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The development of a simple and convenient noninvasive salivary glucose sensor to replace the needle-prick blood collection process can not only enhance early detection and diagnosis but also reduce excess medical care costs due to delayed treatment. This study presents a noninvasive sensor based on a ferrocene/ZnO/nitrogen-incorporated nanodiamond/Si heterojunction structure to measure glucose in saliva. The sensing electrode based on a heterojunction structure composed of ferrocene (FC), Bidens-like zinc oxide (b-ZnO), and nitrogen-incorporated ultra-nanocrystalline diamond (NUNCD) films, which is a kind of nitrogen-incorporated nanodiamond, was constructed on a silicon (Si) substrate. Herein, FC and b-ZnO act as a mediator and a specific surface area promoter, respectively, and NUNCD provides a good nucleation site and conducting path. Glucose oxidase (GOx) was introduced into the system to play the role of enzyme to catalyze the reaction and increase the electrode selectivity. The FC/b-ZnO/NUNCD/Si sensor exhibited superior performance in glucose measurements within the linear ranges (1) 20–100 μM (R2 = 0.9717) with a sensitivity of 1125.18 μA/(mM cm2) and (2) 20–600 μM (R2 = 0.9926) with a sensitivity of 804.11 μA/(mM cm2). Additionally, the sensor has a sensitivity of 1012.35 μA/(mM cm2) within the range 50–400 μM (R2 = 0.9912) for artificial saliva. [ABSTRACT FROM AUTHOR]

This work is the first to describe a bioimaging method that uses highly uniformly sized Ti[O.sub.2] submicrometer and micrometer spheres based on Mie scattering. Transmembrane proteins (HER2) located on the surface of cancer cells were detected by bonded antibody-linked Ti[O.sub.2] spheres using optic microscopy and UV vis spectroscopy. A particular HER2 bond on cancer cells, which has a weaker binding affinity than the biotin/ avidin interaction, can be identified between Ti[O.sub.2] spheres that are linked to anti-HER2 antibodies and those that are linked to nonspecific mouse IgG antibodies by observing the cells under an optical microscope or by measuring absorbance from a UV-vis spectrum. The Ti[O.sub.2] spheres used in this work was prepared by reacting TrIP with carboxylic acid, as described elsewhere and the uniformity of the Ti[O.sub.2] sphere was further improved by adjusting the amount of water used. The water content was inversely related to particle size and the size distribution: as more water was used, smaller spheres with a narrower size distribution were obtained. The most uniform sphere obtained had a diameter of about 1 [micro]m with a size variation of 3%.

Nitrogen-incorporated ovoid-shaped nanodiamond (NOND) film exhibits excellent electrochemical sensing properties owing to its unique characteristics. In this study, to improve the sensitivity of NOND-based biosensors for dopamine (DA) detection, a detailed investigation concerning the growth mechanism of NOND films was conducted, it is found that the NOND films did not directly grow on a Si substrate during the growth process but preferentially originated from the formation of a thin Si3N4 interlayer attributed to the reactions of Si substrate and nitrogen atoms in the plasma in the very early stage of deposition. Subsequently, the diffusion of nitrogen from the inner Si3N4 to the Si3N4/plasma interface produces more active sites for the adsorption of the ionized carbon atoms. As the process proceeded further, the growth of ovoid-shaped diamonds accompanies the decrease of the Si3N4 interlayer thickness owing to the diffusion of nitrogen from Si3N4. Significant Si3N4 peaks are observed from both the Raman and X-ray diffraction analyses when the sample was subjected to NOND deposition for less than 20 min. These peaks then completely disappeared after deposition for 60 min, demonstrating the proposed mechanism. Furthermore, it is also observed that the deposition of the Si3N4 interlayer increased the hydrophilicity of the substrate, which is ascribed to the lower surface free energy of the NOND. To enhance the sensitivity of the NOND, the synthesis of NOND with patterned arrays (P-NOND) is proposed. The high specific surface area of the highly hydrophilic P-NOND obviously enhances the sensitivity of the P-NOND-based electrodes. Application of the P-NOND electrode for DA detection is successfully demonstrated in the mixed DA electrolyte, showing a better performance than that of the pristine NOND. This work reveals that the P-NOND electrode possesses superior sensitivity and selectivity, which is very favorable for DA sensing. [ABSTRACT FROM AUTHOR]

The discovery of a simple high yield synthesis of silver (Ag) nanowires using the in situ generation of a silica shell layer is reported. The a-silica shell is suggested to contain OSiMe3 groups terminated silsesquioxane structures.

