Polyakov S N, Denisov V N, Denisov V V, Zholudev S I, Lomov A A, Moskalenko V A, Molchanov S P, Martyushov S Yu, Terentiev S A, Blank V D
Technological Institute for Superhard and Novel Carbon Materials, Troitsk, Moscow, Russia, 108840.
The PN Lebedev Physical Institute, Moscow, Russia, 119991.
Nanoscale Res Lett. 2021 Feb 8;16(1):25. doi: 10.1186/s11671-021-03484-4.
The detailed studies of the surface structure of synthetic boron-doped diamond single crystals using both conventional X-ray and synchrotron nano- and microbeam diffraction, as well as atomic force microscopy and micro-Raman spectroscopy, were carried out to clarify the recently discovered features in them. The arbitrary shaped islands towering above the (111) diamond surface are formed at the final stage of the crystal growth. Their lateral dimensions are from several to tens of microns and their height is from 0.5 to 3 μm. The highly nonequilibrium conditions of crystal growth enhance the boron solubility and, therefore, lead to an increase of the boron concentrations in the islands on the surface up to 10 cm, eventually generating significant stresses in them. The stress in the islands is found to be the volumetric tensile stress. This conclusion is based on the stepwise shift of the diamond Raman peak toward lower frequencies from 1328 to 1300 cm in various islands and on the observation of the shift of three low-intensity reflections at 2-theta Bragg angles of 41.468°, 41.940° and 42.413° in the X-ray diffractogram to the left relative to the (111) diamond reflection at 2theta = 43.93°. We believe that the origin of the stepwise tensile stress is a discrete change in the distances between boron-carbon layers with the step of 6.18 Å. This supposition explains also the stepwise (step of 5 cm) behavior of the diamond Raman peak shift. Two approaches based on the combined application of Raman scattering and X-ray diffraction data allowed determination of the values of stresses both in lateral and normal directions. The maximum tensile stress in the direction normal to the surface reaches 63.6 GPa, close to the fracture limit of diamond, equal to 90 GPa along the [111] crystallographic direction. The presented experimental results unambiguously confirm our previously proposed structural model of the boron-doped diamond containing two-dimensional boron-carbon nanosheets and bilayers.
利用传统X射线、同步加速器纳米和微束衍射以及原子力显微镜和显微拉曼光谱对合成掺硼金刚石单晶的表面结构进行了详细研究，以阐明其中最近发现的特征。在晶体生长的最后阶段，在(111)金刚石表面上方形成了任意形状的岛状结构。它们的横向尺寸从几微米到几十微米，高度从0.5到3微米。晶体生长的高度非平衡条件提高了硼的溶解度，因此导致表面岛状结构中硼浓度增加到10厘米-3，最终在其中产生显著的应力。发现岛状结构中的应力为体积拉伸应力。这一结论基于在不同岛状结构中金刚石拉曼峰从1328 cm-1向低频逐步移动到1300 cm-1，以及在X射线衍射图中相对于2θ = 43.93°的(111)金刚石反射，2θ布拉格角为41.468°、41.940°和42.413°的三个低强度反射向左移动的观察结果。我们认为，逐步拉伸应力的起源是硼-碳层之间距离以6.18 Å的步长发生离散变化。这一假设也解释了金刚石拉曼峰位移的逐步(5 cm-1步长)行为。基于拉曼散射和X射线衍射数据联合应用的两种方法能够确定横向和法向的应力值。垂直于表面方向的最大拉伸应力达到63.6 GPa，接近金刚石的断裂极限，沿[111]晶体学方向等于90 GPa。所呈现的实验结果明确证实了我们先前提出的包含二维硼-碳纳米片和双层的掺硼金刚石结构模型。
