摘要
磷烯是一种新兴的二维材料，是磷原子通过共价键形成的褶皱蜂窝状结构。磷烯具有可调的直接带隙和高度各向异性的能带结构，在光学和光电子学领域具有潜在的应用价值。本文基于第一性原理计算，研究了磷烯器件中光电流的应变调控和磷烯纳米带的边界磁性。
(1)针对磷烯纳米带，研究了结构弛豫对边界磁性和能带结构的影响。对直接从磷烯晶体结构剪裁得到的纳米带，计算表明，边界原子处于双边铁磁但对边反铁磁的状态(FM-A态)时，系统能量最低。扶手椅边界的纳米带表现为金属，锯齿形边界的纳米带表现为间接带隙的半导体。随着宽度的增加，边界磁性逐渐消失。对完全结构弛豫后的磷烯纳米带，计算表明，扶手椅边界的纳米带没有边界磁性且表现为间接带隙的半导体，锯齿形边界的纳米带只在某个特定的宽度存在FM-A态。相比之下，结构弛豫对石墨烯纳米带的边界磁性和能带结构影响较小。
(2)针对线偏振光垂直照射的二端磷烯器件，研究了光电流的应变调控。在光照区的一部分施加垂直于磷烯平面的门电压，破坏体系的空间反演对称，获得在源-漏偏压为零时的光电流。我们采用基于密度泛函理论与非平衡格林函数相结合的方法计算这种光致电流。在无应变的体系中，光电流具有高度的各向异性且依赖于门电压施加的范围。在强度≈2%的小拉伸应变下，光响应在整个可见光区都被强烈抑制。这说明我们考虑的磷烯器件可用作光电流的机械开关。随着应变强度的增加，沿锯齿形方向的光电流迅速
衰减。在中等应变强度下(如8%)，沿扶手椅方向的光电流在光子能的某个区域会增强。光电流的这种力学可调性有望为基于磷烯的光探测器提供附加的功能。
关键词：磷烯；边界磁性；光电流；应变
Abstract
口道恒河沙复沙Phosphorene is a rising two-dimensional material,which is a puckered hon-eycomb structure formed by covalently-bonded phosphorus atoms.Phosphorene posss a tunable direct band gap and highly-anisotropic band structure.The properties make phosphorene a promising material for optical and optoelectronic applications.Bad on first-principle calculations,we investigate the strain ma-nipulation of photocurrent in phosphorene-bad two-terminal device and edge magnetism in phosphorene nanoribbons.
脖子酸痛
(1)The effect of geometry relaxation on edge magnetism and band struc-ture has been studied for phosphorene nanoribbons.For the nanoribbons tailored directly from phosphorene crystal,our numerical calculations indicate that the lowest enengy appears when ferromagnetically ordered spins align at each edge and the spin directions at two edges are opposite(FM-A state).An armchair-edged nanoribbon behaves as a metal,while a zigzag-edged nanoribbon behave as
an indirect-gap miconductor.As the width increas,the edge magnetism van-ishes gradually.For phosphorene nanoribbons with full geometry relaxation,our calculations indicate that armchair-edged nanoribbons have no edge magnetism and behave as indirect-gap miconductors.A zigzag-edged relaxed nanorib-bon shows FM-A state only under a given width.In comparison,for graphene nanoribbons geometry relaxation has a minor effect on the edge magnetism and band structure.
(2)Strain manipulation of photocurrent has been investigated for a phosphorene-bad two-terminal device irradiated by a linear-polarized light.An out-of-plane gate voltage is applied within the irradiated region to break the inversion symme-
花样馒头的做法大全try of pristine phosphorene so that photocurrent is obtained under zero source-drain bias.Such a photogalvanic current is calculated by the nonequilibrium Green’s function formalism combined with density-functional theory.The pho-tocurrent in the strain-free system is highly anisotropic and depends on the ap-plied region of the gate voltage.Under a small tensile strain with strength≈2%, the photorespon for lights in the whole visible range is suppresd greatly.This
ABSTRACT
indicates that the considered phosphorene device acts as a mechanical switch of photocurrent.The p
臭豆腐的营养hotocurrent along the zigzag direction decays quickly with the strain strength.In contrast,the photocurrent along the armchair direction can be enhanced by a moderate strain strength≈8%in some region of pho-ton energy.Such a mechanical tunability of photogalvanic current could offer additional functionality of phosphorene-bad photodetectors.
KEY W ARDS:phosphorene;edge magnetism;photocurrent;strain
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目录
摘要 (i)
Abstract (ii)
目录 (iv)
第一章绪论 (1)
1.1磷烯 (1)
1.1.1磷烯的晶体结构 (1)
1.1.2磷烯的力学性质 (2)
1.1.3磷烯的光电性质 (3)
1.2磷烯纳米带磁性的尺寸效应 (4)
1.3本文内容安排 (5)
第二章理论计算方法 (7)
2.1密度泛函理论(DFT) (7)
2.2非平衡态下的输运理论 (9)
2.2.1非平衡格林函数(NEGF) (9)
2.2.2NEGF-DFT (11)
2.2.3光电流计算公式 (13)
2.3常用软件包VASP及Nanodcal介绍 (14)
第三章磷烯纳米带的边界磁性 (16)
快乐英语
3.1引言 (16)
3.2计算方法 (17)
3.3结果与讨论 (17)
3.4本章小结 (22)
第四章磷烯器件中光电流的应变调控 (23)
4.1引言 (23)
4.2模型与方法 (23)
夫妻自愿离婚协议书目录
4.3结果与讨论 (26)
4.4小结 (31)
第五章总结和展望 (32)
教室标语参考文献 (33)
发表的文章目录 (41)
g和ml
致谢 (42)
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