bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermally Grown and Reoxidized Nitrides as Alternative Gate Dielectrics
Authors: Ludsteck Alexandra , Dietl Waltraud , Chung Hinyiu , Schulze Joerg , Nenyei Zsolt , Eisele Ignaz
Published: April 2011

The use of high-k materials as gate dielectric still meets a lot of unsolved problems such as thermal instability during post deposition anneals resulting in the formation of interfacial oxide layers or bad process compatibility. As long as these requirements are not accomplished alternative gate dielectrics have to be formed by oxynitrides or gate stacks built of oxynitrides and some high-k material. In order to achieve a low equivalent oxide thickness (EOT) it is necessary to grow homogeneously thin oxynitrides which are nitrogen-rich and which have a high interface quality. Therefore we have studied the growth of thin nitrides and oxynitrides (EOT = 1 – 2nm) formed by rapid thermal nitridation in NH3 and wet reoxidation. By varying the partial pressure of NH3 in the process gas ambient NH3/Ar the nitride quality could be optimized: it was found that an optimized ratio of NH3 and Ar during nitridation improves the electrical properties of the nitrides and oxynitrides significantly. Interface state densities as low as those of dry thermal oxides and leakage current densities reduced by four orders of magnitude compared to SiO2 of the same EOT have been obtained. Due to the high incorporation of nitrogen into the oxynitride by rapid thermal nitridation and following oxidation the leakage current densities are also lower than those of most oxynitrides reported in literature. In addition we present data concerning the suppression of boron diffusion from p+ poly-Si electrodes. In summary the developed oxynitrides are suitable to bridge the gap between common SiO2 and new alternative gate dielectrics or to form gate stacks in combination with high-k materials.
High-k ZrO2 Gate Dielectric on Strained-Si
Authors: Bhattacharya S. , Samanta S. K. , Chatterjee S. , McCarthy John , Armstrong B. M. , Gamble H. S. , Maiti C. K. , Perova T. , Moore A.
Published: April 2011

The growth and structural characterization of UHV-compatible LPCVD grown strained-Si layer on linearly graded relaxed SiGe layer and the electrical properties of the high-k ultrathin ZrO2 films deposited on strained-Si layer using microwave-plasma CVD at low temperature (150°C) are reported. The strained-Si layer has been characterized using AFM, TEM and Raman spectroscopy. The C-V and G-V characteristics of ZrO2 films have been used to calculate the interface trap density, Dit, near the midgap energy, and the fixed oxide charge density, Qf/q. These are found to be 2.24 × 1012 cm−2 eV−1 and 1.45 × 1011 cm−2, respectively. Poole-Frenkel (PF) conduction mechanism is found to dominate the current conduction at room temperature.
Ab-initio study on the γ-Al2O3 surfaces and interfaces.
Authors: Pinto Henry P. , Elliott Simon D.
Published: April 2011

The controlled growth of alumina films by atomic layer deposition (ALD) is of great interest to the electronics industry, as high-k dielectrics are being sought for the next-generation of MOSFETS. We present a theoretical study of the alumina polymorph γ-Al2O3 based on density functional theory (DFT). The predicted bulk structure for γ-Al2O3 has the Al vacancy sites widely separated, which is in agreement with other theoretical predictions. We estimated the energy of several γ-Al2O3 surfaces namely: (111), (110) and (110). The atomic and electronic structure of the most stable (111) surface is discussed and compared with α-Al2O3 (0001). The adsorption and dissociation of the H2O onto the (111) surface is considered and H-diffusion is simulated. Finally, a model for the γ-Al2O3 (111)/aluminium-hydroxide interface is proposed and considered as an intermediate stage in the γ-alumina film growth mechanism.
Bonding and Epitaxial Relationships at High-K Oxide:Si interfaces
Authors: Robertson J , Peacock P W
Published: April 2011

