Multiwalled Carbon Nanotube Probe Research Articles

Amplitude response of conical multiwalled carbon nanotube probes for atomic force microscopy.

Carbon nanotubes are considered as great candidates for atomic force microscopy (AFM) probes because of their high aspect ratio and outstanding mechanical properties. In this work, we report that a conical AFM probe can be fabricated with arc discharge prepared multiwalled carbon nanotubes (MWCNTs) with an individual MWCNT at the apex by dielectrophoresis. The amplitude–displacement curve of the conical MWCNT probe demonstrates that this structure can remain stable until the force exerted on it increases to 14.0 ± 1.5 nN (nanonewton). Meanwhile, the conical MWCNT probes are able to resolve complex structure with high aspect ratio compared to commercial AFM probes, suggesting great potential for various AFM applications.

Static and dynamic pull-in instability of multi-walled carbon nanotube probes by He’s iteration perturbation method

A continuum model is utilized to extract the nonlinear governing equation for Carbon nanotube (CNT) probes near graphite sheets. The van der Waals (vdW) intermolecular force and electrostatic actuation are included in the equation of motion. Static and dynamic pull-in behavior of the system is investigated in this paper. To this end, a new asymptotic procedure is presented to predict the pull-in instability of electrically actuated CNTs by employing an analytic approach namely He’s iteration perturbation method (IPM). The effects of basic non-dimensional parameters such as initial amplitude, intermolecular force, geometrical parameter and actuation voltage on the pull-in instability as well as the fundamental frequency are studied. The obtained results from numerical simulations by employing three mode assumptions verify the strength of the analytical procedure. The qualitative analysis of the system dynamics shows that the equilibrium points of the autonomous system include stable center points and unstable saddle nodes. The phase portraits of the carbon nanotube actuator exhibit periodic and homoclinic orbits.

Interfacing resistances in conducting probe atomic force microscopy with carbon nanotubes functionalised tips

A comparative study for the evaluation of carbon nanotube (CNT) functionalised tips as an interface for the determination of electrical and electronic properties of the surface of materials and devices is presented. The results of current spectroscopy measurements, complemented with force–current testing, reveal a strong dependence of the establishment of tip–sample electrical contact with environmental conditions and procedure. Multiwalled CNT-mediated measurements are compared with the results by commonly used as-purchased probes, metal-coated and Si probes, upon an inert and low-resistance Au substrate. The introduction of CNTs in the tip vicinity represents a drastic advance in the conduction capability as compared with the silicon probes. Despite a certain reduction of conduction as compared with metal-coated probes, a significant improvement of tip apex durability, together with, non-invasive mechanical contact to the sample is demonstrated. The present multiwalled CNT probes are proposed as an ideal element for electronic studies at the nanometre scale by atomic force microscopy.

Three-dimensional evaluation of an independent multi-walled carbon nanotube probe by tomography with high-resolution transmission electron microscope

We evaluated an independent multi-walled carbon nanotube (MWNT) probe by using tomography with a high-resolution transmission electron microscope to verify the three-dimensional structure of the probe tip. The new method of probe evaluation revealed the following features: (i) cutting the end of the MWNT probe caused the wall structure to disintegrate and encapsulated the graphene sheets fragmented by the discharged pulse; (ii) the cap of the MWNT probe was an open cylinder covered by walls similar in shape to a rectangular slit; (iii) the grooves of the inner walls of the MWNT probe, which were created by the discharge cutting method, maintained a cylindrical shape that was different from the peeling-off mechanism.

New approach to model the buckling and stable length of multi walled carbon nanotube probes near graphite sheets

Modeling the buckling of multi walled carbon nanotube (MWCNT) probes/actuators in the vicinity of thin and thick graphite has been carried out for the first time via two analytical approximation methods as well as a numerical one. A hybrid nano-scale continuum model based on Lennard-Jones potential is applied to simulate the intermolecular force-induced deflection of MWCNT. The critical values of MWCNT tip deflection and MWCNT-graphite attraction at the onset of the instability are computed. In addition, minimum nanotube-graphite initial gap and stable length of freestanding CNT are determined as basic parameters for engineering applications and nano-devices design. The stable length of MWCNT is determined as a function of its geometrical and material characteristics, initial gap and number of graphene layers.

Three-Dimensional Evaluation of a Multi-Walled Carbon Nanotube Probe by Using High-Resolution Transmission Electron Microscope

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Analysis of the number of hydrogen bond groups of a multiwalled carbon nanotube probe tip for chemical force microscopy

In this paper, we describe a statistical method of quantification of the number of functional groups at the contact area of a probe tip for atomic force microscopy from the result of repetitive pull-off force measurements. We have investigated laboratory-made carbon nanotube (CNT) probe tips to apply them for chemical force microscopy because limited number of functional groups at the tip-end is expected. Using a CNT tip, we conducted repetitive pull-off force measurements against a self-assembled monolayer terminated with carboxyl group and analyzed them in terms of the number of hydrogen bond groups at the CNT tip. The elementary hydrogen bond rupture force quantum in n-decane medium was estimated to be 84.2 ± 0.5 pN in the present system. Thus it was revealed that only a couple of hydrogen bond groups of the CNT tip were participating in hydrogen bonding with the sample on an average in this experimental system.

