Colloidal quantum structures

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This research programme has two broad overall goals in mind. The first is to develop new quantum dots and rods for deep-tissue optical imaging with high spatial resolution. Deeper light penetration is expected for near-infrared light in the range of 700-1,300 nm, because this light is absorbed and scattered less than UV-Vis light. To this end, initially water-dispersible near-infrared emitting PbS(e)-CdS(e) core-shell quantum dots and rods will be synthesized with high quantum yield of photoluminescence and high (photo-)stability. They will be tested by imaging the blood capillaries in brains of sedated mice, with the aim to go deeper that the standard 600 µm without losing the optical resolution. Quantum rods send out polarised photoluminescence after excitation with polarised light. This anisotropy will be used to study slow (biological) processes, where current optical probes do not perform because their excited lifetimes are too short (nanoseconds) and their tumbling times too fast (picoseconds). The quantum rods have excited state lifetimes of 1-2 µs and tumbling times of ~20 ns at room temperature in colloidal solution, so in principle one has a 5-10 µs time window. Alternatives are also proposed based on abundant and relatively non-toxic elements, e.g. CuFeS2. There are no colloidal syntheses of these reported that have the required size (5-10 nm) and size dispersion control (<5%), and water dispersibility. The second overall goal, and highly risky because there are no precedents in the literature, is the development of colloidal synthesis routes of half-metals. Half-metals have a band structure such that only electrons with a spin up (or spin down) can be conducted, which makes them very interesting for spintronics because they have potentially 100% spin-polarised current. Several different classes of half-metals are being proposed, with the (half-)Heusler compounds being an important class. These (half-)Heusler compounds are ternary alloys that are difficult to make, because their phase diagrams are complicated and not yet fully understood. Besides the new nanomaterials that this programme will generate, it will no doubt have new physical chemistry because quantum size effects are composition, size, and shape dependent.