Quantum dots by ultraviolet and x-ray lithography

Abstract

Highly luminescent semiconductor quantum dots have been synthesized in porous materials with ultraviolet and x-ray lithography. For this, the pore-filling solvent of silica hydrogels is exchanged with an aqueous solution of a group II metal ion together with a chalcogenide precursor such as 2-mercaptoethanol, thioacetamide or selenourea. The chalcogenide precursor is photodissociated in the exposed regions, yielding metal chalcogenide nanoparticles. Patterns are obtained by using masks appropriate to the type of radiation employed. The mean size of the quantum dots is controlled by adding capping agents such as citrate or thioglycerol to the precursor solution, and the quantum yield of the composites can be increased to up to about 30% by photoactivation. Our technique is water-based, uses readily available reagents, and highly luminescent patterned composites are obtained in a few simple processing steps. Polydispersity, however, is high (around 50%), preventing large-scale usage of the technique for the time being. Future developments that aim at a reduction of the polydispersity are presented.

Smart nanocarrier-based drug delivery systems for cancer therapy and toxicity studies: A review

“…To synthesize QDs, either a top-down approach or a bottom-up method can be employed. Molecular beam epitaxy (MBE) [158] , ion implantation, e-beam lithography and X-ray lithography [159] belong to top-down processing; on the other hand, colloidal QDs are prepared by self-assembly in solution following chemical reduction, which is a bottom-up approach [160] .…”

Studies on Lead Sulfide (PbS) Semiconducting Thin Films Deposited from Nanoparticles and Its NLO Application

“…However, as the surface to volume ratio is large in the case of nanostructure materials, it is possible to observe SP mode by Raman scattering measurements. [34][35][36] The Raman scattering is sensitive to small disorders, even at regions as small as few unit cells. Figure 8 shows the Raman spectra of PbS thin¯lms deposited at di®erent substrate temperatures (150 C, 250 C, 350 C and 450 C).…”

X-ray spectroscopy study of local microstructures in CdSe quantum dots prepared by UV photolithography

“…The metal and the chalcogenide precursors tend to react at room temperature even without irradiation. The solutions are refrigerated to avoid reacting at room temperature [22]. The Fig.…”

“…However, progress in this direction has been sluggish. Very recently, patterning of substrates with quantum dots was reported, and it was obtained with a bottom-up approach [21][22][23][24][25].…”

“…Further in colloidal QDs, there is no reason to worry about the environment as nanoparticles are formed in the liquid. In this study the particles are still grown using a chemical method [22] but on a substrate and we have succeeded in patterning with crystallizing clusters; a study of structural properties by X-ray absorption is worthy. The fluorescence extended x ray absorption fine structure method (EXAFS) is a powerful technique for investigating local structures around a specific element at even an extremely low concentration.…”