A.F. Payam

Ulster University · Department of Engineering

Many industrial and technological applications require precise determination of the viscosity and density of liquids. Such measurements can be time consuming and often require sampling substantial amounts of the liquid. These problems can partly be overcome with the use of microcantilevers but most existing methods depend on the specific geometry a...

Fast quantitative mapping of mechanical properties with nanoscale spatial resolution represents one of the major goals of force microscopy. This goal becomes more challenging when the characterization needs to be accomplished with subnanometer resolution in a native environment that involves liquid solutions. Here we demonstrate that bimodal atomic...

Fast, accurate, and robust nanomechanical measurements are intensely studied in materials science, applied physics, and molecular biology. Amplitude modulation force microscopy (tapping mode) is the most established nanoscale characterization technique of surfaces for air and liquid environments. However, its quantitative capabilities lag behind it...

We demonstrate that the phase contrast observed with an amplitude modulation atomic force microscope depends on two factors, the generation of higher harmonics components and the energy dissipated on the sample surface. Those factors are ultimately related to the chemical composition and structure of the surface. Our findings are general, but they...

Due to their facile tunability, metal–organic frameworks (MOFs) are employed as precursors and templates to construct advanced functional materials with unique and desired chemical, physical, mechanical, and morphological properties. By tuning MOF precursor composition and manipulating conversion processes, various MOF‐derived materials commonly kn...

Objective Instrumented mouthguard (iMG) systems use different signal processing approaches limiting field-based inter-study comparisons, especially when artefacts are present in the signal. The objective of this study was to assess the frequency content and characteristics of head kinematic signals from head impact reconstruction laboratory and fie...

The advancement of dynamic and multifrequency atomic force microscopy (AFM) necessitates leveraging the frequency response of cantilevers when it is in contact with the specimen surface. By capturing the vibration response of the cantilever, it becomes possible to map and measure the local properties of materials. Utilizing higher oscillation modes...

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 irretrieva...

Microcantilevers are at the heart of atomic force microscopy (AFM) and play a significant role in AFM‐based techniques. Recent advancements in multifrequency AFM require the simultaneous excitation and detection of multiple eigenfrequencies of microcantilevers to assess more data channels to quantify the material properties. However, to achieve hig...

Many advances in polymers and layered materials rely on a precise understanding of the local interactions between adjacent molecular or atomic layers. Quantifying dispersion forces at the nanoscale is particularly challenging with existing methods often time consuming, destructive, relying on surface averaging or requiring bespoke equipment. Here,...

High-harmonic (HH) frequencies in microcantilever impose several applications in precision detection thanks to the higher sensitivity of the higher modes in comparison to the fundamental modes. In this study, we showed that by tuning the cantilever length via changing the clamped position, the dimensional ratio of the overhang to the main cantileve...

Highly stable and environmentally friendly nitrogen-doped graphite quantum dots consisting of ~12 layers of graphene, average diameter of ~7.3 nm, prepared by atmospheric pressure microplasma are reported to have blue emission due to surface states created by nitrogen doping (9 atomic%) and reaction with oxygen. The low-temperature synthesis method...

Probing material properties at surfaces down to the single-particle scale of atoms and molecules has been achieved, but high-resolution subsurface imaging remains a nanometrology challenge due to electromagnetic and acoustic dispersion and diffraction. The atomically sharp probe used in scanning probe microscopy (SPM) has broken these limits at sur...

Understanding changes in the mechanical features of a single protein from a mutated virus while establishing its relation to the point mutations is critical in developing new inhibitory routes to tackle the uncontrollable spread of the virus. Addressing this, herein, the chemomechanical features of a single spike protein are quantified from alpha,...

This paper presents a simple and robust model to describe the wet adhesion of the AFM tip and substrate joined by a liquid bridge. The effects of contact angles, wetting circle radius, the volume of a liquid bridge, the gap between the AFM tip and substrate, environmental humidity, and tip geometry on the capillary force are studied. To model capil...

