Self-organized nanotube serpentines

Carbon nanotubes have unique mechanical, electronic, optical and thermal properties, which make them attractive building blocks in the field of nanotechnology. However, their organization into well-defined straight or curved geometries and arrays on surfaces remains a critical challenge for their integration into functional nanosystems. Here we show that combined surface- and flow-directed growth enable the controlled formation of uniquely complex and coherent geometries of single-walled carbon nanotubes, including highly oriented and periodic serpentines and coils. We propose a mechanism of non-equilibrium self-organization, in which competing dissipative forces of adhesion and aerodynamic drag induce oscillations in the nanotubes as they adsorb on the surface. Our results demonstrate the use of 'order through fluctuations' to shape nanostructures into complex geometries. The nanotube serpentines and loops are shown to be electrically conducting and could therefore find a wide range of potential applications, such as receiving and transmitting antennas, heating and cooling elements, optoelectronic devices and single-molecule dynamos.     

Self-organized patterns of microparticles in polymer films

A simple method to create self-organized patterns of microparticles in polymer films is demonstrated. Dye-loaded zeolite crystals are used as model microparticles, allowing convenient imaging of the patterns by fluorescence microscopy. The pattern formation can be interpreted within the general framework of the model of local self-activation and lateral inhibition. Two starting parameters, namely the polymer concentration and the wet film thickness, control the size and shape of the particle aggregates in the patterns, as well as their spacing. The size of the aggregates ranges from 50 to 340 μm.     

Self-organized, free-standing TiO2 nanotube membrane for flow-through photocatalytic applications

In the present work we show a simple and robust fabrication process of a dense and free-standing membrane consisting of vertically oriented, both-side-open TiO2 nanotubes. This membrane structure allows direct, size-selective, flow-through photocatalytic reactions with a very high efficiency.     

Self-organized dendritic patterns in the polymer Langmuir-Blodgett film

We report the formation of a self-organized dendritic pattern of nanometer thickness in polymer Langmuir-Blodgett (LB) films. Poly(N-dodecylacrylamide) (pDDA)/chloroform solution was spread on a water surface to form a stable polymer monolayer. A pDDA monolayer was deposited onto a hydrophilic silicon substrate by upward deposition from a water subphase, and a second layer was then deposited by downward deposition. The substrate with the two layers was withdrawn from a clean water surface at a high speed to form the dendritic pattern, which was imaged by atomic force microscopy. The height of the pattern, 3.5 nm, corresponds to the height of a bilayer pDDA LB film, suggesting that the pattern forms when the deposited outermost layer overturns by meniscus oscillation. A similar dendritic structure of narrower width and lower height was fabricated on a hydrophobic silicon substrate.     

Epitaxial growth of antimony electrodeposits on oriented single crystal surfaces of gold and silver

The epitaxial growth of antimony electrodeposits, obtained at 25 and 50° C from a chloride bath on single crystal cathodes of gold and silver, oriented along the (1 0 0), (1 1 0) and (1 1 1) crystallographic planes, has been studied by electron diffraction. Current densities ranging from 10 to 1000 Am^–2 and thicknesses between 1 and 50 m have been investigated. The gold substrate was found to be the more favourable to the formation of oriented crystalline deposits. A tendency to form amorphous antimony was observed on the silver substrate, especially at 25° C. The monocrystalline deposits on (1 0 0) and (1 1 1) planes of gold and silver were oriented with their (1 0 0) plane parallel to the substrate, and the deposits on the (1 1 0) plane of gold and silver with their (1 1 0) and (¯1 1 0) planes parallel to the substrate. The orientation relationships between parallel directions of the deposit and substrate have been determined. The results are discussed in terms of the work of formation of variously oriented nuclei on amorphous substrates, the symmetry elements in the deposit-substrate interface region and the mismatch along the more densely packed parallel directions.     

Wettability changes of TiO2 nanotube surfaces

This study examines the effect of environmental and experimental conditions, such as temperature and time, on the wettability properties of titania nanotube (TNT) surfaces fabricated by anodization. The fabricated TNTs are 60-130 nm inner diameter and 7-10 μm height. One-microliter water droplets were used to define the wettability of the TNT surfaces by measuring the contact angles. A digital image analysis algorithm was developed to obtain contact angles, contact radii and center heights of the droplets on the TNT surfaces. Bare titanium foil is inherently less hydrophilic with approximately 60°-80° contact angle. The as-anodized TNT surfaces are more hydrophilic and annealing further increases this hydrophilic property. Furthermore, it was found that the TNT surface became more hydrophobic when aged in air over a period of three months. It is believed that the surface wettability can be changed due to alkane contamination and organic contaminants in an ambient atmosphere. This work can provide guidelines to better specify the environmental conditions that changes surface properties of TNT surfaces and therefore affect their desirable function in specific applications such as orthopedic implants.     

Carbon nanotube micropillars trigger guided growth of complex human neural stem cells networks

Nano Research - New strategies for spatially controlled growth of human neurons may provide viable solutions to treat and recover peripheral or spinal cord injuries. While topography cues are known...     

