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Biglarbeigi P, Morelli A, Pauly S, Yu Z, Jiang W, Sharma S, Finlay D, Kumar A, Soin N, Payam AF. Unraveling Spatiotemporal Transient Dynamics at the Nanoscale via Wavelet Transform-Based Kelvin Probe Force Microscopy. ACS NANO 2023; 17:21506-21517. [PMID: 37877266 PMCID: PMC10655243 DOI: 10.1021/acsnano.3c06488] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Accepted: 10/11/2023] [Indexed: 10/26/2023]
Abstract
Mechanistic probing of surface potential changes arising from dynamic charge transport is the key to understanding and engineering increasingly complex nanoscale materials and devices. Spatiotemporal averaging in conventional heterodyne detection-based Kelvin probe force microscopy (KPFM) inherently limits its time resolution, causing an irretrievable loss of transient response and higher-order harmonics. Addressing this, we report a wavelet transform (WT)-based methodology capable of quantifying the sub-ms charge dynamics and probing the elusive transient response. The feedback-free, open-loop wavelet transform KPFM (OL-WT-KPFM) technique harnesses the WT's ability to simultaneously extract spatial and temporal information from the photodetector signal to provide a dynamic mapping of surface potential, capacitance gradient, and dielectric constant at a temporal resolution 3 orders of magnitude higher than the lock-in time constant. We further demonstrate the method's applicability to explore the surface-photovoltage-induced sub-ms hole-diffusion transient in bismuth oxyiodide semiconductor. The OL-WT-KPFM concept is readily applicable to commercial systems and can provide the underlying basis for the real-time analysis of transient electronic and electrochemical properties.
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Affiliation(s)
- Pardis Biglarbeigi
- Nanotechnology
and Integrated Bio-Engineering Centre (NIBEC), School of Engineering, Ulster University, York Street, Belfast BT15 1AP, Co. Antrim, Northern
Ireland, United Kingdom
- School
of Science and Engineering, University of
Dundee, Nethergate, Dundee, DD1 4NH, Scotland, United Kingdom
| | - Alessio Morelli
- Nanotechnology
and Integrated Bio-Engineering Centre (NIBEC), School of Engineering, Ulster University, York Street, Belfast BT15 1AP, Co. Antrim, Northern
Ireland, United Kingdom
| | - Serene Pauly
- School
of Mathematics and Physics, Queen’s
University Belfast, University Road, Belfast BT7 1NN, Northern Ireland, United Kingdom
| | - Zidong Yu
- Institute
for Materials Research and Innovation (IMRI), University of Bolton, Deane Road, Bolton BL3
5AB, United Kingdom
| | - Wenjun Jiang
- College
of Transportation Engineering, Dalian Maritime
University, Dalian 116026, China
| | - Surbhi Sharma
- Centre
for New Energy Transition Research Technologies (CfNETR), Federation University Australia, Gippsland Campus, Churchill, Victoria 3810, Australia
| | - Dewar Finlay
- Nanotechnology
and Integrated Bio-Engineering Centre (NIBEC), School of Engineering, Ulster University, York Street, Belfast BT15 1AP, Co. Antrim, Northern
Ireland, United Kingdom
| | - Amit Kumar
- School
of Mathematics and Physics, Queen’s
University Belfast, University Road, Belfast BT7 1NN, Northern Ireland, United Kingdom
| | - Navneet Soin
- Nanotechnology
and Integrated Bio-Engineering Centre (NIBEC), School of Engineering, Ulster University, York Street, Belfast BT15 1AP, Co. Antrim, Northern
Ireland, United Kingdom
- School of
Science, Computing and Engineering Technologies, Swinburne University of Technology,
P.O. Box 218, Hawthorn Victoria 3122, Australia
| | - Amir Farokh Payam
- Nanotechnology
and Integrated Bio-Engineering Centre (NIBEC), School of Engineering, Ulster University, York Street, Belfast BT15 1AP, Co. Antrim, Northern
Ireland, United Kingdom
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2
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Gisbert VG, Garcia R. Insights and guidelines to interpret forces and deformations at the nanoscale by using a tapping mode AFM simulator: dForce 2.0. SOFT MATTER 2023; 19:5857-5868. [PMID: 37305960 DOI: 10.1039/d3sm00334e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Amplitude modulation (tapping mode) AFM is the most versatile AFM mode for imaging surfaces at the nanoscale in air and liquid environments. However, it remains challenging to estimate the forces and deformations exerted by the tip. We introduce a new simulator environment to predict the values of the observables in tapping mode AFM experiments. The relevant feature of dForce 2.0 is the incorporation of contact mechanics models aimed to describe the properties of ultrathin samples. These models were essential to determine the forces applied on samples such as proteins, self-assembled monolayers, lipid bilayers, and few-layered materials. The simulator incorporates two types of long-range magnetic forces. The simulator is written in an open-source code (Python) and it can be run from a personal computer.
