Atomic Force Microscopy in Hydrogen Storage Materials Research

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

Abstract

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.

Nanoscale characterization of charged/discharged lithium-rich thin film cathode by scanning probe microscopy techniques

This dissertation details the development of new fabrication strategies for the preparation of spatially selective surfaces by combining techniques of particle lithography and scanning probe microscopy (SPM). This combination of lithography and nanoscale surface characterization was applied to study the mechanisms of molecular level surface-assembly of organosilanes and porphyrin on surfaces of Si(111). Particle lithography was used to investigate the surface assembly of 4-chloromethylphenyltrichlorosilane (CMPS) within exposed sites of nanoholes in selected solvents and at selected temperatures to gain insight into the details of self-polymerization. Nanopillars of CMPS were generated under selected conditions of solvent and temperature and characterized with atomic force microscopy (AFM). CMPS nanopillars were shown to grow taller with more layers at higher reactions temperatures. It was also observed that CMPS nanopillars grown in toluene formed more fractured pillars with multiple domains from a single nanoholes, compared to nanopillars grown in bicyclohexane that were observed to have more structured growth and less diverse morphology. The self-assembly of CMPS was strictly confined to nanoholes with the surrounding matrix showing very little evidence of non-specific adsorption. Surface platforms of nanopatterned CMPS nanopillars were fabricated within a resistive thin film of octadecyltrichlorosilane (OTS) to spatially direct and pattern the addition of 5,10,15,20-Tetra(4-pyridyl)porphyrin. The generation of CMPS-porphyrin heterostructures was studied ex-situ and confirmed by statistically significant changes in nanostructure height before and after the porphyrin addition. The fabrication of CMPS-porphyrin heterostructures from morphologically diverse CMPS nanopillar foundations was studied to provide insight into the mechanisms of CMPS nanopillar self-assembly. The morphology of final stage heterostructures closely resembled the original morphology of the CMPs nanopillars with little evidence of non-specific adsorption across the OTS thin film resist. Particle lithography was used to fabricate silicon porphyrin nanostructures on surfaces of Si(111) via a porphyrin-silane coupling reaction. Previous steps for nanopatterning porphyrin on a surface included an additional step to of an organosilane linker molecular that the porphyrin molecules could bind and assembly from. This new protocol coordinates a silane to each porphyrin macrocycle though a simple single vessel reaction system developed by Kurihara et al.1 Through this coupling reaction porphyrins can be directly assembled on surfaces of silicon and glass. Porphyrin nanostructures of nanoholes, nanorings and nanopillars as well as porphyrin thin films were generated using this technique.

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

The Plasma Assisted Physic Vapor Deposition (PAPVD) by the pulsed arc technique has been used for deposition of Titanium Zirconium Nitride (Ti,Zr)N coatings, using a segmented target of TiZr. The deposition was performed in a vacuum chamber with two faced electrodes (target and substrate) using nitrogen as working gas, and a power‐controlled source used to produce the arc discharges. Films were deposited on stainless steel 304, and they were characterized using the X‐Ray Photoelectron Spectroscopy (XPS), X‐Ray Diffraction (XRD), Energy Dispersion Spectroscopy (EDS) and Scanning Probe Microscopy (SPM) techniques. The XRD patterns show different planes in which the film grows. Through SPM, using Atomic Force Microscopy (AFM) and Lateral Force Microscopy (LFM) modes, a nanotribologic study of the thin film was made, determining hardness and friction coefficient.

Scanning probe microscope (SPM) techniques, invented 20 years ago, act as eyes for nanotechnology and nanoscience research and development, for imaging and characterizing surface topography and properties at atomic resolution. Particularly for the past decade, atomic force microscopy (AFM, one member of the SPM family) has evolved from laboratory research instrumentation to an industry metrology tool for geometric dimension control in nanoelectronic device manufacturing on production floors. This chapter gives an overview in great technical detail of state-of-the-art AFM applications in process characterization and inline monitoring for semiconductor manufacturing. Use of AFM equally applies for topography, dimension, and sidewall shape metrology in photomask and hard disk recording head processing.

