As a narrow gap, strongly correlated electron semiconductor, FeSb2 single crystals can exhibit a colossal thermopower1 (on the order of −40,000 μV/K or greater) and a relatively high lattice thermal conductivity2 (over 300 W/m-K) at temperatures around 10 K. In this work, a series of FeSb2 polycrystalline samples with different amounts of additional Indium were prepared by a quench-and-anneal method followed by a spark plasma sintering procedure. The x-ray diffraction, scanning electron microscopy, and elemental analysis verified that the Sb/InSb nanoinclusions were formed in situ on the boundaries of coarse FeSb2 grains. The presence of such nanoinclusions and other as-formed multiscale microstructures can scatter phonons and thus dramatically reduce the corresponding lattice thermal conductivity. Furthermore, the electrical properties can be also improved because of the addition of high mobility carriers from the InSb nanoinclusions. Overall, FeSb2-based materials have shown some promising potential for possible thermoelectric cooling applications at cryogenic temperatures.

This study describes the elimination of threading dislocations (TDs) in GaN nanostructures. Cross-sectional transmission electron microscopy (XTEM) analysis reveals that the nominal [0001] line direction of a TD changes when it enters a GaN nanostructure and the dislocation then terminates at a sidewall facet. It is suggested that the driving force for this process is the reduction of dislocation line energy, and for a pure-edge dislocation, this TD elimination process can be accomplished simply by dislocation climb. This mechanism is active whenever a threading defect is in close proximity to a surface. Preliminary XTEM analysis of defects in AlGaN and InGaN core–shell growth onto GaN nanostructures is also shown. Although more work is required to improve the quality of core–shell InGaN epitaxial growth, nanostructures appear to offer a route to defect-free, nonpolar GaN-based devices.

A low-temperature synthesis method for preparing nanosized TiO2 crystallites has been developed based on a Pluronic F127 microemulsion system. Both anatase and rutile polymorphs can be prepared, and there exists a temperature window between 40 and 50 °C where the formation of rutile is favored over anatase. At 60 °C and above, anatase is kinetically favored and only very slowly transforms to rutile at 60 °C. The results differ from previous observations regarding formation kinetics and temperature range for rutile formation as well as in the microscopic aggregation of the formed nanoparticles. This development of a low-temperature synthesis of crystalline titania nanoparticles within the Pluronic block copolymer system is an important and enabling step toward devising a direct synthesis route for the formation of ordered mesoporous and crystalline titania.

Thin-film aggregation characteristics of a series of oligothiophenes with a central thieno[3,4-b]thiophene ester unit and 4 (M5), 8 (M9), and 16 (M17) regioregular hexylthiophene units were investigated. These oligomers exhibited length-dependent self-assembly characteristics upon spin coating. M9 formed long fibers, while M5 and M17 formed random domains. Grazing incidence x-ray diffraction was performed to understand the reason for this length dependence. The M5 had a dominant ester–ester interaction that disrupted long-range order. The M9 morphology was due to a balance of orthogonal backbone and ester effects, which imposed long-range order on the M9 aggregates. Meanwhile, the M17 ester chain had a smaller relative contribution to packing and functioned as a molecular defect, disrupting long-range order. As a result, though the local self-assembly between monomers was very similar for the molecules, backbone length dependent changes in intermolecular forces dominated long-range structure. The analysis of self-assembly characteristics in these materials provides guidance in the design of organic conjugated materials for use in semiconductor devices.

Phase structures of microscale and nanoscale higher manganese silicides (HMSs) were investigated using in situ energy dispersive x-ray diffraction at high temperatures or/and high pressure. A few phase transformations accompanied with the presence of MnSi phase were observed in different temperature regions, which were associated with the interevolution of several incommensurate HMS phases. It was found that in nanostructured HMS, the interevolution of HMS was remarkable and accelerated compared to that in the micropowders. Meanwhile, high pressure was able to influence these phase transformations due to giant strain in the materials. The phase transformations were discussed from thermodynamic aspects with respect to the different formation enthalpy of Mn–Si system and the large surface energy and structural instability of the nanopowders.

Syntaxial growth of Mn11Ge8/Ge nanowire heterostructures was carried out using a vapor–solid–solid (VSS) growth process, and transmission electron microscopy imaging and selected-area electron diffraction were used to study the structure, orientation, and interface of each phase. Preferred crystallographic relationships were found to exist between the Mn11Ge8 seeds, which exhibit a single uniaxial growth direction, and the seeded Ge nanowires, which exhibit multiple growth directions. The crystallographic relationships for individual nanowire heterostructures were characterized in the context of microtexture analysis, which has not previously been applied to nanowire heterostructures. Fiber and off-normal fiber textures were predominant, although examples of epitaxial and uniaxial in-plane textures were also identified. Microtexture analysis of VSS-grown nanowire systems is shown to provide a useful perspective on the products of synthesis that can lead to new insights into growth mechanisms.

