Table of contents

The inaugural conference on Nanoscale Devices and System Integration (NDSI-2004) was held in Miami, Florida, 15-19 February, 2004. The focus of the conference was `real-life' devices and systems that have recently emerged as a result of various nanotechnology initiatives in chemistry and chemical engineering, physics, electrical engineering, materials science and engineering, biomedical engineering, computer science, robotics, and environmental science. The conference had a single session all-invited speaker format, with the presenters making the `Who's Who in Nanotechnology' list. Contributed work was showcased at a special poster session. The conference, sponsored by the Institute of Electrical and Electronics Engineers (IEEE) and the US Air Force, and endorsed by Materials Research Society (MRS), drew more than 160 participants from fourteen countries.

To strengthen the connection between fundamental research and `real-life' applications, the conference featured a large number of presenters from both academia and industry. Among the participating companies were NEC, IBM, Toshiba, AMD, Samsung, Seagate, and Veeco. Nanotechnology has triggered a new wave of research collaborations between researchers from academia and industry with a broad range of specializations. Such a global approach has resulted in a number of breakthrough accomplishments. One of the main goals of this conference was to identify these accomplishments and put the novel technology initiatives and the emerging research teams on the map.

Among the key nanotechnology applications demonstrated at NDSI-2004 were carbon-nanotube-based transistors, quantum computing systems, nanophotonic devices, single-molecule electronic devices and biological magnetic sources.

Due to the unprecedented success of the conference, the organizing committee of NDSI has unanimously chosen to turn NDSI into an annual international nanotechnology event. The next NDSI is scheduled for 4-6 April, 2005, in Houston, Texas. Details can be found on the conference web site at http://www.nanointernational.org.

This special issue of Nanotechnology features selected papers from NDSI-2004.

Self-assembled monolayers, phospholipid bilayers, and membrane bound proteins are assembled on a subwavelength metallic array. These assemblies are assayed with direct infrared absorption spectroscopy which is greatly enhanced due to the extraordinary infrared transmission of the arrays. Stacking the arrays, one upon another, accentuates the surface plasmon properties and provides the basis of a nanospaced capacitive sensor.

Metrology is the science and engineering of measurement. It has played a crucial role in the industrial revolution at the milli-inch length scale and in the semiconductor revolution at the micrometre length scale. It is often proclaimed that we are standing at the threshold of another industrial revolution, brought by the advent and maturing of nanotechnology. We argue that for nanotechnology to have a similarly revolutionary effect a metrology infrastructure at and below the nanometre scale is instrumental and has yet to be developed. This paper focuses on dimensional metrology, which concerns itself with the measurement of lengths and its applications such as pattern placement and feature size control. We describe our efforts to develop grating- and grid-based scales with sub-nanometre accuracy over 300 mm dimensions using the nanoruler—a scanning-beam interference lithography tool.

We discuss the central issues to be addressed for realizing carbon nanotube (CNT) nanoelectronics. We focus on selective growth, electron energy bandgap engineering and device integration. We have introduced a nanotemplate to control the selective growth, length and diameter of CNTs. Vertically aligned CNTs are synthesized for developing a vertical CNT-field effect transistor (FET). The ohmic contact of the CNT/metal interface is formed by rapid thermal annealing. Diameter control, synthesis of Y-shaped CNTs and surface modification of CNTs open up the possibility for energy bandgap modulation. The concepts of an ultra-high density transistor based on the vertical-CNT array and a nonvolatile memory based on the top gate structure with an oxide–nitride–oxide charge trap are also presented. We suggest that the deposited memory film can be used for the quantum dot storage due to the localized electric field created by a nano scale CNT-electron channel.

We report two examples of transport phenomena based on sharp features in the effective density of states of molecular-scale transistors: Kondo physics in C₆₀-based devices, and gate-modulated negative differential resistance (NDR) in 'control' devices that we ascribe to adsorbed contamination. We discuss the need for a statistical approach to device characterization, and the criteria that must be satisfied to infer that transport is based on single molecules. We describe apparent Kondo physics in C₆₀-based single-molecule transistors (SMTs), including signatures of molecular vibrations in the Kondo regime. Finally, we report gate-modulated NDR in devices made without intentional molecular components, and discuss possible origins of this property.