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Affiliation(s)
- Victor G Gisbert
- Instituto de Ciencia de Materiales de Madrid, CSIC c/Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain.
| | - Ricardo Garcia
- Instituto de Ciencia de Materiales de Madrid, CSIC c/Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain.
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3
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Ferri G, Barile G, Leoni A. Editorial for the Special Issue on Electronics for Sensors II. SENSORS (BASEL, SWITZERLAND) 2023; 23:1640. [PMID: 36772679 PMCID: PMC9920723 DOI: 10.3390/s23031640] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Accepted: 01/31/2023] [Indexed: 06/18/2023]
Abstract
Sensor signals are physical, chemical, or biological quantities that evolve over time [...].
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4
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Pettinato S, Girolami M, Rossi MC, Salvatori S. Accurate Signal Conditioning for Pulsed-Current Synchronous Measurements. SENSORS (BASEL, SWITZERLAND) 2022; 22:5360. [PMID: 35891039 PMCID: PMC9321935 DOI: 10.3390/s22145360] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 07/15/2022] [Accepted: 07/16/2022] [Indexed: 06/15/2023]
Abstract
This paper describes a compact electronic system employing a synchronous demodulation measurement method for the acquisition of pulsed-current signals. The fabricated prototype shows superior performance in terms of signal-to-noise ratio in comparison to conventional instrumentation performing free-running measurements, especially when extremely narrow pulses are concerned. It shows a reading error around 0.1% independently of the signal duty cycle (D) in the investigated D = 10−4−10−3 range. Conversely, high-precision electrometers display reading errors as high as 30% for a D = 10−4, which reduces to less than 1% only for D > 3 × 10−3. Field tests demonstrate that the developed front-end/readout electronics is particularly effective when coupled to dosimeters irradiated with the X-rays sourced by a medical linear accelerator. Therefore, it may surely be exploited for the real-time monitoring of the dosimeter output current, as required in modern radiotherapy techniques employing ultra-narrow pulses of high-energy photons or nuclear particles.
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Affiliation(s)
- Sara Pettinato
- Faculty of Engineering, Università degli Studi Niccolò Cusano, Via don Carlo Gnocchi 3, 00166 Rome, Italy;
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), Strada Provinciale 35D 9, Montelibretti, 00010 Rome, Italy
| | - Marco Girolami
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), Strada Provinciale 35D 9, Montelibretti, 00010 Rome, Italy
| | - Maria Cristina Rossi
- Department of Industrial, Electronic and Mechanical Engineering, Roma Tre University, Via Vito Volterra 62, 00146 Rome, Italy;
| | - Stefano Salvatori
- Faculty of Engineering, Università degli Studi Niccolò Cusano, Via don Carlo Gnocchi 3, 00166 Rome, Italy;
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), Strada Provinciale 35D 9, Montelibretti, 00010 Rome, Italy
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5
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Zan W, Wang Y, Liu X, Wang P, Jin B. Envelope Extraction for Vibration Locating in Coherent Φ-OTDR. SENSORS (BASEL, SWITZERLAND) 2022; 22:1197. [PMID: 35161942 PMCID: PMC8838449 DOI: 10.3390/s22031197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 01/29/2022] [Accepted: 02/02/2022] [Indexed: 06/14/2023]
Abstract
In a coherent phase-sensitive optical time-domain reflectometry (Φ-OTDR) sensing system, a frequency shift of hundreds of MHz generated by the pulse modulation of an acoustic optic modulator results in a high central frequency of a beating signal spectrum. In order to reduce the high-performance hardware requirement of signal acquisition, the coherent Φ-OTDR based on envelope extraction is proposed in this paper. Firstly, a theoretical model of a quasi-sinusoidal amplitude-modulated signal is built for the beating signal between local oscillator light and Rayleigh backward scattering light. An envelope detector is then utilized to realize the envelope extraction of beating signals with advantages of a simple structure and quick response. The extracted envelope can be directly used for vibration locating without the conventional orthogonal demodulation. Experiment results present that the sampling rate can be reduced to 10 MHz under the spatial resolution of 10 m and the sensing distance of 31 km. This scheme proves that envelope extraction is a reliable technical route for vibration locating, which can effectively reduce the sampling rate and simplify the data demodulation.
