Optimisation of anatase TiO2 thin film growth on LaAlO3(0 0 1) using pulsed laser deposition

Abstract

Optimisation of epitaxial anatase TiO2 thin films grown on LaAlO3(001) substrates was performed using ultra-high vacuum based pulsed laser deposition (PLD) and studied by insitu reflection high-energy electron diffraction (RHEED). In addition, ex-situ X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were performed to characterise the bulk properties of these thin films. The deposited TiO2 thin film is demonstrated to have anatase phase and bonded directly to the LaAlO3(001) substrate. In a separate ultra-high vacuum system low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) measurements were performed and a well-ordered two-domain (14) and (41) reconstruction of anatase surface was observed. Analysis of the STM measurements indicates the coexistence of atomic steps of both 2.5 Å and 5.0 Å, confirming the existence of two TiO2 domains. The atomic resolution STEM images reveal that the TiO2/LaAlO3 interface to be terminated with LaO layer and that the anatase-TiO2 reconstruction was found to be stable during the film growth.

Influence of substrate on the structure of predominantly anatase TiO2films grown by reactive sputtering

“…It is important to highlight here, that in previous reports, in which the growth of single phase anatase lms on LAO was claimed, the absence of rutile crystallites was not conrmed by inspection of rutile {110} pole gures. 26,36,37,42,43 The present results demonstrate that Bragg-Brentano XRD measurement only may not be sufficient to rule out the presence of small concentrations of rutile crystallites in allegedly singlephase anatase lms. Rutile {110} azimuthal scan for c ¼ 45.0 is shown in Fig.…”

“…Such preferential growth in anatase [001] direction is in agreement with previous reports. 36,37 A low intensity peak, close to the anatase (004) and indicated by an arrow in Fig. 1a, is also observed and assigned to anatase [112] direction.…”

Role of Oxygen Deposition Pressure in the Formation of Ti Defect States in TiO2(001) Anatase Thin Films

“…Thin film growth technology , now enables tuning the growth conditions of TiO 2 anatase films of different thicknesses and oxygen contents. Recent reports have combined scanning probe techniques − and X-ray spectroscopy measurements − to investigate the origin and arrangement of Ti 3+ defect states in films.…”

“…27−31 In particular, low electron mobility in devices often represents the bottleneck of overall performances; 16 thus, the formation of electronic in-gap states and their homogeneous (or not) distribution over depth are crucial parameters for future applications. 32 Thin film growth technology 33,34 now enables tuning the growth conditions of TiO 2 anatase films of different thicknesses and oxygen contents. Recent reports have combined scanning probe techniques 35−37 and X-ray spectroscopy measurements 38−42 to investigate the origin and arrangement of Ti 3+ defect states in films.…”

Favoring the Reactivity of TiO2 Films with Ideal Arrangement of Anatase and Rutile Crystallites

“…In this way, besides maximizing the exposure of anatase {001} on the surfaces of films, it was possible to reach our goal in developing a technique with the potential to produce cost-effective films over large areas to favoring industrial applications of TiO 2 films to photocatalysis. Even though the sapphire (0001) substrates are still relatively expensive, as compared to borosilicate glass or commercial stainless steel, those are much cheaper than LAO (001) substrates, used many times in the growth of epitaxial TiO 2 with the desired (001) surface using MBE , and PLD. − Also, the natural capability of the reactive sputtering in producing homogeneous films over large areas provides remarkable advantage in terms of costs as compared to MBE production. Moreover, using the present set of parameters, we obtained rutile crystals in close contact with the anatase ones which is considered beneficial to the photocatalytic activity of the films. − …”