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Progress of microscopic thermoelectric effects studied by micro- and nano-thermometric techniques

Frontiers of physics 2022年第2期17卷 155-172页

作者： Xue Gong Ruijie Qian Huanyi Xue Weikang Lu Zhenghua An State Key Laboratory of Surface Physics Department of PhysicsFudan UniversityShanghai 200433China Institute for Nanoelectronic Devices and Quantum Computing Fudan UniversityShanghai 200433China Shanghai Qi Zhi Institute 41th FloorAI TowerNo.701 Yunjin RoadXuhui DistrictShanghai 200232China

Heat dissipation is one of the most serious problems in modern integrated electronics with the continuously decreasing devices size. Large portion of the consumed power is inevitably dissipated inthe form of waste heat which not only restricts the device energy-efficiency performance itself, butalso leads to severe environment problems and energy crisis. thermoelectric Seebeck effect is a greenenergy-recycling method, while thermoelectric Peltier effect can be employed for heat management byactively cooling overheated devices, where passive cooling by heat conduction is not sufficiently enough.However, the technological applications of thermoelectricity are limited so far by their very low conversion efficiencies and lack of deep understanding of thermoelectricity in microscopic levels. Probingand managing the thermoelectricity is therefore fundamentally important particularly in nanoscale. Inthis short review, we will first briefly introduce the microscopic techniques for studying nanoscale thermoelectricity, focusing mainly on scanning thermal microscopy (SThM). SThM is a powerful tool formapping the lattice heat with nanometer spatial resolution and hence detecting the nanoscale thermaltransport and dissipation processes. Then we will review recent experiments utilizing these techniques to investigate thermoelectricity in various nanomaterial systems including both (two-material)heterojunctions and (single-material) homojunctions with tailored Seebeck coefficients, and also spinSeebeck and Peltier effects in magnetic materials. Next, we will provide a perspective on the promisingapplications of our recently developed Scanning Noise Microscope (SNoiM) for directly probing thenon-equilibrium transporting hot charges (instead of lattice heat) in thermoelectric devices. SNoiMtogether with SThM are expected to be able to provide more complete and comprehensive understanding to the microscopic mechanisms in thermoelectrics. Finally, we make a conclusion and outlook onthe future development of microscopic studies in

关键词： scanning thermal microscope(SThM) scanning noise microscope(SNoiM) thermoelectric effects Seebeck coefficient Peltier cooling spin caloritronics

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Ultrafast dynamics of photoexcited carriers and coherent phonons in ultrathin Bi;Te;thermoelectric films

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Science China(Physics,Mechanics & Astronomy) 2022年第1期65卷 71-77页

作者： Zemin Xu Jiandong Yao Guowei Yang Tianshu Lai State Key Laboratory of Optoelectronic Materials and Technologies School of PhysicsSun Yat-sen UniversityGuangzhou 510275China State Key Laboratory of Optoelectronic Materials and Technologies Nanotechnology Research CenterSchool of Materials Science&EngineeringSun Yat-sen UniversityGuangzhou 510275China

The ultrafast dynamics of photoexcited carriers and coherent phonons in ultrathin Bi;Te;thermoelectric films are studied through transient differential transmission spectroscopy.An ultralow frequency coherent optical phonon at 0.16 THz emerges,especially in ultrathin films,and it is ascribed to interlayer breathing modes.It can divide the ultrathin films into two groups which have outof-phase vibration along the normal of a film plane,causing a destructive interference between in-plane propagating thermal waves in the two groups of quintuple layers,and thus possibly reducing the thermal conductivity of the ultrathin films.The excitation power dependence of ultrafast dynamics reveals carrier-carrier scattering dominating thermalization,which provides a microscopic understanding of the reported high electrical conductivity and anomalously high power factor of ultrathin Bi;Te;films at room temperature.

关键词： electron-electron interactions coherent phonons carrier dynamics thermoelectric effects

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Energy-resolved spin filtering effect and thermoelectric effect in topological-insulator junctions with anisotropic chiral edge states

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Frontiers of physics 2022年第6期17卷 85-93页

作者： Jia-En Yang Hang Xie School of Electronics and IoT Chongqing College of Electronic EngineeringChongqing 401331China College of Physics Chongqing UniversityChongqing 401331China Chongqing Key Laboratory for Strongly-Coupled Physics Chongqing UniversityChongqing 401331China

Topological edge states have crucial applications in the future nano spintronics devices.In this work,circularly polarized light is applied on the zigzag silicene-like nanoribbons resulting in the anisotropic chiral edge modes.An energy-dependent spin filter is designed based on the topological-insulator(TI)junctions with anisotropic chiral edge states.The resonance transmission has been observed in the TI junctions by calculating the local current distributions.And some strong Fabry–Perot resonances are found leading to the sharp transmission peaks.Whereas,the weak and asymmetric resonance corresponds to the broad transmission peaks.In addition,a qualitative relation between the resonant energy separation TR and group velocity vf is derived:TR=πhvf n/L,that indicated TR is proportional to vf and inversely proportional to the length L of the conductor.The different TR between the spin-up and spin-down cases results in the energyresolved spin filtering effect.Moreover,the intensity of the circularly polarized light can modulate the group velocity vf.Thus,the intensity of circularly polarized light,as well as the conductor-length,play very vital roles in designing the energy-dependent spin filter.Since the transmission gap root in the Fabry–Perot resonances,the thermoelectric(TE)property can be enhanced by adjusting the gap.A schedule to enhance the TE performance in the TI-junction is proposed by modulating the electric field(Ez).The TE dependence on Ez in the nanojunction is investigated,where the appropriate Ez leads to a very high spin thermopower and spin figure of merit.These TI junctions have potential usages in the nano spintronics and thermoelectric devices.

