Two well known, biologically inspired non-dynamical models of stochastic resonance, the threshold-crossing model and the fluctuating rate model are analyzed in terms of channel information capacity and dissipation of energy necessary for small-signal transduction. Using analogies to spike propagation in neurons we postulate the average output pulse rate as a measure of dissipation. The dissipation increases monotonically with the input noise. We find that for small dissipation both models give an asymptotically linear dependence of the channel information capacity on dissipation. In both models the channel information capacity, as a function of dissipation, has a maximum at input noise amplitude that is different from that in the standard signal-to-noise ration vs. input noise plot. Though a direct comparison is not straightforward, for small signals the threshold model gives appreciably higher density of information per dissipation than the exponential fluctuating rate model. We show that a formal introduction of cooperativity in the rate fluctuating model permits us to imitate the response function of the threshold model and to enhance performance. This finding may have direct relevance to real neural spike generation where, due to a strong positive feedback, the ion channel currents are adding up in a synchronized way.

The goal of this research is to improve the modular stability and programmability of DNA-based computers and in a second step towards optical programmable DNA computing. The main focus here is on hydrodynamic stability. Clockable microreactors can be connected in various ways to solve combinatorial optimisation problems, such as Maximum Clique or 3-SAT. This work demonstrates by construction how one micro-reactor design can be programmed to solve any instance of Maximum Clique up to its given maximum size (N). It reports on an implementation of the architecture proposed previously. This contrasts with conventional DNA computing where the individual sequence of biochemical operations depends on the specific problem. In this pilot study we are tackling a graph for the Maximum Clique problem with N<EQ12, with a special emphasis for Nequals6. Furthermore, the design of the DNA solution space will be presented, which is symbolized by a set of bit-strings (words).

Biomineralisation arises due to a partnership between the biological and inorganic components of a living system. The final structure and form of the inorganic material is in some way controlled by the nature of the specific organic entities present. This manifests itself in the initiation of the growth, by providing the appropriate matrix in which the inorganic material forms and/or by providing a defect base such that the inorganic crystal packing may be appropriately perturbed. Working with proteins is not necessarily the best or easiest way to understand a physical process and over past years people have turned to simple organic molecules, surfactants, small biological moieties and organic substrates in order to determine, at least in part, the import of organic/inorganic interactions during the growth of the inorganic material. As one example of these additives, surfactants, which represent approximately 50% of the cell membrane, display a diverse and vast array of geometrical forms in aqueous solution, many of which bare striking resemblance to biominerals, albeit on considerably smaller length scales. They also have the ability to associate in solution with inorganic material precursors, such as calcium ions. Hence, while they may not be the main driving force in the formation of biominerals, they are certainly present during the process and may, when used as model systems, allow us some way into the world of nanomaterials. Surfactants, a series of simple alcohols and carboxylic acids, and proteins extracted from the spines of adult sea urchins, have been used by our group to study the formation of calcium carbonate based inorganic materials. The growth of the calcium carbonate is significantly affected by the inclusions, with deviations varying from simple stepped growth to the formation of curved surfaces.

Ultrasonic waves exert acoustic pressure on microparticles in liquid. Consequently microparticles are trapped at the nodes of a standing wave that is excited between a pair of ultrasonic transducers. If two orthogonal standing waves are excited by using two pairs of transducers, microparticles are trapped at the intersecting points of the nodes. A larger trapping force is attainable by ultrasonic trapping than by laser trapping that utilizes a weak optical pressure. Therefore ultrasonic trapping is suitable for the manipulation of biological tissues which easily suffer thermal damage by the exposure to a focused laser beam. Microorganisms such as euglena and paramecia were trapped by the ultrasonic waves of approximately 3 MHz. Trapped microorganisms could be transferred to desired positions by changing the ultrasonic frequency. The aggregation of microorganisms was achievable by the cyclic frequency change. This ultrasonic trapping technique was also used to fabricate composite materials with lattice structure; i.e., polymer, glass, or metal particles were ultrasonically arranged in a polymer matrix during the solidification process of the host polymer.

