Superstructures from lead sulfide quantum dots
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Superstructures from lead sulfide quantum dots Elena V. Ushakova1, Valery V. Golubkov2, Aleksandr P. Litvin1, Peter S. Parfenov1, Sergei A. Cherevkov1, Anatoly V. Fedorov1, Alexander V. Baranov1 1
ITMO University, 49 Kronverkskiy pr., Saint-Petersburg, 197101, Russia
2
Institute of Silicate Chemistry of Russian Academy of Sciences, 2 Adm. Makarova emb., SaintPetersburg, 199034, Russia ABSTRACT The superstructures of different morphology (superlattices and supercrystals) are obtained by self-organization of lead sulfide quantum dots (QDs) on a substrate. In contrast to the SAXS patterns of isolated QDs in solutions, the X-ray intensity from ordered superstructures is modulated by the interference from the QDs in SLs or SCs leading to occurrence of the intense peaks at small scattering angles. By indexing the peaks in the SAXS patterns it is concluded that QD SLs are close-packed QD ensembles with the lattice parameter close to the dot diameter and QD SCs have primitive orthorhombic crystal lattice. Absorption and photoluminescence bands of superstructures are also analyzed. INTRODUCTION The formation of novel materials with complicated morphology can be reached by means of self-assembly of nanoparticles (NPs), for instance the material assembly on macromolecule patterns and masks and particle self-assembly on substrates or phase boundaries [1, 2]. These methods are used to obtain the 2D and 3D superstructured materials also named as superlattices (SLs) and supercrystals (SCs). Varying the NP type, evaporation rate of the NP colloidal solution and the type of a substrate one can achieve a variety of morphologies of the obtained superstructured materials. Therefore, it will open an opportunity to control and improve optical and electrical properties of such a novel materials. Colloidal lead-sulfide (PbS) QDs are a promising class of narrow-band semiconductors, suitable for a variety of applications, since they possess remarkable properties, including large extinction coefficients, small effective masses of electrons and holes, the possibility of multiexciton generation and a large overlap of the absorption spectrum with the solar radiation spectrum, and hot carrier extraction[3]. Control of the properties of PbS QD superstructures is the key to a variety of novel applications in fields of electronics, optics and photovoltaics [4, 5]. Via controlled PbS QDs self-assembly on the substrates the quantum dot solids, combining the advantages of QD size-dependent energy levels and rapid charge transport due to enhanced electronic coupling between QDs, can be obtained and successfully used in near-IR photovoltaic applications. Despite intensive research, practical applications based on QD superstructured materials remain a future ambition, rather than a present reality. The limited ability to control over the lattice parameters, such as the distance between the QDs and the symmetry of the ordered dot ensembles, is the obstructive factor to the design of nanostructured materials technologies. The process of dot self-assembly