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Affiliation(s)
- Wei Zan
- Key Laboratory of Advanced Transducers and Intelligent Control Systems (Ministry of Education and Shanxi Province), College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China; (W.Z.); (Y.W.)
| | - Yu Wang
- Key Laboratory of Advanced Transducers and Intelligent Control Systems (Ministry of Education and Shanxi Province), College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China; (W.Z.); (Y.W.)
| | - Xin Liu
- College of Information and Computer, Taiyuan University of Technology, Taiyuan 030024, China;
| | - Pengfei Wang
- College of Electrical and Power Engineering, Taiyuan University of Technology, Taiyuan 030024, China;
| | - Baoquan Jin
- Key Laboratory of Advanced Transducers and Intelligent Control Systems (Ministry of Education and Shanxi Province), College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China; (W.Z.); (Y.W.)
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6
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A Simple Low-Cost Electrocardiogram Synchronizer. SENSORS 2021; 21:s21175885. [PMID: 34502776 PMCID: PMC8434309 DOI: 10.3390/s21175885] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 08/24/2021] [Accepted: 08/28/2021] [Indexed: 11/28/2022]
Abstract
Electrocardiogram (ECG) synchronization is useful to avoid the effects of cardiac motion in medical measurements, and is widely used in standard medical imaging. A number of medical equipment include embedded commercial synchronizers. However, the use of independent synchronization modules is sometimes needed when several non-integrated instruments are used, or in the development of new medical instruments and procedures. We present a simple low-cost ECG synchronizer module based on an Arduino controller board that converts the ECG signal into a transistor-transistor-logic (TTL) one, allowing real-time medical measurements triggered at specific phases of the cardiac cycle. The device and conversion algorithm developed is optimized in vitro using synthetic and human ECG signals, and tested in vivo on three swine specimens. Error rates during the in vivo testing stage remain below the 2% of the cycles in all animals and critical false positives are less than 1%, which is sufficient for most applications. Possible algorithm updates are discussed if its performance needs to be improved.
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7
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Farokh Payam A, Biglarbeigi P, Morelli A, Lemoine P, McLaughlin J, Finlay D. Data acquisition and imaging using wavelet transform: a new path for high speed transient force microscopy. NANOSCALE ADVANCES 2021; 3:383-398. [PMID: 36131753 PMCID: PMC9417248 DOI: 10.1039/d0na00531b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Accepted: 09/10/2020] [Indexed: 06/13/2023]
Abstract
The unique ability of Atomic Force Microscopy (AFM) to image, manipulate and characterize materials at the nanoscale has made it a remarkable tool in nanotechnology. In dynamic AFM, acquisition and processing of the photodetector signal originating from probe-sample interaction is a critical step in data analysis and measurements. However, details of such interaction including its nonlinearity and dynamics of the sample surface are limited due to the ultimately bounded bandwidth and limited time scales of data processing electronics of standard AFM. Similarly, transient details of the AFM probe's cantilever signal are lost due to averaging of data by techniques which correlate the frequency spectrum of the captured data with a temporally invariant physical system. Here, we introduce a fundamentally new approach for dynamic AFM data acquisition and imaging based on applying the wavelet transform on the data stream from the photodetector. This approach provides the opportunity for exploration of the transient response of the cantilever, analysis and imaging of the dynamics of amplitude and phase of the signals captured from the photodetector. Furthermore, it can be used for the control of AFM which would yield increased imaging speed. Hence the proposed method opens a pathway for high-speed transient force microscopy.
