Atomic Force Microscopy Probe Tip Research Articles

Atomic Force Microscopy Force Mapping Analysis of an Adsorbed Surfactant above and below the Critical Micelle Concentration.

Force curves collected using an atomic force microscope (AFM) in the presence of adsorbed surfactants are often used to draw conclusions about adsorbed film packing, rigidity, and thickness. However, some noteworthy features of such force curve characteristics have yet to be thoroughly investigated and explained. In this work, we collected force curves from tetradecyltrimethylammonium bromide films adsorbed on highly oriented pyrolytic graphite (HOPG), silica, and silica that had been hydrophobized by functionalization with dichlorodimethyl silane. Breakthrough events in the force curves from several different trials were compared to show that the breakthrough distance, often reported as the adsorbed film thickness, increased with concentration below the critical micelle concentration (CMC) but was approximately 3.5 nm on all surfaces between 2× and 10× CMC; an unexpected result because of the different surface chemistries for the three surfaces. We employed an AFM probe with a different force constant ( k) value as well as a colloidal probe and the breakthrough distance remained approximately 3.5 nm in all cases. Gradient mapping, a variant of force mapping, was also implemented on the three surfaces and resulted in a new technique for visualizing adsorbed surfactant in situ. The resulting maps showed patches of adsorbed surfactant below the CMC and revealed that with increasing concentration, the size of the patches increased resulting in full coverage near and above the CMC. These results are, to our knowledge, the first time force mapping has been used to spatially track patches of adsorbed surfactant. Finally, layers of surfactants on an AFM tip were investigated by collecting a force map on a single AFM tip using the tip of a separate AFM probe. A breakthrough event was observed between the tips, indicating that a layer of surfactant was present on at least one, if not both tips.

Angle-Dependent Atomic Force Microscopy Single-Chain Pulling of Adsorbed Macromolecules from Planar Surfaces Unveils the Signature of an Adsorption-Desorption Transition.

The adsorption–desorption behavior of polymer chains is at the heart of macromolecular surface science and technology. With the current developments in atomic force microscopy (AFM), it has now become possible to address the desorption problem from the perspective of a single macromolecule. Here, we report on desorption of single polymer chains on planar surfaces by AFM-based single molecule force spectroscopy (SMFS) as a function of the pulling angle with respect to the surface-normal direction. SMFS experiments were performed in water with various substrates using different polymers covalently attached to the AFM probe tip. End-grafting at the AFM tip was achieved by surface-initiated polymerization using initiator functionalized tips. We found that the desorption force increases with a decreasing pulling angle, i.e., an enhanced adhesion of the polymer chain was observed. The magnitude of the desorption force shows a weak angular dependence at pulling angles close to the surface normal. A significant increase of the force is observed at shallower pulling from a certain pulling angle. This behavior carries the signature of an adsorption–desorption transition. The angular dependence of the normalized desorption force exhibits a universal behavior. We compared and interpreted our results using theoretical predictions for single-chain adsorption–desorption transitions.

On the Origin of Extended Resolution in Kelvin Probe Force Microscopy with a Worn Tip Apex.

In this work we analyzed the effect of the atomic force microscopy probe tip apex shape on Kelvin Probe Force Microscopy (KPFM) potential sensitivity and spatial resolution. It was found that modification of the apex shape from spherical to planar upon thinning of the conductive coating leads to enhanced apex contribution to the total electrostatic force between the probe and the sample. The effect results in extended potential sensitivity and spatial resolution of KPFM. Experimental results were supported by calculations.

Blind evaluation of AFM tip shape by using optical glass surface with irregular nanostructures as a tip characteriser

Atomic-force microscopy (AFM) is a type of scanning probe microscopy. It possesses nano-scale resolution which is >1000 times better than the optical diffraction limit. An image of AFM is the result of interaction between the tip and the sample. The AFM image is not accurate and distorted due to the finite size of the probe tip. To correct the AFM image and acquire accurate sample morphology information, it needs to evaluate the tip shape and status. The shape of the probe tip is calculated to determine the quality of the probe. The optical glass surface fabricated by free abrasive polishing (traditional mechanical polishing) technique is used as a new tip characteriser to calibrate the AFM probe tip. Meanwhile, an improved blind reconstruction algorithm is adopted to calculate the AFM tip shape and size. In the help of matrices, the blind reconstruction algorithm is elaborated clearly. The optical glass surface with irregular nanostructures ensures that the morphology of probe tip can be determined accurately. Without independent knowledge of the sample morphology, the three-dimensional morphology of the AFM tip can be obtained.

