Spin-dependent transport in nanocomposite C:Co films
Shengqiang Zhou, Markus Berndt, Danilo Buerger, Viton Heera, Kay Potzger, Gintautas Abrasonis, Gyoergy Radnoczi, Gyoergy J. Kovacs, Andreas Kolitsch, Manfred He… 展开作者
Shengqiang Zhou, Markus Berndt, Danilo Buerger, Viton Heera, Kay Potzger, Gintautas Abrasonis, Gyoergy Radnoczi, Gyoergy J. Kovacs, Andreas Kolitsch, Manfred Helm, Juergen Fassbender, Wolfhard Moeller, Heidemarie Schmidt
The magneto-transport properties of nanocomposite C:Co (15 and 40 at.% Co) thin films are investigated. The films were grown by ion beam co-sputtering on thermally oxidized silicon substrates in the temperature range from 200 to 500 degC. Two major effects are reported: (i) a large anomalous Hall effect amounting to 2 μohm cm, and (ii) a negative magnetoresistance. Both the field-dependent resistivity and Hall resistivity curves coincide with the rescaled magnetization curves, a finding that is consistent with spin-dependent transport. These findings suggest that C:Co nanocomposites are promising candidates for carbon-based Hall sensors and spintronic devices.
Nanocomposite thin films formed by gold nanoparticles embedded in a nickel oxide matrix have been synthesized by a new variation of the pulsed laser deposition technique. Two actively synchronized laser sources, a KrF excimer laser at 248 nm and an Nd:YAG laser at 355 nm, were used for the simultaneous ablation of nickel and gold targets in oxygen ambient. The structural, morphological, and electrical properties of the obtained nanocomposite films were investigated in relation to the fluence of the laser irradiating the gold target. The nanocomposite thin films were tested as electrochemical h…
Nanocomposite NiO:Au thin films, formed by gold nanoparticles embedded in a nickel oxide matrix, have been grown by reactive pulsed laser deposition (R-PLD). Two actively synchronized nanosecond laser sources, a KrF excimer laser (248 nm) and a Nd:YAG laser (355 nm), were used for the simultaneous ablation of nickel and gold targets in oxygen ambient. The morphology, composition, and optical properties of the obtained nanocomposites were investigated and were found to correlate with the concentration of Au nanoparticles. Further, the NiO:Au nanocomposites have been tested as hydrogen sensors. …
As grown ZnO:Si nanocomposites of different compositional ratios were fabricated by thermal evaporation techniques. These films were subjected to post deposition annealing under high vacuum at a temperature of $\rm 250C^o$ for 90min. The photoluminescence (PL) spectra of annealed samples have shown marked improvements both in terms of intensity and broadening. For the first time in ZnO:Si nanocomposite films we see huge UV, red and orange peaks at 310, 570 and 640nm. Structural and Raman analysis show formation of a Zn-Si-O shell around ZnO nano clusters wherein on heating $\rm Zn_2SiO_4$ comp…
Nanocomposite thin films of Zinc Oxide and Silicon were grown by co-evaporating powdered ZnO and Si. This resulted in nanocrystallites of ZnO being embedded in Silicon. The mismatch in crystal structures of constituent materials result in the ZnO nanocrystals to exist in a state of stress. This along with oxygen vacancies in the samples result in good Photoluminescence emission at 520nm. Also, Silicon background gave a photoluminescence emission at 620nm. The structure was found quite stable over time since the homgenously dispersed ZnO nanocrystals do not agglomerate. The nanocomposites promi…
In this work we elaborated and characterized nanocomposite thin films using a preselected multiferroic matrix Bi$_{0.9}$Gd$_{0.1}$Fe$_{0.9}$Mn$_{0.1}$O$_3$ (BGFMO) in the aim to enhance their basic ferroelectric and magnetic properties. The local ferroelectric character of these nanocomposites thin films was investigated by piezoresponse force microscopy (PFM). Switching behavior for ferroelectric domains was probed by locally manipulating domains. The magnetic investigation showed that the incorporation of transition metal elements in the BGFMO matrix brings out interesting increase in the ma…
We present a near IR photoresponse study of large area multi-walled carbon nanotube/poly(3-hexylthiophene)-block-polystyrene polymer (MWNT/P3HT-b-PS) nanocomposite films for different loading ratio of MWNT into the polymer matrix. We show that the photocurrent strongly depends on the position of the laser spot with maxiumum photocurrent occurring at the metal - film interface. In addition, compared to the pure MWNT film, the photoresponse is much larger in the MWNT/polymer composite films. The time constant for the photoresponse is slow and varies between 0.6 and 1.2 seconds. We explain the ph…