This contribution presents the potential of an innovative approach for determination of molecular masses of high-mass biopolymers through the aerosol phase. Macromolecular ions were formed by means of a nano-electrospray ionisation. The multiply charged species were charge-reduced to yield neutral, or singly charged airborne particles. Subsequently the so obtained aerosols were size separated according to their electrophoretic mobility in air using a nano-differential mobility analyzer. The particles were then detected by means of a condensation particle counter. The mobility diameters of well-defined proteins were determined and linked with their molecular weights in the range from 3.5 - 2000 kDa showing a correlation coefficient of 0.999. This calibration relationship allowed then the determination of large biocomplexes with a mass accuracy of the order of 5% including supramolecular complexes such as viruses. We investigated the stability of various noncovalent protein complexes as a function of pH. The study on the human rhinoviruses demonstated the capability of the used experimental system to measure the size of the intact infectious virus (HRV2) and its partial thermal dissociation. This research can be viewed as a first documentation of observation of stability of non-covalent complexes and of a real-time virus characterization using nanoaerosol measuring technique.

For many applications, it is essential to be able to control the interface between devices and the biological environment by nanoscale control of the composition of the surface chemistry and the surface topography. Application of molecular thickness coatings of biologically active macromolecules provides predictable interfacial control over interactions with biological media. The covalent surface immobilization of polysaccharides, proteins, and synthetic oligopeptides can be achieved via ultrathin interfacial bonding layers deposited by gas plasma methods, and the multistep coating schemes are verified by XPS analyses. Interactions between biomolecular coatings and biological fluids are studied by MALDI mass spectrometry and ELISA assays. Using a colloid-modified AFM tip, quantitative measurement of interfacial forces is achieved. Comparison with theoretical predictions allows elucidation of the key interfacial forces that operate between surfaces and approaching macromolecules. In this way, it is possible to unravel the fundamental information required for the guided design and optimization of biologically active nanoscale coatings that confer predictable properties to synthetic carriers. We have established for instance the key properties that make specific polysaccharide coatings resistant to the adsorption of proteins, which is applicable to biomaterials, biosensors, and biochips research.

Two-dimensional control over the location of proteins on surfaces is desired for a number of applications including diagnostic tests and tissue engineered medical devices. Many of these applications require patterns of specific proteins that allow subsequent two-dimensionally controlled cell attachment. The ideal technique would allow the deposition of specific protein patterns in areas where cell attachment is required, with complete prevention of unspecific protein adsorption in areas where cells are not supposed to attach. In our study, collagen I was used as an example for an extracellular matrix protein known to support the attachment of bovine corneal epithelial cells. An allylamine plasma polymer was deposited on a silicon wafer substrate, followed by grafting of poly(ethylene oxide). Two-dimensional control over the surface chemistry was achieved using a 248 nm excimer laser. Results obtained by XPS and AFM show that the combination of extremely low-fouling surfaces with excimer laser ablation can be used effectively for the production of spatially controlled protein patterns with a resolution of less than 1 micrometers . Furthermore, it was shown that bovine corneal epithelial cell attachment followed exactly the created protein patterns. The presented method is an effective tool for a number of in vitro and in vivo applications.

Layered Surface Acoustic Wave (SAW)immunosensors based on a substrate crystal cut that allows the propagation of Surface Skimming Bulk Wave (SSBW)have been fabricated. SiO2 and ZnO films with different thicknesses deposited onto the substrate to form the SAW device. The layered SAW device developed is a gravimetric sensor.Upon exposures to solutions containing IgG, the operational frequency of the system incorporating the sensor changes. In this paper, the sensitivity of the SAW devices with different film thicknesses will be compared. Their response to the biochemical components will be investigated.