Wearable head sensor systems use different kinematic signal processing approaches which limits field-based inter-study comparisons, especially when artefacts are present in the signal. The aim of this study is to assess the frequency content and characteristics of head kinematic signals from head impact reconstruction laboratory and field-based env...

Monkeypox disease is caused by a virus which belongs to the orthopoxvirus genus of the poxviridae family. This disease has recently spread out to several non‐endemic countries. While some cases have been linked to travel from endemic regions, more recent infections are thought to have spread in the community without any travel links, raising the ri...

Slip length describes the classical no-slip boundary condition violation of Newtonian fluid mechanics, where fluids glide on the solid surfaces. Here, we propose a new analytical model validated by experiments for characterization of the liquid slip using vibrating solid surfaces. Essentially, we use a microfluidic system integrated with quartz cry...

In this study, the resonance-frequency dependence and modal sensitivity of the flexural vibration modes of overhang/T-shaped microcantilevers to the interaction force and surface stiffness variations were analysed, and a closed-form expression was derived. The Euler–Bernoulli beam theory was used to develop the overhang/T-shaped models, and a chara...

Localized surface plasmon resonance (LSPR) of metallic nanostructures is a unique phenomenon that controls the light in sub-wavelength volumes and enhances the light-matter interactions. Traditionally, the excitation and measurement of LSPR require bulky external light sources, and efforts to scale down to nano-plasmonic devices have predominantly...

A characteristic equation for the frequencies of the T‐shaped and overhang‐shaped cantilevers is derived for the first time. The frequency of higher‐order modes could be tuned by changing the overhang dimensions. Especially, the coupling strength between two cantilevers is κ=η/ξ^3 where η, ξ are the cantilever-to-overhang length, width ratio, resp...

As viruses constantly change due to mutation, variants are expected to emerge demanding development of sensors capable of detecting multiple variants using one single sensor plat- form. Herein, we report the integration of a synthetic binder against SARS-CoV-2 with a nanoplasmonic-based sensing technology, which enables the successful detection of...

Scanning probe microscopies typically rely on the high-precision positioning of a nanoscale probe in order to gain local information about the properties of a sample. At a given location, the probe is used to interrogate a minute region of the sample, often relying on dynamical sensing for improved accuracy. This is the case for most force-based me...

Nitrogen-doped carbon quantum dots are synthesized by a one-step atmospheric pressure microplasma process. The origin of the photoluminescence emission and relationship with nitrogen doping is studied using a range of optical and chemical measurements along with verification by theoretical calculations. Nitrogen doping into the core and functionali...

This study uses image analysis techniques for comparative analysis of the lung HRCT features and RT-PCR of 325 suspected patients to COVID-19 pneumonia. Our findings propose more caution in the interpretation of RT-PCR data, promoting, instead, also the quantification of age and sex-based risk factors using HRCT images. Statistical analysis of our...

In this paper, dynamic behavior and the resonance frequencies of flexural vibration modes of an AFM cantilever with sidewall probe immersed in liquid to surface stiffness variations have been investigated and a closed‐form expression is derived. Using numerical analysis, the flexural resonance frequencies of microcantilever immersed in liquid are c...

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...

Atomic force microscopy (AFM) is a powerful technique for accurate, reliable and non-destructive imaging and characterization of materials at the nanoscale. Among the numerous AFM methods, amplitude modulation or tapping mode AFM (AM-AFM) is an established method for imaging and characterization for most commercial AFM systems. Despite its high spa...

Biosensors and nanoscale analytical tools have seen unprecedented growth in literature in the past 20 years, with a large number of reports on the topic of ’ultra-sensitive’, ’cost-effective’ and ’early-detection’ tools with a potential of ’mass- production’ cited on the web of science. Yet none of these tools are commercially available in the mark...

The nanoscale behavior of liquid molecules and solutes along the interface with solids controls many processes such as molecular exchanges, wetting, electrochemistry, nanofluidics, biomolecular function, and lubrication. Experimentally, several techniques can explore the equilibrium molecular arrangement of liquids near the surface of immersed soli...