Flexible NbC nanocomposite thin films with carbon content ranging from 0 to 99 at.% were deposited at room temperature on Si (100) and polystyrene substrates by non-reactive magnetron sputtering from pure Nb and C targets without applying bias voltage to the substrates. HRTEM images reveal that the films exhibit a nanocomposite structure consisting of NbC nanocrystals (2 to 15 nm in size) embedded in an amorphous carbon matrix. By simply adjusting the Nb flux in the plasma, we can monitor the nanocrystal size and the percent of free-carbon phase in the films, which in turn allows for the tailo…
Nanocomposites made of polymer films embedding silver nanoparticles were prepared by thermal annealing of poly-(vinyl) alcohol films containing AgNO3. Low (2.5% w:w) and high (25% w:w) doping concentration of silver nitrate were considered as well as their effect on the optical properties of thin (30 nm) and thick (300 nm and more) films. The topography and the optical properties (refractive index $n$ and extinction coefficient $k$) of such films were studied by atomic force microscopy and spectroscopic ellipsometry. For a given doping level, the parameters of the surface plasmon-polariton res…
Zero field cooled spontaneous exchange bias (SEB) is observed in epitaxial La0.7Sr0.3MnO3 (LSMO):NiO self-assembled nanocomposite thin films grown on (001) SrTiO3 single crystal substrate by pulsed laser deposition. SEB is displayed by the novel asymmetry in the hysteresis loop of the composite film along with the field cooled conventional exchange bias (CEB) effect. The training effect shows that exchange bias relaxation is disorder mediated. It is revealed from DC magnetization results that such nanocomposite film divulges spin glass like behaviour, which is arising due to competing ferromag…
Nanocomposite films of Zinc Oxide and Silicon were grown by thermal evaporation technique using varying ratios of ZnO:Si in the starting material. Analysis reveal the role of ZnO and amorphous silicon interface in contributing to relatively less common blue photoluminescence emissions (at $\sim$ 400 and 470nm). These blue peaks are observed along with the emissions resulting from band edge transition (370nm) and those related to defects (522nm) of ZnO. Careful analysis shows that along with the grain size of ZnO, a suitable compositional ratio (of ZnO to silicon) is critical for the coexistenc…
Raman studies of nanocomposite SiCN thin film by sputtering showed that with an increase of substrate temperature from room temperature to 500oC, a transition from mostly sp2 graphitic phase to sp3 carbon took place which was observed from the variation of ID/IG ratio and the peak shifts. This process resulted in the growth of C3N4 and Si3N4 crystallites in the amorphous matrix which led to an increase in hardness and modulus obtained through nanoindentation. However, at a further higher temperature of 600oC, again an increase of sp2 C concentration in the film was observed and the H and E val…
Novel MOF-based polymer nanocomposite films were successfully prepared using Zr-based UiO-67 as a metal-organic framework (MOF) and polyurethane (PU) as a polymeric matrix. Synchrotron X-ray powder diffraction (SXRPD) analysis confirms the improved stability of the UiO-67 embedded nanocrystals and scanning electron microscopy images confirm their homogeneous distribution (average crystal size ~100-200 nm) within the 50-um thick film. Accessibility to the inner porous structure of the embedded MOFs was completely suppressed for N2 at cryogenic temperatures. However, ethylene adsorption measurem…
We present a comparative study on the influence of applied magnetic field on the resistance of $C_{1-x}Co_x$ thin films (with $x=0.1$, $0.15$ and $0.2$) grown on $Si$ substrate by pulsed laser deposition technique. It is found that the behavior of magnetoresistance (MR) drastically depends on the temperature. Namely, at low temperatures MR is positive and its behavior is governed by the field mediated weak localization scenario. While at high temperatures MR turns negative and its behavior is dominated by electron scattering on ferromagnetic cobalt atoms.
