One-dimensional defects in graphene have a strong influence on its physical properties, such as electrical charge transport and mechanical strength. With enhanced chemical reactivity, such defects may also allow us to selectively functionalize the material and systematically tune the properties of graphene. Here we demonstrate the selective deposition of metal at chemical vapour deposited graphene's line defects, notably grain boundaries, by atomic layer deposition. Atomic layer deposition allows us to deposit Pt predominantly on graphene's grain boundaries, folds and cracks due to the enhanced chemical reactivity of these line defects, which is directly confirmed by transmission electron microscopy imaging. The selective functionalization of graphene defect sites, together with the nanowire morphology of deposited Pt, yields a superior platform for sensing applications. Using Pt-graphene hybrid structures, we demonstrate high-performance hydrogen gas sensors at room temperature and show its advantages over other evaporative Pt deposition methods, in which Pt decorates the graphene surface non-selectively.

The composition of methylalumoxane (MAO) and its interaction with trimethylaluminum (TMA) have been investigated by a combination of chemical, spectroscopic, neutron scattering, and computational methods. The interactions of MAO with donor molecules such as THF, pyridine, and PPh 3 as a means of quantifying the content of "free" and "bound" TMA have been evaluated, as well as the ability of MAO to produce [Me 2 AlL 2 ] + cations, a measure of the electrophilic component likely to be involved in the activation of single-site catalysts. THF, pyridine, and diphenylphosphinopropane (dppp) give the corresponding TMA−donor ligand complexes accompanied by the formation of [Me 2 AlL 2 ] + cations. The results suggest that MAO contains not only Lewis acid sites but also structures capable of acting as sources of [AlMe 2 ] + cations. Another unique, but still unresolved, structural aspect of MAO is the nature of "bound" and "free" TMA. The addition of the donors OPPh 3 , PMe 3 , and PCy 3 leads to the precipitation of polymeric MAO and shows that about one-fourth of the total TMA content is bound to the MAO polymers. This conclusion was independently confirmed by pulsed field gradient spin echo (PFG-SE) NMR measurements, which show fast and slow diffusion processes resulting from free and MAO-bound TMA, respectively. The hydrodynamic radius R h of polymeric MAO in toluene solutions was found to be 12 ± 0.3 Å, leading to an estimate for the average size of MAO polymers of about 50−60 Al atoms. Small-angle neutron scattering (SANS) resulted in the radius R S = 12.0 ± 0.3 Å for the MAO polymer, in excellent agreement with PFG-SE NMR experiments, a molecular weight of 1800 ± 100, and about 30 Al atoms per MAO polymer. The MAO structures capable of releasing [AlMe 2 ] + on reaction with a base were studied by quantum chemical calculations on the MAO models (OAlMe) n (TMA) m for up to n = 8 and m = 5. Both −O−AlMe 2 −O− and −O−AlMe 2 −μ-Me− four-membered rings are about equally likely to lead to dissociation of [AlMe 2 ] + cations. The resulting MAO anions rearrange, with structures containing separated Al 2 O 2 4-rings being particularly favorable. The results support the notion that catalyst activation by MAO can occur by both Lewis acidic cluster sites and [AlMe 2 ] + cation formation.

Colloidal quantum dots (CQDs) have received recent attention for low cost, solution processable, high efficiency solid-state photovoltaic devices due to the possibility of tailoring their optoelectronic properties by tuning size, composition, and surface chemistry. However, the device performance is limited by the diffusion length of charge carriers due to recombination. In this work, we show that band engineering of PbS QDs is achievable by changing the dipole moment of the passivating ligand molecules surrounding the QD. The valence band maximum and conduction band minimum of PbS QDs passivated with three different thiophenol ligands (4-nitrothiophenol, 4-fluorothiophenol, and 4-methylthiophenol) are determined by UV–visible absorption spectroscopy and photoelectron spectroscopy in air (PESA), and the experimental results are compared with DFT calculations. These band-engineered QDs have been used to fabricate heterojunction solar cells in both unidirectional and bidirectional configurations. The results show that proper band alignment can improve the directionality of charge carrier collection to benefit the photovoltaic performance.

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