Nav: Home

Controlling the charge state of organic molecule quantum dots in a 2D nanoarray

October 15, 2019

Australian researchers have fabricated a self-assembled, carbon-based nanofilm where the charge state (ie, electronically neutral or positive) can be controlled at the level of individual molecules, on a length scale of around one nanometre.

Molecular self-assembly on a metal results in a high-density, 2D, organic quantum-dot array with electric-field-controllable charge state, with the organic molecules used as 'nano-sized building blocks' in fabrication of functional nanomaterials.

Achieved densities are an order of magnitude larger than conventional inorganic systems.

The atomically-thin nanofilm consists of an ordered two-dimensional (2D) array of molecules which behave as 'zero dimensional' entities called quantum dots (QDs).

This system has exciting implications for fields such as computer memory, light-emitting devices and quantum computing.

The School of Physics and Astronomy study shows that a single-component, self-assembled 2D array of the organic (carbon-based) molecule dicyanoanthracene can be synthesised on a metal, such that the charge state of each molecule can be controlled individually via an applied electric field.

"This discovery would enable the fabrication of 2D arrays of individually addressable (switchable) quantum dots from the bottom-up, via self-assembly, says lead author Dhaneesh Kumar.

"We would be able to achieve densities tens of times larger than state-of-the-art, top-down synthesised inorganic systems."


Quantum dots are extremely small - about one nanometre across (ie, a millionth of a millimetre).

Because their size is similar to the wavelength of electrons, their electronic properties are radically different to conventional materials.

In quantum dots, the motion of electrons is constrained by this extremely small scale, resulting in discrete electronic quantum energy levels.

Effectively, they behave as 'zero-dimensional' (0D) objects, where the degree of occupancy (filled or empty) of their quantised electronic states determines the charge (in this study, neutral or negative) of the quantum dot.

Ordered arrays of charge-controllable quantum dots can find application in computing memory as well as light-emitting devices (eg, low-energy TV or smartphone screens).

Arrays of quantum dots are conventionally synthesised from inorganic materials via top-down fabrication approaches. However, using such 'top-down' approaches, it can be challenging to achieve arrays with large densities and high homogeneity (in terms of quantum-dot size and spacing).

Because of their tunability and self-assembling capability, using organic (carbon-based) molecules as nano-sized building blocks can be particularly useful for the fabrication of functional nanomaterials, in particular well-defined scalable ensembles of quantum dots.


The researchers synthesised a homogeneous, single-component, self-assembled 2D array of the organic molecule dicyanoanthracene (DCA) on a metal surface.

The study was led by Monash University's Faculty of Science, with support by theory from the Monash Faculty of Engineering.

This atomic-scale structural and electronic properties of this nanoscale array were studied experimentally via low-temperature scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) (School of Physics and Astronomy, under Dr Agustin Schiffrin). Theoretical studies using density functional theory supported the experimental findings (Department of Material Science and Engineering, under A/Prof Nikhil Medhekar).

The researchers found that the charge of individual DCA molecules in the self-assembled 2D array can be controlled (switched from neutral to negative and vice versa) by an applied electric field. This charge state electric-field-control is enabled by an effective tunneling barrier between molecule and surface (resulting from limited metal-adsorbate interactions) and a significant DCA electron affinity.

Subtle, site-dependent variations of the molecular adsorption geometry were found to give rise to significant variations in the susceptibility for electric-field-induced charging.
Electric field control of molecular charge state in a single-component 2D organic nanoarray was published in ACS Nano. (DOI: 10.1021/acsnano.9b05950 )

As well as funding from the Australian Research Council (Centres of Excellence and Future Fellowship programs), the authors acknowledge the support of the Monash high-performance computing cluster, the National Computing Infrastructure (NCI) and the Pawsey Supercomputing Facility.

ARC Centre of Excellence in Future Low-Energy Electronics Technologies

Related Quantum Dots Articles:

Towards high quality ZnO quantum dots prospective for biomedical applications
Scientists from Warsaw together with colleagues from Grenoble have moved a step closer to creating stable, high quality colloidal zinc oxide quantum dots (ZnO QDs) for use in modern technologies and nanomedicine.
Controlling the charge state of organic molecule quantum dots in a 2D nanoarray
Australian researchers have fabricated a self-assembled, carbon-based nanofilm where the charge state (ie, electronically neutral or positive) can be controlled at the level of individual molecules.
Modified quantum dots capture more energy from light and lose less to heat
Los Alamos National Laboratory scientists have synthesized magnetically-doped quantum dots that capture the kinetic energy of electrons created by ultraviolet light before it's wasted as heat.
Using quantum dots and a smartphone to find killer bacteria
A combination of off-the-shelf quantum dot nanotechnology and a smartphone camera soon could allow doctors to identify antibiotic-resistant bacteria in just 40 minutes, potentially saving patient lives.
Synthesizing single-crystalline hexagonal graphene quantum dots
A KAIST team has designed a novel strategy for synthesizing single-crystalline graphene quantum dots, which emit stable blue light.
US Naval Research Laboratory 'connects the dots' for quantum networks
Researchers at the US Naval Research Laboratory developed a novel technique that could enable new technologies that use properties of quantum physics for computing, communication and sensing, which may lead to 'neuromorphic' or brain-inspired computing.
Quantum rebar: Quantum dots enhance stability of solar-harvesting perovskite crystals
Engineering researchers have combined two emerging technologies for next-generation solar power -- and discovered that each one helps stabilize the other.
2D gold quantum dots are atomically tunable with nanotubes
Gold atoms ski along boron nitride nanotubes and stabilize in metallic monolayers.
Graphene quantum dots for single electron transistors
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, which combines the fabrication procedures of planar and vertical heterostructures in order to assemble graphene-based single-electron transistors of excellent quality.
Quantum dots can spit out clone-like photons
MIT and ETH Zurich researchers have produced coherent single photon emitters, a key component for future quantum computers and communications systems.
More Quantum Dots News and Quantum Dots Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Accessing Better Health
Essential health care is a right, not a privilege ... or is it? This hour, TED speakers explore how we can give everyone access to a healthier way of life, despite who you are or where you live. Guests include physician Raj Panjabi, former NYC health commissioner Mary Bassett, researcher Michael Hendryx, and neuroscientist Rachel Wurzman.
Now Playing: Science for the People

#543 Give a Nerd a Gift
Yup, you guessed it... it's Science for the People's annual holiday episode that helps you figure out what sciency books and gifts to get that special nerd on your list. Or maybe you're looking to build up your reading list for the holiday break and a geeky Christmas sweater to wear to an upcoming party. Returning are pop-science power-readers John Dupuis and Joanne Manaster to dish on the best science books they read this past year. And Rachelle Saunders and Bethany Brookshire squee in delight over some truly delightful science-themed non-book objects for those whose bookshelves are already full. Since...
Now Playing: Radiolab

An Announcement from Radiolab