We present results on the development of nanocomposite NiO:Au thin-film hydrogen sensors, which are able to detect hydrogen concentrations as low as 2 ppm in air, operating at low temperatures in the range 125-150C. Thin NiO films were sputter-deposited on oxidized silicon substrates. The structural, morphological, and nanomechanical properties of the films were investigated with respect to post-deposition annealing. Au nanoparticles were added on the NiO surface via pulsed laser deposition and the films were tested as hydrogen sensors before and after Au deposition. The performance of the NiO…
The present paper report is focused toward the preparation of the flexible and freestanding blend solid polymer electrolyte films based on PEO-PVP complexed with NaPF6 by solution cast technique. The structural/morphological features of the synthesized polymer nanocomposite films have been investigated in detail using X-ray diffraction, Fourier transform infra-red spectroscopy, field emission scanning electron microscope, and atomic force microscopy techniques. The film PEO-PVP+NaPF6 O/Na:8 exhibits highest ionic conductivity ~5.92x10-6 S cm-1 at 40 oC and ~2.46x10-4 S cm-1 at 100 oC. The temp…
Gd0.2Ce0.8O1.9/Y0.16Zr0.84O1.92 (GDC/YSZ) nanocomposite is synthesized by a novel hybrid chemical route, where colloidal crystalline GDC nanoparticles from continuous hydrothermal synthesis are dispersed into a metalorganic YSZ matrix precursor. The result is a mixture of metal oxides in which GDC nanoparticles are finely distributed in a continuous metalorganic polymeric matrix to be crystallized after calcination. The GDC nanoparticles reduce the temperature necessary to obtain crystalline YSZ, which is already formed at 400 °C. The nanocomposite reveals structural stability up to 800 °C whe…
Poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) based pyroelectric as well as magnetoelectric materials offer great promises for energy harvesting for flexible and wearable applications. Hence, this work focus on solar energy harvesting as well as magnetoelectric phenomenon in two phase nanocomposite film where the constituting phases are manganese ferrite (MnFe2O4) nanoparticles and P(VDF-TrFE) polymer. Composite films have been prepared using solution casting technique. X-ray diffraction result shows higher crystallinity of these films. The ferroelectric, magnetic and magnetoelec…
In this paper, we report the high temperature mediated structural phase transformation from B1 to B2 phase in solgel derived Cd0.2Zn0.8O nanocomposite thin film for the temperature range of 700 to 900 degree centigrade. Xray diffraction pattern provides a direct and unambiguous indication of phase evolution with increase in annealing Temperature from 700 to 900 degree centigrade along with coexistence of wurtzite phase throughout the whole transformation regime. In fact, significant reduction in lattice parameters in case of transformed B2 phase, extracted by Rietveld refinement provides a dir…
Osmotic energy (or salinity-gradient energy) is the energy released when water with different salinities is mixed, such as rivers and oceans. By employing a semipermeable membrane to control the mixing process, the osmotic pressure gradient energy can be generated in terms of electrical power via pressure retarded osmosis (PRO) without causing adverse environmental impacts. This work presents the fabrication of thin film nanocomposite (TFN) membranes which are customized to offer high flux in forward osmosis (FO) and high osmotic power in PRO. In this study, the TFN membrane was fabricated by …
Nanocomposite films were fabricated by supersonic cluster beam deposition (SCBD) of palladium clusters on Poly(methyl methacrylate) (PMMA) surfaces. The evolution of the electrical conductance with cluster coverage and microscopy analysis show that Pd cluster are implanted in the polymer and form a continuous layer extending for several tens of nanometers beneath the polymer surface. This allows the deposition, using stencil masks, of cluster-assembled Pd microstructures on PMMA showing a remarkably high adhesion compared to metallic films obtained by thermal evaporation. These results suggest…
Structural and mechanical properties of amorphous and nanocomposite carbon are investigated using tight-binding molecular dynamics and Monte Carlo simulations. In the case of amorphous carbon, we show that the variation of sp^3 fraction as a function of density is linear over the whole range of possible densities, and that the bulk moduli follow closely the power-law variation suggested by Thorpe. We also review earlier work pertained to the intrinsic stress state of tetrahedral amorphous carbon. In the case of nanocomposites, we show that the diamond inclusions are stable only in dense amorph…
