@article{Ruppert2025,

title = {Modulated-Illumination Intermittent-Contact Tip-Enhanced Raman Spectroscopy},

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

doi = {https://doi.org/10.1021/acs.nanolett.4c06397},

year  = {2025},

date = {2025-03-13},

urldate = {2025-03-13},

journal = {ACS Nano Letters},

volume = {25},

issue = {14},

abstract = {This article presents a proof-of-concept for a new imaging method that combines tip-enhanced Raman spectroscopy with intermittent-contact atomic force microscopy to provide simultaneous nanometer-scale mechanical imaging with chemical contrast. The foremost difference from a standard tip-enhanced Raman microscope is the Raman illumination, which is modulated by the cantilever drive signal so that illumination is only active when the tip is close to the surface. This approach significantly reduces contact forces and thermal damage due to constant illumination while simultaneously reducing background Raman signals. Near-field optical and dynamic cantilever simulations highlight the effect of the imaging parameters on the tip–sample force and the evanescent field enhancement. The experimental images obtained with this new imaging method demonstrate a lateral resolution sufficient to identify single-walled carbon nanotube bundles with a full width at half-maximum of 20 nm.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{J23a,

title = {Feasibility of gold nanocones for collocated tip-enhanced Raman spectroscopy and atomic force microscope imaging },

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

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2024/02/J23a-Preprint.pdf},

doi = {10.1002/jrs.6625},

issn = {1097-4555},

year  = {2024},

date = {2024-02-01},

urldate = {2024-02-01},

journal = {Journal of Raman Spectroscopy},

abstract = {Microcantilever probes for tip-enhanced Raman spectroscopy (TERS) have a grainy metal coating that may exhibit multiple plasmon hotspots near the tip apex, which may compromise spatial resolution and introduce imaging artefacts. It is also possible that the optical hotspot may not occur at the mechanical apex, which introduces an offset between TERS and atomic force microscope maps. In this article, a gold nanocone TERS probe is designed and fabricated for 638 nm excitation. The imaging performance is compared to grainy probes by analysing high-resolution TERS cross-sections of single-walled carbon nanotubes. Compared to the tested conventional TERS probes, the nanocone probe exhibited a narrow spot diameter, comparable optical contrast, artefact-free images, and collocation of TERS and atomic force microscope topographic maps. The spot diameter was 12.5 nm and 19 nm with 638 nm and 785 nm excitation, respectively. These results were acquired using a single gold nanocone probe to experimentally confirm feasibility. Future work will include automating the fabrication process and statistical analysis of many probes.},

keywords = {},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{nokey,

title = {Single-Walled Carbon Nanotubes as One-Dimensional Scattering Surfaces for Measuring Point Spread Functions and Performance of Tip-Enhanced Raman Spectroscopy Probes},

author = {L. R. McCourt and B. S. Routley and M. G. Ruppert and V. J. Keast and C. I. Sathish and R. Borah and R. V. Goreham and A. J. Fleming},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2023/02/J22i.pdf},

doi = {10.1021/acsanm.2c01274},

issn = {2574-0970},

year  = {2022},

date = {2022-06-21},

urldate = {2022-06-21},

journal = {ACS Applied Nano Materials},

volume = {5},

issue = {7},

pages = {9024-9033},

abstract = {This Article describes a method for the characterization of the imaging performance of tip-enhanced Raman spectroscopy probes. The proposed method identifies single-walled carbon nanotubes that are suitable as one-dimensional Raman scattering objects by using atomic force microscope maps and exciting the radial breathing mode using 785 nm illumination. High-resolution cross sections of the nanotubes are collected, and the point spread functions are calculated along with the optical contrast and spot diameter. The method is used to characterize several probes, which results in a set of imaging recommendations and a summary of limitations for each probe. Elemental analysis and boundary element simulations are used to explain the formation of multiple peaks in the point spread functions as a consequence of random grain formation on the probe surface.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{McCourt2020,

title = {A comparison of gold and silver nanocones and geometry optimisation for tip-enhanced microscopy},