关键词： electron transport topological edge states 2D materials spintronics thermoelectric effects

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thermoelectric effect of silicon films prepared by aluminum-induced crystallization

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International Journal of Minerals,Metallurgy and Materials 2012年第10期19卷 957-963页

作者： Qing-run Hou Bing-fu Gu Yi-bao Chen Yuan-jin He Department of Physics Tsinghua UniversityBeijing 100084China

Aluminum-induced crystallized silicon films were prepared on glass substrates by magnetron sputtering. Aluminum was added in the silicon films intermittently by the regular pulse sputtering of an aluminum target. The amount of aluminum in the silicon films can be controlled by regulating the aluminum sputtering power and the sputtering time of the undoped silicon layer; thus, the Seebeck coefficient and electrical resistivity of the polyerystaUine silicon films can be adjusted. It is found that, when the sputtering power ratio of aluminum to silicon is 16%, both the Seebeck coefficient and the electrical resistivity decrease with the increasing amount of aluminum as expected; the Seebeck coefficient and the electrical resistivity at room temperature are 0.185-0.285 mV/K and 0.30-2.4 Ω.cm, respectively. By reducing the sputtering power ratio to 7%, however, the Seebeck coefficient does not change much, though the electrical resistivity still decreases with the amount of aluminum increasing; the Seebeck coefficient and electrical resistivity at room temperature are 0.219-0.263 mV/K and 0.26-0.80 Ω·cm, respectively.

关键词： polycrystalline materials thin films silicon thermoelectric effects Seebeck effect electrical resistivity magnetron sputtering

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Enhanced thermoelectric properties in two-dimensional monolayer Si2BN by adsorbing halogen atoms

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Chinese Physics B 2021年第3期30卷 41-47页

作者：吴成伟向长青杨恒玉周五星谢国锋欧宝立伍丹 School of Materials Science and Engineering&Hunan Provincial Key Laboratory of Advanced Materials for New Energy Storage and Conversion Hunan University of Science and TechnologyXiangtan 411201China College of Information Science and Engineering Jishou UniversityJishou 416000China School of Physics and Electronic Science Changsha University of Science and TechnologyChangsha 410114China

Using the first principles calculation and Boltzmann transport theory, we study the thermoelectric properties of Si2BNadsorbing halogen atoms (Si2BN-4X, X = F, Cl, Br, and I). The results show that the adsorption of halogen atoms cansignificantly regulate the energy band structure and lattice thermal conductivity of Si2BN. Among them, Si2BN-4I has thebest thermoelectric performance, the figure of merit can reach 0.50 K at 300 K, which is about 16 times greater than that ofSi2BN. This is because the adsorption of iodine atoms not only significantly increases the Seebeck coefficient due to banddegeneracy, but also rapidly reduces the phonon thermal conductivity by enhancing phonon scattering. Our work proves theapplication potential of Si2BN-based crystals in the field of thermoelectricity and the effective method for metal crystals toopen bandgaps by adsorbing halogens.

关键词： density functional theory thermoelectric effects transport properties electronic structure

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Effect of nanocomposite structure on the thermoelectric properties of 0.7-at% Bi-doped Mg_2 Si nanocomposite

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Chinese Physics B 2011年第10期20卷 355-361页

作者：杨梅君沈强张联盟 Centre for Materials Research and Analysis Wuhan University of Technology State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology

Nanocomposites offer a promising approach to the incorporation of nanostructured constituents into bulk thermo- electric materials. The 0.7-at% Bi-doped Mg2Si nanocomposites are prepared by spark plasma sintering of the mixture of nanoscale and microsized 0.7-at% Bi-doped Mg2Si powders. Microstructure analysis shows that the bulk material is composed of nano- and micrograins. Although the nanograin hinders electrical conduction, the nanocomposite struc- ture is more helpful to reduce thermal conductivity and increase the Seebeck coefficient, hence improving thermoelectric performance. A dimensionless figure of merit of 0.8 is obtained for the 0.7-at% Bi-doped Mg2Si nanocomposite with 50-wt % nanopowder, which is about twice larger than that of the sample without nanopowder.

关键词： intermetallic compounds nanostructures semiconductors thermoelectric effects

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Nanostructuring and thermoelectric Properties of Bulk N-type Mg_2Si

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Journal of Wuhan University of Technology(Materials Science) 2009年第6期24卷 912-916页

作者：杨梅君 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology

Preparation and thermoelectric properties of nanostructured n-type Mg2Si bulk materials were reported. Nanosized Mg2Si powder was obtained by mechanical milling of the microsized Mg2Si powder prepared by solid-state reaction. The bulk materials with 30 nm and 5 μm were prepared by spark plasma sintering of the nanosized and microsized Mg2Si powder, respectively. Both the samples show n-type conduction and the Seebeck coefficient of the sintered samples increase determinately with the grain size decrease from 5 μm to 30 nm. On the other hand, the electrical and thermal conductivity decrease with the decrease of grain size. Accordingly, decreasing their grain size increases their thermoelectric-figure-of-merit. A maximum thermoelectric figure of merit of 0.36 has been obtained for the nanostuctured Mg2Si sample at 823 K, which is 38% higher than that of microsized Mg2Si bulk materials and higher than results of other literatures. It could be expected that the properties of the nanocomposites could be further improved by doping optimization.

关键词： semiconductor thermoelectric effects Mg2Si nanostructuring

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