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{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{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{Moore2020,

title = {AFM Cantilever Design for Multimode Q Control: Arbitrary Placement of Higher-Order Modes},

author = {S. I. Moore and M. G. Ruppert and Y. K. Yong},

url = {https://ieeexplore.ieee.org/document/9006926},

doi = {10.1109/TMECH.2020.2975627},

year  = {2020},

date = {2020-02-21},

journal = { IEEE/ASME Transactions on Mechatronics},

pages = {1-6},

abstract = {In the fast growing field of multifrequency atomic force microscopy (AFM), the benefits of using higher-order modes has been extensively reported on. However, higher modes of AFM cantilevers are difficult to instrument and Q control is challenging owing to their high frequency nature. At these high frequencies, the latencies in the computations and analog conversions of digital signal processing platforms become significant and limit the effective bandwidth of digital feedback controller implementations. To address this issue, this article presents a novel cantilever design for which the first five modes are placed within a 200 kHz bandwidth. The proposed cantilever is designed using a structural optimization routine. The close spacing and low mechanical bandwidth of the resulting cantilever allows for the implementation of Q controllers for all five modes using a standard FPGA development board for bimodal AFM and imaging on higher-order modes.},

note = {Early Access},

keywords = {AFM, Cantilever, MEMS, Multifrequency AFM, Smart Structures, SPM, Vibration Control},

pubstate = {published},

tppubtype = {article}

}

@article{Moore2019c,

title = {An optimization framework for the design of piezoelectric AFM cantilevers},

author = {S. I. Moore and M. G. Ruppert and Y. K. Yong},

url = {https://www.sciencedirect.com/science/article/pii/S0141635919302260},

year  = {2019},

date = {2019-08-15},

journal = {Precision Engineering},

volume = {60},

pages = {130-142},

abstract = {To facilitate further miniaturization of atomic force microscopy (AFM) cantilevers and to eliminate the standard optical beam deflection sensor, integrated piezoelectric actuation and sensing on the chip level is a promising option. This article presents a topology optimization method for dynamic mode AFM cantilevers that maximizes the sensitivity of an integrated piezoelectric sensor under stiffness and resonance frequency constraints. Included in the formulation is a new material model C-SIMP (connectivity and solid isotropic material with penalization) that extends the SIMP model to explicitly include the penalization of unconnected structures. Example cantilever designs demonstrate the potential of the topology optimization method. The results show, firstly, the C-SIMP material model significantly reduces connectivity issues and, secondly, arbitrary cantilever topologies can produce increases in sensor sensitivity or resonance frequency compared to a rectangular topology.},

keywords = {AFM, Cantilever, MEMS, Piezoelectric Transducers and Drives, Smart Structures, 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{Ruppert2018b,

title = {Self-sensing, estimation and control in multifrequency Atomic Force Microscopy. },

author = {M. G. Ruppert},

url = {https://royalsoc.org.au/images/pdf/journal/151-1-Ruppert.pdf},

issn = {0035-9173/18/010111-01},

year  = {2018},

date = {2018-06-01},

journal = {Journal & Proceedings of the Royal Society of New South Wales},

volume = {151},

number = {1},

pages = {111},

abstract = {Despite the undeniable success of the atomic force  microscope  (AFM),  dynamic  techniques still face limitations in terms of spatial resolution, imaging speed and high cost of acquisition. In order to expand the capabilities  of  the  instrument,  it  was  realized  that the information about the nano-mechanical properties  of  a  sample  are  encoded  over  a range of frequencies and the excitation and detection of higher-order eigenmodes of the micro-cantilever  open  up  further  informa-

tion  channels.  The  ability  to  control  these modes and their fast responses to excitation is believed to be the key to unravelling the true potential of these ethods. This work addresses  three  major  drawbacks  of  the standard AFM setup, which limit the feasibility of multi-frequency approaches.



First,   microelectromechanical   system (MEMS)  probes  with  integrated  piezoelectric layers is motivated, enabling the development of novel multimode self-sensing and self-actuating techniques. Specifically, these piezoelectric  transduction  schemes  permit the  miniaturization  of  the  entire  AFM towards  a  cost-effective  single-chip  device with nanoscale precision in a much smaller form factor than that of conventional macroscale instruments.



Second, the integrated actuation enables the development of multimode controllers which  exhibits  remarkable  performance  in arbitrarily  modifying  the  quality  factor  of multiple eigenmodes and comes with inherent  stability  robustness.  The  experimental results  demonstrate  improved  imaging  stability,  higher  scan  speeds  and  adjustable contrast  when  mapping  nano-mechanical properties of soft samples. 



