bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ge-Si based Nanowire Thermoelectric Materials in the Phonon Confinement Regime
Authors: Xiang Jie 
Published: February 2020

For over a decade, nanotechnology has allowed rational synthesis of nanodot, nanowire and nanotube materials with different structure, composition, and with size control at the atomic precision. These nanoscale building blocks make it possible to explore electronic and energy harvesting devices with completely new operating principles. Similar to photonic and electronic confinement regimes where the device size approaches the wavelength of photon and electron wavefunctions, nanoscale semiconductor materials have enabled a new era of phononic engineering to turn waste heat into power and to explore the greener side of silicon. In particular, we have devised a highly sensitive differential bridge thermometry method to characterize thermal transport properties of individual Ge and heterostructure core-shell Ge/Si nanowires with diameters < 20 nm[1]. The resulting drastically suppressed thermal conductance beyond the diffusive boundary scattering limit is the first experimental evidence for the role of confinement effect on acoustic phonon dispersions in nanowires[2]. Lately we have also explored the high carrier mobility and concentration modulation in the semiconductor Ge/Si nanowires using gate modulation, and presented the first field-effect modulated thermoelectric power factor measurement on nanowires with diameters down to 11 nm[3]. The power factor was found to strongly correlate with carrier mobility and can exceed that of bulk Ge in nanowires with high hole mobility. Taken together, the well-established tunable electronic property, excellent thermoelectric power in Ge/Si nanowire materials, combined with thermal transport in the phonic confinement regime, are expected to open up a new level of thermoelectric performance beyond classical avenues.
1. Wingert, M. C.; Chen, Z. C. Y.; Dechaumphai, E.; Moon, J.; Kim, J. H.; Xiang, J.; Chen, R. K. Nano Lett. 2011, 11 (12), 5507−5513.
2. Zou, J.; Balandin, A. J. Appl. Phys. 2001, 89 (5), 2932−2938.
3. J. Moon, J-H. Kim, Z.C.Y. Chen, J. Xiang, and R. Chen, Nano Lett. 2013, 13 (3), 1196–1202.
Thermoelectric Performance of Nanostructured Bismuth-Tellurium and Bismuth-Antimony-Tellurium Powders Fabricated by Galvanic Displacement Reaction Process
Authors: An Chang Yong , Park Jun Young , Chung Chan-Hwa 
Published: February 2020

Thermoelectric devices are of promising interest for applications as heat pumps and power generators. The efficiency of thermoelectric devices can be intended by figure of merit (ZT=(S2σT/κ), where S, σ, κ, T are the seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively [2]. In this study, by utilizing the nanosize powder, it is intended to enhance the figure of merit to obtain a low thermal conductivity.
The powder of bismuth-tellurium and bismuth-antimony-tellurium was fabricated using alumina substrate in acid aqueous solution by galvanic displacement reaction process [3]. The advantage of this process is that it can be relatively simple and easy to produce powders from few micrometer to hundreds nanometer in size, and the mass production is facile.
The morphologies of bismuth-tellurium and bismuth-antimony-tellurium powders were characterized using field emission scanning electron microscope (FESEM, JEOL JSM 7000F). X-ray diffraction (XRD) patterns have been investigated with a Bruker Coporation (Cu kα). The composition ratio of powders was confirmed using ICP (PerkinElmer, Optima-4300 DV).
These nanocrystalline bulk materials were prepared by hot pressing nanopowders at 350 °C for 30min with a uni-axial pressure of approximately 40 MPa to form pellets. The measurements of electrical resistivity and seebeck coefficient of the pellet samples have been carried out by using a equipment ULVAC ZEM-3 for operating temperature range of 30 to163 °C. The thermal conductivities have been measured by using a laser flash (ULVAC-RICO).
Fig 1. SEM images of a) Bi2Te3, and b)Bi0.5Sb1.5Te3powders fabricated by galvanic displacement reaction process.
Reference
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[2] Z. Lu, L.P. Tan, X. Zhao, and H.H. Hng, J. Mater. chem. C, 1, 6271, (2013)
[3] K. Zhuo, M.G. Jeong, and C-H. Chung, RSC Advances, 3, 12611, (2013)
ALD Synthesis of PbSe Thin Films inside Porous Si Templates for Innovative Thermoelectric Applications
Authors: Zhang Kai , Ramalingom Pillai Arun Deepak , Chen Xin , Baumgart Helmut , Kochergin Vladimir 
Published: February 2020

