ABSTRACT Quantum dots remain as one of the smallest semiconductor nanocrystals which made of many of the same materials as ordinary semiconductors ranging in size of 2-10 nanometers.
They are very nearly zero-dimensional. This research attempted to explain clearly and briefly what is quantum dots, what are its application and how the wavelength is associated and connected with quantum dots. The information was collected through research, in written journals and other books and references that is inlined with quantum dots. The study highlights the importances and applications of quantum dots, its types and properties and how quantum dots work.
Based on this research study, it was concluded that quantum dots can be applied in different ways mostly in chemical reaction in a solution and also yield to important applications in the fields of technology and medicine. It also have band gaps that are tunable across a wide range of energy levels by changing its size as it come up with the quantum dots’ color changing phenomenon which make the colors brighter and more attractive. Also, it also resulted to a conclusion that the bigger the quantum dot, the larger its wavelength and smaller its frequency but on the other hand, the color of light given off is not related to the material used in the quantum dots. OBJECTIVES 1. To know what is Quantum Dots. 2. To determine how Quantum Dots are applied in the community 3. To determiner how wavelength is associated with Quantum Dots. INTRODUCTION The normal behavior of matter is much harder to explain as we enter the quantum world We normally consider the color of a chemical substance to be an intensive property because the color does not depend on the amount of the substance that is being considered.
Quantum dots are tiny pieces of matter which is composed of a metal or a semiconductor. The allowed energies of these electrons are quantized as it confined in a small volume. The energy of light omitted from a quantum dot can be tuned by varying the size of the quantum dot because the volume changes as the electrons confined. This phenomenon is due to the wavelike behavior of electrons and is analogous to changing its frequency.
It is quite remarkable to regulate the energy of light the quantum dots can emit as it enable one to generate the visible spectrum using a single chemical substance by varying the size of the quantum dots. Quantum dots also yield to different important applications in the fields of technology and medicine. As it emit light of different colors, it is possible to create devices that produce white light at much lower energy costs than required for incandescent bulbs or even fluorescent bulbs that carry an additional environmental concern as it contain mercury. Quantum dots can also be used to label biological issue as the surface of quantum dots can be chemically and biologically modified to target certain cells such as cancer cells.
In addition, these modified quantum dots have the added potential to act therapeutically. Other potential applications for quantum dots include quantum computing and photovoltaic cells for harvesting solar energy. Quantum dots were created in the early 1980’s. These are nanoparticles of semiconductors that glows a specific color after being illuminated by light. The quantum dots glow a specific color depending on its size. Meaning, that the amount of energy (which is related to wavelength) affects the color that the quantum dots glow.
Quantum dots of semiconductors, metals, and metal oxides have been at the forefront of research recently due to their novel electronic, optical, magnetic, and catalytic properties. The number of atoms in a quantum dot range from 1000 -100 000 which is made up of neither an extended solid structure and a single molecular entity that led to different names attributed to such materials, like nanocrystals and artificial atoms. To date, chemistry, physics, and materials science have provided methods for the production of quantum dots and allow tighter control of factors affecting, for example, particle growth and size, solubility and emission properties. Who invented quantum dots? Alexei Ekimov, a Russian physicist, discovered quantum dots in solids (glass crystals) way back 1980 while working at the Vavilov State Optical Institute. In 1982, an American chemist Louis E.
Brus, who is working at Bell Laboratories, also discovered the same phenomenon in colloidal solutions where in small particles of one substance are dispersed throughout another. He also find out that the wavelength of light emitted or absorbed by a quantum dot changes over a period of days as the crystal grow. The confinement of electrons that gives the particle quantum properties was also distingushed. Their pioneering work lead them to have that award entitled “Optical Society of America’s 2006 R.W. Wood Prize” How are Quantum Dots made? Quantum dots are precise crystals which are made of many of the same materials as ordinary semiconductors mainly the combinations of transition metals and/or metalloids.
They quantum dots extremely small in which it size ranges from 2-10 nanometers. Typical methods iin making quantum dots include Colloidal Synthesis, Plasma Synthesis, Electron Beam Lithography, and Molecular Beam Epitaxy. 1. Colloidal Synthesis of Quantum Dots (III-V semiconductors and II-VI semiconductors) ? Colloidal synthesis is a solution-based chemical process which is also one of the cheapest methos and is able to occur at inmost conditions for synthesizing quantum dots. This involves heating precursor solutions to form nucleated monomers. The size and volume of the quantum dots produced through this process is controlled by regulating the concentration of monomers in a solution while maintaining precise temperature conditions. Additionally, this method can be used to create many quantum dots all at once.
2. Plasma Synthesis of Quantum Dots ? Plasma synthesis is a non-thermal gas-phase process which is used to formulate powder-based quantum dots. This produced nanocrystals which uses high-temperature synthesis methods. There are study that suggest that the plasma synthesis of nanoparticles can be improved by doing another process to produced quantum dots which enables it to have further functionalities. Those quantum dots that are produced by these method is mostly composed of metallic compounds such as Cadmium selenide (CdSe) and Indium phosphide (InP) 3. Electron Beam Lithography ? A suitable etching process is used in this method wherein a pattern is etched by the use of an electron beam device and a semiconducting material is deposited onto it.
