A liftoff technique for molecular nanopatterning

For quantum-dot cellular automata molecular electronic devices, one of the fundamental tasks is to arrange the molecules on a surface in a controlled manner. In this report, we discuss a molecular lift off technique to form nanopatterns toward the development of molecular circuits. In our molecular lift off technique, we use electron beam lithography to form nano-trenches on a polymethylmethacrylate (PMMA) film on a SiO2 wafer. This wafer is soaked in a Creutz-Taube ion [(NH3)5Ru(pyrazine)Ru(NH3)5](o-toluenesulfonate)5 (CT5) aqueous solution. After residual PMMA removal, atomic force microscopy is used to investigate the resulting surface. Thirty-five nanometer CT5 lines are demonstrated on a SiO2 surface. Compared with other molecular nanopatterning techniques, ours is both economical and capable of high-resolution.     

Parallel optical trap assisted nanopatterning on rough surfaces

There exist many optical lithography techniques for generating nanostructures on hard, flat surfaces over large areas. However, few techniques are able to create such patterns on soft materials or surfaces with pre-existing structure. To address this need, we demonstrate the use of parallel optical trap assisted nanopatterning (OTAN) to provide an efficient and robust direct-write method of producing nanoscale features without the need for focal plane adjustment. Parallel patterning on model surfaces of polyimide with vertical steps greater than 1.5?μm shows a feature size uncertainty better than 4% across the step and lateral positional accuracy of 25?nm. A Brownian motion model is used to describe the positional accuracy enabling one to predict how variation in system parameters will affect the nanopatterning results. These combined results suggest that OTAN is a viable technique for massively parallel direct-write nanolithography on non-traditional surfaces.     

Controlled oxidative nanopatterning of microrough titanium surfaces for improving osteogenic activity

To further enhance the biological properties of acid-etched microrough titanium surfaces, titania nanotextured thin films were produced by simple chemical oxidation, without significantly altering the existing topographical and roughness features. The nanotextured layers on titanium surfaces can be controllably varied by tuning the oxidation duration time. The oxidation treatment significantly reduced water contact angles and increased the surface energy compared to the surfaces prior to oxidation. The murine bone marrow stromal cells (BMSCs) were used to evaluate the bioactivity. In comparison, oxidative nanopatterning of microrough titanium surfaces led to improved attachment and proliferation of BMSCs. The rate of osteoblastic differentiation was also represented by the increased levels of alkaline phosphatase activity and mineral deposition. These data indicated that oxidative nanopatterning enhanced the biological properties of the microrough titanium surfaces by modulating their surface chemistry and nanotopography. Based on the proven mechanical interlocking ability of microtopographies, enhancement of multiple osteoblast functions attained by this oxidative nanopatterning is expected to lead to better implant osseointegration in vivo.     

Dual band planar soft surfaces

The design of dual band planar soft surfaces is presented here. Based on previous works, the parameters of a particular planar realisation of soft surfaces are used to create two frequency bands in which surface waves are suppressed. The planar soft surface is made with strips printed over a grounded dielectric slab with grounded vias. The parameters of the soft surface such as the strip width, the period of the vias and the position of such vias across the strip determine the frequency band at which the structure has a bandgap. It is demonstrated that by interleaving two planar soft surfaces with some different parameters over each other, the stopband of each one of them is maintained, and consequently, a dual band operation is obtained. Any of the mentioned parameters can be employed to this aim as shown in this work. The conclusions are supported by experimental results. The agreement between the measurements and the simulation results is good enough to demonstrate the dual band effect.     

Nonlinear plasmonics at planar metal surfaces

We investigate the nonlinear optical response of a noble metal surface. We derive the components of the third-order nonlinear susceptibility and determine an absolute value of χ((3))≈0.2 nm(2) V(-2), a value that is more than two orders of magnitude larger than the values found for typical nonlinear laser crystals. Using nonlinear four-wave mixing (4WM) with incident laser pulses of frequencies ω(1) and ω(2), we generate fields oscillating at the nonlinear frequency ω(4WM)=2ω(1)-ω(2). We identify and discuss three distinct regimes: (i) a regime where the 4WM field is propagating, (ii) a regime where it is evanescent, and (iii) a regime where the nonlinear response couples to surface plasmon polaritons.     

Biotemplated synthesis of novel porous SiC

Amorphous silicon carbide with unique porous structures was synthesised from three biological templates (egg shell membrane, butterfly wing and sea urchin skeleton) using liquid phase infiltration with polycarbosilane at atmospheric pressure followed by heating to 1000 °C under N₂. The structure and porosity of the preform was largely reproduced in the final material, although with egg shell membrane the cellular structure of the preform was compromised after infiltration and heating. The SiC yield of the final material was linearly correlated with the number of infiltration steps in the case of egg shell membrane and butterfly wing. Infiltration of the sea urchin shell was unsuccessful.     