Piezoelectric and ferroelectric materials have garnered significant interest owing to their excellent physical properties and multiple potential applications. Accordingly, the need for evaluating piezoelectric and ferroelectric properties has also increased. The piezoelectric and ferroelectric properties are evaluated macroscopically using laser interferometers and polarization–electric field loop measurements. However, as the research focus is shifted from bulk to nanosized materials, scanning probe microscopy (SPM) techniques have been suggested as an alternative approach for evaluating piezoelectric and ferroelectric properties. In this Progress Report, the recent progress on the nanoscale evaluation of piezoelectric and ferroelectric properties of diverse materials using SPM‐based methods is summarized. Among the SPM techniques, the focus is on recent studies that are related to piezoresponse force microscopy and conductive atomic force microscopy; further, the utilization of these two modes to understand piezoelectric and ferroelectric properties at the nanoscale level is discussed. This work can provide guidelines for evaluating the piezoelectric and ferroelectric properties of materials based on SPM techniques.

Mesoporous materials possess highly ordered periodic arrays of uniformly sized channels. Therefore, these compounds have attracted considerable attention for many researchers (Luo et al., 2000; Xu & Xue, 2006; Liu et al., 2009 a, Salehirad & Anderson, 1996; 1998a; 1998b; 1998c). Since the shape and texture of the materials strongly affect their properties, these materials due to their large surface areas, controllable pore size and easy functionalization have been used in separation science, drug delivery and various processes such as adsorption and catalysis (Liu et al., 2009a; Duan et al., 2008; Liu et al., 2009 b; Liu & Xue, 2008; Mohanty & Landskron, 2008; Salehirad, 2004; Alibouri, 2009a; 2009b). Zeolites as crystalline aluminosilicates are microporous materials with well-defined channels and cavities have been used as ion-exchangers, adsorbents, heterogeneous catalysts and catalyst supports (Zhang et al., 2000; Zhang et al., 2000). Many parameters are found to be highly important in the physical appearance of final zeolite products (Aghabozorg et al., 2001). Morphology and crystal size of these compounds have an important role for their specific applications in industries (Zabala Ruiz et al., 2005). The ability to accommodate various organic and inorganic species in zeolites makes them ideal host materials for supramolecular organization (Bruhwiler & Calzaferri, 2004; Schulz-Ekloff et al., 2002; Sadegh Hassani et al., 2010a). In many cases, surface adsorption sites in zeolites lead to interesting photochemical properties for these compounds. (Zabala Ruiz et al., 2005; Hashimoto, 2003). Studying the surface structure of zeolites and dynamic phenomena occurring on the surface of these compounds under various conditions will accelerate the development of these compounds as catalyst or materials with versatile functions (Sugiyama Ono et al., 2001; Anderson, 2001; Sadegh Hassani et al., 2010a). Nucleation mechanisms and growth of zeolites are not well understood for many of the systems involved. In most cases, the problem is compounded with the presence of a gel phase. This gel also undergoes a continuous polymerization type reaction during nucleation and growth. Improved understanding of zeolite growth should enable a more targeted approach to zeolite synthesis in the future and may ultimately lead to the possibility of zeolite design to order. Numerous techniques have been used for study the structure of the zeolites. Among them, scanning probe microscopy (SPM) is an appropriate technique that can be applied in atmospheric condition. However, many SPM techniques can be used in essentially any environment, including ambient, UHV, organic solvent vapour and

In this paper, we present our recent applications of scanning capacitance microscopy (SCM) on specific devices with sampling window as small as 100nm. The dopant related root causes were successfully identified on those devices fabricated with 90nm CMOS technology. The key step in our approach is the development of a sample preparation technique that allows us to precisely x-section through a transistor without being affected by focused ion beam (FIB) artifacts. FIB was used to mark the area of interest with high precision, but it did not expose the devices of interest. Optical microscope and atomic force microscope (AFM) were used to inspect the mechanically polished surface, thus avoiding beam effects from FIB or SEM. In the first application, a doping anomaly was identified in a PFET poly gate, in a single bit failed SRAM cell. In the second application, an asymmetry of a PWell implant profile in a window of 150nm was identified as the cause of leakage in a capacitor array. Our approach may be applied to other scanning probe microscopy (SPM) techniques in the same category, i.e., scanning spreading resistance microscopy (SSRM) or scanning microwave microscopy (SMM).

