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.

This work presents key modeling aspects that are central to the manipulation of the decoration of metallic nanoparticles by a thin shell of a metal of different chemical nature. The concept of underpotential deposition is generalized to nanoparticles. An all-atom model, taking into account many-body interactions by means of the embedded atom potential, was used to represent nanoparticles of different sizes and atomic adsorbates on them. A full set of state-of-the-art computer simulations are performed for a model system, showing that selective decoration of facets is possible. The trends observed in the present work are in good qualitative agreement with experimental data reported very recently.

The ground-state structural, electronic, magnetic, optical and dielectric properties of MnTiO3 are calculated using density functional theory within the generalized gradient approximation. The structure parameters obtained agree well with experimental results. The electronic structure results show that the G-type antiferromagnetic phase of LN-type MnTiO3 has an indirect band gap of 0.85 eV. The calculated local magnetic moment of Mn ion is 4.19 μB. The calculated Born effective charges (BECs, denoted by tensor Z*) show that the Z* of Ti and O atoms are significantly and anomalously large. Interestingly, ferroelectric spontaneous polarization of large magnitude is predicted to be along [111] direction with a magnitude of 87.95–105.22 μC/cm2. B-site Ti ions in 3 d0 state dominate ferroelectric polarization of multiferroic MnTiO3, whereas A-site Mn ions having partially filled 3 d5 orbitals are considered to contribute to its antiferromagnetic properties. Furthermore, it is predicted that multiferroic MnTiO3 shows good dielectric and optical properties.

Low temperature solid oxide fuel cells (SOFCs) are a promising solution to revolutionize stationary, transportation, and personal power energy conversion efficiency. Through investigation of fundamental conduction mechanisms, we have developed the highest conductivity solid electrolyte, stabilized bismuth oxide (Dy0.08W0.04Bi0.88O0.36). To overcome its inherent thermodynamic instability in the anode environment, we invented a functionally graded bismuth oxide/ceria bilayered electrolyte. For compatibility with this bilayared electrolyte, we developed high performance bismuth ruthenate–bismuth oxide composite cathodes. Finally, these components were integrated into an anode-supported cell with an anode functional layer, resulting in an exceptionally high power density of ∼2 W/cm2 at moderate temperatures (650 °C) and sufficient power down to 300–400 °C for most applications. Moreover, because SOFCs can operate on conventional fuels, these low temperature SOFCs provide one of the most efficient energy conversion technologies available without relying on a hydrogen infrastructure.

The fabrication of capillary cylindrical crystals from colloidal suspension with controllable thickness by evaporation-induced self-assembly method has been investigated. The thickness of the hollow cylinders can be precisely controlled ranging from monolayer to tens of layers by varying the suspension concentration. With the increase of suspension concentration, the particles fill completely inside capillaries to form solid bulk crystals and the critical values are found in capillaries with various diameters. Scanning electron microscope images confirm the face-centered-cubic structure in both crystals, but with two different [111] crystalline directions. The experiment parameters, such as the solvent, concentration of the suspension and inner diameter of capillary are studied for the quality and the number of film layers control. Qualitative analysis has been performed to probe into the solvent evaporation modes and the mechanism of particle arrangement inside the capillary.

In any electrochemical device, the interface between electrolyte and electrode should be the only “legitimate” location where redox reactions happen. Particularly in Li ion batteries, these interfaces become “interphases” due to the reactivity of the electrode materials used, and they mainly consist of chemical species from the sacrificial decomposition of electrolyte components. Since the emergence of Li ion technology, it has been recognized that interphase on graphitic anodes, usually referred as SEI (solid electrolyte interphase) after its electrolyte attributes, is the key component supporting the reversibility of Li+-intercalation chemistry. Research attention focused on this component during the past two decades has led to substantial understanding about both its chemistry and mechanism. This article summarizes these progresses, and elaborates on the relatively recent insights, including the effect of Li+-solvation sheath structure on the interphasial processes at graphitic anode. A new strategy of forming a more desirable interphase is also discussed.