One area that can make use of the miniature size of present day micro electromechanical systems (MEMS) is that of the medical field of minimally invasive interventions. These procedures, used for both diagnosis and treatment, use catheters that are advanced through the blood vessels deep into the body, without the need for surgery. However, once inside the body, the doctor performing the procedure is completely reliant on the information the catheter(s) can provide in addition to the projection imaging of a fluoroscope. A good range of sensors for catheters is required for a proper diagnosis. To this end, miniature sensors are being developed to be fitted to catheters and guide wires. As the accurate positioning of these instruments is problematic, it is necessary to combine several sensors on the same guide wire or catheter to measure several parameters in the same location. This however, brings many special problems to the design of the sensors, such as small size, low power consumption, bio-compatibility of materials, robust design for patient safety, a limited number of connections, packaging, etc. This paper will go into both the advantages and design problems of micromachined sensors and actuators in catheters and guide wires. As an example, a multi parameter blood sensor, measuring flow velocity, pressure and oxygen saturation, will be discussed.

The purpose of this paper is to discuss the background to advanced surface modification technologies and to present a new technique, involving the formation of a titanium oxide ceramic coating, with relatively long-term results of its clinical utilization. Three general techniques are used to modify surfaces: the addition or removal of material and the change of material already present. Surface properties can also be changed without the addition or removal of material, through the laser or electron beam thermal treatment. The new technique outlined in this paper relates to the production of a corrosion-resistant 2000-2500 A thick, ceramic oxide layer with a coherent crystalline structure on the surface of titanium implants. The layer is grown electrochemically from the bulk of the metal and is modified by heat treatment. Such oxide ceramic-coated implants have a number of advantageous properties relative to implants covered with various other coatings: a higher external hardness, a greater force of adherence between the titanium and the oxide ceramic coating, a virtually perfect insulation between the organism and the metal (no possibility of metal allergy), etc. The coated implants were subjected to various physical, chemical, electronmicroscopic, etc. tests for a qualitative characterization. Finally, these implants (plates, screws for maxillofacial osteosynthesis and dental root implants) were applied in surgical practice for a period of 10 years. Tests and the experience acquired demonstrated the good properties of the titanium oxide ceramic-coated implants.

It can be concluded that surface treatment with high power Nd laser pulses induces unique morphology with sizes in ten micron and 50 nanometer ranges and being topologically isomorf with the plane. It is clear that the 1-10 micrometer elements do not change strongly the osseintegration compared to the flat surface. On the other hand this surface in 20-50 micrometer range already enhance the osseointegration indicating a strong size dependens. The effect of the nanosized elements can be suggested also because their density has been increased with laser intensity. These two effects can not be separated with available data. It is evident that several questions in connection with laser treatment of surfaces such as first of all the time course of bone formation await further studies. Namely, if microgeometry plays a role in bone formation then the process of osseointegration should be also studied in conjunction with the comparisons of the various surfaces. It is hoped that our future studies can give responses to more questions and the results will contribute to the implementation of novel clinically successful techniques to improve the reliability of dental implants.

The diversity of biological sensing and biocatalysis is astounding. A considerable effort has been directed at not only understanding the mechanism of these biological processes, but also how this activity can be maintained or duplicated in an artificial environment. We will present work on the formation of functional optical devices that convert biological responses into optical signals through changes in diffraction efficiency and reflection angle. By incorporating biomolecules into monomer systems that can be cured using a two-photon polymerization mechanism, greater spatial resolution and increased biological viability can be achieved. The polymer can be nanopatterned using ultrafast nonlinear holography to create a functional BioMEMS device. Additionally, we will discuss the characterization of the biomolecules and the processing of the gratings that incorporate these functional proteins. This approach is a first step towards the development of a hybrid organic-inorganic composite device.

Carbon nanotubes have fascinating physical properties. In order to use these novel one-dimensional structures for applications (such as in electronic devices, mechanical reinforcements and nano-electromechanical systems) the structure of nanotubes needs to be tailored and various architectures have to be configured using nanotube building blocks. This paper will focus on the directed and self-assembly of nanotubes on planar substrates into hierarchical structures that include oriented arrays, and ordered bundles. This is achieved by patterning substrates with or without metal catalysts. Growth of nanotubes is typically achieved by chemical vapor deposition (CVD). Various strategies to build two-dimensional and three-dimensional architectures of nanotubes will be described by this method. In addition to creating pristine nanotube arrays on planar substrates, the paper will also cover some of our recent efforts in fabricating nanotube polymer hybrids. Recent efforts and challenges in manipulating nanotube on surfaces and measuring transport properties will be discussed. In conclusion, a perspective will be given on our recent efforts in creating controlled structures with nanotubes and measuring some of their properties.

