Control of Surface Work Function by Depositing Insulating Oxide Capping Layers

Abstract

We have studied the work function modulation in pulsed laser deposited nonpolar MgO (100) and polar MgO (100) and LaAlO3 (100) insulating oxide films on Nb:SrTiO3 (100) and (111) substrates using Kelvin probe measurements. The work function modulation in MgO/Nb:SrTiO3 is ∼1 eV, which may be understood by the “electron compression model”, where the leaked-out electrons from Nb:SrTiO3 surface are pushed back by MgO layer, reducing the surface dipole moment. By forming double insulating top layer in LaAlO3/nondoped SrTiO3/Nb:SrTiO3 (100), we have realized the work function as low as ∼2.2 eV, which would be originated in the formation of high-density electrons at the LaAlO3/nondoped SrTiO3 interface and can be very close to the top surface. The present results demonstrate that chemically stable oxides can be used as low work function devices employing heterostructure form.

Origin of charge transfer and enhanced electron–phonon coupling in single unit-cell FeSe films on SrTiO3

“…Thus, we obtain ϕ (STO) = 4.5 eV, ϕ (20uc-FeSe/STO) = 5.1 eV and ϕ (1uc-FeSe/STO) = 4.8–5.2 eV, as summarized in Figure 2b . The obtained work function of STO is consistent with previous reports 35 . When FeSe is deposited onto STO, electrons in STO transfer to FeSe to compensate for the large difference in work functions.…”

Tailoring Work Functions of Heterostructures by Varying the Depth of a Buried Monolayer

“…[22][23][24] Such advances are key to studying the work function of complex materials, which is sensitive to growth parameters and conditions. Whereas some studies have reported work function values for several of these materials, [25][26][27][28] the literature concerning specifically tailored work functions of perovskite oxide heterostructures is rather scarce. [10,21,29] A particularly interesting application motivating this work is that of thermoelectronic energy converters (TECs), [30] which utilize a hot thermionically emitting material and the condensation of electrons on a cold collecting material.…”