Publications

@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 = {AFM, Cantilever, Optics},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{J22a,

title = {Simultaneous tip force and displacement sensing for AFM cantilevers with on-chip actuation: Design and characterization for off-resonance tapping mode},

author = {N. F. S. de Bem and M. G. Ruppert and A. J. Fleming and Y. K. Yong},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2022/03/J22a.pdf},

doi = {10.1016/j.sna.2022.113496},

issn = {0924-4247},

year  = {2022},

date = {2022-03-08},

urldate = {2022-03-08},

journal = {Sensors and Actuators A: Physical},

volume = {338},

pages = {113496},

abstract = {The use of integrated on-chip actuation simplifies the identification of a cantilever resonance, can improve imaging speed, and enables the use of smaller cantilevers, which is required for low-force imaging at high speed. This article describes a cantilever with on-chip actuation and novel dual-sensing capabilities for AFM. The dual-sensing configuration allows for tip displacement and tip force to be measured simultaneously. A mathematical model is developed and validated with finite element analysis. A physical prototype is presented, and its calibration and validation are presented. The cantilever is optimized for use in off-resonance tapping modes. Experimental results demonstrate an agreement between the on-chip sensors and external force and displacement measurements.},

keywords = {AFM},

pubstate = {published},

tppubtype = {article}

}

@article{Ruppert2022,

title = {Experimental Analysis of Tip Vibrations at Higher Eigenmodes of QPlus Sensors for Atomic Force Microscopy},

author = {M. G. Ruppert and D. Martin-Jimenez and Y. K. Yong and A. Ihle and A. Schirmeisen and A. J. Fleming and D. Ebeling},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2022/03/J22c.pdf},

doi = {10.1088/1361-6528/ac4759},

issn = {1361-6528},

year  = {2022},

date = {2022-02-10},

urldate = {2022-02-10},

journal = {Nanotechnology},

volume = {33},

issue = {18},

pages = {185503},

abstract = {QPlus sensors are non-contact atomic force microscope probes constructed from a quartz tuning fork and a tungsten wire with an electrochemically etched tip. These probes are self-sensing and offer an atomic-scale spatial resolution. Therefore, qPlus sensors are routinely used to visualize the chemical structure of adsorbed organic molecules via the so-called bond imaging technique. This is achieved by functionalizing the AFM tip with a single CO molecule and exciting the sensor at the first vertical cantilever resonance mode. Recent work using higher-order resonance modes has also resolved the chemical structure of single organic molecules. However, in these experiments, the image contrast can differ significantly from the conventional bond imaging contrast, which was suspected to be caused by unknown vibrations of the tip. This work investigates the source of these artefacts by using a combination of mechanical simulation and laser vibrometry to characterize a range of sensors with different tip wire geometries. The results show that increased tip mass and length cause increased torsional rotation of the tuning fork beam due to the off-center mounting of the tip wire, and increased flexural vibration of the tip. These undesirable motions cause lateral deflection of the probe tip as it approaches the sample, which is rationalized to be the cause of the different image contrast. The results also provide a guide for future probe development to reduce these issues.},

keywords = {Actuator, AFM, Cantilever, Multifrequency AFM, piezoelectric},

pubstate = {published},

tppubtype = {article}

}

@article{Omidbeike2021,

title = {Five-Axis Bimorph Monolithic Nanopositioning Stage: Design, Modeling, and Characterization},

author = {M. Omidbeike and S. I. Moore and Y. K. Yong and A. J. Fleming},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2022/03/J21g.pdf},

doi = {10.1016/j.sna.2021.113125},

issn = {0924-4247},

year  = {2021},

date = {2021-09-16},

urldate = {2021-09-16},

journal = {Sensors and Actuators A: Physical},

volume = {332},

issue = {1},

abstract = {The article describes the design and modeling of a five-axis monolithic nanopositioning stage constructed from a bimorph piezoelectric sheet. Six-axis motion is also possible but requires 16 amplifier channels rather than 8. The nanopositioner is ultra low profile with a thickness of 1 mm. Analytical modeling and finite-element-analysis accurately predict the experimental performance. The stage was conservatively driven with 33% of the maximum voltage, which resulted in an X and Y travel range of 6.22 μm and 5.27 μm respectively; a Z travel range of 26.5 μm; and a rotational motion of 600 μrad and 884 μrad about the X and Y axis respectively. The first resonance frequency occurs at 883 Hz in the Z axis. Experimental atomic force microscopy is performed using the proposed device as a sample scanner.},

keywords = {AFM, Nanopositioning, piezoelectric},

pubstate = {published},

tppubtype = {article}

}

@article{Ruppert2021,

title = {Active atomic force microscope cantilevers with integrated device layer piezoresistive sensors},

author = {M. G. Ruppert and A. J. Fleming and Y. K. Yong},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2021/01/J21a.pdf},

doi = {10.1016/j.sna.2020.112519},

issn = {0924-4247},

year  = {2021},

date = {2021-01-19},

urldate = {2021-01-19},

journal = {Sensors & Actuators: A. Physical},

volume = {319},

pages = {112519},

abstract = {Active atomic force microscope cantilevers with on-chip actuation and sensing provide several advantages over

