Bulk Nanostructures Research Articles

(Invited) Novel Strategies for the Bottom-up Assembly of Nanowires into Highly Efficient Bulk Thermoelectrics

The predicted exponential increase in the United States’ energy demand over the foreseeable future could be met by supplementing existing sources of energy with new renewable and/or non-renewable energy sources. Alternately, increasing the energy efficiencies of the existing processes and systems through waste heat scavenging could be employed to offset, at least partially, the projected increase in the energy demand. The importance of this alternate scenario could be easily inferred from the data supplied by the Energy Information Administration (EIA), which indicates that 56-57% of all energy produced each year in the US is rejected as waste heat. In the case of automobiles the importance of waste heat recovery becomes more apparent, where approximately 70% of energy generated by burning gasoline is lost either in the engine coolant or through the exhaust. Use of solid-state thermoelectric modules is a minimally invasive method for scavenging waste heat from systems and processes. The lack of any moving parts, portability, very long operational lifetimes, and minimal maintenance make thermoelectrics attractive for waste heat recovery. The lack of the requisite materials for achieving a good $/watt heat-to-electricity conversion metric is currently preventing the large-scale deployment and use of thermoelectrics in terrestrial applications, and limits their use to niche applications (powering up deep space probes). A factor responsible for this bottleneck is the low efficiencies of the current thermoelectric materials, which in turn could be attributed to the lack of a pathway for precisely and independently tuning the thermal and electrical transport through them. Recent theoretical and experimental studies have demonstrated that nanostructuring of materials serves as a route for independently tuning the thermal and electrical transport. Most of these demonstrations were made using the following types of devices: suspended individual nanowire devices, thin-film superlattice devices, and bulk devices that have endotaxial nanostructures embedded within a host material. From these studies it could be concluded that although it appears that nanostructuring of materials for selectively reducing their thermal conductivities is the only essential requirement for enhancing their heat-to-electricity conversion efficiencies, the existence of an epitaxial relationship between the nanostructures after their assembly is also equally important for efficiency enhancement. Experimental methods employed for obtaining epitaxially-oriented bulk nanostructure assemblies require either the use of tedious process (e.g., atomic layer deposition, ALD) or the use of a specific scientific phenomenon (e.g., spinodal decomposition). These requirements not only make it impossible to mass produce thermoelectrics (ALD is a slow and non-scalable process), but also limit the applicability of these strategies to a few material systems (spinodal decomposition is currently only observed in a few materials systems composed of Pb, Bi, Sb, Te and Sr). Finally, the progress made in experimentally demonstrating enhanced thermoelectric performances of large-scale nanowire assemblies is minimal at best. In this context, the aim of our work is the rational design and fabrication of next-generation, highly-efficient thermoelectrics through the development of strategies for mass producing nanowires and assembling them in an interface-engineered manner (1-3). The aim of this presentation is to showcase the progress that has been made in this research area by our group. The strategies useful for the mass production of nanowires and their in-situ functionalization with organic molecules (1), together with the strategies useful for assembling them in an interface-engineered manner on a large-scale into functional thermoelectric devices (2,3), will be presented. Demonstrations of how these strategies afford precise thermal and electrical transport control in bulk nanowire assemblies will be made using interface-engineered Zn3P2 and ZnO nanowire assemblies as illustrative examples (2-4). In addition, strategies for welding nanowires during assembly so as to ensure that the welds between the nanowires have the same chemical composition as those of the nanowires and that the nanowires assemblies have a single-crystalline path for electrical conduction will also be presented (5,6). Illustration of this concept will be made by demonstrating enhanced thermoelectric performance in Mg2Si nanowire assemblies obtained by welding pre-synthesized Si nanowires (6). ACKNOWLEDGEMENTS Partial financial support from NSF/DOE thermoelectrics Partnership (NSF CBET # 1048702) is gratefully acknowledged. REFERENCES L. Brockway, M. Van Laer, Y. Kang, S. Vaddiraju, Physical Chemistry Chemical Physics, 15, 6260-6267, (2013).L. Brockway, V. Vasiraju, S. Vaddiraju, Nanotechnology, 25, 125402 (2014).L. Brockway, V. Vasiraju, H. Asayesh-Ardakani, R. Shahbazian-Yassar, S. Vaddiraju, Nanotechnology, 25, 145401 (2014).L. Brockway, V. Vasiraju, M. K. Sunkara, S. Vaddiraju, ACS Applied Materials & Interfaces 6, 14923-14930 (2014).Y. Kang, L. Brockway, S. Vaddiraju, Materials Letters, 100, 106-110 (2013).Y. Kang, S. Vaddiraju, Chemistry of Materials, 26, 2814-2819 (2014).