We report on the self-assembly of one- and two-dimensional DNA scaffolds, which serve as templates for the targeted deposition of ordered nanoparticles and molecular arrays. The DNA nanostructures are easy to reprogram, and we demonstrate two distinct conformations: sheets and tubes. The DNA tubes and individual DNA molecules are metallized in solution to produce ultra-thin metal wires.

Reconfigurable shadow mask technology, presented in this paper, introduces the use of microsystems for in situ metal deposition, and direct patterning of structures with micron and submicron lateral and vertical dimensions. A multilayer microstructure acts as a set of addressable active shutters and shadow masks in a physical vapour deposition (PVD) system. Design and fabrication of a microactuator allowing submicron controlled displacements combined with the development of a novel self-aligned multilayer fabrication process allows the deposition of metal nanolines using standard photolithographic exposure tools. Not only does this approach remove the need for nanolithography, it also enables compositional and three-dimensional active in situ variation of the nanolines during deposition. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to characterize three-dimensional structures and deposited nanolines.

We report on an 'all-laser' synthesis approach that permits the control of the lateral growth of single wall nanotubes (SWNTs) on SiO₂/Si substrates at selected locations where nanoparticles catalysts were first deposited. This novel two-step growth process uses the same UV laser (KrF excimer; λ = 248 nm) to deposit, in a first step, the CoNi nanoparticle catalysts on patterned SiO₂/Si substrates and, in a subsequent step, to grow the SWNTs. Atomic force microscopy and micro-Raman spectroscopy revealed that the 'all-laser' process leads to the formation of horizontal random networks of SWNT bundles, that bridge two adjacent nanoparticle strips. The diameter of the SWNTs was found to be  nm, while that of the bundles is generally in the 10–15 nm range. The current (I)–voltage (V_SD) characteristics of the fabricated SWNT devices confirmed that the random networks of SWNT bundles exhibit a p-type field-effect transistor behaviour. Conductance (G)–gate voltage (V_G) curves not only demonstrated that transport through the bundle networks was dominated by positive carriers (holes) but also that the bundles consist of mixtures of semiconducting and metallic SWNTs. The extremely high efficiency of our 'all-laser' growth process in producing high-quality SWNTs together with its relative simplicity definitely open new prospects for the development and integration of novel architectures of nanodevices based on SWNT networks.

Prolonging the lifetime of biomolecules in their functional states is critical for many applications where biomolecules are integrated into synthetic materials or devices. A simplified molecular shuttle system, which consists of fluorescently labelled microtubules propelled by kinesin motor proteins bound to the surface of a flowcell, served here as a model system to probe the lifetime of a hybrid device. In this system, the functional decay can easily be assayed by utilizing optical microscopy to detect motility and disintegration of microtubules. We found that the lifetimes of these hybrid systems were mainly limited by the stability of microtubules (MTs), rather than of kinesin. To determine the biocompatibility of polymers widely used in microfabrication, we assembled flowcells with glass bottom surfaces and covers fabricated from glass, poly(urethane) (PU), poly(methyl-methacrylate) (PMMA), poly(dimethylsiloxane) (PDMS) and ethylene-vinyl alcohol copolymer (EVOH). Without illumination, only PU had a substantial negative impact on MT stability, while PMMA, PDMS and EVOH showed stabilities comparable to glass. Under the influence of light, however, the MTs degraded rapidly in the presence of PDMS or PMMA, even in the presence of oxygen scavengers. A similar effect was observed on glass if oxygen scavengers were not added to the medium. Strong bleaching of the fluorophores was again only found on the polymer substrates and photobleaching coincided with an accelerated depolymerization of the MTs.

Compact, physics-based, short-channel models of subthreshold swing and threshold voltage are presented for undoped symmetric double-gate (DG) MOSFETs, including quantum-mechanical and fringe-induced-barrier-lowering effects. Scaling limit projections indicate that individual DG MOSFETs with good turn-off behaviour are feasible at 10 nm scale; however, practical exploitation of these devices toward gigascale integrated systems requires development of novel technologies for significant improvement in process control.

