Tunneling atomic force microscopy (TUNA) was used at ambient conditions to measure the current-voltage $(I\text{−}V)$ characteristics at clean surfaces of highly oriented graphite samples with Bernal and rhombohedral stacking orders. The characteristic curves measured on Bernal-stacked graphite surfaces can be understood with an ordinary self-consistent semiconductor modeling and quantum mechanical tunneling current derivations. We show that the absence of a voltage region without measurable current in the $I\text{−}V$ spectra is not a proof of the lack of an energy band gap. It can be induced by a surface band bending due to a finite contact potential between tip and sample surface. Taking this into account in the model, we succeed to obtain a quantitative agreement between simulated and measured tunnel spectra for band gaps $(12...37)$ meV, in agreement with those extracted from the exponential temperature decrease of the longitudinal resistance measured in graphite samples with Bernal stacking order. In contrast, the surface of relatively thick graphite samples with rhombohedral stacking reveals the existence of a maximum in the first derivative $dI/dV$, a behavior compatible with the existence of a flat band. The characteristics of this maximum are comparable to those obtained at low temperatures with similar techniques.

中文翻译：

---

表面带弯曲对窄带隙半导体的影响：具有伯纳尔和菱面体堆积顺序的石墨的隧穿原子力研究

在环境条件下使用隧道原子力显微镜（TUNA）测量电流-电压 $（\mathrm{一世}\text{-}\mathrm{伏特}）$伯纳尔和菱面体堆积顺序的高取向石墨样品在清洁表面上的特性。可以通过普通的自洽半导体建模和量子力学隧穿电流推导来了解在Bernal堆叠的石墨表面上测得的特性曲线。我们表明，在没有可测量电流的电压区域中，$\mathrm{一世}\text{-}\mathrm{伏特}$光谱不能证明没有能带隙。由于尖端和样品表面之间的有限接触电势而导致的表面带弯曲会引起这种现象。考虑到模型中的这一点，我们成功地获得了带隙的模拟和测量隧道光谱之间的定量协议$（12...37）$ meV，与从以Bernal堆积顺序的石墨样品中测得的纵向电阻的指数温度下降所得出的结果相吻合。相反，相对较厚的带有菱面体堆叠的石墨样品的表面揭示出一阶导数中存在最大值$d\mathrm{一世}/d\mathrm{伏特}$，与扁平带的存在兼容的行为。该最大值的特性可与在低温下使用类似技术获得的特性相媲美。