Search query: boron nitride radio-isotope

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abstract: Hexagonal boron nitride is a model lamellar compound where weak, non local van der Waals interactions ensure the vertical stacking of two dimensional honeycomb lattices made of strongly bound boron and nitrogen atoms. We study the isotope engineering of lamellar compounds by synthesizing hexagonal boron nitride crystals with nearly pure boron isotopes (10B and 11B) compared to those with the natural distribution of boron (20 at% 10B and 80 at% 11B) On the one hand, as with standard semiconductors, both the phonon energy and electronic bandgap varied with the boron isotope mass, the latter due to the quantum effect of zero point renormalization. On the other hand, temperature dependent experiments focusing on the shear and breathing motions of adjacent layers revealed the specificity of isotope engineering in a layered material, with a modification of the van der Waals interactions upon isotope purification. The electron density distribution is more diffuse between adjacent layers in 10BN than in 11BN crystals. Our results open perspectives in understanding and controlling van der Waals bonding in layered materials.
author_names: T Q P Vuong

S Liu

Arie van der Lee

Ramon Cusco

L Artus

Thierry Michel

Pierre Valvin

James H Edgar

Guillaume Cassabois

Bernard Gil
title: Isotope engineering of van der Waals interactions in hexagonal boron nitride.
venue: Nature materials
year: 2018

abstract: A cool way to use isotopes Thermal management of electronics requires materials that can efficiently remove heat. Several promising materials have been found recently, but diamond remains the bulk material with the highest thermal conductivity. Chen et al. found that isotopically pure cubic boron nitride has an ultrahigh thermal conductivity, 75% that of diamond. Using only boron 11 or boron 10 allows the crystal vibrations that carry heat to move more efficiently through the material. This property could be exploited for better regulating the temperature of high power devices. Science, this issue p. 555 Isotopically pure cubic boron nitride has a thermal conductivity almost as high as that of diamond. Materials with high thermal conductivity (k) are of technological importance and fundamental interest. We grew cubic boron nitride (cBN) crystals with controlled abundance of boron isotopes and measured k greater than 1600 watts per meter kelvin at room temperature in samples with enriched 10B or 11B. In comparison, we found that the isotope enhancement of k is considerably lower for boron phosphide and boron arsenide as the identical isotopic mass disorder becomes increasingly invisible to phonons. The ultrahigh k in conjunction with its wide bandgap (6.2 electron volts) makes cBN a promising material for microelectronics thermal management, high power electronics, and optoelectronics applications.
author_names: Ke Chen

Bai Song

Navaneetha Krishnan Ravichandran

Qiye Zheng

Xiyao Chen

Hwijong Lee

Haoran Sun

Shexin Li

Geethal Amila Gamage Udalamatta Gamage

Fei Tian

Zhiwei Ding

Qichen Song

Akash Rai

Hanlin Wu

Pawan Koirala

Aaron J Schmidt

Kenji Watanabe

Bing Lv

Zhifeng Ren

Li Shi

David G Cahill

Takashi Taniguchi

David Broido

Gang Chen
title: Ultrahigh thermal conductivity in isotope enriched cubic boron nitride
venue: Science
year: 2020

abstract: The thermal conductivity, k, of single layers of hexagonal boron nitride (h BN) as well as that of bulk h BN have been calculated utilizing an exact numerical solution of the phonon Boltzmann transport equation. The stronger phonon phonon scattering in h BN is revealed as the cause for its lower k compared to graphite. A reduction in such scattering in the single layer arising mainly from a symmetry based selection rule leads to a substantial increase in k, with calculated room temperature values of over 600WmK. Isotopic enrichment further increases k, with the calculated enhancement exhibiting a peak with temperature whose magnitude shows a dramatic sensitivity to crystallite size. PACS: 63.20.kg, 63.22.Rc, 66.70. f, 65.80.Ck
author_names: David Broido

Lucas Lindsay
title: Enhanced thermal conductivity and isotope effect in single layer hexagonal boron nitride
year: 2011

abstract: Abstract Graphitic carbon nitride (g C3N4) has enormous potential for photocatalysis, but only possesses moderate activity because of excitonic effects and sluggish charge transfer. Herein, metal free heterostructure photocatalyst constructed by boron nitride quantum dots (BNQDs) and ultrathin porous g C3N4 (UPCN) was successfully developed for overcoming these defects. Results showed that the BNQDs loaded UPCN can simultaneously promote the dissociation of excitons and accelerate the transfer of charges owing to the negatively charged functional groups on the surface of BNQDs as well as the ultrathin and porous nanostructure of g C3N4. Benefiting from the intensified exciton dissociation and charge transfer, the BNQDs/UPCN (BU) photocatalyst presented superior visible light driven molecular oxygen activation ability, such as superoxide radical O2 generation and hydrogen peroxide (H2O2) production. The average O2 generation rate of the optimal sample (BU 3) was estimated to be 0.25 mmol L 1 min 1, which was about 2.3 and 1.6 times than that of bulk g C3N4 and UPCN. Moreover, the H2O2 production by BU 3 was also higher than that of bulk g C3N4 (22.77 mmol L 1) and UPCN (36.13 mmol L 1) and reached 72.30 mmol L 1 over 60 min. This work reveals how rational combination of g C3N4 with BNQDs can endow it with improved photocatalytic activity for molecular oxygen activation, and provides a novel metal free and highly efficient photocatalyst for environmental remediation and energy conversion.
author_names: Yang Yang

