Makeswaran Nanthakishore, Orozco Cristian, Battu Anil K, Deemer Eva, Ramana C V
Centre for Advanced Materials Research (CMR), University of Texas at El Paso, 500 W University Ave, El Paso, TX 79968, USA.
White Sands Missile Range (WSMR), White Sands, NM 88002, USA.
Materials (Basel). 2022 Jan 19;15(3):754. doi: 10.3390/ma15030754.
Molybdenum (Mo), which is one among the refractory metals, is a promising material with a wide variety of technological applications in microelectronics, optoelectronics, and energy conversion and storage. However, understanding the structure-property correlation and optimization at the nanoscale dimension is quite important to meet the requirements of the emerging nanoelectronics and nanophotonics. In this context, we focused our efforts to derive a comprehensive understanding of the nanoscale structure, phase, and electronic properties of nanocrystalline Mo films with variable microstructure and grain size. Molybdenum films were deposited under varying temperature (25-500 °C), which resulted in Mo films with variable grain size of 9-22 nm. The grazing incidence X-ray diffraction analyses indicate the (110) preferred growth behavior the Mo films, though there is a marked decrease in hardness and elastic modulus values. In particular, there is a sizable difference in maximum and minimum elastic modulus values; the elastic modulus decreased from ~460 to 260-280 GPa with increasing substrate temperature from 25-500 °C. The plasticity index and wear resistance index values show a dramatic change with substrate temperature and grain size. Additionally, the optical properties of the nanocrystalline Mo films evaluated by spectroscopic ellipsometry indicate a marked dependence on the growth temperature and grain size. This dependence on grain size variation was particularly notable for the refractive index where Mo films with lower grain size fell in a range between ~2.75-3.75 across the measured wavelength as opposed to the range of 1.5-2.5 for samples deposited at temperatures of 400-500 °C, where the grain size is relatively higher. The conductive atomic force microscopy (AFM) studies indicate a direct correlation with grain size variation and grain versus grain boundary conduction; the trend noted was improved electrical conductivity of the Mo films in correlation with increasing grain size. The combined ellipsometry and conductive AFM studies allowed us to optimize the structure-property correlation in nanocrystalline Mo films for application in electronics and optoelectronics.
钼（Mo）是难熔金属之一，是一种很有前景的材料，在微电子、光电子以及能量转换与存储等众多技术领域都有应用。然而，要满足新兴的纳米电子学和纳米光子学的需求，理解纳米尺度下的结构 - 性能关联并进行优化非常重要。在此背景下，我们致力于全面了解具有可变微观结构和晶粒尺寸的纳米晶Mo薄膜的纳米尺度结构、相和电子性能。在不同温度（25 - 500°C）下沉积钼薄膜，得到了晶粒尺寸在9 - 22 nm之间变化的Mo薄膜。掠入射X射线衍射分析表明Mo薄膜具有（110）择优生长行为，不过其硬度和弹性模量值有显著下降。特别是，最大和最小弹性模量值存在相当大的差异；随着衬底温度从25°C升高到500°C，弹性模量从约460 GPa降至260 - 280 GPa。塑性指数和耐磨指数值随衬底温度和晶粒尺寸有显著变化。此外，通过光谱椭偏仪评估的纳米晶Mo薄膜的光学性能表明其对生长温度和晶粒尺寸有显著依赖性。这种对晶粒尺寸变化的依赖性在折射率方面尤为明显，晶粒尺寸较小的Mo薄膜在整个测量波长范围内的折射率落在约2.75 - 3.75之间，而对于在400 - 500°C温度下沉积的样品，其晶粒尺寸相对较大，折射率范围为1.5 - 2.5。导电原子力显微镜（AFM）研究表明与晶粒尺寸变化以及晶粒与晶界传导有直接关联；观察到的趋势是Mo薄膜的电导率随着晶粒尺寸的增加而提高。椭偏仪和导电AFM的联合研究使我们能够优化纳米晶Mo薄膜的结构 - 性能关联，以应用于电子学和光电子学领域。