passive cantilevers which rely on piezoacoustic base-excitation and optical beam deflection measurement. Active

microcantilevers exhibit a clean frequency response, provide a path-way to miniturization and parallelization and

avoid the need for optical alignment. However, active microcantilevers are presently limited by the feedthrough

between actuators and sensors, and by the cost associated with custom microfabrication. In this work, we propose

a hybrid cantilever design with integrated piezoelectric actuators and a piezoresistive sensor fabricated from the

silicon device layer without requiring an additional doping step. As a result, the design can be fabricated using a

commercial five-mask microelectromechanical systems fabrication process. The theoretical piezoresistor sensitivity

is compared with finite element simulations and experimental results obtained from a prototype device. The

proposed approach is demonstrated to be a promising alternative to conventional microcantilever actuation and

deflection sensing},

keywords = {AFM, Cantilever, MEMS, Sensors, Smart Structures},

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 = {AFM, Cantilever, MEMS, Optics, SPM},

pubstate = {published},

tppubtype = {article}

}

@article{Ruppert2020,

title = {Amplitude Noise Spectrum of a Lock-in Amplifier: Application to Microcantilever Noise Measurements},

author = {M. G. Ruppert and N. J. Bartlett and Y. K. Yong and A. J. Fleming},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2020/09/J20f.pdf},

doi = {10.1016/j.sna.2020.112092},

year  = {2020},

date = {2020-05-29},

journal = {Sensors and Actuators A: Physical},

volume = {312},

pages = {112092},

abstract = {The lock-in amplifier is a crucial component in many applications requiring high-resolution displacement sensing; it's purpose is to estimate the amplitude and phase of a periodic signal, potentially corrupted by noise, at a frequency determined by a reference signal. Where the noise can be approximated by a stationary Gaussian process, such as thermal force noise and electronic sensor noise, this article derives the amplitude noise spectral density of the lock-in-amplifier output. The proposed method is demonstrated by predicting the demodulated noise spectrum of a microcantilever for dynamic-mode atomic force microscopy to determine the cantilever on-resonance thermal noise, the cantilever tracking bandwidth and the electronic noise floor. The estimates are shown to closely match experimental results over a wide range of operating conditions.},

keywords = {AFM, Cantilever, Demodulation, MEMS, System Identification},

pubstate = {published},

tppubtype = {article}

}

@article{Harcombe2020,

title = {A review of demodulation techniques for multifrequency atomic force microscopy},

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

editor = {T. Glatzel},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2020/02/J20b-reducedSize.pdf},

doi = {doi:10.3762/bjnano.11.8},

issn = {21904286},

year  = {2020},

date = {2020-01-07},

journal = {Beilstein Journal of Nanotechnology},

volume = {11},

pages = {76-97},

abstract = {This article compares the performance of traditional and recently proposed demodulators for multifrequency atomic force microscopy. 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 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 = {AFM, Demodulation, Multifrequency AFM, SPM},

pubstate = {published},

tppubtype = {article}

}

@article{Ruppert2018b,

title = {Multimodal atomic force microscopy with optimized higher eigenmode sensitivity using on-chip piezoelectric actuation and sensing},

author = {M. G. Ruppert and S. I. Moore and M. Zawierta and A. J. Fleming and G. Putrino and Y. K. Yong},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2019/08/Ruppert_2019_Nanotechnology_30_085503.pdf},

doi = {https://doi.org/10.1088/1361-6528/aae40b},

year  = {2019},

date = {2019-01-02},

journal = {Nanotechnology},

volume = {30},

number = {8},

pages = {085503},

abstract = {Atomic force microscope (AFM) cantilevers with integrated actuation and sensing provide several distinct advantages over conventional cantilever instrumentation. These include clean frequency responses, the possibility of down-scaling and parallelization to cantilever arrays as well as the absence of optical interference. While cantilever microfabrication technology has continuously advanced over the years, the overall design has remained largely unchanged; a passive rectangular shaped cantilever design has been adopted as the industry wide standard. In this article, we demonstrate multimode AFM imaging on higher eigenmodes as well as bimodal AFM imaging with cantilevers using fully integrated piezoelectric actuation and sensing. The cantilever design maximizes the higher eigenmode deflection sensitivity by optimizing the transducer layout according to the strain mode shape. Without the need for feedthrough cancellation, the read-out method achieves close to zero actuator/sensor feedthrough and the sensitivity is sufficient to resolve the cantilever Brownian motion.},

keywords = {AFM, Cantilever, MEMS, Multifrequency AFM, Piezoelectric Transducers and Drives, Sensors, Smart Structures, SPM},

pubstate = {published},

tppubtype = {article}

}

@article{J18c,

title = {Lyapunov Estimation for High-Speed Demodulation in Multifrequency Atomic Force Microscopy},

