Scanning Probe Microscopy Applications Research Articles

Preparation of multi‐tip arrays on flexible substrates for large‐scale microfabrication

Scanning probe microscopy (SPM) provides an important way for micro/nanofabrication. Compared with single-tip mode, parallel multi-tip mode enables an effective way for microfabrication with large scale and high efficiency by SPM. During the preparation of multi-tip array, the height difference between different tips is quite difficult to be eliminated. In the present work multi-tip arrays were prepared on different flexible rubber substrates with good bonding strength. Finite element analysis was carried out based on a hyperelastic constitutive model for selecting a suitable rubber substrate for producing the multi-tip array, and the initial shear modulus C 10 should be from 0.5 to 17. A series of comparative fabrication experiments were conducted by different multi-tip arrays. The multi-tip array with flexible substrates fulfilling the prediction model can compensate obviously the height difference resulting from microsphere size, and the flexible substrate with a lower C 10 in this range is better for the scratching fabrication. Using the multi-tip array, large-scale surface patterning can be fabricated with low cost and easy operation. This work can promote the wide application of SPM and development of the surface texture engineering.

Numerical performance analysis of quartz tuning fork-based force sensors

Quartz tuning fork-based force sensors where one prong is immobilized onto a holder while the other one is allowed to oscillate freely (‘qPlus’ configuration) are in widespread use for high-resolution scanning probe microscopy applications. Due to the small size of the tuning forks (≈3 mm) and the complexity of the sensor assemblies, the reliable and repeatable manufacturing of the sensors has been challenging. In this paper, we investigate the contribution of the amount and location of the epoxy glue used to attach the tuning fork to its holder on the sensor’s performance. Towards this end, we use finite element analysis to model the entire sensor assembly and to perform static and dynamic numerical simulations. Our analysis reveals that increasing the thickness of the epoxy layer between prong and holder results in a decrease of the sensor’s spring constant, eigenfrequency, and quality factor while showing an increasing deviation from oscillation in its primary modal shape. Adding epoxy at the sides of the tuning fork also leads to a degradation of the quality factor even though in this case, spring constant and eigenfrequency rise in tandem with a lessening of the deviation from its ideal modal shape.

A Thermoacoustic Model for High Aspect Ratio Nanostructures

In this paper, we have developed a new thermoacoustic model for predicting the resonance frequency and quality factors of one-dimensional (1D) nanoresonators. Considering a nanoresonator as a fix-free Bernoulli-Euler cantilever, an analytical model has been developed to show the influence of material and geometrical properties of 1D nanoresonators on their mechanical response without any damping. Diameter and elastic modulus have a direct relationship and length has an inverse relationship on the strain energy and stress at the clamp end of the nanoresonator. A thermoacoustic multiphysics COMSOL model has been elaborated to simulate the frequency response of vibrating 1D nanoresonators in air. The results are an excellent match with experimental data from independently published literature reports, and the results of this model are consistent with the analytical model. Considering the air and thermal damping in the thermoacoustic model, the quality factor of a nanowire has been estimated and the results show that zinc oxide (ZnO) and silver-gallium (Ag2Ga) nanoresonators are potential candidates as nanoresonators, nanoactuators, and for scanning probe microscopy applications.

Dimensional comparison between amplitude-modulation atomic force microscopy and scanning ion conductance microscopy of biological samples

The range of scanning probe microscopy (SPM) applications for atomic force microscopy (AFM) is expanding in the biological sciences field, reflecting an increasing demand for tools that can improve our fundamental understanding of the physics behind biological systems. However, the complexity associated with applying SPM techniques in biomedical research hampers the full exploitation of its capabilities. Recently, the development of scanning ion conductance microscopy (SICM) has overcome these limitations and enabled contact-free, high resolution imaging of live biological specimens. In this work, we demonstrate the limitation of AFM for imaging biological samples in liquid due to artifacts arising from AFM tip–sample interaction, and how SICM imaging is able to overcome those limitations with contact-free scanning. We also demonstrate that SICM measurements, when compared to AFM, show better fit to the actual dimensions of the biological samples. Our results highlight the superiority of SICM imaging, enabling it to be widely adopted as a general and versatile research tool for biological studies in the nanoscale.

