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The effectiveness of thin films in lieu of hyperbolic metamaterials in the near field  [PDF]
Owen D. Miller,Steven G. Johnson,Alejandro W. Rodriguez
Physics , 2013, DOI: 10.1103/PhysRevLett.112.157402
Abstract: We show that the near-field functionality of hyperbolic metamaterials (HMM), typically proposed for increasing the photonic local density of states (LDOS), can be achieved with thin metal films. Although HMMs have an infinite density of internally-propagating plane-wave states, the external coupling to nearby emitters is severely restricted. We show analytically that properly designed thin films, of thicknesses comparable to the metal size of a hyperbolic metamaterial, yield a LDOS as high as (if not higher than) that of HMMs. We illustrate these ideas by performing exact numerical computations of the LDOS of multilayer HMMs, along with their application to the problem of maximizing near-field heat transfer, to show that thin films are suitable replacements in both cases.
Annealing Effect on the Thermoelectric Properties of Bi2Te3 Thin Films Prepared by Thermal Evaporation Method  [PDF]
Jyun-Min Lin,Ying-Chung Chen,Chi-Pi Lin
Journal of Nanomaterials , 2013, DOI: 10.1155/2013/201017
Abstract: Bismuth telluride-based compounds are known to be the best thermoelectric materials within room temperature region, which exhibit potential applications in cooler or power generation. In this paper, thermal evaporation processes were adopted to fabricate the n-type Bi2Te3 thin films on SiO2/Si substrates. The influence of thermal annealing on the microstructures and thermoelectric properties of Bi2Te3 thin films was investigated in temperature range 100–250°C. The crystalline structures and morphologies were characterized by X-ray diffraction and field emission scanning electron microscope analyses. The Seebeck coefficients, electrical conductivity, and power factor were measured at room temperature. The experimental results showed that both the Seebeck coefficient and power factor were enhanced as the annealing temperature increased. When the annealing temperature increased to 250°C for 30?min, the Seebeck coefficient and power factor of n-type Bi2Te3-based thin films were found to be about ?132.02?μV/K and 6.05?μW/cm·K2, respectively. 1. Introduction Because the energy sources, such as petroleum, coal, and coal gas, will exhaust in the near future. Therefore, the problem of energy shortage and greenhouse effect become more and more serious, thus energy saving and reduction of the carbon emission become very important topics. Hence, the green technology is getting more and more attention. Thermoelectric (TE) effect is the simplest technology to convert the temperature difference to electrical energy. It generates electrical energy from the useless heat by thermoelectric effect. Thermoelectric materials can directly convert heat into electricity and vice versa. They have a lot of important applications, such as power generator [1] and cooler [2]. The performance of thermoelectric materials is decided by Seebeck coefficient, electrical conductivity, and thermal conductivity. The energy conversion efficiency of the thermoelectric materials is evaluated by the figure of merit , ( , Seebeck coefficient; , electrical conductivity; , absolute temperature; and , thermal conductivity) [3]. According to the formula, in order to obtain the excellent thermoelectric figure of merit, the materials must exhibit large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Among, the is defined as the power factor (PF). Currently, the bismuth telluride (Bi-Te) and antimony telluride- (Sb-Te-) based compounds are found to be the best thermoelectric materials within the room temperature region. Furthermore, Bi-Te- and Sb-Te-based thermoelectric
Effect of Doping on Thermoelectric Property of Spray Deposited Nanostructured CdO Thin Films  [PDF]
D. Mahesh Reddy,B.G. Jeyaprakash,R. John Bosco Balaguru
Journal of Applied Sciences , 2012,
Abstract: Recently nanostructured based metal oxide thin films were preferred for thermoelectric applications due to its lower thermal conductivity than in bulk form. Cadmium oxide in bulk form has lower thermal conductivity and much work on thermoelectric studies in thin film is not reported. Hence in the present study, undoped, Zn and Mn doped CdO thin films were prepared on glass substrate using homemade spray pyrolysis technique and its structural, electrical, surface morphology and thermoelectric properties were analyzed and reported.