Carbon Nano Tubes (CNT) with their unique structure, have already proven to be valuable in their application as tips for scanning probe microscopy, field emission devices, nanoelectronics, H₂- storage, electromagnetic absorbers, ESD, EMI films and coatings and structural composites. For many of these applications, highly purified and functionalized CNT which are compatible with many host polymers are needed. A novel microwave CVD processing technique to meet these requirements has been developed at Penn State Center for the Engineering and Acoustic Materials and Devices (CEEAMD). This method enables the production of highly purified carbon nano tubes with variable size (from 5-40 nm) at lost cost (per gram) and high yield. Whereas, carbon nano tubes synthesized using the laser ablation or arc discharge evaporation method always include impurity due to catalyst or catalyst support. The Penn State research is based on the use of zeolites over other metal/metal oxides in the microwave field for a high production and uniformity of the product. An extended conventional purification method has been employed to purify our products in order to remove left over impurity. A novel composite structure can be tailored by functionalizing carbon nano tubes and chemically bonding them with the polymer matrix e.g. block or graft copolymer, or even cross-linked copolymer, to impart exceptional structural, electronic and surface properties. Bio- and Mechanical-MEMS devices derived from this hybrid composite are presented.

Polymeric light-emitting diodes (LEDs) with sufficient brightness, efficiencies, low driving voltages, and various interesting features have been reported. The relatively short device lifetime, however, still remains as a major problem to be solved before any commercial applications will be realized. In this regard, carbon nanotubes have recently been proposed as more robust electron field emitters for flat panel displays. We have synthesised large arrays of vertically aligned carbon nanotubes, from which micropatterns of the aligned nanotubes suitable for flat panel displays were fabricated on various substrates. In this paper, we summarise our work on the synthesis and microfabrication of electroluminescent polymers and carbon nanotubes for flat panel displays with reference to other complementary work as appropriate.

Mica substrates decorated with a periodic array of gold squares are used to guide the growth of two-dimensional colloidal crystals of charged polystyrene particles. For polystyrene spheres (500 nm in diameter) suspended water, with a dilute surfactant (5 mM sodium dodecylsulphate (SDS)) in the colloidal suspension, the self-assembly process leads to the formation of ordered colloidal monolayers nearly exclusively on gold, confined laterally by the boundaries of the prefabricated gold terraces. This method provides an efficient route to guided growth of novel colloidal monolayers, with potential applications in, e.g., bio-sensing and photonics.

Controlling carrier transport in light emitting polymers is a crucial factor for their efficient use in any organic opto-electronic device. In this work, we demonstrate a novel method of utilizing the interactions between single wall carbon nanotubes (SWNTs) and conjugated polymers to modify the overall mobility of charge carriers within nanotube- polymer nanocomposites. Using a unique, double emitting- organic light emitting diode (DE-OLED) structure, we characterize the hole transport within electroluminescent nanocomposites (nanotubs in poly (m-phenylene vinylene-co- 2,5-dioctoxy-p-phenylene) (PmPV)) and show that devices with chromic tunability can be achieved. This leads naturally to a model for hole transport in SWNT - PmPV blends that provides fundamental insights into the formation of discrete hole traps and the modification to hole mobility. Perhaps more importantly however, these results are suggestive of the significant role that SWNT nanocomposites can play in future organic-based photonic systems such as fully organic optical amplifiers, transistors, and color displays.

The electo-static self-assembly process (ESA) has proved to be extremely successful in creating multi-layer coatings with properties that can be tailored for particular applications. In this process, almost any surface with charged functional groups can be used as a substrate. Alternate dipping in solutions having ions of opposite charge builds up the layers through ionic bonding. One particular application of this process could be to form multi-functional bio-compatible coatings on MEMS devices intended for use in-vivo. In this paper, we describe two different models of the process based on cellular automata. The output of the models consists of three parameters as a function of layer: ionic coverage, film height and film roughness. The results of the models are compared to experimental data to determine which of them more accurately describes the ESA process.

