Tapping-mode Atomic Force Microscope Images Research Articles

Large-range high-speed dynamic-mode atomic force microscope imaging: adaptive tapping towards minimal force

In this paper, a software-hardware integrated approach is proposed for high-speed, large-range tapping mode imaging of atomic force microscope (AFM). High speed AFM imaging is needed in various applications, particularly in interrogating dynamic processes at nanoscale such as polymer crystallization process. Achieving high speed in tapping-mode AFM imaging is challenging as the probe-sample interaction during the imaging process is highly nonlinear, making the tapping motion highly sensitive to the probe sample spacing, and thereby, difficult to maintain at high speed. Increasing the speed via hardware bandwidth enlargement, however, leads to a substantially reduction of the imaging area. Contrarily, the imaging speed can be increased without loss of the scan size through control (algorithm)-based approach. For example, the recently-developed adaptive multiloop mode (AMLM) technique has demonstrated its efficacy in increasing the tapping-mode imaging speed without loss of scan size. Further improvement, however, has been limited by the hardware bandwidth and the online signal processing speed and computation complexity involved. Thus, in this paper, the AMLM technique is further enhanced to optimize the probe tapping regulation, and integrated with a field programmable gate array platform to further increase the imaging speed without loss of quality and scan range. Experimental implementation of the proposed approach demonstrates that high-quality imaging can be achieved at a high-speed scanning rate of 100 Hz and higher, and over a large imaging area of over 20 μm.

Tapping Mode AFM Imaging in Liquids with blueDrive Photothermal Excitation

Abstract

On-Chip Dynamic Mode Atomic Force Microscopy: A Silicon-on-Insulator MEMS Approach

The atomic force microscope (AFM) is an invaluable scientific tool; however, its conventional implementation as a relatively costly macroscale system is a barrier to its more widespread use. A microelectromechanical systems (MEMS) approach to AFM design has the potential to significantly reduce the cost and complexity of the AFM, expanding its utility beyond current applications. This paper presents an on-chip AFM based on a silicon-on-insulator MEMS fabrication process. The device features integrated xy electrostatic actuators and electrothermal sensors as well as an AlN piezoelectric layer for out-of-plane actuation and integrated deflection sensing of a microcantilever. The three-degree-of-freedom design allows the probe scanner to obtain topographic tapping-mode AFM images with an imaging range of up to 8μm × 8μm in closed loop.

Intrinsically high-Q dynamic AFM imaging in liquid with a significantly extended needle tip

Atomic force microscope (AFM) probe with a long and rigid needle tip was fabricated and studied for high Q factor dynamic (tapping mode) AFM imaging of samples submersed in liquid. The extended needle tip over a regular commercially available tapping-mode AFM cantilever was sufficiently long to keep the AFM cantilever from submersed in liquid, which significantly minimized the hydrodynamic damping involved in dynamic AFM imaging of samples in liquid. Dynamic AFM imaging of samples in liquid at an intrinsic Q factor of over 100 and an operational frequency of over 200 kHz was demonstrated. The method has the potential to be extended to acquire viscoelastic material properties and provide truly gentle imaging of soft biological samples in physiological environments.

Chemical Mechanical Polishing of a Ti-Si-N Nanocomposite and AFM Study on Its Nanostructure

Ti-Si-N films were characterized as a nanocomposite consisting of cubic titanium nitride (TiN) nanocrystallites embedded in an amorphous matrix of silicon nitride (Si3N4). Ti-Si-N films have been used as anti-wear coatings due to their mechanical properties and diffusion barriers for copper metallization in semiconductor processing. The surface of Ti-Si-N is so rough that it is hard to characterize its nanostructure with an atomic force microscope (AFM). Therefore, the Ti-Si-N surface should be polished and smoothened to reduce its roughness before an AFM study. In this study, we investigated a chemical mechanical polishing (CMP) process for preparing Ti-Si-N surfaces for an AFM study on the Ti-Si-N nanostructure by using two different types of CMP slurries. Then a characterization of TiN embedded in a Si3N4 matrix was conducted by using a tapping mode AFM and phase shift imaging.

Localized surface plasmon resonance effect on photo-induced alignment of films composed of silver nanoparticles and azopolymers with cyano or methyl substitutes on azobenzene moieties

In this paper, we report the localized surface plasmon resonance of silver nanoparticles on the photo-induced alignment properties of azopolymers. Two series of azopolymer films doped with silver nanoparticles (SNPs) were prepared with different contents of SNPs, in which two side chain azopolymers, with cyano group (AzoCN) and methyl group (AzoCH 3) as substitutes, respectively, were designed and synthesized because of the different interaction between SNPs and each kind of substitute. Tapping-mode atomic force microscope imaging was used to characterize the distribution of SNPs in azopolymer films, from which it was found that in AzoCN film SNPs were almost uniformly distributed, whereas in AzoCH 3 film several decades of single SNP aggregated into a cluster. Photo-induced alignment of azopolymer films doped with SNPs was performed under irradiation of linearly polarized light at 442 nm. The experimental results reveal that there is an obvious difference in photo-induced alignment behavior between two series of azopolymer films. For AzoCN, the alignment rate decreased with the increase of SNPs concentration, and when the SNPs' concentration achieved 0.24% the ratio of alignment rate reached the minimum, about 77% of that of the undoped sample. For AzoCH 3, the alignment rate increased along with the increase of the content of SNPs, showing that the alignment rate, at least for “fast” process, could be enhanced by doping SNPs. This phenomenon resulted from localized surface plasmon resonance of SNPs and was also found to be affected by the chemical structure and the condensed state of azopolymers doped with SNPs.