The bonding at interfaces of Si(100) with SrTiO3, LaAlO3 and HfO2 are considered using simple electron counting models.
p-type in ZnO:N by codoping with Cr
Authors: Kaminska E. , Piotrowska A. , Kossut J. , Butkute R. , Dobrowolski W. , Golaszewska K. , Barcz A. , Jakiela R. , Dynowska E. , Przezdziecka E. , Wawer D.
Published: April 2011

We report on the fabrication of p-ZnO films by thermal oxidation of Zn3N2 deposited by reactive rf sputtering. With additional chromium doping we achieved p-type conductivity with the hole concentration ∼5×1017cm−3 and the mobility of 23.6 cm2/Vs at room temperature. We developed a method of surface passivation of p-ZnO that maintains its p-type conductivity over time-scale of months.
Improved structural properties of sputtered hafnium dioxide on silicon and silicon oxide for semiconductor and sensor applications
Authors: Grüger H. , Kunath Ch. , Kurth E. , Pufe W. , Sorge S.
Published: April 2011

Hafnium dioxide HfO2 is a candidate with promising properties for semiconductor industries as well as for optical and sensorial applications under harsh environments. The material can be deposited using various techniques such as CVD or PVD in different thickness ranges. The chemical inertness of HfO2 and the high band gap draw the attention of this paper towards application in optics as active and protective layer at the same time, chemical and physical sensors, such as moisture sensors and thin film capacities. In order to improve the layer properties with the sensorial application in mind, the deposition process and the post-processing need to be tightly controlled.

Layers with thicknesses between 100 and 150nm have been deposited by r.f. sputtering of a high purity HfO2 target onto bare or oxidized silicon wafers under Ar- or Ar/O2-athmospheres. Initially the HfO2 has a mainly amorphous structure. Subsequent annealing controls the growth of recrystallized areas characterized by grain size and ratio between crystals and amorphous bodies. High heating rates of about 50K/s and annealing temperatures ranging 800 to 1000°C in a rapid thermal annealing (RTA) chamber seem to be advantageous for the properties desired. The layer's structure such as grain size, crystal type and orientation was investigated using AFM, TEM and XRD. Layer tension was evaluated using laser deflection. The differences in structure found have been correlated to the chemical inertness obtained in measurements for layer applications.
Transparent Transistors Based on Semiconducting Oxides
Authors: Kwon Y.W. , Li Y. , Heo Y.W. , Jones M. , Vijay  , Jeong B.S. , Zhou J. , Li S. , Holloway P. , Norton D.P.
Published: April 2011

The synthesis and properties of oxide-based thin film transistors (TFTs) is reported using pulsed laser deposition. The field effect transistors use ZnO as the channel material. Low leakage current density is achieved with amorphous (CeTb)MgAl11O19 (CTMA) serving as the gate oxide, whose dielectric strength is measured to be > 5MV/cm for structures fabricated on Indium Tin oxide (ITO) substrates. Capacitance-voltage properties show that n-type active layers are realized with undoped ZnO. Charge densities in undoped ZnO are measured to be 1018 to 1019 / cm3 using Hall measurement and CV plots. Current-voltage measurements for TFT operation are reported. Channel materials on patterned substrates show high conductance and modulation of channel conductance. C-V measurements with MOS structure using doped ZnO and ZnxMg1-xO will also be described. The properties of depletion mode TFTs fabricated with doped and undoped oxide channel will be discussed in detail.
Fabrication of SrRuO3 Epitaxial Thin Films on YBa2Cu3Ox / CeO2 / YSZ - Buffered Si Substrates by Pulsed Laser Deposition
Authors: Higuchi Takamitsu , Morozumi Koichi , Iwashita Setsuya , Ishida Masaya , Shimoda Tatsuya
Published: April 2011