Dilatation deformation potential, drift mobility and piezoresistance in p-type silicon (quantum kinetic approach)

Analytic expressions for low field mobility and conductivity (resistance) in unstrained and high strained states for p-type silicon bulk crystals and nanostructures have been obtained on base of quantum kinetic equation and special form of the non-equilibrium distribution function. Ionized impurities, acoustic and optic phonons are adopted as scattering system. Calculated temperature dependences of mobility and strain dependences of resistance are compared with known experimental data. Numerical value of the dilatation deformation potential has been found. Proposed model of origin of the anomalous piezoresistance effect in p-type silicon nanostructures at high tensile strains provides not only qualitative but even sufficient quantitative agreement with experimental data.

Ultrasonic Processing of Materials

Irradiation of high-energy ultrasonic vibration in metals and alloys generates oscillating strain and stress fields in solids, and introduces nonlinear effects such as cavitation, acoustic streaming, and radiation pressure in molten materials. These nonlinear effects can be utilized to assist conventional material processing processes. This article describes recent research at Oak Ridge National Labs and Purdue University on using high-intensity ultrasonic vibrations for degassing molten aluminum, processing particulate-reinforced metal matrix composites, refining metals and alloys during solidification process and welding, and producing bulk nanostructures in solid metals and alloys. Research results suggest that high-intensity ultrasonic vibration is capable of degassing and dispersing small particles in molten alloys, reducing grain size during alloy solidification, and inducing nanostructures in solid metals.

ChemInform Abstract: Structure‐Property Relationships of Curved Aromatic Materials from First Principles

AbstractReview: 77 refs.

EMRS Spring Meeting 2014 Symposium D: Phonons and fluctuations in low dimensional structures

The E-MRS 2014 Spring meeting, held from 26-30th May 2014 in Lille included the Symposium D entitled ‘‘Phonons and Fluctuations in Low Dimensional Structures’’, the first edition of its kind. The symposium was organised in response to the increasing interest in the study of phonons in the context of advances in condensed matter physics, electronics, experimental methods and theory and, in particular, the transfer of energy across atomic interfaces and the propagation of energy in the nm-scale. Steering heat by light or vice versa and examining nano-scale energy conversion (as in thermoelectricity and harvesting e.g. in biological systems) are two aspects that share the underlying science of energy processes across atomic interfaces and energy propagation in the nanoscale and or in confined systems. The nanometer scale defies several of the bulk relationships as confinement of electrons and phonons, locality and non-equilibrium become increasingly important. The propagation of phonons as energy carriers impacts not only heat transfer, but also the very concept and handling of temperature in non-equilibrium and highly localised conditions. Much of the needed progress depends on the materials studied and this symposium targeted the interface material aspects as well as the emerging concepts to advance in this field.The symposium had its origins in a series of meetings and seminars including: (1) the first Phonon Engineering Workshop, funded by Catalan Institute for Research and Advanced Studies (ICREA), the then MICINN, the CNRS, VTT, and several EU projects, held in Saint Feliu de Guixols (Girona, Spain) from 24th to 27th of May 2010 with 65 participants from Europe, the USA and Japan; (2) the first Phonons and Fluctuations workshop, held in Paris on 8th and 9th November 2010, supported by French, Spanish and Finnish national projects and EU projects, attended by about 50 researchers; (3) the second Phonon and Fluctuations workshop, held in Paris on 8th and 9th September 2011, attended by 55 researchers and (4) the 3rd Workshop on Phonons & Fluctuations, held in Saint Feliux de Guixols (Girona, Spain) during 21 to 24th May 2012 attended by 65 participants from Europe and the USA.These papers in this proceeding are examples of the work presented at the symposium. They represent the tip of the iceberg, as the symposium attracted over 100 abstracts. The meeting room was usually full with an audience varying between 40 and 100 participants. The plenary presentation was given by Prof. Gang Chen (MIT) on ‘‘Ballistic and Coherent Phonon Heat Conduction in Bulk Materials and Nanostructures’’, which was warmly welcome by an eager and highly motivated audience. The invited speakers were: Prof. Thomas Dehoux (U. Bordeaux), Dr S. Chung (U. New South Wales, Australia), Prof. A. Goni (CSIC-ICMAB), Prof. Giuliano Benenti (U. Insubria), Dr. Davide Donadio (Max Planck Institute for Polymer Research, Mainz), Prof. George Fytas (University of Crete), Prof. Dr. Tobias Kippenberg (EPFL, Switzerland), Prof. Bernard Perrin (INSP, Paris), Prof. Gyaneshwar P. Srivastava, U. Exeter) and Prof. Dr. Achim Kittel (U. Oldenburg). The organisers are very grateful to them for supporting the symposium and sharing their latest research results with the symposium participants.The symposium organisers recognised the participation of students and awarded prizes to the two Best Student Presentations, which went to Valeria Lacatena (IEMN, Lille) with an invited presentation entitled ‘‘Efficient reduction of thermal conductivity in silicon using phononic-engineered membranes’’ and to Yan Qing Liu (Institute Neel, Grenoble) who presented the talk entitled ‘‘Sensitive 3-omega measurements of epitaxial thermoelectric thin films’’. The poster session had about fifty posters and the four best poster prizes went to: Konstanze Hahn et al. (U. Cagliari) poster title ‘‘Determination of Thermal conductivity in (nanostructured) SiGe materials’’, Florian Doehring et al. (U. Goettingen) poster title ‘‘Phonon blocking in Multilayers produced by Pulsed Laser Deposition’’, Jordi Gomis-Bresco et al. (ICN2) poster ‘‘ A 1D PhoXonic Crystal’’, Barcelona and Benjamin J Robinson et al. (U. Lancaster) poster ‘‘Scanning Thermal microscopy studies of 2D materials’’.The symposium organisers are grateful to the Scientific Committee members, Prof. Bahram Djafari-Rouhani (France), Prof. Dr. Thomas Dekorsy (Germany), Prof. Anthony Kent (UK), Prof. Fabio Marchesoni (Italy), Dr. Natalio Mingo (France), Prof. Pascal Ruello, (France) and Prof. Javier Viejo-Rodriguez (Spain), for their help with all aspects of evaluation of the scientific level of the presentations in the symposium.The symposium was sponsored by the FP7 ICT FET Open Coordination Action EUPHONON (GA. 612086) and by the CNRS GDR ‘‘Thermal Nanosciences and NanoEngineering’’. The symposium organisers express their sincere thanks to the staff of the E-MRS for continuous support and timely advice in all organisational aspects. We are indebted to Dr. Erwan Guillotel (ICN2) for his assistance with the organisation of the symposium.

