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Well-ordered arrays of needle-like and cone-like Si nanostructures have been successfully produced on (001)Si substrates. The morphology and dimensions of the tapered Si nanostructure arrays can be readily controlled by adjusting the Ag-nanoparticle catalytic etching/removal (ACER) cycles. All the produced vertical tapered Si nanostructures were single crystalline and their axial crystallographic orientation was the same as that of the (001)Si substrate. The produced long needle-like Si nanowires exhibited superior field emission properties compared to as-produced and short cone-like Si nanowires. The enhanced field emission performance of the long needle-like Si nanowire array can be attributed to the good vertical alignment, sharp tips, high aspect ratio, single-crystalline structure, and well-ordered arrangement. The experimental results present the exciting prospect that with appropriate control, the combined approach proposed here promises to be applicable for fabricating other highly-ordered, vertically-aligned tapered Si-based nanowire arrays and may offer potential applications in constructing various high efficiency Si-based field emission nanodevices.

We present here the results from a systematic investigation on the growth kinetics and surface properties of Al-doped ZnO (AZO) nanowires synthesized on (0 0 1)Si substrates under different hydrothermal conditions. The as-synthesized vertical AZO nanowires exhibited a hydrophilic characteristic and their crystal structures were determined to be perfectly single crystalline with the axis of the wire parallel to the [0 0 0 1] direction. TEM and EDS results revealed that the as-synthesized AZO nanowires have tapered tips, and the Al-doped concentration in the AZO nanowires was about 1.6 at%. After a series of SEM examinations, the average length of AZO nanowires synthesized at each temperature studied was found to follow a linear relationship with the reaction time, indicating that the hydrothermal growth of AZO nanowires was a reaction-controlled process. The activation energy for linear growth of AZO nanowires on Si substrate, as obtained from an Arrhenius plot, was found to be about 46 kJ/mol. From UV–vis spectroscopic measurements, it was found that the Si substrate coated with vertically-aligned AZO nanowire arrays exhibited remarkably reduced reflectance (10–12%) over a wide range of visible wavelengths (400–800 nm) and angles of light incidence (8–60°). The good broadband and omnidirectional antireflection characteristics can be attributed to the light trapping effect and the graded refractive index resulting from the tapered AZO nanowire structures.

Electromigration in Cu has been extensively investigated as the root cause of typical breakdown failure in Cu interconnects. In this study, Cu nanowires connected to Au electrodes are fabricated and observed using in situ transmission electron microscopy to investigate the electro- and thermo-migration processes that are induced by direct current sweeps. We observe the dynamic evolution of different mass transport mechanisms. A current density on the order of 106 A/cm2 and a temperature of approximately 400 °C are sufficient to induce electro- and thermo-migration, respectively. Observations of the migration processes activated by increasing temperatures indicate that the migration direction of Cu atoms is dependent on the net force from the electric field and electron wind. This work is expected to support future design efforts to improve the robustness of Cu interconnects.

The low temperature sintering of micron-sized Cu powders is achieved by ethanol vapor annealing. A Cu-pancake is formed and has enough mechanical strength to sustain the gravitational pull. The electrical resistivity of the Cu-pancake formed by flaky powders is lower than that by spheroidal ones because more contact area of the former facilitates the sintering process. The resistivity of the Cu-pancake grows with decreasing the annealing temperature but it is still about 10−3 Ω cm at 120 °C. The sintered Cu-pancake is characterized by X-ray diffraction and X-ray photoelectron spectroscopy to investigate the sintering mechanism. The low temperature sintering is attributed to the reduction of the native oxide on surfaces of Cu powders by the ethanol vapor. The reduced Cu is very active and tends to sinter with each other to lower the surface energy. This reduction-assisted sintering may be useful in the fabrication of conductive patterns on flexible substrates. The prepared Cu pattern on polyethylene naphthalate exhibits repeatable flexibility and acceptable conductivity.

