Shape-control growth of 2D-In2Se3 with out-of-plane ferroelectricity by chemical vapor deposition

For the potential applications in ferroelectric switching and piezoelectric nano-generator device, the promising ferroelectric properties of two dimensional (2D) layered In2Se3 attracted much attention. In the present study, 2D In2Se3 flakes down to monolayers are grown by chemical vapor deposition (CVD) technique on mica substrate with the structural, optical and ferroelectric properties being studied. The effect of growth parameter (time of growth and Ar flow rate) on the shape and size of the deposited flakes was studied. Optical microscopy study revealed that the flake changed from a circular shape to a sharp face triangle as the Ar flow rate and growth time increased. The Raman spectroscopy and high-resolution scanning transmission electron microscopy (HR-STEM) studies revealed that the flakes were of the α and β phases, each of which has a hexagonal crystal structure. Strong second harmonic generation (SHG) was observed from α-In2Se3, demonstrating its non-centrosymmetric structure. Piezo-force microscopic (PFM) study showed the presence of out of plane (OOP) ferroelectricity with no in Plane (IP) ferroelectricity in CVD grown α-In2Se3 indicating its vertically confined piezoresponse, which was tuned by the applied electric bias and the flake thickness. The present result of shape-controlled growth of In2Se3 with OOP ferroelectricity would open new pathways in the field of 2D ferroelectric switching devices.

鉴于其在铁电开关与压电纳米发电机器件中的潜在应用前景，二维（2D）层状硒化铟（In₂Se₃）优异的铁电性能受到了广泛关注。本研究通过化学气相沉积（CVD）技术在云母衬底上生长了厚度低至单层的二维硒化铟纳米片，并对其结构、光学及铁电性能进行了系统表征。研究了生长参数（生长时长与氩气流量）对沉积所得纳米片形貌与尺寸的影响。光学显微镜观测结果表明，随着氩气流量与生长时长的增加，纳米片形貌由圆形逐渐演变为棱角分明的三角形。拉曼光谱与高分辨扫描透射电子显微镜（HR-STEM）表征结果显示，所得纳米片存在α相与β相两种晶型，二者均具有六方晶体结构。α相硒化铟（α-In₂Se₃）表现出强烈的二次谐波生成（SHG）信号，证实其具有非中心对称的晶体结构。压电力显微镜（PFM）测试结果表明，通过CVD生长的α相硒化铟仅存在面外（OOP）铁电性，而未观测到面内（IP）铁电性，这说明其压电响应受垂直方向限制，且该响应可通过外加电场偏置与纳米片厚度进行调控。本研究实现了形貌可控且具备面外铁电性的硒化铟纳米片生长，该成果将为二维铁电开关器件领域开辟全新的研究路径。