Mechanical properties and applications of custom-built gold AFM cantilevers

Silicon and silicon nitride metal-coated cantilevers have been in use for a long time in several scanning probe microscopy applications that require electrically conductive probes. However, conventional metalized cantilevers present several drawbacks such as limited life-time of the metal layer due to wear, and increased tip radius. This work focuses on monolithic metallic cantilevers developed in order to overcome the limitations of conventional metalized atomic force microscopy (AFM) probes. These custom-made cantilevers are designed for several applications such as in current-sensing AFM (CSAFM), Kelvin probe force microscopy (KPFM), and tip-enhanced Raman spectroscopy (TERS). Determination of the dynamic and static mechanical properties of these cantilevers in a non-destructive way is reported here. Key parameters under investigation are the cantilever spring constant and the frequency response using finite element method (FEM). Gold cantilevers are selected for this study, which allow optimizing the design and the process of developing these metallic cantilevers with parameters engineered for the applications mentioned above. This work contributes to the establishment and applicability of custom-made probes in advanced scanning probe microscopy methods and their performance understanding using computer simulations.

Mass Spectrometry as a Preparative Tool for the Surface Science of Large Molecules.

Measuring and understanding the complexity that arises when nanostructures interact with their environment are one of the major current challenges of nanoscale science and technology. High-resolution microscopy methods such as scanning probe microscopy have the capacity to investigate nanoscale systems with ultimate precision, for which, however, atomic scale precise preparation methods of surface science are a necessity. Preparative mass spectrometry (pMS), defined as the controlled deposition of m/z filtered ion beams, with soft ionization sources links the world of large, biological molecules and surface science, enabling atomic scale chemical control of molecular deposition in ultrahigh vacuum (UHV). Here we explore the application of high-resolution scanning probe microscopy and spectroscopy to the characterization of structure and properties of large molecules. We introduce the fundamental principles of the combined experiments electrospray ion beam deposition and scanning tunneling microscopy. Examples for the deposition and investigation of single particles, for layer and film growth, and for the investigation of electronic properties of individual nonvolatile molecules show that state-of-the-art pMS technology provides a platform analog to thermal evaporation in conventional molecular beam epitaxy. Additionally, it offers additional, unique features due to the use of charged polyatomic particles. This new field is an enormous sandbox for novel molecular materials research and demands the development of advanced molecular ion beam technology.

A fiber-coupled quantum-dot on a photonic tip

We present the experimental realization of a quantum fiber-pigtail. The device consists of a semiconductor quantum-dot embedded into a conical photonic wire that is directly connected to the core of a fiber-pigtail. We demonstrate a photon collection efficiency at the output of the fiber of 5.8% and suggest realistic improvements for the implementation of a useful device in the context of quantum information. We also discuss potential applications in scanning probe microscopy. The approach is generic and transferable to other materials including diamond and silicon.

Combined frequency modulated atomic force microscopy and scanning tunneling microscopy detection for multi-tip scanning probe microscopy applications.

A method which allows scanning tunneling microscopy (STM) tip biasing independent of the sample bias during frequency modulated atomic force microscopy (AFM) operation is presented. The AFM sensor is supplied by an electronic circuit combining both a frequency shift signal and a tunneling current signal by means of an inductive coupling. This solution enables a control of the tip potential independent of the sample potential. Individual tip biasing is specifically important in order to implement multi-tip STM/AFM applications. An extensional quartz sensor (needle sensor) with a conductive tip is applied to record simultaneously topography and conductivity of the sample. The high resonance frequency of the needle sensor (1 MHz) allows scanning of a large area of the surface being investigated in a reasonably short time. A recipe for the amplitude calibration which is based only on the frequency shift signal and does not require the tip being in contact is presented. Additionally, we show spectral measurements of the mechanical vibration noise of the scanning system used in the investigations.

Low-order continuous-time robust repetitive control: Application in nanopositioning

A low-order repetitive control (RC) design in continuous-time for nanopositioning applications is presented. It focuses on achieving high performance and sufficient robustness to uncertainties. The design is mainly applicable to analog implementation, but due to the exceptionally low order, it also results in a fast and efficient digital implementation. Experimental results for an analog implementation using a bucket brigade device (BBD), as well as a digital implementation, is presented. RC can provide fast and accurate tracking of periodic reference signals, which is useful in many scanning probe microscopy and nanofabrication applications.