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Affiliation(s)
- Amir Farokh Payam
- Nanotechnology and Integrated Bioengineering Centre (NIBEC), School of Engineering, Ulster University Jordanstown Shore Road Northern Ireland BT37 0QB UK
| | - Pardis Biglarbeigi
- Nanotechnology and Integrated Bioengineering Centre (NIBEC), School of Engineering, Ulster University Jordanstown Shore Road Northern Ireland BT37 0QB UK
| | - Alessio Morelli
- Nanotechnology and Integrated Bioengineering Centre (NIBEC), School of Engineering, Ulster University Jordanstown Shore Road Northern Ireland BT37 0QB UK
| | - Patrick Lemoine
- Nanotechnology and Integrated Bioengineering Centre (NIBEC), School of Engineering, Ulster University Jordanstown Shore Road Northern Ireland BT37 0QB UK
| | - James McLaughlin
- Nanotechnology and Integrated Bioengineering Centre (NIBEC), School of Engineering, Ulster University Jordanstown Shore Road Northern Ireland BT37 0QB UK
| | - Dewar Finlay
- Nanotechnology and Integrated Bioengineering Centre (NIBEC), School of Engineering, Ulster University Jordanstown Shore Road Northern Ireland BT37 0QB UK
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8
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Ahmed H, Benbouzid M. Gradient Estimator-Based Amplitude Estimation for Dynamic Mode Atomic Force Microscopy: Small-Signal Modeling and Tuning. SENSORS (BASEL, SWITZERLAND) 2020; 20:s20092703. [PMID: 32397441 PMCID: PMC7249209 DOI: 10.3390/s20092703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Revised: 05/04/2020] [Accepted: 05/06/2020] [Indexed: 05/18/2023]
Abstract
Atomic force microscopy (AFM) plays an important role in nanoscale imaging application. AFM works by oscillating a microcantilever on the surface of the sample being scanned. In this process, estimating the amplitude of the cantilever deflection signal plays an important role in characterizing the topography of the surface. Existing approaches on this topic either have slow dynamic response e.g., lock-in-amplifier or high computational complexity e.g., Kalman filter. In this context, gradient estimator can be considered as a trade-off between fast dynamic response and high computational complexity. However, no constructive tuning rule is available in the literature for gradient estimator. In this paper, we consider small-signal modeling and tuning of gradient estimator. The proposed approach greatly simplifies the tuning procedure. Numerical simulation and experimental results are provided to demonstrate the suitability of the proposed tuning procedure.
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Affiliation(s)
- Hafiz Ahmed
- School of Mechanical, Aerospace and Automotive Engineering, The Futures Institute, Coventry University, Coventry CV1 2TL, UK;
| | - Mohamed Benbouzid
- Institut de Recherche Dupuy de Lôme (UMR CNRS 6027), University of Brest, 29238 Brest, France
- Logistics Engineering College, Shanghai Maritime University, Shanghai 201306, China
- Correspondence: ; Tel.: +86-332-9801-8007
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9
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Abstract
With the recent rapid increase in the use of roof top photovoltaic solar systems worldwide, and also, more recently, the dramatic escalation in building grid connected solar farms, especially in Australia, the need for more accurate methods of very short-term forecasting has become a focus of research. The International Energy Agency Tasks 46 and 16 have brought together groups of experts to further this research. In Australia, the Australian Renewable Energy Agency is funding consortia to improve the five minute forecasting of solar farm output, as this is the time scale of the electricity market. The first step in forecasting of either solar radiation or output from solar farms requires the representation of the inherent seasonality. One can characterise the seasonality in climate variables by using either a multiplicative or additive modelling approach. The multiplicative approach with respect to solar radiation can be done by calculating the clearness index, or alternatively estimating the clear sky index. The clearness index is defined as the division of the global solar radiation by the extraterrestrial radiation, a quantity determined only via astronomical formulae. To form the clear sky index one divides the global radiation by a clear sky model. For additive de-seasoning, one subtracts some form of a mean function from the solar radiation. That function could be simply the long term average at the time steps involved, or more formally the addition of terms involving a basis of the function space. An appropriate way to perform this operation is by using a Fourier series set of basis functions. This article will show that for various reasons the additive approach is superior. Also, the differences between the representation for solar energy versus solar farm output will be demonstrated. Finally, there is a short description of the subsequent steps in short-term forecasting.
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10
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Harcombe DM, Ruppert MG, Fleming AJ. A review of demodulation techniques for multifrequency atomic force microscopy. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2020; 11:76-91. [PMID: 31976199 PMCID: PMC6964647 DOI: 10.3762/bjnano.11.8] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Accepted: 12/11/2019] [Indexed: 05/29/2023]
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.