We propose an atom–cavity chip that combines laser cooling and trapping of neutral atoms with magnetic microtraps and waveguides to deliver a cold atom to the mode of a fibre taper coupled photonic bandgap (PBG) cavity. The feasibility of this device for detecting single atoms is analysed using both a semiclassical treatment and an unconditional master equation approach. Single-atom detection seems achievable in an initial experiment involving the non-deterministic delivery of weakly trapped atoms into the mode of the PBG cavity.

A novel self-aligned 'soft masking' method that is compatible with traditional photolithographic processes is demonstrated. This method uses a suspension of ultrafine iron oxide grains (ferrofluid) to protect or de-protect selected areas of a magnetically patterned substrate according to a programmable sequence. Automatic mask formation and registration is controlled by ferromagnetic alignment marks patterned on a substrate. External magnetic field bias applied to the system causes ferrofluid to aggregate only over designated areas on the surface, thereby masking those areas from UV or chemical exposure.

A local oxidation technique using atomic force microscopy (AFM) was performed in order to modify magnetic domain structures in ferromagnetic nanostructures. Co-based nanostructures with a rectangular shape were fabricated by using electron beam lithography followed by AFM nano-oxidation. After fabricating a Co-oxide nanowire across a Co nanodot by AFM nano-oxidation, a domain structure of the dot observed before the nano-oxidation was divided into two parts of the domain. AFM nano-oxidation for a higher aspect ratio of height/width of the fabricated nanostructures was also investigated. By applying a dc bias between an Al₂O₃/Ni double layer film and the AFM tip, the Ni layer was locally oxidized through the capped Al₂O₃ insulating layer. The nanowires of oxide obtained on the Al₂O₃/Ni double layer film were thicker and had a higher aspect ratio of height/width than those obtained on a Ni single layer film.

The magnetic properties of superparamagnetic particles are influenced by the supporting matrix. We have systematically studied the DC magnetic properties of loosely packed manganese–zinc ferrite (Mn_0.68Zn_0.25Fe_2.07O₃) nanoparticles synthesized using a reverse micelle technique. The results have been compared with those for particles suspended in paraffin wax and embedded in a polypyrrole matrix. The polypyrrole-doped particles were prepared using an in situ ultraviolet irradiation method and spin-coated into thin films. The loosely packed particles showed no resolvable coercivity even well below the blocking temperature. On the other hand, the same particles in wax showed the opening up of a large coercivity below the blocking temperature. However, both the samples showed characteristic superparamagnetic transition peaks in the temperature-dependent susceptibility nearly at the same temperature. The particles in the polypyrrole matrix showed a remarkable increase in the blocking temperature and large hysteresis at 300 K. The structural characterization of the polymer-doped sample showed clustering of the nanoparticles.

Magnetic force microscopy (MFM) is a widely used form of scanning probe microscopy (SPM) that is used for obtaining a magnetic image from a surface with nanoscale resolution. Currently, the resolution of MFM is limited to approximately 20 nm due to the long-range nature of magnetic interactions between the MFM probe's tip and the magnetic medium. This paper describes an optimal signal processing solution to the problem of achieving high resolution MFM with the goal of significantly exceeding the level at which MFM metrology currently performs, thus providing metrologists with a means of resolution increase that is believed will enable, for example, the rapid development of high-density magnetic recording media (>100 Gbit in⁻²). This is achieved by using focused-ion beam trimming of a conventional tip to create a probe tip of predictable magnetic characteristics and then, provided that the sample could be approximated as a thin-film, using knowledge of this tip's sensitivity field for performing a deconvolution on the measured signal to better estimate the magnetic state of the surface under study. Stated differently, as the MFM measured signal is modelled as the convolution of the magnetized surface and the tip's sensitivity field, we exploit knowledge of the tip's properties to increase the resolution of the MFM image. Details of the deconvolution approach as well as images resulting from this processing are the focus of this paper.

A high precision nanoengineered device was developed to yield long term zero-order release of drugs for therapeutic applications. The device contains nanochannels that were fabricated in between two directly bonded silicon wafers and therefore poses high mechanical strength. The fabrication is based upon selectively growing oxide and then removing it, and thus defining nanochannels by consuming a specified layer of silicon during oxide growth. Diffusion through the nanochannels is the rate limiting step for the release of drugs. A measurement of glucose released through such nanochannels validates the zero-order release profile. Device design, fabrication details and the glucose release profile through 60 nm channels are presented.