A control approach to cross-coupling compensation of piezotube scanners in tapping-mode atomic force microscope imaging

In this article, an approach based on the recently developed inversion-based iterative control (IIC) to cancel the cross-axis coupling effect of piezoelectric tube scanners (piezoscanners) in tapping-mode atomic force microscope (AFM) imaging is proposed. Cross-axis coupling effect generally exists in piezoscanners used for three-dimensional (x-y-z axes) nanopositioning in applications such as AFM, where the vertical z-axis movement can be generated by the lateral x-y axes scanning. Such x/y-to-z cross-coupling becomes pronounced when the scanning is at large range and/or at high speed. In AFM applications, the coupling-caused position errors, when large, can generate various adverse effects, including large imaging and topography distortions, and damage of the cantilever probe and/or the sample. This paper utilizes the IIC technique to obtain the control input to precisely track the coupling-caused x/y-to-z displacement (with sign-flipped). Then the obtained input is augmented as a feedforward control to the existing feedback control in tapping-mode imaging, resulting in the cancellation of the coupling effect. The proposed approach is illustrated through two exemplary applications in industry, the pole-tip recession examination, and the nanoasperity measurement on hard-disk drive. Experimental results show that the x/y-to-z coupling effect in large-range (20 and 45 microm) tapping-mode imaging at both low to high scan rates (2, 12.2 to 24.4 Hz) can be effectively removed.

Alignment of λ-DNA on Organic Monolayer Surface Patterned by Scanning Probe Lithography

With the combination of a molecular combing technique and scanning probe lithographic patterning, λ-DNA wires were stretched and aligned to form parallel lines on a patterned organic monolayer surface. The patterned organic monolayer was composed of hydrophilic aminopropyltriethoxysilane (APS) in the middle of hydrophobic octadecyltrichlorosilane (OTS) on a silicon surface. The stretching and alignment of λ-DNA wires were induced along the lines of the APS layer which attracted λ-DNA through a coulombic interaction at an early stage of the combing. Weaker van der Waals interaction with the OTS layer induced a settlement of the wire after the sample was dried. The aligned structures were confirmed by tapping-mode atomic force microscope images, aided by positively-charged gold nanoparticles exclusively attached to the DNA backbone.

High-resolution nanowire atomic force microscope probe grownby a field-emission induced process

A technique to grow a nanowire probe on an atomic force microscope (AFM) tip using a field-emission induced growth process has been developed. The simple and highly reproducible technique produces vertically aligned nanowire probes whose length is controlled by the growth duration. Using a cantilever clamping arrangement, nanowire probes can be grown on low-stiffness cantilevers. Experiments using the robust nanowire AFM probe demonstrate its ability to produce high-resolution tapping mode AFM images and improved profiling of structures with steep sidewalls due to its very sharp tip and high aspect ratio. No degradation in imaging performance was observed after a period of continuous scanning and storage.

Atomic Force Microscopy of Single-Walled Carbon Nanotubes Using Carbon Nanotube Tip

We succeeded in observing individual single-walled carbon nanotubes (SWNTs) using an atomic force microscope (AFM) in the tapping mode by paying attention to the preparation of both samples and AFM tips. To disentangle the bundles of SWNTs, we added a small amount of amine into N,N-dimethylformamide. To achieve a high resolution in tapping-mode AFM imaging, we used carbon nanotube (CNT) tips whose radii could be reduced. We were able to image individual SWNTs using CNT tips with widths that were half of those imaged using conventional silicon tips. With this improved resolution, we could clearly resolve the two SWNTs lying parallel on a mica substrate.

5535668 Corrugated pallet: Besaw Larry G; Farley Timothy R, Jasper, IN, United States assigned to The Servants Inc

Through force spectroscopy, we use an atomic force microscope (AFM) to compare the forces between two extra heavy crude oil (EHCO) droplets. This is done in various aqueous environments in order to compare said forces in the presence of a variety of surfactants and ionic species. A crude oil droplet is attached to the AFM cantilever and pressed against other droplets placed on a substrate. Differences in the behavior of the forces as a function of surfactant chemistry, concentration and the velocity of the approach and retract of the droplets are observed for droplets with a range of diameters 10<Ø (µm)<70. The surfactant H4 (dodecyl-polyglucoside, designed at the Instituto Mexicano del Petroleo) is found to cause the highest forces between the droplets and greatest reduction of drop deformation when pressed together. Qualitative agreement is observed with previous theoretical works with regards to the addition of ionic compounds such as sea-water – the droplets approach more closely and coalescence may be favored in some cases. It is possible to observe structure on the surface of other oil drops by tapping mode AFM imaging. It is believed that this is the first time this has been done on extra heavy crude oil droplets.