Nowakowski B K, Smith D T, Smith S T, Correa L F, Cook R F
Nanomechanical Properties Group, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
Rev Sci Instrum. 2013 Jul;84(7):075110. doi: 10.1063/1.4811195.
The design, construction, and performance of a surface-referenced nanoindentation instrument, termed a precision nanoindentation platform (PNP), are presented. The PNP is a symmetrically designed instrument with a centrally located indenter tip attached to a force cell for measuring the forces between the tip and a specimen. Penetration of the indenter tip into the specimen surface is measured using two proximity sensors placed symmetrically about the indenter. Each proximity sensor is attached to a piezoelectric actuator that is servo controlled to maintain the sensor and the reference frame to which it is attached at a constant height relative to the specimen surface. As the indenter tip penetrates the specimen surface, the movement of the tip relative to the two surface reference frames is measured using capacitance gauges and the average of these displacements is used as a measure of penetration depth. The current indenter is capable of applying indentation forces of up to 150 mN with a noise floor below 2 μN rms for a sampling rate of 1 kHz, and measuring displacement with 0.4 nm rms noise for the same sampling rate. The proximity sensors are capable of maintaining surface height variations of less than 1.0 nm with penetration depths of up to 10 μm. Long-term stability tests indicate a total uncertainty in indentation depth less than 10 nm for periods as long as 12 h. To demonstrate instrument accuracy, repeated indention cycles were performed on a fused silica specimen using incrementally increasing indention force. From this test, an average value of 72 GPa ± 1.5 GPa for the Young's modulus was obtained from the elastic unloading curves for 10 measurements ranging in maximum force from 5 mN to 50 mN. To demonstrate longer-term instrument stability, a poly(methyl methacrylate) specimen was subjected to a fixed 5 mN indentation force for 4 h; two distinct creep-like mechanisms were observed.
介绍了一种表面参考纳米压痕仪器的设计、构造和性能，该仪器称为精密纳米压痕平台（PNP）。PNP是一种对称设计的仪器，其中心位置的压头尖端连接到一个力传感器，用于测量尖端与样品之间的力。使用围绕压头对称放置的两个接近传感器来测量压头尖端进入样品表面的深度。每个接近传感器都连接到一个压电致动器，该致动器通过伺服控制，以保持传感器及其所连接的参考框架相对于样品表面的高度恒定。当压头尖端穿透样品表面时，使用电容式传感器测量尖端相对于两个表面参考框架的移动，并将这些位移的平均值用作穿透深度的度量。当前的压头能够在1 kHz的采样率下施加高达150 mN的压痕力，均方根噪声低于2 μN，并且在相同采样率下测量位移时，均方根噪声为0.4 nm。接近传感器能够在高达10 μm的穿透深度下保持小于1.0 nm的表面高度变化。长期稳定性测试表明，在长达12小时的时间段内，压痕深度的总不确定度小于10 nm。为了证明仪器的准确性，使用逐渐增加的压痕力在熔融石英样品上进行了重复的压痕循环。通过该测试，从10次测量的弹性卸载曲线中获得了杨氏模量的平均值为72 GPa±1.5 GPa，最大力范围为5 mN至50 mN。为了证明仪器的长期稳定性，对聚甲基丙烯酸甲酯样品施加固定的5 mN压痕力4小时；观察到了两种不同的类似蠕变的机制。