The thermally induced deflection of bimaterial cantilevers was theoretically examined, and an optimal excitation configuration was determined. The optimal heat spot position, resulting in the maximal deflection, was observed at a central location at a 0.5-0.6 length for short cantilevers and it shifted backwards to the clamped position at 0.4 lengt...

In this paper, a simulation model for frequency modulation atomic force microscopy (FM-AFM) operating in constant amplitude dynamic mode is presented. The model is based on the slow time varying function theory. The mathematical principles to derive the dynamical equations for the amplitude and phase of the FM-AFM cantilever-tip motion is explained...

A miniature three-point bend fatigue stage for in-situ observation of fatigue microcrack initiation and growth behaviour by scanning electron microscopy (SEM) and contact mode high-speed atomic force microscopy (HS-AFM) has been developed. Details of this stage are provided along with finite element simulations of the stress profiles of said stage...

A three-point bend fatigue miniature stage for in-situ observation of fatigue microcrack initiation and growth behaviour by scanning electron microscopy (SEM) and atomic force microscopy (AFM) has been manufactured. Details of the stage design with finite element analysis of the stress profiles on loading are provided. The proposed stage facilitate...

Calibration of the torsional spring constant of atomic force microscopy cantilevers is fundamental to a range of applications, from nanoscale friction and lubrication measurements to the characterization of micro-electromechanical systems and the response of biomolecules to external stimuli. Existing calibration methods are either time consuming an...

Metal–organic frameworks (MOFs) also known as porous coordination polymers (PCP) are crystalline compounds including metal ion or cluster of metal ions coordinated to organic linkers. To provide more functionalities and enhance the MOFs properties, design and construction of MOFs composites have been proposed. MOF composites are materials that cons...

Accurate calibration of the flexural spring constant of microcantilevers is crucial for sensing devices, microactuators, and atomic force microscopy (AFM). Existing methods rely on precise knowledge of cantilever geometry, make significant simplifications, or require potentially damaging contact with the sample. Here, we develop a simple equation t...

Atomic force microscopy (AFM) has become a well-established technique for nanoscale imaging of samples in air and in liquid. Recent studies have shown that when operated in amplitude-modulation (tapping) mode, atomic or molecular-level resolution images can be achieved over a wide range of soft and hard samples in liquid. In these situations, small...

In this paper, based on the slow time varying function theory, dynamical equations for the amplitude and phase of the dynamic atomic force microscope are derived. Then the sensitivity of the amplitude and phase to the dissipative and conservative parts of interaction force is investigated. The most advantage of this dynamical model is the ability t...

Bimodal force microscopy has expanded the capabilities of atomic force microscopy (AFM) by providing high spatial resolution images, compositional contrast and quantitative mapping of material properties without compromising the data acquisition speed. In the first bimodal AFM configuration, an amplitude feedback loop keeps constant the amplitude o...

a b s t r a c t Due to the rapid development of microelectromechanical systems (MEMS) technology and large numbers of candidate materials, material selection for MEMS devices needs systematic approach. In this paper, for different applications of MEMS electrostatic actuators, based on the actuation voltage and force, speed of actuation and electric...

The effect of tip mass on the frequency response and sensitivity of atomic force microscope (AFM) cantilever in the liquid environment is investigated. For this purpose, using Euler-Bernoulli beam theory and considering tip mass and hydrodynamic functions in a liquid environment, an expression for the resonance frequencies of AFM cantilever in liqu...

This paper presents and compares two novel hybrid control algorithms applicable to the conventional capacitive MEMS accelerometer. These schemes are realized by separately adding a sliding-mode and a backstepping controller to a conventional PID closed loop system to achieve higher stability and higher dynamic range and to prevent pull-in phenomena...

In this paper, the effect of the tip mass on the sensitivity of flexural vibration modes of an AFM rectangular cantilever has been studied and a characteristics equation for the AFM cantilever has been derived. Then, based on the characteristics equation, a closed form expression for the flexural modal sensitivity of the rectangular cantilever to t...