In this study we report on the film growth and characterization of thin (approximately 50 nm thick) Ti-Fe-C films deposited on amorphous quartz. The experimental studies have been complemented by first principles density functional theory (DFT) calculations. Upon annealing of as-prepared films, the composition of the metastable Ti-Fe-C film changes. An iron-rich phase is first formed close to the film surface, but with increasing annealing time this phase is gradually displaced toward the film-substrate interface where its position stabilizes. Both the magnetic ordering temperature and the sat…
We present results on the fabrication of chemiresistive nanocomposite NiO:Pd hydrogen sensors, which are able to detect hydrogen concentrations as low as 300 ppb in air, operating at temperatures in the 115-145 C range. Thin NiO films were deposited by radio frequency magnetron sputtering on silicon and quartz substrates and their structural and morphological properties were characterized. Pd nanoparticles were added on the NiO surface via pulsed laser deposition and the films were tested as hydrogen sensors before and after Pd deposition. The presence of Pd nanoparticles improved the sensor p…
Synthesis and Transfer of Freestanding Strain-Engineered Vertically Aligned Nanocomposite Thin Films
Sorbonne Universit\'e, CNRS, Institut des NanoSciences de Paris, INSP, F-75005 Paris, France；Groupe d’Etude de la Mati\`ere Condensée (GEMaC), Universit\'e de Versailles Saint-Quentin-en-Yvelines, CNRS-UMR8635, Universit\'e Paris-Saclay, 78035 Versailles, France；Sorbonne Universit\'e, CNRS, Laboratoire de Chimie Physique Mati\`ere et Rayonnement, LCPMR, Paris, France
The free standing solid polymer nanocomposite films has been prepared through standard solution cast technique. The improvement in structural, microstructural and electrochemical properties has been observed on the dispersion of nanofiller in polymer salt complex. X Ray diffraction studies clearly reflect the formation of complex formation as no corresponding salt peak appeared in the diffractograms. The FTIR analysis suggested a clear and convincing evidence of polymer ion, ion ion and polymer ion nanofiller interaction. The highest ionic conductivity of the prepared solid polymer electrolyte…
Nanocomposite metal oxide thin films exhibit assuring qualities in the field of gas sensors because of the collective opportunities provided by the heterointerface formation. In this work, we present the synthesis of nitrogen doped mesoporous In$_2$O$_3$-ZnO nano-composite thin films by simple wet chemical method using urea as the nitrogen precursor. SEM investigation suggests formation of mesoporous nano-composite thin films, where the uniformity of surface pore distribution depends on the relative proportion of In$_2$O$_3$ and ZnO in the composites. HRTEM investigation suggest formation of s…
Vanadium (IV) oxide is one of the most promising materials for thermochromic films due to its unique, reversible crystal phase transition from monoclinic (M1) to rutile (R) at its critical temperature (T$_c$) which corresponds to a change in optical properties: above T$_c$, VO$_2$ films exhibit a decreased transmittance for wavelengths of light in the near-infrared region. However, a high transmittance modulation often sacrifices luminous transmittance which is necessary for commercial and residential applications of this technology. In this study, we explore the potential for synthesis of VO$…
Transverse thermoelectric devices produce electric fields perpendicular to an incident heat flux. Classically, this process is driven by the Nernst effect in bulk solids, wherein a magnetic field generates a Lorentz force on thermally excited electrons. The spin Seebeck effect (SSE) also produces magnetization-dependent transverse electric fields. SSE is traditionally observed in thin metallic films deposited on electrically insulating ferromagnets, but the films' high resistance limits thermoelectric conversion efficiency. Combining Nernst and SSE in bulk materials would enable devices with s…
With 780-nm, 250-fs laser pulses, ultrafast optical nonlinearity has been observed in a series of thin films containing PMMA-TiO2 nanocomposites, which are synthesized by a simple technique of in-situ sol-gel/polymerization. The best figures of merit are found in one of the films prepared with a 60% weight percentage of titanium isopropoxide. TEM shows the presence of the 5-nm-diameter particles in the film. The observed optical nonlinearity has a recovery time of ~1.5 ps. These findings suggest the strong potential of PMMA-TiO2 nanocomposites for all-optical switching.