Determination of the attractive force, adhesive force, adhesion energy and Hamaker constant of soot particles generated from a premixed methane/oxygen flame by AFM

Abstract Atomic force microscopy (AFM) was used to characterize the attractive force, adhesive force and adhesion energy between an AFM probe tip and nanometric soot particle generated by a premixed methane/oxygen flame. Different attractive force distributions were found when increasing the height above burner (HAB), with forces ranging from 1.1–3.5 nN. As the HAB was increased, the average attractive force initially increased, briefly decreased, and then underwent a gradual increase, with a maximum of 2.54 nN observed at HAB = 25 mm. The mean adhesive force was 6.5–7.5 times greater than the mean attractive force at the same HAB, and values were in the range of 13.5–24.5 nN. The adhesion energy was in the range of 2.0–5.6 × 10 −17 J. The variations observed in the average adhesion energy with increasing HAB were different from those of the average adhesion force, implying that the stretched length of soot particles is an important factor affecting the average adhesion energy. The Hamaker constants of the soot particles generated at different HABs were determined from AFM force-separation curves. The average Hamaker constant exhibited a clear correlation with the graphitization degree of soot particles as obtained from Raman spectroscopy.

Effect of roughness on the layer-dependent friction of few-layer graphene

Friction on few-layer graphene is known to exhibit unique layer dependence where friction measured via atomic force microscopy (AFM) on the nanometer scale is generally observed to decrease with increasing number of layers. However, this trend is not always observed for AFM probe tips with different sizes and for graphene on different substrates. Within this context, the precise role played by the interface, in particular, the size of the contact and substrate roughness, in the layer dependence of friction on graphene is not yet completely understood. Here, we probe the origins of the roughness dependence of layer-dependent friction on graphene by a combination of AFM measurements and molecular dynamics (MD) simulations. In the experiments, friction is observed to monotonically decrease with increasing number of graphene layers for tips with various apex radii, while the roughness of the sample surface is observed to decrease. In the simulations, two opposite layer-dependence trends for friction are observed on few-layer graphene on substrates with different roughness values. The underlying mechanisms are investigated using atomistic details obtained from the simulations, where the different friction trends are found to originate from an interplay between surface roughness, the trajectory of the tip, and the number of atoms in contact. Finally, the effect of topographical correlation length on the layer dependence of friction on graphene is discussed.

An edge reversal method for precision measurement of cutting edge radius of single point diamond tools

A method, which is referred to as the edge reversal method, is proposed for precision measurement of the cutting edge radius of single point diamond tools. An indentation mark of the cutting edge which replicates the cutting edge geometry is firstly made on a soft metal substrate surface. The cutting edge of the diamond tool and its indentation mark, which is regarded as the reversal cutting edge, are then measured by utilizing an atomic force microscopy (AFM), respectively. The cutting edge radius can be accurately evaluated through removing the influence of the AFM probe tip radius, which is comparable to the cutting edge radius, based on the two measured data without characterization of the AFM probe tip radius. The results of measurement experiments and uncertainty analysis are presented to demonstrate the feasibility of the proposed method.

Electrochemical direct writing and erasing of silver nanostructures on phosphate glass using atomic force microscopy

This paper reports a liquid-free, mask-less electrochemical direct-write lithographic technique using an atomic force microscopy (AFM) probe for writing silver nanostructures in minutes on an optically transparent substrate. Under ambient conditions, silver is locally and controllably extracted to the surface of superionic (AgI)0.25 (AgPO3)0.75 glass by bringing a conductive AFM probe tip in contact with it, biasing the probe with a negative voltage, and regulating the resulting current. The growth mechanism of the resulting nanostructure is explored by extracting silver with a stationary AFM tip on the surface of the silver. A moving tip was then used to produce continuous lines, solid films and discrete dots of silver by implementing continuous and pulsed current writing approaches. The line dimensions depend on writing speed and current flowing in the electrochemical circuit, while the size and spacing of the dots depend on the parameters (magnitude, duration and frequency) of the current pulses and the writing speed of the AFM tip. Line-widths in the ∼100 nm range are demonstrated. Our investigation also shows that a threshold potential must be overcome to be able to draw and reduce silver ions on the glass surface. When polarity between the electrodes is reversed, the patterned silver ionizes back into the glass, thus offering the capability to erase and rewrite Ag patterns on the glass surface.

