Ultrahigh Vacuum Noncontact Atomic Force Research Articles

How Precisely Can Individual Molecules Be Analyzed? A Case Study on Locally Quantifying Forces and Energies Using Scanning Probe Microscopy.

Recent advances in scanning probe microscopy methodology have enabled the measurement of tip-sample interactions with picometer accuracy in all three spatial dimensions, thereby providing a detailed site-specific and distance-dependent picture of the related properties. This paper explores the degree of detail and accuracy that can be achieved in locally quantifying probe-molecule interaction forces and energies for adsorbed molecules. Toward this end, cobalt phthalocyanine (CoPc), a promising CO2 reduction catalyst, was studied on Ag(111) as a model system using low-temperature, ultrahigh vacuum noncontact atomic force microscopy. Data were recorded as a function of distance from the surface, from which detailed three-dimensional maps of the molecule's interaction with the tip for normal and lateral forces as well as the tip-molecule interaction potential were constructed. The data were collected with a CO molecule at the tip apex, which enabled a detailed visualization of the atomic structure. Determination of the tip-substrate interaction as a function of distance allowed isolation of the molecule-tip interactions; when analyzing these in terms of a Lennard-Jones-type potential, the atomically resolved equilibrium interaction energies between the CO tethered to the tip and the CoPc molecule could be recovered. Interaction energies peaked at less than 160 meV, indicating a physisorption interaction. As expected, the interaction was weakest at the aromatic hydrogens around the periphery of the molecule and strongest surrounding the metal center. The interaction, however, did not peak directly above the Co atom but rather in pockets surrounding it.

Preface

The 2022 2nd International Conference on Measurement Control and Instrumentation (MCAI 2022) was held in Guangzhou, China from July 22 to 24, 2022. In view of the current COVID-19 pandemic, it was chosen to be held online. MCAI 2022 promoted research and developmental activities in the fields of “Measurement Control” and “Instrumentation” as well as scientific information interchange between researchers, engineers, and practitioners working all around the world.In the conference, we had the honor of having invited both Prof. Guixiong Liu from South China University of Technology, China and Prof. Zhen Zhou, Guangzhou Hexin Instrument Co., Ltd., China to serve as our Conference General Chairs. The conference consisted of keynote speeches, oral presentations and online Q&A discussion, attracting 100 individuals and institutions worldwide. Primarily, keynote speakers were each allocated 30-45 minutes to hold their speeches. Then in the oral presentations, the excellent papers we had selected were presented by their authors by turns.We were delighted and honored to invite three prominent professors as keynote speakers to deliver their speeches. For a start, Prof. Zongmin Ma from North University of China showed us his research: Non-contact Atomic Force Microscopy Instruments and Atomic Scale Precision Measurements. By developing the ultra-high vacuum non-contact atomic force microscope (NC-AFM), he solved the key technologies of probe vibration control and precise detection, force spectrum measurement, and realized atomic scale imaging characterization in terms of non-destructive imaging of magnetic information and uncoupled measurement of surface charge. Besides, Assoc. Prof. Zhiwei Shi from Guangdong University of Technology, China made a report on Multi-sensor Information Fusion Technology for Intelligent Networked Vehicles. Aiming at the development of intelligent networked vehicles, he proposed a vehicle headlight far-light system based on multi-sensor information fusion, which mainly includes three major parts: information fusion, drive control and optical design, ensuring in a maximum degree the intelligent lighting functions and simple structure, low cost. The wonderful speeches of each keynote speaker had triggered heated discussion. Besides, every participant praised this conference for disseminating useful and insightful knowledge.List of Committee member is available in this pdf.

Advancements in emerging superlubricity: A review of the atomistic models, simulation techniques and their applications to explore the state of ultra-low friction

Abstract It has been a prime focus to reduce the undesirable effects of friction as much as possible. Recent advances in attaining ultra-low friction state has shown significant improvement in predicting the tribological response of materials using computer simulations which has been used side-by-side with advanced in-situ experimental setups such as ultra-high vacuum non-contact atomic force microscopy and friction force microscopy to investigate and validate the simulation results at the microscale and nanoscale lengths. Hence, this review has been designed keeping the recent trends in the investigation of superlubric interfaces in focus with main emphasis on discussing the atomistic models and molecular dynamics (MD) simulations along with their application in studying the intricate details pertaining to reduction of friction. The complexities involved in replicating the nanoscale models to reduce friction at the macroscale has also been discussed along with the potential remedies to overcome those challenges.