We describe a novel technique for the fabrication of nanoscale structures, based on the development of localized chemical modification caused in a PMMA resist by the implantation of single ions. The implantation of 2 MeV He ions through a thin layer of PMMA into an underlying silicon substrate causes latent damage in the resist. On development of the resist we demonstrate the formation within the PMMA layer of clearly defined etched holes, of typical diameter 30 nm, observed using an atomic force microscope employing a carbon nanotube SPM probe in intermittent-contact mode. This technique has significant potential applications. Used purely to register the passage of an ion, it may be a useful verification of the impact sites in an ion-beam modification process operating at the single-ion level. Furthermore, making use of the hole in the PMMA layer to perform subsequent fabrication steps, it may be applied to the fabrication of self-aligned structures in which surface features are fabricated directly above regions of an underlying substrate that are locally doped by the implanted ion. Our primary interest in single-ion resists relates to the development of a solid-state quantum computer based on an array of ³¹P atoms (which act as qubits) embedded with nanoscale precision in a silicon matrix. One proposal for the fabrication of such an array is by phosphorous-ion implantation. A single-ion resist would permit an accurate verification of ³¹P implantation sites. Subsequent metalisation of the latent damage may allow the fabrication of self-aligned metal gates above buried phosphorous atoms.

Ablation rate of polymers in laser ablation-based microfabrication depends on both laser parameters and polymer characteristics. This study aims to establish a scaling relationship linking the ablation rate and the properties of polymers commonly used in microfluidics. Ablation rate of polymers was determined experimentally using 193nm, 248nm and 308nm radiations. Polymer descriptors included thermal and surface properties. Statistical analysis was carried out for laser fluence against various polymer descriptors and/or their combinations. Analysis results show a relatively high correlation coefficient of 0.82 for the polymer ablation data when we compare fluence against the product of ablation rate and the difference between glass transition temperature and room temperature.

An attempt to simulate the interaction between an AFM tip and a protein surface by employing the concept of Connolly molecular surface with a carbon probe has been investigated. A methodology has been developed to permit the computation of the Connolly surface for a protein, where numerous atoms are simultaneously interacting each other. The van der Waals and electrostatic interactions between the probe and the relevant Connolly surface elements are integrated to obtain the total interaction, resulting in a precise theoretical account for a variety of interaction components. The simulation offers a meaningful opportunity for AFM scientists to interpret AFM surface mapping results more precisely or on a more general level the polymer surface-protein surface interactions.

Liquid handling of volumes down to a few nanoliters is a key issue for modern bioanalytical and pharmaceutical research and industry. In this paper we present a modular dispensing device for the highly accurate delivery of liquids in the range of 10 nL - 500 nL at a precision of better than 5 % and a dosage rate up to 1000 nL/s. The reported dispensing technology is based on a fast mechanical displacement of liquid within a micromachined silicon chip (termed dosage chip). It overcomes limitations known from piezo-drop-on-demand dispensers or syringe-solenoid systems presently used in laboratory automation. The accurate and very robust multi channel system which is modularly built out of individual dispensers is able to handle a variety of different liquids simultaneously. A wide range of liquids with different physical properties can be handled with an up to now unequalled precision in that volume range. The working principle of the device as well as newest characterization results are presented.

In general, the Reynolds number is low in microfluidic channels. This means that the viscous force plays a dominant role. As a result, the flow is most likely to be laminar under normal conditions, especially for liquids. Therefore, diffusion, rather than turbulence affects the mixing. In this work, the commercial computational fluid dynamics tool for microfluidics, known as FlumeCAD, is used to study the mixing of two liquids in a Y channel and the results are presented. To improve mixing, obstacles have been placed in the channel to try to disrupt flow and reduce the lamella width. Ideally, properly designed geometric parameters, such as layout and number of obstacles, improve the mixing performance without sacrificing the pressure drop too much. In addition, various liquid properties, such as viscosity, diffusion constant, are also evaluated for their effect on mixing. The results indicate that layout of the obstacle has more effect on the mixing than the number of the obstacles. Placing obstacles or textures in the microchannels is a novel method for mixing in microfluidic devices, and the results can provide useful information in the design of these devices.

