Preparation of highly conductive, self-assembled gold/polyaniline nanocables and polyaniline nanotubes

One-dimensional gold/polyaniline (Au/PANI-CSA) coaxial nanocables with an average diameter of 50-60 nm and lengths of more than 1 mum were successfully synthesized by reacting aniline monomer with chlorauric acid (HAuCl(4)) through a self-assembly process in the presence of D-camphor-10-sulfonic acid (CSA), which acts as both a dopant and surfactant. It was found that the formation probability and the size of the Au/PANI-CSA nanocables depends on the molar ratio of aniline to HAuCl(4) and the concentration of CSA, respectively. A synergistic growth mechanism was proposed to interpret the formation of the Au/PANI-CSA nanocables. The directly measured conductivity of a single gold/polyaniline nanocable was found to be high (approximately 77.2 S cm(-1)). Hollow PANI-CSA nanotubes, with an average diameter of 50-60 nm, were also obtained successfully by dissolving the Au nanowire core of the Au/PANI-CSA nanocables.     

Electrodeposition of Ni and Te‐doped Cobalt Triantimonide in Citrate Solutions

Skutterudite compounds form a new class of potential candidates for thermoelectric applications. Cobalt triantimonide (CoSb₃) shows good thermoelectric properties at medium and high temperatures. Doping this system with substitution elements, for either Co or Sb or both, may result in an increase of the thermoelectric figure of merit (ZT). This work focused on the electrochemical doping and characterization of films and nanowires of Co‐Sb system in citrate solutions using gold‐coated PCTE templates. The electrodeposition was performed on gold surface that was pre‐treated electrochemically to ensure reproducible results. The electrochemical treatment acted as an annealing process for the surface, which resulted in an increase in Au(111) as demonstrated by XRD. Detailed electrochemical studies including deposition‐stripping experiments was performed in order to develop a better understanding of the co‐deposition kinetics and a better control over the composition of doped Co‐Sb system. Scanning electron microscopy (SEM/EDS) helped study the morphology and the composition of the doped and undoped Co‐Sb system. Co‐deposition of Co‐Sb showed that the amount of Co is higher in nanowires than in film or mushroom caps due to the slow Sb deposition rate dictated by slow Sb(III) complex diffusion. Doped nanowires have been also obtained. Both Ni and Te electrochemical doping of the Co‐Sb system affected the composition of the deposit but there was no effect on nanowire morphology.     

Facile Synthesis of Quasi‐One‐Dimensional Au/PtAu Heterojunction Nanotubes and Their Application as Catalysts in an Oxygen‐Reduction Reaction

An intermediate‐template‐directed method has been developed for the synthesis of quasi‐one‐dimensional Au/PtAu heterojunction nanotubes by the heterogeneous nucleation and growth of Au on Te/Pt core–shell nanostructures in aqueous solution. The synthesized porous Au/PtAu bimetallic nanotubes (PABNTs) consist of porous tubular framework and attached Au nanoparticles (AuNPs). The reaction intermediates played an important role in the preparation, which fabricated the framework and provided a localized reducing agent for the reduction of the Au and Pt precursors. The Pt₇Au PABNTs showed higher electrocatalytic activity and durability in the oxygen‐reduction reaction (ORR) in 0.1 M HClO₄ than porous Pt nanotubes (PtNTs) and commercially available Pt/C. The mass activity of PABNTs was 218 % that of commercial Pt/C after an accelerated durability test. This study demonstrates the potential of PABNTs as highly efficient electrocatalysts. In addition, this method provides a facile strategy for the synthesis of desirable hetero‐nanostructures with controlled size and shape by utilizing an intermediate template.     

Mechanism of film growth of tellurium by electrochemical deposition in the presence and absence of cadmium ions