There are two growth modes, tip- and base-growth modes, in carbon nanotube (CNT) synthesis. We have shown that the determining factor for the growth mode is the adhesion force of the catalytic metal particles to the substrate through a systematic study of the synthesis in the plasma-enhanced chemical vapour deposition method (PECVD). The experiment was further expanded to a series of syntheses on various substrates having different surface morphologies while using thermal CVD to avoid the plasma bombardment effect on the adhesion force. Synthesis on substrates of sapphire, alumina deposited by atomic layer deposition (ALD), and an anodized aluminium oxide (AAO) membrane was carried out. They are similar in chemical stoichiometry, but the surface roughnesses are different. Only the CNTs grown on the backside of the AAO membrane revealed the tip-growth mode regardless of the coating method, kind of catalyst, and thickness of the catalytic metal films due to its high roughness.

Carbon nanotubes (CNTs) and carbon nanofibres (CNFs) were synthesized by the thermal chemical vapour deposition (CVD) process using an Ni–MgO catalyst. The Ni–MgO catalyst was treated by a mechanochemical (MC) process to govern its size and morphology. The grinding time in the MC process and pyrolytic temperature in the CVD process are regarded as the main factors to tailor the size and morphology of the CNTs and CNFs synthesized. CNTs with a diameter 25 and 15 nm, twisted CNFs with a diameter 65 and 100 nm, and straight CNFs with a diameter 70 nm were synthesized. After purification, they were used as the electrode platinum support for fuel cell application. 20% Pt was loaded on the CNTs and CNFs. The fuel cell performance with twisted CNFs was found to be better than that with straight CNFs, and the performance of CNTs and CNFs with smaller diameter was better than that of bigger ones. The best performance of the fuel cell voltage of 645 mV at a current density of 500 mA cm⁻² was given by twisted CNFs with diameter 65 nm. The dispersal of the loaded Pt and the resistivity of the membrane electrode assembly were considered to affect their performance.

We present a Monte Carlo simulation and modelling method for single-electron nanocrystal memories including the nanocrystal inter-dot effect. A nanocrystal memory is modelled as a network of modified single-tunnel junctions for its programme operation and as a network of channel resistances for simulating drain current to extract its threshold voltage. Additionally, in each modelling, capacitive coupling between each geometrical element was determined using a device simulator. The results show that nanocrystal memory parameters are closely related to both static and dynamic programming characteristics, especially in the single-charging property. When the inter-dot spacing is large, a step-like single-charging feature becomes salient, but the threshold voltage shift between each state decreases. In contrast, when the dots are spatially closer, the threshold voltage shift between each state increases, while the step-like shape vanishes and resembles that of conventional flash memories. From the dynamic viewpoint, a closer spacing of dots makes it easier to charge the nanocrystal memory quantum dots more uniformly. The presented method will be helpful for the design of single-electron nanocrystal memories.

Micro-electro-mechanical-system (MEMS)-based scanning-probe data storage devices are emerging as potential ultra-high-density, low-access-time, and low-power alternatives to conventional data storage. One implementation of probe-based storage uses thermomechanical means to store and retrieve information in thin polymer films. One of the challenges in building such devices is the extreme accuracy and the short latency required in the navigation of the probes over the polymer medium. This paper focuses on the design and characterization of a servomechanism to achieve such accurate positioning in a probe-based storage prototype. In our device, the polymer medium is positioned on a MEMS scanner with x/y-motion capabilities of about 100 µm. The device also includes thermal position sensors that provide x/y-position information to the servo controller. Based on a discrete state-space model of the scanner dynamics, a controller is designed using the linear quadratic Gaussian approach with state estimation. The random seek performance of this approach is evaluated and compared with that of the conventional proportional, integrator, and derivative (PID) approach. The results demonstrate the superiority of the state-space approach, which achieves seek times of about 4 ms in a ± 50 µm range. Finally, the experimental results show that closed-loop track following using the thermal position-sensor signals is feasible and yields a position-error standard deviation of approximately 2 nm.