AFM induced self-assembling and self-healing mechanism of silicon oxide nanoparticle linear array domains templated on Moiré superlattice patterns on HOPG

Silicon oxide nanocluster suspensions were drop-cast on highly oriented pyrolytic graphite (HOPG) and investigated using ultra-high vacuum non-contact atomic force microscopy (AFM). The assembly of silicon oxide nanoparticle arrays was observed during consecutive scanning of the surface using AFM. The patterns and alignments of the nanoparticle arrays were consistent with templating on a Moiré pattern in the top layers of the HOPG substrate. By halting and restarting the scanning process it was shown that the formation of nanoparticle arrays was driven by the AFM scan itself. Vacancy defects identified within the nanoparticle arrays were found to fill over time with nanoparticles; it was demonstrated that diffusion was preferred along the symmetry lines. This ‘self-healing’ mechanism was also shown to be driven by the AFM scanning. The recovery of defects within the arrays, and other observations of array dynamics, implied that the nanoparticle arrays had liquid-like qualities.

Purely Armchair or Partially Chiral: Noncontact Atomic Force Microscopy Characterization of Dibromo-Bianthryl-Based Graphene Nanoribbons Grown on Cu(111).

We report on the atomic structure of graphene nanoribbons (GNRs) formed via on-surface synthesis from 10,10'-dibromo-9,9'-bianthryl (DBBA) precursors on Cu(111). By means of ultrahigh vacuum noncontact atomic force microscopy with CO-functionalized tips we unveil the chiral nature of the so-formed GNRs, a structure that has been under considerable debate. Furthermore, we prove that-in this particular case-the coupling selectivity usually introduced by halogen substitution is overruled by the structural and catalytic properties of the substrate. Specifically, we show that identical chiral GNRs are obtained from 9,9'-bianthryl, the unsubstituted sister molecule of DBBA.

Atomistics of superlubricity

Abstract Friction is a phenomenon observed ubiquitously in daily life, yet its nature is complicated. Friction between rough surfaces is considered to arise primarily because of macroscopic roughness. In contrast, interatomic forces dominate between clean and smooth surfaces. “Superlubricity”, where friction effectively becomes zero, occurs when the ratio of lattice parameters in the pair of surfaces becomes an irrational number. Superlubricity has been found to exist in a limited number of systems, but is a very important phenomenon both in industry and in mechanical engineering. New atomistic research on friction is under way, with the aim of refining theoretical models that consider interactions between atoms beyond mean field theory and experiments using ultrahigh vacuum non-contact atomic force microscopy. Such research is expected to help clarify the nature of microscopic friction, reveal the onset conditions of friction and superlubricity as well as the stability of superlubricity, discover new superlubric systems, and lead to new applications.

Back Cover: Resolving oxide surfaces – From point and line defects to complex network structures (Phys. Status Solidi B 5/2013)

High resolution imaging and spectroscopy signifi cantly improves our understanding of surface structure and chemistry for complex materials. In the Feature Article by Markus Heyde et al. (pp. 895–921) low temperature ultrahigh vacuum noncontact atomic force and scanning tunneling microscopy has been employed to characterize surface structures ranging from periodic and ordered via defective towards amorphous networks. In the presented studies it has been shown how modern scanning probe microscopy techniques can complete and clarify the atomistic models, which have been derived so far mainly from diffraction experiments. The benefi ts of locally resolving complex surface structures are obvious. A direct atomic assignment from the obtained images is possible. Surface structures with increasing dimensionality from 0D to 2D are discussed. In this article three different sample systems are highlighted, namely, magnesia on Ag(001), alumina on NiAl(110) and silica on Ru(0001).

Thermal noise limit for ultra-high vacuum noncontact atomic force microscopy.

The noise of the frequency-shift signal Δf in noncontact atomic force microscopy (NC-AFM) consists of cantilever thermal noise, tip–surface-interaction noise and instrumental noise from the detection and signal processing systems. We investigate how the displacement-noise spectral density dz at the input of the frequency demodulator propagates to the frequency-shift-noise spectral density dΔf at the demodulator output in dependence of cantilever properties and settings of the signal processing electronics in the limit of a negligible tip–surface interaction and a measurement under ultrahigh-vacuum conditions. For a quantification of the noise figures, we calibrate the cantilever displacement signal and determine the transfer function of the signal-processing electronics. From the transfer function and the measured dz, we predict dΔf for specific filter settings, a given level of detection-system noise spectral density dzds and the cantilever-thermal-noise spectral density dzth. We find an excellent agreement between the calculated and measured values for dΔf. Furthermore, we demonstrate that thermal noise in dΔf, defining the ultimate limit in NC-AFM signal detection, can be kept low by a proper choice of the cantilever whereby its Q-factor should be given most attention. A system with a low-noise signal detection and a suitable cantilever, operated with appropriate filter and feedback-loop settings allows room temperature NC-AFM measurements at a low thermal-noise limit with a significant bandwidth.

