Abstract
Graphene nanosheets (GNSs) were grown on a Si nanoporous pillar array (Si-NPA) via chemical vapour deposition, using a thin layer of pre-deposited Ni nanocrystallites as catalyst. GNSs were determined to be of high quality and good dispersivity, with a typical diameter size of 15 × 8 nm. Light absorption measurements showed that GNSs had an absorption band edge at 3.3 eV. They also showed sharp and regular excitonic emitting peaks in the ultraviolet and visible region (2.06–3.6 eV). Moreover, phonon replicas with long-term stability appeared with the excitonic peaks at room temperature. Temperature-dependent photoluminescence from the GNSs revealed that the excitonic emission derived from free and bound excitonic recombination. A physical model based on band energy theory was constructed to analyse the carrier transport of GNSs. The Ni nanocrystallites on Si-NPA, which acted as a metal-enhanced fluorescence substrate, were supposed to accelerate the excitonic recombination of GNSs and enhanced the measured emission intensity. Results of this study would be valuable in determining the luminescence mechanism of GNSs and could be applied in real-world optoelectronic devices.
Highlights
Graphene nanostructures can be engineered to emit photoluminescence (PL) over the visible region, even extending into the near infrared region [1,2,3]
We developed an Metal-enhanced fluorescence (MEF) substrate by precipitating nickel nanocrystallites (nc-Ni) on Si nanoporous pillar array (Si-NPA) and grew graphene nanosheets (GNSs) on it via chemical vapour deposition (CVD)
These results implied that graphene had been deposited on Si-NPA after the CVD reaction in samples A and B
Summary
Graphene nanostructures can be engineered to emit photoluminescence (PL) over the visible region, even extending into the near infrared region [1,2,3]. PL from graphene nanostructures has different origins, such as the recombination of free excitons, quantum confinement or edge effects [4,5]. Excitonic effects play a critical role in the optical properties of graphene [6,7,8]. Carriers are geometrically confined, which typically leads to fast recombination of the excitons before nonradiative recombination can occur. This condition results in a high radiative recombination probability and strong PL. The excitonic emission is responsible for the high efficiency of LEDs based on InxGa12xN nanorods, nanowire or multiple 2D quantum wells [9 – 11]. The creation of nanostructures from graphene may be a promising route for realizing bright PL from this material
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