No abstract

Creating oxide interfaces with precise chemical specificity at the atomic layer level is desired for the engineering of quantum phases and electronic applications, but highly challenging, owing partially to the lack of in situ tools to monitor the chemical composition and completeness of the surface layer during growth. Here we report the in situ observation of atomic layer-by-layer inner potential variations by analysing the Kikuchi lines during epitaxial growth of strontium titanate, providing a powerful real-time technique to monitor and control the chemical composition during growth. A model combining the effects of mean inner potential and step edge density (roughness) reveals the underlying mechanism of the complex and previously not well-understood reflection high-energy electron diffraction oscillations observed in the shuttered growth of oxide films. General rules are proposed to guide the synthesis of atomically and chemically sharp oxide interfaces, opening up vast opportunities for the exploration of intriguing quantum phenomena at oxide interfaces.

Transition metal oxide heterostructures and interfaces host a variety of exciting quantum phases and can be grown with atomic-scale precision by utilising the intensity oscillations of in situ reflection high-energy electron diffraction (RHEED). However, establishing a stable oscillation pattern in the growth calibration of complex oxides films is very challenging and time consuming. Here, we develop a substantially more efficient and reliable growth calibration method for complex oxide films using molecular beam epitaxy. PACS numbers: Keywords:Transition metal oxide heterostructures and interfaces exhibit a wide variety of exotic correlated quantum phases and hold the promise of exciting electronic applications [1][2][3][4]. High quality oxide heterostructures and interfaces can be fabricated with atomic-scale precision using advanced growth techniques with the application of reflection high-energy electron diffraction (RHEED). RHEED intensity oscillations reflect the film growth kinetics and the period corresponds to the growth of a repeat unit (e.g. an unit cell) [5][6][7][8][9][10]. To achieve most atomically sharp heterostructures and interfaces, a method that can precisely deposit one monolayer at a time would be preferred if the growth parameters can be calibrated precisely. SrTiO 3 is a prototype perovskite oxide that can be grown at a wide range of temperature and partial pressures of oxygen and on various templates including Silicon [2,9,[11][12][13][14]. In the growth of SrTiO 3 films using a shuttered method by molecular beam epitaxy (MBE), SrO and TiO 2 monolayers are deposited alternatively and the film is grown in a layer-by-layer manner. Typically, the RHEED intensity increases as the growth of SrO layer and decreases as the growth of TiO 2 layer [5, 6] although opposite phenomena were also reported [15]. During the calibration process, the precise shutter times of Sr and Ti sources for the deposition of full SrO and TiO 2 monolayers are obtained by stabilizing the RHEED intensity oscillation till it shows no clear amplitude change or overall intensity drift. Using these calibrated shutter times, high quality SrTiO 3 films and SrTiO 3 based superlattices and interfaces can thus be grown [5][6][7][8]. However, the RHEED oscillation patterns of complex oxides are very complicated and minor variations of the electron beam incident angle or shutter times can result in significant deviations [5,6,15,16]. Therefore, it is very challenging and time consuming to establish a stable RHEED oscillation pattern in calibrating the growth parameters of complex oxides, hindering the growth of more sophisticated oxide heterostructures and interfaces.In this letter, we show that the co-deposition method, a technique deposing atoms of all species simultaneously, is substantially more efficient and reliable than the conventional shuttered method in calibrating the growth parameters for complex oxide films.Epitaxial SrTiO 3 and Ruddlesden-Popper (RP) layered strontium titanate (Sr n+1 Ti n O 3n+1 ) films were grown o...