The article presents an experiment on the molecular-shape-selectivity behavior of zeolites. A simple gas chromatography setup using a zeolite column was applied on the experiment. It states that the adsorption and temperature programmed desorption test of hydrocarbons can be monitored through flame ion detector (FID) signals of gas chromatography (GC). As a result, the hydrocarbon isomers adsorption on zeolite framework structures can be realized. It also aids students to observe the shape selectivity principle of the mineral through the measurement of hexane isomers sorption behavior.

Recently, carbon nanotubes (CNTs) have been reported to be an effective MALDI matrix for small molecules (Anal. Chem. 2003, 75, 6191). In a somewhat related study, we have employed CNTs produced by using NaH-treated anodic aluminum oxide (Na@AAO) as a reactive template as the assisting matrix for MALDI analysis upon the addition of high concentrations of citrate buffer. Our results indicate that the mass range can be extended to ca. 12,000 Da and that alkali metal adducts of analytes are effectively reduced. Furthermore, we have employed citric acid-treated CNTs as affinity probes to selectively concentrate traces of analytes from aqueous solutions. High concentrations of salts and surfactants in the sample solutions are also tolerated. This approach is very suitable for the MALDI analysis of small proteins, peptides, and protein enzymatic digest products. [Copyright &y& Elsevier]

Gas sensors based on semiconductors have outstanding sensitivity compared with the oxide-based devices; however, the high operation temperature greatly hinders its development in practical applications. Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death worldwide, and the patients with severe COPD with or without exacerbation tend to have airflow obstruction, which results in an increase of CO 2 concentration and subsequent hypercapnic respiratory failure. At present, COPD detection relies on professional operation; however, the patients suffer great discomfort during the arterial blood sampling. All these facts reduce patient's willingness to test their physical health. Thus, noninvasive monitoring of CO 2 levels is crucial for the early diagnosis of high-risk COPD patients. A nitrogen-incorporated ultrananocrystalline diamond (NUNCD) film exhibits excellent properties in biosensing and polyetherimide-polyethylene glycol (PEI-PEG) polymer possesses a great capability of CO 2 capturing. By incorporating NUNCD into PEI-PEG film, this work focuses on ameliorating the sensitivity and selectivity of the present semiconductor CO 2 sensor. From the theoretical regression analyses of the experimental results, it is found that the excellent performance of the PEI-PEG/ZnO/NUNCD/Si electrode is contributed by two main reaction layers, the adsorption layer (PEI-PEG) and the electric transfer layer (ZnO/NUNCD). The selectivity is dominated by the PEI-PEG adsorption layer and the sensitivity is directly related to the changes in the work function of the ZnO/NUNCD interface. The high aspect ratio (>10) of the flower-like ZnO structure, growth from ZnO nanoparticles, can provide a more active adsorption area, as a result, extremely enhancing the sensitivity of the CO 2 sensor., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

In this work, we report the fabrication and performance of supercapacitors made from carbonized peanut shells, which are renewable materials with a huge annual yield and are usually discarded directly by people. With proper treatment, peanut shells could be used for many applications. Herein, we demonstrate that the peanut shells treated with carbonization and activation processes not only possess an extremely high surface area but also provide a hierarchical structure for energy storage. The performance of the electrode can be further improved by nitrogen doping and adding graphene oxide to the electrode. The electrode shows a specific capacitance of 289.4 F/g, which can be maintained at an acceptable level even at a high scanning rate. In addition, a good capacitance retention of 92.8% after 5000 test cycles demonstrates that the electrode possesses an excellent electrochemical property., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