The growth morphology and the kinetics of a thin film of Te on Au during electrochemical deposition at -62 mV (vs Ag/AgCl/3 M NaCl) have been studied. The deposition conditions are similar to those used previously by us to grow nanowires inside Au nanotubes by electrochemical deposition in the presence of Cd ions (Cd(2+)). By using electrochemical deposition on a planar Au electrode, we explored the growth of the Te film for two conditions: in the presence of Cd(2+) (0.1 mM TeO(2) + 1 mM CdSO(4) + 50 mM H(2)SO(4) solution) and in the absence of Cd(2+) (0.1 mM TeO(2) + 50 mM H(2)SO(4) solution). We used several surface investigation techniques to study the growth such as: in situ electrochemical atomic force microscopy (EC-AFM), in situ electrochemical surface plasmon resonance (EC-SPR), electrochemical methods, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). In the presence of Cd(2+), in situ electrochemical atomic microscopy showed that Cd(2+) acted as a mediator at the early deposition stage and caused smoothing of the Te deposit obtained. In the absence of Cd(2+), Te had an island growth. The electrochemical surface plasmon resonance showed that the deposit was characterized by a slower deposition rate in the presence of Cd(2+) than in the absence of Cd(2+). Additionally, the thickness of the film was evaluated using EC-AFM measurements, electrochemical stripping analysis, and EC-SPR. The results obtained from all three measurements agree well with the Te film obtained in the presence of Cd(2+), where a continuous and uniform film was formed. In the presence of Cd(2+), a Te film with a thickness of 1.04 nm and atomically flat surface was deposited on an ultraflat Au surface. The XPS spectrum showed no significant amount of Cd in the deposit, indicating that the Cd ion acted as a mediator and not as a co-deposition element.     

碲在金衬底上的不可逆吸附行为及其欠电位沉积机制的研究

研究了碲在金衬底上的不可逆吸附行为特征及其对碲原子欠电位沉积行为的影响. 同时也探讨了碲原子于金衬底上的欠电位沉积机制. 结果显示在开路条件下碲原子在金衬底表面具有不可逆的吸附行为, 证实了在金的双电层范围内很难将这种碲的吸附物移走. 为了完全移走碲的吸附物, 需要采用特定的电化学清洗程序. 发现碲的吸附物移走发生在电位循环至金的氧化区域, 且在该区域这种碲的吸附物移走与金的表面氧化同时发生. 扫描速率分析结果证实碲欠电位沉积在金表面符合Sanchez-Maestre模型的三个标准, 说明碲原子于金衬底上欠电位沉积符合二维形核和生长机制.     

Spontaneous reduction of metal ions on the sidewalls of carbon nanotubes

Nanotube/nanoparticle hybrid structures are prepared by forming Au and Pt nanoparticles on the sidewalls of single-walled carbon nanotubes. Reducing agent or catalyst-free electroless deposition, which purely utilizes the redox potential difference between Au3+, Pt2+, and the carbon nanotube, is the main driving force for this reaction. It is also shown that carbon nanotubes act as a template for wire-like metal structures. The successful formation of the hybrid structures is monitored by atomic force microscopy (AFM) and electrical measurements.     

Template-synthesized nanotubes for chemical separations and analysis

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubes that span the thickness of the support membrane. The support is a commercially-available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubes are prepared by electroless deposition of Au onto the pore walls, that is, the pores acts as templates for the nanotubes. We have shown that by controlling the Au deposition time, Au nanotubes that have effective inside diameters of molecular dimensions (<1 nm) can be prepared. These nanotube membranes can be used to cleanly separate small molecules on the basis of molecular size. Furthermore, use of these membranes as a novel electrochemical sensor is also discussed. This new sensing scheme involves applying a constant potential across the Au nanotube membrane and measuring the drop in the transmembrane current upon the addition of the analyte. This paper reviews our recent progress on size-based based transport selectivity and sensor applications in this new class of membranes.     

Molecular sieving and sensing with gold nanotube membranes

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubes that span the thickness of the support membrane. The support is a commercially available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubes are prepared via electroless deposition of Au onto the pore walls; i.e., the pores act as templates for the nanotubes. We have shown that by controlling the Au deposition time, Au nanotubes that have effective inside diameters of molecular dimensions (<1 nm) can be prepared. These nanotube membranes can be used to cleanly separate small molecules on the basis of molecular size. Furthermore, use of these membranes as a novel electrochemical sensor is also discussed. This new sensing scheme involves applying a constant potential across the Au nanotube membrane and measuring the drop in the transmembrane current upon the addition of the analyte. This paper reviews our recent progress on size-based transport selectivity and sensor applications in this new class of membranes.     

Modeling electrochemical deposition inside nanotubes to obtain metal-semiconductor multiscale nanocables or conical nanopores

Nanocables with a radial metal-semiconductor heterostructure have recently been prepared by electrochemical deposition inside metal nanotubes. First, a bare nanoporous polycarbonate track-etched membrane is coated uniformly with a metal film by electroless deposition. The film forms a working electrode for further deposition of a semiconductor layer that grows radially inside the nanopore when the deposition rate is slow. We propose a new physical model for the nanocable synthesis and study the effects of the deposited species concentration, potential-dependent reaction rate, and nanopore dimensions on the electrochemical deposition. The problem involves both axial diffusion through the nanopore and radial transport to the nanopore surface, with a surface reaction rate that depends on the axial position and the time. This is so because the radial potential drop across the deposited semiconductor layer changes with the layer thickness through the nanopore. Since axially uniform nanocables are needed for most applications, we consider the relative role of reaction and axial diffusion rates on the deposition process. However, in those cases where partial, empty-core deposition should be desirable (e.g., for producing conical nanopores to be used in single nanoparticle detection), we give conditions where asymmetric geometries can be experimentally realized.     