Chen Zhang

Danlian Huang

Guangming Zeng

Jinhui Jeanne Huang

Cui Lai

Chengyun Zhou

Wenjun Wang

Hai Guo

Wen-jing Xue

Rui Deng

Min Cheng

Weiping Xiong
title: Boron nitride quantum dots decorated ultrathin porous g C3N4: Intensified exciton dissociation and charge transfer for promoting visible light driven molecular oxygen activation
venue: Applied Catalysis B: Environmental
year: 2019

abstract: For more than seven decades, hexagonal boron nitride (hBN) has been employed as an inert, thermally stable engineering ceramic; since 2010, it has also been used as the optimal substrate for graphene in nanoelectronic and optoelectronic devices. Recent research has revealed that hBN exhibits a unique combination of optical properties that enable novel (nano)photonic functionalities. Specifically, hBN is a natural hyperbolic material in the mid IR range, in which photonic material options are sparse. Furthermore, hBN hosts defects that can be engineered to obtain room temperature, single photon emission; exhibits strong second order nonlinearities with broad implications for practical devices; and is a wide bandgap semiconductor well suited for deep UV emitters and detectors. Inspired by these promising attributes, research on the properties of hBN and the development of large area bulk and thin film growth techniques has dramatically expanded. This Review offers a snapshot of current research exploring the properties underlying the use of hBN for future photonics functionalities and potential applications, and covers some of the remaining obstacles.Hexagonal boron nitride (hBN) is highly sought after for mid IR nanophotonics, nonlinear and quantum optics, and as an efficient UV emitter. This Review surveys its fundamental physical properties, applications and synthesis.
author_names: Joshua D Caldwell

Igor Aharonovich

Guillaume Cassabois

James H Edgar

Bernard Gil

Dmitri N Basov
title: Photonics with hexagonal boron nitride
venue: Nature Reviews Materials
year: 2019

abstract: As the first in a large family of 2D van der Waals (vdW) materials, graphene has attracted enormous attention owing to its remarkable properties. The recent development of simple experimental techniques for combining graphene with other atomically thin vdW crystals to form heterostructures has enabled the exploration of the properties of these so called vdW heterostructures. Hexagonal boron nitride is the second most popular vdW material after graphene, owing to the new physics and device properties of vdW heterostructures combining the two. Hexagonal boron nitride can act as a featureless dielectric substrate for graphene, enabling devices with ultralow disorder that allow access to the intrinsic physics of graphene, such as the integer and fractional quantum Hall effects. Additionally, under certain circumstances, hexagonal boron nitride can modify the optical and electronic properties of graphene in new ways, inducing the appearance of secondary Dirac points or driving new plasmonic states. Integrating other vdW materials into these heterostructures and tuning their new degrees of freedom, such as the relative rotation between crystals and their interlayer spacing, provide a path for engineering and manipulating nearly limitless new physics and device properties.This is an overview of the new physics that emerges in van der Waals heterostructures consisting of graphene and hexagonal boron nitride, including the integer and fractional quantum Hall effects, novel plasmonic states and the effects of emergent moire superlattices.Key pointsAtomically thin flakes of van der Waals materials such as graphene and hexagonal boron nitride (hBN) can be mixed and matched into heterostructures with fundamentally new optoelectronic properties.Graphene encapsulated in hBN has very high mobility, with very low charge carrier inhomogeneity and ballistic transport characteristics over micrometre length scales at low temperature.High mobility graphene devices exhibit well developed multicomponent integer and fractional quantum Hall effects, as well as additional exotic correlated electronic phases in a magnetic field.When the graphene and hBN crystals are rotationally aligned, a long wavelength moire superlattice emerges, which creates new, finite energy Dirac points in the graphene bandstructure and leads to the Hofstadter butterfly spectrum.Graphene hBN heterostructures host new hybrid polaritons, as well as plasmonic excitations with exceptionally long lifetimes that can be tuned with a moire superlattice.
author_names: Matthew Yankowitz