The IV-VI lead chalcogenides are considered as prospective thermoelectric materials which have their potential applications in green renewable energy by waste heat recovery and infrared devices. Among these materials, PbSe demonstrates a remarkable thermoelectric performance, The thermoelectric figure of merit ZT exceeds 1 for both n-type and p-type PbSe at high temperature. ZT is defined as ZT=σS2T/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity, respectively. In addition, Se element is more abandant and less costly than Te which is a scarce element [1].
PbSe thin films on Si substrates have been synthesized by various methods. However, a careful literature search reveals, there are few if any reports on the synthesis of PbSe thin films by atomic layer deposition (ALD). The ALD technique exhibits self-limiting surface reactions in each ALD cycle which consequently results in precise layer thickness control, stoichiometry, composition, uniformity of large area on the substrate. ALD also can be used to deposit conformal film onto very complex substrates or nano-porous template surfaces. This is the one advantageous property of ALD which renders it more competitive and promising in porous template nano-structures. In contrast, magnetron sputtering and PLD cannot be used to coat complex 3D structures with PbSe. Furthermore, the growth temperature of ALD is rather low in comparison with other fabrication processes.
In this work we report on the successful synthesis of multiple PbSe thin films on silicon substrates and inside microporous Si templates by thermal ALD, using lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2) and (trimethylsilyl) selenide ((Me3Si)2Se) as the chemical ALD precursors for lead and selenide, respectively. The repetitive structure of nano-porous Si templates offers an additional degree of periodicity in the quest for high ZT thermoelectric films.
The XRD and FE-SEM results reveal that the Lead selenide thin films are polycrystalline at deposition temperatures of 170 °C based on Volmer Weber Island growth mode and have characteristic FCC rock-salt crystal structure as shown in Figure (1), (2) and (3).
References:
H. Wang, Z. M. Gibbs, Y. Takigawa, G. J. Snyder, Energy Environ. Sci., 7, 804 (2014).
Transparent Electrodes Based on Three-Dimensional Nanohelixes Light Harvesting Applications
Authors: Kim Jong Kyu , Choi Ilyong , Kwon Hyunah , Lee Seung Hee , Oh Seung Jae 
Published: February 2020

We present transparent electrodes based on 3-dimensional nanohelix array for light harvesting applications. Arrays of nanohelixes fabricated by electron-beam oblique-angle deposition (OAD) of various metal oxides including TiO2, WO3 and ITO have been used for improving the performance of dye-sensitized solar cells (DSSCs), Photoelectrochemical (PEC) cells for water splitting, and organic photovoltaics (OPVs), respectively. Such light harvesting devices with transparent electrodes based on metal-oxides nanohelixes array show enhanced performances such as higher light absorption and power conversion efficiency than devices with conventional thin-film and sintered nanoparticle electrodes. This is attributed to the unique optical, microstructural, and electrical properties of metal-oxides nanohelixes such as enhanced light scattering and large specific area enabled by 3-dimensional geometry, and improved separation and transportation of photo-generated carriers by the near-single-crystallinity of metal-oxides nanohelixes. In addition, a number of applications including dichroic filters for high efficiency white light-emitting diodes, near-perfect anti-reflection coatings for solar cells, and high performance chemical sensors will be discussed.