Conventional methods of producing micro-scale components for BioMEMS applications such as microfluidic devices are limited to relatively simple geometries and are inefficient for prototype production. Rapid prototyping techniques may be applied to overcome these limitations. Fused Deposition Modelling is one such rapid prototyping process, which can build parts using layer by layer deposition technique with layers as low as 0.178 mm thick and using a select group of thermoplastic building materials. This paper presents the potential of Fused Deposition Modelling (FDM) system, available at IRIS, in building prototypes of scaled microchannels for experimental study and verification of fluid flow in microfluidic devices. The scope and application of FDM system as a powerful and flexible rapid prototyping device is described. Microchannels of different geometries are produced in ABS material on the FDM3000 rapid prototyping system and a methodology is presented for experimental study of the mixing of fluids in microchannels in conjunction with the theoretical analysis using FlumeCAD system.

This paper presents the use of scanning tunnelling microscopy (STM) and digital image processing for accurate atomic-scale imaging of molecules. The project has involved the development of image enhancement techniques and a calibration procedure for STMs. Graphite imaging has been successfully used as a reliable method for instrument calibration. This calibration is required due to the undesirable effects that are characteristic of STMs, which result in improper scaling and skewing of images. Image enhancement techniques have been created to reduce the noise effects due to thermal drift and tip hysteresis. These techniques were developed for graphite images, but have also been successfully applied to imaging of molecular adsorbates. Low tunnelling currents are used in STM experiments since any experiment uses a tunneling mechanism. This implies low signal-to-noise ratios, resulting in the need for reliable noise removal techniques. These techniques are a necessary step towards the extended use of STM in imaging molecular adsorbates.

Conduction noise measurements were carried out in the 0.3 to 45 Hz frequency range on Au films covered by a thin layer of tungsten trioxide (WO₃) nanoparticles. Exposing the films to alcohol vapor resulted in a gradually increased noise intensity which went through a maximum after an exposure time of the order of 15 min. The maximum noise intensity could increase by several orders of magnitude above the initial level. Longer exposure times made the noise decrease and approach its original value. This effect was not observed in the absence of WO₃ nanoparticles. The phenomenon is discussed in terms of a new invasion noise model in which the noise is related to the insertion and extraction of mobile chemical species.

In this paper we present an evaporation-condensation route to produce single sized SnOx nanoparticles using a Differential Mobility Analyser (DMA). The nanostructure and size distribution of the particles were studied as a function of the evaporation and sintering temperature. Transmission Electron Microscope (TEM) micrographs were taken to study the morphology of the nanoparticles. X-ray diffraction (X-ray), Rutherford backscattering (RBS), Auger electron microscopy (AES) and electron diffraction measurements were used to study the structure and stoichiometry of the deposited material. After an annealing process at Tequals300 degree(s)C in synthetic air particle size dependent conductivity measurements of monosized 10nm, 20nm and 30nm particles, such as Sensitivity S and dynamic behavior of the thin films acting as a gas sensor, were done.

MoO₃-WO₃ thin films have been fabricated via the sol-gel method. FESEM, TEM, RBS and SIMS analysis techniques have been employed to analyse the films and material properties for use as gas sensors to detect CO and NO₂. FESEM shows the film made up of segregated molybdenum crystals. TEM highlights the nano-sized grains sructure and crystallinity. RBS analysis confirmed the films are stoichimetric and that the Mo component of the system decreases as the annealing temperature is increased. SIMS illustrates the interesting elemental depth profiles of the films. The films were exposed to CO and NO₂. MoO₃-WO₃ shows better NO₂ sensitivity and selectivity compared to its single metal oxide constituents.