Pseudocubic SrRuO3 (100) epitaxial thin films were fabricated on Si (100) with a YBa2Cu3Ox / CeO2 / YSZ (yttria-stabilized-zirconia) triple buffer layer ∼ 14 nm thick by pulsed laser deposition (PLD). Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) revealed that the first buffer layer of YSZ (100) was epitaxially grown on naturally oxidized Si (100) substrates with the process condition of PB (base pressure) = 1×10-Torr, PO2 (oxygen partial pressure) = 5×10- Torr, and Ts (substrate temperature) = 700 °C. Higher deposition rate of YSZ in the range of 0 ∼ 0.6 nm/min brought about better crystallinity with a smaller value of a full-width at half maximum (FWHM) in the YSZ (200) rocking curve. Subsequent deposition of CeO2, YBa2Cu3Ox, and SrRuO3 resulted in an SrRuO3 (100) epitaxial thin film exhibiting good crystallinity with FWHM = 1.7° in the SrRuO3 (200) rocking curve.
Elementary processes during the epitaxial growth of metal oxides: MgO/MgO(001).
Authors: Geneste Gregory , Morillo Joseph , Finocchi Fabio , Hayoun Marc
Published: April 2011

Elementary processes governing the epitaxial growth of metal oxides, like adsorption and diffusion, have been studied theoretically in the prototypical case of MgO/MgO(001). Most of these processes need to be investigated in an ab initio approach since they are usually accompanied by strong modifications of the electronic structure. This study has been carried out within the density functional theory, and complemented by molecular dynamics simulations using a rigid-ion potential. The growth of the oxide passes through several oxido-reduction reactions at the surface. The adsorption and the diffusion of Mg and O are strongly different from each other, and change considerably at steps from flat terraces. All these results point out the need of realistic models for the growth of metal oxides that take into account the chemical behaviour of the involved species as well as the influence of the defects.
Electrical Characteristics of Metal - (La0.27Y0.73)2O3 - Silicon Capacitors
Authors: Preisler E. J. , Bojarczuk N. A. , Guha S.
Published: April 2011

An investigation of metal-insulator-silicon capacitors, utilizing single crystal (La0.27Y0.73)2O3 as the insulator is presented. Crystalline insulators are of interest because of the possibilities of obtaining an atomically flat interface and entirely eliminating the presence of dangling bonds at the interface.

Capacitance – voltage measurements performed on MIS capacitors demonstrate a dielectric constant of 11.4 and suggest the absence of any interfacial silicon oxide layer. The equivalent oxide thickness of the sample with the thinnest dielectric layer is 15 Å. The density of interface states for the best samples is found to be in the mid 1012 cm−2eV−1 range and did not vary significantly after typical annealing treatments.
Hetero-Epitaxy of Crystalline Perovskite Oxides on GaAs(001)
Authors: Liang Y. , Kulik J. , Wei Y. , Eschrich T. , Curless J. , Craigo B. , Smith S.
Published: April 2011

Hetero-epitaxy of crystalline perovskite SrTiO3 and BaTiO3 on GaAs(001) was achieved using molecular beam epitaxy. A number of surface and interface techniques were used to characterize the growth, structural, and chemical properties of epitaxial oxide films on GaAs. Reflection-high-energy-electron diffraction of SrTiO3 and BaTiO3 showed streaky diffraction features and low diffraction background through out growth, indicating that the epitaxial SrTiO3 and BaTiO3 films had good crystallinity. X-ray diffraction showed an epitaxial relationship between these perovskite oxides and GaAs(001) substrates. Transmission electron microscopy and scanning probe microscopy revealed an abrupt oxide/GaAs interface and smooth SrTiO3 and BaTiO3 surfaces. The success of growth of epitaxial perovskite oxides on GaAs enabled us to integrate a number of functional oxides such as piezoelectric and magnetic oxides epitaxially on GaAs substrates.
Molecular Simulations of Recognitive Polymer Networks Prepared by Biomimetic Configurational Imprinting as Responsive Biomaterials
Authors: Henthorn David B. , Peppas Nicholas A.
Published: April 2011

