Yuan Yue, Lanza Mario
Materials Science and Engineering Program, Physical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955, Saudi Arabia.
Department of Materials Science and Engineering, National University of Singapore, Singapore, 117575, Singapore.
Adv Mater. 2024 Dec;36(51):e2405932. doi: 10.1002/adma.202405932. Epub 2024 Sep 11.
Conductive atomic force microscopy (CAFM) analyzes electronic phenomena in materials and devices with nanoscale lateral resolution, and it is widely used by companies, research institutions, and universities. Most data published in the field of CAFM is collected in air at a relative humidity (RH) of 30-60%. However, the effect of RH in CAFM remains unclear because previous studies often made contradictory claims, plus the number of samples and locations tested is scarce. Moreover, previous studies on this topic did not apply current limitations, which can degrade the CAFM tips and generate false data. This article systematically analyzes the effect of RH in CAFM by applying ramped voltage stresses at over 17,000 locations on ten different samples (insulating, semiconducting, and conducting) under seven different RH. An ultra-reliable setup with a 110-pA current limitation during electrical stresses is employed, and excellent CAFM tip integrity after thousands of tests is demonstrated. It is found that higher RH results in increased currents due to the presence of a conductive water meniscus at the tip/sample junction, which increases the effective area for electron flow. This trend is observed in insulators and ultra-thin semiconductors; however, in thicker semiconductors the electron mean free path is high enough to mask this effect. Metallic samples show no dependence on RH. This study clarifies the effect of relative humidity in CAFM, enhances understanding of the technique, and teaches researchers how to improve the reliability of their studies in this field.
导电原子力显微镜（CAFM）可在具有纳米级横向分辨率的情况下分析材料和器件中的电子现象，被公司、研究机构和大学广泛使用。CAFM领域发表的大多数数据是在相对湿度（RH）为30%-60%的空气中收集的。然而，CAFM中RH的影响仍不明确，因为先前的研究常常得出相互矛盾的结论，而且测试的样本数量和位置较少。此外，先前关于该主题的研究没有应用电流限制，这可能会使CAFM探针退化并产生虚假数据。本文通过在七种不同的RH条件下，对十个不同样本（绝缘、半导体和导电）的17000多个位置施加斜坡电压应力，系统地分析了CAFM中RH的影响。采用了一种在电应力期间具有110-pA电流限制的超可靠装置，并展示了经过数千次测试后CAFM探针的优异完整性。研究发现，由于尖端/样品交界处存在导电水弯月面，较高的RH会导致电流增加，这增加了电子流动的有效面积。在绝缘体和超薄半导体中观察到了这种趋势；然而，在较厚的半导体中，电子平均自由程足够高，足以掩盖这种效应。金属样品对RH没有依赖性。这项研究阐明了CAFM中相对湿度的影响，增进了对该技术的理解，并指导研究人员如何提高该领域研究的可靠性。