Fabrication and characterization of ultralong Ag/C nanocables, carbonaceous nanotubes, and chainlike beta-Ag2Se nanorods inside carbonaceous nanotubes

A novel complex-assisted hydrothermal route is presented to fabricate ultralong Ag/C nanocables with length ranging from 100 to 180 microm on a large scale, based on the reaction of sulfamic acid silver and salicylic acid. By chemical etching of these Ag/C nanocables, high-quality carbonaceous nanotubes can be obtained at room temperature. Using the as-prepared Ag/C nanocables as templates, a new strategy for introducing guest materials into hollow nanotubes is addressed. We take Ag(2)Se as an example and validate the feasibility of this strategy. All of the products are characterized in detail by multiform techniques: X-ray diffraction, Fourier transform IR, energy-dispersive X-ray analysis, field emission scanning electron microscopy, transmission electron microscopy (TEM), and high-resolution TEM. The formation mechanisms of these products are tentatively proposed.     

化学沉积法制备Ni-P纳米线与纳米管有序阵列

以多孔氧化铝膜为模板, 在室温下的酸性化学镀镍槽中通过化学沉积法生长出纳米线与纳米管有序阵列. 分别用X射线衍射仪(XRD)与透射电子显微镜(TEM)对纳米线、纳米管阵列进行表征. 并通过对纳米线与纳米管的生长方式进行分析比较, 系统地研究了多孔氧化铝模板的前处理对纳米阵列生长的影响. 结果表明, 生成的纳米线与纳米管均为非晶态的镍磷合金. 室温下镍纳米管的生成主要取决于敏化、活化过程, 而当纳米管的厚度达到一定程度后就不再随时间变化.     

Electroplating of metal nanotubes and nanowires in a high aspect-ratio nanotemplate

Ordered metal (Co, Pt, and CoPt alloy) nanotube and nanowire structures were fabricated by a simple electroplating method in high aspect-ratio anodic aluminum oxide (AAO) membrane. The growth rate in pulse mode is always larger than that in constant-current mode, which represents that diffusion limitation exists in this electroplating condition. It is also found that the sputtered Au layer structure could influence the electroplating. Traditional nanowires could be fabricated in the template with a uniform Au layer as conducting contact. In case of unblocked AAO membrane, metal electroplating begins from the Au particles which were attached inside the holes during the sputtering step and produces metal nanotubes. Pt and CoPt nanotubes could be easily prepared by this method and might be applied as catalyst and magnetic material.     

Template synthesized gold nanotube membranes for chemical separations and sensing

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubes that span the thickness of the support membrane. The support is a commercially-available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubes are prepared via electroless deposition of Au onto the pore walls; i.e., the pores acts as templates for the nanotubes. We have shown that by controlling the Au deposition time, Au nanotubes that have effective inside diameters of molecular dimensions (< 1 nm) can be prepared. These membranes are a new class of molecular sieves and can be used to separate both small molecules and proteins on the basis of molecular size. In addition, the use of these membranes in new approaches to electrochemical sensing is reviewed here. In this case, a current is forced through the nanotubes, and analyte molecules present in a contacting solution phase modulate the value of this transmembrane current.     

Template-synthesized Protein Nanotubes with Controlled Size Based on Layer-by-layer Method

The protein nanotubes fabricated by a layer‐by‐layer deposition method using the porous alumina membrane as the template were described. The combination of the template method and the layer‐by‐layer assembly technique for the fabrication of protein nanotubes presented simplicity and versatility. The nanotubes composed of two kinds of proteins (bovine serum albumin and hemoglobin lyophilized bovine erythrocytes) with different sizes could be synthesized through this method. The outside diameter of the obtained nanotubes was determined by the diameter of the pores of the template. And the wall thickness of the protein nanotubes increased with the increase of the number of protein layers that made up of the walls of nanotubes. Such biodegradable nanotubes with good biocompatibility should be useful for in vivo applications.     