References

[1] Hyunah Kwon and Jong Kyu Kim et al., Advanced Energy Materials, Accepted (2014).
[2] Seung Hee Lee and Jong Kyu Kim et al., Optics Express (2014).
[3] Xing Yan et al., Advanced Functional Materials 23, 583 (2013).
Transparent Conductive Vanadium Oxide-Based Thin Films from Liquid Precursors
Authors: Glynn Colm , Aureau Damien , Collins Gillian , Etcheberry Arnaud , O'Dwyer Colm 
Published: February 2020

New types of transparent conducting materials (TCMs) are being sought due to the increase in demand for their use in next generation electronics and photovoltaics. Methods to improve transparency be inferred by controlling porosity (graded refractive index), or from a change in the crystal structure of some materials that are not inherently transparent at visible frequencies. Transparent materials with tunable optical properties are important in conductive and capacitive displays, tandem solar cells, organic PVs and other devices. In thin film oxide deposition, where non-uniformities and porosity are not ideal, diffusion from glass substrates into oxide thin films during thermal treatment has previously been considered detrimental and was suppressed using diffusion barriers such as thick coatings of SiO2. In this work, we show how the transparency and conductivity of a dip-coated thin film of vanadium oxide can be markedly improved by substrate diffusion during thermal treatment, resulting in a completely transparent thin film of vanadium oxide-based material with an order of magnitude increase in electrical conductivity. The phase change and stoichiometry variation during thermal annealing of the vanadium oxide dip-coated from liquid precursors is elucidated using X-Ray photoelectron spectroscopy (XPS) and Raman scattering spectroscopy. Angle-resolved transmission spectra correlated the transparency to the changes in optical properties of the thin films and electron microscopy confirms no formal structural change contributes to the change in transparency. Hall probe measurements demonstrate improved conductivity with transparency due to diffusion of cations from the substrate into the host material lattice.
References:

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C. O’Dwyer, M. Szachowicz, G. Visimberga, V. Lavayen, S. B. Newcomb and C. M. S. Torres, Nature Nanotechology, 4, 239 (2009).

J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu and J. A. Smart, Nature Photonics, 1, 176 (2007).

C. O'Dwyer and C. M. S. Torres, Front. Physics, 1, 18 (2013).

C. Glynn, D. Creedon, H. Geaney, J. O'Connell, J. D. Holmes and C. O'Dwyer, ACS Appl. Mater. Interfaces, 6, 2031 (2014).

K. K. Banger, Y. Yamashita, K. Mori, R. L. Peterson, T. Leedham, J. Rickard and H. Sirringhaus, Nature Materials, 10, 45 (2011).

J. Mannhart and D. G. Schlom, Science, 327, 1607 (2010).

F. Nicholas, M. P. Sean, W. H. Mark and S. S. N. Bharadwaja, Journal of Physics D: Applied Physics, 42, 055408 (2009).

T. Manning, I. Parkin, Polyhedron,
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Simulation on the Microelectrode of Cell Electrofusion Chip
Authors: Xianwei Han 
Published: February 2020

The process of cell electrofusion including cell alignment, cell electroporation cell electrofusion. Cell manipulation mainly related to the electric field gradient and electroporation is concerned with the intensity of the electric field. The first thing to consider in the design of Cell electrofusion chip is the control of the cell capacity , which depends on the intensity and distribution of the electric field, and this is associated with the applied voltage and the shape and distribution of the microelectrode. In the experiment, we can change the applied voltage, but the shape and distribution of the microelectrodes is hard to change. In order to improve the efficiency of the experiment, the optimum distribution and the size of the microelectrode in the chip should be determined before the experiment. Using COMSOL Multiphysics software to model and simulate the cell electrofusion chip to provide theoretical guidance for optimum chip design and experimental study late.
In this study, five different cell electrofusion chip are simulated. Using the finite element analysis method, combined with COMSOL simulation software, the electric field around the chip microelectrode is simulated and analyzed. Through the establishment of simulation model, to explore the influence on the internal electric field of the cell electrofusion chip be different parameters, including the distribution and spacing of microelectrode, , microelectrode length, width, and the size of the microstructure. Thus, best design parameters of chip microelectrode are achieved.
Simulation and Experimental Studies of the Impact of EOF on the Electroformation of GUVs
Authors: Wang Qiong , Yang Jun , Hu Ning , Liao Yan-jian , Luo Hong-yan 
Published: February 2020