Graphene‐Directed Supramolecular Assembly of Multifunctional Polymer Hydrogel Membranes

Polymer‐based nanoporous hydrogel membranes hold great potential for a range of applications including molecular filtration/separation, controlled drug release, and as sensors and actuators. However, to be of practical utility, polymer membranes generally need to be fabricated as ultrathin yet mechanically robust, have a large‐area yet be defect‐free and in some cases, their structure needs the capability to adapt to certain stimuli. These stringent and sometimes self‐conflicting requirements make it very challenging to manufacture such bulk nanostructures in a controllable, scalable and cost‐effective manner. Here, a versatile approach to the fabrication of multifunctional polymer‐based hydrogel membranes is demonstrated by a single step involving filtration of an aqueous dispersion containing chemically converted graphene (CCG) and a polymer. With CCG uniquely serving as a membrane‐ and pore‐forming directing agent and as a physical cross‐linker, a range of water soluble polymers can be readily processed into nanoporous hydrogel membranes through supramolecular interactions. With the interconnected CCG network as a robust and porous scaffold, the membrane nanostructure can easily be fine‐tuned to suit different applications simply by controlling the chemistry and concentration of the incorporated polymer. This work provides a simple and versatile platform for the design and fabrication of new adaptive supramolecular membranes for a variety of applications.

Nanostructure-thermal conductivity relationships in protic ionic liquids.