Synthesis and optical properties of nanorattles and multiple-walled nanoshells/nanotubes made of metal alloys

The galvanic replacement reaction between silver and chloroauric acid has been exploited as a powerful means for preparing metal nanostructures with hollow interiors. Here, the utility of this approach is further extended to produce complex core/shell nanostructures made of metals by combining the replacement reaction with electroless deposition of silver. We have fabricated nanorattles consisting of Au/Ag alloy cores and Au/Ag alloy shells by starting with Au/Ag alloy colloids as the initial template. We have also prepared multiple-walled nanoshells/nanotubes (or nanoscale Matrioshka) with a variety of shapes, compositions, and structures by controlling the morphology of the template and the precursor salt used in each step of the replacement reaction. There are a number of interesting optical features associated with these new core/shell metal nanostructures. For example, nanorattles made of Au/Ag alloys displayed two well-separated extinction peaks, a feature similar to that of gold or silver nanorods. The peak at approximately 510 nm could be attributed to the Au/Ag alloy cores, while the other peak was associated with the Au/Ag alloy shells and could be continuously tuned in the spectral range from red to near-infrared.     

Au nanocrystal growth on nanotubes controlled by conformations and charges of sequenced peptide templates

A new biological approach to fabricate Au nanowires was examined by using sequenced peptide nanotubes as templates. The sequenced histidine-rich peptide molecules were assembled on nanotubes, and the biological recognition of the sequenced peptide selectively trapped Au ions for the nucleation of Au nanocrystals. After Au ions were reduced, highly monodisperse Au nanocrystals were grown on nanotubes. The conformations and the charge distributions of the histidine-rich peptide, determined by pH and Au ion concentration in the growth solution, control the size and the packing density of Au nanocrystals. The diameter of Au nanocrystal was limited by the spacing between the neighboring histidine-rich peptides on nanotubes. A series of TEM images of Au nanocrystals on nanotubes in the shorter Au ion incubation time periods reveal that Au nanocrystals grow inside the nanotubes first and then cover the outer surfaces of nanotubes. Therefore, multiple materials will be coated inside and outside the nanotubes respectively by controlling doping ion concentrations and their deposition sequences. It should be noted that metallic nanocrystals in diameter around 6 nm are in the size domain to observe a significant conductivity change by changing the packing density, and therefore this system may be developed into a conductivity-tunable building block.     

Preparation of Si/O/C nanotubes using Ge nanowires as template

The silicon oxycarbide Si/O/C nanotubes were prepared by two-step procedure. First, a nanostructure deposit mainly composed of nanocables with germanium core was synthetized by low pressure chemical vapor deposition (LPCVD) using hexamethyldigermane Ge₂Me₆ and 1,1,3,3-tetramethyldisilazane (Me₂SiH)₂NH as the volatile precursors. Second, LPCVD was followed by annealing at 850 °C in vacuum to evaporate germanium core. As a result Si/O/C nanotubes were formed. Various techniques such as Raman spectroscopy, TEM, SEM/EDX, XPS and HRTEM were used to study the physical and chemical properties.     

ZnS-Zn nanocables and ZnS nanotubes

ZnS-Zn nanocables and ZnS nanotubes have been synthesized by a thermochemical process in a simple and safe way. The as-prepared nanocables consist of a single crystal Zn core with a diameter of 20 nm and a polycrystalline ZnS sheath with a thickness of 8 nm. The evaporation of the Zn core leads to the formation of ZnS nanotubes.     

Synthesis of heterosegment-junctioned hybrid nanotubes of polythiophene and heterometallic nanoparticles by sequential template-based electropolymerization

New heterosegment-junctioned hybrid nanotubes of polythiophene and heterometallic nanoparticles (Pd, Au NPs) have been synthesized by sequential electropolymerization of terthiophene-modified Pd and Au NPs in a nanoporous template.     

Zigzag Assembly of Carbon Nanotubes inside Au Microtrenches

We report the self-assembly of zigzag patterns consisting of aligned carbon nanotubes inside Au microtrenches by chemical vapor deposition using ferrocene/xylene solution as the precursor. The zigzag nanotubes have uniform size and constant interpattern distance, which can be controlled by simply changing the width of the Au trenches. We demonstrated the tunable length and orientation of nanotubes during self-assembly, leading to a predictable motion of zigzag patterns. A growth model was proposed for the zigzag assembly of nanotubes, including the formation and subsequent splitting of an amorphous carbon layer on the pattern top. Rows of nanotube micropatterns regularly distributed along the Au trench are potential candidates as integrated arrays of thermal or mechanical detectors and actuators.