Optics on a silicon chip provides a new platform for the monolithic integration of optics and microelectronics and can open the door to a new technology that is free from conventional microelectronics. However, the difficulty in controlling light and diverting its path on silicon needs to be addressed before this technology can successfully be used to resolve current microelectronics bottlenecks. Here we use highly confined photonic structures for tailoring the optical mode of the structures and enhancing the electro-optical and nonlinear properties of silicon. We show high fibre to waveguide coupling efficiency and optical switching on-chip with very low powers.

A CMOS compatible direct write laser lithography technique has been developed for cantilever fabrication on pre-fabricated standard CMOS. We have developed cantilever based sensors for mass measurements in vacuum and air. The cantilever is actuated into lateral vibration by electrostatic excitation and the resonant frequency is detected by capacitive readout. The device is integrated on standard CMOS circuitry. In the work a new direct write laser lithography (DWL) technique is introduced. This laser lithography technique is based on direct laser writing on substrates coated with a resist bi-layer consisting of poly(methyl methacrylate) (PMMA) on lift-off resist (LOR). Laser writing evaporates the PMMA, exposing the LOR. A resist solvent is used to transfer the pattern down to the substrate. Metal lift-off followed by reactive ion etching is used for patterning the structural poly-Si layer in the CMOS. The developed laser lithography technique is compatible with resist exposure techniques such as electron beam lithography. We demonstrate the fabrication of sub-micrometre wide suspended cantilevers as well as metal lift-off with feature line widths down to approximately 500 nm.

We have calculated the dynamic susceptibility of patterned cobalt and Permalloy pillars with a diameter of 50 nm and different pillar heights using micromagnetic simulations. The resonance modes obtained from these simulations are compared to the results obtained from an analytical solution of Kittel's equation for spheroids. We also compared directly to Kittel's equation with the simulation of cobalt spheroids.

In this paper, we present a nanoscale memory architecture for molecular electronics. A large memory is designed as a collection of smaller molecular-based crossbar subarrays, each of which realizes a part of the large memory. Redundancies at the row/column level in each subarray and at the subarray level are used to tolerate defects generated during the nanofabrication process. Spare subarrays with address translation in the CMOS layer are used to cope with the expected high rate of defects in chemically fabricated nanocircuits. Molecular crossbars on top of a silicon-based die providing address translation will demonstrate a notable improvement in the scalability of defect-prone molecular memories.

Narrow permalloy ring elements with different symmetries have been investigated. Two stable states of opposite polarity at remanence and simple switching have been observed using magnetic-force microscopy.

Development issues required to advance localized electro-deposition for integration with commercial fabrication techniques are presented through both experimental demonstrations and theoretical modelling of the various aspects of the process. The process is a potential candidate solution for challenges facing current fabrication technologies, and definitely has great potential for post-processing and rapid prototyping applications, especially when considering high aspect ratio structures. The various interactions determining the process mechanisms and rate are well understood through mass transfer modes as demonstrated by the agreement between simulation and experimental results of the deposition profile evolution under various process conditions. The process compatibility for integration with current commercial fabrication processes as well as automation is high. Up-to-date demonstration of the process resolution suggests suitability for many applications requiring structures with micron and possibly submicron scale dimensions, but would require further development to achieve nanometre resolution. It is concluded that the achievement of foreseen developments requires collaboration of interdisciplinary efforts.

Chiral biomolecules conjugated with silver nanoparticles were investigated by circular dichroism (CD) spectroscopy. Silver nanoparticles were prepared by the citrate reduction method and were characterized by UV spectroscopy and TEM. Conjugation of thiol group-containing biomolecules, such as cysteine, glutathione and penicillamine, with silver nanoparticles resulted in the generation of new characteristic CD signals in the region of 240–400 nm, whereas no CD signal changes were found with lysine or glutamine. Association through hydrogen bonding among the biomolecules is considered to be essential for CD signal generation, which was confirmed by experiment with cysteine methyl ester. Interestingly, Au nanoparticles were not found to generate CD signals in the wavelength region tested, indicating that this phenomenon is a unique feature of silver nanoparticles, distinguished from gold nanoparticles.