A new synthetic method to grow O-deficient rutile TiO 2(s) nanorods (NRs) and nanowires (NWs) by a vapor-solid reaction growth method is developed. TiCl 4(g) was employed to react with commercially supplied CaTiO 3(s) (size 2-4 μm) at 973 K under atmospheric pressure to generate TiO 2(s) NRs (diameters 80-120 nm, lengths 1-4 μm). The reaction employing TiCl 4(g) and CaO (s) at 973 K also generated CaTiO 3(s) (size 4-13 μm) as the intermediate which reacted further with TiCl 4(g) to produce NWs (diameters 80-120 nm, lengths 4-15 μm). This is the first report of 1D rutile TiO 2(s) nanostructure with such a high aspect ratio. Both of the NRs and the NWs, with compositions TiO 1.81 and TiO 1.65 , respectively, were single crystals grown in the [001] direction. Their morphology was affected by the reaction temperature, the concentration of TiCl 4(g) , and the particle size of CaTiO 3(s) . The NRs and the NWs were investigated as anode materials for Li + -ion batteries. At constant current rates 1, 2, and 5 C (1 C = 170 mA g -1 ) for 100 cycles, the cycling (1.0-3.0 V) performance data of the NRs were 146, 123, and 104 mA h g -1 , respectively. On the other hand, the cycling performance data of the NWs were 120, 80, and 52 mA h g -1 , respectively. This is attributed to the high Li + ion diffusion rate ( D Li + ) of the NRs (29.52 × 10 -15 cm 2 s -1 ), which exceeds that of the NWs (8.61 × 10 -15 cm 2 s -1 ). Although the [001] growth direction of the NR crystals would provide the fastest channels for the diffusion of Li + ions and enhance the battery capacity, the extremely long channels in the NWs could hamper the diffusion of the Li + ions. The O-deficiency in the structure would increase the conductivity of the electrode material and improve the stable cycling stability of the batteries also. The long-term cycling test at 2 C for the battery constructed from the NRs retained 121 mA h g -1 after 200 cycles and 99.2 mA h g -1 after 800 cycles. The device has an excellent long-term cycling stability with a loss of only 0.04% per cycle., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

The glucose level is an important biological indicator for diabetes diagnosis. In contrast with costly and unstable enzymatic glucose sensing, oxide-based glucose sensors own the advantages of low fabrication cost, outstanding catalytic ability, and high chemical stability. Here, we fabricate a self-supporting spiky Cu x O/Cu nanowire array structure by electrochemical cycling treatment. The spiky Cu x O/Cu nanowire is identified to be a Cu core passivated by a conformal Cu 2 O layer with extruded CuO petals, which provides abundant active sites for electrocatalytic reaction in glucose detection. An interruptive potential sweeping experiment is presented to elucidate the growth mechanism of the spiky Cu x O/Cu nanostructure during the potential cycling treatment. The spiky Cu x O/Cu nanowire array electrode exhibits a sensitivity of 1210 ± 124 μA·mM -1 ·cm -2 , a wide linear detection range of 0.01-7 mM, and a short response time (<1 s) for amperometric glucose sensing. The study demonstrates a route to modulate oxide phase, crystal morphology, and electrocatalytic properties of metal/oxide core-shell nanostructures., Competing Interests: The authors declare no competing financial interest.

An Au/K bicatalyst-assisted chemical vapor deposition process using C 2 H 2(g) to grow high-density carbon nanocoils (CNCs) uniformly on the fibers in carbon fiber cloth substrates three-dimensionally was developed. An as-deposited substrate (2.5 × 1.0 cm 2 ) showed a high electrochemical active surface area (16.53 cm 2 ), suggesting its potential usefulness as the electrode in electrochemical devices. The unique one-dimensional (1D) helical structure of the CNCs shortened the diffusion pathways of the ions in the electrolyte and generated efficient electron conduction routes so that the observed serial resistance R s was low (3.7 Ω). By employing two-electrode systems, a liquid-state supercapacitor (SC) in H 2 SO 4(aq) (1.0 M) and a solid-state SC with a polypropylene (PP) separator immersed in H 2 SO 4(aq) (1.0 M)/polyvinylalcohol were assembled and investigated by using CNC-based electrodes. Both devices exhibited approximate rectangular shape profiles in the cyclic voltammetry measurements at various scan rates. The observations indicated their electric double-layer capacitive behaviors. From their galvanostatic charge/discharge curves, the specific capacitances of the liquid SC and the solid SC were measured to be approximately 137 and 163 F/g, respectively. In addition, the solid-state CNC-based SC possessed excellent energy density (15.3 W h/kg) and power density (510 W/kg). The light weight solid SC (0.1965 g, 2.5 × 1.0 cm 2 ) was bendable up to 150° with most of the properties retained., Competing Interests: The authors declare no competing financial interest.

