Metal quantum wells with all electrons confined:  Na films and islands on graphite

Breitholtz, M.; Kihlgren, T.; Lindgren, S.Å.; Olin, Håkan; Wahlström, Erik; Walldén, L.

doi:10.1103/physrevb.64.073301

Cited by 24 publications

(29 citation statements)

References 20 publications

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“…6,12,13 The formation energies of the open shell systems Na, Na 3 , and Na 5 are larger than those of closed shell cases Na 2 and Na 4 . This is related to the spin-degeneracy of the highest molecular orbital (odd-even staggering) and, in contrast to free metal clusters, gives rise to increased stability of odd cluster sizes on HOPG.…”

Section: Discussionmentioning

confidence: 99%

“…While lithium atoms either intercalate between the graphene layers 4 or form a planar incommensurate hcp superstructure on HOPG, 11 it has been suggested that sodium nucleates only in buckled (110) bcc overlayers. 12,13 The larger alkali atoms (K,Ru,Cs) are found to intercalate via surface defects 6,9 or to adsorb in a (2 × 2) phase occupying hollow sites of the hexagonal substrate. 6,9,14,15 In addition, cesium can exist in an incommensurate hexagonal or a more sparse ( √ 7 × √ 7)R19.11 • phase, 6,14,15 and a dense ( √ 3 × √ 3)R30 • structure has been proposed for potassium.…”

Section: Introductionmentioning

confidence: 99%

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Sodium atoms and clusters on graphite by density functional theory

2004

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Sodium atoms and clusters (N ≤ 5) on graphite (0001) are studied using density functional theory, pseudopotentials and periodic boundary conditions. A single Na atom is observed to bind at a hollow site 2.45Å above the surface with an adsorption energy of 0.51 eV. The small diffusion barrier of 0.06 eV indicates a flat potential energy surface. Increased Na coverage results in a weak adsorbate-substrate interaction, which is evident in the larger separation from the surface in the cases of Na 3 , Na 4 , Na 5 , and the (2×2) Na overlayer. The binding is weak for Na 2 , which has a full valence electron shell. The presence of substrate modifies the structures of Na 3 , Na 4 , and Na 5 significantly, and both Na 4 and Na 5 are distorted from planarity. The calculated formation energies suggest that clustering of atoms is energetically favorable, and that the open shell clusters (e.g. Na 3 and Na 5 ) can be more abundant on graphite than in the gas phase. Analysis of the lateral charge density distributions of Na and Na 3 shows a charge transfer of ∼ 0.5 electrons in both cases.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sodium atoms and clusters on graphite by density functional theory

2004

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“…Recently, NDR was also observed in quantum-dot structures based on a newly discovered physical effect, Coulomb blockade of carrier trapping, [10][11][12] and metal quantum well structures based on resonant tunneling process. [13][14][15] Ferromagnet/semiconductor heterostructures are of growing interest for development of spintronic devices. In particular, magnetic quantum-dot (MQD) structures could permit investigation of the interaction of strongly localized carriers with the magnetic environment.…”