Fabrication of nanoscale Bi Hall sensors by lift-off techniques for applications in scanning probe microscopy

Bismuth Hall effect sensors with active sizes in the range of 0.1–2 μm have been fabricated by electron beam lithography and lift-off techniques for applications in scanning Hall probe microscopy. The Hall coefficients, offset resistances and minimum detectable fields of the sensors have been systematically characterised as a function of device size. The minimum detectable field of 100 nm probes at 300 K and dc currents of 5 μA was found to be Bmin = 0.9 mT Hz−0.5 with scope for up to a factor of ten reduction by using higher Hall probe currents. This is significantly lower than in similar samples fabricated by focused ion beam (FIB) milling of continuous Bi films, suggesting that the elimination of FIB damage and Ga+ ion incorporation through the use of lift-off techniques leads to superior figures of merit. A number of ways in which the room temperature performance of our sensors could be further improved are discussed.

Atomic resolution scanning tunneling microscopy in a cryogen free dilution refrigerator at 15 mK

Pulse tube refrigerators are becoming more common, because they are cost efficient and demand less handling than conventional (wet) refrigerators. However, a downside of a pulse tube system is the vibration level at the cold-head, which is in most designs several micrometers. We implemented vibration isolation techniques which significantly reduced vibration levels at the experiment. These optimizations were necessary for the vibration sensitive magnetic resonance force microscopy experiments at milli-kelvin temperatures for which the cryostat is intended. With these modifications we show atomic resolution scanning tunneling microscopy on graphite. This is promising for scanning probe microscopy applications at very low temperatures.

Nanoscale Characterization of SiC Interfaces and Devices

This paper reviews some recent advances in the application of scanning probe microscopy (SPM) electrical characterization techniques to several critical surface and interface issues in SiC technology. High resolution carrier profiling capabilities in SiC of scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) were employed for several applications. These included two-dimensional (2D) imaging of doped regions in SiC devices (to be used as input for device simulations or as a feedback for device processing) and the quantitative evaluation of the electrically active profiles of P (or N) and Al implanted 4H-SiC after high temperature treatments. Furthermore, the electrical modification of the SiO2/4H-SiC interface in MOS devices subjected to post-oxide-deposition treatments in NO or N2O and POCl3 have been investigated, providing quantitative information on the electrical activation of incorporated N or P in the few-nm-thick SiC interfacial region. The lateral homogeneity of metal/SiC interfaces was probed at nanoscale by conductive atomic force microscopy (CAFM), with a special emphasis given to the case of Schottky contacts on 3C-SiC, where the diode behaviour is strongly affected by the high density of electrically active defects in the substrate. Finally, CAFM has been employed to study the current transport in epitaxial graphene (EG) grown on 4H-SiC (0001), revealing the impact of the substrate morphology (terraces and steps or facets) on the local conductivity.

Application of Scanning Probe Microscopy with Length Extension Resonator to Investigate Sample Morphologies

Application of Scanning Probe Microscopy with Length Extension Resonator to Investigate Sample Morphologies

Study Sub-Membrane Structure and Corresponding Functions of Conductive Bacteria Cable by SPMs

As a kind of surface characterization tool, traditional scanning probe microscopy (SPM), especially atomic force microscopy (AFM), is hard to explore the structures underneath sample surface and correlate them with the corresponding functions. With the development of advanced AFMs, this obstacle has been overcome gradually, for example, with the application of quantitative dynamic AFM mapping, the hollow helical amyloid self-assembly fibrils have been identified;[1] and the protein structure flexibility on inner/outer sides of membrane is also possible to determine[2]. However, distinguishing the sub-surface features and corresponding function of macro-size biological samples, such as bacteria and cells, is still challenging to SPM. In this presentation, we combined quantitative dynamic AFM, AFM based manipulation, electrostatics force microscopy and scanning ion conductance microscopy to illustrate the inside membrane feature of recently identified conductive bacteria cable[3]. Basing on the SPM results, we proposed the model to explain the reason of the bacterial function to transport electrons over centimeter distance along cable direction. On one hand, this work will help biologists to understand the bacterial cable and promote the future application in nano-conductive cable field; on the other hand, it will inspire the further applications of SPM to beyond surface limitation on macro-size bio-systems.1. Zhang, S., et al., Coexistence of ribbon and helical fibrils originating from hIAPP20-29 revealed by quantitative nanomechanical atomic force microscopy. PNAS, 2013.2. Dong, M.D., S. Husale, and O. Sahin, Determination of protein structural flexibility by microsecond force spectroscopy. Nat. Nano., 2009. 4(8): p. 514-517.3. Pfeffer, C., et al., Filamentous bacteria transport electrons over centimetre distances. Nature, 2012. 491(7432).

