Scanning Probe Microscopy in Nanoscience and Nanotechnology 3

Nanoscale science and technology demands novel approaches and new knowledge for further development. Nanofabrication has been widely employed in modern science and engineering. Probe-based nanolithography is a common technique to manufacture nanostructures. This research contributes fundamental understanding in surface science through development of a new methodology. A delicate hardware system was designed and constructed to realize the nanometer-scale direct writing. A simple and unique process, namely, laser-assisted scanning probe alloying nanolithography (LASPAN), to fabricate well-defined nanostructures has been developed. The LASPAN system, process, and the application in gold-silicon (Au-Si) binary system have been discussed in this chapter.

This chapter will be divided in two main parts. In the first one, we will show a detailed analysis of the dynamics of quartz tuning fork resonators which are being increasingly used in scanning probe microscopy as force sensors. We will also show that a coupled harmonic oscillators model, which includes a finite coupling between the prongs, is in remarkable agreement with the observed motion of the tuning forks. Relevant parameters for the tuning fork performance such as the effective spring constant can be obtained from our analysis. In the second one, we will present an implementation of a quartz tuning fork supplemented with optimized tips based on carbon fibers. The remarkable electrical and mechanical properties of carbon fiber make these tips more suitable for combined and/or simultaneous STM and AFM than conventional metallic tips. The fabrication and the characterization of these carbon fiber tips as well as their performance in STM/AFM will be detailed.

Mesoscale contact junctions, formed by mechanical interaction of elastic, viscoelastic, and elastoplastic solids, play a crucial role in a wide range of physical phenomena, going from rubber friction and adhesion to biological adhesion in filamentary attachment pads and cell adhesion and interaction with physical scaffolds. Moreover, they affect the response of several microelectromechanical systems and impact the performance of novel lithographies that manipulate objects, pattern surfaces, and transfer molecules with nanoscale accuracy. It is well known that the behavior of contact spots is highly complex since it depends on different factors, namely, contact geometry, bulk and surface (visco)elasticity, plasticity, physical and chemical adhesion. The introduction of novel experimental strategies, aimed to tightly correlate the junction response with their relevant interfacial properties, is certainly mandatory and highly promising. In this chapter, we present atomic force microscopy as an ideal tool for contact mechanics investigations on individual and multiple contact junctions. In particular, we focus on the fabrication of custom probes, with characteristic size from a few hundred nanometers to several microns, and on their use in nanoindentation studies. We also discuss paradigmatic experiments addressing the role of interfacial roughness, viscoelasticity, plasticity, and adhesion on the mechanical response of mesoscale contacts.

The knowledge of the effects of single-nucleotide polymorphisms (SNPs) in the human genome greatly contributes to better comprehension of the relation between genetic factors and diseases. Sequence analysis of genomic DNA in different individuals reveals positions where variations that involve individual base substitutions can occur. Single-nucleotide polymorphisms are highly abundant and can have different consequences at phenotypic level. Several attempts were made to apply atomic force microscopy (AFM) to detect and map SNP sites in DNA strands. The most promising approach is the study of DNA mutations producing heteroduplex DNA strands and identifying the mismatches by means of a protein that labels the mismatches. MutS is a protein that is part of a well-known complex of mismatch repair, which initiates the process of repairing when the MutS binds to the mismatched DNA filament. The position of MutS on the DNA filament can be easily recorded by means of AFM imaging.

The use of the atomic force microscope (AFM) in ambient conditions has some key advantages for characterising isolated nanostructures over other operating environments. The lack of a bulk liquid environment minimises motion of the sample to maximise resolution, while humidity control allows retention of surface water, keeping biomolecules sufficiently hydrated. The use of relatively stiff cantilevers in air (k > 10 N/m) prevents significant energy being transferred to higher modes or frequencies. This enables reliable modelling of the cantilever dynamics with relatively straightforward point mass and spring models. We show herein that combining modelling with experiment leads to robust interpretation of dynamic AFM in air. This understanding has led to new ways of operation, including a true non-contact mode in ambient and small amplitude small set-point (SASS) modes. These modes will be important to gain quantitative information about structure and processes on the nanoscale. We also discuss interpretation of height information obtained from AFM on the nanoscale and summarise a framework for recovery of apparent height loss for nanostructures. A combination of these methods will lead to a new era of quantitative AFM for nanoscience and nanotechnology.