In this study, we develop a new synthetic method to grow anatase TiO 2 crystals composed of truncated octahedral bipyramids (TOBs) with exposed {001} and {101} facets by a vapor-solid reaction growth (VSRG) method. The VSRG method employs TiCl 4(g) to react with CaO (s) /Ca(OH) 2(s) at 823-1043 K under atmospheric pressure. The O-deficient pale-blue TOB TiO 2 crystals display high amount of both {001} and {101} facets. Together, they decompose methylene blue photocatalytically under UV-visible (UV-vis) light irradiation. The most-efficient TOB catalyst VT923 (grown at 923 K, average edge length 400 nm, average thickness 200 nm, and surface area 4.20 m 2 /g) shows a degradation rate constant k , 0.0527 min -1 . This is close to that of the P25 standard 0.0577 min -1 . However, the surface area of P25 (46.8 m 2 /g) is about 12 times that of VT923. The extraordinary performance of VT923 is attributed to the presence of high amount of coexisting {001} and {101} facets to form effective surface heterojunctions. They would separate photogenerated electrons and holes effectively on {101} and {001} surfaces, respectively. For VT923, the {001}/{101} ratio is 0.764, which is close to 1, the highest value observed for all TOB samples grown in this study. The surface heterojunctions prolong the electron-hole separation so that VT923 demonstrates the excellent photocatalytic capability. In addition, residual Cl atoms on the exposed faces are easily removed to show clean TiO surface layers with sufficient amount of O-deficient sites in the current samples., Competing Interests: The authors declare no competing financial interest.

We report a versatile strategy to exploit parafilm waste as a carbon precursor for fabrication of freestanding, hollow few-layer graphene fiber mesh (HFGM) structures without use of any gaseous carriers/promoters via an annealing route. The freestanding HFGMs possess good mechanical flexibility, tailorable transparency, and high electrical conductivity, consequently qualifying them as promising electrochemical electrodes. Because of the hollow spaces, electrolyte ions can easily access into and contact with interior surfaces of the graphene fibers, accordingly increasing electrode/electrolyte interfacial area. As expected, solid-state supercapacitors based on the HFGMs exhibit a considerable enhancement in specific capacitance (20-30 fold) as compared to those employing chemical vapor deposition compact graphene films. Moreover, the parafilm waste is found to be beneficial for one-step fabrication of nanocarbon/few-layer graphene composite meshes with superior electrochemical performance, outstanding superhydrophobic property, good self-cleaning ability, and great promise for oil spill cleanup.

We developed an innovative approach of self-biased sputtering solid doping source process to synthesize doped crystalline Si film on flexible polyimide (PI) substrate via microwave-plasma-enhanced chemical vapor deposition (MWPECVD) using SiCl4/H2 mixture. In this process, P dopants or B dopants were introduced by sputtering the solid doping target through charged-ion bombardment in situ during high-density microwave plasma deposition. A strong correlation between the number of solid doping targets and the characteristics of doped Si films was investigated in detail. The results show that both P- and B-doped crystalline Si films possessed a dense columnar structure, and the crystallinity of these structures decreased with increasing the number of solid doping targets. The films also exhibited a high growth rate (>4.0 nm/s). Under optimal conditions, the maximum conductivity and corresponding carrier concentration were, respectively, 9.48 S/cm and 1.2 × 10(20) cm(-3) for P-doped Si film and 7.83 S/cm and 1.5 × 10(20) cm(-3) for B-doped Si film. Such high values indicate that the incorporation of dopant with high doping efficiency (around 40%) into the Si films was achieved regardless of solid doping sources used. Furthermore, a flexible crystalline Si film solar cell with substrate configuration was fabricated by using the structure of PI/Mo film/n-type Si film/i-type Si film/p-type Si film/ITO film/Al grid film. The best solar cell performance was obtained with an open-circuit voltage of 0.54 V, short-circuit current density of 19.18 mA/cm(2), fill factor of 0.65, and high energy conversion of 6.75%. According to the results of bending tests, the critical radius of curvature (RC) was 12.4 mm, and the loss of efficiency was less than 1% after the cyclic bending test for 100 cycles at RC, indicating superior flexibility and bending durability. These results represent important steps toward a low-cost approach to high-performance flexible crystalline Si film-based photovoltaic devices.