Among various materials for microelectromechanical systems (MEMS) devices, piezoelectric thin films have attracted considerable attention since they are one of the essential materials in microfabricated devices such as microsensors and microactuators. In this study, we propose a new and simple cantilever type Pb(Zr,Ti)O₃ [PZT] microsensor using RuO₂ which could detect the resonance frequency varation. Since RuO₂ has good electrical conductivity and stiffness, it can replace the double layer of electrode and supporting layer to a single layer in a cantilever beam. Also, Si substrate was isotropically etched from the surface using SF₆ plasma. These unique technique simplifies the structure and process of a cantilever. The cantilever consists of Al, PZT and RuO₂ layers. To find relationships between resonance frequency and shape of cantilever, microsensors with various widths and lengths were fabricated and their resonance frequencies were measured by laser doppler vabrometer (LDV) system. In addition, detection sensitivity of microsensor was investigated. The resonance frequency decreased as the length of cantilever increased.

Iron nanoparticles, with both fcc and bcc structure and with a protective carbon shell against oxidation, were generated by laser-assisted photolytic chemical vapor decomposition of ferrocene (FeCp₂). Amorphous W and WN_0,3 nanoparticles were formed by laser ablation of solid W in Ar and in N2 ambient, respectively. Laser-assisted chemical vapor deposition of W yielded crystalline tungsten nanoparticles (b phase) from WF₆H₂/Ar gas mixture. ArF excimer laser was used as radiation source for all the experiments. Measurements and analysis of the emitted blackbody-like radiation from the laser heated particles were performed, dominant cooling processes as evaporation and heat transfer by the ambient gases were identified. The particles could be heated up to the boiling and melting point of iron and tungsten, respectively. Lognormal particle size-distributions were found for Fe/C and W nanoparticles generated by vapor decomposition or deposition processes respectively, furthermore modeled at low particle concentration (with no coagulation) limit. The thickness of the carbon shell was practically independent on the laser fluence, while the size of the iron core could be varied with it for the Fe/C particles. The laser ablation yielded no lognormal type of distribution for the amorphous WN_0,3 particles.

Ratchets are systems that combine asymmetry with non-equilibrium processes to generate directed particle flow. A brief general introduction to ratchets is given, and the relevance of the ratchet model for biological motor proteins is highlighted. While biological motor proteins operate classically, ratchet systems that employ quantum effects are of interest from a fundamental point of view. A recent experimental realization of a tunnelling ratchet for electrons is reviewed. Such electron tunnelling ratchets can not only be used to generate particle currents, but also to pump heat. Using a realistic model, the heat pumping properties of the experimental electron ratchet are analysed.

Microarray-like chips are based on effective immobilisation of surface biomolecules and preservation of their bioactivities. We have applied the concept of Connolly molecular surface for modelling and computation of the pure surface properties of proteins, which are of fundamental importance to surface-based protein science and engineering, especially for protein microarray chips. This is achieved by de-convoluting various molecular interaction components into single surface elements, and integrating a specific property of the atoms mostly close to the surface element to obtain the pure surface property of a protein. A methodology for obtaining electron charge, hydrophobicity as well as a-helix and b-pleated sheet structural indices has been developed. A parallel study shows that this technique is useful for modelling and computation of protein-protein and protein-polymer interactions, including protein attachment in molecularly confined spaces.

Thin films were made by spinning a dispersion of tin-doped indium-oxide particles, having an average diameter of 14 nm, onto glass substrates. As-deposited thin films displayed a resistivity (rho) of 0.3 (Omega) m and some optical absorption. Annealing in vacuum at 200 to 400 degree(s)C for 2 h, and subsequently in air at 500 degree(s)C for 2 h, produced films with (rho) equals10^--3 (Omega) m and a visible transmittance exceeding 90 %. Leaving out the vacuum treatment yielded higher resistivity.

This paper details our experimental progress towards the synthesis of self-assembled nanostructures that may exhibit collective computational activity. Self assembled two dimensional networks of heterostructured quantum dots, linked by resistive and capacitive connections, can function as Boolean logic circuits, associative memory, image processors, and combinatorial optimizers. Computational or signal processing activity is elicited from simple charge interactions between the dots which act as non-linear resistors. Such circuits could be massively parallel, fault-tolerant, ultrafast, ultradense and dissipate very little power.