The characterization of cell adhesion between two living cells at the single-molecule level, i.e., between one adhesion receptor and its counter-receptor, appears to be an experimental challenge. Atomic force microscopy (AFM) can be used in its force spectroscopy mode to determine unbinding forces of a single pair of adhesion receptors, even with a living cell as a probe. This chapter provides an overview of AFM force measurements of the integrin family of cell adhesion receptors and their ligands. A focus is given to major integrins expressed on leukocytes, such as lymphocyte function-associated antigen 1 (LFA-1) and very late antigen 4 (VLA-4). These receptors are crucial for leukocyte trafficking in health and disease. LFA-1 and VLA-1 can be activated within the bloodstream from a low-affinity to a high-affinity receptor by chemokines in order to adhere strongly to the vessel wall before the receptor-bearing leukocytes extravasate. The experimental considerations needed to provide near-physiological conditions for a living cell and to be able to measure adequate forces at the single-molecule level are discussed in detail. AFM technology has been developed into a modern and extremely sensitive tool in biomedical research. It appears now that AFM force spectroscopy could enter, within a few years, medical applications in diagnosis and therapy of cancer and autoimmune diseases.

Despite the large and well-documented characterization of the microbial cell wall in terms of chemical composition, the determination of the mechanical properties of surface molecules in relation to their function remains a key challenge in cell biology.The emergence of powerful tools allowing molecular manipulations has already revolutionized our understanding of the surface properties of fungal cells. At the frontier between nanophysics and molecular biology, atomic force microscopy (AFM), and more specifically single-molecule force spectroscopy (SMFS), has strongly contributed to our current knowledge of the cell wall organization and nanomechanical properties. However, due to the complexity of the technique, measurements on live cells are still at their infancy.In this chapter, we describe the cell wall composition and recapitulate the principles of AFM as well as the main current methodologies used to perform AFM measurements on live cells, including sample immobilization and tip functionalization.The current status of the progress in probing nanomechanics of the yeast surface is illustrated through three recent breakthrough studies. Determination of the cell wall nanostructure and elasticity is presented through two examples: the mechanical response of mannoproteins from brewing yeasts and elasticity measurements on lacking polysaccharide mutant strains. Additionally, an elegant study on force-induced unfolding and clustering of adhesion proteins located at the cell surface is also presented.

This chapter uses various research examples to illustrate how recent developments in scanning force microscopy (SFM) allow a detailed understanding of complex soft matter structures. The central focus lies in the introduction to the technical working principle of quasi in situ SFM (QIS-SFM) which is supported by selected applications for the analysis of dynamic and structural behavior of block copolymer films under solvent vapor annealing in the presence of a high electric field. We demonstrated that the internal film structure can be reconstructed tomographically with high depth resolution by a combination of topography and phase imaging after successive surface erosion via low-pressure plasma treatment. The QIS-SFM has a large potential, which goes significantly beyond the problems and systems reported here.

The surface composition of a solid substrate is able to strongly the crystallization of a semicrystalline polymer adsorbed on the substrate. Interfacial interaction between polymer and substrate is indeed able to govern adsorbed chains conformation and consequently crystalline organization.The aim of this chapter is to illustrate the role of the substrate surface chemistry on the crystalline structure of polyamides. Different polyamides were adsorbed onto chemically controlled surfaces, such as thiol self-assembled monolayers (terminated by different chemical functions) grafted on gold substrates. The crystalline morphology of polyamide nanofilms adsorbed on grafted gold is analyzed by atomic force microscopy. Results show that the crystalline organization directly depends on the surface chemistry. Explanations based on interactions between the polyamide chains and the chemical groups present on the substrate are proposed.

