Traditionally, the formation of heterostructures is known to impose challenges on the mechanical reliability of devices due to lattice and thermal mismatch strains. On the contrary, our observations on the chemical vapor deposition (CVD) growth of WS₂ reveal that the formation of heterophases cancels the competing thermal mismatch and lattice strains and stabilizes crack free monolayer heterostructures while homophase WS₂ monolayers suffer from severe cracking. To shed light on this unique thermal strain relaxation in heterophase WS₂ monolayers, a systematic investigation with the aid of in situ Raman spectroscopy has been carried out from 4 K to near room temperature (330 K). First-order temperature coefficients of the metallic 1T phase: E_2g ∼ −0.0090; A_1g ∼ −0.0109, semiconducting 1H phase: E_2g ∼ −0.0093; A_1g ∼ −0.0143 and semi-metallic 1T′ phase: E_2g ∼ −0.0095; A_1g ∼ −0.0124 are estimated for the investigated temperature range from 90 K to 330 K. The measured thermal expansions of CVD grown WS₂ monolayers with coexisting 1H–1T and 1H–1T′ polymorphic phases are used to estimate the thermal mismatch strain. The tensile strain arising from the thermal expansion mismatch is found to be cancelled by the compressive lattice strain arising in heterophase WS₂ monolayers. Phase engineered WS₂ monolayers with differential thermal expansions of different polymorphic phases are relevant for the design of robust heterostructure based nanoscale devices.

中文翻译：

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无裂纹WS ₂面内异质结构的竞争性热膨胀失配和晶格应变工程生长†

传统上，由于晶格和热失配应变，异质结构的形成对器件的机械可靠性提出了挑战。相反，我们对WS ₂的化学气相沉积（CVD）生长的观察表明，异相的形成消除了竞争性的热失配和晶格应变，并稳定了无裂纹单层异质结构，而同相WS ₂单层则遭受了严重的开裂。为了阐明异相WS ₂单层中这种独特的热应变松弛，借助原位系统研究拉曼光谱已在4 K至接近室温（330 K）的温度范围内进行。第一阶金属1T相位的温度系数：电子_2克〜-0.0090; 甲_1克〜-0.0109，半导体1H阶段：电子_2克〜-0.0093; 甲_1克〜-0.0143和半金属1T'相：电子_2克〜-0.0095; 甲_1克〜-0.0124估计为所研究的温度范围从90 K至330 K.测量CVD生长的热膨胀WS ₂共存1H-1T和1H-1T'多态相的单分子层用于估算热失配应变。发现由热膨胀失配引起的拉伸应变被异相WS ₂单层中产生的压缩晶格应变所抵消。具有不同多晶型相的不同热膨胀的相工程WS ₂单层与基于鲁棒异质结构的纳米级器件的设计有关。