Aggregation and electronically induced migration of oxygen vacancies inTiO2anatase

Abstract

The influence of the electric field and electric current on the behavior of oxygen vacancies (VOs) in TiO2 anatase was investigated with Scanning Tunneling Microscopy (STM). At the anatase (101) surface VOs are not stable; they migrate into the bulk at temperatures above 200 K. Scanning a clean anatase (101) surface at a sample bias greater than ≈+4.3 V results in surface VOs in the scanned area, suggesting that subsurface VOs migrate back to the surface. To test this hypothesis, surface VOs were first created through bombardment with energetic electrons. The sample was then mildly annealed, which caused the VOs to move to the subsurface region, where they formed vacancy clusters. These VO clusters have various, distinct shapes. Scanning VO clusters with a high STM bias reproducibly converts them back into groupings of surface VO, with a configuration that is characteristic for each type of cluster. The dependence of the subsurface-to-surface VO migration on the applied STM bias voltage, tunneling current, and sample temperature was investigated systematically. The results point towards a key role of energetic, 'hot' electrons in this process. The findings are closely related to the memristive behavior of oxides and oxygen diffusion in solid-oxide membranes.

Formation and stability of reduced TiOx layers on anatase TiO2(101) : Id

“…In this work, we focus on anatase, the TiO 2 phase usually found in nanomaterials and most relevant in photocatalysis and photovoltaics [1,15,16], and use DFT calculations to explore the stability and properties of highly reduced TiO x overlayers formed by CSPs on or near its most 3 stable and frequently exposed (101) surface [10,15,17] [20,21]. In agreement with these findings, our calculations show that a subsurface V O (site 4 in Fig.…”

Resolving the Structure of a Well-Ordered Hydroxyl Overlayer on In2O3(111): Nanomanipulation and Theory

“…During the past decade, such controlled manipulations have been developed as a valuable tool to identify and differentiate adsorbed surface entities with atomic-scale precision, for example, by their charge state, 38 as well as subsurface species, such as oxygen vacancies in anatase TiO 2 . 39 Furthermore, such manipulations allow us to study the tip–adsorbate and adsorbate–surface interactions and to trigger single chemical reactions. 40 Classified by the mechanism, STM manipulations operate via forces (pushing, pulling, sliding), 41 electric field (field evaporation and diffusion), 40 or electric current (inelastic tunneling, vibrational and electronic excitations).…”

Creating Excess Electrons at the Anatase TiO2(101) Surface

“…The anatase (101) surface has previously been investigated by low-energy electron diffraction (LEED) [10] and scanning probe microscopy [4,[11][12][13][14][15][16][17][18][19][20] as well as photoemission [21][22][23][24][25][26], infrared reflection absorption [13] and near edge X-ray absorption fine structure [23] spectroscopies. The surface presents a non-reconstructed (1 9 1) bulk termination, as shown in Fig.…”

“…Similar to rutile (110), the O 2c atoms at the anatase (101) surface can be removed during sample preparation or by electron bombardment [11,18], forming oxygen vacancies (O-vacs). The creation of O-vacs leads to a reduced surface, and induces Ti 3d band gap states (BGS) *1 eV below the Fermi level (E F ) [24,[27][28][29].…”