Natural polymers work in complete harmony, much like an orchestra, because nature finds ways to minimize the amount of materials and energy used to perform its vital functions. Polymer scientists and students are truly nature’s apprentices and should be inspired to develop sustainable innovations based on observations of the natural world. With the current challenges in the world regarding environmental issues, the development of new sources of energy, and the substitution of synthetic polymers for natural materials, the study of polymers has naturally been gaining momentum. Therefore, an understanding of nature allows polymer scientists to reinvent and innovate materials and processes.

Achieving topography and chemistry control at the nanoscale of polymer surfaces constitutes a highly challenging objective in nanotechnology. Advances in this field suppose the development of characterization methodology with sub-100-nm resolution. Many imaging techniques based on scanning probe microscopy (SPM) were recently developed to achieve this goal [1]. Among them, pulsed force mode (PFM) atomic force microscopy (AFM), which has been proposed firstly by Marti [2], is still a method of interest since this nonresonant mode designed to allow approach curves being recorded along the scanning path provides the topography of the sample and a direct and simple local characterization of adhesion and stiffness.This chapter is aimed at demonstrating the interest of this technique to investigate polymer surfaces patterned with photochemical methods. Both topography and chemical contrast at the sub-100-nm scale can be probed, which gives new insights into photoinduced processes at the nanoscale.After an introduction focusing on the main techniques used for the analysis of the chemical contrast at micro- and nanopatterned polymer surfaces, the first part will deal with the utility of AFM in the investigation of photopolymer surfaces.In the second part, the principle of PFM and its interest in polymer surface analysis will be detailed.The third part will focus on a recent application dealing with the nanopatterning of plasma polymer surfaces using DUV photolithography techniques. Analysis of interactions between the AFM tip and the polymer surface allows acquiring relevant information on the light-induced modifications at the nanoscale.

Free energy is one of the most fundamental thermodynamic functions, determining relative phase stability and serving as a generating function for other thermodynamic quantities. The calculation of free energies is a challenging enterprise. In equilibrium statistical mechanics, the free energy is related to the canonical partition function. The partition function itself involves integrations over all degrees of freedom in the system and, in most cases, cannot be easily calculated directly. In 1997, Jarzynski proved a remarkable equality that allows computing the equilibrium free-energy difference between two states from the probability distribution of the nonequilibrium work done on the system to switch between the two states. The Jarzynski equality provides a powerful free-energy difference estimator from a set of irreversible experiments. This method is closely related to free-energy perturbation approach, which is also a computational technique for estimating free-energy differences. The ability to map potential profiles and topologies is of major significance to areas as diverse as biological recognition and nanoscale friction. This capability has been demonstrated for frictional studies where a force between the tip of the scanning force microscope and the surface is probed. The surface free-energy corrugation produces a detectable friction forces. Thus, friction force microscopy (FFM) should be able to discriminate between energetically different areas on the probed surface. Here, we apply the Jarzynski equality for the analysis of FFM measurements and thus obtain a variation of the free energy along a surface.

Because their thickness dimension is very small compared with other dimensions, the one-dimensional (1D) nanostructures (such as nanowire, nanotube, and nanobelt) and two-dimensional (2D) nanostructures (such as graphene) are highly prone to bend. Because of their large bending flexurality, the 1D and 2D nanostructures exhibit different contact behavior from those chunky ones. Without considering the flexurality effect, the analysis on the experimental data of 1D and 2D nanostructures can lead to different and even contradicting results/conclusions on their mechanical properties. One focus of this chapter is on what can go wrong in the indentation and three-point bending tests of 1D nanostructures if the flexurality effect is not accounted. At the same time, the 1D and 2D nanostructures also exhibit abnormal friction behavior. The assumptions of the classical contact are reviewed, and their possible deficiencies and difficulties of being used to analyze the contact and friction of 1D/2D nanostructures are also discussed.

