bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Properties of Polymer-Embedded Silicon Nanoparticles
Authors: Kirkey William D. , Cartwright Alexander N. , Li Xuegeng , He Yuanqing , Swihart Mark T. , Sahoo Yudhisthira , Prasad Paras N. 
Published: April 2011

ABSTRACTWe seek to use electrically conducting polymers, such as those commonly utilized in polymeric LEDs, as hosts for silicon nanoparticles. The proper design of multilayered devices based on these materials will yield efficient light-emitters in which charge carriers localize and recombine within the nanoparticles. Furthermore, these may combine the flexibility and processability of polymeric LEDs with the reliability of inorganic materials. We have synthesized luminescent silicon nanoparticles and have characterized their photoluminescence (PL) using continuous-wave and time-resolved spectroscopy. These particles have been incorporated into a variety of transparent solid hosts. The photoluminescence obtained from particle-containing poly(methyl methacrylate) (PMMA) matrices is very similar to that of the particles in solution, both in spectral content and PL decay characteristics. However, when incorporated into a variety of conducting polymers, such as poly(N-vinylcarbazole) (PVK), the nanoparticles do not retain their photoluminescence properties. A variety of chemical species have been reported as effective PL quenchers for porous silicon. We believe that these polymers quench the luminescence through similar mechanisms. Protective passivation of the nanoparticle surface is suggested as a strategy for overcoming this quenching.
Growth of InGaN Nanorods as the Blue Light Source for White Light Emitting Devices
Authors: Kim Hwa-Mok , Kang Tae Won , Chung Kwan Soo 
Published: April 2011

ABSTRACTThis work demonstrates the properties of InGaN nanorod arrays with various In mole fractions by modified HVPE using In metal at the low growth temperature. The nanorods grown on (0001) sapphire substrates are preferentially oriented in the c-axis direction. We found that the In mole fractions in the nanorods were linearly increased at x ≤ 0.1. However, In mole fractions were slightly increased at x > 0.1 and then were gradually saturated at x = 0.2. CL spectra show strong blue emissions from 428 nm (x = 0.1, 2.89 eV) to 470 nm (x = 0.2, 2.64 eV) at room temperature. From this result, we found the fact that increasing In mole fraction in the InGaN nanorod shift the peak position of CL spectrum emitted from InGaN nanorod to the low energy region.
Trap Effects in PbS Quantum Dots
Authors: Persans Peter D. , Filin Aleksey , Huang Feiran , Vitek Andrew , Rao Pratima G.N. , Doremus Robert H. 
Published: April 2011

ABSTRACTWe have found that traps can dominate important relaxation processes in PbS nanoparticles prepared by precipitation in borosilicate glass. The primary photoluminescence peak energy falls about 50 meV below the lowest absorption peak energy and has a long decay time of ∼4 μs. Photoinduced bleaching of the lowest absorption peak also has a long decay lifetime of ∼2 μs. Photoinduced bleaching also exhibits a surprisingly long rise time of hundreds of nanoseconds. Such long-lifetime effects must be attributed to multiple traps.
Probing the Long Range Distance Dependence of Noble Metal Nanoparticles
Authors: Haes Amanda J. , Van Duyne Richard P. 
Published: April 2011

ABSTRACTThe localized surface plasmon resonance (LSPR) of noble metal nanoparticles has recently been the subject of extensive studies. Previously, it has been demonstrated that Ag nanotriangles that have been synthesized using nanosphere lithography (NSL) behave as extremely sensitive and selective chemical and biological sensors. The present work reveals information regarding the long range distance dependence of the localized surface plasmon resonance (LSPR) of silver and gold nanoparticles. Multilayer adsorbates based on the interaction of HOOC(CH2)10SH and Cu2+were assembled onto surface-confined nanoparticles. Measurement of the LSPR extinction peak shift versus number of layers and adsorbate thickness is non-linear and has a sensing range that is dependent on the composition, shape, in-plane width, and out-of-plane height of the nanoparticles. Theoretical modeling confirms and offers a mathematical interpretation of these results. These experiments indicate that the LSPR sensing capabilities of noble metal nanoparticles can be tuned to match the size of biological and chemical analytes by adjusting the aforementioned properties. The optimization of the LSPR nanosensor for a specific analyte will improve an already sensitive nanoparticle-based sensor.
Photoluminescence of CuInS2 nanowires
Authors: Wakita Kazuki , Miyoshi Yoshihiro , Iwai Masaya , Fujibuchi Hideto , Ashida Atsushi 
Published: April 2011