Proteins, enzymes, and antibodies have the ability to discern specific molecules out of a whole host of species and selectively bind them with remarkable affinity. A route that would enable the creation of synthetic polymers with this binding ability would be a great advance with subsequent applications in chemical sensors, single-molecule separations, and even artificial enzymes. In this work we study the molecular imprinting process whereby a controlled nanostructure consisting of distinct binding sites is created in a polymer network through a templating procedure. Simulations were done to better understand the underlying network structure that gives rise to the increased uptake. An all-atom molecular dynamics simulation was coupled with a kinetic gelation approach to study network formation in the presence of a template. The monomers used were first studied with density-functional theory in order to parameterize a force field for various methacrylates. Simulation results showed three key functional group interactions that lead to successful imprinting and subsequent rebinding.
Isomeric glucose recognition using molecularly imprinted polymer hydrogels
Authors: Parmpi Paraskevi , Bolisay Linden D.V. , Kofinas Peter
Published: April 2011

The goal of this research is to produce molecular imprinted polymers (MIPs), which selectively bind glucose over other sugars. MIP hydrogels against glucose exhibited binding capacities in excess of 0.6 grams of glucose per gram of dry gel in a 100 % DI H2O glucose solution, as well as in a 50–50 % glucose-fructose solution mixture. Equilibrium binding capacities of fructose were lower than those observed with respect to glucose, indicating an isomeric preference for the binding of glucose over fructose. Although it is expected that imprinted cavities will be distorted due to the swelling of the hydrogel in water, our experiments show that even the swollen gels exhibit remarkable glucose recognition. This synthetic and characterization methodology for MIPs might thus offer exciting avenues for novel biomimetic recognition and isomeric separation techniques.
Molecularly Imprinted Micro- and Nano-Particles by Precipitation Polymerization
Authors: Ye Lei
Published: April 2011

Molecularly imprinted micro- and nano-particles can be conveniently prepared using precipitation polymerization method. By controlling the initial reaction composition, the resulting polymer particles may be obtained as uniform beads that display favourable binding characteristics. Incorporation of a novel reporter element resulted in an imprinted scintillation polymer that displayed an enhanced signalling efficiency.
Preparation of Metal Oxide Nanowires by Hydrothermal Synthesis in Supercritical Water
Authors: Hakuta Yukiya , Hayashi Hiromichi , Arai Kunio
Published: April 2011

Three kinds of single metal oxide (MnO2, ZnO, and AlO(OH)) and one complex metal oxide (K2O·6TiO2) having nano structure of wire, rod and ribbon were rapidly synthesized by hydrothermal synthesis in supercritical water. Aqueous Mn(NO3)2, Zn(NO)2, Al(NO3)3 solutions and mixtures of TiO2 sols and KOH solutions were used as starting materials, respectively. Syntheses of these nanostructured materials were performed by a flow type apparatus. We investigated the relationship between reaction parameters (temperature, pH and reaction time) and morphologies of the products. Reaction temperatures were 350, 400, and 420 °C. Reaction time is in the range of 1.8 – 116 s. The product was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that particle morphologies strongly depend on pH for MnO2 and ZnO. MnO2 nanowires with 10 nm in diameter and ZnO nanorods with 50 nm in diameter were obtained from acidic metal salt solutions. In the case of AlO(OH), temperature and time were key parameters for crystal growth. In the case of K2O6TiO2, larger fibrous particles with 50 nm in diameter were obtained at higher reaction temperature.
ZnS nanoparticles synthesis and characterization
Authors: Axmann Yvonne , Petri Alke , Hofmann Heinrich
Published: April 2011

ZnS:Mn2+ nanoparticles were synthesized via a wet chemical method with L-cysteine as the stabilizing agent. The obtained aqueous dispersions show an orange luminescence, which is typical for the 4T1 → 6A1 transition within the Mn2+ d-orbitals. The fluorescence quantum yield has been determined with quinine sulphate as a dye reference. It can be increased after formation of a SiO2 shell around the particles by a factor of three. The particle size was determined with transmission electron microscopy (TEM), X-ray diffraction and PCS measurements.
Photocurrent in a hybrid system of 1-thioglycerol and HgTe quantum dots
Authors: Kim Hyunsuk , Cho Kyoungah , Min Byungdon , Lee Jong Soo , Sung Man Young , Kim Sung Hyun , Kim Sangsig
Published: April 2011