Quantitative probing of tip-induced local cooling with a resistive nanoheater/thermometer

This article reports the investigation of tip-induced local cooling when an atomic force microscope (AFM) cantilever tip scans over a joule-heated Pt nanowire. We fabricated four-point-probe Pt resistive nanothermometers having a sensing area of 250 nm × 350 nm by combining electron-beam lithography and photolithography. The electrical resistance of a fabricated nanothermometer is ∼27.8 Ω at room temperature and is linearly proportional to the temperature increase up to 350 K. The equivalent temperature coefficient of resistance is estimated to be (7.0±0.1)×10−4 K−1. We also joule-heated a nanothermometer to increase its sensing area temperature up to 338.5 ± 0.2 K, demonstrating that the same device can be used as a nanoheater. An AFM probe tip scanning over a heated nanoheater/thermometer's sensing area induces local cooling due to heat conduction through solid-solid contact, water meniscus, and surrounding air. The effective contact thermal conductance is 32.5 ± 0.8 nW/K. These results contribute to the better understanding of tip-substrate thermal interactions, which is the fundamental subject in tip-based thermal engineering applications.

New optical near-field nanolithography with optical fiber probe laser irradiating atomic force microscopy probe tip

ABSTRACTA new optical near-field nanolithography scheme with optical fiber probe laser irradiating atomic force microscopy (AFM) probe tip is proposed. Through optical theoretical analysis, if the metallic AFM probe tip is in the evanescent field of optical fiber probe tip, the secondary near-field enhancement effect can appear underneath the metallic AFM probe tip. Based on the independently developed AFM system and optical system, the nanolithography platform is built and nanocraters structures can be successfully created, which demonstrates that the new scheme is an effective and promising nanolithography approach for the future nanoelectronics, nanobiotechnology, nanowelding, etc.

(Invited) Strain and Phonon-Carrier Interactions in Ge-Si0.5Ge0.5 Core-Shell Nanowires Probed Using Tip-Enhanced Raman Spectroscopy

Group IV nanowires and nanowire heterostructures are of current interest for a broad range of applications including field-effect transistors with enhanced carrier mobility, and thermoelectric devices with engineered thermal and carrier transport properties. The energy band alignments among Si, Ge, and SixGe1-x alloys enable quantum confinement of either holes or electrons, while compositional variations and structural morphology at the nanoscale can lead to new phonon scattering and confinement effects. Because of the lattice mismatch between Si and Ge, however, the dimensions and alloy compositions in nanowire heterostructures must be carefully controlled and characterized to maintain coherent strain. Here we describe the use of tip-enhanced Raman spectroscopy to characterize nanoscale correlations between strain and nanowire dimensions in Ge-SixGe1-x core-shell nanowires grown by ultrahigh-vacuum chemical vapor deposition, and to elucidate phonon-carrier interactions that are manifested via shifts in Raman peaks originating from Ge-Ge vibrational modes within the quantum-confined hole gas formed at the Ge-SixGe1-x interface. Typical nanowire structures consisted of a Ge core 35-55nm in diameter surrounded by a 5nm thick Si0.5Ge0.5 shell, leading to compressive strain in the Ge core and formation of a quantum-confined hole gas at the Ge-Si0.5Ge0.5 interface. Tip-enhanced Raman spectroscopy (TERS) was performed under ambient atmospheric conditions on nanowires dispersed on an Au surface using an Au-coated atomic force microscope probe tip and 633nm laser excitation in a side illumination geometry. Tip-enhanced Raman spectra exhibit two distinct peaks associated with Ge-Ge vibrational modes – one arising from Ge-Ge vibrations in the nanowire Ge core region, and the other from Ge-Ge vibrations occurring within the quantum-confined hole gas at the Ge-Si0.5Ge0.5 interface. Both peaks exhibit a dependence of Raman shift on local nanowire diameter consistent with coherent strain in the nanowire, demonstrating that the TERS measurements provide the ability to probe strain at the nanoscale. The difference in Raman shift associated with these peaks is shown to be a consequence of coupling between intervalence band transitions and the Ge-Ge phonon mode that leads to Fano resonance behavior and a shift in the phonon self-energy. In addition, positioning of the Au-coated probe tip in closer proximity to the nanowire leads directly to an increase in the separation between these peaks and in the relative amplitude of the peak from the Ge-Si0.5Ge0.5 interface region, confirming that the TERS measurement is sensitive to phenomena within an extremely localized region in the vicinity of the probe tip apex. Computational electromagnetic simulations confirm that proximity to the probe tip leads to a large increase in electromagnetic field amplitude in the nanowire within ~10-20nm of the probe tip surface, and provide insight into the dependence of coupling to intervalence-band carrier transitions on proximity to the probe tip during the TERS measurement. Figure 1

