Electronic confinement at nanoscale dimensions remains a central means of science and technology. We demonstrate nanoscale lateral confinement of a quasi–two-dimensional electron gas at a lanthanum aluminate–strontium titanate interface. Control of this confinement using an atomic force microscope lithography technique enabled us to create tunnel junctions and field-effect transistors with characteristic dimensions as small as 2 nanometers. These electronic devices can be modified or erased without the need for complex lithographic procedures. Our on-demand nanoelectronics fabrication platform has the potential for widespread technological application.

http://absimage.aps.org/image/MAR09/MWS_MAR09-2008-000600.pdf

Oxide Nanoelectronics On Demand

Inserting molecular monolayers within metal/semiconductor interfaces provides one of the most powerful expressions of how minute chemical modifications can affect electronic devices. This topic also has direct importance for technology as it can help improve the efficiency of a variety of electronic devices such as solar cells, LEDs, sensors, and possible future bioelectronic ones. The review covers the main aspects of using chemistry to control the various aspects of interface electrostatics, such as passivation of interface states and alignment of energy levels by intrinsic molecular polarization, as well as charge rearrangement with the adjacent metal and semiconducting contacts. One of the greatest merits of molecular monolayers is their capability to form excellent thin dielectrics, yielding rich and unique current–voltage characteristics for transport across metal/molecular monolayer/semiconductor interfaces. We explain the interplay between the monolayer as tunneling barrier on the one hand, and th...

Chemical Modification of Semiconductor Surfaces for Molecular Electronics

Structure-property relationship and chemical aspects of oxide-metal hybrid nanostructures.

Low-energy deposition of neutral ${\mathrm{P}\mathrm{d}}_{N}$ clusters ($N=2--7$ and $13$) on a MgO(001) surface F center (FC) was studied by spin-density-functional molecular dynamics simulations. The incident clusters are steered by an attractive ``funnel'' created by the FC, resulting in adsorption of the cluster, with one of its atoms bonded atop of the FC. The deposited ${\mathrm{P}\mathrm{d}}_{2}\mathrm{\text{\ensuremath{-}}}{\mathrm{P}\mathrm{d}}_{6}$ clusters retain their gas-phase structures, while for $Ng6$ surface-commensurate isomers are energetically more favorable. Adsorbed clusters with $Ng3$ are found to remain magnetic at the surface.

Supported magnetic nanoclusters: Soft-landing of Pd clusters on a MgO surface

Inserting molecular monolayers within metal / semiconductor interfaces provides one of the most powerful expressions of how minute chemical modifications can affect electronic devices. This topic also has direct importance for technology as it can help improve the efficiency of a variety of electronic devices such as solar cells, LEDs, sensors and possible future bioelectronic devices, which are based mostly on non-classical semiconducting materials (section 1). The review covers the main aspects of using chemistry to - control alignment of energy levels at interfaces (section 2): - passivate interface states (section 3), - insert molecular dipoles at interfaces (section 4), - induce charge rearrangement at and around interfaces (section 5). After setting the stage, we consider the unique current-voltage characteristics that result from transport across metal / molecular monolayer / semiconductor interfaces. Here we focus on the interplay between the monolayer as tunneling barrier on the one hand, and the electrostatic barrier within the semiconductor, due to its space-charge region (section 6), on the other hand, as well as how different monolayer chemistries control each of the these barriers. Section 7 provides practical tools to experimentally identify these two barriers, and distinguish between them, after which section 8 concludes the story with a summary and a view to the future. While this review is concerned with hybrid semiconductor / molecular effects (see Refs. 1,2 for earlier reviews on this topic), issues related to formation of monolayers and contacts, as well as charge transport that is solely dominated by molecules, have been reviewed elsewhere[3-6], including by us recently[7].

Molecular Electronics by Chemical Modification of Semiconductor Surfaces

The electronic band structure and the work function of MgO thin films epitaxially grown on Ag(001) have been investigated using x-ray and ultraviolet photoelectron spectroscopy for various oxide thicknesses. The deposition of thin MgO films on Ag(001) induces a strong diminution in the metal work function. The p-type Schottky barrier height is constant at 3.85+/-0.10 eV above two MgO monolayers and the experimental value of the ionization potential is 7.15+/-0.15 eV. Our results are well consistent with the description of the Schottky barrier height in terms of the Schottky-Mott model corrected by an MgO-induced polarization effect.

