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ABSTRACTMost publications on (opto)electronic devices based on 2D materials rely on single monolayers embedded in classical 3D semiconductors, dielectrics and metals. However, heterostructures of different 2D materials can be employed to tailor the performance of the 2D components by reduced defect densities, carrier or exciton transfer processes and improved stability. This translates to additional and unique degrees of freedom for novel device design. The nearly infinite number of potential combinations of 2D layers allows for many fascinating applications. Unlike mechanical stacking, metal-organic vapour phase epitaxy (MOVPE) can potentially provide large-scale highly homogeneous 2D layer stacks with clean and sharp interfaces. Here, we demonstrate the direct successive MOVPE of MoS2/WS2 and WS2/MoS2 heterostructures on 2” sapphire (0001) substrates. Furthermore, the first deposition of large-scale MoS2/graphene and WS2/graphene heterostructures using only MOVPE is presented and the influence of growth time on nucleation of WS2 on graphene is analysed.

Strong enhancement of green photoluminescence ͑PL͒ from microporous alumina xerogels, highly doped with terbium ͑from 30 to 60 wt % as Tb 2 O 3 ͒, is reported. The regular structure of a 30 m thick, mesoporous anodic alumina layer was exploited for spin-on deposition of the alumina xerogel in a single step. The green PL, associated with predominant 5 D 4 → 7 F 5 transitions, along with 5 D 4 → 7 F j , j ϭ 3, 4, 5, 6 transitions of Tb 3ϩ , was found to increase with terbium concentration in the alumina xerogel. This effect is attributed to cross-relaxation. The thermal quenching of the green terbium-related emission does not exceed a factor of two within a temperature range from 10 to 300 K for any of the alumina xerogels confined in anodic alumina. Further, such quenching is much reduced with the rise of temperature compared with (i) Tb-doped titania xerogel, ͑ii͒ Tb-implanted thermally grown silicon dioxide film, and ͑iii͒ Tb-doped alumina xerogels fabricated onto monocrystalline silicon. Thus, the terbium-doped structure comprising alumina xerogel/anodic alumina is proposed as a basis for green room-temperature luminescent images. ver the last decade, the low-cost sol-gel method for fabricating luminescent structures containing incorporated optically active lanthanides has been investigated intensively. The sol-gel method allows diverse xerogel films, highly doped with lanthanides, to be produced. Spin-on deposition was usually employed in fabrication of films doped with optically active erbium, 1,2 neodymium, 3 terbium, 4 and other lanthanides. Unlike the dry processes, 5 the sol penetrates the mesopores of porous silicon, promoting synthesis of a xerogel film in the pore volume of a layer of several micrometers thickness. Strong 1.53 m photoemission from porous silicon, coated with a spin-on, erbium-doped silica gel film, has been shown. 1,6 Exploitation of the mesoporous layer avoids procedures involving numerous sequential spin-on depositions, which are needed to obtain strong room-temperature photoluminescence ͑PL͒ from lanthanide ions in a xerogel film of several micrometers thickness.Recently, we reported enhancement of terbium PL from a terbium-doped titania xerogel, mesoscopically confined in porous anodic alumina. 4 Porous anodic alumina exhibits a regular porous morphology, with pores at the centers of approximately hexagonally packed cells. 7 The regular morphology of porous anodic alumina, with pores passing normally to the macroscopic substrate surface, possesses some advantages over the irregular geometry of mesoporous silicon 8 for synthesis of sol-gel derived products. In addition, their regular mesoscale morphology can be extended to thicknesses of 100 m. Porous alumina has been demonstrated to be an excellent support for xerogel solids doped with the optically active lanthanides. 4,9,10 The combination of mesoporous layers and xerogels doped with optically active lanthanides enhances the lanthanide photoluminescence. This has already been confirmed for lanthanides incorporated within xerogel ...

The issues and challenges of growing GaN-based structures on large area Si substrates have been studied. These include Si slip resulting from large temperature non-uniformities and cracking due to differential thermal expansion. Using an AlN nucleation layer in conjunction with an AlGaN buffer layer for stress management, and together with the interactive use of real time in-situ optical monitoring it was possible to realise flat, crack-free and uniform GaN and LED structures on 6-inch Si (111) substrates. The EL performance of processed LED devices was also studied on-wafer, giving good EL characteristics including a forward bias voltage of ~3.5 V at 20 mA from a 500 μm x 500 μm device.

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