Chen Xiaodan, van Huis Marijn A
Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
Electron Microscopy Center, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands.
Materials (Basel). 2023 Feb 2;16(3):1291. doi: 10.3390/ma16031291.
WO is a versatile material occurring in many polymorphs, and is used in nanostructured form in many applications, including photocatalysis, gas sensing, and energy storage. We investigated the thermal evolution of cubic-phase nanocrystals with a size range of 5-25 nm by means of in situ heating in the transmission electron microscope (TEM), and found distinct pathways for the formation of either 2D WO nanosheets or elemental W nanoparticles, depending on the initial concentration of deposited WO nanoparticles. These pristine particles were stable up to 600 °C, after which coalescence and fusion of the nanocrystals were observed. Typically, the nanocrystals transformed into faceted nanocrystals of elemental body-centered-cubic W after annealing to 900 °C. However, in areas where the concentration of dropcast WO nanoparticles was high, at a temperature of 900 °C, considerably larger lath-shaped nanosheets (extending for hundreds of nanometers in length and up to 100 nm in width) were formed that are concluded to be in monoclinic WO or WO. phases. These lath-shaped 2D particles, which often curled up from their sides into folded 2D nanosheets, are most likely formed from the smaller nanoparticles through a solid-vapor-solid growth mechanism. The findings of the in situ experiments were confirmed by ex situ experiments performed in a high-vacuum chamber.
WO是一种具有多种多晶型的多功能材料，以纳米结构形式应用于许多领域，包括光催化、气体传感和能量存储。我们通过在透射电子显微镜（TEM）中进行原位加热，研究了尺寸范围为5-25nm的立方相纳米晶体的热演化，发现根据沉积的WO纳米颗粒的初始浓度，形成二维WO纳米片或元素W纳米颗粒有不同的途径。这些原始颗粒在高达600°C时是稳定的，之后观察到纳米晶体的聚结和融合。通常，纳米晶体在退火至900°C后转变为体心立方元素W的多面纳米晶体。然而，在滴铸的WO纳米颗粒浓度较高的区域，在900°C的温度下，形成了相当大的板条状纳米片（长度延伸数百纳米，宽度可达100nm），据推测其为单斜WO或WO相。这些板条状二维颗粒通常从侧面卷曲成折叠的二维纳米片，很可能是由较小的纳米颗粒通过固-气-固生长机制形成的。原位实验的结果通过在高真空室中进行的非原位实验得到了证实。
