Helium implantation in epitaxial thin films is a way to control the out-of-plane deformation independently from the in-plane strain controlled by epitaxy. In particular, implantation by means of a helium microscope allows for local implantation and patterning down to the nanometer resolution, which is of interest for device applications. We present here a study of bismuth ferrite (${\mathrm{BiFeO}}_3$) films where strain was patterned locally by helium implantation. Our combined Raman, x-ray diffraction, and transmission electron microscopy (TEM) study shows that the implantation causes an elongation of the ${\mathrm{BiFeO}}_3$ unit cell and ultimately a transition towards the so-called supertetragonal polymorph via states with mixed phases. In addition, TEM reveals the onset of amorphization at a threshold dose that does not seem to impede the overall increase in tetragonality. The phase transition from the R-like to T-like ${\mathrm{BiFeO}}_3$ appears as first-order in character, with regions of phase coexistence and abrupt changes in lattice parameters.

中文翻译：

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通过氦气注入在具有有效负压的BiFeO3薄膜中增强四边形的图案

在外延薄膜中注入氦是一种独立于外延控制的面内应变来控制面外变形的方法。特别地，借助于氦显微镜的植入允许局部植入和图案化直至纳米分辨率，这对于装置应用是令人感兴趣的。我们在这里介绍铋铁氧体（${\mathrm{二氧化铁}}_3$）薄膜，其中通过氦注入在局部形成应变。我们对拉曼光谱，X射线衍射和透射电子显微镜（TEM）的综合研究表明，植入会导致晶状体的伸长。${\mathrm{二氧化铁}}_3$晶胞，并最终通过具有混合相的状态向所谓的超四边形多晶型物过渡。另外，TEM显示出阈值剂量下的非晶化的开始，这似乎并不妨碍四方性的整体增加。从类R到类T的相变${\mathrm{二氧化铁}}_3$ 表现为一阶特征，具有相共存的区域和晶格参数的突变。