The effects of Cu and Au ion implantation on the structural and electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films were investigated. High electrical conductivity of 186 (Ω•cm)(-1) and enhanced EFE properties with low turn-on field of 4.5 V/μm and high EFE current density of 6.70 mA/cm(2) have been detected for Au-ion implanted UNCD (Au-UNCD) films that are superior to those of Cu-ion implanted UNCD (Cu-UNCD) ones. Transmission electron microscopic investigations revealed that Au-ion implantation induced a larger proportion of nanographitic phases at the grain boundaries for the Au-UNCD films in addition to the formation of uniformly distributed spherically shaped Au nanoparticles. In contrast, for Cu-UNCD films, plate-like Cu nanoparticles arranged in the row-like pattern were formed, and only a smaller proportion of nanographite phases along the grain boundaries was induced. From current imaging tunneling spectroscopy and local current-voltage curves of scanning tunneling spectroscopic measurements, it is observed that the electrons are dominantly emitted from the grain boundaries. Consequently, the presence of nanosized Au particles and the induction of abundant nanographitic phases in the grain boundaries of Au-UNCD films are believed to be the authentic factors, ensuing in high electrical conductivity and outstanding EFE properties of the films.

Grain boundaries and microstructures of ultrananocrystalline diamond (UNCD) films are engineered at nanoscale by controlling the substrate temperature (TS) and/or by introducing H2 in the commonly used Ar/CH4 deposition plasma in a microwave plasma enhanced chemical vapor deposition system. A model for the grain growth is proposed. The films deposited at low TS consist of random/spherical shaped UNCD grains with well-defined grain boundaries. On increasing TS, the adhering efficiency of CH radical onto diamond lattice drops and trans-polyacetylene (t-PA) encapsulating the nanosize diamond clusters break due to hydrogen abstraction activated, rendering the diamond phase less passivated. This leads to the C2 radical further attaching to the diamond lattice, resulting in the modification of grain boundaries and promoting larger sized clustered grains with a complicated defect structure. Introduction of H2 in the plasma at low TS gives rise to elongated clustered grains that is attributed to the presence of atomic hydrogen in the plasma, preferentially etching out the t-PA attached to nanosized diamond clusters. On the basis of this model a technologically important functional property, namely tribology of UNCD films, is studied. A low friction of 0.015 is measured for the film when ultranano grains are formed, which consist of large fractions of grain boundary components of sp(2)/a-C and t-PA phases. The grain boundary component consists of large amounts of hydroxylic and carboxylic functional groups which passivates the covalent carbon dangling bonds, hence low friction coefficient. The improved tribological properties of films can make it a promising candidate for various applications, mainly in micro/nanoelectro mechanical system (M/NEMS), where low friction is required for high efficiency operation of devices.

