Three decades of scanning tunnelling microscopy that changed the course of surface science

Three decades ago, with a tiny tip of platinum, the scientific world saw the real space imaging of single atoms with unprecedented spatial resolution. This signalled the birth of one of the most versatile surface probes, based on the physics of quantum mechanical tunnelling: the scanning tunnelling microscope (STM). Invented in 1981 by Gerd Binnig and Heinrich Rohrer of IBM, Zurich, it led to their award of the 1986 Nobel Prize.

Atoms, once speculated to be abstract entities used by theoreticians for mere calculations, can be seen to exist for real with the nano-eye of an STM tip that also gives real-space images of molecules and adsorbed complexes on surfaces. From a very fundamental perspective, the STM changed the course of surface science and engineering. STM also emerged as a powerful tool to study various fundamental phenomena relevant to the properties of surfaces in technological applications such as tribology, medical implants, catalysis, sensors and biology—besides elucidating the importance of local bonding geometries and defects, non-periodic structures and the co-existence of nano-scale phases.

Atom-level probing, once considered a dream, has seen the light with the evolution of STM. An important off-shoot of STM was the atomic force microscope (AFM) for surface mapping of insulating samples. Then followed the development of a flurry of techniques under the general name of scanning probe microscopy (SPM). These techniques (STM, AFM, MFM, PFM etc) designed for atomic-scale-resolution imaging and spectroscopy, have led to brand new developments in surface analysis. All of these novel methods enabled researchers in recent years to image and analyse complex surfaces on microscopic and nanoscopic scales. All of them utilize a small probe for sensing the surface.

The invention of AFM by Gerd Binnig, Calvin Quate and Christopher Gerber opened up new opportunities for characterization of a variety of materials, and various industrial applications could be envisaged. AFM observations of thin-film surfaces give us a picture of surface topography and morphology and any visible defects. The growing importance of ultra-thin films for magnetic recording in hard disk drive systems requires an in-depth understanding of the fundamental mechanisms occurring during growth.

This special issue of Journal of Physics D: Applied Physics covers all of the different aspects of SPM that illustrate the achievements of this methodology: nanoscale imaging and mapping (Chiang, and Douillard and Charra), piezoresponse force microscopy (Soergel) and STM engineering (Okuyama and Hamada, and Huang et al). Chiang takes the reader on a journey along the STM imaging of atoms and molecules on surfaces. Jesse and Kalinin explore the band excitations that occur during the corresponding processes. Jia et al propose STM and molecular beam epitaxy as a winning experimental combination at the interface of science and technology.

Douillard and Charra describe the high-resolution mapping of plasmonic modes using photoemission and scanning tunnelling microscopy. Cricenti et al demonstrate the importance of SPM in material science and biology. Wiebe et al have probed atomic scale magnetism, revealed by spin polarized scanning tunnelling microscopy.

In addition, Simon et al present Fourier transform scanning tunnelling spectroscopy and the possibility to obtain constant energy maps and band dispersion using local measurements. Lackinger and Heckl give a perspective of the use of STM to study covalent intermolecular coupling reactions on surfaces. Okuyama and Hamada investigated hydrogen bond imaging and engineering with STM. Soergel describes the study of substrate-dependent self-assembled CuPc molecules using piezo force microscope (PFM).

We are very grateful to the authors and reviewers for the papers in this special issue of Journal of Physics D: Applied Physics. Their contributions have provided a comprehensive picture of the evolution, status and potential of scanning probe microscopy, conveying to the readers the full excitement of this forefront domain of physics.

This review discusses nearly 30 years of scanning tunnelling microscopy (STM) work on high resolution imaging of numerous materials systems, giving a historical perspective on the field through the author's work. After a brief discussion of early STM and atomic force microscope (AFM) instrumentation development, the review discusses high resolution STM imaging on semiconductors, metals on semiconductors, Au(1 1 1), metal on metals including surface alloys, oxygen on metals, molecules adsorbed on metals, and AFM measurements of friction on graphite and mica.

Photonic properties of dense metal nanostructures are currently under intense investigation because of the possible local enhancements of electromagnetic fields induced by plasmonic excitations. In this review paper, we present examples of plasmonic-field mappings based on multiphoton photoemission or STM-induced light emission, two techniques among those which offer today's best spatial resolutions for plasmon microscopy. By imaging the photoemitted electrons, using well-established electron optics, two-dimensional intensity maps reflecting the actual distribution of the optical near-field are obtained. The imaging technique involves no physical probe altering the measure. This approach provides full field spectroscopic images with a routine spatial resolution of the order of 20 nm (down to 2 nm with recent aberration corrected instruments). Alternatively, an unfamiliar property of the junction of scanning tunnelling microscope is its ability to behave as a highly localized source of light. It can be exploited to probe opto-electronic properties, in particular plasmonic fields, with ultimate subnanometre spatial resolution, an advantage balanced by a sometimes delicate deconvolution of local-probe influence.

Piezoresponse force microscopy (PFM) detects the local piezoelectric deformation of a sample caused by an applied electric field from the tip of a scanning force microscope. PFM is able to measure deformations in the sub-picometre regime and can map ferroelectric domain patterns with a lateral resolution of a few nanometres. These two properties have made PFM the preferred technique for recording and investigating ferroelectric domain patterns. In this review we shall describe the technical aspects of PFM for domain imaging. Particular attention will be paid to the quantitative analysis of PFM images.