In this paper, the sensitivity of flexural and torsional vibration modes of a rectangular cantilever immersed in a fluid to surface stiffness variations has been analyzed and a closed-form expression is derived. To represent this sensitivity, we use analytical formulas for the vibrational resonant frequencies of a rectangular cantilever beam immers...

In this paper, the resonance frequencies and modal sensitivity of flexural vibration modes of a rectangular atomic force microscope (AFM) cantilever immersed in a liquid to surface stiffness variations have been analyzed and a closed-form expression is derived. For this purpose, the Euler-Bernoulli beam theory is used to develop the AFM cantilever...

The vibrational characteristics of an atomic force microscope (AFM) cantilever beam play a key role in dynamic mode of the atomic force microscope. As the oscillating AFM cantilever tip approaches the sample, the tip–sample interaction force influences the cantilever dynamics. In this paper, we present a detailed theoretical analysis of the frequen...

In this paper, an analytical model is derived for computation of the capillary force between AFM tip and sample surface. Several tip geometries are considered with the both symmetric and asymmetric liquid/solid interfaces. To investigate the validity and efficiency of the derived models, we have performed numerical analysis and the effect of variou...

This paper describes a novel Direct Torque Control (DTC) method for adjustable speed Doubly-Fed Induction Machine (DFIM) drives which is supplied by a two-level Space Vector Modulation (SVM) voltage source inverter (DTC-SVM) in the rotor circuit. The inverter reference voltage vector is obtained by using input-output feedback linearization control...

Based on the method of energy principle, an analytical approach for computing the capillary force for sphere/sphere geometry is presented in this paper. In modeling the capillary force, we consider spheres with both equal and non-equal radii, for both symmetric and asymmetric configurations at liquid/solid interfaces. We use numerical analysis to i...

In this paper, a theoretical method has been developed for the electric double layer interaction under condition of the variable dielectric permittivity of water. Using Poisson-Boltzmann equation (PBE), for one plate and two plates having similar or dissimilar constant charge or constant potential, we have investigated the electric double layer pot...

This paper presents a novel smart MEMS accelerometer which employs a hybrid control algorithm and an estimator. This scheme is realized by adding a sliding-mode controller to a conventional PID closed loop system to achieve higher stability and higher dynamic range and to prevent pull-in phenomena by preventing finger displacement from passing a ma...

In this paper, a nonlinear controller is presented for Doubly-Fed Induction Machine (DFIM) drives. The nonlinear controller is designed based on the input-output feedback linearization control technique, combined with a sliding-mode observer, using the fifth order mo del of the doubly-fed induction machine in fixed stator d-q axis reference frame w...

Identification of the probe height above the sample surface is a highly useful method to acquire atomic-resolution AFM images. Most AFM systems in non-contact mode use amplitude or phase measurement to identify the sample-probe distance and thereby the sample topography. However, this process is time consuming. For the purpose of sample height esti...

Operation of atomic force microscope in dynamic mode has received great attention due to its ability to image compliant materials and also due to the fact that it can prevent the tip and sample damages during scanning. In this paper a model is proposed for AFM micro-cantilever-tip system based on Euler-Bernoulli beam theory and is solved numericall...

In this paper, a nonlinear controller is proposed for Doubly-Fed Induction Machine (DFIM) drives. The nonlinear controller is designed based on an adaptive backstepping control technique, using a fifth order model of an induction machine in the synchronous d & q axis rotating reference frame, whose d axis coincides with the space voltage vector of...

This paper presents design procedure for a neural feedforward controller which can be used as an atomic force microscope system. We have used a three layered feed forward neural network for designing Feedforward Controller with Plant Inverse Learning. The effectiveness and validity of the designed controller were investigated by computer simulation...

High precision control and hysteresis compensation are two important factors in nanopositioning. To reduce the tracking error and compensate the hysteresis effect in the piezoelectric actuator, in this paper we present a nanopositioning control scheme for piezoelectric platform. A Bouc-Wen model is established to describe the nonlinear hysteretic e...

In this paper a new method for determination of flicker source in power system is proposed. This method is based on the energy of flicker signal; therefore, an expression for flicker energy signals is defined, which can be successfully utilized for detection of the flicker source. The main advantage of this method is its simplicity which can be imp...