Biomedical nanotechnology is a rapidly emerging field that encompasses many disciplines including medicine, molecular biology, materials physics and chemistry, engineering, etc. The complexity of the targeted systems demands cross-disciplinary research and international collaboration. In the materials front, understanding the fundamental properties at molecular level is important to the realization of the full potential of substances and the fruition of eventual technological applications. Neutron-scattering characterization of biomolecular systems can in principle provide unique information pertinent to nanotechnological applications. But the method is not widely utilized because neutron facilities are not normally located at industrial laboratories and university campuses. We introduce the techniques of neutron scattering for studying the organization of nanoscale structural units and their dynamic response to physical–chemical conditions. Examples are given to illustrate neutron characterization of nanostructured biomaterials and the implications for biotechnology.

The carbon nanotube (CNT) has been widely studied for its electrical, mechanical, and chemical properties since its discovery. However, to manipulate these nanosize tubes, atomic force microscopy (AFM) is typically used to manipulate them one-by-one. This is time-consuming and unrealistic for batch fabrication. In this paper, we will present the manipulation of carbon nanotubes using dielectrophoretic manipulation to rapidly build practical nanosensors. Thus far, we have demonstrated thermal sensors for temperature and fluid-flow measurements. We have also shown that this electrokinetic based manipulation technique is compatible with MEMS fabrication processes, and hence, MEMS structures embedded with carbon nanotube sensing elements can be built in the future with new functionalities.

Nanostructured diamond and diamond-like materials having good field electron emission properties have been prepared using a hot-filament assisted chemical vapour deposition system fed with ethanol/hydrogen/helium mixtures. The changes in the structure of the samples were determined by the hydrogen content in the gas mixture and varied from samples of nanocrystalline diamond with graphitic connection between the grains (for helium concentration <40 vol %) to samples of porous interconnected graphenes (for helium concentrations >40 vol %). Although the samples had such structural differences, low threshold values for electron field emission in vacuum were observed for representative samples of low and high hydrogen concentrations in the gas feed.

Proteins are naturally occurring nanosystems, optimized by the process of evolution. Biotechnology of protein based nanostructures offers vast opportunities to re-engineer and combine them with other nanomaterials for technological applications. Our primary interest is to interface proteins like bacteriorhodopsin (bR) with carbon nanotubes and silicon surfaces for application in storage devices and biosensors. We have carried out extensive computer simulations to study the dynamics of carbon nanotubes and their interaction with proteins. The immobilization of the protein on the carbon nanotubes is carried out by either covalent bonding or aromatic π stacking. Our simulation studies reveal the difference between the π stacking and covalent bonding.

We review our research on the application of scanning tunnelling microscopy (STM) and non-contact atomic force microscopy (NC-AFM) for magnetic imaging in high spatial resolution even down to the atomic scale. In the first part, we propose a new experimental scheme of spin-polarized STM (SP-STM) with a GaAs spin probe to obtain a large contribution of spin-polarized electrons in the tunnelling current. This is yielded by injecting the spin-polarized photo-excited electrons in an optically pumped GaAs tip into the spin-polarized empty states near the Fermi level of a bcc-Fe(001) surface. According to the bandgap energy of GaAs and the surface state of the sample observed at 0.4 eV above the Fermi level, the spin-dependant electron injection can be achieved by applying a sample bias voltage of −1 V. The tunnel current in the positive bias region depends on the helicity of the circular polarized pumping light, and is modified when the applied magnetic field is reversed. Mapping the current asymmetry provides a spin-dependent SP-STM image. In the second part, we describe the progress towards spin imaging with NC-AFM. The spin imaging can be achieved by detecting short-range magnetic interaction such as exchange interaction between a ferromagnetic tip and a magnetic sample. We demonstrate the capabilities of NC-AFM by imaging the spin structure of an antiferromagnetic NiO(001) surface on the atomic scale. The cross-sectional line profiles of the atomically resolved images obtained using several ferromagnetic tips (Fe, Ni) were analysed by adding the atomic corrugation amplitude on the basis of the periodicity of the image. The results of the analysis show that the difference of the neighbouring maxima depends on the crystal direction. On the other hand, no significant indication of the directional dependency can be seen on the images obtained by using a non-magnetic Si tip. The directional dependency coincides with the antiferromagnetic spin alignment of the NiO(001) surface.