Clusters are collections of atoms lying between individual atoms/molecules and bulk materials. In some materials, certain collections of atoms are more preferred due to energy minimization and exhibiting stable structures and providing unique properties to the materials. These collections of atom providing stable structures to the materials are called as MAGIC NUMBER. For example, one of the combination of 55 atoms of gold provides stable structure and hence its magic number is 55
What is cluster in nanotechnology?
Clusters are small aggregates of atoms and molecules. Small means really tiny pieces of matter—they are composed of a few to thousands of units and have a diameter of nanometers. Nanoclusters have at least one dimension between 1 and 10 nm and a narrow size distribution. Nanoclusters are composed of up to 100 atoms, but bigger ones containing 1000 or more are called nanoparticles.
What are nanoclusters used for?
Nanoclusters have potential uses in chemical reactors, telecommunications, microelectronics, optical data storage, catalysts magnetic storage, spintronic devices, electroluminescent displays, sensors, biological markers, switches, transducers and many other fields. The florescence silver nanoclusters have been extensively used as biological markers for photodynamic therapy.
What are metal nanoclusters?
Metal nanoclusters (NCs) are composed of a small number of atoms, up to dozens. These nanoclusters can consist of a single element or multiple elements, usually smaller than 2 nm. Compared with their larger counterparts, this nanocluster exhibits attractive electronic, optical and chemical properties. These particles have quasi-continuous energy levels and display intense colors due to surface plasmon resonance. If their dimension is further reduced to the size approaching the Fermi wavelength of electrons, the band structure becomes discrete energy levels. The ultrasmall metal nanoparticles display molecule-like properties and no longer exhibit plasmonic behavior. Metal NCs, such as AuNCs, AgNCs, CuNCs, and PtNCs, exhibit a marked photoluminescence property due to quantum confinement. The most studied among these metal NCs are AuNCs, AgNCs, and CuNCs.
What are gold nanoclusters?
Nanocluster are collective groups composed of a specific number of atoms or molecules held together through a certain interaction mechanism. Gold nanoclusters attract increasing attention due to their potential applications in sensing, catalysis, optoelectronics, and biomedicine.
How are gold nanoclusters made?
In one example, green-emitting gold nanoclusters could be prepared by adding mercaptoundecanoic acid (MUA) into small AuNP solutions prepared by the reduction of HAuCl4 with tetrakis(hydroxymethyl)phosphonium chloride (THPC).
Size
Nanoclusters: Typically have at least one dimension between 1–10 nanometers (nm).
Quantum dots: Typically have a diameter of 2–10 nm.
Composition
Nanoclusters: Made up of up to 100 atoms, but larger ones can contain 1000 or more atoms.
Quantum dots: Made of a semiconducting material.
Properties
Nanoclusters: Have strong fluorescence emission, good photostability, and high conductivity.
Quantum dots: A type of semiconductor nanocrystal.
Nanocomposites
Composite materials are prepared from the combination of two or more different materials with distinct chemical or physical characteristics. The resultant composite exhibits properties which are superior to its constituent materials.
Nanocomposites are broad range of materials consisting of two or more components, with at least one component having dimensions in the nm range (i.e. between 1 and 100 nm)
Nanocomposites consist of two phases (i.e nanocrystalline phase + matrix phase)
Nanocomposite means nanosized particles (i.e metals, semiconductors, dielectric materials, etc) embedded in different matrix materials (ceramics, glass, polymers, etc).
Nanocomposites differ from traditional composites in the smaller size of the particles in the matrix materials.
Classification:
nanocomposites can also be classified into three categories based on the matrix material type:
Polymer-matrix Nanocomposites - These nanocomposites are made from polymer matrix materials such as thermoplastic, thermoset polymers, layered silicates, and polyester
Ceramic-matrix Nanocomposites - These nanocomposites are made from ceramic matrix materials such as Al2O3 or SiC.
Metal-matrix Nanocomposites - These nanocomposites are made from a ductile metal or alloy matrix with nanosized reinforcement material.
