Video-rate Atomic Force Microscopy Research Articles

Effect of Potential on the Nanostructure Dynamics of Ethylammonium Nitrate at a Graphite Electrode.

Video-rate atomic force microscopy (AFM) is used to study the near-surface nanostructure dynamics of the ionic liquid ethylammonium nitrate (EAN) at a highly oriented pyrolytic graphite (HOPG) electrode as a function of potential in real-time for the first time. The effects of varying the surface potential and adding 10wt% water on the nanostructure diffusion coefficient are probed. For both EAN and the 90wt% EAN-water mixture, disk-like features ≈9nm in diameter and 1nm in height form above the Stern layer at all potentials. The nanostructure diffusion coefficient increases with potential (from OCP -0.5V to OCP +0.5V) and with added water. Nanostructure dynamics depends on both the magnitude and direction of the potential change. Upon switching the potential from OCP -0.5V to OCP +0.5V, a substantial increase in the diffusion coefficients is observed, likely due to the absence of solvophobic interactions between the nitrate (NO3 - ) anions and the ethylammonium (EA+ ) cations in the near-surface region. When the potential is reversed, EA+ is attracted to the Stern layer to replace NO3 - , but its movement is hindered by solvophobic attractions. The outcomes will aid applications, including electrochemical devices, catalysts, and lubricants.

Extremely slow dynamics of ionic liquid self-assembled nanostructures near a solid surface

Hypothesis: The dynamics of the self-assembled liquid nanostructure of the ionic liquids (ILs) near a mica surface can be determined from video-rate atomic force microscopy (AFM) data.Experiments: Video-rate AFM has been used to record the nanostructure dynamics of two most widely studied ILs, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI) and ethylammonium nitrate (EAN), as well as EAN-water mixtures, above a model anode, mica. Diffusion coefficients were extracted from the AFM videos using dynamic differential microscopy and direct tracking.Findings: Video rate AFM is able to record the movement of the IL nanostructure. This is the first time that any liquid has been directly visualized at a scale of 10 nm × 10 nm in real-time. Diffusion coefficients determined from AFM videos reveal IL nanostructures near surfaces diffuse orders of magnitude more slowly than individual ions in the bulk. Thus, rather than free-flowing liquid, the near-surface nanostructure is better conceptualized as self-assembled aggregates of IL ions diffusing slowly over the cation-rich Stern layer, akin to adsorbed surfactant micelles in aqueous systems. This new and surprising insight affects wide-ranging processes involving the interfacial dynamics of concentrated electrolytes.

Iterative Learning Control for Video-Rate Atomic Force Microscopy

We present a control scheme for video-rate atomic force microscopy with rosette pattern. The controller structure involves a feedback internal-model-based controller and a feedforward iterative learning controller. The iterative learning controller is designed to improve tracking performance of the feedback-controlled scanner by rejecting the repetitive disturbances arising from the system nonlinearities. We investigate the performance of two inversion techniques for constructing the learning filter. We conduct tracking experiments using a two-degree-of-freedom microelectromechanical system (MEMS) nanopositioner at frame rates ranging from 5 to 20 frames per second. The results reveal that the algorithm converges rapidly and the iterative learning controller significantly reduces both the transient and steady-state tracking errors. We acquire and report a series of high-resolution time-lapsed video-rate AFM images with the rosette pattern.

A Survey on Modelling and Compensation for Hysteresis in High Speed Nanopositioning of AFMs: Observation and Future Recommendation

This paper surveys the recent advances on the modeling and control of hysteresis of piezoelectric actuators (PTAs) in the context of high precision applications of atomic force microscopes (AFMs). The current states, findings, and outcomes on hysteresis modeling and control in terms of achievable bandwidth and accuracy are discussed in detailed. Future challenges and the scope of possible research are presented to pave the way to video rate atomic force microscopy.

Rosette-scan video-rate atomic force microscopy: Trajectory patterning and control design.

We present an analysis and a systematic design methodology for a novel nonraster scan method based on a rosette pattern and demonstrate its application in video-rate atomic force microscopy. This pattern is traced when the lateral axes of a parallel kinematic scanner are commanded to follow a combination of two sinusoids with identical amplitudes and different frequencies. We design an internal-model-based controller to enhance the tracking performance of this pattern and implement the scheme on a microelectromechanical system scanner. The results reveal high-precision tracking of the rosette pattern in order to acquire time-lapsed atomic force microscope images at the rate of 10 frames/s.

Preparation of DNA Quadruplex Nanogels and Their Application to DDS Carriers

We have recently and successfully developed DNA quadruplex hydrogel, which instantly turn into gel in response to K + or Na + addition, by directly coupling several deoxyguanosine residues to the both ends of polyethylene glycols utilizing High-Efficiency Liquid-Phase (HELP) large-scale DNA synthesis technique. In this study, we examined a utility of this hydrogel as a Drug Delivery System (DDS) carrier. We found that nanoparticles of 100–200 nm diameter can be efficiently prepared by forming gels in sufficiently diluted solution of the macromonomers. The nanogels were fully characterized by dynamic light scattering (DLS) and atomic force microscopy (AFM). High-speed video-rate AFM measurements enabled direct and real-time observation of selective dissolution of DNA Quadruplex nanogels triggered by the addition of a crown ether into the system. Drug loading of G-quaduplex-binding anticancer drug and its delivery into cells were also accomplished.

