Graphene nanosensors for scanning Hall microscopy and susceptometry

许多最重要的科学技术进步都是通过仪器仪表的同步发展才得以实现的。例如，微芯片的发展，现在在我们的日常生活中如此普遍，如果没有电子显微镜可以通过原型设备对横截面进行成像，就不可能发生。扫描霍尔显微镜是一种所谓的“扫描探针”成像技术，其中一个微小的传感器在样品表面光栅，以创建磁场的地图。在这种情况下，传感器依赖于霍尔效应，当导电样品中的电子流被磁场弯曲时，产生与主电流方向成直角的霍尔电压。目前，扫描霍尔显微镜是一种相对小众的技术，主要局限于在低温（通常低于-170℃）下对磁性材料进行测量。这是因为尽管现有的霍尔效应传感器在低温下具有很高的灵敏度，但在室温下，当使用其他扫描探针成像方法（例如磁力显微镜）时，这种灵敏度会变得非常差。石墨烯技术的最新发展意味着这种情况即将改变。石墨烯是碳的单原子层，2004年由曼彻斯特的科学家首次分离出来，并于2010年获得了诺贝尔物理学奖。石墨烯具有非常高的导电性和机械强度，并且石墨烯中的载流子能够比铜中的电子更自由地移动。最近，科学家们已经证明，如果将石墨烯夹在一层被称为氮化硼的绝缘体之间，则可以获得更高的导电性。通过这种方式，霍尔传感器的性能在室温下可以提高100倍以上，与其他可用的磁成像技术相媲美。我们还计划开发新的“磁化率”成像模式，当霍尔探头测量样品对集成在传感器中的微小线圈产生的小振荡磁场的响应时。这将允许研究新类型的样本，并可以解决不同类型的问题。我们的新型传感器的目标应用在三个重要的技术领域。我们将使用霍尔显微镜绘制第二代高温超导带的纳米级电流分布，该带在无损电力传输和能量存储方面具有巨大的应用潜力。霍尔电纳计将用于“3D打印”材料（例如钢）的非侵入性缺陷检测，这些缺陷已知在结构失效中起关键作用。最后，我们将探讨如何将霍尔电纳法用于薄膜铁磁材料的磁性均匀性的常规过程控制，以应用于数据存储。

Many of the most important advances in science and technology have only been made possible by parallel developments in instrumentation. For example, the development of microchips, which are now so common in our everyday lives, could not have taken place without the availability of electron microscopy to image cross-sections through prototype devices. Scanning Hall microscopy is a so-called "scanning probe" imaging technique where a tiny sensor is rastered across the surface of a sample to create a map of the magnetic fields. In this case the sensors rely on the Hall effect which arises when the electron flow in a conducting sample is bent by a magnetic field creating a Hall voltage at right angles to the main current direction. At present scanning Hall microscopy is a relatively niche technique that is mainly confined to making measurements of magnetic materials at low temperatures (typically less than -170C). This is due to the fact that although existing Hall effect sensors have high sensitivity at low temperatures, this becomes very much worse at room temperature when other scanning probe imaging methods, for example magnetic force microscopy, are preferred. Recent developments in graphene technology mean that this situation is about to change. Graphene is a single atomic layer of carbon that was first isolated by scientists in Manchester in 2004, leading to the award of the physics Nobel Prize in 2010. It is remarkable for its very high conductivity and mechanical strength, and the electrical carriers in graphene are able to move very much more freely than electrons in copper. Recently scientists have shown that still higher conductivities can be obtained if the graphene is sandwiched between thin layers of an insulator called boron nitride. In this way an improvement in Hall sensor performance of more than a hundred times is possible at room temperature, rivalling the other available magnetic imaging techniques. We also plan to develop new "susceptibility" imaging modes when the Hall probe measures the response of a sample to a small oscillating magnetic field generated by a tiny coil integrated into the sensor. This will allow new types of samples to be studied, and different types of problems can be addressed. Our new sensors target applications in three important technological areas. We will use Hall microscopy to map the nanoscale current distribution in second generation high temperature superconducting tapes that have enormous potential for applications in lossless power transmission and energy storage. Hall susceptometry will be used for the non-invasive detection of defects in "3D printed" materials (for example steel) which are known to play a critical role in structural failure. Finally we will explore how Hall susceptometry can be used for routine process control of the uniformity of the magnetic properties of thin film ferromagnetic materials for applications in data storage.