Photocurrent mechanism in a hybrid system of 1-thioglycerol and HgTe quantum dots(QDs) was studied for the first time in the intra-red (IR) range. 1-thioglycerol-capped HgTe QDs were prepared using colloidal method in aqueous solution; the synthesis and size of the HgTe QDs were examined by x-ray diffraction, Raman scattering, and high-resolution transmission electron microscopy. Absorption and photoluminescence spectra of the capped HgTe QDs revealed the strong excitonic peaks in the range from 900 to 1100nm, because of their widened band gap due to the shrinkage of their sizes to about 3 nm. The wavelength dependence of the photocurrent for the hybred system of the 1-thioglycerol and HgTe QDs was very close to that of the absorption spectrum, indicating that charge carriers photoexcited in the HgTe QDs give direct contribution to the photocurrent in the medium of 1-thioglycerol. In this hybrid system, the photo-excited electrons in the HgTe QDs are strongly confined, but the photo-excited holes act as free carriers. Hence, in the photocurrent mechanism of the this hybrid system, only holes among electron-hole pairs created by incident photons in the HgTe QDs are transferred to 1-thioglycerol surrounding HgTe QDs and contribute photocurrent flowing in the medium of 1-thioglycerol.
Visible Light Emission from Erbium Doped Yttria Stabilized Zirconia
Authors: Cross Michael , Varhue Walter
Published: April 2011

ABSTRACT: One of the major shortcomings of silicon (Si) as a semiconductor material is its inability to yield efficient light emission. There has been a continued interest in adding rare earth ion impurities such as erbium (Er) to the Si lattice to act as light emitting centers. The low band gap of Si however has complicated this practice by quenching and absorbing this possible emission. Increasing the band gap of the host has been successfully tried in the case of gallium nitride (GaN) [1] and Si-rich oxide (SRO) [2] alloys. A similar approach has been tried here, where Er oxide (ErOx) nanocrystals have been formed in a yttria stabilized zirconia (YSZ) host deposited on a Si (100) substrate. The YSZ is deposited as a heteroepitaxial, insulating layer on the Si substrate by a reactive sputtering technique. The Er is also incorporated by a sputtering process from a metallic target and its placement in the YSZ host can be easily controlled. The device structure formed is a simple metal contact/insulator/phosphor sandwich. The device has been found to emit visible green light at low bias voltages. The advantage of this material is that it is much more structured than SiO2 which can theoretically lead to higher emission intensity.
Monocrystalline InP Nanotubes
Authors: Bakkers Erik. P. A. M. , Feiner Louis F. , Verheijen Marcel. A. , van Dam Jorden A. , Franceschi Silvano De , Kouwenhoven Leo
Published: April 2011

Indium phosphide (InP) nanowires and nanotubes have been synthesized via the vapor-liquid-solid (VLS) growth mechanism. The wires as well as the tubes are crystalline and have the (bulk) zinc blende structure. Compared to the nanowires the nantubes are formed at higher temperatures. A simple model for the formation of the nanotubes is presented. The diameter of the wires and the wall thickness of the tubes can be controlled by the synthesis temperature. Photoluminescence measurements on individual wires show a strong polarization dependency. Moreover, the nanostructures exhibit a considerable blue shift with respect to bulk emission as a result of size-quantization. In addition, this blue shift indicates that the optical properties are not dominated by defect states.
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

We 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

This 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

We 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

The 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

CuInS2 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

The 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

The 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.
Solvothermal preparations of nanocrystalline Bi2Te3 powders and the study on their characterizations
Authors: Ji Xiaohua , Zhao Xinbing , Zhang Yanhua , Lu Bo-hui , Ni Hualiang
Published: April 2011

[Abstract] Bi2Te 3 nanoparticles of 15∼25nm were prepared via solvothermal processes in which pyridine, absolute ethanol and distilled water were used as reaction medium respectively. The XRD and TEM have been applied to analyze the samples, and the grain sizes have also been calculated by Scherrer Equation. The results showed that in these experiments, all of the reaction products' purity, crystallization, grain size and tropism increased with dielectric constant and polarity of the solvent. A novel Bi2Te3 nanowires with several tens to a hundred nanometers diameter and up to more than ten microns length have been prepared when distilled water was used as reaction medium.
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