Interaction at the nanoscale of fundamental biological molecules with minerals

The availability of advanced nanotechnological methodologies (experimental and theoretical) has widened the investigation of biological/organic matter in interaction with substrates. Minerals are good candidates as substrates because they may present a wide variety of physico-chemical properties and surface nanostructures that can be used to actively condense and manipulate the biomolecules. Scanning Probe Microscopy (SPM) is one of the best suited techniques used to investigate at a single molecule level the surface interactions. In addition, the recent availability of high performance computing has increased the possibility to study quantum mechanically the interaction phenomena extending the number of atoms involved in the simulation. In the present paper, firstly we will briefly introduce new SPM technological developments and applications to investigate mineral surfaces and mineral-biomolecule interaction, then we will present results on the specific RNA-mineral interaction and recent basics and applicative achievements in the field of the interactions between other fundamental biological molecules and mineral surfaces from both an experimental and theoretical point of view.

Fabrication and characterization of areal roughness specimens for applications in scanning probe microscopy

Reference structures are urgently required to characterize the performance of scanning probe microscopes for the quantitative measurement of micro-/nano-scale roughness. In this paper, preliminary areal roughness specimens are fabricated by electron beam lithography (EBL) and direct laser writing (DLW). The geometric topography and statistical quantities of the surface structures are specially designed. Precise registration between the design template and the measured data has been carried out to evaluate the fabrication quality. Two matching algorithms, the iterative closest point method and the Levenberg–Marquardt method, are compared. Results imply that the latter method prevails against the former one with improved accuracy and efficiency. It is demonstrated that the typical root-mean-square residuals of the EBL and DLW fabricated surfaces are approximately 43.5 and 195.3 nm, respectively. The spectral properties of the fabricated structures are also analyzed. These areal roughness specimens have a potential for validating scanning probe microscopes and other nano-measurement instruments for areal roughness measurements.

Characterization of multilayer nitride coatings by electron microscopy and modulus mapping

Abstract This paper discusses multi-scale characterization of physical vapour deposited multilayer nitride coatings using a combination of electron microscopy and modulus mapping. Multilayer coatings with a triple layer structure based on TiAlN and nanocomposite nitrides with a nano-multilayered architecture were deposited by Cathodic arc deposition and detailed microstructural studies were carried out employing Energy Dispersive Spectroscopy, Electron Backscattered Diffraction, Focused Ion Beam and Cross sectional Transmission Electron Microscopy in order to identify the different phases and to study microstructural features of the various layers formed as a result of the deposition process. Modulus mapping was also performed to study the effect of varying composition on the moduli of the nano-multilayers within the triple layer coating by using a Scanning Probe Microscopy based technique. To the best of our knowledge, this is the first attempt on modulus mapping of cathodic arc deposited nitride multilayer coatings. This work demonstrates the application of Scanning Probe Microscopy based modulus mapping and electron microscopy for the study of coating properties and their relation to composition and microstructure.

Gated Systems for Multifunctional Optoelectronic Devices

Paolo Samori (1971) is Distinguished Professor (PRCE) and director of the Institut de Science et d’Ingenierie Supramoleculaires (ISIS) of the Universite de Strasbourg where he is also head of the Nanochemistry Laboratory. He is also Fellow of the Royal Society of Chemistry (FRSC) and junior member of the Institut Universitaire de France (IUF). He obtained a Laurea in Industrial Chemistry at University of Bologna in 1995. In 2000 he received his Ph.D. in Chemistry from the Humboldt University Berlin (Prof. J.P. Rabe). He was permanent research scientist at Istituto per la Sintesi Organica e la Fotoreattivita of the Consiglio Nazionale delle Ricerche of Bologna and Visiting Professor at ISIS. His research activity is focussed on applications of scanning probe microscopies beyond imaging, hierarchical self-assembly of hybrid architectures at surfaces, supramolecular electronics, and the fabrication of organic-based multifunctional nanodevices.

Development and Application of Scanning Probe Microscopy with Externally Applied Stress and Strain

Development and Application of Scanning Probe Microscopy with Externally Applied Stress and Strain

Single molecule labeling of an atomic force microscope cantilever tip.

In this paper, we present a method to functionalize the very apex of an atomic force microscope cantilever with a single or a few molecules. In force spectroscopy or interaction mapping, the cantilever must be functionalized with only a few molecules to avoid noise or spurious measurements. Here, we covalently attached single molecules to the cantilever by touching it to a paper wetted with a solution of quantum dots. The paper competes with wicking up the hydrophilic surface of the tip. This method has broad applications in scanning probe microscopy where small numbers of molecules are needed on the tip.