We fabricate and compare nanocomposite thin-film ZnO chemoresistive acetone sensors with gold or palladium nanoparticles on the surface, at low operating temperatures. The sensors are fabricated by pulsed laser deposition and operate in the temperature range 159-200oC. The ZnO films are polycrystalline, crystallizing mainly at the (002) and (101) orientations of the hexagonal phase. The nanocomposite ZnO:Au and ZnO:Pd sensors have a lower detection limit and show a response enhancement factor between 2-7, compared with pure ZnO sensors. The ZnO:Pd sensor performs better than the ZnO:Au sensor.…
Some of the most promising candidates for next generation thermoelectrics are nanocomposites due to their low thermal conductivities that result from phonon scattering on the boundaries of the various material phases. However, in order to maximize the figure of merit ZT, it is important to understand the impact of such features on the thermoelectric power factor. In this work we consider the effect that nanoinclusions and voids have on the electronic and thermoelectric coefficients of two dimensional geometries using the fully quantum mechanical Non Equilibrium Greens Function method. This met…
Active nanowires and nanofibers can be realized by the electric-field induced stretching of polymer solutions with sufficient molecular entanglements. The resulting nanomaterials are attracting an increasing attention in view of their application in a wide variety of fields, including optoelectronics, photonics, energy harvesting, nanoelectronics, and microelectromechanical systems. Realizing nanocomposite nanofibers is especially interesting in this respect. In particular, methods suitable for embedding inorganic nanocrystals in electrified jets and then in active fiber systems allow for cont…
Metal-insulator (CoFeB)$_x$(LiNbO$_3$)$_{100-x}$ nanocomposite films with different content of the ferromagnetic (FM) phase $x$ are investigated by ferromagnetic resonance (FMR) technique. A strong change of the FMR line shape is observed in the vicinity of metal-insulator transition (MIT) of the film, where the hopping-type conductivity $σ$ modifies to the regime of a strong intergranular tunnelling, characterized by a logarithmic dependence $σ(T)$ at high temperatures. It is shown that below MIT, the FMR linewidth is mainly determined by the inhomogeneous distribution of the local anisotropy…
The local structure and chemical bonding in two-phase amorphous Cr$_{1-x}$C$_{x}$ nanocomposite thin films are investigated by Cr $K$-edge ($1s$) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies in comparison to theory. By utilizing the computationally efficient \textit{stochastic quenching} (SQ) technique, we reveal the complexity of different Cr-sites in the transition metal carbides, highlighting the need for large scale averaging to obtain theoretical XANES and EXAFS spectra for comparison with measurements. As shown in this w…
The shape recovery ability of shape-memory alloys vanishes below a critical size (~50nm), which prevents their practical applications at the nanoscale. In contrast, ferroic materials, even when scaled down to dimensions of a few nanometers, exhibit actuation strain through domain switching, though the generated strain is modest (~1%). Here, we develop free-standing twisted architectures of nanoscale ferroic oxides showing shape-memory effect with a giant recoverable strain (>10%). The twisted geometrical design amplifies the strain generated during ferroelectric domain switching, which cannot …
The existence of magnetostriction in bulk BiFeO3 is still a matter of investigation and it is also an issue to investigate the magnetostriction effect in nano BiFeO3. Present work demonstrates the existence of magnetostrictive strain in superparamagnetic BiFeO3 nanoparticles at room temperature and the magnetoelectric coupling properties in composite form with P(VDFTrFE). Despite few reports on the magnetostriction effect in bulk BiFeO3 evidenced by the indirect method, the direct method (strain gauge) was employed in this work to examine the magnetostriction of superparamagnetic BiFeO3. In ad…
