The ability to tune the functional interface of single-walled carbon nanotubes in a versatile manner is key to the success of deploying them as an active material in chemical and biological sensors. Here we present an overview of our device strategies demonstrating the use of controlled electrochemical functionalization to tune this interface by bringing in different functionalities ranging from metallic nanoparticles to biomolecules onto the nanotube surface. The extent of such a functionalization is tunable, providing us with a good control over sensitivity, selectivity, and detection limit of the realized sensors. Moreover, the sensor mechanisms have been analyzed. Taken together the methods and results outlined here constitute a general framework for the rational design of nanoscale field-effect-based chemical sensors and biosensors.

We use the first-principles GW + Bethe–Salpeter equation approach to study the electronic structure and optical absorption spectra of uniaxial strained graphene. Applied strain induces an anisotropic Fermi velocity and tilts the axis of the Dirac cone. As a result, the optical response of strained graphene is dramatically changed; the optical absorption is anisotropic; the characteristic single optical absorption peak of pristine graphene is split into two peaks with enhanced excitonic effects. Within the infrared regime, the optical absorbance of uniaxial strained graphene is no longer a constant because of the broken symmetry and anisotropic excitonic effects. Within the visible-light regime, we observe a prominent optical absorption peak due to an enhanced red shift by electron–hole interactions, enabling us to change the visible color and transparency of stretched graphene. Finally, we also reveal enhanced excitonic effects within the ultraviolet regime, where a few nearly bound excitons are identified.

Large-scale industrial production of carbon nanotubes (CNTs) has recently become available, but there are relatively few reports of the investigation of these industrially produced bulk CNTs as potential electrode materials for electrochemical energy storage such as lithium-ion batteries (LIBs). Here, we report our evaluation of the electrochemical performance of the industrially produced CNTs from one manufacturer and our utilization of a kinetically controlled, vapor diffusion synthesis method combined with in-situ carbothermal reduction to homogeneously grow nanocrystalline tin (Sn) particles (∼200 nm) in the matrix of the CNTs, yielding a Sn@CNTs composite. After surface coating with a layer of carbon coating (3–4 nm), this composite was transformed to a surface-modified Sn@CNTs composite that exhibited much higher reversible capacity, initial Coulombic efficiency, and rate capacity than the pristine CNTs as anode materials for LIB.

A TiO2/carbon nanotubes (TiO2/CNTs) composite was synthesized by chemical vapor deposition method with in situ growth of CNTs using hydrothermally treated TiO2 as the starting material. The nanocomposite was characterized by powder x-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectrum, and nitrogen adsorption/desorption isotherms and was investigated as an anode material for lithium-ion batteries. The underlying mechanism for the improvement was analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. The in situ synthesized composite showed better electrochemical performance than the pristine TiO2. The in situ formed CNTs not only supply an efficient conductive network but also keep the structural stability of the TiO2 particles, leading to improved electrochemical performance.

We report synthesis of nanosize LiFePO4 and C-LiFePO4 powders with a narrow particle size distribution (20–30 nm) by ethanol-based sol–gel method using lauric acid (LA) as a surfactant for high specific capacity lithium-ion battery cathode material. X-ray diffraction measurements demonstrated that the samples were single-phase materials without any impurity phases. The average crystallite size was found to decrease slightly from 29 nm to approximately 23 nm with carbon coating. The ratio of the Raman D-band (∼1350 cm−1) to G-band (∼1590 cm−1) intensities (ID/IG) and electronic conductivity of these materials show strong dependence on the amount of surfactant coverage. Remarkably, cell prepared with carbon-coated LiFePO4 synthesized using 0.25 M solution of LA showed a very large specific capacity approaching the theoretical limit of 170 mAh/g, in stark contrast to the specific capacity of cell consisting of pure of LiFePO4 (∼75 mAh/g) measured at the same C/2 discharge rate.

The role played by catalyst aggregates in the growth of carbon nanocoils (CNCs) by a chemical vapor deposition (CVD) method has been studied. The experimental results show that CNCs can be grown from the discrete aggregates on a substrate with a porous surface, while only some irregular carbon nanofibers are grown from those on a flat substrate. It is accepted from the viewpoint of mechanics that the spiral motion of a CNC should generate a torsional moment on its base that attaches to an aggregate. The catalyst particles readily expand on the flat substrate during the CVD process and form a loose aggregate, which cannot provide a strong interaction between the aggregate and the base of a carbon fiber grown from there. On the contrary, the expansion of catalyst particles in a microsized hole is restricted by the surrounding wall of the hole, leading to the formation of a compact aggregate that fixes the base of the grown fiber. A perfect CNC can be grown only under the condition that its base is firmly fixed by an aggregate that can balance the torsional moment of the CNC during its spiral growth.

A strategic scheme for controlling the shape of titania nanorods while maintaining their highly crystallized state was investigated in terms of the effects of reactant concentration and temperature change on the formation mechanism. Lowering the temperature from 433 to 413 K markedly slowed down the reaction rate and resulted in the coexistence of amorphous-like films and crystalline titania nanorods due to the concurrence of nucleation out of the amorphous phase and particle growth by crystallization. Based on these findings, a strategy for shape control was proposed and long, high aspect ratio titania nanorods in a highly crystallized state were successfully synthesized.

