Mechanisms of surface anodization produced by scanning probe microscopes

In this chapter, we discuss recent developments in the characterization of polarization doped wide bandgap semiconductor (WBS) heterojunctions with an emphasis on characterization by scanning probe microscopy (SPM). Wide bandgap semiconductors, such as SiC and GaN, have a wide variety of applications in electronic and optoelectronic devices [1–6]. The operation of devices made from these materials is dominated by the polarization properties of III-N and SiC semiconductor crystals. For example, polarization doped 2 dimensional electron gas (2DEG) channels in undoped GaN/AlGaN and SiC polytypic heterojunctions have been fabricated with current densites in excess of 1A/mm. Other effects, such as surface charge instability stemming from polarization, offer interesting potentials and challenges.While some of these effects may be studied using more conventional techniques such as currentvoltage (IV) and capacitance-voltage (CV) techniques (described in sections 2 and 3), others require probes capable of investigation on the nanometer scale. Transmission electron microscopy (TEM) can be used to investigate such polarizationinduced phenomena with atomic resolution, but involves destructive and laborious sample preparation. SPM techniques offer powerful, non-destructive tools to effectively and conveniently probe electronic materials and devices. Since the discovery of scanning tunneling microscopy (STM) in 1981 by Binnig and Rohrer [7], the field of SPM has advanced to encompass a large number of variations including, (i) STM, (ii) Atomic force microscopy (AFM), (iii) Electrostatic force microscopy (EFM), (iv) Scanning capacitance microscopy (SCM), (v) Scanning conduction microscopy (SCM), (vi) Magnetic force microscopy (MFM), (vii) Piezoelectric force microscopy (PFM), and (vii) Near field scanning optical microscopy (NSOM). Of the above modes, the first five modes have been extensively used for semiconductor characterization [8–15]. For WBS characterization, especially III-N, AFM, EFM and SCM modes are the most important due to the strong polarization of III-N and SiC. In the latter half of this chapter, we focus on the characterization of III-N by EFM operated in

Scanning probe microscopy (SPM) can be successfully used in biological investigations1. Scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) are two main SPM techniques and they are capable of imaging biological objects at molecular level under in situ conditions. With this advantage, STM and AFM are applied to study not only the topographical structures of bio-samples in their natural environment, but also their electrochemical properties at liquid-solid interfaces. The electrochemical properties of biomolecules are usually studied by integral electrochemical methods, like cyclic voltammetry. The degree of surface coverage, the surface orientation of enzymes and the activity of a single enzyme remain a question of dispute, however, electrochemical SPM techniques can bring clarification. Electrochemical scanning tunnelling microscopy (EC-STM) and electrochemical atomic force microscopy (EC-AFM) provide visual topological information of biomolecules adsorbed on the electrode surface at single-molecular level. Some experimental issues, such as the requirement of the sample being conductive, potential damage to samples caused by the tunnelling current or tip-sample force, may limit their application. Scanning electrochemical potential microscopy (SECPM), a technique that measures the surface potential distribution at zero current, can be a promising alternative. SECPM shares most of the hardware setup with EC-STM except for the current amplifier being substituted by a potentiometer. It is easy to switch between SECPM and EC-STM to compare the topographical profile of the same area by mapping electron density and surface potential2. In our study, SPM techniques are used to study various biological objects, from nanometer-sized DNA and redox proteins to micrometer-sized bacteria spores. Since high-resolution images of DNA origami nanostructures can be achieved by using AFM3, we use both EC-AFM and SECPM techniques to investigate the morphology and potential-dependent adsorption behaviour of DNA scaffold and origamis4 on the modified HOPG surface. We found DNA scaffold can adsorb on HOPG in a certain potential range, and the adsorption structure changes with the applied electrochemical potential. Horseradish peroxidase (HRP), a redox enzyme, was studied using both, EC-STM and SECPM under in situ conditions5. HRP molecules were adsorbed on highly oriented pyrolytic graphite (HOPG) surfaces and imaged in phosphate buffered saline. We found that SECPM shows a better resolution than EC-STM in imaging this biomolecule. SECPM is also capable of measuring the surface charge distribution of the adsorbed biomolecules at the electrochemical interfaces. AFM in liquid was used to investigate the morphology and cellular process of Streptomycetes venezuelae both the wild type and the mutant6. To immobilize the bacteria on the surface for imaging, we use SiC patterned by photolithography with hole arrays (1.5×1.5×0.6 µm) to trap the bacteria and then measure under the physiological condition. The designed hole arrays trap the bacteria without causing any denaturation and due to the high electronic conductivity, they can serve as the working electrode under electrochemical conditions for EC-AFM and SECPM studies. EC-AFM was applied to image the morphology of the bacterial spore under different potential, and we found the morphology of the spore didn’t change in the wide potential window. (1) Choi, E.; Kim, A.; Son, H.; Pyo, S. G. J. Nanosci. Nanotechnol. 2014, 14 (1), 924. (2) Herpich, M.; Friedl, J.; Stimming, U. In Surface Science Tools for Nanomaterials Characterization; Springer Berlin Heidelberg: Berlin, Heidelberg, 2015; pp 1–67. (3) Bald, I.; Keller, A. Molecules 2014, 19 (9), 13803. (4) Kozyra, J.; Ceccarelli, A.; Torelli, E.; Lopiccolo, A.; Gu, J.-Y.; Fellermann, H.; Stimming, U.; Krasnogor, N. ACS Synth. Biol. 2017, 6 (7), 1140. (5) Baier, C.; Stimming, U. Angew. Chem. Int. Ed. Engl. 2009, 48 (30), 5542. (6) Santos-Beneit, F.; Gu, J.-Y.; Stimming, U.; Errington, J. Heliyon. Accepted

