Interviews with Faculty Researchers

– Interview with Dr Kathy Leng
Assistant Professor, Department of Applied Physics

Organic-inorganic hybrid perovskites (OIHPs) have garnered substantial attention as leading contenders for the next wave of electronic and optoelectronic innovations. When OIHPs are scaled down to their single-layer form, they offer exciting prospects for delving into 2D photonics and electronics within a hybrid framework. This potential breakthrough holds great promise for advanced smart device applications, enabling precise manipulation of their optoelectronic properties through methods such as strain, electromagnetic influences, or electric fields, thereby facilitating the creation of intelligent and multifunctional devices.

The research conducted by Dr Kathy Leng centers on the optoelectronic properties and mechanical behavior of ultrathin 2D HOIPs under the influence of strain. These materials, categorized as Ruddlesden-Popper perovskites (RPPs), are characterized by alternating layers of flexible organic molecules and rigid inorganic layers. Dr Leng’s investigation delved into how these materials respond to external strain and the consequent modifications in their surface structure.

To fabricate devices, molecularly thin RPPs were exfoliated from bulk crystals to make the first monolayer photodetectors. Dr Leng discovered that photoluminescence (PL) produced from the ultrathin crystals was correlated to the dynamic structures of the surfaces, which can be changed reversibly by laser irradiation. Additionally, taking advantage of the thinness of the RPPs, Dr Leng fabricated field effect transistors (FETs) on RPPs and tuned their electron density using an electric field; this is a significant breakthrough because it has been very challenging to fabricate FET on thick crystals.

To capture how the structures of these ultrathin crystals correlate with optical properties, a combination of in-situ Scanning Tunneling microscopy (STM) and PL spectroscopy techniques was employed. Dr Leng observed that the crystals with different layers of inorganic and organic components showed different degrees of surface reconstructions related to octahedral tilting, which modifies the energy of their photoluminescence.

These research outcomes underscore that ultrathin HOIPs are a new class of 2D material and present a rich platform for physics research. Dr Leng’s investigation contributes valuable protocol to the field on how to prepare molecularly thin RPPs for device fabrication.

有機無機雜化鈣鈦礦- 先進智能器件的前景

– 冷凱博士專訪
應用物理學系助理教授

憑著卓越的光學和電學特性，有機無機雜化鈣鈦礦（OIHPs）引起了廣泛關注，被視為下一代電子和光電創新浪潮材料。當這些物料的厚度被縮小到單層形式時，它們為在有機無機雜化框架內深入研究二維光子學和電子學提供了令人興奮的前景。這一潛在的材料突破為先進的智慧器件應用帶來了巨大的潛力，可透過應變、電磁影響或電場等方法，精確地操控其光電特性，從而實現智慧和多功能設備的創造。

冷凱博士的研究主要關注受應變影響下超薄二維HOIPs的光電特性和力學行為。這些材料歸屬Ruddlesden-Popper鈣鈦礦（RPPs），其結構特點是柔性有機分子和剛性無機層交替排列。冷博士的研究深入探究這些材料對外部壓力的反應，及由此引起的表面結構變化。

在器件製造方面，冷博士從塊狀晶體中剝離出分子厚度的RPPs，製作出第一個單層OIHP光電探測器。冷博士發現，超薄單晶所產生的光致發光與表面的動態結構相關，這些結構可以透過激光照射可逆地改變。此外，利用單層RPPs的薄度，她製造了RPP場效應晶體管（FET），並使用電場來調節其電子密度；這是一項重大突破，因為在厚晶體上製造FET極具挑戰性。

為了準確記錄超薄OIHP的結構與光學特性的關聯性，她結合了原位掃描隧道顯微鏡和光致發光光譜技術。冷博士觀察到，具有不同無機和有機組分層的鈣鈦礦結晶，會表現出不同程度與八面體傾斜相關的表面重構，從而改變了它們光致發光的能量。

這些研究結果突顯了超薄OHIPs是一類新型的二維材料，它的出現為物理性質的研究提供了豐富的平臺。冷博士的研究為如何製備分子厚度RPPs器件提供了寶貴的方案。