Section: Zns Schottky Barrier Embedded With Fe Quantum Dotsmentioning

confidence: 99%

MBE-Grown II–VI and Related Nanostructures

Sou

Lok

Wang

et al. 2010

Journal of Elec Materi

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Nanostructures of II-VI semiconductor materials could potentially offer novel and superior physical (in particular, optoelectronic) properties with respect to their bulk counterparts. Herein, we present our most recent research on several II-VI and related nanostructures grown by molecular beam epitaxy (MBE) technique. These include a ZnSe nanograting. This nanograting structure was realized at the surface of Fe/ZnSe bilayers grown on GaAs(001) substrates by thermal annealing. A model based on an Ewald construction is presented to explain its unusual reflection high-energy electron diffraction (RHEED) patterns. The formation mechanism of this one-dimensional (1D) nanostructure is possibly related to surface energy minimization, together with an Fe-Se exchange interaction and Fe-induced decomposition of several top ZnSe atomic layers during thermal annealing. Another nanostructure investigated was the ZnS Schottky barrier embedded with Fe quantum dots (QDs). Here, a Au/ZnS/Fe-QDs/ZnS/n + -GaAs(100) Schottky barrier structure containing five layers of spherical Fe quantum dots with a diameter of $3 nm was fabricated. Its I-V characteristic measured from 5 K to 295 K displays negative differential resistance (NDR) for temperature £50 K. Staircase-like I-V characteristics were also observed at low temperature in some devices fabricated from this structure. Possible mechanisms that can account for the observed unusual I-V characteristic in this structure are presented. Finally, laterally grown Fe nanowires (NWs) on a ZnS surface were prepared. Under high growth/annealing temperature, two types of Fe NWs with specific orientations can be grown on the ZnS(100) surface. We propose a mean-field model that the torque exerted by type A Fe NWs could effectively turn the two components of type B Fe NWs slightly toward the ZnS [110] direction, leading to the observed misalignment of type B Fe NWs. ZnSe NANOGRATINGRecently, a number of self-assembly techniques have been used in the fabrication of low-dimensional structures such as quantum dots and nanowires. 1,2 These techniques enjoy the advantages of being able to achieve a true nanosize scale of the nanostructures and most importantly large product area by an in situ non-time-consuming fabrication process. In recent years, using state-of-the-art molecular beam epitaxy (MBE) technique, we have been able to study the growth mechanism and/or quantum size effects of several self-assembled nanostructures. 3-5 Herein, we report a novel approach for fabricating a highly aligned nanograting structure on a ZnSe(001) surface by thermal annealing an Fe/ZnSe bilayer grown on a GaAs(001) substrate.In this study, three samples were fabricated on GaAs(001) substrates using a VG V80H MBE system. The substrate of sample I1 was first deoxided at 580°C, and then a thin ZnSe film ($30 nm) was deposited at 250°C using a ZnSe compound effusion

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“…W emphasize that angle-resolved or angle-integrated XPS measurements cannot confirm intercalation because changes in the intensity of XPS lines from a monolayer of Na (K, Cs) adsorbed on Gr/Ni(111) are often caused by formation of thick islands of adsorbates on top rather than intercalation 22,32,43,44 . Our measurements provide strong evidence that Na on top of Gr/Ni(111) reduces coupling between graphene and the substrate, and cause lowering the π-to-π* energy gap from 2.8 eV to 1.3 eV.…”

mentioning

confidence: 99%

“…Adsorption at low temperatures cause aggregation of Na while adsorption at higher temperatures causes that adatoms are mobile and dispersed randomly on the surface 43,48,49 . This is consistent with our observations that poor morphology of Na on top cause a weaker decoupling, and might explain a recent observation that adsorption at 133 K does not induce major changes to the band structure of Gr/Ni(111) 15 .…”

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confidence: 99%

Controlling the electronic structure of graphene using surface-adsorbate interactions

et al. 2015

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We show that strong coupling between graphene and the substrate is mitigated when 0.8 monolayer of Na is adsorbed and consolidated on top graphene-on-Ni(111). Specifically, the π state is partially restored near the K-point and the energy gap between the π and π* states reduced to 1.3 eV after adsorption, as measured by angle-resolved photoemission spectroscopy. We show that this change is not caused by intercalation of Na to underneath graphene but it is caused by an electronic coupling between Na on top and graphene. We show further that graphene can be decoupled to a much higher extent when Na is intercalated to underneath graphene. After intercalation, the energy gap between the π and π* states is reduced to 0 eV and these states are identical as in freestanding and n-doped graphene. We conclude thus that two mechanisms of decoupling exist: a strong decoupling through intercalation, which is the same as one found using noble metals, and a weak decoupling caused by electronic interaction with the adsorbate on top.

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Metal quantum wells with all electrons confined: Na films and islands on graphite

Cited by 24 publications

References 20 publications

Sodium atoms and clusters on graphite by density functional theory

Sodium atoms and clusters on graphite by density functional theory

MBE-Grown II–VI and Related Nanostructures

Controlling the electronic structure of graphene using surface-adsorbate interactions

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