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Affiliation(s)
- David M Harcombe
- School of Electrical Engineering and Computing, The University of Newcastle, Callaghan, NSW, 2308, Australia
| | - Michael G Ruppert
- School of Electrical Engineering and Computing, The University of Newcastle, Callaghan, NSW, 2308, Australia
| | - Andrew J Fleming
- School of Electrical Engineering and Computing, The University of Newcastle, Callaghan, NSW, 2308, Australia
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11
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Shen S, Wu J, Chen N. Quadrature demodulation in line-scan focal modulation microscopy for imaging three-dimensional zebrafish neural structure. JOURNAL OF BIOPHOTONICS 2020; 13:e201900170. [PMID: 31343833 DOI: 10.1002/jbio.201900170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Revised: 06/23/2019] [Accepted: 07/23/2019] [Indexed: 06/10/2023]
Abstract
Visualizing biological processes in neuroscience requires in vivo functional imaging at single-neuron resolution, high image acquisition speed and strong optical sectioning ability. However, due to light scattering of in tissue, very often conventional wide-field fluorescence microscopes are unable to resolve cells in the presence of a strong out-of-focus background. Line-scan focal modulation microscopy enables high temporal resolution and good optical sectioning ability at the same time. Here we demonstrate a quadrature demodulation method to extract the focal information with an extended frequency bandwidth and therefore higher spatial resolution. The performance of the demodulation scheme in line-scan focal modulation microscope has been evaluated by performing imaging experiments with fluorescence beads and zebrafish neural structure. Reduced background, reduced artifacts and more detailed morphological information are evident in the obtained images.
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Affiliation(s)
- Shuhao Shen
- Department of Biomedical Engineering, National University of Singapore, Singapore, Singapore
| | - Jian Wu
- Institute of Biomedical Engineering, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China
| | - Nanguang Chen
- Department of Biomedical Engineering, National University of Singapore, Singapore, Singapore
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12
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Harcombe DM, Ruppert MG, Ragazzon MRP, Fleming AJ. Lyapunov estimation for high-speed demodulation in multifrequency atomic force microscopy. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2018. [PMID: 29515961 PMCID: PMC5815288 DOI: 10.3762/bjnano.9.47] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
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 3.5 MHz is implemented for higher harmonic amplitude and phase imaging up to 1 MHz.
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Affiliation(s)
- David M Harcombe
- School of Electrical Engineering and Computing, The University of Newcastle, Callaghan, NSW, 2308, Australia
| | - Michael G Ruppert
- School of Electrical Engineering and Computing, The University of Newcastle, Callaghan, NSW, 2308, Australia
| | - Michael R P Ragazzon
- Department of Engineering Cybernetics, NTNU, Norwegian University of Science and Technology, Trondheim, Norway
| | - Andrew J Fleming
- School of Electrical Engineering and Computing, The University of Newcastle, Callaghan, NSW, 2308, Australia
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Tajaddodianfar F, Moheimani SOR, Owen J, Randall JN. On the effect of local barrier height in scanning tunneling microscopy: Measurement methods and control implications. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:013701. [PMID: 29390696 DOI: 10.1063/1.5003851] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A common cause of tip-sample crashes in a Scanning Tunneling Microscope (STM) operating in constant current mode is the poor performance of its feedback control system. We show that there is a direct link between the Local Barrier Height (LBH) and robustness of the feedback control loop. A method known as the "gap modulation method" was proposed in the early STM studies for estimating the LBH. We show that the obtained measurements are affected by controller parameters and propose an alternative method which we prove to produce LBH measurements independent of the controller dynamics. We use the obtained LBH estimation to continuously update the gains of a STM proportional-integral (PI) controller and show that while tuning the PI gains, the closed-loop system tolerates larger variations of LBH without experiencing instability. We report experimental results, conducted on two STM scanners, to establish the efficiency of the proposed PI tuning approach. Improved feedback stability is believed to help in avoiding the tip/sample crash in STMs.
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Affiliation(s)
- Farid Tajaddodianfar
- Department of Mechanical Engineering, Erik Jonsson School of Engineering and Computer Science, The University of Texas at Dallas, Richardson, Texas 75080, USA
| | - S O Reza Moheimani
- Department of Mechanical Engineering, Erik Jonsson School of Engineering and Computer Science, The University of Texas at Dallas, Richardson, Texas 75080, USA
| | - James Owen
- Zyvex Labs LLC, 1301 N Plano Rd., Richardson, Texas 75081, USA
| | - John N Randall
- Zyvex Labs LLC, 1301 N Plano Rd., Richardson, Texas 75081, USA
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