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

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2020/09/J20e.pdf},

doi = {https://doi.org/10.1002/jrs.5987},

year  = {2020},

date = {2020-11-01},

urldate = {2020-08-24},

journal = {Journal of Raman Spectroscopy},

volume = {51},

issue = {11},

pages = {2208-2216},

abstract = {In this article, boundary element method simulations are used to optimise the geometry of silver and gold nanocone probes to maximise the localised electric field enhancement and tune the near-field resonance wavelength. These objectives are expected to maximise the sensitivity of tip-enhanced Raman microscopes. Similar studies have used limited parameter sets or used a performance metric other than localised electric field enhancement. In this article, the optical responses for a range of nanocone geometries are simulated for excitation wavelengths ranging from 400 to 1000 nm. Performance is evaluated by measuring the electric field enhancement at the sample surface with a resonant illumination wavelength. These results are then used to determine empirical models and derive optimal nanocone geometries for a particular illumination wavelength and tip material. This article concludes that gold nanocones are expected to provide similar performance to silver nanocones at red and nearinfrared wavelengths, which is consistent with other results in the literature. In this article, 633 nm is determined to be the shortest usable illumination wavelength for gold nanocones. Below this limit, silver nanocones will provide superior enhancement. The use of gold nanocone probes is expected to dramatically improve probe lifetime, which is currently measured in hours for silver coated probes. Furthermore, the elimination of passivation coatings is expected to enable smaller probe radii and improved topographical resolution.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{J19e,

title = {Scanning Laser Lithography with Constrained Quadratic Exposure Optimization},

author = {A. J. Fleming and O. T. Ghalehbeygi and B. S. Routley and A. G. Wills},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2020/02/J19e.pdf},

doi = {10.1109/TCST.2018.2836910},

isbn = {1063-6536},

year  = {2019},

date = {2019-09-01},

journal = {IEEE Transactions on Control Systems Technology},

volume = {27},

number = {5},

pages = {2221-2228},

abstract = {Scanning laser lithography is a maskless lithography method for selectively exposing features on a film of photoresist. A set of exposure positions and beam energies are required to optimally reproduce the desired feature pattern. The task of determining the exposure energies is inherently non-linear due to the photoresist model and the requirement for only positive energy. In this article, a nonlinear programming approach is employed to find an optimal exposure profile that minimizes the feature error and total exposure energy. This method is demonstrated experimentally to create a features with sub-wavelength geometry.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{J17j,

title = {Gradient-based optimization for efficient exposure planning in maskless lithography},

author = {O. T. Ghalehbeygi and A. G. Wills and B. S. Routley and A. J. Fleming},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2017/09/J17j.pdf},

doi = {10.1117/1.JMM.16.3.033507},

year  = {2017},

date = {2017-09-01},

journal = {Journal of  Micro/Nanolithography, MEMS, and MOEMS},

volume = {16},

number = {3},

pages = {033507},

abstract = {Scanning laser lithography is a maskless method for exposing photoresist during semiconductor manufacturing. In this method, the energy of a focused beam is controlled while scanning the beam or substrate. With a positive photoresist material, areas that receive an exposure dosage over the threshold energy are dissolved during development. The surface dosage is related to the exposure profile by a convolution and nonlinear function, so the optimal exposure profile is nontrivial. A gradient-based optimization method for determining an optimal exposure profile, given the desired pattern and models of the beam profile and photochemistry, is described. This approach is more numerically efficient than optimal barrier-function-based methods but provides near-identical results. This is demonstrated through simulation and experimental lithography},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{J16b,

title = {Exposure Optimization in Scanning Laser Lithography},

author = {A. J. Fleming and A. G. Wills and B. S. Routley},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2016/08/J16b.pdf},

doi = {10.1109/MPOT.2016.2540039},

issn = {0278-6648},

year  = {2016},

date = {2016-12-01},

journal = {IEEE Potentials},

volume = {35},

number = {4},

pages = {33-39},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{J15f,

title = {A Closed-Loop Phase-Locked Interferometer for Wide Bandwidth Position Sensing},

author = {A. J. Fleming and B. S. Routley},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2015/12/J15f.pdf},

doi = {10.1063/1.4935469},

year  = {2015},

date = {2015-12-31},

journal = {Review of Scientific Instruments},

volume = {86},

pages = {115001(1-7)},

abstract = {This article describes a position sensitive interferometer with closed-loop control of the reference mirror. A calibrated nanopositioner is used to lock the interferometer phase to the most sensitive point in the interfer- ogram. In this conguration, large low-frequency movements of the sensor mirror can be detected from the control signal applied to the nanopositioner and high-frequency short-range signals can be measured directly from the photodiode. It is demonstrated that these two signals are complementary and can be summed to find the total displacement. The resulting interferometer has a number of desirable characteristics: it is optically simple, does not require polarization or modulation to detect the direction of motion, does not require fringe-counting or interpolation electronics, and has a bandwidth equal to that of the photodiode. Experimental results demonstrate the frequency response analysis of a high-speed positioning stage. The proposed instru-

ment is ideal for measuring the frequency response of nanopositioners, electro-optical components, MEMs devices, Ultrasonic devices, and sensors such as surface acoustic wave detectors.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}