Development of nano-alloyed CdTeS quantum dots via two-phase synthesis method

Abstract

The 20th century was called as the golden age for the science since the significant discoveries that is going to affect human life was made in that century. The science around that time opened the new gate to the mysterious world that humankind had been take advantage of it without even realizing but they had never been able to discover. The humankind had tried to explore and investigate the unfamiliar materials which came from especially nano scale at that time. The new characterization techniques like X-ray lead to finding of properties of these novel materials which is not visible to human eye. They have only from 1 to 100 nm dimensions, however; their surface and physical properties are way better than bulk materials that no one can argue. Therefore, since then the interest to the nano science have been increased day by day. And this new world has named as nanomaterials for last 30 years. The main cause for unique properties of nanomaterials comes from the confinement of electrons which bulk materials don't display. As a result of the confinement, discrete energy levels are formed due to interaction between valance and conjugation band under Bohr radius. On other words, it can be said that electrons have no freedom to move in nano dimension, their motion is confined. One type of the quantum nanostructures are zero-dimensional materials which named after restriction in all dimensions. Quantum dots which is zero-dimensional nano structure displays exclusive physical properties like high photoluminescence, wide adsorption and narrow emission. QDs in other words semiconductor nanocrystals, which synthesized for the first time in 1981 by Ekimov and was took its name in 1984, used 2000 years ago by Romans and Greeks and due to its discrete energy levels in their structure, they also are named as artificial atoms. Besides the discrete energy levels in QDs, high surface-to-volume-ratio properties makes them ideal candidate from diagnostic to photovoltaic cells. Their adsorption wavelength is broad from infrared to ultraviolet which means different size of the QDs can be excited with the same wavelength. At the same time, they have narrow emission wavelength that are altered with QDs' size and composition. In other words, QDs can emit different kind of wavelength with the same composition by changing the size. They are generally composed of II-VI and III-V elements from periodic table. Among these properties, QDs are more stable and brighter than organic dyes. As the properties of these nanomaterials have been understood, the attraction for these materials have increased especially last 20 year. There has been more attempt to use it for treatment, diagnosis of illness and for the solar cells to increase efficiency of photovoltaic cells. According to application area, different types of QDs, having diverse size, composition and structures, can be desired which is achievable with the help of the different types of the fabrication techniques. However, the main challenge part is to fabricate them effectively under the mild conditions without giving harm to the nature. Today, the manufacture methods are divided into two parts: top-down and bottom-up. Both have its own advantages and drawbacks. Bottom-up methods mean the self-assembly of the atom or molecules to constitute desired structure. Self-assembly is the key part of these methods. Method starts with the nucleation and goes on with the self-assembly and when the free energy reaches the maximum level, the production finishes.