Quantum computers offer the promise of formidable computational power for certain tasks. Of the various possible physical implementations of such a device, silicon based architectures are attractive for their scalability and ease of integration with existing silicon technology. These designs use either the electron or nuclear spin state of single donor atoms to store quantum information. Here we describe a strategy to fabricate an array of single phosphorus atoms in silicon for the construction of such a silicon based quantum computer. We demonstrate the controlled placement of single phosphorus bearing molecules on a silicon surface. This has been achieved by patterning a hydrogen mono-layer resist with a scanning tunneling microscope (STM) tip and exposing the patterned surface to phosphine (PH₃) molecules. We also describe preliminary studies into a process to incorporate these surface phosphorus atoms into the silicon crystal at the array sites.

We describe progress in a range of nanofabrication processes for the production of silicon-based quantum computer devices. The processes are based upon single-ion implantation to place phosphorus-31 atoms in accurate locations, precisely self-aligned to metal control gates. These fabrication schemes involve multi-layer resist and metal structures, electron beam lithography and multi-angled aluminium shadow evaporation. The key feature of all fabrication schemes is a gate pattern defined in a resist structure using electron beam lithography, used in conjunction with a second pattern written in another resist layer. The locations where the two patterns overlap define channels down to the substrate through which ions can be implanted, with the remaining metal/resist structure behaving as a mask. Further processing on the resist structures allows for deposition of the control gates and read-out structures. Central to this process is a new technique which allows for control of the implantation process at a single-ion level.

So far proposed quantum computers use fragile and environmentally sensitive natural quantum systems. Here we explore the notion that synthetic quantum systems suitable for quantum computation may be fabricated from smart nanostructures using topological excitations of a neural-type network that can mimic natural quantum systems. These developments are a technological application of process physics which is a semantic information theory of reality in which space and quantum phenomena are emergent.

This paper describes a novel laser-based method for preparing microchannels in a bilayer system consisting of a UV sensitive polymer, acetophenone O-acryloyloxime (AAPO), layered with bovine serum albumin (BSA); BSA acts as a common blocking agent to prevent biomolecular attachment to the unexposed regions. The focus of the paper is on the use of a computer-controlled laser ablation system comprising a research-grade inverted optical microscope, a pulsed nitrogen laser emitting at 337 nm and a programmable X-Y-Z stage. By using a 100x oil immersion objective, channels of 1micrometers width and ca. 1 mm depth can be etched into the BSA-coated polymer. The precise width of the channel can be controlled by simply adjusting both the laser power and focusing. The addition of myosin to the base of these channels provides tracks on which actin filaments can move. By adjusting the width of the tracks, it is possible to regulate the direction of motion of the actin filaments.

Heavy meromyosin (HMM), a proteolytically cleaved derivative of myosin has previously been shown to interact with actin in well-established in vitro motility assays on nitrocellulose surfaces. In this study, the assays were conducted to demonstrate that the motility of actin filaments is confined in the micron-sized channels fabricated via laser ablation in a layer of the photosensitive resist polymer (O-acryloyloxime acetophenone oxime, AAPO). A solution containing myosin labelled with fluorophore 5-iodoacetamidofluorescein (5-IAF) was applied to the microfabricated AAPO surface and shown to bind specifically to the micron-size channels. In the motility assay, HMM, rhodamine-phalloidin labelled actin and ATP were sequentially added and the movement of the actin filaments was observed by fluorescence microscopy and recorded with a CCD camera. The experiments prove that although the actin filaments show an only-partial propensity for attachment in myosin-rich areas, their motility is confined to a large extent in micro- channels.

Single-spin detection will be crucial for solid-state quantum computer architectures in which information is encoded in the spin-state of single nuclear or electron spins. The formidable problem of single-spin detection in a solid can be mapped to a more tractable problem of single-charge detection through spin-dependent electron transfer which may be observed using ultra-sensitive solid-state nanostructure electrometers. Here we describe a readout architecture using single electron transistors (SETs) that can detect the charge-state of two coupled metal dots, which simulates charge transfer in a two-quantum bit (qubit) spin system. This twin-SET architecture allows significant reduction of random charge noise by correlating two detector outputs, reducing the probability of readout errors in the quantum computer.