Optimization of machining process plan for planar surfaces

In manufacturing parts, multiple processes are frequently used in sequence to produce the designed feature. The sequence of processes can easily be identified from previous experience. But no work has been done to determine whether any of the processes in the sequence are really necessary. A mixed integer mathematical programming model has been set up to determine the optimal set of processes and the amount of material to be removed by each process to minimize either the total process time or the total production cost.     

Engineering controllable bidirectional molecular motors based on myosin

Cytoskeletal motors drive the transport of organelles and molecular cargoes within cells and have potential applications in molecular detection and diagnostic devices. Engineering molecular motors with controllable properties will allow selective perturbation of mechanical processes in living cells and provide optimized device components for tasks such as molecular sorting and directed assembly. Biological motors have previously been modified by introducing activation/deactivation switches that respond to metal ions and other signals. Here, we show that myosin motors can be engineered to reversibly change their direction of motion in response to a calcium signal. Building on previous protein engineering studies and guided by a structural model for the redirected power stroke of myosin VI, we have constructed bidirectional myosins through the rigid recombination of structural modules. The performance of the motors was confirmed using gliding filament assays and single fluorophore tracking. Our strategy, in which external signals trigger changes in the geometry and mechanics of myosin lever arms, should make it possible to achieve spatiotemporal control over a range of motor properties including processivity, stride size and branchpoint turning.     

Active beating modes of two clamped filaments driven by molecular motors

Biological cilia pump the surrounding fluid by asymmetric beating that is driven by dynein motors between sliding microtubule doublets. The complexity of biological cilia raises the question about minimal systems that can re-create similar patterns of motion. One such system consists of a pair of microtubules that are clamped at the proximal end. They interact through dynein motors that cover one of the filaments and pull against the other one. Here, we study theoretically the static shapes and the active dynamics of such a system. Using the theory of elastica, we analyse the shapes of two filaments of different lengths with clamped ends. Starting from equal lengths, we observe a transition similar to Euler buckling leading to a planar shape. When further increasing the length ratio, the system assumes a non-planar shape with spontaneously broken chiral symmetry after a secondary bifurcation and then transitions to planar again. The predicted curves agree with experimentally observed shapes of microtubule pairs. The dynamical system can have a stable fixed point, with either bent or straight filaments, or limit cycle oscillations. The latter match many properties of ciliary motility, demonstrating that a two-filament system can serve as a minimal actively beating model.     

钼酸铁空心微球的生物模板法制备及其催化性能研究

以酵母细胞为模板,通过生物模板法制得钼酸铁空心微球材料,采用XRD、SEM、FTIR以及氮气吸脱附等手段,对样品的物相、微观形貌及比表面积等进行表征;并以亚甲基蓝模拟染料废水为研究对象,评价了样品的高级氧化催化性能。结果表明:生物模板法得到的钼酸铁空心微球为单斜晶系Fe_2(MoO_4)_3,样品分散度良好,形貌一致,较好地保持了酵母细胞椭圆形的形貌,平均尺寸约为5.6μm×3.7μm,比表面积为14.9m~2/g;钼酸铁空心微球作为类Fenton催化剂应用于亚甲基蓝模拟染料废水处理,表现出优异的高级氧化催化活性,当催化剂用量为1g/L、H_2O_2浓度为300mmol/L、反应温度25℃、pH=5时,反应60min后对100mg/L模拟染料废水中亚甲基蓝的去除率可达98%以上。     

Size effects in percolation of small regions on planar and cylindrical surfaces

The size effect (behavior of the percolation probability as a function of the size of a region under consideration) in some two-dimensional problems of percolation theory for planar and cylindrical surfaces is studied.     

Thermal stability of self-assembled octadecyltrichlorosilane monolayers on planar and curved silica surfaces

Understanding the structural and functional integrity of self-assembled monolayers (SAMs) of alkytrichlorosilane on Si/SiO₂ interface with change in temperature is critical for realizing their utility as antistiction coatings during the fabrication and functioning of microelectromechanical systems. Here we describe the thermal stability of two dimensional (2D) octadecyltrichlorosilane (OTS) monolayers on both n-type Si substrate (planar surface) and silica spheres (curved surface) using results of various surface sensitive spectroscopic techniques like the grazing angle Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Densely packed OTS monolayer on n-type Si surface is found to be thermally stable up to 525 K, while a significant enhancement in the thermal stability is interestingly observed for the case of OTS SAM (up to 625 K) on freshly prepared spherical silica surfaces. Despite this difference in the thermal stability, the results of temperature dependent infrared spectra demonstrate monolayer decomposition in both cases through the involvement of both Si-C and C-C bonds leaving Si-O-Si bond intact.     