In recent years, functional oxide-metal based vertically aligned nanocomposite (VAN) thin films have gained interest due to their intriguing physical properties and multifunctionalities stemming from the complex interactions between the two phases in the film and the substrate. In this work, we develop a model for studying the energetics of these thin film systems, including the effects of both lattice mismatch and capillary forces due to interface curvature. Each phase is incorporated into the model using a phase indicator function, and we introduce the capillary forces as body forces using a…
In view of their immensely intriguing properties, two dimensional materials are being intensely researched in search of novel phenomena and diverse application interests, however, studies on the realization of nanocomposites in the application-worthy thin-film platform are rare. Here we have grown MoS2-hBN composite thin films on different substrates by the pulsed laser deposition technique and made comparative studies with the pristine MoS2 and hBN films. The Raman, XPS and HRTEM confirm the concomitant presence of both the 1T (conducting) and 2H (semiconducting) polymorphs of MoS2 in the com…
The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni$_{1-x}$C$_{x}$ (0.05$\leq$x$\leq$0.62) thin films have been investigated by high-resolution X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and soft X-ray absorption spectroscopy. By using X-ray as well as electron diffraction, we found carbon-containing hcp-Ni (hcp-NiC$_{y}$ phase), instead of the expected rhombohedral-Ni$_{3}$C. At low carbon content (4.9 at\%) the thin film consists of hcp-NiC$_{y}$ nanocrystallites mixed with a smaller am…
Low thermal conductivity of polymers, which is one of the considerable drawbacks of commonly used composite structures, has been the focus of many researchers aiming to achieve high-performance polymer-based nanocomposites through the inclusion of highly thermally conductive fillers inside the polymer matrices. Thus, in the present study, a multiscale scheme using non-equilibrium molecular dynamics (NEMD) and finite element (FE) method is developed to explore the impact of different nano-sized fillers (carbon-nitride and graphene) on the effective thermal conductivity of polyethylene-based nan…
3D lattice Monte Carlo modeling of morphology formation of Si/SiOx nanocomposites during phase separation of nonstoichiometric Si oxide films
Educational Scientific Institute of High Technologies, Taras Shevchenko National University of Kyiv（基辅塔拉斯舍甫琴科国立大学高等技术教育科学研究所）；V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine（乌克兰国家科学院瓦西里拉什卡廖夫半导体物理研究所）；National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”（乌克兰国立技术大学“伊戈尔·西科尔斯基基辅理工学院”）
Graphene-Polyvinyl alcohol (PVA) nanocomposite films with thickness $120 μm$ were synthesized by solidification of PVA in a solution with dispersed graphene nanosheets. Electrical conductivity data were explained as arising due to hopping of carriers between localized states formed at the graphene-PVA interface. Dielectric permittivity data as a function of frequency indicated the occurrence of Debye-type relaxation mechanism. The nanocomposites showed a magnetodielectric effect with the dielectric constant changing by 1.8% as the magnetic field was increased to 1 Tesla. The effect was explain…
In the present work, the effect of different nanofiller (BaTiO3, CeO2, Er2O3 or TiO2) on blend solid polymer electrolyte comprising of PEO and PVC complexed with bulky LiPF6 have been explored. The XRD analysis confirms the polymer nanocomposite formation. FTIR provides evidence of interaction among the functional groups of the polymer with the ions and the nanofiller in terms of shifting and changing peak profile. The highest ionic conductivity is ~2.3x10-5 S cm-1 with a wide electrochemical stability window of ~3.5 V for 10 wt. % Er2O3. The real and imaginary part of dielectric permittivity …
As grown ZnO:Si nanocomposite films fabricated by thermal evaporation showed broad photoluiminescence (PL) spectra due to merging of four prominent peaks viz 370, 410, 470 and 520 nm. Investigations revealed the role of interface in contributing to the two blue peaks at 410 and 470 nm. While the 470 nm is found to vary with ZnO grain size and their density, the 410 nm peak is attributed to the volume of shell surrounding ZnO nanoparticles. This study shows the contribution of ZnO cluster size and their density, as influenced by film thickness, in the PL spectra of the samples.
