Influence of Gas Ambient on Charge Writing at the LaAlO₃/SrTiO₃ Heterointerface

Abstract

We investigated the influences of charge writing on the surface work function (W) and sheet resistance (R) of the LaAlO3/SrTiO3 (LAO/STO) heterointerface in several gas environments: H2(2%)/N2(98%), air, N2, and O2. The decrease in W and R due to charge writing was much larger in air (ΔW = -0.45 eV and ΔR = -40 kΩ/S) than in O2 (ΔW = -0.21 eV and ΔR = -19 kΩ/S). The reduced R could be maintained more than 100 h in H2/N2. Such distinct behaviors were quantitatively discussed, based on the proposed charge-writing mechanisms. Such analyses showed how several processes, such as carrier transfer via surface adsorbates, surface redox, electronic state modification, and electrochemical surface reactions, contributed to charge writing in each gas.

Ferroelectric or non-ferroelectric: Why so many materials exhibit “ferroelectricity” on the nanoscale

“…In comparison, on the nanoscale the electrochemical and ionic processes are enabled at much lower temperatures, as analyzed in Ref. 278,279 Notably, many phenomena such as unusual behavior of LaAlO3-SrTiO3 (LAO-STO) system 280 and domain wall conductance in ferroelectrics were originally interpreted in the context of purely physical models (polar catastrophe for LAO STO 280,281 and band-gap lowering for domain walls 11 ) and were further shown to have strong chemical components including vacancy dynamics and surface water electrochemistry (see refs [282][283][284][285] for LAO-STO and refs [286][287][288] for domain walls).…”

Enhanced Surface-and-Interface Coupling in Pd-Nanoparticle-coated LaAlO3/SrTiO3 Heterostructures: Strong Gas- and Photo-Induced Conductance Modulation

“…The LaAlO 3 /SrTiO 3 (LAO/STO) heterointerface, consisting of two wide-bandgap insulators, exhibits unexpected high-mobility two-dimensional electron gas (2DEG) behavior, which has generated an intense surge in research activities by the oxide electronics community 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 . Discovery of additional peculiar physical properties of the LAO/STO system, including a metal–insulator transition 2 3 4 5 , superconductivity 6 , magnetic ordering 7 8 , thermoelectricity 9 , strong electron correlation effect 10 , and a huge photoresponse 11 12 13 14 15 , has continued. Thus, investigations of these intriguing phenomena have surfaced as the most interesting and challenging topics in relevant fields.…”

“…A nm-thick LAO film possesses large capacitance, and hence a slight change in the free/bound charges at the LAO surface should significantly modulate the carrier concentration at the LAO/STO interface. Surface charge modification, via biased AFM tip scanning 2 3 4 5 or polar molecule adsorption 30 31 , clearly reveals notable interactions between the surface and interface charges of the LAO/STO 2DEG system. Ferroelectric distortion, if any, could further modify the carrier concentration at the LAO/STO interface 11 32 .…”

“…Hereafter the LAO/STO heterostructures without and with the Pd NPs will be called as LAO/STO and Pd/LAO/STO, respectively. Figure 1b schematically illustrates the measurement setup: transport and Kelvin probe force microscopy (KPFM) measurements were simultaneously performed in a glove box while varying the ambient gas environments 5 , such as H 2 (2%)/N 2 (98%), N 2 , and O 2 , and with and without UV light (wavelength: 365 nm and intensity: ≥10 mW/cm 2 ) illumination.…”

“…As mentioned above, the LAO/STO sample can be regarded as a capacitor. Thus, the change in the potential drop across the LAO layer, V ', should alter the sheet electron density at interface, σ , where ε LAO is the dielectric constant of LAO, e is the unit charge, and d LAO is the thickness of LAO 5 30 .…”