ABSTRACTCuInS2 nanowires synthesized by a chemical treatment method were examined using X-ray diffraction and field emission-scanning electron microscopy (FE-SEM). The nanowires, which were identified to have a chalcopyrite structure of CuInS2, were 30–100 nm in diameter and several micrometers in length. A remarkable correlation between the color of a sample with nanowires and their FE-SEM image was disclosed. Photoluminescence spectra of the obtained nanowires were also studied. At low temperatures (∼ 10K) a broad peak centered at photon energy of 2.05 eV was observed. This energy is by 0.5 eV larger than the energy gap of the well-studied crystalline bulk samples of CuInS2. The observed rise in energy can be ascribed to quantum size effects expectedly developing in CuInS2 samples with nanosize dimensions.
Photoluminescence Properties and Zeta Potential of Water-Dispersible CdTe Nanocrystals
Authors: Ando Masanori , Li Chunliang , Murase Norio 
Published: April 2011

ABSTRACTThe photoluminescent (PL) properties and zeta potential of green-emitting CdTe nanocrystals (diameter: 3 nm) capped with a stabilizing surfactant, thioglycolic acid (TGA), have been investigated as a function of pH of the aqueous solution. The green PL intensity reached the maximum at pH5.1 and was somewhat lower in the pH range of 6–10, which was similar to the previously reported result. However, when the pH was at and below 4, the green PL intensity decreased drastically. The relative ratio of the dissociation form of the carboxyl group of TGA showed a large diminution at and below pH5 accompanied by a significant decrease of the absolute value of zeta potential. Since the absolute value of zeta potential reflects the stability of nanocrystals, the results obtained shows that the TGA-capped CdTe nanocrystals are stable only in basic to neutral regions and that the agglomeration of the nanocrystals in acidic range reflects the transition from the dissociated (charged) form to the non-dissociated (non-charged) form of a carboxyl group in TGA. Encapsulation of nanocrystals in glass is a promising way to further improve the long-term photostability of nanocrystals. Therefore, we chose an alkoxide having an amino group for a matrix for the encapsulation. The amino group has a good affinity to TGA as well as promotes the sol-gel reaction. As the result, the CdTe nanocrystals have been dispersed finely in the glass matrix without a deterioration of PL intensity.
Thermoelectric power, electrical and thermal resistance, and magnetoresistance of nanowire composites.
Authors: Heremans Joseph P. 
Published: April 2011

ABSTRACTThe thermoelectric power of bismuth nanowires is theoretically calculated to be greatly enhanced over that of bulk Bi. This is a result of the size-quantization of the electron wavefunction in nanowires with diameters below 50 nm. The effect is expected to lead to the development of high figure of merit thermoelectric materials. We review here the experimental observation of such enhancement in composites containing nanowires with diameters down to 9 nm. When the wire diameter is further decreased, localization effects take over and limit the thermopower. The theory further predicts the appearance of an energy gap in bismuth nanowires with diameters below 50 nm. We observe such a gap in the temperature dependence of the resistivity. The dependence of the gap on nanowire diameter is consistent with theory. Comparisons of the transport properties of Bi nanowires with those in other nanowire systems show the influence of localization effects.
The Synthesis of Ce-Filled CoSb3 and Characterization of its Magnetic and Structural Properties
Authors: Smalley Arwyn L. E. , Howe Brandon , Johnson David C. 
Published: April 2011

ABSTRACTA series of cerium-containing CoSb3 samples were synthesized, with cerium quantities varying from 0 to 2 stoichiometric equivalents. These samples were annealed at low temperatures to crystallize the kinetically stable phases CexCo4Sb12 (x = 0–0.5). X-ray diffraction showed that these samples were phase pure, and Rietveld analysis on x-ray diffraction data from powder samples indicated that these samples were 25–88% crystalline. Electrical measurements showed that these samples are n-type, which was previously unknown in CexCo4Sb12. Magnetic measurements showed that the samples were paramagnetic due to the cerium being incorporated into the diamagnetic CoSb3 compound. In addition, they contained a ferromagnetic component that was attributed to the amorphous, cerium-containing phase.
New Directions for Low Dimensional Thermoelectricity
Authors: Dresselhaus M. S. , Lin Y. M. , Black M. R. , Rabin O. , Dresselhaus G. 
Published: April 2011

