2024 |
||
9. | L. R. McCourt; B. S. Routley; M. G. Ruppert; A. J. Fleming Feasibility of gold nanocones for collocated tip-enhanced Raman spectroscopy and atomic force microscope imaging Journal Article Forthcoming In: Journal of Raman Spectroscopy, Forthcoming, ISSN: 1097-4555. Abstract | Links | BibTeX | Tags: AFM, Cantilever, Optics @article{J23a, 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. | |
2022 |
||
8. | M. G. Ruppert; D. Martin-Jimenez; Y. K. Yong; A. Ihle; A. Schirmeisen; A. J. Fleming; D. Ebeling Experimental Analysis of Tip Vibrations at Higher Eigenmodes of QPlus Sensors for Atomic Force Microscopy Journal Article In: Nanotechnology, vol. 33, iss. 18, pp. 185503, 2022, ISSN: 1361-6528. Abstract | Links | BibTeX | Tags: Actuator, AFM, Cantilever, Multifrequency AFM, piezoelectric @article{Ruppert2022, 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. | |
2021 |
||
7. | M. G. Ruppert; N. F. S. de Bem; A. J. Fleming; Y. K. Yong Characterization of Active Microcantilevers Using Laser Doppler Vibrometry Book Chapter In: Vibration Engineering for a Sustainable Future , Chapter 45, Springer, 2021, ISBN: 978-3-030-48153-7. Abstract | Links | BibTeX | Tags: AFM, Cantilever, MEMS, Piezoelectric Transducers and Drives, Smart Structures @inbook{Ruppert2021b, Active atomic force microscope cantilevers with on-chip actuation and sensing provide several advantages over passive cantilevers which rely on piezoacoustic base-excitation and the optical beam deflection measurement. Most importantly, these cantilevers provide clean frequency responses, the possibility of down-scaling and parallelization to cantilever arrays as well as the absence of optical interferences. In this paper, we demonstrate the analysis and calibration steps for three active cantilever geometries with integrated piezoelectric actuation. For this purpose, laser Doppler vibrometry (LDV) is used to experimentally obtain the deflection mode shapes of the first three eigenmodes, calibrate actuation gains, and to determine the dynamic modal stiffnesses using the Brownian spectrum of the cantilever. The experimental values are compared with finite element simulations. | |
6. | M. G. Ruppert; A. J. Fleming; Y. K. Yong Active atomic force microscope cantilevers with integrated device layer piezoresistive sensors Journal Article In: Sensors & Actuators: A. Physical, vol. 319, pp. 112519, 2021, ISSN: 0924-4247. Abstract | Links | BibTeX | Tags: AFM, Cantilever, MEMS, Sensors, Smart Structures @article{Ruppert2021, 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 | |
2020 |
||
5. | L. McCourt; M. G. Ruppert; B. S. Routley; S. Indirathankam; A. J. Fleming A comparison of gold and silver nanocones and geometry optimisation for tip-enhanced microscopy Journal Article In: Journal of Raman Spectroscopy, vol. 51, iss. 11, pp. 2208-2216, 2020. Abstract | Links | BibTeX | Tags: AFM, Cantilever, MEMS, Optics, SPM @article{McCourt2020, 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. | |
4. | M. G. Ruppert; N. J. Bartlett; Y. K. Yong; A. J. Fleming Amplitude Noise Spectrum of a Lock-in Amplifier: Application to Microcantilever Noise Measurements Journal Article In: Sensors and Actuators A: Physical, vol. 312, pp. 112092, 2020. Abstract | Links | BibTeX | Tags: AFM, Cantilever, Demodulation, MEMS, System Identification @article{Ruppert2020, 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. | |
2019 |
||
3. | L. McCourt; B. S. Routley; M. G. Ruppert; A. J. Fleming Resolution and Enhancement of Probes for Tip Enhanced Raman Spectroscopy Conference International Conference on Nanophotonics and Micro/Nano Optics (NANOP), Munich, Germany, 2019. Abstract | BibTeX | Tags: AFM, Cantilever, Lithography @conference{McCourt2019, Two photon apertureless nearfield lithography allows sub diffraction limited features for integrated circuit production. It involves exciting surface plasmons on a metallic atomic force microscopy probe, which generates an enhancement of the localised electric field, exposing a photoresist. Costing less than extreme ultra violet lithography, and reducing exposure from scattered light compared to one photon nearfield lithography, this technique is suited for device prototyping or low volume production. The work here considers the material and geometry of an ideal AFM probe in terms of resolution (producing the smallest features) and electric field enhancement. | |