Nanoscale patterning of colloidal quantum dots on transparent and metallic planar surfaces

The patterning of colloidal quantum dots with nanometer resolution is essential for their application in photonics and plasmonics. Several patterning approaches, such as the use of polymer composites, molecular lock-and-key methods, inkjet printing and microcontact printing of quantum dots have been recently developed. Herein, we present a simple method of patterning colloidal quantum dots for photonic nanostructures such as straight lines, rings and dot patterns either on transparent or metallic substrates. Sub-10?nm width of the patterned line could be achieved with a well-defined sidewall profile. Using this method, we demonstrate a surface plasmon launcher from a quantum dot cluster in the visible spectrum.     

How cross-disciplinary is bionanotechnology? Explorations in the specialty of molecular motors

Nanotechnology has been presented in the policy discourse as an intrinsically interdisciplinary field, requiring collaborations among researchers with different backgrounds, and specific funding schemes supporting knowledge-integration activities. Early bibliometric studies supported this interdisciplinary vision (Meyer & Persson, 1998), but recent results suggest that nanotechnology is (yet) a mixed bag with various mono-disciplinary subfields (Schummer, 2004). We have reexamined the issue at the research project level, carrying out five case studies in molecular motors, a specialty of bionanotechnology. Relying both in data from interviews and bibliometric indicators, we have developed a multidimensional analysis (Sanz-Menéndez et al., 2001) in order to explore the extent and types of cross-disciplinary practices in each project. We have found that there is a consistent high degree of cross-disciplinarity in the cognitive practices of research (i.e., use of references and instrumentalities) but a more erratic and narrower degree in the social dimensions (i.e., affiliation and researchers’ background). This suggests that cross-disciplinarity is an eminently epistemic characteristic and that bibliometric indicators based on citations and references capture more accurately the generation of cross-disciplinary knowledge than approaches tracking co-authors’ disciplinary affiliations. In the light of these findings we raise the question whether policies focusing on formal collaborations between laboratories are the most appropriate to facilitate cross-disciplinary knowledge acquisition and generation.     

Biotemplated synthesis of metallic nanoparticle chains on an alpha-synuclein fiber scaffold

Biomolecular templates provide an excellent potential tool for bottom-up device fabrication. Self-assembling alpha-synuclein protein fibrils, the formation of which has been linked to Parkinson's disease, have yet to be explored for potential device fabrication. In this paper, alpha-synuclein fibrils were used as a template for palladium (Pd), gold (Au) and copper (Cu) nanoparticle chains synthesis. Deposition over a range of conditions resulted in metal-coated fibers with reproducible average diameters between 50 and 200 nm. Active elemental palladium deposited on the protein fibrils is used as a catalyst for the electroless deposition of Au and Cu. Nanoparticle chains were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray energy dispersive spectrometry (XEDS), and electron energy loss spectrometry (EELS).     

STM manipulation of molecular moulds on metal surfaces

Molecular Landers are a class of compounds containing an aromatic board as well as bulky side groups which upon adsorption of the molecule on a surface may lift the molecular board away from the substrate. Different molecular Landers have extensively been studied as model systems for nanomachines and the formation of molecular wires, as well as for their function as “molecular moulds”, i.e., acting as templates by accommodating metal atoms underneath their aromatic board. Here, we investigate the adsorption of a novel Lander molecule 1,4-bis(4-(2,4-diaminotriazine)phenyl)-2,3,5,6-tetrakis(4-tert-butylphenyl)benzene (DAT, C₆₄H₆₈N₁₀) on Cu(110) and Au(111) surfaces under ultrahigh vacuum (UHV) conditions. By means of scanning tunneling microscopy (STM) imaging and manipulation, we characterize the morphology and binding geometries of DAT molecules at terraces and step edges. On the Cu(110) surface, various contact configurations of individual DAT Landers were formed at the step edges in a controlled manner, steered by STM manipulation, including lateral translation, rotation, and pushing molecules to an upper terrace. The diffusion barrier of single DAT molecules on Au(111) is considerably smaller than on Cu(110). The DAT Lander is specially designed with diamino-triazine side groups making it suitable for future studies of molecular self-assembly by hydrogen-bonding interactions. The results presented here are an important guide to the choice of substrate for future studies using this compound. This article is published with open access at Springerlink.com These authors contributed equally to this work     

Mathematical theory of molecular motors and a new approach for uncovering motor mechanism

Molecular motors operate in an environment dominated by thermal fluctuations. A molecular motor may produce an active force at the reaction site to directly move the motor forward. Alternatively a molecular motor may generate a unidirectional motion by rectifying thermal fluctuations. In this case, the chemical reaction establishes free energy barriers to block the backward fluctuations. The effect of the chemical reaction on the motor motion can be represented by the motor potential profile (rectifying barrier andor active driving force). Different motor mechanisms are characterised by different motor potential profiles. The mathematical theory and properties of molecular motors are discussed and a mathematical framework is developed for extracting the motor potential profile from measured time series of motor position. As an example, we discuss the binding zipper model for the F(1) ATPase, which was motivated mainly by the fact that the motor potential profile of the F(1) ATPase is nearly a constant slope.