Abstract

The formation of unoccupied electronic states and the boundary potential barrier during thermal deposition of tetracyanoquinodimethane (TCNQ) films to 7 nm in thickness on a (SiO₂)n-Si surface has been studied. The electronic characteristics of the surface under study are measured by the total current spectroscopy (TCS) using a testing electron beam with energies from 5 to 20 eV above the Fermi level. The formation of a boundary potential barrier in the (SiO₂)n-Si/TCNQ structure is accompanied by an increase in the work function of the surface from 4.2 ± 0.1 to 4.7 ± 0.1 eV. Using the results of the TCS experiments, the DOUS dependences of the TCNQ films have been built. To analyze the experimental DOUS dependences, the orbital energies of the TCNQ molecules are calculated by the density functional theory (DFT) at the B3LYP/6-31G(d) level with subsequent correction and the inclusion of the polarization energy of the condensed medium. In the energy range indicated above, DOUS of the TCNQ films has four main maxima. The DOUS maximum at energy 7.0 eV above E_F is predominantly formed by π* orbitals. Three DOUS maxima in the energy range from 8.0 to 20 eV above E_F are formed by approximately the same amount of the π* and σ* orbitals.

中文翻译：

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低能电子在氧化硅表面超薄TCNQ层中的传播和未占据状态的密度

摘要

研究了在（SiO ₂）n -Si表面热沉积厚度达7 nm的四氰基喹二甲烷（TCNQ）膜期间未占据的电子态的形成和边界势垒。通过总电流光谱法（TCS）使用测试电子束测量被研究表面的电子特性，该电子束的能量比费米能级高5至20 eV。在（SiO ₂）n中形成边界势垒-Si / TCNQ结构伴随着表面的功函数从4.2±0.1 eV增加到4.7±0.1 eV。使用TCS实验的结果，已经建立了TCNQ胶片的DOUS依赖性。为了分析实验性DOUS依赖性，通过密度泛函理论（DFT）在B3LYP / 6-31G（d）能级上计算了TCNQ分子的轨道能，随后进行了校正并包括了冷凝介质的极化能。在上述能量范围内，TCNQ膜的DOUS具有四个主要最大值。在E _F之上的能量7.0 eV处的DOUS最大值主要由π*轨道形成。能量范围内的三个DOUS最大值比E _F高8.0至20 eV 由大约相同数量的π*和σ*轨道形成。