the main challenges has been growing uniform single crystals of bilayer or multilayer graphene over large areas; epitaxial growth and the new CVD (mentioned above) are among the new promising methods under investigation. Organic semiconducting single crystals are different from the inorganic crystals. The weak intermolecular bonds mean lower melting temperatures, and higher vapor pressures and greater solubility. For single crystals to grow, the purity of the material is crucial and the production of organic materials usually require many steps to reach the necessary purity. Extensive research is being done to look for materials that are thermally stable with high charge-carrier mobility. Past discoveries include naphthalene, tetracene, and 9,10-diphenylanthacene (DPA). Triphenylamine derivatives have shown promise, and recently in 2021, the single-crystal structure of α-phenyl-4′-(diphenylamino)stilbene (TPA) grown using the solution method exhibited even greater potential for semiconductor use with its anistropic hole transport property. Optical application Single crystals have unique physical properties due to being a single grain with molecules in a strict order and no grain boundaries. This includes optical properties, and single crystals of silicon is also used as optical windows because of its transparency at specific infrared (IR) wavelengths, making it very useful for some instruments. Sapphires: Better known as the alpha phase of aluminum oxide (Al2O3) by scientists, sapphire single crystals are widely used in hi-tech engineering. It can be grown from gaseous, solid, or solution phases. The diameter of the crystals resulting from the growth method are important when considering electronic uses after. They are used for lasers and nonlinear optics. Some notable uses are as in the window of a biometric fingerprint reader, optical disks for long-term data storage, and X-ray interferometer. Indium Phosphide: These single crystals are particularly appropriate for combining optoelectronics with high-speed electronics in the form of optical fiber with its large-diameter substrates. Other photonic devices include lasers, photodetectors, avalanche photo diodes, optical modulators and amplifiers, signal processing, and both optoelectronic and photonic integrated circuits. Germanium: This was the material in the first transistor invented by Bardeen, Brattain, and Shockley in 1947. It is used in some gamma-ray detectors and infrared optics. Now it has become the focus of ultrafast electronic devices for its intrinsic carrier mobility. Arsenide: Arsenide III can be combined with various elements such as B, Al, Ga, and In, with the GaAs compound being in high demand for wafers. Cadmium Telluride: CdTe crystals have several applications as substrates