We demonstrated the growth of carbon nanocoils (CNCs) via chemical vapor deposition (CVD) using Au and K metals as the catalysts to assist the thermal decomposition of C(2)H(2). Typical CNCs (wire diameter: 50-80 nm, coil diameter: 110-140 nm, pitch: 100-200 nm, tens of micrometers), identified as amorphous coiled carbon fibers by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were grown at proper combinations of reaction parameters. Au nanoparticles (NPs), identified by energy dispersion X-ray spectroscopy (EDX) and electron diffraction (ED), were located at the tips of the CNCs. The observations suggested that a tip-growth mechanism involving the Au NPs as the nucleation sites was in operation. In the reaction, the liquid-phase K metal assisted the decomposition of C(2)H(2) by lowering the reaction temperature. We propose that acetylide and hydride intermediates were formed in the reaction. Further decomposition of the acetylide intermediates generated solid-phase carbon to grow the CNCs. Effects of varying the reaction conditions on the CNC growth were investigated. On the basis of the results, a Au and K bicatalyst enhanced tip-growth vapor-liquid-solid (VLS) mechanism was proposed to rationalize the CNC formation process. Electron field emission (EFE) characteristics of the CNCs were studied. The best EFE result showed a turn-on field (E(to)) of 3.78 V/μm and a field enhancement factor (β) of 1852. In addition, the current density (J) was as high as 43 mA/cm(2) at 6.87 V/μm. The data suggest that the CNCs could be employed for field emission device applications.

In this study, we fabricated Au nanowires (NWs), nanoslices (NSs), and nanocorals (NCs) on flexible polyethylene terephthalate (PET) substrates via direct current electrochemical depositions. Without any surface modification, the Au nanostructures were used as the electrodes for dopamine (DA) sensing. Among them, the Au NW electrode performed exceptionally well. The determined linear range for DA detection was 0.2-600 μM (N = 3) and the sensitivity was 178 nA/μM cm(2), while the detection limit was 26 nM (S/N = 3). After 10 repeated measurements, 95% of the original anodic current values were maintained for the nanostructured electrodes. Sequential additions of citric acid (CA, 1 mM), uric acid (UA, saturated), and ascorbic acid (AA, 1 μM) did not interfere the amperometric response from the addition of DA (0.1 μM).

The design and fabrication of well-defined nanostructures have great importance in nanoelectronics. Here we report the precise growth of sub-2 nm (c-diamond) and above 5 nm (n-diamond) size diamond grains from energetic species (chemical vapor deposition process) at low growth temperature of about 460 °C. We demonstrate that a pre-nucleation induced interface can be accounted for the growth of c-diamond or n-diamond grains on Si-nanoneedles (Si-NN). These preferentially grown allotropic forms of diamond on Si-NN have shown high electron field-emission properties and signify their high potential towards diamond-based electronic applications.

Enhanced electron field emission (EFE) properties have been observed for ultrananocrystalline diamond (UNCD) films grown on Au-coated Si (UNCD/Au-Si) substrates. The EFE properties of UNCD/Au-Si could be turned on at a low field of 8.9 V/μm, attaining EFE current density of 4.5 mA/cm(2) at an applied field of 10.5 V/μm, which is superior to that of UNCD films grown on Si (UNCD/Si) substrates with the same chemical vapor deposition process. Moreover, a significant difference in current-voltage curves from scanning tunneling spectroscopic measurements at the grain and the grain boundary has been observed. From the variation of normalized conductance (dI/dV)/(I/V) versus V, bandgap of UNCD/Au-Si is measured to be 2.8 eV at the grain and nearly metallic at the grain boundary. Current imaging tunneling spectroscopy measurements show that the grain boundaries have higher electron field emission capacity than the grains. The diffusion of Au into the interface layer that results in the induction of graphite and converts the metal-to-Si interface from Schottky to Ohmic contact is believed to be the authentic factors, resulting in marvelous EFE properties of UNCD/Au-Si.

Tunnel-structured potassium titanate with a K(3)Ti(8)O(17) phase was synthesized by direct oxidation of titanium powder mixed with KF(aq) in water vapor at 923 K. The reaction conditions were adjusted so that uniform single crystalline potassium titanate nanowires with [010] growth direction (length: 5-30 μm, diameter: 80-100 nm) were obtained. Nitridation of the nanowires by NH(3)(g) at 973-1073 K converted the titanate nanowires into rock-salt structured cubic phase single crystalline titanium oxynitride TiN(x)O(y) nanotubes (x = 0.88, y = 0.12, length = 1-10 μm, diameter = 150-250 nm, wall thickness = 30 - 50 nm) and nanorods (x = 0.5, y = 0.5, length = 1-5 μm, diameter = 100-200 nm) with rough surfaces and [200] growth direction. The overall conversion of the titanate nanowires into the nanotubes and the nanorods can be rationalized by Ostwald ripening mechanism. We fabricated an electrode by adhering TiN(x)O(y) nanotubes (0.2 mg) on a screen-printed carbon electrode (geometric area: 0.2 cm(2)). Electrochemical impedance spectroscopy demonstrated its charge transfer resistance to be 20Ω. The electrochemical surface area of the nanotubes on the electrode was characterized by cyclic voltammetry to be 0.32 cm(2). This property suggests that the TiN(x)O(y) nanostructures can be employed as potential electrode materials for electrochemical applications., (© 2011 American Chemical Society)