Electroformation is widely used to prepare giant unilamellar vesicles (GUVs) because of its simplicity and high-efficiency. As mentioned by many previous studies, electroosmotic flow (EOF) is an important influence factor in the lipid vesicle electroformation, which may induce the peeling off, rearranging, breaking, and self-assembling of deposited amphiphilic molecules (lipid film) to form vesicles finally. However, the influencing mechanism of EOF is not really clear.
In this study, numerical simulation and experimental methods have been used to study the impact of EOF on lipid vesicle electroformation. Simulation results show that EOF can generate vortex near the walls, which will act on the lipid film and induce the formation of lipid vesicles. These results are matched with some previous studies well, and can give some reasonable explanations of those experimental observations. For example, failure to carry out electroformation of GUVs in buffers with high ionic strength is because zeta potential z decreases with increased ionic strengths and then weakens EOF significantly.
According to the simulation results, the electric field within the traditional electroformation method is optimized by applying electric field coplanar with the deposited lipid film. It can solve the terrible vesicle electroformation in high ionic strength buffers and increase the yield, because the strongest EOF appears near the plane in parallel with the electric field in a closed chamber. On-chip experiments show that attached vesicles on the bottom were pulled by EOF and tilted to its direction, so transverse EOF helps the electrofomation. Furthermore, production of GUVs was demonstrated to be several orders of magnitude higher than those of traditional methods.
Figure. Lipid film was deposited on the substrate of the chamber. A 2D modeling of the vertical chamber was numerically studied. A) and B) Velocity profile and streamlines of EOF formed when applying a non-coplanar electric field and a coplanar one, respectively. Arrows illustrate the electric field applied. C) Velocity distributed on the bottom under the effect of different field, which demonstrated the advantage of coplanar electric filed apparently. D) Vesicles generated under the coplanar field. The production proved to be several orders of magnitude higher than those under non-coplanar filed. Vesicles under the arrow were pulled by EOF and tilted to its direction.
GaN Based Optoelectronic Devices: From Ultraviolet Detectors and Visible Emitters Towards THz Intersubband Devices
Authors: McClintock Ryan , Razeghi Manijeh 
Published: February 2020

III-Nitride material system (AlGaInN) possesses unique optical, electrical and structural properties such as a wide tunable direct bandgap, large longitudinal optical phonon energy, inherit fast carrier dynamics; good carrier transport properties, high breakdown fields; and high robustness and chemical stability. Thanks to these inherit advantages, they are investigated for everyday to military and scientific applications such as illumination sources; bio-agent detection, concealed weapons/drugs detection; and space exploration.
In the first part of the talk, we will be focusing on ultraviolet (UV) spectrum. Ultraviolet region is very important as many biological agents (such as anthrax) are luminescent in UV. Scattering of short-wavelengths in atmosphere enables non-line-of-sight secure communications in rugged terrains whereas strong reflection/absorption of UV at ionosphere promises secure space-to-space communications. Where photomultiplier tubes are found to be bulky and fragile, and Si(C)-based photodiodes require external filter elements, compact high performance UV (Al)GaN avalanche photodiodes (APDs) can be employed. Via Geiger-mode operation of these APDs, single UV photons can be counted that could enable quantum computing and data encryption in near future.
In the second part of the talk, we will be focusing on visible spectrum. The total annual energy consumption in the United States for lighting is approximately 800 Terawatt-hours and costs $80 billion to the public. The energy consumed for lighting throughout the world entails to greenhouse gas emission equivalent to 70% of the emissions from all the cars in the world. InGaN-based novel light emitting diodes are the key components of an affordable, durable and environmentally benign lighting solution that can achieve unique spectral quality and promise superior energy conversion efficiency than current lighting sources.
In the third part of the talk, we will be focusing towards Terahertz (THz) spectrum. Terahertz spectral range offers promising applications for science (such as cancer detection), industry (such as product defect detection), and military (such as drug, concealed weapon or explosives detection), and III-Nitrides are the integral part of unique quantum cascade laser designs that are theoretically capable of THz lasing at room temperature (RT). Recently, AlN/GaN and AlGaN/GaN superlattices are employed to show intersubband absorption in near- and mid-infrared spectra, respectively. Moreover, AlN/GaN resonant tunneling diodes have been shown to possess negative differential resistance at RT. These recent demonstrations motivate THz emitters at RT.
In conclusion, with continuous developments in material growth/characterization and device processing/measurement technologies, gap engineered III-Nitride materials extend their unique solutions from ultraviolet and visible regime towards THz spectra.
Progress on Large Diameter Single Crystal Growth of SiC
Authors: Ruland Gary , Wu Ping , Xu Xueping , Rengarajan Varatharajan , Zwieback Ilya , Gupta Avi , Ramm Mark 
Published: February 2020