Disentangling the magnetoelectric and thermoelectric transport in topological insulator thin films  [PDF]
Jinsong Zhang,Xiao Feng,Yong Xu,Minghua Guo,Zuocheng Zhang,Yunbo Ou,Yang Feng,Kang Li,Haijun Zhang,Lili Wang,Xi Chen,Zhongxue Gan,Shou-Cheng Zhang,Ke He,Xucun Ma,Qi-Kun Xue,Yayu Wang
Physics , 2015, DOI: 10.1103/PhysRevB.91.075431
Abstract: We report transport studies on (Bi,Sb)2Te3 topological insulator thin films with tunable electronic band structure. We find a doping and temperature regime in which the Hall coefficient is negative indicative of electron-type carriers, whereas the Seebeck coefficient is positive indicative of hole-type carriers. This sign anomaly is due to the distinct transport behaviors of the bulk and surface states: the surface Dirac fermions dominate magnetoelectric transport while the thermoelectric effect is mainly determined by the bulk states. These findings may inspire new ideas for designing topological insulator-based high efficiency thermoelectric devices.
Polaron transport and thermoelectric behavior in La-doped SrTiO3 thin films with elemental vacancies  [PDF]
Woo Seok Choi,Hyang Keun Yoo,Hiromichi Ohta
Physics , 2015, DOI: 10.1002/adfm.201403023
Abstract: Electrodynamic properties of La-doped SrTiO3 thin films with controlled elemental vacancies have been investigated using optical spectroscopy and thermopower measurement. In particular, we observed a correlation between the polaron formation and thermoelectric properties of the transition metal oxide (TMO) thin films. With decreasing oxygen partial pressure during the film growth (P(O2)), a systematic lattice expansion was observed along with the increased elemental vacancy and carrier density, experimentally determined using optical spectroscopy. Moreover, we observed an absorption in the mid-infrared photon energy range, which is attributed to the polaron formation in the doped SrTiO3 system. Thermopower of the La-doped SrTiO3 thin films could be largely modulated from -120 to -260 {\mu}V K-1, reflecting an enhanced polaronic mass of ~3 < mpolron/m < ~4. The elemental vacancies generated in the TMO films grown at various P(O2) influences the global polaronic transport, which governs the charge transport behavior, including the thermoelectric properties.
Enhanced thermoelectric figure-of-merit in boron-doped SiGe thin films by nanograin boundaries  [PDF]
Jianbiao Lu,Ruiqiang Guo,Weijing Dai,Baoling Huang
Physics , 2014, DOI: 10.1039/c5nr00181a
Abstract: Boron-doped polycrystalline silicon-germanium (SiGe) thin films are grown by low-pressure chemical vapor deposition (LPCVD) and their thermoelectric properties are characterized from 120 K to 300 K for the potential applications in integrated microscale cooling. The naturally formed grain boundaries are found to play a crucial role in determining both the charge and thermal transport properties of the films. Particularly, the unique columnar grain structures result in remarkable thermal conductivity anisotropy with the in-plane thermal conductivities of SiGe films about 50% lower than the cross-plane values. By optimizing the growth conditions and doping level, a high figure of merit (ZT) of 0.2 for SiGe films is achieved at 300 K, which is about 100% higher than the previous record for p-type SiGe alloys, mainly due to the significant reduction in the in-plane thermal conductivity caused by nanograin boundaries. The low cost and excellent scalability of LPCVD render these high-performance SiGe films ideal candidates for thin-film thermoelectric applications.