Ever-increasing hardware capabilities and computation powers have enabled acquisition and analysis of big scientific data at the nanoscale routine, though much of the data acquired often turn out to be redundant, noisy and/or irrelevant to the problems of interest, and it remains nontrivial to draw clear mechanistic insights from pure data analytics. In this work, we use scanning probe microscopy (SPM) as an example to demonstrate deep data methodology for nanosciences, transitioning from brute-force analytics such as data mining, correlation analysis and unsupervised classification to informed and/or targeted causative data analytics built on sound physical understanding. Three key ingredients of such deep data analytics are presented. A sequential excitation scanning probe microscopy (SE-SPM) technique is first developed to acquire high-quality, efficient and physically relevant data, which can be easily implemented on any standard atomic force microscope (AFM). Brute-force physical analysis is then carried out using a simple harmonic oscillator (SHO) model, enabling us to derive intrinsic electromechanical coupling of interest. Finally, principal component analysis (PCA) is carried out, which not only speeds up the analysis by four orders of magnitude, but also allows a clear physical interpretation of its modes in combination with SHO analysis. A rough piezoelectric material has been probed using such a strategy, enabling us to map its intrinsic electromechanical properties at the nanoscale with high fidelity, where conventional methods fail. The SE in combination with deep data methodology can be easily adapted for other SPM techniques to probe a wide range of functional phenomena at the nanoscale.

In this study, the physical properties of transition metal oxide surfaces were examined using scanning probe microscopic (SPM) techniques for elucidating the antimicrobial activity of molybdenum trioxide (MoO3), tungsten trioxide (WO3), and zinc oxide (ZnO) embedded into the polymers thermoplastic polyurethane (TPU) and polypropylene (PP). We utilized atomic force microscopy (AFM) in the contact imaging mode and its derivative single-pass Kelvin probe force microscopy for investigating samples that were presumably identical in their compositions, but showed different antimicrobial activity in bacterial adhesion tests. Our results revealed that surfaces with larger roughness and higher surface potential variation showed stronger antimicrobial activities compared to smoother and homogeneously charge-distributed surfaces. In addition, capacitance gradient (dC/dZ) measurements were performed to elucidate the antimicrobial activity arising from the different dielectric behavior of the transition metal oxides in this heterogeneous polymer surface. We found that the nano-scale exposure of transition metal oxides on polymer surfaces provided strong antimicrobial effects. Applications arising from our studies will be useful for public and healthcare environments.

Scanning microwave impedance microscopy (sMIM) is an emerging technique that can provide detailed information beyond that of conventional scanning capacitance microscopy (SCM), and other electrical scanning probe microscopy (SPM) techniques, for the investigation and failure analysis (FA) of semiconductor devices. Integration of new dielectric materials at lower levels of the device structure with the need for quantification of dielectric and dopants in semiconductor devices with sub-micron spatial resolution pushes the practical boundaries of typical atomic force microscopy (AFM) electrical modes. sMIM can measure both linear and non-linear materials (insulators and doped semiconductors, respectively) simultaneously. sMIM has a linear response to log k (dielectric number) and log N (doping concentration) making it an ideal method for providing quantitative measurements of semiconductor devices over a large range of values. This work demonstrates an example of a practical application of sMIM for quantitative measurement of the dopant concentration profile in production semiconductor devices. A planar dopant calibration sample is used to calibrate the sMIM prior to performing the measurements on an “unknown” production device. We utilize nanoscale C-V data to establish a calibration curve for both n- and p-type carriers and apply the calibration curve to an “unknown” device, presenting the measurements in units of doping concentration.

Investigations on the use of the scanning probe microscope (SPM) in the atomic force microscopy (AFM) mode for topography imaging and the magnetic force microscopy (MFM) mode for magnetic imaging are presented for a thin‐film recording head. Results showed that the SPM is suitable for imaging the surface profile of the recording head, determining the width of the pole gap region, and mapping the magnetic field patterns of the recording head excited under current bias conditions of different polarity. For the cobalt sputter‐coated tips used in MFM imaging, it was found that the magnetic field patterns obtained under different polarities of the current bias to the recording head were similar. This can be explained by the nature of the thin‐film MFM tip, in which the direction of the tip magnetic moment can follow the stray magnetic field of the sample as the current bias to the recording head reverses in direction.