Fabrication of advanced probes for atomic force microscopy using focused ion beam

In this work the results of experimental studies of a fabrication of advanced probes for Atomic Force Microscopy (AFM) using Focused Ion Beam (FIB) and nanolithography are reported. Ability to restore the functionality of broken AFM probe tips is shown. The superior performance of FIB-fabricated probes by observing AFM images of the nanostructures is demonstrated. It is shown that the formation of multiprobe AFM cantilevers by FIB-induced deposition of tungsten allows creating an electrical measurement tool for nanotechnology and high-performance instrument for probe nanolithography. It is shown that the use of modified cantilevers for the diagnostics of submicron structures allows one to minimize the artefacts of AFM images, as well as to increase the accuracy of the obtained results.

Nanospot Soldering Polystyrene Nanoparticles with an Optical Fiber Probe Laser Irradiating a Metallic AFM Probe Based on the Near-Field Enhancement Effect

With the development of nanoscience and nanotechnology for the bottom-up nanofabrication of nanostructures formed from polystyrene nanoparticles, joining technology is an essential step in the manufacturing and assembly of nanodevices and nanostructures in order to provide mechanical integration and connection. To study the nanospot welding of polystyrene nanoparticles, we propose a new nanospot-soldering method using the near-field enhancement effect of a metallic atomic force microscope (AFM) probe tip that is irradiated by an optical fiber probe laser. On the basis of our theoretical analysis of the near-field enhancement effect, we set up an experimental system for nanospot soldering; this approach is carried out by using an optical fiber probe laser to irradiate the AFM probe tip to sinter the nanoparticles, providing a promising technical approach for the application of nanosoldering in nanoscience and nanotechnology.

Optical imaging beyond the diffraction limit by SNEM: effects of AFM tip modifications with thiol monolayers on imaging quality.

Tip-enhanced nanoscale optical imaging techniques such as apertureless scanning near-field optical microscopy (a-SNOM) and scanning near-field ellipsometric microscopy (SNEM) applications can suffer from a steady degradation in performance due to adhesion of atmospheric contaminants to the metal coated tip. Here, we demonstrate that a self-assembled monolayer (SAM) of ethanethiol (EtSH) is an effective means of protecting gold-coated atomic force microscopy (AFM) probe tips from accumulation of surface contaminants during prolonged exposure to ambient air. The period over which they yield consistent and reproducible results for scanning near-field ellipsometric microscopy (SNEM) imaging is thus extended. SNEM optical images of a microphase separated polystyrene-block-poly (methylmethacrylate) (PS-b-PMMA) diblock copolymer film, which were captured with bare and SAM-protected gold-coated AFM probes, both immediately after coating and following five days of storage in ambient air, were compared. During this period the intensity of the optical signals from the untreated gold tip fell by 66%, while those from the SAM protected tip fell by 14%. Additionally, gold coated AFM probe tips were modified with various lengths of alkanethiols to measure the change in intensity variation in the optical images with SAM layer thickness. The experimental results were compared to point dipole model calculations. While a SAM of 1-dodecanethiol (DoSH) was found to strongly suppress field enhancement we find that it can be locally removed from the tip apex by deforming the molecules under load, restoring SNEM image contrast.