Microelectromechanical systems are especially sensitive to adhesion as a result of their large surface area-to-volume ratios, small surface separations, and compliant components. Interfacial forces that can contribute to the overall adhesion between micromachined surfaces include van der Waals, capillary meniscus, electrostatic, and solid bridging forces. In this chapter, we focus on van der Waals and capillary meniscus forces between polycrystalline silicon micromachined surfaces and describe a joint experimental-modeling technique that examines in depth when these forces are active and how they change with different processing and environmental conditions. In the experiments, microcantilever test structures were brought into contact with a landing pad in an environmental chamber. Adhesion energies were extracted from measured deflection profiles using finite element analysis. As roughness increased, the adhesion at a given relative humidity (RH) decreased, while the RH at which adhesion abruptly jumped, or the threshold RH, increased. Once the jump occurred, the adhesion increased toward the upper limit of \(2\gamma \cos \theta \), where γ is the liquid-vapor surface energy and θ is the contact angle. A detailed model based on the topography of the polysilicon surfaces as measured by atomic force microscopy was developed. Below the threshold RH, the adhesion could be modeled with only van der Waals forces active. Above the threshold RH, the adhesion was modeled by assuming that capillary menisci had nucleated. It was found that the effect of asperity plasticity was small while the effects of topographic surface correlations and disjoining pressure were important. Several possible mechanisms that might explain the threshold RH are examined.

The high lateral resolution imaging and its technical versatility in property evaluation, together with the relatively straightforward characterization of viable biological structures in liquid media, render the AFM an unrivaled instrument in the definition of novel structural–functional relationships in bioengineering domains. This chapter provides an overview of the AFM-based techniques employed in the analysis of biological structures and biomaterials.A brief introduction to the working principles of the AFM is followed by a description of application developments. Relevant findings on the structural and functional characterization of biomaterials and biological structures at submicrometric scales are highlighted.

The physical and chemical composition of surfaces determine various important properties of solids such as corrosion rates, adhesive properties, frictional properties, catalytic activity, wettability, contact potential and – finally and most importantly – failure mechanisms. Very thin, weak layers (of man-made and biological origin) on much harder substrates that reduce friction are the focus of the micro- and nanotribological investigations presented in this chapter.Biomolecular layers fulfil various functions in organs of the human body. Examples comprise the skin that provides a protective physical barrier between the body and the environment, preventing unwanted inward and outward passage of water and electrolytes, reducing penetration by destructive chemicals, arresting the penetration of microorganisms and external antigens and absorbing radiation from the sun, or the epithelium of the cornea that blocks the passage of foreign material, such as dust, water and bacteria, into the eye and that contributes to the lubrication layer that ensures smooth movement of the eyelids over the eyeballs.Monomolecular thin films, additive-derived reaction layers and hard coatings are widely used to tailor tribological properties of surfaces. Nanotribological investigations on these substrates can reveal novel properties regarding the orientation of chemisorbed additive layers, development of rubbing films with time and the relation of frictional properties to surface characteristics in diamond coatings.Depending on the questions to be answered with the tribological research, various micro- and nanotribological measurement methods are applied, including scanning probe microscopy (AFM, FFM), scanning electron microscopy, microtribometer investigations, angle-resolved photoelectron spectroscopy and optical microscopy. Thoughts on the feasibility of a unified approach to energy-dissipating systems and how it might be reached (touching upon new ways of scientific publishing, dealing with over-information regarding the literature and the importance of specialists as well as generalists in tribology) conclude this chapter.

The introduction of nanotechnology opened new horizons previously unattainable by thermoelectric devices. The nano-scale phenomena began to be exploited through techniques of thin-film depositions to increase the efficiency of thermoelectric films. This chapter reviews the fundamentals of the phenomenon of thermoelectricity and its evolution since it was discovered in 1822. This chapter also reviews the thermoelectric devices, the macro to nano devices, describing the most used techniques of physical vapor depositions to deposit thermoelectric thin-films. A custom made deposition chamber for depositing thermoelectric thin films by the thermal co-evaporation technique, where construction issues and specifications are discussed, is then presented. All the steps for obtaining a thermoelectric generator in flexible substrate with the custom deposition chamber (to incorporate in thermoelectric microsystems) are described. The aim of thermoelectric microsystem relays is to introduce an energy harvesting application to power wireless sensor networks (WSN) or biomedical devices. The scanning probe measuring system for characterization of the thermoelectric thin films are also described in this chapter. Finally, a few of the prototypes of thermoelectric thin films (made of bismuth and antimony tellurides, \({\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}\), and \({\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}\), respectively) obtained by co-evaporation (using the custom made deposition chamber) and characterized for quality assessment are dealt with. All the issues involved in the co-evaporation and characterization are objects of analysis in this chapter.