The scanning tunnelling microscope (STM) has been a valuable tool in surface science for the study of structures and electronic states of metal surfaces. The recent advance of STM as a state-of-the-art technique to probe and manipulate individual molecules has made it possible to investigate molecular dynamics and chemical reactions at the surface in a single-molecule limit. In this review paper, we present an overview of our recent work of H-bond imaging, manipulating and engineering at a metal surface. From individual water molecules, a variety of H-bonded structures including water clusters, hydroxyl clusters and water–hydroxyl complexes are assembled on Cu(1 1 0), whose properties and dynamics are studied in real space in collaboration with density-functional-theory calculations.

Low temperature scanning tunnelling microscopy is widely used to image and manipulate individual atoms and molecules on surfaces, as well as to investigate surface molecular processes such as diffusion, desorption, and configuration switching, at the atomic scale. The aim of this contribution is to highlight our recent progress in understanding the interface between small organic molecules and different substrates, focusing on two model systems: copper hexadecafluorophthalocyanine (F₁₆CuPc) on HOPG, Ag(1 1 1), Bi/Ag(1 1 1), and copper(II) phthalocyanine (CuPc) on perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) and C₆₀ pre-covered surfaces. The influence of the underlying substrates on the molecular packing is discussed.

In the three decades since scanning probe microscopy (SPM) methods have entered the scientific arena, they have become one of the main tools of nanoscale science and technology by offering the capability for imaging topography, magnetic, electrical and mechanical properties on the nanometre scale. The vast majority of force-based SPM techniques to date are based on single-frequency sinusoidal excitation and detection. Here, we illustrate the intrinsic limitations of single-frequency detection that stem from the fundamental physics of dynamic systems. Consequently, many aspects of nanoscale materials functionality including quantitative mechanical, magnetic and electrical measurements, as well as probing dissipative interactions, remain unexplored. Band excitation is illustrated as a universal alternative to traditional single-frequency techniques that allows quantitative and reliable studies of dissipative and conservative phenomena, and can be universally applied to all ambient and liquid SPM methods.

It has been 30 years since the scanning tunnelling microscope (STM) was invented by G Binnig and H Rohrer. Rapid developments have made STM increasingly powerful as an extremely versatile technique for many disciplines in condensed matter physics, chemistry, biology and other areas. As a state-of-the-art growth method, molecular beam epitaxy (MBE) is a gifted technique for epitaxial growth with atomic-level control. In this paper, by giving several examples, we will show that an STM–MBE combined system is more powerful and unique for studies on low-dimensional and new functional materials.

A review of the activity of scanning probe microscopy at our Institute is presented, going from instrumentation to software development of scanning tunnelling microscopy, atomic force microscopy and scanning near-field optical microscopy (SNOM). Some of the most important experiments in material science and biology performed by our group through the years with these SPM techniques will be presented. Finally, infrared applications by coupling a SNOM with a free electron laser will also be presented.

This review focuses on recent advances in the magnetic imaging of atoms adsorbed on a nonmagnetic solid surface (adatoms) by means of spin-resolved scanning tunnelling spectroscopy (SP-STS). Magnetic field dependent spectroscopy using magnetically stable spin-polarized tips has been pushed to enable magnetometry on the single atomic-spin limit. We give a detailed review of the technique for the example of Co adatoms on Pt(1 1 1). We discuss the issues concerning the basic magnetic properties of individual adatoms as well as concerning their substrate mediated interactions that have been addressed.

We present here an overview of the Fourier-transform scanning tunnelling spectroscopy technique (FT-STS). This technique allows one to probe the electronic properties of a two-dimensional system by analysing the standing waves formed in the vicinity of defects. We review both the experimental and theoretical aspects of this approach, basing our analysis on some of our previous results, as well as on other results described in the literature. We explain how the topology of the constant-energy maps can be deduced from the FT of dI/dV map images which exhibit standing waves patterns. We show that not only the position of the features observed in the FT maps but also their shape can be explained using different theoretical models of different levels of approximation. Thus, starting with the classical and well known expression of the Lindhard susceptibility which describes the screening of electron in a free electron gas, we show that from the momentum dependence of the susceptibility we can deduce the topology of the constant-energy maps in a joint-density-of-states approximation (JDOS). We describe how some of the specific features predicted by the JDOS are (or are not) observed experimentally in the FT maps. The role of the phase factors which are neglected in the rough JDOS approximation is described using the stationary-phase conditions. We present also the technique of the T-matrix approximation, which accurately takes into account these phase factors. This technique has been successfully applied to normal metals, as well as to systems with more complicated constant-energy contours. We present results recently obtained on graphene systems which demonstrate the power of this technique, and the usefulness of local measurements for determining the band structure, the map of the Fermi energy and the constant-energy maps.

'Covalent self-assembly', i.e. the on-surface synthesis of covalent organic aggregates and networks, has received considerable attention. This review covers recent scanning tunnelling microscopy (STM) based studies on intermolecular reactions carried out on solid substrates that resulted in surface-confined covalently interlinked organic nanostructures. Experiments showed that their defect density crucially depends on the targeted dimensionality: while zero-dimensional aggregates and one-dimensional chains and ribbons can be synthesized on surfaces with utmost structural perfection, i.e. without any topological defects, realization of long-range ordered two-dimensional (2D) covalently interlinked organic networks has revealed itself as a paramount challenge for on-surface chemists. Different types of reactions, foremost condensation and addition reactions have been proven suitable as polymerization reactions for 2D cross-linked covalent networks. Yet, the emergence of topological defects during the polymerization is difficult to avoid. However, the combined experience and creativity of chemists and surface scientists has yielded encouraging first results which may open up ways for realization of extended, long-range ordered 2D polymers. This review summarizes and compares different approaches, i.e. reaction types, monomers, environments and conditions, for the on-surface synthesis of covalent organic nanostructures. The focus on STM as an analytical tool appears justified, since its unique capabilities render the STM an ideal instrument to study and even control covalent coupling reactions of organic molecules on surfaces.