Imaging micro-cracks in gold films: a comparative study of scanning tunneling and atomic force microscopies

INTRODUCTION Background History of Microscopy SCANNING PROBE MICROSCOPES (SPMS) Scanning Tunneling Microscope Electron Tunneling Atomic Force Microscope (AFM) Modes of Operation of AFM Simultaneous AFM and Scanning Near-Field Fluorescence (SNOM and SNOM-AFM) Friction Force Microscopy (FFM) STM and AFM Studies under Fluids Sample Preparation Procedures for STM and AFM Calibration and Image Analysis of STM and AFM Comparative Studies of Diverse Molecules by STM and AFM LIPID-LIKE MOLECULES ON SOLIDS AND SAMS Collapsed Lipid Monolayers (Self-Assembly) Domain Patterns in Monomolecular Film Assemblies Mixed Lipid Molecule Assemblies Holes in LB Films of Self-Assembly Monolayers Visualization of Vesicles by AFM LB Films of Liquid Crystals STM and AFM Studies of Diverse Molecules on Solids STM Studies on the Effect of Functional Group BIOPOLYMERS AND SYNTHETIC POLYMERS STRUCTURES BY STM AND AFM DNA Structures by STM and AFM SPM Studies of Three-Dimensional Protein Structures Protein Adsorption Studies by AFM Biological Macromolecular Structures Synthetic Polymers Studies by SPMs Mixed Monolayers of Macromolecules and Lipids Diverse Macromolecular Properties as Studied by SPMs Monolayers of Synthetic Polyamino Acids Biopolymer SAM Structures at Interfaces by STM and AFM CRYSTAL STRUCTURES BY STM AND AFM Crystal Structures of Small Molecules Surface Adsorption Studies by SPMs Macromolecule Crystals by STM and AFM STUDIES OF SOLID SURFACES BY SPMS Wetting Properties of Solid Surfaces AFM Analyses of Surface Acid-Base Properties Measurement of Attractive and Repulsive Forces by Atomic Force Microscope (AFM) DIVERSE APPLICATIONS OF SPMS (STM AND AFM, ETC.) AND NANOTECHNOLOGY STM and AFM in Organic Chemistry Semiconductor Study by SPM STM and AFM in Inorganic Chemistry Nanolithography and Nanomachining Qualitative and Quantitative Analyses at Nanoscale Application of SPMs under Dynamic Conditions Application of AFM to Immunodiagnostic Systems Applications of STM and AFM in Industry SPM Studies of Nanoscale Reactors Nanoscale Evaluation of Surface Roughness by SPMs Application of STM and AFM in Pollution Control Friction Force Microscope (FFM) Time-Resolved Analyses by STM REFERENCES

