What are quantum dots?
Quantum dots, or QDs, are semiconductor nanoparticles or nanocrystals, usually in the range of 2-10 nanometers (10-50 atoms) in size. Their small size and high surface-to-volume ratio affects their optical and electronic properties and makes them different from larger particles made of the same materials. Quantum dots confine the motion of conduction band electrons, valence band holes, or excitons (bound pairs of conduction band electrons and valence band holes) in all three spatial directions. Quantum dots are also sometimes referred to as ‘artificial atoms’, a term that emphasizes that they are a single object with bound, discrete electronic states, similarly to naturally occurring atoms or molecules.
Many types of quantum dot are fluorescent - they emit light of specific frequencies if electricity or light is applied to them. These frequencies can be tuned by changing the dots' size, shape and material, opening the door to diverse applications. Generally speaking, smaller dots appear blue while larger ones tend to be more red. Specific colors also vary depending on the exact composition of the QD.
Thanks to their highly tunable properties, QDs are attracting interest from various application developers and researchers. Among these potential applications are displays, transistors, solar cells, diode lasers, quantum computing, and medical imaging. Additionally, their small size enables QDs to be suspended in solution, which leads to possible uses in inkjet printing and spin-coating. These processing techniques may result in less-expensive and less time consuming methods of semiconductor fabrication.
Quantum dots are considered especially suitable for optical applications, thanks to their ability to emit diverse colors, coupled with their high efficiencies, longer lifetimes and high extinction coefficient. Their small size also means that electrons do not have to travel as far as with larger particles, thus electronic devices can operate faster. Examples of applications that take advantage of these electronic properties include transistors, solar cells, quantum computing, and more. QDs can greatly improve LED screens, offering them higher peak brightness, better colour accuracy, higher color saturation and more.
QDs are also very interesting for use in biomedical applications, since their small size allows them to travel in the body, thus making them suitable for applications like medical imaging, biosensors, etc.
What is graphene?
Graphene is a material made of carbon atoms that are bonded together in a repeating pattern of hexagons. Graphene is so thin that it is considered two dimensional. Graphene's flat honeycomb pattern gives it many extraordinary characteristics, such as being the strongest material in the world, as well as one of the lightest, most conductive and transparent. Graphene has endless potential applications, in almost every industry (like electronics, medicine, aviation and much more).
The single layers of carbon atoms provide the basis for many other materials. Graphite, like the substance found in pencil lead, is formed by stacked graphene. Carbon nanotubes are made of rolled graphene and are used in many emerging applications from sports gear to biomedicine.
Graphene quantum dots
The term graphene quantum dots (GQDs) is usually used to describe miniscule fragments, limited in size, or domains, of single-layer to tens of layers of graphene. GQDs often possess properties like low toxicity, stable photoluminescence, chemical stability and pronounced quantum confinement effect, which make them attractive for biological, opto-electronics, energy and environmental applications.
The synthesis of graphene quantum structures, such as graphene quantum dots, has become a popular topic in recent years. While graphene usually does not have a bandgap - which is a problem for many applications - graphene quantum dots do contain a bandgap due to quantum confinement and edge effects, and that bandgap modifies graphene's carrier behaviors and can lead to versatile applications in optoelectronics. GQDs were also found to have four quantum states at a given energy level, unlike semiconductor quantum dots, which have only two. These additional quantum states, according to researchers, could make GQDs beneficial for quantum computing.
Additional properties of GQDs such as high transparency and high surface area have been proposed for energy and display applications. Because of the large surface area, electrodes using GQDs are applied for capacitors and batteries.
Various techniques have been developed to produce GQDs. Top-down methods include solution chemical, microwave, and ultrasonic methods. Bottom-up methods include hydrothermal and electrochemical methods.
The latest graphene quantum dots news:
Dotz Nano reports a successful pilot trial for its graphene-based quantum dots anti-counterfeiting system
Dotz Nano recently reported a successful industrial production pilot to mark special packages with its advanced marker named ValiDotz, to prevent counterfeiting of top brands in China.
The production pilot was performed together with Kecai Printing Company (a subsidiary of Brilliant Circle Holding International Limited, the industry leader in China's cigarette packaging industry), at their top-tier Shenzhen facilities, and its results were deemed as a success.
Green Science Alliance, part of the Fuji Pigment corporation, has created graphene quantum dot inkjet ink. The prepared graphene quantum dot inkjet ink can be printed on various types of substrates including regular paper and films.
The ink is invisible under normal room light and becomes visible when lit by specific light types. In addition, emission spectra peak will be different depending on the different wavelength of illuminated light, which can be useful for anti-counterfeiting applications.
Dotz Nano has secured a “firm purchase order” for 10 kilograms of its graphene quantum dots product called Validotz. According to Dotz Nano CEO Dr Moti Gross, the purchase order represents the company’s “transition from R&D to a commercially orientated company as it moves our Validotz into the realm of industrial sectors.”
Validotz are graphene quantum dots made from plain and simple coal for use in optical, medical imaging, bio-med, sensing, electronic, photovoltaic and monitoring applications. According to Dotz Nano, in contrast to classic silicon quantum dots, the alternative graphene-based dots are biocompatible, photostable and inherit superior thermal, electrical, and mechanical properties.
Two novel 2D materials, graphene and hexagonal boron nitride, and the tip of a scanning tunneling microscope – these were the ingredients used to create a novel kind of a so-called “quantum dot”. These extremely small nanostructures allow delicate control of individual electrons by fine-tuning their energy levels directly. Such devices can be key for modern quantum technologies.
The theoretical simulations for the new technology were performed at TU Wien. The experiment involved RWTH Aachen and the team around Nobel-prize laureates Andre Geim and Kostya Novoselov from Manchester who prepared the samples.
Dotz Nano is now planning to sell its graphene quantum dots into Australia and New Zealand after entering an exclusive distribution agreement with Australia-based Recochem. The agreement between the companies allows for a five-month evaluation period where the companies can explore each other’s performance in the regions’ markets, with a comprehensive agreement to be finalized by June.
Under the initial MoU, Dotz Nano will provide Recochem with samples of its graphene quantum dots for numerous applications, with sales terms to be agreed on a customer-by-customer basis.