Problemática de la prevención

In summary, the graphene-DLC/NDLC/FDLC heterostructure were investigated in terms of the surface morphology, chemical composition, and microstructure by means of AFM, Raman spectroscopy, XPS and Hall Effect system. Different terminations changed the roughness of DLC films, which induced the Raman D and G peak shifting with the increase of disorders and sp2 C=C transiting to sp3 C-C shown from XPS results owing to C-N/F groups. Raman and XPS analysis for graphene-DLC heterostructure suggests graphene properties changed by interaction between two layers and different addition groups. GFDLC show better electronic mobility, while GNDLC reveals metallic-like characters. Based on this research and IBM high frequency FET results, better graphene transistors will be achieved. Different DLC support substrates may offer better 2D device applications.

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Chapter 6

Graphene-Nanodiamond Heterostructure and

their Applicant of Field Effect Transistors

6.1. Introduction

Current studies have typically employed readily available Si/SiO2 wafers as the substrate,

which creates a thermal capacity problem reducing the current capacity of graphene due to the highly thermally resistive SiO2 layer1,2. In an attempt to overcome this problem, diamond

and diamond-like-carbon (DLC) have been explored as they offer insulating properties whilst being superior in terms of thermal conductivity, with a large optical phonon energy and potentially a lower surface trap density1.3. Graphene devices on ultrananocrystalline diamond (UNCD) and single crystal diamond (SCD) have been shown to increase the amount of current that graphene devices are capable of handling3. For commercial electronics, substrates that can be produced using large volume production and at low cost are essential for any new technology. Here, the potential advantages of the use of low-cost, large area compatible nanodiamond (ND) thin films, rather than UNCD and SCD for fabricating graphene-nanodiamond heterostructure devices are explored. ND inherits most of the outstanding properties of bulk diamond, but delivers them at the nanoscale, including hardness, high thermal conductivity, chemical stability, electrical resistivity and a large bandgap4-6. NDs fabricated by a detonation process (~5nm) are readily available at low cost and can be readily attached to any 2D or 3D materials through simple sonication from solution4. To control the surface performance of the NDs, hydrogen termination of the ND

nanostructures7-9. Compared with high cost SCD, with the highest thermal conductivity of bulk materials, the low cost and easily deposited ND films have been found to have high thermal conductivity around 5-50 W/mK10, which is higher than the thermal conductivity of UNCD (8.6-16.6 W/mK) and diamond-like-carbon (0.2-3.5 W/mK)11.12.

In this chapter, a cost effective and mass producible method to create a monolayer ND capable of tuning the properties of graphene for the fabrication of Field-Effect Transistors (FETs) is demonstrated. Compared to the pristine graphene transferred onto SiO2/Si

substrates, the mobility increased by 60% on graphene on hydrogen terminated nanodiamond (GrHND). The detailed material properties of graphene on ND surface with and without hydrogen termination treatment have been investigated using Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. It shows that the hydrogen termination treatment not only removed surface contamination from monolayer ND, but also provided a suitable linkage between ND and graphene to form a conductive path, as demonstrated in electrochemical impedance spectroscopy (EIS) measurements. The carrier mobility of GrHND is no less than that of graphene on hydrogen terminated SCD (GrHSCD). In addition, GrHND demonstrated a stable Hall mobility with temperature. High-k dielectric top-gate graphene transistors with gate length of 200 nm and 500 nm were fabricated using focused ion beam (FIB) using Tungsten carbide (WC) contacts to improve the energy transfer between diamond and metal6. This research offers a new approach for commercial graphene transistor applications.