Study on the rapid relocation method of nano target for AFM

The atomic force microscope (AFM) has high observation resolution and operation precision, which plays an irreplaceable role in the characterization of nanomaterials and the assembly of nanodevices. The selection of AFM scan area depends on an optics microscope, whose resolution is generally no more than 200 nm due to the limitation of wavelength of visible light. Therefore, it is extreme challenge to relocate the AFM probe precisely to the initial scan area when the AFM probe is replaced or the sample is moved. In this paper, we study and present a new label-free method for the relocation of AFM probe. This method can cope with the variation of relative position between the AFM probe tip and target sample, which is caused by the angle rotation and position offset. Two easily-recognized features on the sample substrate are used as the reference points to realize the blind location of AFM probe with micron scale precision based on the principle of coordinate transformation. The high precision relocation of nano targets is obtained through matching AFM images and modifying the scanning parameters. The main advantage of this method is that the special man-made marks at the target sample area are not necessary. The relocation process of AFM probe is simple and rapid, with a wide location range and high accuracy. Experiments demonstrate that this method is very efficient to track the nanospheres, SWCNTs and nanoscratch.

High aspect ratio AFM Probe processing by helium-ion-beam induced deposition.

A Scanning Helium Ion Microscope (SHIM) is a high resolution surface observation instrument similar to a Scanning Electron Microscope (SEM) since both instruments employ finely focused particle beams of ions or electrons [1]. The apparent difference is that SHIMs can be used not only for a sub-nanometer scale resolution microscopic research, but also for the applications of very fine fabrication and direct lithography of surfaces at the nanoscale dimensions. On the other hand, atomic force microscope (AFM) is another type of high resolution microscopy which can measure a three-dimensional surface morphology by tracing a fine probe with a sharp tip apex on a specimen's surface.In order to measure highly uneven and concavo-convex surfaces by AFM, the probe of a high aspect ratio with a sharp tip is much more necessary than the probe of a general quadrangular pyramid shape. In this paper we report the manufacture of the probe tip of the high aspect ratio by ion-beam induced gas deposition using a nanoscale helium ion beam of SHIM.Gas of platinum organic compound was injected into the sample surface neighborhood in the vacuum chamber of SHIM. The decomposition of the gas and the precipitation of the involved metal brought up a platinum nano-object in a pillar shape on the normal commercial AFM probe tip. A SHIM system (Carl Zeiss, Orion Plus) equipped with the gas injection system (OmniProbe, OmniGIS) was used for the research. While the vacuum being kept to work, we injected platinum organic compound ((CH3)3(CH3C5H4)Pt) into the sample neighborhood and irradiated the helium ion beam with the shape of a point on the apex of the AFM probe tip. It is found that we can control the length of the Pt nano-pillar by irradiation time of the helium ion beam. The AFM probe which brought up a Pt nano-pillar is shown in Figure1. It is revealed that a high-aspect-ratio Pt nano-pillar of ∼40nm diameter and up to ∼2000 nm length can be grown. In addition, for possible heating by the helium ion beam, it was observed that an original probe shape was transformed. AFM measurement of a reference sample (pitch 100-500 nm, depth 100 nm) of the lines and spaces was performed using the above probes. The conventional probes which did not bring up platinum was not able to get into the ditch enough. Therefore it was found that a salient was big and a reentrant was shallow. On the other hand, the probe which brought up platinum was able to enter enough to the depths of the ditch.jmicro;63/suppl_1/i30-a/DFU075F1F1DFU075F1Fig.1.SHIM image of the AFM probe with the Pt nano-pillar fabricated by ion-beam induced deposition.

Fabrication of AFM probe with CuO nanowire formed by stress-induced method

A novel method to fabricate an atomic force microscope (AFM) probe with CuO nanowire was proposed using a stress-induced method which can form nanowire easily. By heating a commercial AFM probe which is eliminated its tip and is coated with Ta and Cu films, Cu hillock and CuO nanowires on the hillock can be formed at the probe end. To obtain the CuO nanowire of high aspect ratio that can use as an AFM probe tip, thickness of coating films, heating temperature and heating time were investigated. As the result, the probe tip approximately 5 μm high and the nanowire approximately 25 nm in diameter were successfully obtained. In the results that the measurement resolution was evaluated, the measurement resolution of the CuO nanowire probe slightly worse than that of a commercial AFM probe. However, from the viewpoint of the dimensional measurement, the precision was almost equal between both probes.

