Need for complementary techniques for reliable characterization of MoS2-like layers
Need for complementary techniques for reliable characterization of MoS2-like layers
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DOI：
10.1116/6.0002701
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发表时间：
2023-06
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影响因子：
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通讯作者：
Aditya M. Deshpande;Koki Hojo;Koichi Tanaka;Pedro Arias;H. Zaid;M. Liao;M. Goorsky;S. Kodambaka
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作者：
Aditya M. Deshpande;Koki Hojo;Koichi Tanaka;Pedro Arias;H. Zaid;M. Liao;M. Goorsky;S. Kodambaka
在拉曼光谱中分别在 408 和 382 cm−1 附近观察到的特征 A1g 和 E2g1 峰被认为是 2H 结构 MoS2 的证据，MoS2 可能是研究最广泛的过渡金属二硫属化物。在这里，我们结合使用 X 射线衍射、X 射线光电子能谱和共振拉曼光谱，表明仅在拉曼光谱中检测到 A1g 和 E2g1 模式可能并不一定意味着 MoS2 的存在。通过在 20 m Torr (2.67 Pa) 下对 Mo 靶材进行超高真空直流磁控管溅射，在 1073 K 温度下在单晶 Al2O3(0001) 基板上生长出一系列厚度约为 20 nm 的 Mo–S 薄膜，其与 H2S 分压、pH2S（= 总压的 0、0.01%、0.1% 和 1%）有关。 Ar/H2S 气体混合物。在纯 Ar 放电中，pH2S 高达 0.1%，即 pH2S ≤ 2.67 × 10−3 Pa，我们获得体心立方 (bcc)、110 纹理薄膜，其晶格参数 a 从 0.3148 nm（纯 Ar 中）增加到 0.3151 nm（在 pH2S = 2.67 × 10−4 Pa 时）和 0.3170 nm （在 pH2S = 2.67 × 10−3 Pa 时），我们将其归因于 Mo 晶格中 S 掺入的增加。使用 1% H2S，即 pH2S = 2.67 × 10−2 Pa，我们获得 000l 取向的 2H 结构 MoS2.0±0.1 层。使用 0.1%（和 1%）H2S 生长的薄膜的拉曼光谱显示在 412 (408) 和 380 cm−1 (382 cm−1) 附近有峰，这可以解释为 2H-MoS2 的 A1g 和 E2g1 拉曼模式。通过比较 MoS2.0±0.1 和 Mo:S 薄膜的拉曼光谱，我们确定了 A1g 和 E2g1 峰位置以及缺陷敏感峰相对于 A1g 峰强度的差异，这有助于区分纯 MoS2 与非化学计量 MoS2−x 和多相 Mo:S 材料。
The observation of characteristic A1g and E2g1 peaks, at around 408 and 382 cm−1, respectively, in Raman spectroscopy is considered the evidence of 2H-structured MoS2, probably the most extensively studied transition-metal dichalcogenide. Here, using a combination of x-ray diffraction, x-ray photoelectron spectroscopy, and resonant Raman spectroscopy, we show that the detection of A1g and E2g1 modes in Raman spectra alone may not necessarily imply the presence of MoS2. A series of Mo–S films, ≈ 20-nm-thick, are grown on single-crystalline Al2O3(0001) substrates at 1073 K as a function of H2S partial pressure, pH2S (= 0, 0.01%, 0.1%, and 1% of total pressure) via ultra-high vacuum dc magnetron sputtering of a Mo target in 20 m Torr (2.67 Pa) Ar/H2S gas mixtures. In pure Ar discharges and with pH2S up to 0.1%, i.e., pH2S ≤ 2.67 × 10−3 Pa, we obtain body centered cubic (bcc), 110-textured films with lattice parameter a increasing from 0.3148 nm (in pure Ar) to 0.3151 nm (at pH2S = 2.67 × 10−4 Pa), and 0.3170 nm (at pH2S = 2.67 × 10−3 Pa), which we attribute to increased incorporation of S in the Mo lattice. With 1% H2S, i.e., pH2S = 2.67 × 10−2 Pa, we obtain 000l oriented 2H-structured MoS2.0±0.1 layers. Raman spectra of the thin films grown using 0.1% (and 1%) H2S show peaks at around 412 (408) and 380 cm−1 (382 cm−1), which could be interpreted as A1g and E2g1 Raman modes for 2H-MoS2. By comparing the Raman spectra of MoS2.0±0.1 and Mo:S thin films, we identify differences in A1g and E2g1 peak positions and intensities of defect-sensitive peaks relative to the A1g peaks that can help distinguish pure MoS2 from non-stoichiometric MoS2−x and multiphase Mo:S materials.