Last, in light of the demand for constantly increasing  imaging  speeds  while  providing multi-frequency flexibility, the estimation of multiple components of the high-frequency deflection signal is performed with a linear time-varying multi-frequency Kalman filter. The chosen representation allows for an efficient high-bandwidth implementation on a Field  Programmable  Gate  Array. Tracking bandwidth, noise performance and trimodal AFM imaging on a two-component polymer sample  are  verified  and  shown  to  be  superior to that of the commonly used lock-in amplifier.},

keywords = {Cantilever, MEMS, Multifrequency AFM, Sensors, Smart Structures, SPM, System Identification, Vibration Control},

pubstate = {published},

tppubtype = {article}

}

@article{Ruppert2017b,

title = {Note: Guaranteed collocated multimode control of an atomic force microscope cantilever using on-chip piezoelectric actuation and sensing},

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

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2017/08/2017_JNote_RSI_Vol88_086109-2.pdf},

doi = {10.1063/1.4990451},

year  = {2017},

date = {2017-08-15},

journal = {Review of Scientific Instruments},

volume = {88},

number = {086109},

abstract = {The quality (Q) factor is an important parameter of the resonance of the microcantilever as it determines

both imaging bandwidth and force sensitivity. The ability to control the Q factor of multiple

modes is believed to be of great benefit for atomic force microscopy techniques involving multiple

eigenmodes. In this paper, we propose a novel cantilever design employing multiple piezoelectric

transducers which are used for separated actuation and sensing, leading to guaranteed collocation

of the first eight eigenmodes up to 3 MHz. The design minimizes the feedthrough usually observed

with these systems by incorporating a guard trace on the cantilever chip. As a result, a multimode

Q controller is demonstrated to be able to modify the quality factor of the first two eigenmodes over

up to four orders of magnitude without sacrificing robust stability.},

keywords = {AFM, Cantilever, MEMS, Multifrequency AFM, Piezoelectric Transducers and Drives, System Identification, Vibration Control},

pubstate = {published},

tppubtype = {article}

}

@article{Moore2017,

title = {Design and Characterization of Cantilevers for Multi-Frequency Atomic Force Microscopy},

author = {S. I. Moore and Y. K. Yong},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2017/01/MNL.2016.0586.pdf},

doi = {10.1049/mnl.2016.0586},

year  = {2017},

date = {2017-03-01},

journal = {Micro & Nano Letters},

volume = {12},

number = {5},

pages = {315-320},

abstract = {The experimental characterisation of a set of microcantilevers targeted at use in multi-frequency atomic force microscope is presented. The aim of this work is to design a cantilever that naturally amplifies its harmonic oscillations which are introduced by nonlinear probe–sample

interaction forces. This is performed by placing the modal frequencies of the cantilever at integer multiples of the first modal frequency. The developed routine demonstrates the placement of the frequency of the second to fifth mode. The characterisation shows a trend that

lower-order modes are more accurately placed than higher-order modes. With two fabricated designs, the error in the second mode is at most 2.26% while the greatest error in the fifth mode is at 10.5%.},

keywords = {Cantilever, MEMS, Multifrequency AFM, SPM},

pubstate = {published},

tppubtype = {article}

}

@article{Moore2017b,

title = {Multimodal cantilevers with novel piezoelectric layer topology for sensitivity enhancement},

author = {S. I. Moore and M. G. Ruppert and Y. K. Yong},

url = {https://www.precisionmechatronicslab.com/wp-content/uploads/2017/02/2190-4286-8-38.pdf},

year  = {2017},

date = {2017-02-06},

journal = {Beilstein Journal of Nanotechnology},

volume = {8},

pages = {358--371},

abstract = {Self-sensing techniques for atomic force microscope (AFM) cantilevers have several advantageous characteristics compared to the optical beam deflection method. The possibility of down scaling, parallelization of cantilever arrays and the absence of optical interference associated imaging artifacts have led to an increased research interest in these methods. However, for multifrequency AFM, the optimization of the transducer layout on the cantilever for higher order modes has not been addressed. To fully utilize an integrated piezoelectric transducer, this work alters the layout of the piezoelectric layer to maximize both the deflection of the cantilever and measured piezoelectric charge response for a given mode with respect to the spatial distribution of the strain. On a prototype cantilever design, significant increases in actuator and sensor sensitivities were achieved for the first four modes without any substantial increase in sensor noise. The transduction mechanism is specifically targeted at multifrequency AFM and has the potential to provide higher resolution imaging on higher order modes.},

keywords = {Cantilever, Multifrequency AFM, Piezoelectric Transducers and Drives, SPM},

pubstate = {published},

tppubtype = {article}

}