Phase Transitions in Nanofriction

纳米摩擦中的相变

• 批准号: 471451947
• 负责人: Dr. Dirk Dietzel
• 金额: --
• 依托单位: Institut für Angewandte Physik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/471451947?language=en
• 关键词: Phase; Transitions; Nanofriction

For our understanding of friction, it is of considerable importance to recognize the fundamental mechanisms, which facilitate energy dissipation, i.e. which are involved in the conversion from kinetic energy to heat. On the microscopic scale, this problem is closely related to the assumption, that realistic interfaces are formed as multi-asperity contacts, where a single asperity is usually considered as the most fundamental building block of friction. In scanning probe microscopy, such a single-asperity contact is formed between the tip and the sample and the technique is thus considered to provide an ideal model system to study the nanoscale origins of friction.However, while measuring quantitative friction values is relatively straightforward, it still remains a challenge to identify the mechanisms of energy dissipation. Here, a new approach to address this question lies in the analysis of friction phenomena across phase transitions. In solid state physics, phase transitions are usually an area of great interest and phase transitions are already very well analyzed for a large variety of materials. This opens up the possibility to induce well-defined changes of the material properties using an external control parameter, like e.g. temperature, and correlate these changes to the accompanying variations of the interfacial friction. This approach becomes particularly apparent for the case of the so-called electronic friction, which addresses the role of electrons for the energy dissipation process. Here, e.g. superconductors can be analyzed, where the electrical resistance vanishes below a certain threshold temperature and effects relevant for friction like e.g. electron-phonon coupling are changing likewise.At the same time, also structural phase transitions can be analyzed. In this case, scanning probe microscopy can be utilized as a kind of mechanical spectroscopy, where the force interaction between tip and sample allows to probe the changes within the materials during the phase transition. Using this approach, general energy dissipation mechanisms can be analyzed, while also the phase transition itself can be of interest.Despite this potential, phase transitions have so far rarely been targeted by nanoscale friction experiments, which is partially due to the experimental challenge to perform atomic force microscopy measurements as a function of temperature. Up to now, even the fundamental differences between first and second order phase transitions have not yet been addressed experimentally.All in all, this project thus offers new insight into very fundamental questions of nantribology. In addition, applying scanning probe microscopy also allows to characterize the effects related to phase transitions with a spatial resolution in the nanometer range.

对于我们对摩擦的理解，认识到促进能量耗散的基本机制非常重要，即涉及从动能到热的转换。在微观尺度上，这个问题与假设密切相关，即现实界面形成为多个粗糙体接触，其中单个粗糙体通常被认为是摩擦的最基本组成部分。在扫描探针显微镜中，尖端和样品之间形成这种单粗糙体接触，因此该技术被认为提供了研究纳米级摩擦起源的理想模型系统。然而，虽然测量定量摩擦值相对简单，但识别能量耗散机制仍然是一个挑战。在这里，解决这个问题的新方法在于分析相变的摩擦现象。在固态物理学中，相变通常是人们非常感兴趣的领域，并且已经对多种材料的相变进行了很好的分析。这开辟了使用外部控制参数（例如，控制参数）引起材料属性明确变化的可能性。温度，并将这些变化与界面摩擦的伴随变化相关联。这种方法对于所谓的电子摩擦的情况变得尤其明显，它解决了电子在能量耗散过程中的作用。在这里，例如可以分析超导体，其中电阻在低于特定阈值温度时消失以及与摩擦相关的效应，例如摩擦力。电子-声子耦合也在发生同样的变化。同时，还可以分析结构相变。在这种情况下，扫描探针显微镜可以用作一种机械光谱学，其中尖端和样品之间的力相互作用允许探测相变期间材料内的变化。使用这种方法，可以分析一般的能量耗散机制，同时相变本身也可以引起人们的兴趣。尽管有这种潜力，但到目前为止，相变很少成为纳米级摩擦实验的目标，部分原因是执行原子力显微镜测量随温度变化的实验挑战。到目前为止，甚至一级相变和二级相变之间的根本差异也尚未通过实验得到解决。总而言之，该项目因此为纳米摩擦学的非常基本的问题提供了新的见解。此外，应用扫描探针显微镜还可以以纳米范围的空间分辨率来表征与相变相关的效应。