Work function shifts, Schottky barrier height, and ionization potential determination of thin MgO films on Ag(001)

By combining x-ray excited Auger electron diffraction experiments and multiple scattering calculations we reveal a layer-resolved shift for the Mg $K{L}_{23}{L}_{23}$ Auger transition in MgO ultrathin films (4--6 \AA{}) on Ag(001). This resolution is exploited to demonstrate the possibility of controlling Mg atom incorporation at the $\mathrm{MgO}/\mathrm{Ag}(001)$ interface by exposing the MgO films to a Mg flux. A substantial reduction of the $\mathrm{MgO}/\mathrm{Ag}(001)$ work function is observed during the exposition phase and reflects both band-offset variations at the interface and band bending effects in the oxide film.

/pdf/layer-resolved-study-of-mg-atom-incorporation-at-the-mgo-ag-2xvysh0ztu.pdf

Layer-resolved study of Mg atom incorporation at the MgO/Ag(001) buried interface.

The properties of MgO/Ag(001) ultrathin films with substitutional Mg atoms in the interface metal layer have been investigated by means of Auger electron diffraction experiments, ultravio-let photoemission spectroscopy, and density functional theory (DFT) calculations. Exploiting the layer-by-layer resolution of the Mg KL23L23 Auger spectra and using multiple scattering calcula-tions we first determine the inter-layer distances as well as the morphological parameters of the MgO/Ag(001) system with and without Mg atoms incorporated at the interface. We find that the Mg atom incorporation drives a strong distortion of the interface layers and that its impact on the metal/oxide electronic structure is an important reduction of the work function (0.5 eV) related to band-offset variations at the interface. These experimental observations are in very good agreement with our DFT calculations which reproduce the induced lattice distortion and which reveal (through a Bader analysis) that the increase of the interface Mg concentration results in an electron transfer from Mg to Ag atoms of the metallic interface layer. Although the local lattice distortion appears as a consequence of the attractive (repulsive) Coulomb interaction between O 2− ions of the MgO interface layer and the nearest positively (negatively) charged Mg (Ag) neighbors of the metallic interface layer, its effect on the work function reduction is only limited. Finally, an analysis of the induced work function changes in terms of charge transfer, rumpling, and electrostatic compression contributions is attempted and reveals that the metal/oxide work function changes induced by inter-face Mg atoms incorporation are essentially driven by the increase of the electrostatic compression effect.

https://hal-univ-rennes1.archives-ouvertes.fr/hal-01101454/document

Induced work function changes at Mg-doped MgO/Ag(001) interfaces: Combined Auger electron diffraction and density functional study

We present an experimental investigation of the interface electronic structure of thin MgO films epitaxially grown on Ag(001) by x-ray and ultraviolet photoemission spectroscopy as a function of the oxide growth conditions. It is shown that the Schottky barrier height at MgO/metal interface can be tuned over 0.7 eV by a modification of the oxygen partial pressure or the sample temperature. These experimental results are explained in the framework of the extended Schottky-Mott model and the MgO-induced polarization effect by Mg enrichment of the silver surface region.

Tuning the Schottky barrier height at MgO/metal interface

The interface resistance at metal/semiconductor junctions has been a key issue for decades. The control of this resistance is dependent on the possibility to tune the Schottky barrier height. However, Fermi level pinning in these systems forbids a total control over interface resistance. The introduction of 2D crystals between semiconductor surfaces and metals may be an interesting route towards this goal. In this work, we study the influence of the introduction of a graphene monolayer between a metal and silicon on the Schottky barrier height. We used X-ray photoemission spectroscopy to rule out the presence of oxides at the interface, the absence of pinning of the Fermi level and the strong reduction of the Schottky barrier height. We then performed a multiscale transport analysis to determine the transport mechanism. The consistency in the measured barrier height at different scales confirms the good quality of our junctions and the role of graphene in the drastic reduction of the barrier height.

/pdf/a-low-schottky-barrier-height-and-transport-mechanism-in-4wa4yrdbt7.pdf

Gabriel Delhaye

Papers

Work function shifts, Schottky barrier height, and ionization potential determination of thin MgO films on Ag(001)

Layer-resolved study of Mg atom incorporation at the MgO/Ag(001) buried interface.

Induced work function changes at Mg-doped MgO/Ag(001) interfaces: Combined Auger electron diffraction and density functional study

Tuning the Schottky barrier height at MgO/metal interface

A low Schottky barrier height and transport mechanism in gold–graphene–silicon (001) heterojunctions