Projects

@conference{Fleming2020,

title = {Overcoming the Limitations of Tip Enhanced Raman Spectroscopy with Intermittent Contact AFM},

author = {A. J. Fleming and M. G. Ruppert and B. S. Routley and L. McCourt},

year  = {2020},

date = {2020-10-27},

booktitle = {8th Multifrequency AFM Conference},

address = {Madrid, Spain},

abstract = {Tip enhanced Raman spectroscopy (TERS) is a promising technique for mapping the chemical composition of surfaces with molecular scale. However, current TERS methods are limited by a  number  of  issues  including  high  tip-sample  forces,  high  laser  power,  low  topographical resolution, and short probe lifetime. As a result, TERS methods are best suited to robust samples that can tolerate high optical intensity. To overcome these issues and extend the application of TERS to delicate samples, a number of new probes andimaging modes are in development at the University of Newcastle. This talk will provide an overview of these methods and present preliminary results, including new methods for optical probe optimization and fabrication, and a new dynamic-mode AFM method to reduce contact forces and applied laser power.},

keywords = {},

pubstate = {published},

tppubtype = {conference}

}

@conference{Ruppert2020b,

title = {Traditional and Novel Demodulators for Multifrequency Atomic Force Microscopy},

author = {M. G. Ruppert and D. M. Harcombe and A. J. Fleming},

year  = {2020},

date = {2020-10-27},

booktitle = {8th Multifrequency AFM Conference},

address = {Madrid, Spain},

abstract = {A number of multifrequency atomic force microscopy (MF-AFM) methods make use of the excitation and detection of higher harmonics of the fundamental frequency, higher flexural eigenmodes or intermodulation products generated by the non-linear tip-sample force [1]. Schematically, these methods are depicted in Figure 1(a) where the main difference is the resulting spacing and amplitude of the frequency components in the generated spectrum shown in Figure 1(b). Regardless of which particular MF-AFM method is employed, each requires a demodulator to obtain amplitude and phase to form observables for the characterization of nanomechanical sample information. Since high-speed non-synchronous demodulators such as the peak-hold method, peak detector and RMS-to-DC converter are incompatible with MF-AFM [2], there is a need for high-bandwidth demodulation techniques capable of estimating multiple frequencies at once while maintaining robustness against unwanted frequency components [3]. In this talk, the performance of traditional and recently proposed demodulators for multifrequency atomic force microscopy is assessed experimentally. The compared methods include the lock-in amplifier, coherent demodulator, Kalman filter, Lyapunov filter, and direct-design demodulator. Each method is implemented on a field-programmable gate array (FPGA) with a sampling rate of 1.5 MHz. The metrics for comparison include implementation complexity, the sensitivity to other frequency components and the magnitude of demodulation artifacts for a range of demodulator bandwidths. Performance differences are demonstrated through higher harmonic atomic force microscopy imaging.},

keywords = {},

pubstate = {published},

tppubtype = {conference}

}