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.

针对铁电开关和压电纳米发电机装置的潜在应用，二维（2D）层状In2Se3所展现出的卓越铁电特性引起了广泛关注。在本研究中，采用化学气相沉积（CVD）技术在云母衬底上生长了单层以下的2D In2Se3薄片，对其结构、光学和铁电特性进行了研究。生长参数（生长时间和氩气流量）对沉积薄片形状和尺寸的影响进行了探讨。光学显微镜研究表明，随着氩气流量和生长时间的增加，薄片从圆形变为尖锐的三角形。拉曼光谱和超高分辨率扫描透射电子显微镜（HR-STEM）研究表明，薄片为α和β相，均具有六方晶格结构。α-In2Se3中观察到强烈的二次谐波产生（SHG），证明了其非中心对称结构。压电力显微镜（PFM）研究表明，在CVD生长的α-In2Se3中存在出平面（OOP）铁电性，而无平面内（IP）铁电性，表明其压电响应在垂直方向上受限，这一特性可通过施加的电压偏置和薄片厚度进行调节。本研究所得的关于In2Se3形状可控生长及其OOP铁电性的结果，将为二维铁电开关器件领域开辟新的途径。