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

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2018/02/J18c.pdf},

doi = {10.3762/bjnano.9.47},

issn = {21904286},

year  = {2018},

date = {2018-02-28},

journal = {Beilstein Journal of Nanotechnology},

volume = {9},

pages = {490-498},

abstract = {An important issue in the emerging field of multifrequency atomic force microscopy (MF-AFM) is the accurate and fast demodulation of the cantilever-tip deflection signal. As this signal consists of multiple frequency components and noise processes, a lock-in amplifier is typically employed for its narrowband response. However, this demodulator suffers inherent bandwidth limitations as high frequency mixing products must be filtered out and several must be operated in parallel. Many MF-AFM methods require amplitude and phase demodulation at multiple frequencies of interest, enabling both z-axis feedback and phase contrast imaging to be achieved. This article proposes a model-based multifrequency Lyapunov filter implemented on a Field Programmable Gate Array (FPGA) for high-speed MF-AFM demodulation. System descriptions and simulations are verified by experimental results demonstrating high tracking bandwidths, strong off-mode rejection and minor sensitivity to cross-coupling effects. Additionally, a five-frequency system operating at 3.5MHz is implemented for higher harmonic amplitude and phase imaging up to 1MHz.},

keywords = {AFM, Multifrequency AFM},

pubstate = {published},

tppubtype = {article}

}

@article{J17k,

title = {An Ultra-thin Monolithic XY Nanopositioning Stage Constructed from a Single Sheet of Piezoelectric Material},

author = {A. J. Fleming and Y. K. Yong},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2018/01/J17k.pdf},

doi = {10.1109/TMECH.2017.2755659},

isbn = {1083-4435},

year  = {2017},

date = {2017-12-20},

journal = {IEEE/ASME Transactions on Mechatronics},

volume = {22},

number = {6},

pages = {2611-2618},

abstract = {The article describes an XY nanopositioning stage constructed from flexures and actuators machined into a single sheet of piezoelectric material. Ultrasonic machining is used to remove piezoelectric material and create electrode features. The constructed device is 0.508mm thick and has a travel range of 8.8um in the X and Y axes. The first resonance mode occurs at 597Hz which makes the device suitable for a wide range of standard nanopositioning applications where cost and size are considerations. Experimental atomic force microscopy is performed using the proposed device as a sample scanner.},

keywords = {AFM, Nanopositioning},

pubstate = {published},

tppubtype = {article}

}

@article{J17h,

title = {A Review of Demodulation Techniques for Amplitude Modulation Atomic Force Microscopy},

author = {M. G. Ruppert and D. M. Harcombe and M. R. P. Ragazzon and S. O. R. Moheimani and A. J. Fleming},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2020/08/2190-4286-8-142.pdf},

doi = {10.3762/bjnano.8.142},

year  = {2017},

date = {2017-09-01},

journal = {Bellstein Journal of Nanotechnology},

volume = {8},

pages = {1407–1426},

abstract = {In this review paper, traditional and novel demodulation methods applicable to amplitude modulation atomic force microscopy are implemented on a widely used digital processing system. As a crucial bandwidth-limiting component in the z-axis feedback loop of an atomic force microscope, the purpose of the demodulator is to obtain estimates of amplitude and phase of the cantilever deflection signal in the presence of sensor noise or additional distinct frequency components. Specifically for modern multifrequency techniques, where higher harmonic and/or higher eigenmode contributions are present in the oscillation signal, the fidelity of the estimates obtained from some demodulation techniques is not guaranteed. To enable a rigorous comparison, the performance metrics tracking bandwidth, implementation complexity and sensitivity to other frequency components are experimentally evaluated for each method. Finally, the significance of an adequate demodulator bandwidth is highlighted during high-speed tapping-mode AFM experiments in constant height mode.},

keywords = {AFM, SPM},

pubstate = {published},

tppubtype = {article}

}

@article{J17e,

title = {Lyapunov Estimator for High-Speed Demodulation in Dynamic Mode Atomic Force Microscopy},

author = {M. R. P. Ragazzon and M. G. Ruppert and D. M. Harcombe and A. J. Fleming and J. T. Gravdahl},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2017/09/J17e.pdf},

year  = {2017},

date = {2017-08-01},

journal = {IEEE Transactions on Control Systems Technology},

volume = {26},

number = {2},

pages = {765-772},

abstract = {In dynamic mode atomic force microscopy (AFM), the imaging bandwidth is governed by the slowest component in the open-loop chain consisting of the vertical actuator, cantilever and demodulator. While the common demodulation method is to use a lock-in amplifier (LIA), its performance is ultimately bounded by the bandwidth of the post-mixing low-pass filters. This article proposes an amplitude and phase estimation method based on a strictly positive real Lyapunov design approach. The estimator is designed to be of low complexity while allowing for high bandwidth. Additionally, suitable gains for high performance are suggested such that no tuning is necessary. The Lyapunov estimator is experimentally implemented for amplitude demodulation and shown to surpass the LIA in terms of tracking bandwidth and noise performance. High-speed AFM images are presented to corroborate the results.},

keywords = {AFM, SPM},

pubstate = {published},

tppubtype = {article}

}