A 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

Low 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

We 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

The 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

We 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

Experiments 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

Thin-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

Thermolectric 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

The 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

This 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

Since 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

Polycrystalline 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.
Synthesis and Characterization of Bismuth Sulfide and Bismuth Telluride Nanorods and their Polyaniline Nanocomposites
Authors: Reddy Ven B. , Garrity Patrick L. , Stokes Kevin L.
Published: April 2011

We present here a simplified approach to the synthesis of bismuth sulfide and bismuth telluride nanorods and their polyaniline(PAN)-coated nanocomposites. The present method gives highly crystalline nanorods of bismuth sulfide of varying aspect ratio depending on the capping ligand employed, and involves reacting bismuth(III) trioleate with thioacetamide in phenyl ether at elevated temperatures in the presence of excess capping ligand. Bismuth telluride was obtained in high yields by reacting bismuth(III) trioleate with trioctylphosphine telluride at relatively low temperature. Oleic acid, sodium dodecylsulfonate and sodium dodecylbenzene sulfonate, used as capping ligands, did not have significant effect on the aspect ratio of Bi2Te3 nanorods. The nanostructured materials obtained this way were then coated with polyaniline (PAN) by heating a specific amount of material with half as much PAN in toluene close to reflux temperature for 6–8 h. It was necessary to keep the mixture thoroughly stirred and intermittently sonicated in order to ensure that the particles remain dispersed at all times. Bismuth chalcogenide nanoparticles as well as their composites were characterized using transmission electron microscopy and X-ray powder diffraction.
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.
Mechanical strain evolution in Cu/low K interconnect lines
Authors: Besser Paul R. , Jiang Qing-Ting
Published: April 2011

The mechanical stresses in Cu interconnect lines arise from thermal expansion (CTE) differences, and the magnitude of the stress can be calculated based on the measured strain. In the current work, the strain (and stress) state of narrow Cu lines fabricated in oxide and porous organic spin-on dielectrics (low K) has been determined with X-Ray diffraction (XRD) during annealing. The room temperature stress along the length (X) and width (Y) of the lines are not dramatically different while the Z component is somewhat smaller with the spin-on ILD. These small perturbations in the magnitude of the Cu stress do not reflect the dramatic differences in the CTE. More insight into the materials system is obtained by studying the strain-temperature behavior, which illustrates the effect of the ILD clearly. The X strain is similar in magnitude and variation with temperature for both ILDs, supporting strain being imposed by the substrate. However, the Z strain is compressive at RT and linearly increases with temperature for Cu in low K, reflecting the lack of constraint by the ILD and the higher CTE of the ILD.
Use of the curvature method to determine the misfit stress of epitaxial semiconducting systems: the case of samples thinned for TEM observation.
Authors: Ponchet A. , Cabié M. , Durand L. , Rivoal M. , Rocher A.
Published: April 2011

The curvature method which allows to measure the stress in epitaxial layers has been adapted to transmission electron microscopy observations. The samples thinned by the substrate side present some particular mechanical characteristics. The ratio between the substrate thickness and the layer thickness should be taken into account. The experimental conditions allowing a reliable determination of the stress have been established. A finite element calculation has been used to show that the dimensions of the area where the measure is performed can not systematically be neglected. This method has been applied to the semiconducting systems Ga1-xInxAs/GaAs and Ga1-xInxAs/InP.
A Theoretical Study on the Indentation of Viscoelastic Materials
Authors: Fu Guanghui
Published: April 2011

Nanoindentation experiments have been used to investigate mechanical properties of polymeric thin films. In this paper, the problem is modeled as normal indentation of a viscoelastic half-space by a rigid smooth frictionless axisymmetric polynomial indenter. An analytical solution, which relates the indentation load to the penetration depth, is presented. The solution is valid as long as the contact region is simply connected and the indenter is in complete contact with the half-space. It shows that a similar fundamental relation exists in Laplace space.