A free standing transparent film of solid state polymer electrolyte based on PEO/PAN + NaPF6 with different compositions of nano sized TiO2 in weight percent (x = 0, 1, 2, 5, 10, 15, 20 ) is synthesized by using standard solution cast technique. The homogeneous surface of above polymer composition is examined by FESEM. The microscopic interaction among polymer, salt and nanoceramic filler has been analyzed by Fourier Transformed Infra-Red (FTIR) spectroscopy. The reduction of ion pair formation in polymeric separator is clearly observed on addition of nanofiller in the polymer salt complex fil…
Silicon carbide nanoparticles with diameters around 8 nm and with narrow size distribution have been finely mixed with doped silicon nanopowders and sintered into bulk samples to investigate the influence of nanoinclusions on electrical and thermal transport properties. We have compared the thermoelectric properties of samples ranging from 0-5% volume fraction of silicon carbide. The silicon carbide nanoinclusions lead to a significant improvement in the thermoelectric figure of merit, ZT, largely due to an enhancement of the Seebeck coefficient. A semiclassical Boltzmann transport equation is…
The thermal transport properties of porous silicon and nano-hybrid "porous silicon/water" systems are presented here. The thermal conductivity was evaluated with equilibrium molecular dynamics technique for porous systems made of spherical voids or water-filled cavities. We revealed large thermal conductivity enhancement in the nano-hybrid systems as compared to their dry porous counterparts, which cannot be captured by effective media theory. This rise of thermal conductivity is related to the increases of the specific surface of the liquid/solid interface. We demonstrated that significant di…
Carboxylic functionalization (-COOH groups) of carbon nanotubes is known to improve their dispersion properties and increase the electrical conductivity of carbon-nanotube - polymer nanocomposites. We have studied experimentally the effects of this type of functionalization on the thermal conductivity of the nanocomposites. It was found that while even small quantities of carbon nanotubes (~1 wt%) can increase the electrical conductivity, a larger loading fraction (~3 wt%) is required to enhance the thermal conductivity of nanocomposites. Functionalized multi-wall carbon nanotubes performed th…
Successful preparation of polymer nanocomposites, exploiting graphene-related materials, via melt mixing technology requires precise design, optimization and control of processing. In the present work, the effect of different processing parameters during the preparation of poly (butylene terephthalate) nanocomposites, through ring-opening polymerization of cyclic butylene terephthalate in presence of graphite nanoplatelets (GNP), was thoroughly addressed. Processing temperature (240°C or 260°C), extrusion time (5 or 10 minutes) and shear rate (50 or 100 rpm) were varied by means of a full fact…
We have created superconductor-ferromagnet composite films in order to test the enhancement of critical current density, Jc, due to magnetic pinning. We co-sputter the type-II superconductor niobium (Nb) and the low-temperature ferromagnet dysprosium (Dy) onto a heated substrate; the immiscibility of the two materials leads to a phase-separated composite of magnetic regions within a superconducting matrix. Over a range of compositions and substrate temperatures, we achieve phase separation on scales from 5 nm to 1 micron. The composite films exhibit simultaneous superconductivity and ferromagn…
We study the temperature dependence of thermoelectric transport properties of four FeSb2 nanocomposite samples with different grain sizes. The comparison of the single crystals and nanocomposites of varying grain size indicates the presence of substantial phonon drag effects in this system contributing to a large Seebeck coefficient at low temperature. As the grain size decreases, the increased phonon scattering at the grain boundaries leads to a suppression of the phonon-drag effect, resulting in a much smaller peak value of the Seebeck coefficient in the nanostructured bulk materials. As a c…
Magnetotransport properties in a nanocrystalline La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/micron sized Al$_{2}$O$_{3}$ granular composite with different concentrations of Al$_{2}$O$_{3}$ have been studied. The resistivity curves in absence of magnetic field and the various transport mechanisms which might account for the upturn in resistivity at low temperature, has been discussed. Enhancement of low field magnetoresistance at room temperature with the introduction of Al$_{2}$O$_{3}$ has been observed.