Development of Ultra-High Vacuum Non-Contact Atomic Force Microscope and Its Applications

Development of Ultra-High Vacuum Non-Contact Atomic Force Microscope and Its Applications

NC-AFM Observation of Atomic Scale Structure of Rutile-type TiO2(110) Surface Prepared by Wet Chemical Process

We succeeded in observing the atomic scale structure of a rutile-type TiO2(110) single-crystal surface prepared by the wet chemical method of chemical etching in an acid solution and surface annealing in air. Ultrahigh vacuum noncontact atomic force microscopy (UHV-NC-AFM) was used for observing the atomic scale structures of the surface. The UHV-NC-AFM measurements at 450 K, which is above a desorption temperature of molecularly adsorbed water on the TiO2(110) surface, enabled us to observe the atomic scale structure of the TiO2(110) surface prepared by the wet chemical method. In the UHV-NC-AFM measurements at room temperature (RT), however, the atomic scale structure of the TiO2(110) surface was not observed. The TiO2(110) surface may be covered with molecularly adsorbed water after the surface was prepared by the wet chemical method. The structure of the TiO2(110) surface that was prepared by the wet chemical method was consistent with the (1 x 1) bulk-terminated model of the TiO2(110) surface.

Ultrahigh Vacuum Non-Contact Atomic Force Microscope Observation of Reconstructed Si(110) Surface

We tried to observe a reconstructed Si(110) surface using an ultrahigh-vacuum (UHV) non-contact atomic force microscope (NC-AFM). The Si(110) surface has several characteristic structures, such as the 16 x 2, (17, 15, 1) 2 x 1, 1 x 1, zigzag structures. We succeeded in the AFM observation of the surface formed upon annealing the samples in direct current heating so as to clean the surface. We obtained the same structures in the AFM observation as the proposed 16 x 2 model of a Si(110) reconstruction in a STM observation. The UHV NC-AFM results demonstrate that the Si(110) surface has a characteristic 16 x 2 structure for the first time observation.

Mapping Contact Potential Differences with Noncontact Atomic Force Microscope Using Resonance Frequency Shift versus Sample Bias Voltage Curves

We have measured cantilever resonance frequency versus sample bias voltage and generated frequency vs bias ( f–V) curves using an ultrahigh-vacuum noncontact atomic force microscope (UHV NC-AFM). Using the f–V data, we calculated the contact potential difference (CPD) between the tip and the sample. These CPD measurements were compared with those that were directly observed with a scanning Kelvin probe force microscope (SKPM) on the same atomically resolved area of the sample using a UHV-AFM. The CPD values obtained by both methods were similar, however, it was difficult to obtain CPD values that agreed precisely on the atomic scale.

Interface-reaction-mediated formation of two-dimensional Si islands on CaF2

The growth of Si on thin (∼3 nm thick) CaF2/Si(111) films in the temperature range of 500–700 °C was investigated using ultrahigh-vacuum noncontact atomic force microscopy. At 500 °C, the morphology is dominated by small cluster-like shaped Si islands due to weak binding between Si and CaF2; with increasing growth temperatures these islands coexist with an increasing amount of triangular-shaped, flat Si islands. The formation of flattened triangular islands is attributed to an increased binding of Si to the CaF2 film at higher temperatures. The binding changes as a result of an interface reaction leading to the removal of fluorine atoms and the formation of Ca–Si bonds.

Alkanethiol self-assembled monolayers on Au(111) surfaces investigated by non-contact AFM

Self-assembled monolayers (SAMs) of alkanethiol molecules (CH3–(CH2)n-1–SH, Cn) deposited on Au(111) surfaces were investigated by ultrahigh vacuum non-contact atomic force microscopy (UHV-NC-AFM). Octanethiol SAMs (C8) and hexadecanethiol (C16) SAMs self-assembled from ethanol solutions were used. Molecularly resolved NC-AFM images of longer-chain alkanethiol (C16) SAMs, which are difficult to be observed by STM, are presented for the first time. The results show that the molecules in this film are hexagonally packed, making (√3×√3)R30° structures. Imaging conditions were more stable in the case of SAMs with longer-chain molecules. This is probably because the “rigidity” depends on the chain length of the molecules. In addition, the high-resolution images of the stripe structures in lower-density region of C8 SAMs were obtained by NC-AFM.

