Paul O’Brien

Quantum-dot concentrator and thermodynamic model for the global redshift

The use of quantum dots can turn the old concept of a luminescent solar collector into a practical concentrator. The quantum efficiency, tunability of absorption threshold, and size of the redshift make quantum dots an ideal replacement for the organic dyes whose performance limited this inexpensive technology. Progress in photovoltaic cells, in particular, the ability of quantum-well cells to tune the band gap, also suggests high efficiency is possible in solar and thermophotovoltaic applications. A thermodynamic model is used to show quantitatively how the separation of absorption and luminescent peaks under global illumination is related to the spread of quantum-dot sizes. Hence, the redshift can be determined during the growth process. The model can be used to optimize concentrator performance and to study the effect of reabsorption, which is important for high concentration even if the quantum efficiency is unity. This model provides a quantitative explanation for the contribution of the spread of sizes to the redshift, which should help in the extraction of the much smaller, single-dot effects.

Synthesis of PbS nanocrystallites using a novel single molecule precursors approach : X-ray single-crystal structure of Pb(S2CNEtPri)2

The synthesis and characterisation of some lead(ii) dithiocarbamato complexes Pb(S 2 CNRR′) 2 is reported. These compounds were used as single molecule precursors to produce nanocrystalline PbS by their thermolysis in trioctylphosphine oxide. The optical and morphological properties of the resulting PbS nanocrystallites were investigated; the influence of experimental parameters, such as precursor, growth time and temperature, on the final nanodispersed materials is also reported.

Tin(II) Sulfide (SnS) Nanosheets by Liquid-Phase Exfoliation of Herzenbergite: IV–VI Main Group Two-Dimensional Atomic Crystals

The liquid-phase exfoliation of tin(II) sulfide to produce SnS nanosheets in N-methyl-2-pyrrolidone is reported. The material is characterized by Raman spectroscopy, atomic force microscopy, lattice-resolution scanning transmission electron microscope imaging, and energy dispersive X-ray spectrum imaging. Quantum chemical calculations on the optoelectronic characteristics of bulk and 10-layer down to monolayer SnS have been performed using a quantum chemical density functional tight-binding approach. The optical properties of the SnS and centrifugally fractionated SnS nanosheet dispersions were compared to that predicted by theory. Through centrifugation, bilayer SnS nanosheets can be produced size-selectively. The scalable solution processing of semiconductor SnS nanosheets is the key to their commercial exploitation and is potentially an important step toward the realization of a future electronics industry based on two-dimensional materials.

Recent advances in the preparation of semiconductors as isolated nanometric particles: new routes to quantum dots

Nanoparticles of semiconductor materials have been the subject of intense research in the last five years owing to the novel electronic, catalytical and optical properties observed in such materials. The unusual properties of these so called quantum dots can be attributed to two main factors: the large surface to volume ratio of atoms and the confinement of charge carriers in a ‘quantum mechanical box’. Small particles of semiconductors have been prepared by a number of routes, often using colloidal chemistry methods but more recently using organometallic routes. The recent advances have resulted in high quality nanoparticles which have been incorporated into simple devices. In this article we cover some of the key advances in the preparation of nanometric particles of semiconductors. The cover illustration depicts three sizes of TOPO capped CdSe.

Synthesis and X-ray single crystal structures of bis(diisobutyldithiophosphinato)cadmium(II) or zinc(II): Potential single-source precursors for II/VI materials

Abstract Bis(diisobutyldithiophosphinato)cadmium(II) (1) and bis(diisobutyldithiophosphinato)zinc(II) (2) have been synthesised and their X-ray single crystal structures determined. Both compounds have been used as precursors to grow thin films of CdS and ZnS, respectively, by low-pressure metal organic chemical vapour deposition (LP-MOCVD).

Cross-linking Bi2S3 ultrathin nanowires: a platform for nanostructure formation and biomolecule detection.

This paper describes the use of chemical cross-linking of ultrathin inorganic nanowires as a bottom-up strategy for nanostructure fabrication as well as a chemical detection platform. Nanowire microfibers are produced by spinning a nanowire dispersion into a cross-linker solution at room temperature. Nanomembranes with thicknesses down to 50 nm were obtained by injecting the nanowire dispersion at the cross-linker-solution/air interface. Furthermore, the sensitivity of the nanowire to amine cross-linkers allowed development of a novel sensing platform for small molecules, like the neurotransmitter serotonin, with detection limits in the picomolar regime.

Novel low temperature solution deposition of perpendicularly orientated rods of ZnO: substrate effects and evidence of the importance of counter-ions in the control of crystallite growth

Perpendicularly orientated ZnO rods have been grown on thin ZnO templates, from aqueous solutions of zinc acetate and hexamethylenetetraamine (HMT); growth along the c-axis of the ZnO crystallites is promoted by the presence of acetate in the bath.

Cd(NH2CSNHNHCSNH2)Cl2: a new single-source precursor for the preparation of CdS nanoparticles

Abstract The complex of cadmium with dithiobiurea, [Cd(NH 2 CSNHNHCSNH 2 )Cl 2 ], has been used as a precursor for the synthesis of CdS nanoparticles. The precursor was decomposed in tri- n -octylphosphine oxide to give CdS nanoparticles that show quantum confinement effects with characteristic close to band edge luminescence. The broad diffraction in the XRD pattern and diffused diffraction rings of the SAED pattern are typical of nanometer-sized particles. The particle morphology was found to depend on the temperature of injection of the precursor. Transmission electron microscopy shows irregular non-spherical particles prepared by injection at 150 °C, whilst with injection at 240 °C the particles are formed as spherical aggregates of relatively uniform size (50 nm).

Studies of the thermal decomposition of some diselenocarbamato complexes of cadmium or zinc : molecular design for the deposition of MSe films by CVD

The compounds M(Se 2 CNEt 2 ) 2 , M = Zn 1 or Cd 2, M(Se 2 CNMe n Hex) 2 , M = Zn 3 or Cd 4, and ZnEt(Se 2 CNEt 2 ) 5 have been investigated by GC-MS and EI-MS in an attempt to determine why 1 and 2 often deposit films containing an excess of selenium by metal organic chemical vapour deposition (MOCVD) whereas 3, 4 and 5 give MSe (M = Zn or Cd). The EI-MS of all five selenium compounds revealed similar decomposition pathways, which start with loss of an alkyl group. However, studies of compounds 1–5 by pyrolysis GC-MS showed that selenium clusters Se n , n = 1–7, are formed in the vapour phase from 1 and 2. Compounds 1, 2 and 5 also form significant quantities of diethyl diselenide (EtSe 2 Et) in the ratio of 1∶0.9∶0.2 respectively, as detected by GC-MS, whereas 3 and 4 do not.

Preparation of zinc containing materials

There has been an immense recent interest in zinc oxide and chalcogenide materials because of their potential use in many devices. The synthesis and characterisation of ZnE (E = O, S, Se and Te) thin films or types of quantum dots has as a consequence become topical. A close interplay between the development of new or improved synthetic methods and the resulting material properties has evolved.