Ge纳米结构的形貌与铁磁性研究

Morphology and ferromagnetism of Ge nanostructure

利用等离子体增强化学气相沉积技术制备了厚度不同的Ge薄膜,随着样品厚度的减小,样品表现出了室温铁磁性.厚度为12nm样品经过300C退火后,由于颗粒细化,颗粒之间的界面增加,界面缺陷增加,样品表现出最大的铁磁性(50emu/cm3).场冷却和零场冷却曲线测试表明居里温度约为350K.进行600C退火后,颗粒团聚,样品的铁磁性最小.当样品厚度进一步减小为6nm时,沉积态样品表现出铁磁性和顺磁性共存.对6nm厚的样品进行300C退火后,样品只具有铁磁性.进行600C退火后,样品却只具有顺磁性.12nm和6nm厚的Ge纳米结构薄膜随退火温度变化表现出不同的磁性规律,我们认为是由于样品的颗粒大小和颗粒分布不同造成的.样品越薄,Si基底与Ge薄膜之间的界面缺陷越明显,界面缺陷以及Ge颗粒之间的界面缺陷为样品提供了未配对电子,未配对电子的铁磁性耦合强度与样品颗粒的分布以及颗粒之间的结合有一定的关系.颗粒之间分散或颗粒之间的融合程度大都将会降低样品的铁磁性.

A series of Ge films with varying thickness is prepared by plasma enhanced chemical vapor deposition technology. With the thickness of the sample becoming thinner, the sample shows ferromagnetism. When the 12-nm-thick sample is annealed at 300 ？C, the partile size becomes smaller, and thus the number of interface defects between the particles increases, so the sample gives a largest magnetic signal at room temperature （50 emu/cm3）. FC-ZFC measurement shows that Curie temperature is 350 K. For a higher temperature （600 ？C, the coalescence of small Ge particles makes surface area decline, so magnetic signal becomes weak. With the thickness being 6 nm, the paramagnetism and the ferromagnetism coexist in the 6-nm-thick Ge film. When the 6-nm-thick sample is annealed under nitrogen atmosphere at 300 ？C, the sample only shows ferromagnetism. However, annealed at 600 ？C, the sample only presents paramagnetism. With the annealing temperature changing, the 12-nm-thick film and the 6-nm-thick film show different magnetic phenomena. Particle size and particle distribution cause different magnetic phenomena. It is supposed that the Ge nannostructure unpaired electrons are provided mainly by the interface defect between Si matyix and Ge film and the surface defect of Ge particles. The ferromagnetism coupling of the unpaired electrons is related to the distribution of sample particles and the junction among particles. The fusion between particles will reduce the ferromagnetism of the sample.