13 research outputs found
Understanding the impact of heavy ions and tailoring the optical properties of large-area Monolayer WS2 using Focused Ion Beam
Focused ion beam (FIB) has been used as an effective tool for precise
nanoscale fabrication. It has recently been employed to tailor defect
engineering in functional nanomaterials such as two-dimensional transition
metal dichalcogenides (TMDCs), providing desirable properties in TMDC-based
optoelectronic devices. However, the damage caused by the FIB irradiation and
milling process to these delicate atomically thin materials, especially in the
extended area, has not yet been elaboratively characterised. Understanding the
correlation between lateral ion beam effects and optical properties of 2D TMDCs
is crucial in designing and fabricating high-performance optoelectronic
devices. In this work, we investigate lateral damage in large-area monolayer
WS2 caused by the gallium focused ion beam milling process. Three distinct
zones away from the milling location are identified and characterised via
steady-state photoluminescence (PL) and Raman spectroscopy. An unexpected
bright ring-shaped emission around the milled location has been revealed by
time-resolved PL spectroscopy with high spatial resolution. Our finding opens
new avenues for tailoring the optical properties of TMDCs by charge and defect
engineering via focused ion beam lithography. Furthermore, our study provides
evidence that while some localised damage is inevitable, distant destruction
can be eliminated by reducing the ion beam current. It paves the way for the
use of FIB to create nanostructures in 2D TMDCs, as well as the design and
realisation of optoelectrical devices on a wafer scale
Case studies of electrical characterisation of graphene by terahertz time-domain spectroscopy
Graphene metrology needs to keep up with the fast pace of developments in graphene growth and transfer. Terahertz time-domain spectroscopy (THz-TDS) is a non-contact, fast, and non-destructive characterization technique for mapping the electrical properties of graphene. Here we show several case studies of graphene characterization on a range of different substrates that highlight the versatility of THz-TDS measurements and its relevance for process optimization in graphene production scenarios
Transfer and interface characterization of 2D materials for microelectronic devices
International audience2D materials have attracted a lot of attention since the last decade due to their unique properties especially in the microelectronics field [1]. However thermal budgets engaged for the synthesis of high quality 2D materials are, most of the time, not compatible for the direct growth into device structures. Therefore, transferring synthesized layers from the growth substrate to a desired one is required for functional device fabrication [2]. However, the transfer process could modify or degrade the material properties, and the quality of interface between the transferred materials and the targeted substrates should be carefully controled to achieve the expected properties. [3]Our work focuses on the development of a clean room compatible large-scale transfer process based on spalling method for its integration into microelectronic devices such as photonics, RF switches or memories. We report here a physico-chemical characterization of 2D layers before and after transfer using microscope SEM and TEM, AFM, XPS and Raman spectroscopy to study the impact of our transfer process. The electrical properties are also studied using four probes and Van Der Pauw measurement after transfer to verify the electrical interface while optimizing the process to get a good copy of the as grown materials by keeping the growth interface safe from solvent or other impurities
Understanding the impact of heavy ions and tailoring the optical properties of large-area monolayer WS2 using focused ion beam
Abstract Focused ion beam (FIB) is an effective tool for precise nanoscale fabrication. It has recently been employed to tailor defect engineering in functional nanomaterials such as two-dimensional transition metal dichalcogenides (TMDCs), providing desirable properties in TMDC-based optoelectronic devices. However, the damage caused by the FIB irradiation and milling process to these delicate, atomically thin materials, especially in extended areas beyond the FIB target, has not yet been fully characterised. Understanding the correlation between lateral ion beam effects and optical properties of 2D TMDCs is crucial in designing and fabricating high-performance optoelectronic devices. In this work, we investigate lateral damage in large-area monolayer WS2 caused by the gallium focused ion beam milling process. Three distinct zones away from the milling location are identified and characterised via steady-state photoluminescence (PL) and Raman spectroscopy. The emission in these three zones have different wavelengths and decay lifetimes. An unexpected bright ring-shaped emission around the milled location has also been revealed by time-resolved PL spectroscopy with high spatial resolution. Our findings open up new avenues for tailoring the optical properties of TMDCs by charge and defect engineering via focused ion beam lithography. Furthermore, our study provides evidence that while some localised damage is inevitable, distant destruction can be eliminated by reducing the ion beam current. It paves the way for the use of FIB to create nanostructures in 2D TMDCs, as well as the design and realisation of optoelectrical devices on a wafer scale
Wafer-Scale Synthesis of Graphene on Sapphire: Toward Fab-Compatible Graphene
The adoption of graphene in electronics, optoelectronics and photonics is
hindered by the difficulty in obtaining high quality material on
technologically-relevant substrates, over wafer-scale sizes and with metal
contamination levels compatible with industrial requirements. To date, the
direct growth of graphene on insulating substrates has proved to be
challenging, usually requiring metal-catalysts or yielding defective graphene.
In this work, we demonstrate a metal-free approach implemented in commercially
available reactors to obtain high-quality monolayer graphene on c-plane
sapphire substrates via chemical vapour deposition (CVD). We identify via low
energy electron diffraction (LEED), low energy electron microscopy (LEEM) and
scanning tunneling microscopy (STM) measurements the Al-rich reconstruction
root31R9 of sapphire to be crucial for obtaining epitaxial graphene. Raman
spectroscopy and electrical transport measurements reveal high-quality graphene
with mobilities consistently above 2000 cm2/Vs. We scale up the process to
4-inch and 6-inch wafer sizes and demonstrate that metal contamination levels
are within the limits for back-end-of-line (BEOL) integration. The growth
process introduced here establishes a method for the synthesis of wafer-scale
graphene films on a technologically viable basis.Comment: 15 main text pages, 4 main text figures, 13 supplementary information
pages, 12 supplementary figures, 3 supplementary table
Nucleation and coalescence of tungsten disulfide layers grown by metalorganic chemical vapor deposition
International audienc