<p xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" class="first" dir="auto" id="d6099e80">The rising cost of liquid helium, traditionally used for cooling sophisticated low-temperature instruments, is increasingly impacting the operational costs of such systems. Recent advances in cryogenic technology have made closed-cycle cooling an attractive alternative, gradually replacing conventional "wet" cryostat designs. These closed-cycle systems now offer enhanced cooling power, temperature stability, and reduced vibration, making them suitable for integration with highly sensitive instruments, such as scanning probe microscopes (SPM). However, to achieve ultimate stability, sample purity, and the highest spatial and energy resolution, ultra-high vacuum (UHV) environments are essential. <p xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" dir="auto" id="d6099e82">To meet the specific needs of the low-temperature SPM community, we have developed a UHV-based closed-cycle SPM dedicated for both scanning tunneling microscopy (STM) and atomic force microscopy (AFM) [ <a class="xref-link" href="#r1">1</a>]. Designed to be compact and acoustically quiet, this system can fit seamlessly into any laboratory environment. Unlike other commercially available systems, our solution provides long-term and stable operation at temperatures below 10 K, capable of running continuously for up to two years without interruption. The instrument’s compact SPM head allows easy optical access and can be integrated with optical components for advanced techniques, such as tip-enhanced Raman spectroscopy (TERS) or luminescence experiments. This innovative system offers a robust and sustainable platform for state-of-the-art research in nanotechnology and surface science.

Scanning probe microscope (SPM)(including atomic force microscope (AFM), scanning tunneling microscope (STM) and Kelvin force probe microscope (KPFM)), etc.), tips have a great influence on physical and chemical properties of the sample surface. In this research, we explore the relationship between tip and structure of sample surface using AFM on Cu(110)-O surface. We observed two different types of c(6×2) phase on which Cu shows bright spot when the tip apex is O-terminated; on the other hand, O atoms shows bright spot when the tip apex is Cu-terminated. We also obtained that the tip has a great influence on the resolution, imaging, etc. Thus, we gave an explanation for both phenomena. This technique can be used for the fingerprinting and the identification of the chemical species on sample surfaces. And it is very important for the development of SPM technique.

In his famous 1959 speech titled “There is plenty of room at the bottom” (1), Nobel prize winning physicist Richard P. Feynman predicts that matter will be controlled and manipulated at the atomic scale in the foreseeable future. Furthermore, he proclaims that “it should be possible to see... individual atoms.” In many ways, Feynman's vision was realized with the invention of the scanning tunneling microscope (STM) by Gerd Binnig and Heinrich Rohrer in 1982, for which they were awarded the Nobel prize in physics (2). With the STM, quantum mechanical tunneling of electrons from a sharp metal tip to a conductive substrate is used to detect individual surface atoms with atomic resolution. The ability to “see” atoms in real space immediately solved many controversies in surface science including the complicated 7 × 7 reconstruction of the Si(111) surface (3). One complication with the STM is that the tunneling current is a function of not only the surface topography but also the local electronic structure. On the graphite surface, there are two different types of carbon atoms in the basal plane, as distinguished by the presence (α) or absence (β) of a carbon atom in the plane immediately below the surface. Coupling of 2pz orbitals from α carbon atoms of adjacent layers lowers their bonding energies. Thus, the 2pz orbitals from β carbon atoms form the highest occupied (and lowest unoccupied) orbitals where the Fermi level crosses. These local electronic structure variations imply that the STM can only detect every other atom on the graphite surface. Consequently, an alternative imaging mechanism is required to detect the “hidden” α atoms on the graphite surface. The article by Hembacher et al. (4) in this issue of PNAS outlines a novel scanning probe microscope that solves the hidden atom problem. Their …

In this paper, a novel scanning probe microscope (SPM) modeling technique is presented. The novelty of this technique is that it exploits the SPM's probe-surface interaction measurement capabilities [e.g., the topography signal in atomic force microscopy (AFM)] to determine the SPM's lateral positioning dynamics. SPM operation speed is limited due to mechanical vibrations induced by movement of the SPM nanopositioner. In order to facilitate high-speed SPM operation, the dynamics of the SPM can be modeled and used to design feedforward and feedback controllers that reduce nanopositioner vibrations. The proposed technique seeks to develop a transfer function model of the SPM dynamics using only the SPM probe-surface interaction signal obtained while scanning a calibration sample. The technique is presented in the context of an AFM example, errors associated with the method are analyzed, and the method is experimentally verified using a commercial AFM. Experimental modeling results show that the method is capable of modeling the dynamics of SPM systems.

