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[IEEE 2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) - Seoul, Korea (South) (2019.1.27-2019.1.31)] 2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) - High-Frequency Hexagonal Boron Nitride (h-BN) Phononic Waveguides
摘要： This digest paper presents the first experimental demonstration of nanoscale phononic waveguides based on a two-dimensional (2D) layered crystalline material, namely hexagonal boron nitride (h-BN). Taking advantage of the planar geometry, the challenges in nanofabrication of 2D materials can be circumvented through a heterogeneous integration approach. Rich wave propagation characteristics of h-BN phononic waveguides are revealed in both finite element method (FEM) simulations and transmission measurements. Numerical analysis further indicates that the frequency response of the designed h-BN phononic waveguides can be finely tuned by varying the thickness or tension level of the h-BN crystals, across the high frequency (HF, 3?30 MHz) to very high frequency (VHF, 30?300 MHz) bands. Manipulation and guiding of high frequency mechanical waves on integratable 2D device platforms will open new opportunities in radio-frequency (RF) signal processing and on-chip quantum information technologies.
关键词： phononic waveguides,very high frequency (VHF),radio-frequency (RF) signal processing,quantum information technologies,high frequency (HF),hexagonal boron nitride (h-BN)
更新于2025-09-12 10:27:22
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Direct Examination of the Deactivation of the Boron–Oxygen Center in Cz-Si Solar Cells Under Regeneration Conditions via Electroluminescence
摘要： We examine the regeneration kinetics of the boron–oxygen defect in boron-doped p-type Czochralski-grown silicon (Cz-Si) solar cells as a function of the excess carrier concentration Δn at the regeneration conditions, i.e., at elevated temperature (140 °C). To perform the regeneration, we apply different forward-bias voltages (Vappl) to solar cells in darkness and measure directly the emitted electroluminescence (EL) signal at different time steps during the regeneration of the cell. Measuring the EL signal emitted by the solar cell during regeneration, we are able to directly determine Δn during regeneration for each applied voltage. In addition to the EL signal, we measure the electric current flowing through the solar cell during the regeneration process. This current is proportional to the overall recombination rate in the cell and, hence, reflects the changing bulk recombination during the regeneration process. From the measured time-dependent cell current, we determine the deactivation rate constant Rde of the boron–oxygen defect. Our experimental results unambiguously show that Rde increases proportionally with Δn during the regeneration process.
关键词： Boron–oxygen defect,injection,regeneration,electroluminescence (EL),carrier,passivated emitter and rear cells (PERCs),Czochralski-grown silicon,light-induced degradation (LID)
更新于2025-09-12 10:27:22
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Highly Efficient and Thermal-Stable QD-LEDs Based on Quantum Dots-SiO <sub/>2</sub> -BN Nanoplate Assemblies
摘要： Silica encapsulation effectively elevates the resistance of quantum dots (QDs) against water and oxygen. However, QDs-SiO2 composites present low thermal conductivity and strong thermal accumulation, leading to considerable fluorescent quenching of QDs in optoelectronic devices at high power. Here, a sandwich structural QDs-SiO2-BN nanoplate assembly material (QDs-SiO2-BNAs) is developed to reduce the thermal quenching and enhance the stability of QDs in LEDs. The QDs-SiO2-BNAs is fabricated by embedding QDs-SiO2 into the interlayer of layer-by-layer assembled BN nanoplates, and the BN nanoplates are pretreated by SiO2 encapsulation to strengthen the interaction with QDs-SiO2. This assembly structure endows the QDs with fast heat dissipation and double surface protection against air. The medium power QDs-converted LEDs (QD-LEDs) fabricated by directly on-chip packaging of the QDs-SiO2-BNAs gain 44.2 ℃ temperature reduction at 0.5 W in comparison with conventional QD-LEDs. After aging, the resulting QD-LEDs present degradation of only 1.2% under sustained driving for 250 hours. The QD-LEDs also pass the one-week reliability test at 85 ℃ / 85% RH with <±0.01 shift of the color coordinates, demonstrating the profound potential of the QDs-SiO2-BNAs in LED lighting and display applications.