We report here the first study of the growth kinetics of vertically-aligned ZnO nanowire arrays grown on Al-doped ZnO (AZO) seed layer-coated substrates by a hydrothermal method. The as-synthesized vertical ZnO nanowires possess a single-crystalline wurtzite structure and a preferred growth orientation along the [0001] direction. The ZnO nanowires were found to grow following the reaction-controlled process and their lengths could be tuned from several to over ten micrometers by adjusting the hydrothermal temperature and time. By measuring the growth rates at different synthesis temperatures, the activation energy for the linear growth of vertical ZnO nanowires on AZO-seeded substrates derived from the slope of the Arrhenius plot was around 35 kJ mol−1. The obtained value is smaller than that of ZnO nanowires grown in bulk solution, which can be explained by the different nucleation mechanisms. From water contact angle measurements, it is found that the as-synthesized ZnO nanowires are hydrophilic in nature, and their surface wettability can be adjusted by the storage time and heat treatment conditions. Furthermore, the reversible switching of the surface wettability of ZnO nanowires has been accomplished by alternate annealing in vacuum and oxygen atmospheres. The ZnO nanowires with switchable surface wettability will find promising applications in surface engineering.

We developed a method to fabricate arrays of nanostructured carbon materials of high quality, via direct pyrolysis of poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) block copolymer (BCP) as thin films without small organic molecules incorporated as carbon resources. Prior to pyrolysis, the nanodomains were cross-linked with UV radiation under nitrogen (UVIN). As upon pyrolysis thermal energy imparts mobility to nanodomains to overcome the constraints imposed by cross-linked chains, the free surface is inevitably covered with the PS block that has a smaller surface energy; unless favorable interactions with the P2VP block exist at the free surface, the outer layer of carbonaceous films is predominantly composed of the pyrolyzed PS block. To overcome this problem, films were capped with a SiO2 layer after UVIN. The capping layer appears to have two advantages – increased areal yields and an improved morphological fidelity. As a result, arrays of nanostructured carbon of great quality were fabricated even at temperatures far above the decomposition temperatures of PS and P2VP blocks.

In this study, we reported the design, fabrication, and characterization of wellordered arrays of vertically-aligned, epitaxial NiSi2/Si heterostructures and single-crystalline NiSi2 nanowires on (001)Si substrates. The epitaxial NiSi2 with $$\{ \bar 111\}$$ facets was found to be the first and the only silicide phase formed inside the Si nanowires after annealing at a temperature as low as 300 °C. Upon annealing at 500 °C for 4 h, the residual parts of Si nanowires were completely consumed and the NiSi2/Si heterostructured nanowires were transformed to fully silicided NiSi2 nanowires. XRD, TEM and SAED analyses indicated that all the NiSi2 nanowires were single crystalline and their axial orientations were parallel to the [001] direction. The obtained vertically-aligned NiSi2 nanowires, owing to their well-ordered arrangement, single-crystalline structure, and low effective work function, exhibit excellent field-emission properties with a very low turn-on field of 1.1 V/m. The surface wettability of the nanowires was found to switch from hydrophobic to hydrophilic after the formation of NiSi2 phase and the measured water contact angle decreased with increasing extent of Ni silicidation. The increased hydrophilicity can be explained by the Wenzel model. The obtained results present the exciting prospect that the new approach proposed here will provide the capability to fabricate other highly-ordered, vertically-aligned fully silicided nanowire arrays and may offer potential applications in constructing vertical silicide-based nanodevices.

The influence of Al addition on the phase transformation and thermal stability of Ni silicides on (0 0 1)Si has been systematically investigated. The presence of Al atoms is found to slow down the Ni 2 Si–NiSi phase transformation but significantly promote the NiSi 2− x Al x formation during annealing. The behavior of phase transformation strongly depends on the Al concentration of the initial Ni 1− x Al x alloys. Compared to the Ni 0.95 Pt 0.05 /Si and Ni 0.95 Al 0.05 /Si system, the Ni 0.91 Al 0.09 /Si sample exhibits remarkably enhanced thermal stability, even after high temperature annealing for 1000 s. The relationship between microstructures, electrical property, and thermal stability of Ni silicides is discussed to elucidate the role of Al during the Ni 1− x Al x alloy silicidation. This work demonstrated that thermally stable Ni 1− x Al x alloy silicides would be a promising candidate as source/drain (S/D) contacts in advanced complementary metal–oxide-semiconductor (CMOS) devices.