This paper demonstrates that the scanning probe microscopy (SPM; scanning tunneling microscopy (STM) and atomic force microscopy (AFM)) is capable of performing in situ nanoscopic observation of localized damage in an operating environment: initiation and growth processes of corrosion products, pitting corrosion and intergranular corrosion as well as stress corrosion cracking of metals. This technique is also applied to examine brittle fracture surfaces of various engineering materials including metals, ceramics and single crystal silicon, and the nanoscopic fracture features are discussed. We discuss the related issues in in situ SPM visualization, advantages and disadvantages of STM and AFM, and nanoscopic damage mechanisms based upon nanoscopic observation of damage process; we show that an AFM is more suitable for performing in situ, serial observation of corrosion processes.

Using scanning probe microscopy techniques, at low temperatures and in ultrahigh vacuum, individual molecules adsorbed on surfaces can be probed with ultrahigh resolution to determine their structure and details of their conformation, configuration, charge states, aromaticity, and the contributions of resonance structures. Functionalizing the tip of an atomic force microscope with a CO molecule enabled atomic-resolution imaging of single molecules, and measurement of their adsorption geometry and bond-order relations. In addition, by using scanning tunneling microscopy and Kelvin probe force microscopy, the density of the molecular frontier orbitals and the electric charge distribution within molecules can be mapped. Combining these techniques yields a high-resolution tool for the identification and characterization of individual molecules. The single-molecule sensitivity and the possibility of atom manipulation to induce chemical reactions with the tip of the microscope open up unique applications in chemistry, and differentiate scanning probe microscopy from conventional methods for molecular structure elucidation. Besides being an aid for challenging cases in natural product identification, atomic force microscopy has been shown to be a powerful tool for the investigation of on-surface reactions and the characterization of radicals and molecular mixtures. Herein we review the progress that high-resolution scanning probe microscopy with functionalized tips has made for molecular structure identification and characterization, and discuss the challenges it will face in the years to come.

In recent years, various electronic devices, including micromachine technology (MEMS), have been developed by nanotechnology. Since electrodeposition in an aqueous solution does not require a vacuum environment, various microfabrication and epitaxial control using electrodeposition have been investigated. Therefore, it is important to precisely and rapidly control the nanoscale interface structure during the electrodeposition process, and it is essential to elucidate the reaction process in the small region.Various methods have been studied for in-situ observation. The scanning probe microscope have given a way for atomic-scale observation, which can be applied to electrochemical nucleation and growth processes in an aqueous solution. However, the conventional scanning probe microscopes (scanning tunneling microscope: STM, atomic force microscope: AFM) require a few minutes to measure a surface, making it difficult to catch up the dynamic nucleation.A high-speed scanning probe microscope has the potential to overcome both the temporal and spatial problems. Magnussen et al. invented the video-rate STM and observed electrochemical interfacial phenomena such as metal nucleation, adatom diffusion, and molecular adsorption [1]. On the other hand, High-speed AFM (HS-AFM) was studied for biological samples [2]. Therefore, it is applicable to the imaging of soft surfaces and weakly adsorbed specimens.Taking advantage of the features of HS-AFM, we have observed Cu [3] and Zn deposition and dissolution (Fig. 1) as well as electrolytic nanobubble evolution [4]. In may talk, I would like to present dynamic behaviors of electrochemical nucleation and growth.

We studied the O2 dissociated state under the different O2 exposed temperatures with atomic resolution by scanning probe microscopy (SPM) and imaged the O adatom by simultaneous atomic force microscopy (AFM)/scanning tunneling microscopy (STM). The effect of AFM operation mode on O adatom contrast was investigated, and the interaction of O adatom and the subsurface defect was observed by AFM/STM. Multi-channel exploration was performed to investigate the charge transfer between the adsorbed O and the TiO2(110) by obtaining the frequency shift, tunneling current and local contact potential difference at an atomic scale. The tunneling current image showed the difference of the tunneling possibility on the single O adatom and paired O adatoms, and the local contact potential difference distribution of the O-TiO2(110) surface institutively revealed the charge transfer from TiO2(110) surface to O adatom. The experimental results are expected to be helpful in investigating surface/interface properties by SPM.

