石墨烯具有優(yōu)異的電學(xué)與光學(xué)性能、極高的電荷載流子遷移率、室溫量子霍爾效應(yīng)等，因而被認(rèn)為在納米電子學(xué)領(lǐng)域有著非常廣泛的應(yīng)用前景。然而，本征石墨烯零帶隙的特點(diǎn)以及過(guò)低的載流子濃度大大限制了其在數(shù)字電路中的應(yīng)用。

對(duì)石墨烯進(jìn)行氮摻雜有望彌補(bǔ)本征石墨烯零帶隙和載流子密度低的缺憾，實(shí)現(xiàn)其在電子器件領(lǐng)域的廣泛應(yīng)用。然而，目前氮摻雜石墨烯(NG)的合成主要面臨兩個(gè)問(wèn)題：

氮摻雜石墨烯中的氮濃度普遍很低，除利用特殊的芳香烴分子合成的氮原子周期性分布的碳氮二維材料以外，目前報(bào)道的氮摻雜石墨烯中氮原子的摻雜濃度不高于20%，這使得NG中載流子濃度的調(diào)控受到很大限制。

NG中的摻雜氮原子通常以吡啶氮、吡啶氮氧化物、吡咯氮、石墨氮等多種形式共存，并且摻雜氮原子在石墨烯的面內(nèi)排列無(wú)序，這也使得載流子在輸運(yùn)過(guò)程中遭遇更強(qiáng)的散射，導(dǎo)致載流子遷移率大大降低。

現(xiàn)階段，如何可控地制備高濃度、高有序的NG是一個(gè)極富挑戰(zhàn)性的難題。 理解氮原子摻雜濃度低、摻雜類型和位置不可控的本質(zhì)是實(shí)現(xiàn)高濃度、高有序的NG制備的前提。來(lái)自華東師范大學(xué)精密光譜科學(xué)與技術(shù)國(guó)家重點(diǎn)實(shí)驗(yàn)室的博士生補(bǔ)賽玉（昆士蘭大學(xué)交流學(xué)生）及其導(dǎo)師袁清紅研究員與澳大利亞昆士蘭大學(xué)澳大利亞生物工程及納米科技研究所的Debra J. Searles教授等人，采用第一性原理計(jì)算與粒子群優(yōu)化算法相結(jié)合的方法，分別對(duì)吡啶氮和石墨氮摻雜石墨烯的最穩(wěn)定結(jié)構(gòu)進(jìn)行了預(yù)測(cè)。發(fā)現(xiàn)氮摻雜石墨烯的穩(wěn)定結(jié)構(gòu)與其中的氮原子濃度密切相關(guān)，低氮摻雜濃度下，NG中的石墨氮和吡啶氮具有相近的形成能，因而更易形成石墨氮和吡啶氮共摻雜的結(jié)構(gòu)。

隨著氮原子摻雜濃度的增加，石墨氮摻雜石墨烯的形成能要高于吡啶氮摻雜石墨烯的形成能，因而更易形成吡啶氮摻雜的石墨烯結(jié)構(gòu)。 特別是，當(dāng)?shù)訐诫s濃度高于0.25時(shí)，NG中以吡啶氮摻雜為主。此外，該研究還表明，低氮摻雜濃度的NG具有更低的形成能。這一系列研究結(jié)果解釋了目前實(shí)驗(yàn)上NG中氮原子濃度低，以及多種類型的氮混合摻雜的實(shí)驗(yàn)現(xiàn)象。進(jìn)一步，研究人員結(jié)合理論推導(dǎo)計(jì)算出含碳或氮的前驅(qū)體分子中的碳或氮的化學(xué)勢(shì)隨溫度、壓強(qiáng)的表達(dá)式，提出可通過(guò)控制NG合成過(guò)程中的前驅(qū)體類型、溫度、壓強(qiáng)實(shí)現(xiàn)碳和氮原子化學(xué)勢(shì)的調(diào)控，從而實(shí)現(xiàn)NG中氮原子的類型和氮摻雜濃度的調(diào)控。該研究通過(guò)對(duì)不同氮濃度下的NG結(jié)構(gòu)和能量進(jìn)行研究，為實(shí)驗(yàn)上實(shí)現(xiàn)氮摻雜石墨烯的可控合成提供了理論依據(jù)。 該文近期發(fā)表于npj Computational Materials6:128 (2020)，英文標(biāo)題與摘要如下，點(diǎn)擊左下角“閱讀原文”可以自由獲取論文PDF。

Design of two-dimensional carbon-nitride structures by tuning the nitrogen concentration

Saiyu Bu, Nan Yao, Michelle A. Hunter, Debra J. Searles & Qinghong Yuan

Nitrogen-doped graphene (NG) has attracted increasing attention because its properties are significantly different to pristine graphene, making it useful for various applications in physics, chemistry, biology, and materials science. However, the NGs that can currently be fabricated using most experimental methods always have low N concentrations and a mixture of N dopants, which limits the desirable physical and chemical properties. In this work, first principles calculations combined with the local particle-swarm optimization algorithm method were applied to explore possible stable structures of 2D carbon nitrides (C1?xNx) with various C/N ratios. It is predicted that C1?xNx structures with low N-doping concentration contain both graphitic and pyridinic N based on their calculated formation energies, which explains the experimentally observed coexistence of graphitic and pyridinic N in NG. However, pyridinic N is predominant in C1?xNx when the N concentration is above 0.25. In addition, C1?xNx structures with low N-doping concentration were found to have considerably lower formation energies than those with a high N concentration, which means synthesized NGs with low N-doping concentration are favorable. Moreover, we found the restrictions of mixed doping and low N concentration can be circumvented by using different C and N feedstocks, and by growing NG at lower temperatures.

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原文標(biāo)題：npj: 氮摻雜石墨烯的結(jié)構(gòu)調(diào)控—路在何方？

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