Although ammonium nitrate (AN) is a clean burning (chlorine free), non-corrosive, low-hazard, low-flame temperature, inexpensive, easily available energetic material and gives maximum gas horse power per unit weight, propellants incorporating AN suffer from three significant drawbacks: (1) polymorphic (phase) transition near ambient temperature, (2) caking and smoke generation upon burning, and (3) poor flowability for packing. The first two disadvantages could be minimized by forming non-hygroscopic, smokeless 1:1 co-crystals of ammonium nitrate–benzo-18-crown-6 (1:1 co-crystals of AN–B18C6) with a melting point of 125–129 °C, produced from the antisolvent precipitation method based on the systems of: ethanol–methyl-tert-butyl-ether (MTBE), methanol–ethyl acetate and methanol–MTBE. From the smoke test and burning characteristics, 1:1 co-crystals of AN–B18C6 is smokeless upon heating and exhibits a slower burning rate than the one of AN. Therefore, co-crystallization may become a solid-state modification method in the areas of propellants and explosives. The third drawback could further be eliminated by forming spherical agglomerates of 1:1 co-crystals of AN–B18C6 through the addition of water as a bridging liquid into the co-crystal slurry resulted at the end of the antisolvent precipitation method. Spherical agglomerates of 1:1 co-crystals of AN–B18C6 grown from Phase IV AN powders (0.32 mmol) and B18C6 crystals (0.32 mmol) in 0.64 mL methanol + 11.6 mL MTBE + 0.08 mL water gave relatively high yield of 87.3%, high population density of 20.6/cm3, high sphericity, of 0.86, high friability of 100 showing a greater strength, and low angle of repose of 25.2° indicating a good flowability.

This study fabricates the optically active uniform SiGe/Si multiple quantum well (MQW) nanorod and nanodot arrays from the Si0.4Ge0.6/Si MQWs using nanosphere lithography (NSL) combined with the reactive ion etching (RIE) process. Compared to the as-grown sample, we observe an obvious blueshift in photoluminescence (PL) spectra for the SiGe/Si MQW nanorod and nanodot arrays, which can be attributed to the transition of PL emission from the upper multiple quantum dot-like SiGe layers to the lower MQWs. A possible mechanism associated with carrier localization is also proposed for the PL enhancement. In addition, the SiGe/Si MQW nanorod arrays are shown to exhibit excellent antireflective characteristics over a wide wavelength range. These results indicate that SiGe/Si MQW nanorod arrays fabricated using NSL combined with RIE would be potentially useful as an optoelectronic material operating in the telecommunication range.

The taste sensing capabilities of a “biomimetic tongue” based on the photoluminescence (PL) responses of metal–organic frameworks (MOFs), [In(OH)(bdc)] n (bdc=1,4-benzenedicarboxylate), [Tb(btc)] n (MOF-76, btc=benzene-1,3,5-tricarboxylate), and [Ca 3 (btc) 2 (DMF) 2 (H 2 O) 2 ]·3H 2 O are proven on aqueous solutions of five basic tastants: sucrose (sweet), caffeine (bitter), citric acid (sour), sodium chloride (salty) and monosodium glutamate (umami). For [In(OH)(bdc)] n , the tastant interacts stereochemically with poly(acrylic acid) (PAA) and alters its conformations. The frequency and magnitude of chelation between COO − pendant groups of PAA and In 3+ nodes of [In(OH)(bdc)] n framework influence the corresponding PL reponses. For MOF-76, the tastant interacts with incorporated water in MOF-76 through hydrogen bonding. The limitation of O–H bond stretching of water results in the enhancement of the PL intensity. For [Ca 3 (BTC) 2 (DMF) 2 (H 2 O) 2 ]·3H 2 O, it is added as a third MOF component to increase the precision on taste discrimination. The significance of MOF-based “biomimetic tongue” includes: (1) PAA on [In(OH)(bdc)] n mimics the taste receptor cells (TRCs) for their structural flexibility, (2) the Weber-Fechner law of human sensing that sensation is proportional to the logarithm of the stimulus intensity is observed between the PL emission response of MOF-76 and the concentration of tastant, (3) the strength of taste is quantified by the τ scale and the PL emission intensity of MOF-76, which are dependent on the logarithmic tastant concentration, (4) the tastant is identified by the shape of the 3D principal component analysis contour map (i.e., pattern recognition method), and (5) the fabrication of [In(OH)(bdc)] n /PAA film by brushing is illustrated.

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