Mark Skilbeck
I am a final year Ph.D. student jointly supervised by Dr. Rachel Edwards (Ultrasound group) and Dr. Neil Wilson (Microscopy group). I specialise in atomic force microscopy (AFM), particularly combining ultrasound with AFM and investigation of mechanical properties.
I also help maintain both the AFMs in the group - an Asylum Research MFP-3D and a Veeco Multimode. If you have any problems or questions about either AFM, feel free to ask me.
Research
My research has been split over 3 major topic areas, covered below:
Ultrasonic Force Microscopy (UFM)
UFM is a contact mode technique in which a sample surface is oscillated out of plane at frequencies well above the cantilever resonance. This high frequency oscillation is not followed by the cantilever, but instead the cantilever deflects an addtional amount, the magnitude of which depends primarily on the mechanical stiffness of the sample near to to the surface. By modulating the ultrasonic oscillations at a frequency between the pixel scanning rate and the cantilever resonance the additional deflection can be decoupled from the deflection due to sample topography through use of a lock-in amplifier operating at the modulation frequency.
My research has been focussed on combining UFM with other contact mode techniques, such as friction force microscopy and conductive AFM, using the period in the modulation in which the ultrasound is turned off to acquire the information wanted. This allows combined mechanical measurements with techniques that are incompatible with other mechanical AFM methods. An additional benefit is that UFM demonstrates a superlubricity phenomenon, in which the tip applies very little sustained lateral force to the sample, allowing for the imaging of delicate samples (such as carbon nanotubes) with significantly reduced damage.
I have published this research in IOP Nanotechnology: Multimodal microscopy using 'half and half' contact mode and ultrasonic force microscopy
I have also presented this work at conferences:
Talk at UK SPM 2013: "Friction Free Friction Force Microscopy"
Talk at RMS MMC 2014: "Multimodal Micrscopy Using "Half and Half" Contact Mode and Ultrasonic Force Microscopy"
Poster at Euro AFM 2014, RMS MMC 2014 (pdf) and ICU 2015 (pdf).
Ultrasonic Non Destructive Testing (NDT) in an AFM
The AFM can be used as a pickup for ultrasonic waves at the surface of a sample. By generating waves within a sample (e.g. using an electro magnetic acoustic transducer [EMAT]) and the measuring the response at different locations, positions of defects in the sample can be seen. AFM presents benefits over other pickup techniques in both sensitivty and resolution, though lacks in frequency range (limited by the cantilever resonance and photodiode response). Additionally, out of plane and in plane waves excite different channels in the AFM (deflection and lateral deflection, respectively), which allows both to be picked up simultaneously in a distinguishable manner, which is not possible with other pickup techniques (e.g. EMATs), providing interesting information about the wave modes present within the sample.
I have presented this work as a poster at ICU 2015 (pdf).
Mechanical Properties of 2D Films
The mechanical properties of 2D films, such as graphene and it's derivatives (graphene oxide) are useful to know when evaluating their potential uses. By suspending the films over circular holes and acquring force curves in the centre information about their mechanical stiffness and breaking strength can be acquired. Much of this work was focused on atomation of data acquisition to allow for large statistical datasets to be acquired, allowing for comparison between differentent materials and points in transition between two (e.g. the oxidation of graphene).
I have presented this work as a poster at RMS MMC 2015 (pdf)
