文章信息/Info

Title:

Theoretical study of negative thermal expansion in 2D graphene/h-BN heterostructure

作者:

武明義 ; 孫強 *; 賈瑜; 梁二軍

鄭州大學(xué)物理工程學(xué)院

Author(s):

Wu Mingyi;  Sun Qiang; Jia Yu; Liang Erjun

關(guān)鍵詞:

石墨烯' target="_blank" rel="external"> FONT-FAMILY: 宋體">石墨烯;  FONT-FAMILY: "; Calibri"; "; sans-serif"; ">h-BN ' target="_blank" rel="external"> FONT-FAMILY: 宋體">; 負(fù)熱膨脹; 格林奈森參數(shù); 范德瓦爾斯相互作用

DOI:

10.7502/j.issn.1674-3962.2015.07.04

文獻(xiàn)標(biāo)志碼:

A

摘要:

二維材料由于存在著“膜效應(yīng)”—即在垂直于薄膜方向的熱漲落，使得沿著二維薄膜面內(nèi)方向出現(xiàn)反常的負(fù)熱膨脹現(xiàn)象。這種熱效應(yīng)對薄膜的穩(wěn)定性及電子性質(zhì)可產(chǎn)生重要影響。基于第一性原理計算和準(zhǔn)諧近似，我們系統(tǒng)地研究了二維單層石墨烯、h-BN和石墨烯/h-BN異質(zhì)結(jié)構(gòu)的電子、聲子以及熱膨脹性質(zhì)，計算了三種結(jié)構(gòu)不同振動模式的格林奈森參數(shù)，討論了引起這三種結(jié)構(gòu)負(fù)熱膨脹的振動模式。計算表明，由于垂直薄膜方向的熱振動，石墨烯和h-BN在薄膜面內(nèi)均具有較大的負(fù)熱膨脹系數(shù)；它們形成的異質(zhì)結(jié)構(gòu)依靠弱的范德瓦爾斯相互作用結(jié)合在一起，這種層間弱相互作用對薄膜垂直方向的熱振動產(chǎn)生影響，使得形成的異質(zhì)結(jié)構(gòu)的負(fù)膨脹系數(shù)介于石墨烯和h-BN之間。通過分析異質(zhì)結(jié)構(gòu)的振動模式，發(fā)現(xiàn)引起面內(nèi)熱收縮的ZA振動模式受到了層間范德瓦爾斯相互作用影響，導(dǎo)致異質(zhì)結(jié)構(gòu)的負(fù)熱膨脹系數(shù)大于石墨烯而小于h-BN。我們的研究表明，可以在實驗上通過范德瓦爾斯相互作用來改變層狀結(jié)構(gòu)材料的負(fù)熱膨脹性質(zhì)，從而提高薄膜材料結(jié)構(gòu)和電子性質(zhì)的熱穩(wěn)定性。

Abstract:

Two dimensional (2D) materials generally exhibit negative thermal expansion (NTE) along the in-plane directions due to the so called "membrane effect"，i.e. the thermal fluctuation in vertical direction. The thermal phenomenon may drastically impact the stability and electronic property of the low dimensional materials. Based on first-principles calculations and qusiharmonic approximation, electronic structures, phonon spectra and expansion property of the two dimensional materials: graphene, h-BN sheet and graphene/h-BN heterostructure are systematically studied. The mode grüneisen parameters are calculated and the vibrational modes which contribute to the NTE in the three systems are discussed. The calculated results show that both graphenen and h-BN exhibit pronounced NTE in the in-plane directions due to the vertical thermal vibration. The graphenen/h-BN heterostructure is formed through van der Waals (vdW) interaction between the monolayer graphene and the h-BN sheet and this weak interaction may influence the vertical thermal vibration of the monolayer graphene and the h-BN sheet, and consequently the thermal contraction of the heterostructure is significant smaller than that of the h-BN, but larger than the graphene. Our results indicate that NTE of the two dimensional materials can be altered through the vdW interactions in experiment and enhance the thermal stability of the stucture and electronic property.