Amplitude Response of Multiwalled Carbon Nanotube Probe with Controlled Length during Tapping Mode Atomic Force Microscopy

Multiwalled carbon nanotube (MWCNT) atomic force microscope (AFM) probes were fabricated with controlled length using nanomanipulators inside scanning electron microscope. The amplitude-distance responses of MWCNT AFM probes were systematically studied experimentally. Several special characteristics of CNT AFM probes were observed, such as amplitude jump-into-zero, rebounds after the probe already touched the surface and large hysteresis during retraction. Transition from attractive to repulsive regions was also observed when the CNT is long and the amplitude is large. Tapping mode amplitude-distance curves were found to change regularly with the length of the carbon nanotubes and their tilting angle relative to the substrate surface normal. The results were comparable with previous theoretical predictions. Through direct observations by electron microscopes, MWCNT AFM probes were found to bend homogenously even when they were pushed toward the SiO2 wafer for several hundred nanometers after they had touched the surface of the substrate. By analyzing the results obtained from several probes it was found that the MWCNT AFM probes in tapping mode should be suitable for stable operation with proper length and working condition.

Length dependent behavior of a carbon nanotube interacting at liquid-air interface

We report the irreversible structural failure of individual multiwalled carbon nanotube (MWNT) tips after water submersion. We used 11 individual MWNTs with varying geometries and showed length dependent MWNT failure with scanning electron microscopy. Shorter MWNTs are more likely to survive penetration of the water-air interface. We observed the bending of MWNT probes on the water surface using optical microscopy. Surface tension force acting on MWNTs at the water-air interface was calculated. Compared to shorter MWNTs, the calculations suggest that longer MWNTs exert a smaller bending restoring force with respect to surface tension force, leading to MWNT bending until failure.

Feasibility of multi-walled carbon nanotube probes in AFM anodization lithography

Multi-walled carbon nanotube (CNT) tips were used in atomic force microscope (AFM) anodization lithography to investigate their advantages over conventional tips. The CNT tip required a larger threshold voltage than the mother silicon tip due to the Schottky barrier at the CNT–Si interface. Current-to-voltage curves distinguished the junction property between CNTs and mother tips. The CNT–platinum tip, which is more conductive than the CNT–silicon tip, showed promising results for AFM anodization lithography. Finally, the nanostructures with high aspect ratio were fabricated using a pulsed bias voltage technique as well as the CNT tip.

The Measurement of Solvation Forces with Application to Biological Systems

M. J. Higgins,* T. Uchihashi,* M. Polcik,* J. E. Sader,** S.P. Jarvis* *Centre for Research on Adaptive Nanostructures and Nanodevices, University of Dublin, Trinity College, Dublin 2, Ireland **Department of Mathematics and Statistics, University of Melbourne, Victoria 3010, Australia Directly measuring forces in aqueous environments with a mechanical probe of lateral dimensions comparable to that of a single molecule provides an invaluable insight into the processes controlling if and how a molecule approaches another molecule or a membrane. In the immediate vicinity of the molecule, continuum models break down and the aqueous environment will often form a discrete layered structure depending on the nature of the molecule. The absence or presence of such structure may be fundamental in influencing the promotion or inhibition of protein adsorption, biological function and membrane recognition. In order to perform such measurements it has been necessary to combine a number of innovative techniques with a standard atomic force microscopy (AFM). For high-resolution imaging we use the highly sensitive frequency modulation detection scheme (FM-AFM) in liquid [1, 2] and have subsequently used the method of Sader and Jarvis to extract quantitative force values from frequency shift measurements [3]. To implement FM-AFM successfully in liquid we have used magnetically activated dynamic mode (MAD-mode!) where a small magnetic particle is attached to the end of the cantilever (Fig. 1) and an external magnetic field applied via a current carrying coil. To increase the sensitivity of the measurement to the interaction local to the tip apex we have used a high aspect ratio multiwalled carbon nanotube probe (Fig. 2). This reduces the hydrodynamic squeeze damping between the surface and the bulk of the tip. The nanotube is attached in a specially designed field emission scanning electron microscope, which permits us some control over both the length and direction of the probe. We have directly measured localised density changes in ultra-pure water at small tip-sample separations and have combined this with nanometer resolution images of the surface. Careful characterisation of the nanotube probe using electron microscopy after the measurement has allowed us to normalise interaction forces as a function of probe radius [4]. Using self-assembled monolayers with varying end groups, we have been able to investigate the role of local surface chemistry and morphology on measured water structure and tip-surface interaction. This has been extended to observations of quantified differences in localised structures in the presence of ions with the structures being dependent on the choice of ion. Further, we have investigated whether oscillatory forces corresponding to water structure are present at the surface of lipid bilayers (Fig.3). We aim to understand the effects of various physiological conditions on water structure, the relevant length scales over which hydration forces interact and the influence of water structure on biological processes.

Multiwalled carbon nanotube AFM probes for surface characterization of micro/nanostructures

A multiwalled carbon nanotube (MWNT) probe was used as a scanning probe in an atomic force microscope (AFM) to obtain surface height maps of micro/nano structures. The surface height maps acquired by the MWNT probe are compared with those by a conventional silicon probe on the four samples: silicon ruler, polymer microchannels, silicon nanomembrane and nanocomposite metal particle (MP) tapes. The results of the silicon ruler, microchannels and membrane samples show that the surface height maps by the MWNT probe have a better resolution than those by a conventional silicon tip due to the sharper tip with the larger aspect ratio of the MWNT. A MWNT probe is especially useful to observe surface height maps of the structures that have larger aspect ratio.

Orthopedic Treatment of Multiwalled Carbon Nanotube Probes

We have developed an orthopedic process to adjust the length and to sharpen the tip of multiwalled carbon nanotube probes. A nanotube was bridged between a Pt-coated knife-edge and a Pt-coated Si tip under a scanning electron microscope. Introducing an excess current into the bridged nanotube peeled off its shells layer by layer from the outermost one at the center and finally cut it. Then the cut ends were sharpened and the length from the Si tip was adjusted by changing the gap between the knife-edge and Si tip. The length-adjusted and sharpened nanotube probes have been applied to noncontact atomic force microscopy to clarify their advantages.