Influence of pulsed laser deposition growth conditions on the thermoelectric properties of Ca3Co4O9 thin films  [PDF]
H. Eng,W. Prellier,S. Hebert,D. Grebille,L. Mechin,B. Mercey
Physics , 2004, DOI: 10.1063/1.1823582
Abstract: Thin films of the misfit cobaltite Ca3Co4O9 were grown on (0001)-oriented (c-cut) sapphire substrates, using the pulsed-laser deposition techniques. The dependence of the thermoelectric/transport properties on the film growth conditions was investigated
Thermoelectric properties of Bi2Te3 atomic quintuple thin films  [PDF]
Ferdows Zahid,Roger Lake
Physics , 2010, DOI: 10.1063/1.3518078
Abstract: Motivated by recent experimental realizations of quintuple atomic layer films of Bi2Te3,the thermoelectric figure of merit, ZT, of the quintuple layer is calculated and found to increase by a factor of 10 (ZT = 7.2) compared to that of the bulk at room temperature. The large enhancement in ZT results from the change in the distribution of the valence band density of modes brought about by the quantum confinement in the thin film. The theoretical model uses ab initio electronic structure calculations (VASP) with full quantum-mechanical structure relaxation combined with a Landauer formalism for the linear-response transport coefficients.
Fabrication of Thermoelectric Sensor and Cooling Devices Based on Elaborated Bismuth-Telluride Alloy Thin Films  [PDF]
Abdellah Boulouz,Alain Giani,Brice Sorli,Lahcen Koutti,Abdellah Massaq,Frederique Pascal-Delannoy
Journal of Materials , 2014, DOI: 10.1155/2014/430410
Abstract: The principal motivation of this work is the development and realization of smart cooling and sensors devices based on the elaborated and characterized semiconducting thermoelectric thin film materials. For the first time, the details design of our sensor and the principal results are published. Fabrication and characterization of Bi/Sb/Te (BST) semiconducting thin films have been successfully investigated. The best values of Seebeck coefficient (α(T)) at room temperature for Bi2Te3, and (Bi1?xSbx)2Te3 with x = 0.77 are found to be ?220?μV/K and +240?μV/K, respectively. Fabrication and evaluation of performance devices are reported. 2.60°C of cooling of only one Peltier module device for an optimal current of ?mA is obtained. The values of temperature measured by infrared camera, by simulation, and those measured by the integrated and external thermocouple are reported. A sensitivity of the sensors of 5?mV?Torr?1?mW?1 for the pressure sensor has been found with a response time of about 600?ms. 1. Introduction Thermoelectric microdevices are used in a variety of applications [1–4]. They are used by the military for night vision equipment, electronic equipment cooling, sensors, and portable refrigerators. Thermoelectric modules can also be used as thermocouples for measuring temperature or providing the temperature-sensing element in a thermostat. The Seebeck effect has two main applications including temperature measurement and power generation [2]. This effect is used for elaboration of thermoelectric cooling and sensor devices. The potential of a material for thermoelectric applications is determined by the figure of merit [2]: where represent the Seebeck coefficient, the electrical resistivity, and the total thermal conductivity where is the lattice part and is the electronic part [2, 5]. The conversion efficiency of thermoelectric materials can be improved either by lowering their thermal conductivity or by enhancing their capacity for producing electricity. As known, there are two approaches which can be used for preparing high ZT materials: (1) the multiquantum well structures (MQW) with quantum confinement effects and (2) the concept of reducing lattice thermal conductivity (especially in high temperature applications) in PGEC (phonon glass electron crystal) systems. PGEC systems (e.g., skutterudites based on CoSb3) are studied mainly as bulk materials [6]. The concept of MQW mainly dealt with thin films and superlattices [7–9]. The alloys of bismuth telluride with antimony telluride have attractive properties and are most used in the energy
Preparation and thermoelectric properties of p-type Bi0.52Sb1.48Te3 + 3% Te thin films
JianSheng Zhang,JunYou Yang,ShuangLong Feng,ZhengLai Liu,JiangYing Peng
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-012-5018-1
Abstract: Thin films of p-type Bi0.52Sb1.48Te3 + 3% Te were deposited on glass substrates by flash evaporation. X-ray diffraction and field-emission scanning electron microscopy were performed to characterize the thin films, and the effects of preparation and annealing parameters on the thermoelectric properties were investigated. It was shown that the power factors of the films increased with increasing deposition temperature. Annealing the as-deposited films improved the power factors when the annealing time was less than 90 min and the annealing temperature was lower than 250°C. A maximum power factor of 10.66 μW cm 1 K 2 was obtained when the film was deposited at 200°C and annealed at 250°C for 60 min.
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