ABSTRACTLow dimensionality provides opportunities to modify the properties of bulk materials dramatically and to control materials properties independently in a manner that is not possible for bulk materials. The special characteristics of low dimensional materials to enhance thermoelectric performance have already been demonstrated in quantum wells, quantum wires and quantum dots. The main focus of this review is a summary of advances made in the modeling of quantum dot superlattice nanowires. Several new research directions for low dimensional thermoelectricity or inspired by this research are briefly mentioned.
Approaches to thermal isolation with thin-film superlattice thermoelectric materials
Authors: Addepalli Pratima , Reddy Anil J. , Venkatasubramanian Rama 
Published: April 2011

ABSTRACTWe propose the use of hetero-structured high ZT materials in thermally isolated thermoelectric couples for the purpose of improving overall device efficiency. Use of high ZT material incorporated in convective flow devices will yield a two-fold improvement in COP over isothermal TE devices. The analytical approach presented in this paper requires optimization of TE element aspect ratio according to available ΔT at location in the device. We discuss the limitations on thermoelectric element characteristics and geometry to achieve high COP. We also utilize moderate temperature differentials to meet the target of high COP. If space requirements are restrictive, or materials processing is limited, the materials described herein provide the unique ability to alter Seebeck coefficient, thermal conductivity, and electrical such that the required aspect ratio is suitable. Improvement in Seebeck coefficient and electrical resistivity independently increase COP by as much as 25% or more when applied to thermally isolated device considered.
SiGeC Cantilever Micro Cooler
Authors: Zeng Gehong , Shakouri Ali , Croke Edward , Zhang Yan , Christofferson James , Bowers John E. 
Published: April 2011

ABSTRACTThe fabrication and characterization of SiGeC cantilever microcoolers are described. Silicon on insulator (SOI) was used as the substrate, and two layers of 3 μm p-SiGe0.07C0.0075 and 1.14 μm n-SiGe0.07C0.0075 lattice matched to silicon were grown using molecular beam epitaxy. The uni couple cooler was fabricated using conventional integrated circuit (IC) processing, and the cantilever structure was finally formed by removing the backside Si of SOI substrate by deep reactive ion etching. Devices with different n- and p-side length ratios were characterized. Cooling by 1.2K has been measured at room temperature. Modeling showed that the device performance was dominated by the smaller cooling temperature of the p-SiGeC leg of the cantilever structure. Parasitic heat conduction through the Si buffer layer is the main limitation to the device performance.
Experimental Characterization and Modeling of InP-based Microcoolers
Authors: Singh Rajeev , Vashaee Daryoosh , Zhang Yan , Negassi Million , Shakouri Ali , Okuno Yae , Zeng Gehong , LaBounty Chris , Bowers John 
Published: April 2011

ABSTRACTWe present experimental and theoretical characterization of InP-based heterostructure integrated thermionic (HIT) coolers. In particular, the effect of doping on overall device performance is characterized. Several thin-film cooler devices have been fabricated and analyzed. The coolers consist of a 1μm thick superlattice structure composed of 25 periods of InGaAs well and InGaAsP (λgap ≈ 1.3μm) barrier layers 10 and 30nm thick, respectively. The superlattice is surrounded by highly-doped InGaAs layers that serve as the cathode and anode. All layers are lattice-matched to the n-type InP substrate. N-type doping of the well layers varies from 1.5×1018cm−3 to 8×1018cm−3 between devices, while the barrier layers are undoped. Device cooling performance was measured at room-temperature. Device current-versus-voltage relationships were measured from 45K to room-temperature. Detailed models of electron transport in superlattice structures were used to simulate device performance. Experimental results indicate that low-temperature electron transport is a strong function of well layer doping and that maximum cooling will decrease as this doping is increased. Theoretical models of both I-V curves and maximum cooling agree well with experimental results. The findings indicate that low-temperature electron transport is useful to characterize potential barriers and energy filtering in HIT coolers.
Cooling Power Density of SiGe/Si Superlattice Micro Refrigerators
Authors: Zeng Gehong , Fan Xiaofeng , LaBounty Chris , Croke Edward , Zhang Yan , Christofferson James , Vashaee Daryoosh , Shakouri Ali , Bowers John E. 
Published: April 2011