关键词： stability,quantum dots,boron nitride,assembly,light-emitting diodes
更新于2025-09-12 10:27:22
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Molecular Acceptors Based on a Triarylborane Core Unit for Organic Solar Cells
摘要： Triarylboranes that exhibit p-π* conjugation serve as versatile building blocks to design n-type organic/polymer semiconductors. Here, we report a series of new molecular acceptors based on triarylborane. These molecules are designed with a boron atom that bears a bulky 2,4,6-tri-tert-butylphenyl substituent at the core and strong electron-withdrawing 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile units as the endcapping groups that are linked to the core by bithiophene bridges. Butyl or butoxy groups are introduced to tune the optoelectronic properties. These molecules show nearly planar backbones with highly localized steric hindrance at the core, low LUMO/HOMO energy levels, and broad absorption bands spanning the visible region, which are all very desirable characteristics for use as electron acceptors in organic solar cell (OSC) applications. The attachment of butyl groups to the bithiophene bridges brings about a slightly twisted backbone, which in turn promotes good solubility and homogeneous donor/acceptor blend morphology, while the introduction of butoxy groups leads to improved planarity, favorable stacking in the film state and a greatly reduced bandgap. OSC devices based on these molecules exhibit encouraging photovoltaic performances with power conversion efficiencies reaching up to 4.07%. These results further substantiate the strong potential of triarylboranes as the core unit of small molecule acceptors for OSC applications.
关键词： organic boron chemistry,organic solar cells,n-type organic/polymer semiconductors,triarylboranes,molecular acceptors
更新于2025-09-12 10:27:22
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Dual growth mode of boron nitride nanotubes in high temperature pressure laser ablation
摘要： The morphological analysis of the end of boron nitride nanotubes (BNNTs) using high-resolution transmission electron microscopy (HR-TEM) can provide valuable insight into the growth mechanism in high temperature pressure (HTP) laser ablation where the best quality of BNNT materials can be obtained so far. Two growth modes of BNNT coexisting during the synthesis process have been proposed based on HR-TEM observation and length analysis. One is the root growth mode, in which boron nitride (BN) species formed via the surface interaction between surrounding N2 molecules and boron nanodroplets incorporate into the tubular structure. Another mode called open-end growth mode means the prolongation of tube growth from the exposed BN edge surrounding the surface of boron nanodroplets which is constructed by the heterogeneous nucleation of absorbed BN radicals from the gas plume. The statistical data, the proportions of end structures and the length of BNNTs, could be fitted to two growth modes, and the open-end growth mode is found to be especially effective in producing longer nanotubes with a higher growth rate. The scientific understanding of the growth mechanism is believed to provide the control for optimized production of BNNTs.
关键词： growth mechanism,high temperature pressure laser ablation,open-end growth mode,root growth mode,boron nitride nanotubes,HR-TEM
更新于2025-09-12 10:27:22
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Isotopic Analysis and Characterization of Boric Acid Diffused Emitters in n-type c-Si Solar Cells
摘要： Boric acid (BA) is one of the boron dopant sources used in recent years to fabricate emitters for n-type c- Si solar cells. Boric acid solution with concentrations less than 4% is sufficient enough to get doping concentrations with sheet resistance values 10 ?/sq to 90 ?/sq under different diffusion conditions. Isotopic analysis of BA diffused emitter, optimized for different sheet resistances have been studied in this work. Cs ions of 1KV 300x300 raster ions have been used for the emitters and it has resulted detection of 11B and 28Si isotopes in all the boron diffused samples. Isotopic analysis of borosilicate glass (BSG) and boron rich layer (BRL), corresponding to different dopant concentrations, also shows isotope detections and they vary according to natural abundance.