Qiong Ma

Pablo Jarillo-Herrero

Brian J LeRoy
title: van der Waals heterostructures combining graphene and hexagonal boron nitride
year: 2019

abstract: A recent experiment reported a large anomalous Hall effect in Magic Angle Twisted Bilayer Graphene (TBG) aligned with a hexagonal boron nitride(h BN) substrate at \frac{3}{4} filling of the conduction band. In this paper we study this system theoretically, and propose explanations of this observation. We emphasize that the physics for this new system is qualitatively different from the pure TBG system. The aligned h BN breaks in plane two fold rotation symmetry and gaps out the Dirac crossings of ordinary TBG. The resulting valence and conduction bands of each valley carry equal and opposite Chern numbers $C=\pm 1$ A useful framework is provided by a lattice extended Hubbard model for this system which we derive. An obvious possible explanation of the anomalous Hall effect is that at $3/4$ filling the system is a spin valley polarized ferromagnetic insulator where the electrons completely fill a Chern band. We also examine an alternate more radical proposal of a compressible valley polarized but spin unpolarized composite ferm liquid metallic state. We argue that either state is compatible with current experiments, and propose ways to distinguish between them in the future. We also briefly discuss the physics at $1/2$ filling.
author_names: Ya-hui Zhang

Dan Mao

T Senthil
title: Twisted bilayer graphene aligned with hexagonal boron nitride: Anomalous Hall effect and a lattice model
year: 2019

abstract: We investigate the electronic structure of the flat bands induced by moire superlattices and electric fields in nearly aligned ABC trilayer graphene (TLG) boron nitride (BN) interfaces where Coulomb effects can lead to correlated gapped phases. Our calculations indicate that valley spin resolved isolated superlattice flat bands that carry a finite Chern number C=3 proportional to the layer number can appear near charge neutrality for appropriate perpendicular electric fields and twist angles. When the degeneracy of the bands is lifted by Coulomb interactions, these topological bands can lead to anomalous quantum Hall phases that embody orbital and spin magnetism. Narrow bandwidths of ~10 meV achievable for a continuous range of twist angles th0.6deg with moderate interlayer potential differences of ~50 meV make the TLG BN systems a promising platform for the study of electric field tunable Coulomb interaction driven spontaneous Hall phases.
author_names: Bheema Lingam Chittari

Guorui Chen

Yuanbo Zhang

Feng Wang

Jeil Jung
title: Gate Tunable Topological Flat Bands in Trilayer Graphene Boron Nitride Moire Superlattices.
venue: Physical review letters
year: 2019

abstract: Industrial production of NH3 from N2 and H2 significantly relies on Haber Bosch process, which suffers from high energy consume and CO2 emission. As a sustainable and environmentally benign alternative process, electrochemical artificial N2 fixation at ambient conditions, however, is highly required efficient electrocatalysts. In this study, we demonstrate that hexagonal boron nitride nanosheet (h BNNS) is able to electrochemically catalyze N2 to NH3. In acidic solution, h BNNS catalyst attains a high NH3 formation rate of 22.4 mg*h 1*mg 1cat. and a high Faradic efficiency of 4.7% at 0.75 V vs. reversible hydrogen electrode, with excellent stability and durability. Density functional theory calculations reveal that unsaturated boron at the edge site can activate inert N2 molecule and significantly reduce the energy barrier for NH3 formation.
author_names: Ya Juan Zhang

Huitong Du

Yongjun Ma

Lei Ji

Haoran Guo

Ziqi Tian

Hongyu Chen

Hong Huang

Guanwei Cui

Abdullah Mohamed Asiri

Fengli Qu

Liang Chen

Xuping Sun
title: Hexagonal boron nitride nanosheet for effective ambient N2 fixation to NH3
venue: Nano Research
year: 2019

abstract: Atomically thin boron nitride is one of the best thermal conductors among semiconductors and insulators. Heat management has become more and more critical, especially in miniaturized modern devices, so the exploration of highly thermally conductive materials with electrical insulation is of great importance. Here, we report that high quality one atom thin hexagonal boron nitride (BN) has a thermal conductivity (k) of 751 W/mK at room temperature, the second largest k per unit weight among all semiconductors and insulators. The k of atomically thin BN decreases with increased thickness. Our molecular dynamic simulations accurately reproduce this trend, and the density functional theory (DFT) calculations reveal the main scattering mechanism. The thermal expansion coefficients of monolayer to trilayer BN at 300 to 400 K are also experimentally measured for the first time. Owing to its wide bandgap, high thermal conductivity, outstanding strength, good flexibility, and excellent thermal and chemical stability, atomically thin BN is a strong candidate for heat dissipation applications, especially in the next generation of flexible electronic devices.
author_names: Qiran Cai

Declan Scullion

Weiliang Gan

Aleksey Falin

Shenmin Zhang

Kenji Watanabe

Takashi Taniguchi

Ying Ian Chen

Elton J G Santos

Luhua Li
title: High thermal conductivity of high quality monolayer boron nitride and its thermal expansion
venue: Science Advances
year: 2019