The thermal conductivities of nine protic ionic liquids (ILs) have been investigated between 293 and 340 K. Within this range, the thermal conductivities are between 0.18 and 0.30 W · m(-1) · K(-1). These values are higher than those typically associated with oils and aprotic ILs, but lower than those of strongly hydrogen bonding solvents like water. Weak linear decreases in thermal conductivity with temperature are noted, with the exception of ethanolammonium nitrate (EtAN) where the thermal conductivity increases with temperature. The dependence of thermal conductivity on IL type is analyzed with use of the Bahe-Varela pseudolattice theory. This theory treats the bulk IL as an array of ordered domains with intervening domains of uncorrelated structure which enable and provide barriers to heat propagation (respectively) via allowed vibrational modes. For the protic ILs investigated, thermal conductivity depends strongly on the IL cation alkyl chain length. This is because the cation alkyl chain controls the dimensions of the IL bulk nanostructure, which consists of charged (ordered domains) and uncharged regions (disordered domains). As the cation alkyl chain controls the dimensions of the disordered domains, it thus limits the thermal conductivity. To test the generality of this interpretation, the thermal conductivities of propylammonium nitrate (PAN) and PAN-octanol mixtures were examined; water selectively swells the PAN charged domain, while octanol swells the uncharged regions. Up to a certain concentration, adding water increases thermal conduction and octanol decreases it, as expected. However, at high solute concentrations the IL nanostructure is broken. When additional solvent is added above this concentration the rate of change in thermal conductivity is greatly reduced. This is because, in the absence of nanostructure, the added solvent only serves to dilute the salt solution.

On the synthesis and electrochemical characterization of ordered hierarchical NiO micro bouquets with trimodal pore size distribution

The present study demonstrates a novel approach by which ‘bulk nanostructured’ NiO micro bouquets can be processed into a high surface area electrode for supercapacitor applications. A detailed study has been performed to elucidate the impact of porosity and redox reactions on the electrochemical behavior. The spheres were synthesized using a soft template technique. An intrinsic correlation between the surface area, capacitance and the internal resistance has been deduced and explained on the basis of relative contributions from the faradic properties of NiO. These NiO spheres exhibited specific mass capacitance values as high as 1950Fg−1. Further, coin cells employing these rechargeable electrodes were also demonstrated which exhibits energy and power densities of 17 Whkg−1 and 24 kWkg−1. It has been shown that these electrodes based on such bulk nanostructures can allow significant room for high performance supercapacitor devices.

Solvation of Inorganic Nitrate Salts in Protic Ionic Liquids

The bulk nanostructure of several inorganic salt solutions in protic ionic liquids is elucidated using neutron diffraction and empirical potential structure refinement modeling. The protic ionic liquids studied are ethylammonium nitrate (EAN) and ethanolammonium nitrate (EtAN), which are mixed with either LiNO3, Mg(NO3)2, Ca(NO3)2, or Al(NO3)3 at 1:10 or 1:30 solute:solvent mol:mol ratios. The models show inorganic metal ions are solvated within the polar domains of the nanostructure and can induce significant differences in bulk solvent nanostructure from that of the pure ionic liquids. For EtAN, the uncharged groups aggregate and form an apolar domain in spite of the cation’s reduced amphiphilicity because the trans rotamer is favored when an inorganic salt is added.

Mechanical properties of bulk carbon nanostructures: effect of loading and temperature.

Carbon-based bulk nanostructures are believed to entail certain advantages over their parent low-dimensional materials and are promising candidates for supercapacitors due to their unique properties such as extremely high specific surface area and high conductivity. Herein the mechanical and structural properties of four types of carbon nanopolymorph-based nanomaterials were calculated using molecular dynamics simulations. Bulk carbon nanostructures composed of structural units of bent graphene flakes, short carbon nanotubes, fullerenes and their mixture were considered. The effect of the loading scheme and temperature was studied and constitutive relationships describing the deformation of the materials were given. The simulation results revealed that the effect of the loading scheme significantly depends on the type of structural units, and was slightly affected by the temperature especially for high densities. The constitutive equations obtained in this work can be applied to describe the mechanical behavior of new bulk carbon nanostructures.

Deep-level emission in ZnO nanowires and bulk crystals: Excitation-intensity dependence versus crystalline quality

The excitation-intensity dependence of the excitonic near-band-edge emission (NBE) and deep-level related emission (DLE) bands in ZnO nanowires and bulk crystals is studied, which show distinctly different power laws. The behavior can be well explained with a rate-equation model taking into account deep donor and acceptor levels with certain capture cross sections for electrons from the conduction band and different radiative lifetimes. In addition, a further crucial ingredient of this model is the background n-type doping concentration inherent in almost all ZnO single crystals. The interplay of the deep defects and the background free-electron concentration in the conduction band at room temperature reproduces the experimental results well over a wide range of excitation intensities (almost five orders of magnitude). The results demonstrate that for many ZnO bulk samples and nanostructures, the relative intensity R = INBE/IDLE can be adjusted over a wide range by varying the excitation intensity, thus, showing that R should not be taken as an indicator for the crystalline quality of ZnO samples unless absolute photoluminescence intensities under calibrated excitation conditions are compared. On the other hand, the results establish an all-optical technique to determine the relative doping levels in different ZnO samples by measuring the excitation-intensity dependence of the UV and visible luminescence bands.