To study the effect of nanotwins on thermal stability, a comprehensive characterization study was performed on two types of ultrafine grained (UFG) copper samples, with and without nanotwins. The two samples were sequentially heat-treated at elevated temperatures, and the grain size, grain boundary character, and texture were characterized after each heat treatment. The as-prepared nanotwinned (nt) copper foil had an average columnar grain size of ∼700 nm with a high density of coherent twin boundaries (CTBs) (twin thickness, ∼40 nm), which remained stable up to 300 °C. In contrast, the other UFG sample had few CTBs, and rapid grain growth was observed at 200 °C. The thermal stability of nt copper is discussed with respect to the presence of the low energy nanotwins, triple junctions between the twins and columnar grains, texture and grain growth.

In this paper, a novel sintering method is introduced for the forming of microcomponents in which the loose powders were loaded directly into the die, sintered with an external electric field, a thermal field, and an external stress field (called coupled multifields activation), where the fields were generated by a Gleeble thermal simulation instrument. Two kinds of 316L stainless steel powders of different particle sizes (20 and 70 μm) with no binder were sintered with microforming using a multifield coupling method. For particle size of 20 μm, a nearly fully densified microsintered compact (relative density is 99.2%) was manufactured at a relatively low sintering temperature (900 °C) and within a relatively short sintering time (4 min). The fluctuated temperature–time curve reveals that the rapid mass transfer of liquid phase is the dominant densification mechanism in the compacts with a starting particle size of 20 μm.

The effects of the barium/titanium (Ba/Ti) ratio on the crystalline phase, Curie temperature, and dielectric properties of solid-state-reacted BaTiO3 powder were investigated. The experimental results showed that tetragonality decreased and the Curie temperature shifted to lower temperature when the Ba/Ti ratio strayed from 1.0. The BaTiO3 powder had the maximum dielectric constant when the Ba/Ti approaching 1.0.

The high-density tungsten bronze (TB) Sr2-xCaxNaNb5O15 (SCNN, 0.05 ≤ x ≤ 030) lead-free ceramics were prepared by two-step solid-state reaction method. With increasing Ca2+ substitution, the crystal structure of SCNN ceramics slightly distorted from the TB tetragonal phase and became orthorhombic phase at room temperature. The smaller ionic radius of Ca2+ (1.34Å) compared with that of Sr2+ (1.44Å) contributed to the shrinkage of the crystal structure. Dielectric spectra of all compositions displayed two phase transitions: the ferroelastic orthorhombic to ferroelectric tetragonal phase transition (Te) at lower temperatures, and the ferroelectric to paraelectric phase transition (Tc) at higher temperatures. With increasing Ca2+ substitution, Te and Tc shifted towards higher temperature regions, while the maximum values of dielectric constant (εme and εm), Pr, Ec and d33 increased at first and then decreased. The ceramics with most homogeneous microstructure and highest density were obtained at x = 0.15, resulting in optimized properties.

The indentation size effect (ISE) and the bilinear behavior for pure face centered cubic (FCC) metals including aluminum, nickel, silver, and 70/30 copper–zinc (α-brass) alloy using a single Berkovich indenter tip in a single test machine were investigated. The results confirmed that this behavior is mechanistic in nature and were consistent with those reported by A.A. Elmustafa and D.S. Stone [J. Mech. Phys. Solids51, 357–381 (2003)] of the ISE and the bilinear behavior using two separate indenter tips (Berkovich and Vickers) from two separate machines. Therefore, the bilinear behavior is present regardless of tip geometry or machine used. We also investigated the cause for a deviation in the continuous stiffness measurement (CSM) data from discrete data points obtained using the load control protocol at shallow depth. We conducted experiments near grain boundaries to determine if the CSM deviation at shallow depths were caused by a hardening effect due to dislocation interaction with the interface.