2. | D. M. Harcombe; M. G. Ruppert; A. J. Fleming Modeling and Noise Analysis of a Microcantilever-based Mass Sensor Proceedings Article In: Int. Conference on Manipulation, Automation and Robotics at Small Scales (MARSS), Helsinki, Finland, 2019, ISSN: 978-1-7281-0948-0. Abstract | Links | BibTeX | Tags: AFM, Cantilever, MEMS, Sensors, Smart Structures @inproceedings{Harcombe2019, Nanomechanical devices have the potential for practical applications as mass sensors. In microcantilever based sensing, resonance frequency shifts are tracked by a phase-locked loop (PLL) in-order to monitor mass adsorption. A major challenge in minimizing the mass detection limit comes from the noise present in the system due to thermal, sensor and oscillator noise. There is numerical difficulty in simulating PLLs, as both low frequency phase estimates and high frequency mixing products need to be captured resulting in a stiff problem. By using linear system-theoretic modeling an in-depth analysis of the system is able to be conducted overcoming this issue. This provides insight into individual noise source propagation, dominant noise sources and possible ways to reduce their effects. The developed model is verified in simulation against the non-linear PLL, with each achieving low picogram sensitivity for a 100 Hz loop bandwidth and realistically modeled noise sources. | |
1. | M. G. Ruppert; S. I. Moore; M. Zawierta; A. J. Fleming; G. Putrino; Y. K. Yong Multimodal atomic force microscopy with optimized higher eigenmode sensitivity using on-chip piezoelectric actuation and sensing Journal Article In: Nanotechnology, vol. 30, no. 8, pp. 085503, 2019. Abstract | Links | BibTeX | Tags: AFM, Cantilever, MEMS, Multifrequency AFM, Piezoelectric Transducers and Drives, Sensors, Smart Structures, SPM @article{Ruppert2018b, 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. |
2024 |
||
9. | Feasibility of gold nanocones for collocated tip-enhanced Raman spectroscopy and atomic force microscope imaging Journal Article Forthcoming In: Journal of Raman Spectroscopy, Forthcoming, ISSN: 1097-4555. | |
2022 |
||
8. | Experimental Analysis of Tip Vibrations at Higher Eigenmodes of QPlus Sensors for Atomic Force Microscopy Journal Article In: Nanotechnology, vol. 33, iss. 18, pp. 185503, 2022, ISSN: 1361-6528. | |
2021 |
||
7. | Characterization of Active Microcantilevers Using Laser Doppler Vibrometry Book Chapter In: Vibration Engineering for a Sustainable Future , Chapter 45, Springer, 2021, ISBN: 978-3-030-48153-7. | |
6. | Active atomic force microscope cantilevers with integrated device layer piezoresistive sensors Journal Article In: Sensors & Actuators: A. Physical, vol. 319, pp. 112519, 2021, ISSN: 0924-4247. | |
2020 |
||
5. | A comparison of gold and silver nanocones and geometry optimisation for tip-enhanced microscopy Journal Article In: Journal of Raman Spectroscopy, vol. 51, iss. 11, pp. 2208-2216, 2020. | |
4. | Amplitude Noise Spectrum of a Lock-in Amplifier: Application to Microcantilever Noise Measurements Journal Article In: Sensors and Actuators A: Physical, vol. 312, pp. 112092, 2020. | |
2019 |
||
3. | Resolution and Enhancement of Probes for Tip Enhanced Raman Spectroscopy Conference International Conference on Nanophotonics and Micro/Nano Optics (NANOP), Munich, Germany, 2019. | |
2. | Modeling and Noise Analysis of a Microcantilever-based Mass Sensor Proceedings Article In: Int. Conference on Manipulation, Automation and Robotics at Small Scales (MARSS), Helsinki, Finland, 2019, ISSN: 978-1-7281-0948-0. | |
1. | Multimodal atomic force microscopy with optimized higher eigenmode sensitivity using on-chip piezoelectric actuation and sensing Journal Article In: Nanotechnology, vol. 30, no. 8, pp. 085503, 2019. |