Revealing the Origins of 3D Anisotropic Thermal Conductivities of Black Phosphorus

Abstract

optical, [6][7][8] and thermal properties. [9][10][11][12][13][14][15][16][17][18] BP has an orthorhombic structure with puckered layers of sp 3 -hybridized phosphorus atoms along the armchair direction and van der Waals interactions between layers. [ 2 ] The structure of BP makes it the most thermodynamically stable phosphorus allotrope at ambient temperature and pressure. Both monolayer (also called phosphorene) and few-layer BP fl akes obtained from mechanical exfoliation [ 19,20 ] have proven to be anisotropic 2D semiconductors with high carrier mobility, [ 5,[19][20][21] possessing a direct band gap tunable from 0.3 to 1.0 eV. [ 22 ] This combination of properties makes BP a great candidate for use in the next generation nanoelectronic and nanophotonic devices, compared even favorably to other well-studied 2D materials such as graphene, hexagonal boron nitride, and molybdenum disulfi de. [23][24][25] One unique feature of BP is the inverse dependence of its in-plane electronic and thermal transport on the crystalline orientation: a higher electrical conductivity is associated with a lower thermal conductivity in the armchair direction and vice versa for the zigzag direction, which has been predicted in previous studies. [ 4,9 ] To date, experimental investigations on the anisotropic thermal properties of BP mainly focused on thin fi lms; thermal

Black Phosphorus Rediscovered: From Bulk Material to Monolayers

“…[105][106][107][108][109][110][111][112][113] Ah igher ZT value at ag iven temperature requires as uitable combination of high electrical conductivity and al ow thermal conductivity.AZT value of about 1i sc rucial for good thermoelectric materials to compete with conventional power generators.I nterestingly,t he electrical and thermal conductance of BP is not only anisotropic but exhibit orthogonally preferred conducting directions. TE materials undergo ad irect solid-state interconversion of thermal to electric energy.T he TE performance and efficiency are characterized by the dimensionless TE figure of merit ZT.…”

“…[61,[105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121] Firstprinciples simulations of single-layer BP predict a ZT value greater than 1a tr oom temperature and may reach 2.5 at 500 K. [108] Thehighest ZT value for bulk BP is found to be 0.72 at 800 K, which could be enhanced to 0.87 by applying an appropriate strain. [62,109,[123][124][125][126][127][128][129][130][131] BP has ag ood mechanical flexibility with ad irectiondependent Youngsm odulus [ ** ] that is one order of magnitude smaller than those of other 2D layered materials (i.e. [106] BP belongs to ag roup of materials known as topological insulators.…”

Accelerating evaluation of converged lattice thermal conductivity

“…However, the results obtained differ with each other unacceptably by even one order of magnitude. [12][13][14][40][41][42][43][44][45][46] It is also claimed for phosphorene that there exists a size-dependent κ along the zigzag direction, which is similar to graphene. 12 Based on the proposed strategy, we show clearly in Fig.…”

Thermal Transport in Phosphorene

“…Since high‐performance thermal management plays a key role in all the above mentioned applications, such as minimized thermal conductivity for thermoelectrics and efficient heat dissipation (maximal thermal conductivity) for nano‐/optoelectronic devices, tremendous amount of efforts have been dedicated to studying the thermal transport properties of phosphorene . The thermal conductivity of single‐layer phosphorene and bulk BP were investigated theoretically by independent groups using various methods . Besides the theoretical calculations, there are also reports on the thermal conductivity of phosphorene films and bulk BP from experimental measurements .…”

“…The thermal conductivity of single‐layer phosphorene and bulk BP were investigated theoretically by independent groups using various methods . Besides the theoretical calculations, there are also reports on the thermal conductivity of phosphorene films and bulk BP from experimental measurements . Due to the limitations of the synthesis technique, only the results of phosphorene films with thickness ranging from 9.5 to 552 nm are available .…”