We have demonstrated resistance switching using polycrystalline HfO2 film with a Cu top electrode for nonvolatile memory applications and revealed the Cu diffusion into the HfO2 layer during the filament formation process. Resistive switching was clearly observed in the Cu/HfO2/Pt structure by performing a current–voltage measurement. The current step from a high-resistive state to a low-resistive state was of the order of 103–104 Ω, which provided a sufficient on/off ratio for use as a switching device. The filament formation process was investigated by employing hard x-ray photoelectron spectroscopy under bias operation. The application of a bias to the structure reduced the Cu2O state at the interface and the intensity ratio of Cu 2p3/2/Hf 3d5/2, providing evidence of Cu2O reduction and Cu diffusion into the HfO2 layer. These results also provide evidence that the resistance switching of the Cu/HfO2/Pt structure originates in a solid electrolyte (nanoionics model) containing Cu ions.

Optimizing thermoelectric (TE) materials and modules are important factors, which can lead to widespread adoption of waste heat recovery systems. The analytic co-optimization of the TE leg, heat sink, and the load resistance shows that all parameters entering the figure-of-merit (Z) do not have the same impact on cost/performance trade-off. Thermal conductivity of the TE material plays a more important role than the power factor. This study also explores the impact of heat losses and the required contact resistances. Finally, we present the theoretical cost performance ($/W) of TE waste heat recovery systems for vehicle waste heat recovery application, assuming hot side gas temperature of 600 °C and a cooling water temperature of 60 °C.

Amorphous films [BaTiO3 (BTO), SrTiO3 (STO), SrRuO3] on substrates and self-supported films (BTO and STO) were produced by controlling the film/substrate adhesion energy (level of clamping). The stress value in an as-deposited film depends on the clamping level, which defines the stress relief mode. In highly stressed films, the stress abatement is achieved via plastic transformation resulting in formation of “the strain-arranged structure of elastic domains.” Film fractures and delamination occur if the stress magnitude is too high and exceeds the elastic limit of the material. If the stress magnitude is low, the conditions favorable for nucleation and crystallization can arise. Stress in self-supported films is relieved mainly via shape change during film preparation, and the conditions favorable for nucleation and crystallization in annealed self-supported films arise more frequently.

We present experimental evidence of enhancement of thermoelectric properties in tellurium (Te) nanoparticle-embedded bismuth antimony telluride (BiSbTe) alloys. Bi0.5Sb1.5Te3 films with a high density of Te particles of 10–20 nm size were prepared by growth of alternating multilayers of ultrathin Te and Bi0.5Sb1.5Te3. As the amount of Te nanoinclusions increased up to ∼15%, the Seebeck coefficient and thermoelectric power factor were increased. Based on the concept of band bending at heterointerfaces as a carrier energy filter, the energy relaxation calculation was made to confirm that the Te nanoinclusions result in a carrier energy filtering effect in p-type bismuth antimony telluride. In addition, thermal conductivities were reduced in the Te-embedded samples, permitting possible further enhancement of the thermoelectric figure of merit. The advantages of Te nanoinclusions in p-type Bi0.5Sb1.5Te3alloys on thermoelectric performance are experimentally realized by both electron- and phonon scattering.

In view of the complexity of thin-film solar cells, which are comprised of a multitude of layers, interfaces, surfaces, elements, impurities, etc., it is crucial to characterize and understand the chemical and electronic structure of these components. Because of the high complexity of the Cu2ZnSn(S,Se)4 compound semiconductor absorber material alone, this is particularly true for kesterite-based devices. Hence, this paper reviews our recent progress in the characterization of Cu2ZnSnS4 (CZTS) thin films. It is demonstrated that a combination of different soft x-ray spectroscopies is an extraordinarily powerful method for illuminating the chemical and electronic material characteristics from many different perspectives, ultimately resulting in a comprehensive picture of these properties. The focus of the article will be on secondary impurity phases, electronic structure, native oxidation, and the CZTS surface composition.