The electron beam device which is used in this method convert the components into quantum dots in a very small points. However, this method needs a high effort and is somewhat result to poor reproducibility. 4. Molecular beam epitaxy ? In this method, III-V semiconductors is used to produced quantum dots wherein a thin layer of crystals can be produced when the constituent elements are heated separately and then vaporized simultaneously which allow them to react on a water surface. Alternatively, they can also be produced quantum dots by using a gas phase deposition.
In addition, the quantum dots in this method are created directly on the substance acted upon required for an application. How do quantum dots work? Electrons are energized and move on its excited state when an energy is applied to an atom. And as the electron returns to its lower and stable state, it emits an additional energy Quantum dots work the same way as those electrons but a quantum dot crystal acts as one huge atom. Ultraviolet light is also used as an energy source to stimulate a quantum dot.
The frequency or color of light release by is related to the size of the quantum dot but is not connected to the material it used. Why are Quantum Dots called Artificial Atoms? Just like in an atom, where the electrons can only evolve and goes in the nucleus on certain orbits, electrons in these quantum dots are forced into discrete quantum states. Quantum dots are called an artificial atoms as it absorb and re-emit light in pure colors as it considered as one of the photo-active semiconductor. The dots it emit is determined by their size – bigger dots give-off red light while smaller dots produce blue. There are different ways of creating artificial atoms: The simplest one is putting electrons into tiny flakes then cutting it out in a a thin layer of the material.
At the same time, the electrons are forced into tiny circular orbits by applying a magnetic field as Libisch explained that if we would only use an electric field, the effects of the quantum allow the electrons to quickly escape on the trap. With regard to this topic, the new artificial atoms now open up new possibilities for many quantum technological experiments: Four localized electron states with the same energy allow for switching between various quantum states for information to store as Joachim Burgdörfer said. The electrons can preserve arbitrary superpositions in a span of a long period of time. In addition, it should be possible to fit many such artificial atoms on a small chip in order to use them for quantum information applications.
Types of Quantum Dots 1. Core-Type Quantum Dots ? Quantum dots can be single component materials that have a uniform internal compositions, such as chalcogenides (selenides, sulfides or tellurides) of metals like cadmium, lead or zinc, example, CdTe. The photo- and electroluminescence properties of core-type nanocrystals can be fine-tuned by simply having a change of the size of the crystallite. 2. Core-Shell Quantum Dots ? The gleam properties of quantum dots turn out from the recombination of electron-hole pairs (exciton decay) through radiative pathways. However, the exciton decay can also occur through nonradiative methods, reducing the illuminescence quantum yield.
One of the methods used to enhance the efficiency and brightness of semiconductor nanocrystals is raising shells of another higher band gap semiconducting material around them. These quantum dots with small regions of one material immerse in one another with a wider band gap known as core-shell quantum dots (CSQDs) or core-shell semiconducting nanocrystals (CSSNCs). 3. Alloyed Quantum Dots ? Changing the size of the crystallite while having the ability to tune optical and electronic properties has become a hallmark of quantum dots. But tuning optical may cause problems with size restrictions in many applications. There is an alternative method to tune properties without changing crystallite size as the multicomponent quantum dots offers.
Alloyed semiconductor quantum dots with both homogeneous and gradient internal structures allow tuning of the optical and electronic properties by merely having a change on the composition and internal structure without changing the size of the crystallite ? Alloying combined two semiconductors with different band gap energies which formed alloyed semiconductor quantum dots exhibited interesting properties distinct. Thus, an additional composition-tunable properties aside from the properties that emerge due to quantum confinement effects and novel were possessed by alloyed nanocrystals. Properties of Quantum Dots The peculiar size and composition tunable electronic property of these very tiny, semiconducting quantum dots make them very useful in a different varieties of applications and new technologies. Quantum dots are particularly expressive for applications in opticals owing the bright, and pure colors along with their ability to emit rainbow of colors together with their high efficiencies, longer lifetimes and high extinction coefficient. LEDs and solid state lighting, displays and photovoltaics are some example. Being zero dimensional, it have a sharper density of states than higher-dimensional structures.
Their small size also means that electrons do not have to travel as far as with larger particles wherein electronic devices can operate faster. Examples of applications having an huge benefit of these unique electronic properties include solar cells, transistors, ultrafast logic gates and all-optical switches, and quantum computing, among many others. Additionally, the small size of the quantum dots allow them to go anywhere in the body making them suitable for different bio-medical applications like biosensors, medical imaging, etc. Today, biosensors-based fluorescence depends on organic dyes with a broad spectral width, which limits their effectiveness to a small number of colors and shorter lifetimes to tag the agents. On the other hand, quantum dots can emit the whole spectrum brighter and having a bit degradation over time thus proving them superior to traditional organic dyes used in the applications of biomedical.