Development of low temperature ultrahigh vacuum noncontact atomic force microscope with PZT cantilever

We constructed a low temperature (LT) ultrahigh vacuum (UHV) atomic force microscope (AFM) system using a frequency modulation (FM) technique. As the displacement sensor, we used a lead zirconate titanium (PZT) cantilever to detect the force interaction between the tip and sample. Although the PZT film can be used as the actuator to oscillate the cantilever, an external piezoactuator is used to oscillate the PZT cantilever for small oscillation amplitude stably. The PZT cantilever does not require any alignment mechanisms for displacement detection and does not have thermal source due to resistive heating. Therefore, it is one of the promising force sensors under LT environments. Attractive force interaction was detected by the PZT cantilever. We presented the preliminary result of imaging of atomic steps on Si(111) surface measured by noncontact-AFM at room temperature and LT environment.

High resolution imaging of contact potential difference using a novel ultrahigh vacuum non-contact atomic force microscope technique

An ultrahigh vacuum scanning Kelvin probe force microscope (UHV SKPM) based on the gradient of electrostatic force was developed using the technique of a UHV non-contact atomic force microscope (NC-AFM) capable of atomic level imaging, and used for simultaneous observation of contact potential difference (CPD) and NC-AFM images. The CPD images with a potential resolution of less than 10 meV were observed in the UHV SKPM, demonstrating an atomic level resolution. The change of potential corresponding to the charges on the insulated surface of polypropylene have been observed in UHV SKPM. We also demonstrated a reliable method to obtain the CPD from the bias voltage dependence curves of the frequency shift in all of the scanning area. The results are consistent with comparing the barrier height images in that the work functions of adatoms are greater than the work function of corner holes.

Scanning Probe Microscopy: Present Status and New Development. Status and Development of Atomic Force Microscopy.

In 1995, a true atomic resolution was achieved for the first time, using an ultrahigh-vacuum noncontact-atomic force microscope (AFM) with frequency modulation (FM) detection method that enables to measure change in mechanical resonant frequency (frequency shift) of an atomic force probe (AFM cantilever). At present, noncontact AFM method is established as a novel microscopy with true atomic resolution, which can observe even insulator. Here, to make clear the next development on AFM, we introduced a force mapping of atomic force on an atomic scale, i.e., atomic force mi-crospectroscopy and control of atomic force by change of atom on tip apex of an atomic force probe. AFM, which utilizes atomic force itself based on the atomic interaction, can provide observation, spectroscopy, discrimination, identification, control and manipulation of individual atomic force and atom, so that AFM has large possibility as the coming generation of atomic and molecular technique and is expected to develop in very wide fields of science and engineering.

High-resolution imaging of contact potential difference with ultrahigh vacuum noncontact atomic force microscope

An ultrahigh vacuum scanning Kelvin probe force microscope (UHV SKPM) utilizing the gradient of electrostatic force, was developed based on an ultrahigh vacuum noncontact atomic force microscope (NC-AFM) capable of atomic level imaging, and used for simultaneous observation of contact potential difference (CPD) and NC-AFM images. CPD images of a Si(111) surface with Au deposited, clearly showed the potential difference in phases between 7×7 and 5×2 structures. When Ag was deposited as a submonolayer on the Si(111) 7×7 reconstructed surface, the atomic level lateral resolution was observed in CPD images as well as in NC-AFM topographic images.

Observation of Silicon Surfaces Using Ultrahigh Vacuum Noncontact Atomic Force Microscope

The advantage of noncontact atomic force microscope (NC-AFM) is, that the interaction between the tip and the sample is reduced as compared with the other AFM techniques. Furthermore, in the ultrahigh vacuum (UHV) NC-AFM, the atomic resolution images can be obtained, as the capillary forces between the cantilever tip and the sample are eliminated. A UHV NC-AFM with a unique frequency modulation (FM) technique has been developed. We have obtained atomic resolution images of the Si(111) 7×7, Si(100) 2×1 structures and oxygen adsorption Si(111)7×7 surface along with the scanning tunneling microscope (STM) images. Using a similar technology, a UHV scanning Kelvin probe microscope (SKPM) utilizing the gradient of electrostatic force has also been developed. In the SKPM it is possible to simultaneously observe the contact potential difference (CPD) and the NC-AFM topographic images. The CPD image of Si(111) surface with deposited Au clearly shows the potential difference between the 7×7 and the 5×2 phases. A high resolution image of the Ag-deposited Si(111)7×7 surface is obtained by simultaneous observation of the CPD and the NC-AFM topographic images.