metal-oxide-semiconductor field effect transistor is investigated. Defects in this dielectric layer give rise to microwave resonances that are electrically detected via the channel current. The lifetime of the excited state is inferred from the quality factor of the resonance. A single shot measurement, carried out on the same resonance, is used to characterize the transient behavior and to directly measure the lifetime of the excited state. Possible applications of transient measurements on high-k dielectric layers are discussed.

We present an approach for sensing protein aggregation using microcantilever systems. Results from both single cantilever experiments with internal reference and multicantilever array measurements with dedicated reference cantilevers are discussed. We show that in both cases protein aggregation on the sensor can be detected through associated changes in surface stress.

The variation in morphology of zinc oxide when it crystallises is one of the fascinating aspects of this important semiconductor. Alterations in hydrothermal growth conditions can allow the synthesis of a wide range of shapes and structures, including nanowires and layered structures, formed via a secondary growth regime but, to date, little work has investigated the effect changes in growth conditions can have and their influence on the optical properties. Here, systematic changes in growth conditions and reactants were carried out and the results studied using scanning electron microscopy, X-ray diffraction, optical transmission, cathodoluminescence and Raman spectroscopy and atomic force microscopy. We demonstrate that the choice of the reactants can have a significant effect not just on the morphologies of the structure, but on the fundamental properties of the crystalline state such as alterations into the defect states within the system. Furthermore, secondary growth is shown to be dependent on the underlying primary growth morphology, and general reaction conditions for laminar growth are suggested.

Since its introduction by Binnig et al.,(1) the Scanning Tunnelling Microscope (STM) has engendered much excitement among surface scientists, not only for the atomically resolved surface topography it can achieve, but also for the range of surface spectroscopy possible. In this chapter we discuss scanning tunnelling microscopy in the context of the study of thin films (for example, an organic adsorbate on a metal substrate), highlighting the strengths and weaknesses of the technique. Greater detail may be found in the literature; in particular, the review by Hansma and Tersof(2) provides a wide survey of the field. For more general reviews of tunnelling and tunnelling spectroscopy the reader is directed to the books by Wol(3) and Hansma.(4)

CoSi2 films were investigated using a scanning tunneling microscope (STM) to understand the film surface topology. The STM images showed that the as-deposited amorphous film had a nano-meter scale roughness which agrees with cross-sectional transmission electron microscope (TEM) observations and also had a uniform granular structure. Images of the crystallized film clearly show the crystal grain structure at the surface and the surface topography change associated with crystallization. In-situ crystallization was accomplished by operating the STM with a high bias; dome shape crystallites were produced at the surface of the amorphous films.

The vapor-liquid-solid growth of nanostructures is simulated using a two-dimensional kinetic Monte Carlo model. The model considers the deposition of reactants from the vapor, solute diffusion in the solution droplet, and the nucleation and growth of the precipitated solid phase. The extrusion of the solid from the solution into the vapor is also modeled. A morphological transition from one-dimensional to two-dimensional growth is observed in response to changes in reactant vapor pressure and to changes in the solute diffusivity at the liquid-vapor interface. The morphology is determined by the dominant growth direction of the solid and is dependent on the speed at which deposited solute species can be diffused from the surface. Such a fundamental change in morphology has been observed experimentally in the growth of silicon carbide nanostructures and insight into the cause of this transition is achieved.

Semiconducting nanowires provide routes for realizing high-performance electronic devices, but for many applications of such devices low-cost manufacturing techniques are needed. The authors demonstrate here top-gated zinc oxide nanowire field effect transistors (NW-FETs) fabricated by ink-jet printing. High resolution submicrometer gold gaps between source and drain electrodes were defined by a self-aligned ink-jet printing technique, and the nanowires were deposited from solution onto these electrode arrays and gated from the top using a spin-coated poly(methyl methacrylate) gate dielectric. The typical NW-FETs exhibited a mobility of 2–4cm2∕Vs, a current on/off ratio of 104, and a transconductance of 20.5nS. The process provides a pathway for fabrication of NW-FETs by low-cost, large-area solution processing and direct printing techniques.

What insight can nanoscience provide into amyloid diseases such as Alzheimer's, which are caused by nanowires of protein deposits?

An increasing number of technologies require the fabrication of micro- and nanostructures over large areas. Soft lithographic methods are gaining in popularity for the manufacture of low-cost micrometre and sub-micrometre structures. Increasingly, these methods developed to structure organic resists can also be used to pattern inorganic materials. Here we introduce a simple lithographic technique that is able to pattern ceramic TiO2 micro- and nanostructures with high fidelity. Our method makes use of an electrohydrodynamic (EHD) film instability that is controlled by a laterally modulated electric field. A spin-coated film of a stabilized metal alkoxide precursor material was patterned using EHD lithography followed by a heat treatment at 400 °C to yield crystalline TiO2 micropatterns. Our technique is rather general and can be extended to a number of single- and multicomponent oxide systems.

A field effect transistor (FET) using a zinc oxide nanowire with significantly enhanced performance is demonstrated. The device consists of single nanowire and self-aligned gate electrodes with well defined nanosize gaps separating them from the suspended nanowire. The fabricated FET exhibits excellent performance with a transconductance of 3.06μS, a field effect mobility of 928cm2∕Vs, and an on/off current ratio of 106. The electrical characteristics are the best obtained to date for a ZnO transistor. The FET has a n-type channel and operates in enhancement mode. The results are close to those reported previously for p-type carbon nanotube (CNT) FETs. This raises the possibility of using ZnO as the n-type FET with a CNT as the p-type FET in nanoscale complementary logic circuits.

We discuss the application of atomic force microscopy to characterize supra-molecular ordering in elongated protein aggregates such as amyloid fibrils. The measurements reveal that the one-dimensional defect density along these structures is comparable to that found in true three-dimensional macromolecular crystals. The high level of structural order has important implications for understanding the nature of the interactions responsible for protein aggregation, and sheds light on the involvement of amyloid fibrils in aberrant biological pathways.