Large-diameter SiC single crystals are grown at II-VI by physical vapor transport (PVT). II-VI manufactures up to 150 mm diameter substrates of two types: vanadium doped semi-insulating and nitrogen doped n-type. We have previously discussed in some detail the practice of SiC crystal growth at II-VI [1], and reported on the properties of the grown crystals, including dominating defects and their evolution during growth [2]. This paper is an update on the progress of the growth of high quality large diameter substrates over the past 18 months.
SiC single crystals grown by sublimation exhibit relatively high dislocation densities and may contain slightly misoriented grains. Defect data will be presented on wafers that have been characterized by etch pit density and X-ray rocking curves and topography. Resistivity was characterized by an eddy current measurement for conducting and capacitive based measurement for semi-insulating substrates. Using these methods a comparison of progress will be provided.
We have achieved stacking fault and micro pipe free wafers with a typical total dislocation density of 6x103 cm-2, TSD density of ~1.2x103 cm-2, and typical BPD density of 5x102 cm-2 in 150mm substrates and 3x102 cm-2 in 100mm substrates. For semi-insulating wafers we have achieved resistivities in excess of 1E11ohms*cm.
[1] A. Gupta et al., “Status of Large Diameter SiC Single Crystals”, Materials Science Forum, 2012, vol. 717-720, pp. 3-8.
[2] P. Wu et al., “Defect Evolution during Growth of SiC Crystals”, J. Cryst. Growth, Vol. 310, 7-9 (2008), pp. 1804-1809.
The Materials and Reliability of Power Electronics Devices
Authors: Christou Aris , McCluskey P 
Published: February 2020

Small signal commercial electronics have traditionally been designed to operate at temperatures from 0°C to 70°C. Increased temperature often compromises performance and when combined with the higher voltages, current densities, and heat dissipations associated with power electronics can result in an increased susceptibility to oxide breakdown, electromigration, and other catastrophic on-chip failure mechanisms. Furthermore, the large temperature swings of extreme environments and the rapid temperature cycles resulting from turning on and off large amounts of power can cause fatigue of the die, wires, die attach, and substrate in the package. The course sequence focuses on understanding the device technologies, and developing packaging and thermal management strategies that mitigate risks related to the operating temperatures and large temperature cycles common in extreme temperature and power electronics.
Included will be issues related to the effect of high and low operating temperatures on device and packaging reliability, power device (IGBT, MOSFET, BJT) and material (Si, SiC, GaN) selection, passive component and packaging materials selection, thermal management, and assembly of reliable high power and extreme temperature electronic systems. Finally, failure mechanism models for high temperature and power electronics will be presented together with a discussion of design options to mitigate failure.

Topics covered : Reliable design and manufacture of power semiconductor components;Reliable design of power inverters and converters;Effects of temperature on device performance and reliability;Reliable packaging of power modules and assemblies.

The development of robust and reliable power electronic systems for sustainable energy systems requires an understanding of the fundamental degradation processes that can cause failure at the device, interconnection, and packaging level in the environments encountered in a wide range of energy systems applications. The course sequence will present the dominant failure mechanisms at each of these levels, along with selected models and reliability assessment methodologies. Mechanisms to be covered include degradation in GaN and SiC devices; fatigue and fracture of wirebonds, die attach, and substrates in power electronic modules; corrosion and conductive filament formation in boards; and fatigue of solder joints.
Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications. Of the various materials and device technologies, the AlGaN/GaN high-electron mobility transistor has been developed and has reached the market. While GaN device and circuit technology is poised to break out in the commercial arena, certain risks or barriers to entry in the market should not be overlooked. The relative technology immaturity of GaN with respect to Silicon and GaAs leave issues like long-term reliability unanswered. The courses also present the main degradation mechanisms of GaN-based HEMTs devices.