Graphene quantum dots for single electron transistors

Something about the structure of Boron-Nitride, Platinum and oxidized Silicon that supports this:
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Graphene quantum dots for single electron transistors
March 7, 2019, National Research University Higher School of Economics


Read more at: https://phys.org/news/2019-03-graphene-quantum-dots-electron-transistors.html#jCp

(pics at link above:)

Scientists from the Higher School of Economics, Manchester University, the Ulsan National Institute of Science & Technology and the Korea Institute of Science and Technology have developed a novel technology that combines the fabrication procedures of planar and vertical heterostructures in order to assemble graphene-based single-electron transistors of excellent quality.

This technology could considerably expand the scope of research on two-dimensional materials by introducing a broader platform for the investigation of various devices and physical phenomena. The manuscript is published as an article in Nature Communications.

In the study, it was demonstrated that high-quality graphene quantum dots (GQDs), regardless of whether they were ordered or randomly distributed, could be successfully synthesised in a matrix of monolayer hexagonal boron nitride (hBN). Here, the growth of GQDs within the layer of hBN was shown to be supported catalytically by the platinum (Pt) nanoparticles distributed in between the hBN and supporting oxidised silicon (SiO2) wafer, when the whole structure was treated by the heat in the methane gas (CH4). Due to the same lattice structure (hexagonal) and small lattice mismatch (~1.5 percent) of graphene and hBN, graphene islands grow in the hBN with passivated edge states, thereby giving rise to the formation of defectless quantum dots embedded in the hBN monolayer.
Graphene quantum dots for single electron transistors
Optical micrograph (100X) of one of the devices with the highlighted layers of graphene electrodes Credit: Davit Ghazaryan

Such planar heterostructures incorporated by means of standard dry-transfer as mid-layers into the regular structure of vertical tunnelling transistors were studied through tunnel spectroscopy at low temperatures (3He, 250mK). The study demonstrated the location where well-established phenomena of the Coulomb blockade for each graphene quantum dot manifests as a separate single electron transmission channel.

"Although the outstanding quality of our single electron transistors could be used for the development of future electronics," explains study co-author Davit Ghazaryan, associate professor at the HSE Faculty of Physics, and Research Fellow at the Institute of Solid State Physics (RAS). "This work is most valuable from a technological standpoint as it suggests a new platform for the investigation of physical properties of various materials through a combination of planar and van der Waals heterostructures."


Read more at: https://phys.org/news/2019-03-graphene-quantum-dots-electron-transistors.html#jCp

Boron can form a purely honeycomb, graphene-like 2-D structure
March 14, 2018, Science China Press

(Pics and more at link..)

High resolution STM images of borophene monolayer with honeycomb lattice on Al(1 1 1). Credit: Science China Press

Borophene is known to have triangular lattice with holes, while a honeycomb lattice of boron was predicted to be energetically unstable. However, a research team led by Prof. K. H. Wu at Institute of Physics, Chinese Academy of Sciences, successfully fabricated a pure graphene-like borophene by using an Al(111) surface as the substrate and molecular beam epitaxy in ultrahigh vacuum, providing an ideal platform for artificial boron-based materials with intriguing electronic properties such as Dirac states and superconductivity behavior.

Low-dimensional boron allotropes have attracted considerable interest in recent decades, and theoretical works predict the existence of monolayer boron. As boron has only three valence electrons, the electron deficiency makes a honeycomb lattice of boron energetically unstable. Instead, a triangular lattice with periodic holes was predicted to be more stable. In 2015, Prof. Wu led a research team at Institute of Physics, Chinese Academy of Sciences, and successfully synthesized 2-D borophene sheets on a silver surface, which exhibit the predicted triangular lattice with different arrangements of hexagonal holes.

An intriguing question is whether it is possible to prepare a borophene monolayer with a pure honeycomb lattice. Honeycomb borophene will naturally host Dirac fermions, and thus, intriguing electronic properties resembling other group IV elemental 2-D materials. Additionally, a honeycomb 2-D boron lattice may enable superconductivity. In the well-known high Tc superconductor, MgB2, the crystal structure consists of boron planes with intercalated Mg layers, where the boron plane has a pure honeycomb structure like graphene. It is remarkable that in MgB2, superconductivity occurs in the boron planes, while the Mg atoms serves as electron donors.

Recently, the research team led by Prof. Wu reported the successful preparation of a honeycomb-shaped graphene-like borophene, by using an Al(1 1 1) surface as the substrate and molecular beam epitaxy (MBE) growth in ultrahigh vacuum. Scanning tunneling microscopy (STM) images reveal perfect monolayer borophene with a planar, non-buckled honeycomb lattice similar to graphene. Theoretical calculations show that the honeycomb borophene on Al(1 1 1) is energetically stable. Remarkably, nearly one electron charge is transferred to each boron atom from the Al(1 1 1) substrate and stabilizes the honeycomb borophene structure. This work demonstrates the manipulation of the borophene lattice by controlling the charge transfer between the substrate and the borophene. And the honeycomb borophene provides attractive possibility to construct boron-based atomic layers with unique electronic properties such as Dirac states, as well as to control superconductivity in boron-based compounds.

Explore further: New two-dimensional 'borophene' sheet


Read more at: https://phys.org/news/2018-03-boron-purely-honeycomb-graphene-like-d.html#jCp