Nanoimprint lithography (NIL) is a technology that allows the fabrication of low-cost nanostructure devices at high throughput and accuracy. The most popular NIL method is ultraviolet (UV) nanoimprinting because it is a room-temperature process that does not require a thermal cycle. When demolding, the force required is the result of adhesion and friction between the antisticking layer and the resin, and a high demolding force produces pattern defects. Scanning probe microscopy (SPM) is a useful technique for evaluating the performance at the nanometer scale of both the antisticking layer and the UV-curable resin. In this chapter, we describe the evaluation, using techniques of scanning probe microscopy, of a number of properties of antisticking layers and UV-curable resins used in nanoimprint lithography.

The application of electrical modes in scanning probe microscopy is of eminent importance for understanding the electrical function and interaction of materials that are structured on the nanometer scale. Many researchers use the scanning probe microscope (SPM) for the investigation of surface topography. Here, we accentuate the use of electrical modes that are unique for the correlation of structural and electric information on a nanometer scale. This is particularly important for analyzing inorganic and organic solar cell configurations. We will introduce SPM modes that enable the study of surface potentials, electrical conductance, or local photocurrents at surfaces. Then, we review applications of these modes for the visualization of nanoscale electrical functions in photovoltaic energy materials. Special focus is given to experiments aiming at the investigation of light-induced processes which requires the integration of an additional light source into the SPM setup. Finally, we address future challenges for SPM investigation of energy materials, advanced sample preparation, and upcoming and possible future developments of electrical SPM modes.

The increasing miniaturization of electronic devices requires the miniaturization of devices that provide energy to them. Autonomous devices of reduced energy consumption are increasingly common and they have benefited from energy harvesting techniques. However, these devices often have peak power consumption, requiring storage of energy.This chapter presents the fabrication and characterization of thin-films for solid-state lithium battery. The solid-state batteries stand out for the possibility of all materials being solid and therefore ideal for microelectronics fabrication techniques. Lithium batteries are composed primarily of three materials, the cathode, the electrolyte and the anode. The positive electrode (cathode) and negative (anode) have high electrical conductivity and capacity for extraction and insertion of lithium ions. The electrolyte’s main features are the high ionic conductivity and high electrical resistivity. The materials chosen for the battery are lithium cobalt oxide (cathode), lithium phosphorus oxynitride (electrolyte), and metallic lithium (anode).The lithium cobalt oxide cathode (LiCoO₂) was deposited by RF sputtering and characterized using the XRD, EDX, SEM techniques, and electrical resistivity. Fully crystalline \({\mathrm{LiCoO}}_{2}\) was achieved with an annealing of \(65{0}^{\circ }\mathrm{C}\) in vacuum for 2 h. Electrical resistivity of \(3.7\,\Omega \cdot \)mm was achieved.The lithium phosphorus oxynitride electrolyte (LIPON) was deposited by RF sputtering and characterized using the techniques EDX, SEM, ionic conductivity, DSC, and TGA. Ionic conductivity of \(6.3 \times 1{0}^{-7}\,\mathrm{S} \cdot {\mathrm{cm}}^{-1}\) for a temperature of \(2{6}^{\circ }\mathrm{C}\) was measured. The thermal stability of LIPON up to \(40{0}^{\circ }\mathrm{C}\) was also proved.The metallic lithium anode (Li) was deposited by thermal evaporation and its electrical resistance measured at four points during the deposition. Resistance of about 3. 5 Ω was measured for a thickness of 3 μm. The oxidation rate of the lithium in contact with the ambient atmosphere was evaluated. The patterning process of the battery was developed by means of shadow masks.