Characterization of Thin MgO Films on Ag(001) by Low-Energy Electron Diffraction and Scanning Tunneling Microscopy

Ouvrard, A.; Niebauer, Johannes; Ghalgaoui, Ahmed; Barth, Clemens; Henry, Claude R.; Bourguignon, Bernard

doi:10.1021/jp1095823

Cited by 24 publications

(48 citation statements)

References 58 publications

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“…However, such a description is quite complicated [53] if the growth is influenced by defects on the surface as is the case here: a defect-driven growth takes place for NaCl on silver since all NaCl islands are located at the steps at almost all temperatures. This clearly contrasts with the situation of MgO thin films on the same substrate: many MgO islands can be found on the atomically flat terraces of silver at almost all temperatures (373 < T Ag < 673 K) [45]. For the latter film, two branches were observed in the density versus temperature curves ( E 1 = 0.23 eV and E 2 = 0.8 eV [45]), which can be assigned to the low and high temperature cases of an MgO island growth.…”

Section: Film Growthcontrasting

confidence: 57%

“…Because almost all islands nucleate at the Ag steps, even at T Ag = 306 K, it can be anticipated that the mean diffusion length of NaCl molecules on silver (001) must be quite large. The diffusion length is at least comparable to the mean distance between the steps of the silver surface (mean distance: 36 ± 11 nm) and larger than the diffusion length of MgO [45]. An important finding is that the island shape is anisotropic at T Ag = 343 K ( figure 1(b))-the islands grow along the steps.…”

Section: Film Growthmentioning

confidence: 88%

“…expand on the upper and lower Ag terraces, indicating a strong inter-step diffusion. Films that are prepared at the highest temperature of 443 K exhibit very large islands with an average edge length of up to 400 nm, which strongly contrasts with MgO films on the same substrate [45]. Very important to mention is that, starting from T Ag = 373 K, all the islands have a base layer 2 ML thick (base islands).…”

Section: Island Size Density and Orientationmentioning

confidence: 97%

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Thin NaCl films on silver (001): island growth and work function

2012

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The surface work function (WF) and substrate temperature dependence of the NaCl thin-film growth on Ag(001) have been studied by noncontact atomic force microscopy and Kelvin probe force microscopy. In the sub-monolayer range, the NaCl film is composed of large crystalline islands, which decrease in density and increase in size with increasing temperature during deposition. Each island is composed of a large base island 2 monolayers (ML) thick (for T > 343 K), which collects impinging NaCl molecules that form adislands on top. Kelvin probe force microscopy (KPFM) measurements show a reduction of the silver WF by ϕ = ϕ Ag − ϕ NaCl/Ag = 0.69 ± 0.03 eV with no dependence on the film thickness (1-6 ML), in agreement with recent theoretical calculations. The previously observed nanometer-sized moiré pattern on islands that are 45 • rotated with respect to the silver lattice could be observed in the scanning tunneling microscopy mode. However, no contrast could be obtained in KPFM images.

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Section: Film Growthcontrasting

confidence: 57%

Section: Film Growthmentioning

confidence: 88%

Section: Island Size Density and Orientationmentioning

confidence: 97%

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Thin NaCl films on silver (001): island growth and work function

2012

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“…20 STM experiments 15,21 demonstrate that Ag islands appear alongside MgO clusters in the thin (2−4 MgO layer) film samples. The experimentally measured shift of the WF, Δϕ, for MgO/Ag(001) depends on both film preparation and method of WF measurement.…”

Section: Introductionmentioning

confidence: 99%

Effects of Oxide Roughness at Metal Oxide Interface: MgO on Ag(001)

2013

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Defects in thin oxide films on metal substrates affect metal work function and determine the chemical and physical properties of an oxide. However, accurately predicting properties of these heterogeneous systems is still challenging. Here we use a new approach to treat a mixed metal/metal oxide system within density functional theory, which is based on the application of the auxiliary density matrix method (J. Chem. Theory Comput. 2010, 6, 2348) to calculate the exchange interaction at a sharp interface between the two materials, as implemented in the CP2K code. This method is used to calculate the shift of the Ag work function in the MgO/Ag(001) system as a function of the MgO film morphology as well as charge state, position, and density of oxygen vacancies. An accurate band alignment between metal and oxide allows us to predict the relative stabilities of different charge states of oxygen vacancies in MgO as a function of their position with respect to the interface with Ag. Our results confirm that F + centers are the most stable defects at terrace sites of MgO clusters and show that F 0 and F + centers can have comparable energies at low-coordinated sites, such as steps and corners. They show how thin oxide film roughness as well as oxygen deficiency can affect the metal work function.

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“…We first consider the growth of films in the sub-ML range to compare the films with those ones previously obtained after a low-temperature growth. 12 Figure 1 shows a nc-AFM topography image ( Figure 1a In the topography image (Figure 1a), two types of islands in a dark and bright contrast can be found, which we call as embedded MgO a (dark) and supported MgO b islands (bright) according to previous works. 11,12 They have a total density of 2 × 10 11 islands/cm 2 and a mean lateral size of ∼20 nm, both leading to a total coverage of ∼54% of the silver surface.…”

Section: ■ Experimental Methodsmentioning

confidence: 73%

Morphology, Work Function, and Silver Ad-Structures of High-Temperature Grown Ultrathin MgO Films on Ag(001)

Mechehoud

Barth

2015

J. Phys. Chem. C

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We characterized the high-temperature growth of ultrathin MgO films on Ag(001) at 783 K through analyzing the film's morphology and work function by noncontact atomic force microscopy (nc-AFM), scanning tunneling microscopy (STM), Kelvin probe force microscopy (KPFM) and assisting low-energy electron diffraction (LEED). At submonolayer coverage, one-atomic-plane-high MgO islands are formed, which are preferentially embedded into the silver surface and which are larger and more regular than the islands of those films normally grown between 500 and 600 K. KPFM shows that embedded MgO islands decrease the silver work function (WF) by Δϕ MgO−Ag = −50 ± 20 meV, whereas a small amount of supported islands increase the WF by Δϕ MgO−Ag = +50 ± 20 meV. When the MgO film starts to cover entirely the silver surface, ad-islands, nanoparticles (NPs), and much larger particles of silver are formed, which is due to the high mobility of silver and the embedding of the MgO islands into the silver surface. Our work opens the general perspective to prepare a thin oxide film and at the same time metal NPs from the metal surface via a high-temperature growth.

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Characterization of Thin MgO Films on Ag(001) by Low-Energy Electron Diffraction and Scanning Tunneling Microscopy

Cited by 24 publications

References 58 publications

Thin NaCl films on silver (001): island growth and work function

Thin NaCl films on silver (001): island growth and work function

Effects of Oxide Roughness at Metal Oxide Interface: MgO on Ag(001)

Morphology, Work Function, and Silver Ad-Structures of High-Temperature Grown Ultrathin MgO Films on Ag(001)

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