Tip-enhanced Raman spectroscopy (TERS) has been developed by using atomic force microscopy and scanning tunneling microscopy since its birth in the early 2000s. Because, in principle, any scanning probe microscopy (SPM) can be combined with TERS, there is an increasing interest in extending TERS to other SPMs, especially the liquid-phase ones, targeting applications in biological or catalytic systems. We present the design, construction, and characterization of a laser-coupled scanning ion-conductance microscope (SICM) integrated with TERS for near-field spectroscopy under liquid environments. Key design elements include a full sample-scanning SICM, optics for TERS, and noise-isolating methods. The SICM-TERS system demonstrates direct-current and alternating-current SICM imaging modes on polydimethylsiloxane (PDMS) structures. Furthermore, the TERS capability was tested using silica-nanosphere-grafted PDMS. This work illustrates the feasibility and performance of SICM-TERS as a versatile tool for label-free nanoscale spectroscopy, opening new possibilities for real-time, in situ analysis of soft matter, electrochemical, and biological systems.

This thesis deals with the development of microfabrication technologies based on photoplastic structuring by lithographic and molding techniques. These technologies, combined with an original releasing method, allow for the simple fabrication of pseudo three-dimensional, soft, photoplastic microstructures with features and shapes that are difficult to obtain with standard micro-machining. The photoplastic material used is the SU-8 photoresist, a material that is used increasingly in the growing field of micro-electro-mechanical systems (MEMS). Photoplastic SU-8 microstructure fabrication is based on a combination of multi-layer spin-coating, molding and photolithographic processing of the resist on a prestructured silicon substrate. The final product is obtained by release of the structure from the substrate. This thesis describes several SU-8 microstructures which have been developed with an emphasis on atomic force microscopy (AFM) and scanning-near field optical microscopy (SNOM) probes. Scanning probe microscopy is a well-established technique for surface analysis, but batch-fabricated, low-cost probes still remain a challenging issue. Using a polymer for the cantilever facilitates the realization of mechanical properties that are difficult to achieve with classical silicon technology. The design, fabrication and testing of single lever and cassettes of multiple single-lever probes are presented and demonstrates the potential for fabrication structures with complicated shape and features. The fabrication process for SU-8 AFM probes is a simple batch process in which the integrated tips and the levers are defined in one photolithography step. Tip radii of curvature smaller than 15 nm have been obtained. The cantilever thickness depends on the spin-coating parameters, hence it can be very well controlled over a full wafer. Photoplastic cantilevers with thicknesses ranging from 1 to 6 μm have been produced. Imaging soft, condensed matter with photo-plastic levers, which uses laser beam deflection sensing, exhibits a resolution that compares well with that of commercially available silicon cantilevers. Lateral resolution of 5–6 nm has been estimated from imaging DNA-plasmid molecules. A vertical resolution of the order of 0.1 nm has been found. A similar fabrication technique was also developed to fabricate photo-plastic tips for SNOM that are to be attached to optical fibers. This technique allows optical apertures to be integrated at the end of the well-defined tip directly by probe fabrication, without the need for any post-processing for the aperture formation. Sub-100 nm aperture have been fabricated using this technique. Simple fabrication, as well as topographical and optical imaging demonstrate the potential of photoplastic-based probes for both AFM and SNOM applications, as well as for future combined probes development. In addition, the fabrication of functional microstructures by using SU-8 processing needs to be combined with other microfabrication techniques. Simple releasing of the molded structures from the substrate is especially of great importance. A sacrificial layer technique based on electrochemical etching enhancement has been developed and combined with the fabrication of the different photoplastic SU-8 probes presented. This technique allows the fast releasing of large microstructures and has been demonstrated by releasing other SU-8 photoplastic microfabricated devices.

Nanoscale electrical phase-change in GeSb 2Te 4 films with scanning probe microscopes