Y. Norman Zhou

Hydrothermal growth of free standing TiO2 nanowire membranes for photocatalytic degradation of pharmaceuticals

Highly entangled TiO(2) nanowires were directly synthesized by hydrothermal growth on Ti substrates at 180 °C utilizing various organic solvents to oxidize Ti. The growth mechanism, microstructure and phase transition of TiO(2) nanowire membranes were investigated in detail. TiO(2) nanowires, with diameters of 10-20 nm and lengths up to 100 μm, show a phase transition from Type-B to anatase by annealing at 700 °C. Robust, free standing TiO(2) nanowire membranes with millimeter level thickness can be cleaved from Ti substrates or directly prepared from thin Ti foils. These porous TiO(2) membranes, while effective for mechanical microfiltration, can also photocatalytically degrade pharmaceuticals such as trimethoprim under UV irradiation.

Joining of Silver Nanomaterials at Low Temperatures: Processes, Properties, and Applications.

A review is provided, which first considers low-temperature diffusion bonding with silver nanomaterials as filler materials via thermal sintering for microelectronic applications, and then other recent innovations in low-temperature joining are discussed. The theoretical background and transition of applications from micro to nanoparticle (NP) pastes based on joining using silver filler materials and nanojoining mechanisms are elucidated. The mechanical and electrical properties of sintered silver nanomaterial joints at low temperatures are discussed in terms of the key influencing factors, such as porosity and coverage of substrates, parameters for the sintering processes, and the size and shape of nanomaterials. Further, the use of sintered silver nanomaterials for printable electronics and as robust surface-enhanced Raman spectroscopy substrates by exploiting their optical properties is also considered. Other low-temperature nanojoining strategies such as optical welding of silver nanowires (NWs) through a plasmonic heating effect by visible light irradiation, ultrafast laser nanojoining, and ion-activated joining of silver NPs using ionic solvents are also summarized. In addition, pressure-driven joining of silver NWs with large plastic deformation and self-joining of gold or silver NWs via oriented attachment of clean and activated surfaces are summarized. Finally, at the end of this review, the future outlook for joining applications with silver nanomaterials is explored.

Preparation of PVP coated Cu NPs and the application for low-temperature bonding

There is an increasing interest in developing a low temperature interconnection process using nanoparticles. Some studies focus on bonding using Ag nanoparticles (Ag NPs). However, few studies investigate a bonding process using Cu nanoparticles (Cu NPs) due to the easy oxidation in air. Here we achieve a robust bonding of Cu wires to Cu pads with polyvinylpyrrolidone (PVP) coated Cu NPs at a low temperature of 170 °C. The PVP coating can effectively prevent the oxidation of Cu NPs when heated in air. The bonding is formed through the sintering of Cu NPs and direct metallic bonding between the sintered Cu particles and Cu pads. Electrical measurements of the Cu NPs demonstrate that Cu NPs have a low resistivity of 8.6 × 10−5 Ω cm after being sintered under pressure. This method has the potential to be used in the electrical packaging industry due to its economic cost, easy operation, and high conductivity.

Room-temperature pressureless bonding with silver nanowire paste: towards organic electronic and heat-sensitive functional devices packaging†

Heat-sensitive components packaging requires low temperature joining technology. The present study considers the feasibility of room-temperature pressureless joining of copper wires using silver nanowire paste. These joints achieve a tensile strength of 5.7 MPa and exhibit ultralow resistivity in the range of 101 nΩ m. An “in situ cleaning” action of PVP is proposed during the bonding process.

Palladium Nanoparticles Loaded on Carbon Modified TiO2 Nanobelts for Enhanced Methanol Electrooxidation

Carbon modified TiO2 nanobelts (TiO2-C) were synthesized using a hydrothermal growth method, as a support material for palladium (Pd) nanoparticles (Pd/TiO2-C) to improve the electrocatalytic performance for methanol electrooxidation by comparison to Pd nanoparticles on bare TiO2 nanobelts (Pd/TiO2) and activated carbon (Pd/AC). Cyclic voltammetry characterization was conducted with respect to saturated calomel electrode (SCE) in an alkaline methanol solution, and the results indicate that the specific activity of Pd/TiO2-C is 2.2 times that of Pd/AC and 1.5 times that of Pd/TiO2. Chronoamperometry results revealed that the TiO2-C support was comparable in stability to activated carbon, but possesses an enhanced current density for methanol oxidation at a potential of −0.2 V vs. SCE. The current study demonstrates the potential of Pd nanoparticle loaded on hierarchical TiO2-C nanobelts for electrocatalytic applications such as fuel cells and batteries.