Urchin-like silver nanowires are prepared by reacting AgNO(3)(aq) with copper metal in the presence of cetyltrimethylammonium chloride and HNO(3)(aq) on a screen-printed carbon electrode at room temperature. The diameters of the nanowires are about 100 nm, and their lengths are up to 10 μm. Using Raman spectroscopy, the detection limit of Rhodamine 6G (R6G) on the urchin-like silver nanowire substrate can be as low as 10(-16) M, while the analytical enhancement factor is about 10(13). Raman mapping images confirm that a single R6G molecule on the substrate can be detected.

Fabricating a low-cost virtual germanium (Ge) template by epitaxial growth of Ge films on silicon wafer with a Ge(x)Si(1-x) (0 < x < 1) graded buffer layer was demonstrated through a facile chemical vapor deposition method in one step by decomposing a hazardousless GeO(2) powder under hydrogen atmosphere without ultra-high vacuum condition and then depositing in a low-temperature region. X-ray diffraction analysis shows that the Ge film with an epitaxial relationship is along the in-plane direction of Si. The successful growth of epitaxial Ge films on Si substrate demonstrates the feasibility of integrating various functional devices on the Ge/Si substrates.

Free standing and vertically aligned silicon rice-straw- like array emitters were fabricated by modified electroless metal deposition (EMD), using HF-H(2)O(2) as an etching solution to reduce the emitter density and to make the emitter end of the formed silicon rice-straw arrays shaper than those formed by conventional EMD. These silicon rice-straw array emitters can be turned on at E(0) = 4.7 V/μm, yielding an EFE (electron field emission) current density of J(e) = 139 μA/cm(2) in an applied field of 12.8 V/μm. According to a simple simulation, the excellent EFE performance of the silicon rice-straw array emitters originates in not only the favorable distribution of emitter arrays, but also the shape of the emitter apexes. The modified-EMD method is easily scaled up without expensive equipment, so silicon rice-straw array emitters are a promising alternative to silicon-based field emitters.

A straightforward electrochemical deposition process was developed to grow gold nanostructures, including nanocoral, nanothorn, branched belt, and nanoparticle, on carbon electrodes by reducing HAuCl4 under constant potentials in mixtures containing CTAC and/or NaNO3. Among the nanostructures, the quasi-one-dimensional nanocoral electrode showed the highest surface area. Because of this, it provided excellent electrochemical performances in cyclic voltammetric (CV) studies for kinetic-controlled enzyme-free glucose oxidation reactions. In amperometric studies carried out at 0.200 V in PBS (pH 7.40, 0.100 M), the nanocoral electrode showed the highest anodic current response. It also offered the greatest sensitivity, 22.6 μAmM(-1)cm(-2), an extended linear range, 5.00×10(-2) mM to 3.00×10(1) mM, and a low detection limit, 1.00×10(1) μm among the electrodes investigated in this study. In addition, the glucose oxidation by the nanocoral electrode started at -0.280 V, more negative than the one of using a commercial Au electrode as the working electrode. This is attributed to the presence of exposed Au (110) surfaces on the electrode. The feature was applied to oxidize glucose selectively in the presence of ascorbic acid (AA) and uric acid (UA), common interferences found in physiological analytes. With an applied voltage at -0.100 V, the AA oxidation (started at -0.080 V) can be avoided while the glucose oxidation still provides a significant response.