Prepration:
Synthetic methods are commonly employed to prepare nanocomposites, such as lamination, soft lithography, solution casting, and spin-coating. Homogenous nanoparticle dispersion is a primary challenge during preparation. Dispersion affects phase interfaces and the final nanocomposite properties.
Different materials, structures, and compositions allow for fine-tuning of nanocomposite properties, such as electrical, mechanical, thermal, acoustical, and magnetic properties. Nanocomposites have given rise to the field of multifunctional materials.
Application Areas
Application areas in the automotive industry include engine covers, intake manifolds, door handles, mirror housings, and timing belt covers in various vehicle types. Applications in other commercial areas include vacuum impellers and blades, mower hoods, mobile phone covers, and power tool housings.
Nanocomposites in Food Packaging
Nanoclays, which are added to,polypropylene or polylactic acid packaging films, prevent the diffusion of oxygen or flavorings and thus prolong the shelf life of foods. Nanosilver has an antimicrobial effect and can be used in plastics composites, for example to manufacture food packaging such as films or containers to protect food from spoilage.
This post deals with Quantum dots, a new class of materials
that is neither molecular nor bulk. They have the
same structure and atomic composition as bulk
materials, but their properties can be tuned using
a single parameter, the particle’s size.
What is a quantum dot?
Quantum dots are tiny crystals of semiconducting material. The crystals are so small – just a few nanometers wide (diameter of 2–10 nm) – that their physical size actually confines the electrons in the material to the point that it changes their behaviour. This means that quantumphenomena determine the properties of these tiny crystals – hence the name quantum dots.
Changing the size of the particle changes its properties in a predictable way. This effect can be used to tune the band gap of the semiconductor so that dots emit different colours of light when illuminated by a single-wavelength source – smaller dots (e.g., 2-3 nm) providing higher energy emissions will emit blue light, while larger ones (e.g., 5-6 nm) providing lower energy emissions emit at the red end of the visible spectrum. This property is sometimes referred to as “quantum confinement.
Like other semiconductors, quantum dots tend to be made of combinations of transition metal and metalloid elements. Cadmium selenide and cadmium telluride are among the most regularly used materials.
Quantum Dot Production
There are various methods of producing quantum dots. The most typical is via a colloidal synthesis, which is the process of heating a solution, causing the precursors to decompose to form monomers, which then produce nanocrystals.
Quantum dots produced using this method can consist of compounds including indium arsenide, lead sulfide, lead selenide, and cadmium sulfide. Colloidal synthesis is a popular method as quantum dots can be produced in batches large enough to be potentially used for commercial applications.
Plasma synthesis is another popular technique for the production of quantum dots. This process enables the control of the composition, surface, size, and shape of the quantum dot, and it also reduces the challenges associated with doping.
Not every nanoparticle is a quantum dot. Only some materials (such as semiconductors) will show quantum size effects in their electronic structure when they are made into nanoscale particles.
Working Principle of a Quantum Dot
Within a quantum dot, there are confined valence band holes, conduction band electrons, or excitons. These are the particles that carry the electricity, and because of this confinement, the quantum dot has a distinct energy level. The optical absorption and emission of CdSe quantum dots can be tuned across nearly the entire visible range of the optical spectrum. This is possible because the energy bandgap of CdSe quantum dots varies between 1.8 eV (its bulk value) to 3 eV (in the smallest quantum dots)
Applications:
One of their most widely known uses is in forming the basis QLED television screens recognized as the “Q” in QLED TVs. where dots of different sizes are excited by blue light and then emit pure red and green light to give the three-colour output of the pixels in a TV screen. But they also have uses in biotechnology, catalysis, sensors, solar cells and more. In particular, the Nobel committee highlighted the use of quantum dots in medical devices that are used to map biological tissue because the dots’ fluorescence is brighter and longer-lived than that of other fluorescent tags such as molecular fluorophores. This means they can help to guide surgeons when removing tumours, for example.