Generation of oxygen vacancies in visible light activated one-dimensional iodine TiO2 photocatalysts

A facile and efficient way of generating oxygen vacancies in visible light activated one-dimensional iodine doped TiO2 photocatalysts was first reported in this work. A two-step hydrothermal synthesis was used to synthesize TiO2 nanomaterials modified by iodic acid (HIO3) as a dopant. Detailed analysis was conducted to illustrate the intrinsic doping/reaction mechanisms of iodic acid in the modification of the TiO2 matrix. The phase and structure evolution were deduced from X-ray diffraction (XRD), Raman, and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was conducted to analyze the generation of oxygen vacancies and the formation of I–O–Ti bonds in the TiO2 lattice. Multi-valences of iodine, due to the reduction of iodic acid, facilitated the generation of oxygen vacancies and 3d state Ti3+ species in the TiO2 lattice. The visible light absorption and enhanced photocatalytic activity of the TiO2 nanomaterials were attributed to existing oxygen vacancies, iodine multi-valences in I–O–Ti bonds, and 3d state Ti3+ sites in the TiO2 lattice. The photocatalytic degradation efficiency under visible light (λ > 400 nm) followed a pseudo first-order kinetic model. Rutile nanowires using a two-step synthesis method produced the highest methylene blue (10 mg L−1) degradation rate constant, Kap, of 7.92 × 10−3 min−1 compared to other synthesized nanomaterials. The Kap value obtained was an order of magnitude greater than commercial P25 (3.87 × 10−4 min−1) and pristine TiO2 nanowires (4.18 × 10−4 min−1). The iodine doped TiO2 photocatalysts can be used in TiO2/light irradiation advanced oxidation processes (AOPs) in water treatment using sunlight or a visible light source, rather than an ultraviolet irradiation source.

Highly localized heat generation by femtosecond laser induced plasmon excitation in Ag nanowires

Photo-excitation of plasmons in nano-systems initially results in highly localized heating, but the final temperature distribution in irradiated nanostructures is almost uniform because heat diffusion equilibrates the overall temperature within ∼10−12 s. Here, we show that irradiation with femtosecond pulses enables visualization of the location of plasmonic heating because thermal effects such as plasmon-induced melting are frozen in at the initial location of energy deposition. Simulations show plasmonic heating is related to the orientation of the laser polarization and to the geometry of partially melted nanowires. This may provide a useful tool in joining, cutting, and reshaping nano-objects.

Polymer-Protected Cu-Ag Mixed NPs for Low-Temperature Bonding Application

A simple method has been proposed to prepare polymer-protected Cu-Ag mixed nanoparticles (NPs), which are suitable for use as low-temperature bonding materials. The polymer coated on the Cu-Ag mixed NPs can protect them from oxidation effectively when heated in air at temperature lower than 280°C. The low-temperature bonding process utilizing Cu-Ag mixed NPs as the bonding material is investigated. The bonding experiments show that robust joints are formed using Cu-Ag mixed NPs at 160°C in air. The shear test shows that addition of copper to silver is helpful for improving joint strength. This novel sintering-bonding technology using Cu-Ag mixed NPs as an interconnection material has potential for application in the electronics packaging industry.

Functionalization of silver nanowire surfaces with copper oxide for surface-enhanced Raman spectroscopic bio-sensing

A facile method to fabricate copper oxide functionalized silver nanowires with high sensitivity to biomolecules is reported for the first time. The enhanced surface roughness of silver nanowire and the molecule capture capability of copper oxide nanoparticles account for the high sensitivity of this nanocomposite.

Microscopy study of snail trail phenomenon on photovoltaic modules

Snail trails on photovoltaic modules are a source of enormous concern to the solar industry as no scientific reports on the mechanisms producing this global phenomenon were previously available. Here, for the first time, we clarify the origin of these snail trails as a product of the formation of silver carbonate nanoparticles which discolor the silver grid. Micropore arrays on the silicon substrate within the snail trail region could accelerate the discoloration by offering reactive compounds via penetration and release. The potential mechanisms of photovoltaic module discoloration are proposed, yielding clues as to how snail trail formation can be mitigated by technical solutions. Aging tests on the discolored modules suggest no significant power degradation or discolored area enlargement after accelerated aging.