• Mills, Benjamin
• Eason, Robert W.
• Praeger, Matthew

Abstract

Graphene growth is typically optimized for uniformity over relatively large areas; however, this can place undesirable limitations on the design of graphene-based devices and can mandate the use of additional lithographic processing steps. Localized transfer of graphene can therefore offer significant benefits, permitting greater freedom in device design thereby enabling new applications. <br/>We present results obtained using a laser transfer method which is capable of localized deposition of graphene onto transparent receiver materials such as glass (using just a single fs laser pulse per deposited structure). In this method (laser induced backwards transfer, LIBT [1-3]) a pulsed laser beam is focussed through the receiving substrate and onto the donor substrate (hence the requirement for the receiver to be transparent). In this case the receiver is a microscope cover glass which is held in close contact with the donor during LIBT. The donor is a nickel coated glass slide upon which large-area monolayer graphene is transferred via the floating film technique with the aid of a PMMA support layer that is subsequently dissolved. The focused laser pulse is absorbed within the metal layer of the donor causing rapid, localized, thermal expansion (a shockwave). This ejects the graphene from the donor surface (only where the laser was focused) and transfers it to the receiver substrate. In this manner, microscale patterning of graphene on the receiver substrate is achieved.<br/>Additionally, we present details of spatial beam modulation via a digital micromirror device (DMD, [4, 5])which allows the shape and size of the deposited graphene to be precisely, computer controlled in the micron range. This innovation could help to facilitate rapid prototyping of graphene-based devices, allowing numerous design variations to be tested quickly and without requiring the purchase of multiple, costly, lithographic masks. This work extends on previous results obtained by the authors at a laser wavelength of 800nm [6] by using an optical parametric amplifier (OPA) to generate laser light at 1650nm and additionally introduces control over laser pulse duration, allowing switching between 200fs and 1200fs pulses.<br/>The presence of graphene on a surface creates a slight change in optical reflectance and so it is often possible (although difficult) to observe the presence of localized deposits of graphene via optical microscopy. We have developed image processing methods (with contrast enhancement and image segmentation steps) that greatly simplify the identification of graphene coated regions. These methods have been evaluated using Raman microscopy and have proved to be an accurate and convenient tool (see Figure 1) which we believe may be of interest to other researchers in this field.

Topics

• Deposition
• impedance spectroscopy
• surface
• nickel
• glass
• glass
• thermal expansion
• optical microscopy
• Raman microscopy