Growth of amorphous carbon nanocoil (CNC) from acetylene on Si substrates was achieved by using nanosized Ag and K as the catalysts. The deposition of CNC was carried out inside a hot-wall reactor at 723 K using H2 as the carrier gas. Based on the observed results, we propose a cooperative bimetal catalyst enhanced vapor-liquid-solid (VLS) growth mechanism to rationalize the CNC growth. In the reaction, the liquid phase metallic K dehydrogenated acetylene into the solid-state carbon, while the Ag nanoparticle assisted the extension of carbon one-dimensionally (1-D) via a tip-growth mechanism. Due to the adhesive force between the K liquid and the carbon, the 1-D solid curled along the C-K interface into the nanocoil shape. Some CNC samples were further heat-treated at 1423 K and showed very good field emission properties. They emitted electrons (10 microA/cm2) at a turn-on field Eto of 2.51 V/microm, while Jmax reached 17.71 mA/cm2 at 5.64 V/microm. The field enhancement factor beta was calculated to be 2124, comparable to other carbon nanotube (CNT) and CNC based emitters. The CNC was also characterized by using the electrochemical behavior of K3[Fe(CN)6] via cyclic voltammetry (CV). The electrochemical surface area of a CNC electrode (geometric surface area 0.078 cm2) was calculated to be 0.143 cm2. These properties suggest that the CNC electrodes may have potential applications in field emission and electrochemical devices.

A simple galvanic reduction for direct growth of Au nanowires on silicon wafers is developed. The nanowires were prepared by reacting HAuCl4aq with Sns in the presence of CTACaq (cetyltrimethylammonium chloride) and NaNO3aq, which were important to the product morphology development. The nanowire diameter was 50-100 nm, and the length was more than 20 microm.

Carbon nanoparticles, like nanocones and nanodiscs, can be obtained by mechanical treatment of carbon nanofilaments. Microstructural studies suggest that in nanocones the conical graphene stacking with progressively increasing apex (cone) angles does not fully agree with current theoretical geometry models, such as a closed cones model and a cone-helix model. The unusual stacking form of nanocones was taken into account in a modified cone-helix model. The formation mechanism of the distinctive microstructure is attributed to the inclined anchoring effect, and the relaxation of internal stresses, which were induced by the confined pyrolysis process, resulting in easier disintegration by sonication the nanofilaments. This is disclosed for the first time in literature regarding the attainment of uniform carbon nanoparticles.

We demonstrate the syntheses of single crystalline Cu nanobelt and Ag belt-like materials via CTAC-assisted (CTAC, cetyltrimethylammonium chloride) galvanic reductions. The single crystalline face-centered cubic phase Cu nanobelt was prepared by reacting CuCl2(aq) with Al(s) in an aqueous solution of CTAC and HNO3. The Cu nanobelt exhibited a high-quality ribbon-like nanostructure with a thickness less than 15 nm, a width of 30-150 nm, and a length up to 10 microm. The belt-like Ag, with a thickness less than 10 nm, a width of 30-100 nm, a length up to 5 microm, and a novel single crystalline 4H structure, was prepared by reacting AgNO3(aq) and Cu(s) in an aqueous solution of CTAC.

Porous carbon materials with pore sizes from 3 to 200 nm were synthesized by reacting hexafluorobenzene with Na liquid at 623 K. NaF crystals, a byproduct formed in the reaction, acted as nanotemplate to assist the pore formation. By employing hexafluorobenzene to react with Na incorporated within the channels (diameter 200 nm) of anodized aluminum oxide (AAO) membranes at 323-623 K, the carbon material can be fabricated into aligned porous nanotube arrays (ca. 250 nm in diameter, ca. 20 nm in wall thickness, ca. 0.06 mm in length, and ca. 3-90 nm in pore diameter). These materials were characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray energy dispersive spectroscopy, electron diffraction, thermal gravimetric analysis, and nitrogen physical adsorption experiments.

C(6)F(6) vapor is employed to react with CaC(2) and Mg(3)N(2) to grow CaF(2)/a-C and Mg(2)F(2)/a-C core/shell nanowires (tens of micrometers in length, tens to hundreds of nanometers in wire diameter, and tens of nanometers in core diameter), respectively, in high yields. The growth mechanism is proposed to proceed via a reaction at the interface of the vapor and solid reactants.