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xuexi9825

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The Raman spectrum shows the expected vibrational modes at 131, 306, 370, 493, and 628 cm−1, which is an unambiguous signature of the cubic In2O3 structure. The factor group analysis predicts 4Ag (Raman) + 4Eg (Raman) + 14Tg (Raman) + 5Au (inactive) + 5Eu (inactive) + 16Tu (IR) modes for cubic In2O3 [21]. The modes observed here correspond to bcc-In2O3, agreeing well with the values reported in the literatures [22, 23]. The Raman results further evidence the good crystallinity of cubic In2O3 nanoplatelets. This suggests the obtained In2O3 nanoplatelets would promise application in sensor with high sensitivity and stability since the microstructure broken (especially at higher temperature) can be avoided owing to the good crystallinity.
Optical absorption experiments were also carried out to elucidate the band gap energy, which is one of the most important electronic parameters for semiconductor nanomaterials. Fig. 6 shows a typical UV-vis absorption spectrum of the In2O3 nanoplatelets. In2O3 is an n-type semiconductor, and its optical band gap can be estimated using the following formula:
(αhν)n = B(hν − Eg) (1)
where, α is the absorption coefficient, hν is the photon energy, B is a constant characteristic of the material, Eg is the band gap, and n is either 1/2 for an indirect transition or 2 for a direct transition. The (αhν)2 versus hν curve for the product is shown in the inset in Fig. 6. Extrapolation of the linear portion of the curve to α = 0 gives the optical band gap value of 3.1 eV for the In2O3 nanoplatelets. In addition, the best fit of Eq. (1) to the absorption spectrum of the product gives n = 2, suggesting that the as-obtained In2O3 nanoplatelets are semiconducting with a direct transition at this energy. Among the published reports, the band gap of In2O3 calculated varied from 2.3 to 3.8 eV, such as 3.7 eV for bulk In2O3 [24], 3.4 and 3.8 eV for In2O3 films [25], 3.2 eV for undoped In2O3 films [26], 2.6 eV for In2O3 nanoparticles [27]. Although the reason for the big band-gap change of In2O3 is not still clear, the stoichiometry, crystallinity and density of oxygen vacancies in In2O3 should have an effect on the band gap, and a special study may be necessary to clarify this issue.

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1楼 2011-03-31 15:04:20

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sltmac

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xuexi9825(金币+35, 翻译EPI+1): 2011-04-01 19:49:39

拉曼光谱显示期望的振动峰在131, 306, 370, 493, and 628 cm−1,这很明显符合In2O3的立方结构，群因素分析预测对于立方In2O3 [21]有着4Ag (Raman) + 4Eg (Raman) + 14Tg (Raman) + 5Au (inactive) + 5Eu (inactive) + 16Tu (IR)的关系。观测到的峰符合bcc-In2O3，与文献报道中的一致[22, 23]。拉曼光谱进一步证实了In2O3纳米片有着较好的晶相。这意味着得到的In2O3纳米片由于其好的晶型会保证在传感器的应用中有高的灵敏度和稳定性除非微孔结构被破坏（尤其在较高的温度下）。
同时进行的光学吸附实验也说明了对于半导体材料来说是很重要的一个电学参数：帯隙能。图6是一个典型的In2O3纳米片紫外吸收光谱图。In2O3是n型半导体，其带宽可以用下面公式计算：
(αhν)n = B(hν − Eg) (1)
其中a是吸附系数，hv是光子能，B是材料的固定特性参数，Eg是带宽，n是间接帯隙的一半或者是直接帯隙的2倍。(αhν)2对hv的曲线见图6,。由该曲线的线性部分外推算得In2O3纳米片的带宽为2.1eV。另外，当n=2该材料的的紫外吸收光谱用方程1拟合最合适，意味着得到的In2O3纳米片半导体在该能量处有这直接帯隙。在已有的报道中，算得的n2O3纳米片的带宽从2.3到3.8 eV都有，比如体材料的In2O3 [24]帯隙宽为3.7eV，In2O3膜的帯隙宽分别为3.4和3.8 eV [25]，为掺杂的In2O3膜的帯隙宽为3.2eV [26]，In2O3纳米粒子的帯隙宽为2.6eV [27].尽管In2O3帯隙宽变化之大的原因还不清楚，化学计量，晶型以及In2O3中O缺陷都会对其有重要影响，仍有必要进行一些特别的实验来弄清该问题。

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