锌微晶辅助碳纳米管图案化

利用锌微晶沸点较低易于蒸发以及形态丰富多变的特点,在微米尺度的锌晶粒介入下采用两种方式实现碳纳米管的组装.方法一:先蒸发得到一定尺度的锌微晶,然后以其为牺牲模板基于化学气相沉积生长技术实现碳纳米管的原位组装;方法二:与方法一的工艺过程相反,先在SiO2基片上气相沉积获得定向碳纳米管膜,然后以其为基板蒸发沉积锌微米晶对生长后的碳纳米管膜进行形貌调控和组装.结果表明,尽管两种组装方式的过程和原理不同,但都可获得碳纳米管的组装图案,且过程简单可控.这一技术可为碳纳米管的组装提供新途径.     

Mo-Co catalyst nanoparticles: Comparative study between TiN and Si surfaces for single-walled carbon nanotube growth

Highly pure single-walled carbon nanotubes (SWNT) were synthesized by alcohol catalytic chemical vapor deposition on silicon substrates partially covered by a thin layer of TiN. The TiN coating selectively prevented the growth of carbon nanotubes. Field emission scanning electron microscopy and Raman spectroscopy revealed the formation of high purity vertically aligned SWNT in the Si region. X-ray Photoelectron Spectroscopy and Atomic Force Microscopy indicated that Co nanoparticles are present on the Si regions, and not on the TiN regions. This clearly explains the obtained experimental results: the SWNT only grow where the Co is presented as nanoparticles, i.e. on the Si regions.     

"Drawing with nanotubes": creating nanowires with complex geometries by pulsed electrodeposition on self-organized carbon nanotube patterns

We present a new approach for the creation of nanowires with well-defined complex geometries by electrodeposition onto self-organized single-walled carbon nanotubes. The concept is demonstrated by generation of continuous Au nanowires with various geometries, including parallel arrays, serpentines, and coils. The generality of this approach is further illustrated by synthesizing Bi(2)Te(3) nanowires. Our concept of "drawing with nanotubes" offers to combine different material properties with complex geometries on the route to new functional nanosystems.     

Adhesion and growth of electrically active cortical neurons on polyethylenimine patterns microprinted onto PEO-PPO-PEO triblockcopolymer-coated hydrophobic surfaces

This paper describes the adhesion and growth of dissociated cortical neurons on chemically patterned surfaces over a time period of 30 days. The presence of neurons was demonstrated by measurement of spontaneous bioelectrical activity on a micropatterned multielectrode array. Chemical patterns were prepared with a combination of neurophobic layers of polyethylenoxide-polypropylenoxide-polyethylenoxide (PEO-PPO-PEO) triblockcopolymers adsorbed onto hydrophobic surfaces and neurophilic microprinted tracks of polyethylenimine (PEI). Results showed that commercially available PEO-PPO-PEO triblockcopolymers F108 and F127 (Synperonics, ICI) significantly reduced the adhesion of neuronal tissue when adsorbed on hydrophobic Polyimide (PI) and Fluorocarbon (FC) surfaces over a time period of eight days. In general, both F108- and F127-coated PI displayed equal or better neurophobic background properties after 30 days. Viability of neuronal tissue after 30 days on PEI microprinted F108- and F127-coated PI was comparable with relatively high viability factors between 0.9 and 1 (scale from 0 to 1). Summarizing, the strategy to combine the neurophobic adsorbed triblock-copolymers F108 and F127 onto hydrophobic surfaces with neurophilic microprinted PEI resulted in relatively long-term neuronal pattern preservation with high numbers of viable neurons present after 30 days.     

Silicide-induced multi-wall carbon nanotube growth on silicon nanowires

A novel multi-walled carbon nanotube (MWNT) growth process is reported based on carbon incorporation in a nickel catalyst layer deposited via plasma-enhanced atomic layer deposition (PEALD) on silicon nanowires and silicon wafer substrates. As-deposited PEALD Ni films containing relatively high amounts of carbon (>18?at.%) were observed to promote the growth of MWNTs upon post-deposition rapid thermal annealing. For these films the carbon originated from the ALD precursor ligand and MWNT growth occurred in the absence of a vapor-phase carbon feedstock. MWNT growth relied on the formation of nickel silicide at the PEALD Ni/Si interface which increased the local carbon concentration in the Ni film sufficiently to promote carbon saturation/precipitation at Ni catalyst grains and nucleate MWNT growth. Similar MWNT growth from annealed PEALD Ni films was not observed on SiO(2)-coated Si wafer substrates, consistent with the role of silicidation in the observed Ni-catalyzed MWNT growth on Si. This MWNT growth mode requires neither the catalytic decomposition of a gaseous hydrocarbon source nor the high-temperature pyrolysis of metallocene materials and purposely avoids a catalyst diffusion barrier at the Si substrate, commonly used in MWNT growth processes on Si.