Interrod regions exist between the enamel rods and are known to have different crystallite orientations and a higher organic content compared to the enamel rods (the intrarod regions). This study aims to characterize the mechanical properties of both regions especially the time-dependent properties by using spherical indentation. Despite the very small amount of proteins, the interrod region shows statistically significantly higher inelastic energy dissipation than the intrarod region with increased deformation times. The total displacement under constant load (creep), viscosity, and stress relaxation behavior of both regions are also reported. Similar to the observation of previous studies, the elastic modulus and hardness in the intrarod region are significantly higher than in the interrod region.

Polyaniline (PANI) microtubes were successfully synthesized by a simple way without using any templates. Their structure was characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, ultraviolet–visible absorption spectra, and Fourier transform infrared spectroscopy. The average length and diameter of the microtubes were about 12.0 and 3.0 μm, respectively. In addition, silver microrods were further prepared using the PANI microtubes as templates. Scanning electron microscopy, energy-dispersive x-ray spectra, x-ray diffraction, and ultraviolet–visible absorption spectra analyses were performed to characterize the structure of the sample. The results indicated the formation of silver microrods inside PANI microtubes. Moreover, the microwave absorption and electrical properties of PANI microtubes, PANI particles, and silver microrods were compared. It shows that the silver microrods coated with PANI have good microwave absorption and electrical properties, which can apply on electromagnetic interference shielding and microwave absorption materials.

Protocols are developed to assess viscoelastic moduli from unloading slopes in Berkovich nanoindentation across four orders of magnitude in time scale (0.01–100 s unloading time). Measured viscoelastic moduli of glassy polymers poly(methyl methacrylate), polystyrene, and polycarbonate follow the same trends with frequency (1/unloading time) as viscoelastic moduli generated from dynamic mechanical analysis and broadband viscoelastic spectroscopy but are 18–50% higher. Included in the developed protocols is an experimental method based on measured indent area to remove from consideration indents for which viscoplastic deformation takes place during unloading. Ancillary measurements of indent area and depth reveal no detectable (∼1%) change in area between 200 s and 4.9 days following removal of indenter.

The relationship between hardness and flow stress in glassy polymers is examined. Materials studied include poly(methylmethacrylate), polystyrene, and polycarbonate. Properties are strongly rate dependent, so broadband nanoindentation creep (BNC) is used to measure hardness across a broad range of indentation strain rates (10−4 to 10 s−1). Molybdenum (Mo) is also studied to serve as a “control” whose rate-dependent hardness properties have been measured previously and whose flow stress, unlike the polymers, is pressure insensitive. The BNC hardness data are converted to uniaxial flow stress using two methods based on the usual Tabor–Marsh–Johnson correlation. With both methods the resulting BNC-derived uniaxial flow stress data agree closely with literature compression uniaxial flow stress data for all materials. For the polymers, the BNC hardness data depend on initial rate of loading, indicating that the measured properties are path dependent. Path dependence is not detected in Mo.

This article presents a novel microscratch technique for the determination of the fracture toughness of materials from scratch data. While acoustic emission and optical imaging devices provide quantitative evidence of fracture processes during scratch tests, the technique proposed here provides a quantitative means to assess the fracture toughness from the recorded forces and depth of penetration. We apply the proposed method to a large range of materials, from soft (polymers) to hard (metal), spanning fracture toughness values over more than two orders of magnitude. The fracture toughness values so obtained are in excellent agreement with toughness values obtained for the same materials by conventional fracture tests. The fact that the proposed microscratch technique is highly reproducible, almost nondestructive, and requires only small material volumes makes this technique a powerful tool for the assessment of fracture properties for microscale materials science and engineering applications.

Dynamic tensile strength of polyurea is measured at an ultrahigh strain rate of 1.67 × 107 s−1 by generating spall failures inside thick polyurea coatings bonded to steel plates using laser-generated stress waves of several nanoseconds in duration. Specifically, thick polyurea films were cast on a steel plate whose backside was provided with water glass–covered Al film. The Al film was melted by focusing a high-energy Nd:YAG laser pulse over 3-mm-diameter area. Exfoliation of the Al generated a compressive stress wave toward the polyurea coating, which turned tensile upon reflection from the free surface. At a threshold laser energy, the amplitude of the returning tensile stress wave exceeded the dynamic tensile strength of polyurea. The stress wave profile inside the steel plate was interferometrically recorded at the threshold laser fluence and was used in a wave mechanics simulation to calculate the peak tensile stress. The polyurea was modeled as a viscoelastic solid.

Bulk ceramics In2−xGexO3 have been synthesized in air by using citrate gel process. Nanoparticles of less than 20 nm have been synthesized through an accurate control of the processing parameters. X-ray diffraction and scanning electron microscopy studies confirmed that the solubility limit of Ge in In2O3 (xℓ) is very small and that additions of more than about 0.5 at.% Ge lead to the presence of In2Ge2O7 inclusions. Thanks to a high interdispersion of metal ions and homogeneity in elemental composition of the nanopowders obtained by citrate gel process, well-dispersed In2Ge2O7 secondary phases can be formed in the Ge-doped In2O3 matrix. An abrupt increase in the electrical conductivity and in the carrier concentration with x is observed in the monophasic region (x < xℓ), whereas in the biphasic region (x > xℓ), these values do not vary significantly. Similarly, the thermopower |S| value is correlated to this variation decreasing as x increases for x < xℓ. Above the solubility limit, the decrease in the lattice thermal conductivity is shown to be dependent on the presence of well-dispersed In2Ge207 secondary phases. The dimensionless figure of merit value is increased up to 0.3, thanks to electron doping and phonon scattering.