This paper presents a novel MEMS capacitive accelerometer which employs an estimator. This scheme is realized by adding an adaptive nonlinear observer to the conventional PID closed loop system. This estimator is used for online estimation of the parameter variations for MEMS accelerometers and gives the capability of self testing to the system. Th...

This paper presents a novel hybrid control algorithm for the conventional capacitive MEMS accelerometer. This scheme is realized by adding a backstepping controller to a conventional PID closed loop system to achieve higher stability and higher dynamic range and to prevent pull-in phenomena by preventing linger displacement from passing a maximum p...

In this paper a model and a nonlinear control scheme for an atomic force microscope are developed. For this reason a backstepping control algorithm is developed to achieve asymptotic cantilever tip tracking for bounded tip trajectories. In addition, the micro cantilever is modeled by the interaction between sample and cantilever with the Van der wa...

In this paper a nonlinear controller is presented for Doubly-Fed Induction Machine (DFIM) drives. The nonlinear controller is designed based on input-output feedback linearization control technique, using the fifth order model of induction machine in fixed stator d ,q axis reference frames with stator currents and rotor flux components as state var...

This paper presents a new estimator for the conventional capacitive MEMS accelerometer. This scheme is realized by adding an adaptive nonlinear observer to a conventional PID closed loop system. This estimator is used for online estimation of the parameter variations for MEMS accelerometers and gives the capability of self testing to the system. We...

This paper presents two fuzzy-based controllers designed to scan non-contact atomic force microscopes (AFM) over a specimen surface. Firstly, we develop a conventional fuzzy controller to achieve asymptotic probe tip tracking for bounded tip trajectories. Secondly, a hybrid PD-fuzzy controller is designed for the same purpose where the PD gains are...

In this paper a new energy method for determination of flicker source in power system is proposed This method is based on the energy of flicker signal; therefore, an expression for flicker energy signals is defined, which can be successfully utilized for detection of the flicker source. The main advantage of this method is its simplicity which can...

In this paper a nonlinear controller is presented for doubly-fed induction machine (DFIM) drives. The nonlinear controller is designed based on adaptive input-output feedback linearization control technique, using the fifth order model of induction machine in fixed stator d, q axis reference frames with stator currents and rotor flux components as...

In this paper, a novel nonlinear speed sensorless control scheme is presented for doubly-fed induction machine drive (DFIM). The proposed controller Is designed on the basis of input-output feedback linearization and sliding-mode control with adaptive backstepping observer. Considering the DFIM fifth order model in a stator two axis reference frame...

In this paper, the robust nonlinear sliding-mode speed sensorless speed controller for a DC servo motor is proposed. Based on state-space model representing the speed and current dynamics, the nonlinear sliding mode control is designed to track a linear reference model. An observer based on adaptive backstepping approach is used to estimate speed a...

In this paper a nonlinear controller is presented for doubly-fed induction machine (DFIM) drives. The nonlinear controller is designed based on input-output feedback linearization control technique, combined with sliding-mode observer. Using the fifth order model of induction machine in fixed stator d ,q axis reference frames with stator current an...

In this paper using adaptive backstepping approach an adaptive rotor flux observer which provides stator and rotor resistances estimation simultaneously for induction motor used in series hybrid electric vehicle is proposed. The controller of induction motor (IM) is designed based on input-output feedback linearization technique. Combining this con...

In this paper a nonlinear controller is presented for doubly-fed induction machine (DFIM) drives. The nonlinear controller is designed based on adaptive backstepping control technique, using the fifth order model of induction machine in a synchronous d & q axis rotating reference frame with the d axis coincide with space voltage vector for the main...

In this paper a robust nonlinear controller is presented for doubly-fed induction machine (DFIM) drives. The nonlinear controller is designed based on combination of Sliding-Mode (SM) and Adaptive-Backstepping control techniques. Using the fifth order model of DFIM in a stator d, q axis reference frames with stator currents and rotor fluxes as stat...