STM/AFM Studies of Nitrogen-doped graphene on Pt(111) surface

Abstract

Scanning probe microscopy techniques provide an exceptional opportunity to characterize and manipulate objects at the atomic scale with remarkable precision, allowing for manipulation and characterization at the level of individual atoms. Scanning tunneling microscopy (STM) is unique among these techniques due to its ability to obtain high-resolution images of surfaces, revealing intricate details. If offers exceptional energy resolution of the electronic states when operated at low temperatures. Furthermore, the integration of non-contact atomic force microscopy (nc-AFM) with STM in a single setup enables simultaneous investigation of both the electronic and geometric structures of individual adsorbates. Nitrogen-doped graphene (NG) has sparked great interest in graphene application due to its unique physical and chemical properties. Numerous approaches have been employed to investigate the controllable doping configurations in NG, which play a essential role in fine-tuning its properties. Different configurations within the carbon lattice exhibit distinct electronic and chemical characteristics. In this study, we synthesized NG on Pt(111) surface utilizing pyridine (C¬5H5N) as a nitrogen-containing precursor. Through simultaneous STM/AFM measurements to characterize the synthesized sample, we identified two types of defects: graphitic-N and pyridinic-N. Notably, we achieved atomic resolution in AFM imaging of each defect. The presence of graphitic-N and pyridinic-N in the graphene layer was experimentally demonstrated using STM/AFM and X-ray photoelectron spectroscopy (XPS) measurements, and theoretically supported by density functional theory (DFT) calculations. Additionally, we observed a dissolved pyridine molecule, which was theoretically predicted to be a transient phase during NG formation. This observation is expected to provide important insights into the growth mechanisms of various nitrogen defects during the CVD process.;주사형 탐침 현미경법(Scanning tunneling microscopy, STM)은 개별 원자 수준의 정밀도로 물질 표면의 고해상도 이미지를 얻을 수 있는 기술이다. 극저온 고진공(UHV)환경에서 STM 기술을 비접촉 원자 현미경(nc-atomic force microscope, nc-AFM)과 결합하면 개별 흡착물의 전자 및 기하학적 구조를 동시에 조사할 수 있다. 본 논문에서는 질소 결함을 가진 그래핀 (NG)의 독특한 물리학 및 화학적 특성에 기인하여, NG의 특성을 미세하게 조정하는데 필수적인 역할을 하는 질소 결함의 구조를 조사하였다. 그래핀 탄소 격자내의 결함 구조들은 각 구조에 따라 뚜렷한 전자 및 화학적 특성을 나타낸다. 본 연구에서는 피리딘 분자를 질소 함유 전구체로 사용하여 Pt(111) 표면에서 NG를 합성하였다. 합성된 샘플을 특성화 하기 위해 STM/AFM 을 동시 특정하여 각각의 구조를 비교하였고, 발견된 결함 유형들을 식별하였다. 특히, 우리는 각 결함의 AFM 결과에서 원자 분해능을 달성하여 질소 원자의 위치를 특정할 수 있었다. 이러한 관찰은 다양한 질소 결함의 성장 메커니즘에 대한 통찰력을 제공할 것으로 기대된다.