CVD法制备MoS2薄膜的A1g模式拉曼光谱非线性温度效应研究 - CSDN文库

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"CVD生长的单层和多层MoS2薄膜的A1g模式激发机理和拉曼位移的非线性温度依赖性成因" 这篇研究论文深入探讨了化学气相沉积（CVD）法制备的单层及多层MoS2薄膜的振动特性，特别是光学声子的拉曼散射光谱。MoS2是一种二维过渡金属二硫属化物，因其独特的电子结构和光学性质，在电子器件和光电子学领域具有广泛的应用潜力。在实验中，MoS2薄膜被生长在SiO2/Si衬底上，并通过拉曼散射光谱技术在90K至540K的温度范围内进行了研究。当使用514.5nm激光时，观察到了单层、双层以及多层MoS2的1L2g_E和A1g模的拉曼峰。而使用785nm激光时，仅在单层MoS2中检测到1L2g_E模式的拉曼峰。这一差异揭示了A1g模式的电子-声子交换激发机制，这是首次在实验中确认这一现象。拉曼光谱是研究固体材料中声子行为的重要工具，其峰位变化反映了材料的内部结构和热力学性质。对于MoS2薄膜，A1g和1L2g_E模式的拉曼位移显示出非线性的温度依赖性，这可能是由于声子与电子、晶格缺陷以及层间相互作用的复杂相互作用导致的。非线性效应可能源于温度引起的晶格振动的增强，进而影响电子态的分布和能带结构。此外，多层MoS2与单层MoS2相比，其拉曼散射特性有所不同，这归因于层间的相互作用和量子 confinement效应。多层结构中，相邻层之间的耦合会改变声子的振动模式，导致拉曼谱图的差异。这项工作揭示了CVD生长的MoS2薄膜中A1g模式的激发机制，以及拉曼位移随温度变化的非线性关系，为理解和控制二维材料的物理性能提供了关键信息。这些发现对优化MoS2基电子设备的性能，特别是在高温环境下的应用，具有重要的科学价值和实际意义。同时，这也为进一步研究其他二维材料的声子行为和电子结构提供了理论基础。

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1. Introduction

Two-dimensional transition-metal dichalcogenide (TMDC) materials, such as molybdenum

disulfide (MoS

2

), are promising for the next generation of electronic and optoelectronic

devices [1] because of their unique electrical, optical, and mechanical properties [2–9]. In

contrast to graphene, MoS

2

atomic layers have a band gap which transits from indirect 1.2 eV

to direct 1.9 eV as the thickness of MoS

2

reduces from bulk to monolayer [3,5]. Those unique

properties of MoS

2

make it very suitable for fabrication of electronic and optoelectronic

devices. Single-layer MoS

2

field effect transistors [10–12], heterojunction [13] and

ultrasensitive photodetectors [14], have been reported. Field emission and photoresponse of

MoS

2

thin films are also detailed investigated [15].Even the integrated circuits based on

bilayer MoS

2

transistors have also been demonstrated [16]. It may be predicted that the degree

of integration of MoS

2

transistor-based integrated circuits will be much higher than one of

current Si-based microelectronic integrated circuits because MoS

2

transistors are in nanometer

scale. Heat dissipation or thermal conductivity has been one of the most significant

constraints on design and fabrication of current Si-based integrated electronic circuits.

Consequently, it may be predicted that heat dissipation or thermal conductivity will be critical

in near future in design and fabrication of single layer MoS

2

integrated circuits. For thermal

manipulation, it is very necessary to study electron-phonon interactions, dynamics and

thermodynamics of phonons in MoS

2

thin films.

Raman spectroscopy is a powerful tool to access thermal properties of materials,

especially nanomaterials, and has been extensively used to investigate thermal properties and

microstructures of TMDC films and other materials [17–23], revaling their doping effect [24],

electronic and structural properties [25], and the vibration property of nanoribbons and

nanosheets [26–28]. Several comprehensive studies on the vibration frequency and peak

width evolution of phonon modes of MoS

2

mono- and few-layers with temperature have also

been reported so that thermal conductivity and phonon dynamics of MoS

2

could be revealed

[29–35]. However, some controversial experimental results were reported [29–35]. Both

Taube et al. [29] and Yan et al. [30] investigated the temperature dependence of Raman shifts

of

1

2

g

E

and A

1g

modes of monolayer MoS

2

within a low temperature range of 80 – 350 K,

respectively on SiO

2

/Si and sapphire (suspended) substrates. Although the MoS

2

monolayer

samples studied by the two groups were all fabricated from mechanical exfoliation of MoS

2

single crystals, Taube et al. [29] found nonlinear temperature dependence of Raman shifts of

both

1

2

g

E

and A

1g

modes, while Yan et al. [30] observed linear temperature dependence for

either a sapphire substrate or the suspended. Inversely, Lanzillo et al. [31] and Najmaei et al.

[32] studied the temperature dependence of Raman shifts of

1

2

g

E

and A

1g

modes of monolayer

MoS

2

on SiO

2

/Si substrates within a high temperature range of 300 – 500 K, respectively

prepared by chemical vapor deposition (CVD) and mechanical exfoliation. Both groups

observed linear temperature dependence of Raman shifts of both

1

2

g

E

and A

1g

modes. Lanzillo

et al. [31] obtained the first-order temperature coefficient of

1

2

g

E

mode as −0.013 cm

−1

/K, but

Najmaei et al. [32] gave out one as −0.0179 cm

−1

/K. An obvious difference on the first-order

#260899

Received 9 Mar 2016; revised 17 May 2016; accepted 18 May 2016; published 26 May 2016

© 2016 OSA

30 May 2016 | Vol. 24, No. 11 | DOI:10.1364/OE.24.012281 | OPTICS EXPRESS 12283

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