It was observed that silicon and germanium nanowires can exhibit significant electrostatic charging and respond strongly to externally applied electric fields. This includes nanowires in air and dispersed in low-conductivity, low-dielectric-constant solvents such as hexane, toluene, and benzene. The electrostatic charging of semiconductor nanowires was investigated as a tool for nanowire manipulation. By charging a substrate, nanowires could be deposited on surfaces with very high coverage and onto selected locations of the surface. The density of deposited nanowires could be adjusted systematically by varying the strength of the electric field. Alternating electric fields, applied between two electrodes, resulted in nanowires oriented with respect to the field orientation.

We have developed novel photovoltaic systems composed of the fullerene derivative (6,6)-phenyl C61 butyric acid methyl ester as electron acceptor with a second functional organic molecule, in this case bacteriochlorophyll c, as the light-harvesting and photosensitizing part. It was found that heat treatment of a thin film of bacteriochlorophyll c altered the morphological states of the aggregates and conductivity of the thin film could be regulated through the annealing process. Blended fullerene derivative and bacteriochlorophyll c thin films were fabricated on the surface of an indium-tin oxide/poly(ethylene dioxythiophene) doped with polystyrene sulfonic acid substrate layer and their photovoltaic properties were characterized and evaluated. Formation of fullerene-coordinated bacteriochlorophyll c complex was confirmed by changes in the visible absorption spectra and by FTIR. Such complexation promoted generation of photocurrent in the region of the Qyband and the current density of the thin film increased. A maximum incident photon-to-current conversion efficiency of 5.1% was attained at 745 nm.

Nowotny chimney-ladder compounds RuAl2 and RuGa2 have been substituted with p- and n-type dopants to study the resistivity, Seebeck and Hall coefficients, and thermal conductivity of resulting compounds in the temperature range of 80–300 K. The resistivity and Seebeck coefficient suggest that these compounds are degenerate semiconductors. Hall measurements reveal that the carrier concentration has indeed been changed by an order of magnitude, particularly in p-type RuGa2 by substituting Cr and Mn. Compared to p-type samples, the resistivity is an order of magnitude larger for n-type samples, for a similar level of carrier concentration. Interestingly, the hole mobility is two to three orders of magnitude larger, reaching the highest value of ∼750 cm2/V·s. The electron mobility is temperature independent and is typically in the range of ∼1–4 cm2/V·s. Thermal conductivity shows characteristics of mixed scattering with impurity scattering contributing appreciably in heavily substituted compositions.

The Y-doped (Hf0.6Zr0.4)1-xYxNiSn (x = 0, 0.01, 0.02, 0.04, 0.06, 0.1, and 0.2) half-Heusler alloys have been prepared by levitation melting and spark plasma sintering. The effect of Y doping on thermoelectric properties of the alloys was investigated in the temperature range of 300–900 K. Y-doped samples had the lower electrical conductivity compared with the parent compound without Y doping. The thermal conductivity had weak dependence on Y doping content. The absolute values of Seebeck coefficient decreased significantly when x < 0.04. The sign of Seebeck coefficient turned from negative to positive at room temperature for x = 0.04 and 0.1, which means that the hole carriers became dominant in these alloys. However, the alloys changed to n-type conduction again at high temperatures. The maximum figure of merit value of about 0.45 was obtained at 780 K for the undoped sample.

SrAl2O4:Eu2+,Dy3+ polynary complex nanobelts with long-persisting phosphorescence were synthesized via a facile but efficient combustion method followed by a postannealing reaction at temperature above 900 °C. All the samples emit greenish-yellow light from the d-f transition of Eu2+, and moreover, their wavelength redshifts with increasing calcination temperature since the increase in crystal size and crystalline quality causes a large average optical path and high crystal symmetry, respectively. The decay constant of the sample calcined at low temperature is smaller than that of the one annealed at high temperature owing to the presence of higher densities and depths of electron traps donated by host defects, and the initial brightness of the sample calcined at low temperature is relatively low owing to the small volume fraction from relatively low crystallinity.

The self-assembling properties of two rationally designed discotic π-conjugated hexaazatrinaphthylene (HATNA) molecules have been studied. In appropriate solvent systems, both ester-dodecyl-substituted and amide-dodecyl-substituted HATNAs self-assembled into nanowires and formed organogels. These nanowires could be easily transferred onto solid supports through spin casting for morphological study. In addition to the solution-based self-assembly method, solvent-vapor annealing (SVA) was explored as an alternative way to control the organization of supramolecular nanowires on surfaces. It was found that amorphous thin film of HATNA molecules transformed gradually into nanowire structures through a nucleation and growth mechanism during the SVA process. Several parameters including the preordering of molecules in the original thin film, choice of solvent vapors, annealing times, and surface properties were tuned to create different supramolecular organizations. Under particular conditions, aligned nanowires with preferential direction can be achieved.

