Atomic-Scale Investigation of Oxidation at the Black Phosphorus Surface

Abstract

Black phosphorus (BP) exhibits extraordinary electronic properties that are desirable for a wide variety of electronic and optoelectronic applications. However, applications of BP are hindered by its rapid degradation in ambient conditions. Despite significant advances that have been made in understanding the degradation mechanism, no consensus has yet been reached on how BP oxidation occurs at the atomic scale as experimental studies have been mostly restricted to averaged effects of degradation over a micron- to millimeter-sized region. Here, BP oxidation is investigated using scanning tunneling microscopy/spectroscopy (STM/S). Introducing O2 gas to the BP surface in ultrahigh vacuum at a pressure of 10–5 mbar for 1 min creates two new types of defects on the surface. We identify these defects as dangling atomic oxygen and phosphorus multivacancies using density functional theory simulations. In addition to the structural changes to the surface, the electronic structure is also drastically altered by the introduction of oxygen. The 300 meV band gap of BP is lifted due to dosing. This change in the electronic structure is reversible through STM tip manipulation. These are the first experimental results showing the atomic-scale oxidation of BP, an important step toward understanding the degradation process.

Interaction of Water and Oxygen Molecules with Phosphorene: An Ab Initio Study

“…The phase diagram, whose construction is explained in Section 3 shows that the Otermination is more stable than all other possible terminations, and it is, in general, more stable than the pristine layer, except in conditions that are extremely poor in terms of oxygen. This result agrees with the experimental observation that phosphorene oxidation most easily occurs in air [18,27]. Interestingly, phosphorene oxidation preserves the peculiar geometry of 2D phosphorene, which can give rise to incommensurate low-friction layer orientations [16].…”

“…Phosphorene usage in the above-described fields is, however, jeopardized by its strong tendency to degrade under ambient conditions [17][18][19][20][21]. The atomic-scale mechanisms of oxidation of phosphorene have been investigated theoretically [22][23][24][25][26] and experimentally [18,27,28], giving rise to different interpretations of the role played by water. Ultimately, oxidation was found to be induced by the interaction with O 2 , whereas water alone does not seem to react with pristine phosphorene, even if it may act as a catalyst for O 2 -induced oxidation [18,22].…”

Recent progress of 2-dimensional layered thermoelectric materials

“…其他过渡金属硫化物在热电领域也有着巨大的潜力，理论计算和实验都证 明，由于过渡金属硫化物的热传输性能可利用硫族元素进行调节 [110,111] ，硫族元 素从S到Se的变化会使热导率下降，这会更加有益于热电应用。理论上也对部分 过渡金属硫化物的ZT值进行了预测 [112] ，其中过渡金属硫化物通常有着极高的热 电应用潜力，且低维材料相比体块在热电方面有着巨大的发展前景。对于WSe 2 来说，Saito等人利用电子双层结构场效应晶体管离子液体掺杂的方法研究了 WSe 2 的热电性能 [107] ，如图5a，发现其展现着双极性的传输行为，且在n型和p型 [113] ，然而它也有着一个相对较大的68.1 mW/cm•K的晶格热导率，因此未来可以通过进一步降低其晶格热导率来提高它 的热电性能。对于PdSe 2 ，理论预测发现其最高有着ZT=1.1的极高的热电优值 [114] 。 2017年，Xiao等人 [115] 首次制备并解离出少层的PdSe 2 晶体，发现PdSe 2 有着各向 异性的传输性能和极强的空气稳定性，并利用拉曼光谱和FET等手段对其做了深 入的表征，发现其有着双极性的电传输行为和金属至半导体电传输行为的转变， 该系列结果为之后的研究做出了十分重要的贡献。2020年，Zhao等人首次测量 了具有特殊晶格结构的PdSe 2 的热电性质 [108] ，如图5b所示，发现其有着优异的双 极性传输行为和极高的迁移率，并且由于其随着层数的降低会出现能带简并度 的增加和 量子限制效应，因此可以提高功率因数PF(5 nm厚PdSe 2 高达1.5 mW/m•K 2 ) ，并且由于其褶皱的五角晶格结构导致其有着极低的热导率 [116] ，这 极其有利于热电应用的需求，其特殊的晶格结构导致其层间耦合异常强烈，因 此给予我们可通过层数的调控进而调控其热电性质的途径。同样，2022年也有 研究者利用DFT和玻尔兹曼理论计算了单层PdSe 2 在中高温度下的热电性能 [117] ， [121] ，并且，黑 磷有着极其褶皱的晶格结构且有着强烈的面内各向异性，分为 ZZ 方向和 AC 方 向，如图 6a 所示。黑磷与石墨烯等材料一致，面间由范德瓦尔斯键相连，借助 于机械解离可获得少层样品。但由于黑磷极易氧化，导致其不能在空气中长时 间暴露，也阻碍了人们对它的研究 [122][123][124][125] 。 图 6：( a)黑磷晶体结构的示意图 [126] ；( b)黑磷纳米带在 AC 和 ZZ 方向的热导率和杨氏模 量测量值，其中热导率和杨氏模量有着相似的各向异性比值(分别为 2.24 和 2.05) [127] ；( c) AC 方向和 ZZ 方向的黑磷纳米带电导率和(d)塞贝克系数随温度的变化关系 [128] ；( e)黑 磷塞贝克系数的少层实验数据和体块理论计算数值(实线为 x S ，虚线为 y S )的比较 [25] ； (f)210 K 下，少层黑磷的功率因数随栅极电压的变化关系 [25] 。 Fig6. (a) Schematic image of BP.…”

Low-dimensional optoelectronic synaptic devices for neuromorphic vision sensors

“…Under light excitation, many photo-generated carriers can be trapped by the surface state, resulting in an increased carrier lifetime and the formation of the persistent photoconductivity (PPC) effect. Black phosphorus (BP) materials spontaneously produce numerous defect states [104,105].…”