ABSTRACTExperiments were carried out to determine the cooling power density of SiGe/Si superlattice microcoolers by integrating thin film metal resistor heaters on the cooling surface. By evaluating the maximum cooling of the device under different heat load conditions, the cooling power density was directly measured. Both micro thermocouple probes and the resistance of thin film heaters were used to get an accurate measurement of temperature on top of the device. Superlattice structures were used to enhance the device performance by reducing the thermal conductivity, and by providing selective emission of hot carriers through thermionic emission. Various device sizes were characterized. The maximum cooling and the cooling power density had different dependences on the micro refrigerator size. Net cooling over 4.1 K below ambient and cooling power density of 598 W/cm2 for 40 × 40 μm2 devices were measured at room temperature.
Superlattice Thin-film Thermoelectric Materials and Devices
Authors: Venkatasubramanian Rama , O'Quinn Brooks , Siivola Edward , Coonley Kip , Addepally Pratima , Napier Mary , Colpitts Thomas 
Published: April 2011

ABSTRACTThin-film nano-structured materials offer the potential to enhance the performance of thermoelectrics, with near-term capabilities like small-footprint coolers for lasers and microprocessors. Our recent focus has been to transition the enhanced figure-of-merit (ZT) in p-type Bi2Te3/Sb2Te3 and n-type Bi2Te3/Bi2Te3-xSex superlattices to performance at the module level with several device demonstrations. We have been able to obtain a best ZT of ∼2 in a p-n couple, the fundamental cooling or power conversion unit in an operational module. In addition, we have been able to demonstrate p-n couple ZT of as much as 1.6 from heat-to-power efficiency data. The thermal interface resistances between the active device and the external heat source have been optimized. A power level of 38 mW per couple for a ΔT of about 107K, with 4-micron-thick element, was obtained. This translates to an active power density of ∼54 W/cm2 and a mini-module power density of ∼10.5 W/cm2. In short, power devices with thin-film superlattices are a real possibility. In the cooling arena, we have been able to obtain over 50K active cooling with thin-film modules, useable in several laser and microprocessor cooling needs. This is in spite of severe thermal management issues that had to be overcome noting that the “true” hot-side temperature, and hence the “true” ΔT, across the device are much higher. Even so, we have p-n superlattice couples that show twice the cooling ΔTmax, compared to the best bulk p-n couples at cryogenic temperatures. Some of the challenges that remain to be addressed in the full development of this materials technology and thoughts on further progress in nano-structured materials are presented.
Thermal Stability of p-type Bi2Te3/Sb2Te3 and n-type Bi2Te3/Bi2Te2-xSex Thermoelectric Superlattice Thin Film Devices
Authors: Coonley K. D. , O'Quinn B. C. , Caylor J. C. , Venkatasubramanian R. 
Published: April 2011

ABSTRACTThermolectric devices have been constructed using Bi2Te3/Sb2Te3 and Bi2Te3/Bi2Te2-xSex superlattice thin films. Since these devices are intended for use in systems that will operate at elevated temperatures over their lifetime as in many power conversion applications, thermal stability of the thermoelectric figure of merit is an important consideration. The ZTe of p-type and n-type superlattice thin film elements was evaluated at specific intervals during exposure to elevated temperatures of 150°C for up to 60 hrs. Results indicate that the figure of merit for p- and n-type superlattice films is not compromised over time when exposed to these operating temperatures. In fact, both p- and n-type superlattice thin film ZTe remains very constant or improves slightly when subjected to continuous exposure to elevated temperatures. Evaluation of these thin film thermoelements is reported and implications of these results are considered for thin film thermoelectric modules.
Structural analysis and thermoelectric properties of Type-I clathrate compounds in the Ba-Ge-Ga system
Authors: Okamoto Norihiko L. , Nishii Takumi , Oh Min Wook , Inui Haruyuki 
Published: April 2011