Structure-property relationships of curved aromatic materials from first principles.

CONSPECTUS: Considerable effort in the past decade has been extended toward achieving computationally affordable theoretical methods for accurate prediction of the structure and properties of materials. Theoretical predictions of solids began decades ago, but only recently have solid-state quantum techniques become sufficiently reliable to be routinely chosen for investigation of solids as quantum chemistry techniques are for isolated molecules. Of great interest are ab initio predictive theories for solids that can provide atomic scale insights into properties of bulk materials, interfaces, and nanostructures. Adaption of the quantum chemical framework is challenging in that no single theory exists that provides prediction of all observables for every material type. However, through a combination of interdisciplinary efforts, a richly textured and substantive portfolio of methods is developing, which promise quantitative predictions of materials and device properties as well as associated performance analysis. Particularly relevant for device applications are organic semiconductors (OSC), with electrical conductivity between that of insulators and that of metals. Semiconducting small molecules, such as aromatic hydrocarbons, tend to have high polarizabilities, small band-gaps, and delocalized π electrons that support mobile charge carriers. Most importantly, the special nature of optical excitations in the form of a bound electron-hole pairs (excitons) holds significant promise for use in devices, such as organic light emitting diodes (OLEDs), organic photovoltaics (OPVs), and molecular nanojunctions. Added morphological features, such as curvature in aromatic hydrocarbon structure, can further confine the electronic states in one or more directions leading to additional physical phenomena in materials. Such structures offer exploration of a wealth of phenomenology as a function of their environment, particularly due to the ability to tune their electronic character through functionalization. This Account offers discussion of current state-of-the-art electronic structure approaches for prediction of structural, electronic, optical, and transport properties of materials, with illustration of these capabilities from a series of investigations involving curved aromatic materials. The class of curved aromatic materials offers the ability to investigate methodology across a wide range of materials complexity, including (a) molecules, (b) molecular crystals, (c) molecular adsorbates on metal surfaces, and (d) molecular nanojunctions. A reliable pallet of theoretical tools for such a wide array relies on expertise spanning multiple fields. Working together with experimental experts, advancements in the fundamental understanding of structural and dynamical properties are enabling focused design of functional materials. Most importantly, these studies provide an opportunity to compare experimental and theoretical capabilities and open the way for continual improvement of these capabilities.

Indium selenides: structural characteristics, synthesis and their thermoelectric performances.

Indium selenides have attracted extensive attention in high-efficiency thermoelectrics for waste heat energy conversion due to their extraordinary and tunable electrical and thermal properties. This Review aims to provide a thorough summary of the structural characteristics (e.g. crystal structures, phase transformations, and structural vacancies) and synthetic methods (e.g. bulk materials, thin films, and nanostructures) of various indium selenides, and then summarize the recent progress on exploring indium selenides as high-efficiency thermoelectric materials. By highlighting challenges and opportunities in the end, this Review intends to shine some light on the possible approaches for thermoelectric performance enhancement of indium selenides, which should open up an opportunity for applying indium selenides in the next-generation thermoelectric devices.

Electronic stopping power from first-principles calculations with account for core electron excitations and projectile ionization

We use Ehrenfest dynamics and time-dependent density functional theory to calculate electronic stopping power ${S}_{e}$ of energetic ions in graphitic targets from first principles. By treating core electrons as valence electrons within the projected augmented wave framework, we demonstrate that this approach provides an accurate description of ${S}_{e}$ for a wide range of ions and ion energies, even when not only valence, but also core electron excitations are essential. Our impact-parameter-dependent approach capable of describing the stopping of both low- and high-energy ions is a significant step forward in ${S}_{e}$ calculations, as it makes it possible to monitor projectile charge state during impacts, estimate contributions of core and valence electron excitations to ${S}_{e}$, and it gives a quantitative description of electronic stopping in the cross-over region for bulk solids and nanostructures from first principles.