Phenolic Porphyrins Assembled at Surfaces: Hydrogen-Bonding and Binary Systems

Supramolecular arrangement of porphyrins and other molecules has great potential in the fields of molecular information storage and sensing due to their ease of deposition and good chemical and thermal stabilities. In particular, porphyrins of relatively large molecular weights can be applied in thermal deposition while tetrapyrrole molecules have had an extensive synthetic chemistry developed, which enables synthesis of complex derivatives. In this work, we present complementary examples of porphyrin nanoarchitectonics. Starting from simple symmetrical phenol derivatives, we describe the effects of steric hindrance about the respective hydroxyl groups1,2 and also the effects of conformational variation on the self-assembly structures.3 We also investigated fabrication of binary molecular monolayers using two different porphyrin molecules tetrakis(3,5-di-t-butyl-4-hydroxyphenyl) porphyrin and tetrakis(4-pyridyl) porphyrin by deposition in ultrahigh vacuum.4 This leads to two unusual heteromolecular monolayer structures were observed with one exhibiting good separation of molecules within the monolayer. Meanwhile, a synthetic nanoarchitectonic approach was used to prepare self-assembled molecular nanowires at a mica substrate. The nanowires could be observed growing using atomic force microscopy (AFM) and the network structures of the nanowires can be influenced by manipulation using the AFM probe tip.4,5Formation of molecular monolayers with chromophores positioned remote from the substrate surface will also be discussed.References(1) J. P. Hill, Y. Wakayama, W. Schmitt, T. Tsuruoka, T. Nakanishi, P. A. Karr, M. L. Zandler, A. L. McCarty, F. D’Souza, L. R. Milgrom, K. Ariga, Chem. Commun. 2006, 2320–2322 (2) J. P. Hill, Y. Wakayama, M. Akada, Katsuhiko Ariga, J. Phys. Chem. C. 2007, 111, 16174–16180 (3) J. P. Hill, Y. Wakayama, K. Ariga, Phys. Chem. Chem. Phys. 2006, 8, 5034–5037 (4) J. P. Hill, Y. Xie, M. Akada, Y. Wakayama, L. K. Shrestha, Q. Ji, K. Ariga, Langmuir (2013) 29(24), 7291–7299 (5) Y. Xie, M. Akada, J. P. Hill, Q. Ji, R. Charvet K. Ariga, Chem. Commun. 2011, 47, 2285–2287.Figure. Self-assembled phenol-substituted porphyrins on Cu(111) surface.

Nanoscale scanning near-field ellipsometric microscopy (SNEM) imaging of heterogeneous polymers

ABSTRACTIn this study a scanning near-field ellipsometric microscope (SNEM), a hybrid device of an atomic force microscope (AFM) and an ellipsometer, is used to obtain optical images of heterogeneous polymer thin films with a resolution below the diffraction limit of light. SNEM optical images of a microphase separated PS-b-P2VP block copolymer film collected with gold coated and bare silicon AFM probe tips were compared to obtain a deeper insight into the nature of the SNEM contrast mechanism. Furthermore, intensity vs. distance curves were recorded on a PS-b-PMMA block copolymer film simultaneously during the acquisition of force-displacement curves to study the far-field contribution of the optical signal to the optical image.

Characterization of single 1.8-nm Au nanoparticle attachments on AFM tips for single sub-4-nm object pickup

This paper presents a novel method for the attachment of a 1.8-nm Au nanoparticle (Au-NP) to the tip of an atomic force microscopy (AFM) probe through the application of a current-limited bias voltage. The resulting probe is capable of picking up individual objects at the sub-4-nm scale. We also discuss the mechanisms involved in the attachment of the Au-NP to the very apex of an AFM probe tip. The Au-NP-modified AFM tips were used to pick up individual 4-nm quantum dots (QDs) using a chemically functionalized method. Single QD blinking was reduced considerably on the Au-NP-modified AFM tip. The resulting AFM tips present an excellent platform for the manipulation of single protein molecules in the study of single protein-protein interactions.