ABSTRACTThe crystal structure and thermoelectric properties of Type-I clathrate compounds in the Ba-Ge-Ga system (Ba8GaXGe46-X) have been investigated as a function of Ga content. While all ternary compounds containing more than 3 Ga exhibit a crystal structure of normal Type-I clathrates with the space group Pm 3 n, the binary compound possesses a composition Ba8Ge43, which is leaner in Ge than the stoichiometric composition, and has a crystal structure different from that of normal Type-I clathrates because of the ordering of Ge vacancies in 6c sites of the parent normal Type-I clathrate structure. The temperature dependence of electrical resistivity of binary Ba8Ge43 is of semiconductor while that for all the ternary compounds is metallic. The value of Seebeck coefficient increases with the increase in the Ga content. The value of dimensionless figure of merit (ZT) increases with the increase in the Ga content, exhibiting a high value of 0.76 at 700°C for Ba8Ga16Ge30.
Quantum Well Thermoelectric Devices
Authors: Ghamaty S. , Elsner N. B. 
Published: April 2011

ABSTRACTThis paper discloses the recent developments of high efficiency quantum well thermoelectrics at Hi-Z Technology, Inc. The performance of the latest P type B4C/B9C- N-type Si/SiGe couple will be presented as well as data for the new N-type Si/SiC that will replace Si/SiGe and improve couple efficiency.Preliminary calculations regarding the development of actual quantum well modules will be presented for power prediction. These modules can be used in future energy conversion system as well as air conditioning system designs.Our current efforts to produce quantum well films more rapidly will be discussed.
Properties of metallic NaxCo2O4 thermoelectric materials
Authors: Tang Xiaofeng , Tritt Terry M. , Abbott Ed , Kolis J. K. 
Published: April 2011

AbstractSince the quite favorable thermoelectric properties of transition-metal oxide NaCo2O4 were first reported by Terasaki in 1997, extensive research work has been conducted, including the efforts to improve TE properties through doping or new synthesis approaches. In addition, theoretical investigations about the enhanced thermopower coupled with the small resistivity values for the metallic NaxCo2O4 have been investigated. The advent of the large thermopower and low resistivity appears not able to be explained via conventional free-electron theory. In this paper, thermoelectric and magnetic properties, including resistivity, thermopower, thermal conductivity, magnetic susceptibility and moment of single crystals and polycrystalline NaxCo2O4 are reported. The effect of Na concentration on the transport properties will also be discussed.
CoGe1.5Se1.5: Synthesis and characterization
Authors: Ertenberg R. , Beekman M. , Martin J. , Fowler G. , Nolas G.S. 
Published: April 2011

ABSTRACTPolycrystalline CoGe1.5Se1.5 was synthesized and characterized. The compound is a member of the class of compounds with the skutterudite crystal structure. Synthesis assuming the above stoichiometry resulted in a n-type semiconductor with composition CoGe1.452Se1.379. The specimen exhibits a large room temperature Seebeck coefficient and resistivity. The electron mobility is very low and the thermal conductivity is lower than that of the binary skutterudite CoSb3. These properties can be attributed to the vacancies in the crystal lattice due to the non-stoichiometric nature of the specimen. The potential for thermoelectric applications of ternary skutterudites is also discussed.
Effects of alloying elements on thermoelectric properties of ReSi1.75
Authors: Oh Min Wook , Gu Jia-Jun , Kuwabara Kosuke , Inui Haruyuki 
Published: April 2011

ABSTRACTS:The thermoelectric properties as well as microstructure of binary and some ternary ReSi1.75 have been investigated. Binary ReSi1.75 exhibits a nice thermoelectric property as exemplified by the high value of dimensionless figure of merit (ZT) of 0.70 at 800 °C when measured along [001], although the ZT value along [100] is just moderately high. Mo substitution for Re in ReSi1.75 considerably increases the ZT value along [001] because of the decreased electrical resistivity, while the property improvement is not significant along [100]. On the other hand, Al and Ge substitutions for Si in ReSi1.75 considerably increase the ZT value along [100]. This is also because of the decreased electrical resistivity. When Al is added to ReSi1.75, the value of electrical resistivity is significantly reduced when compared to the binary counterpart and the temperature dependence of electrical resistivity changes from of semiconductor for the binary alloy to of metal for the Al-added alloys.