Half-Heusler (HH) and especially TiNiSn-based alloys have shown high potential as thermoelectric (TE) materials for power generation applications. The reported transport properties show, however, a significant spread of results, due mainly to the difficulty in fabricating single-phase HH samples in these multicomponent and multiphased systems. In particular, little attention has been paid to the influence of the various minority phases on the TE performance of these compounds. A clear understanding of these issues is mandatory for the design of improved and stable TE HH-based composites. This study examines the structural and compositional influence of the residual metallic (Sn) and intermetallic phases (mainly Ti6Sn5 and the Heusler compound TiNi2Sn) on the TE properties of the TiNiSn HH compounds processed by spark plasma sintering.

Five lipids were self-assembled in aqueous dispersions into high axial ratio nanostructures. Thermal analysis was conducted on a glycolipid self-assembled into nanotubes, previously developed by Kamiya et al. [S. Kamiya, H. Minamikawa, J-H. Jung, B. Yang, M. Masuda, and T. Shimizu, Langmuir21, 743 (2005)], showing a dry melting onset of 148.2 °C and evidence of a highly ordered supramolecular structure. A novel hybrid structure of the glycolipid nanotubes decorated with silver nanoparticles was created. The self-assembly of four new amphiphiles, with serine and glutamic acid head groups attached to vaccenic acid and diacetylenic hydrophobic tails, was also investigated. The morphologies of these aggregates included high axial ratio nanostructures, such as nanotubes; and flat, twisted, and helical ribbons. The supramolecular aggregates of the five lipids reflect aspects of the molecular structure, such as chirality, providing evidence that such organized aggregates can be created by a rational approach to molecular design.

A simple and controllable fabrication of TiO2 nanowires by electrospinning and their applications to the electron transporting layer for hybrid organic–inorganic photovoltaic cells are reported. TiO2 nanowires were directly electrospun onto an indium tin oxide on glass substrate from a solution in methanol of polyvinylpyrrolidone, titanium(IV) butoxide, and acetylacetone. The nanowire electrode obtained was consequently subjected to calcination at 450 °C. Solution of blended [6,6]-phenyl-C61-butyric acid methyl ester and poly(3-hexylthiophene) was spin coated on the TiO2 nanowire electrode, followed by thermal annealing and deposition of Au electrode. Hybrid organic–inorganic photovoltaic cells made of TiO2 nanowires exhibited remarkable improvement of the cell efficiencies in terms of photocurrent density and open-circuit voltage as compared with those of references, TiO2 flat films. Maximum energy conversion efficiency of hybrid organic–inorganic photovoltaic cells made of TiO2 nanowires of 1.27% was achieved.

One of the challenges in the development of molecular scale devices is the integration of nano-objects or molecules onto desired locations on a surface. This integration comprises their accurate positioning, their alignment, and the preservation of their functionality. Here, we proved how capillary assembly in combination with soft lithography can be used to perform DNA molecular combing to generate chips of isolated DNA strands for genetic analysis and diagnosis. The assembly of DNA molecules is achieved on a topologically micropatterned polydimethylsiloxane stamp inducing almost simultaneously the trapping and stretching of single molecules. The DNA molecules are then transferred onto aminopropyltriethoxysilane-coated surfaces. In fact, this technique offers the possibility to tightly control the experimental parameters to direct the assembly process. This technique does not induce a selection in size of the objects, therefore it can handle complex solutions of long (tens of kbp) but also shorter (a few thousands of bp) molecules directly in solution to allow the construction of future one-dimensional nanoscale building templates.

The extremely low thermal conductivity (κ) coupled with suitable Seebeck (S) and electrical conductivity (σ) values makes β-Zn4Sb3 a promising candidate for intermediate temperature (200–400 °C) thermogenerator applications. However, the poor thermal stability makes it difficult to reproduce the high thermoelectric figure of merit originally reported for this material.1 Using a combination of surface scanning techniques (Potential Seebeck microprobe, electron backscatter diffraction, and x-ray diffraction), we investigate specimens of β-Zn4Sb3 prepared under different synthesis conditions. Our results indicate the presence of multiple phases of Zn4Sb3 with distinct room temperature S values ranging from 70 to 140 μV/K. Though crystallographically similar, these phases have very different lattice contribution to the thermal conductivity (κL), which vary between 0.45 and 1.0 W/mK and might predominantly reflect the degree of Zn disorder among the different phases.

Ga2O3/SnO2 core–shell nanowires were synthesized by combining thermal evaporation and atomic layer deposition (ALD), and nanowire network sensors were fabricated by directly depositing them on the substrate with interdigitated Pt electrodes. Crystalline Ga2O3 nanowires of ∼20 nm diameter were grown on Au-catalyzed substrate at 800 °C. ALD-grown SnO2 shell layer was composed of interconnected nanoparticles of <10 nm, and its thickness was varied depending on the number of ALD cycles. The core–shell nanowire sensors exhibited the highest ethanol gas response at 400 °C, which was ∼200 °C lower than that for Ga2O3 nanowire sensor. The 100 cycle SnO2-coated nanowire sensor whose shell thickness was close to the Debye length of SnO2 had higher ethanol gas response in all the temperatures investigated. In addition, the core–shell nanowire sensors showed an order of magnitude higher gas response toward ethanol against other gases, such as H2, CO, and NH3.