Collocated Z-Axis Control of a High-Speed Nanopositioner for Video-Rate Atomic Force Microscopy

A key hurdle to achieve video-rate atomic force microscopy (AFM) in constant-force contact mode is the inadequate bandwidth of the vertical feedback control loop. This paper describes techniques used to increase the vertical tracking bandwidth of a nanopositioner to a level that is sufficient for video-rate AFM. These techniques involve the combination of: a high-speed XYZ nanopositioner; a passive damping technique that cancels the inertial forces of the Z actuator which in turns eliminates the low 20-kHz vertical resonant mode of the nanopositioner; an active control technique that is used to augment damping to high vertical resonant modes at 60 kHz and above. The implementation of these techniques allows a tenfold increase in the vertical tracking bandwidth, from 2.3 (without damping) to 28.1 kHz. This allows high-quality, video-rate AFM images to be captured at 10 frames/s without noticeable artifacts associated with vibrations and insufficient vertical tracking bandwidth.

Video-Rate Lissajous-Scan Atomic Force Microscopy

Raster scanning is common in atomic force microscopy (AFM). The nonsmooth raster waveform contains high-frequency content that can excite mechanical resonances of an AFM nanopositioner during a fast scan, causing severe distortions in the resulting image. The mainstream approach to avoid scan-induced vibrations in video-rate AFM is to employ a high-bandwidth nanopositioner with the first lateral resonance frequency above 20 kHz. In this paper, video-rate scanning on a nanopositioner with 11.3-kHz resonance frequency is reported using a smooth Lissajous scan pattern. The Lissajous trajectory is constructed by tracking two sinusoidal waveforms on the lateral axes of the nanopositioner. By combining an analog integral resonant controller (IRC) with an internal model controller, 1- and 2-kHz single tone set-points were successfully tracked. High-quality time lapsed AFM images of a calibration grating recorded at 9 and 18 frames/s without noticeable image distortions are reported.

Video Rate Atomic Force Microscopy: Use of compressive scanning for nanoscale video imaging

Atomic Force Microscopy (AFM) is a powerful instrument for studying and exploring the nanoworld [1]. AFM can obtain ultrahigh-resolution images at the subnanoscale level. However, AFM has a very significant drawback of slow imaging speed, which is due to its working principle. A conventional AFM conducts a raster scan of an entire area to generate a topography image. Therefore, the frame rate is low, making it impossible for observation of biological and physical processes that are dynamic in nature with a lifespan of a few minutes or even seconds, such as the structural change of cells, carbon nanotube shape change, and so forth [2]?[5]. In addition, for AFM-based nanomanipulations and nanomeasurement, the low frame rate makes it difficult to achieve a real-time visual guide manipulation [6], [7]. Operators usually have to wait for finishing imaging to visualize the manipulating results. Therefore, there is an increasing demand on a fast-imaging AFM system that can capture a continuous phenomenon occurring in seconds.

Invited Review Article: High-speed flexure-guided nanopositioning: Mechanical design and control issues

Recent interest in high-speed scanning probe microscopy for high-throughput applications including video-rate atomic force microscopy and probe-based nanofabrication has sparked attention on the development of high-bandwidth flexure-guided nanopositioning systems (nanopositioners). Such nanopositioners are designed to move samples with sub-nanometer resolution with positioning bandwidth in the kilohertz range. State-of-the-art designs incorporate uniquely designed flexure mechanisms driven by compact and stiff piezoelectric actuators. This paper surveys key advances in mechanical design and control of dynamic effects and nonlinearities, in the context of high-speed nanopositioning. Future challenges and research topics are also discussed.

Real time observation of crystallization in polyethylene oxide with video rate atomic force microscopy

Video rate atomic force microscopy (VideoAFM), with a frame rate of 14 frames/s and a tip velocity of up to 15 cms −1, is used to image polyethylene oxide films during crystal growth. The capabilities of VideoAFM when applied to semicrystalline polymer surfaces are explored. Image quality comparable to that found with conventional contact AFM is achieved but with a nearly 1000 times improvement in time resolution. By applying the technique to the real-time observation of crystal growth, different modes of rapid crystallization are followed in real time. Observation of the spherulite growth front allows measurement of growth rates at the lamellar scale, from which a factor of two difference in the rate of radial growth to the rate of tangential growth is observed, confirming that the elongated nature of spherulite lamellae is due to geometric constraints rather than an inherent fibrillar character. Measurements on screw dislocation growth, when large amounts of crystallizable material is trapped at the surface show that the terrace height does not influence the rate of crystal growth, confirming that under these conditions processes at the lamellar growth front control the rate of growth. When only a thin film of molten material is left on the surface of the already crystallized film dendritic growth is observed, implying a diffusion controlled process under these far from equilibrium conditions.