Effects of nitrogen on microstructural evolution of biomedical Co–Cr–W alloys during hot deformation and subsequent cooling

The present study investigated how nitrogen affected the high-temperature deformation and microstructural evolution of biomedical Ni-free Co–Cr–W alloys during hot deformation. Hot compression tests of undoped and N-doped Co–28Cr–9W–1Si–0.05C (mass%) alloys were performed at deformation temperatures ranging from 1323 to 1473K at strain rates of 10−3 to 10s−1. The microstructures, which were subjected to a true strain of 0.92 (60% in compression), were characterized using electron backscatter diffraction (EBSD) analysis and transmission electron microscopy (TEM). Dynamic recrystallization (DRX) was found to occur in both alloys during hot deformation. The grain size (d) decreased considerably with an increase in the Zener–Hollomon (Z) parameter. Although adding nitrogen to the alloys barely affected dynamic-recrystallization-induced grain refinement, it increased the magnitude of the flow stress and delayed static recrystallization during post-deformation cooling. Consequently, the N-doped alloy contained bulk nanostructures whose average grain size was 0.9μm.

Nonlinear absorption of light pulses under conditions of two-photon resonance in bulk crystals and nanostructures in the femtosecond pump-probe spectroscopy mode

A theory of nonlinear absorption of femtosecond light pulses by bulk crystals and nanostructures of different dimensions in the pump-probe spectroscopy mode has been developed. Expressions for the energy absorbed from the probe pulse under conditions of two-photon resonances are derived for transitions between the discrete or band electronic states and between the size-quantization subband states in quantum wells and quantum wires. The dependences of the energy absorbed from the probe pulse on the two-photon resonance detuning and on the time delay between the pulses are analyzed. The dependence of the power absorbed from the probe pulse on the time is also obtained.

Solid state adaptive natural density partitioning: a tool for deciphering multi-center bonding in periodic systems

A new tool to elucidate chemical bonding in bulk solids, surfaces and nanostructures has been developed. Solid State Adaptive Natural Density Partitioning (SSAdNDP) is a method to interpret chemical bonding in terms of classical lone pairs and two-center bonds, as well as multi-center delocalized bonds. Here we extend the domain of AdNDP to bulk materials and interfaces, yielding SSAdNDP. We demonstrate the versatility of the method by applying it to several systems featuring both localized and many-center chemical bonding, and varying in structural complexity: boron α-sheet, magnesium diboride and the Na8BaSn6 Zintl phase.

A Stepwise “Micellization–Crystallization” Route to Oblate Ellipsoidal, Cylindrical, and Bilayer Micelles with Polyethylene Cores in Water

Micellar polymorphism from block copolymers has been well documented, but most attention has focused on noncrystalline hydrophobic systems. We have investigated the micellization in water of model diblock copolymers with semicrystalline polyethylene (PE) as the core-forming component. Poly(N,N-dimethylacrylamide)–polyethylene (AE) diblock copolymers were synthesized by a combination of anionic and RAFT polymerizations. The bulk nanostructures were probed by small-angle X-ray scattering (SAXS) and AE diblock copolymers were found to be moderately segregated at 140 °C. Dispersions of AE amphiphiles in water were prepared by direct dissolution at 120 °C (i.e., above the melting transition of PE) followed by cooling to 25 °C. By manipulating the composition of AE diblock copolymers, discrete structures with oblate ellipsoidal, cylindrical, and bilayer morphologies were produced, as evidenced in cryogenic transmission electron microscopy (cryo-TEM). The self-assembled aggregates were also studied by small-angle neutron scattering (SANS) and dilute solution rheology. The semicrystalline nature of the nanostructures was further revealed by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). A stepwise “micellization–crystallization” process was proposed as the micelle formation mechanism, as supported by the existence of similar nanostructures at 120 °C using SANS. This strategy holds promise for a general protocol toward the production of giant wormlikemore » micelles and vesicles with semicrystalline polymeric cores.« less

Prediction of the thermal conductivity of ZnO nanobelts

A prediction tool, based on a kinetic theory of gas model, previously developed for the thermal properties prediction of ZnO bulk crystal and nanostructures is used in order to be compared with existing literature results. As thermal conductivity measurement for nanostructures are seldom, the aim is to understand the validity range of the models and discuss their reliability. The estimation of the specific heat is in excellent agreement with data of bulk samples measured by other researchers. For the thermal conductivity, the comparison with other prediction tools and experimental results is done for nanowires and nanofilms. The agreement and the differences are discussed. It allows defining the complementarity of the prediction tools.

Laser Assisted Flow Deposition: a New Method to Grow ZnO

Zinc oxide (ZnO) has been one of the most studied materials in the last decades. Either as bulk material, epilayers or nanostructures, this direct wide band gap semiconductor is known to possess great potential for fundamental science and modern technology applications.