关键词： isotopic analysis,boron rich layer,sheet resistance values
更新于2025-09-12 10:27:22
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Tunable reflected group delay from the graphene/hBN heterostructure at infrared frequencies
摘要： In this paper, we theoretically investigated the re?ected group delay from the graphene/hexagonal boron nitride (hBN) heterostructure in the infrared band. Since the signi?cant Lorentz resonance characteristic of the dielectric constant of hBN in the bands of near 7.28 μm and 12.72 μm, the new graphene/hBN heterostructure is used to realize ?exible switching of re?ected group delay by the Lorentz resonance mechanism. It is shown that the re?ected group delay can be e?ectively enhanced by tuning the Fermi energy or the number of graphene layers. Moreover, the re?ected group delay can be tuned positive or negative depending on the hBN thickness or incident angle. These results will be useful for design of graphene-based optical delay devices in the infrared band.
关键词： Graphene,Hexagonal boron nitride (hBN),Group delay,Infrared band
更新于2025-09-12 10:27:22
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Elusive super-hard B6C accessible through the laser-floating zone method
摘要： Boron carbide is among the most promising ceramic materials nowadays: their mechanical properties are outstanding, and they open potential critical applications in near future. Since sinterability is the most critical drawback to this goal, innovative and competitive sintering procedures are attractive research topics in the science and technology of this carbide. This work reports the pioneer use of the laser-floating zone technique with this carbide. Crystallographic, microstructural and mechanical characterization of the so-prepared samples is carefully analysed. One unexpected output is the fabrication of a B6C composite when critical conditions of growth rate are adopted. Since this is one of the hardest materials in Nature and it is achievable only under extremely high pressures and temperatures in hot-pressing, the use of this technique offers a promising alternative for the fabrication. Hardness and elastic modulus of this material reached to 52 GPa and 600 GPa respectively, which is close to theoretical predictions reported in literature.
关键词： mechanical properties,microstructure,superhard materials,laser-floating zone technique,Boron carbide
更新于2025-09-12 10:27:22
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Channeled Implantations of p-Type Dopants into 4H-SiC at Different Temperatures
摘要： Channeling of B and Al ions in 4H-SiC(0001), has been investigated by secondary ion mass spectrometry (SIMS). Ion implantations have been performed between room temperature (RT) and 600 °C at various fluences. Before implantation, the major crystal axes were determined and the sample was aligned using the blocking pattern of backscattered protons. As expected, the depth distribution of the implanted ions along a crystal direction penetrates much deeper compared to non-channeling directions. At elevated temperatures, the channeling depth for 100 keV Al-ions is decreased due to lattice vibrations. For 50 keV B-ions, the temperature effect is minor, indicating a smaller interaction between target atoms and B. Simulations has been performed using SIIMPL, a Monte Carlo simulation code based on the binary collision approximation, to predict experimental data and get a deeper insight in the channeling process.
关键词： Channeling,Boron,SIMS,Ion implantation,Aluminum
更新于2025-09-12 10:27:22
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Fabrication and characterization of quantum dot devices based on tetralayer graphene/hexagonal boron nitride heterostructures
摘要： We report on low temperature carrier transport property of quantum dot devices based on hexagonal boron nitride-encapsulated tetralayer graphene heterostructures. In the device with single dot geometry, we demonstrate a stochastic Coulomb blockade, suggesting formation of multiple dots coupled each other in series/parallel. Under a perpendicular magnetic field, the overlapping Coulomb diamonds are lifted at zero bias voltage and the charging energy is decreased. These imply the suppression of multiple dots behavior. Our results pave a way toward the investigation of interlayer correlation on single electron transport in few-layer graphene quantum dots.
关键词： magnetic field,hexagonal boron nitride,Coulomb blockade,tetralayer graphene,quantum dot
更新于2025-09-12 10:27:22