With the development of quantum mechanics in the early 20^th century, mankind’s perception of nature was stretched to a great degree leading to new axioms, and the recognition of the particle-wave dualism. It was found that particles with small masses such electrons could interchangeably be described as waves or as corpuscular objects. With the wave character of matter, particles exhibit a probability of existence at places, where they can classically not exist. One of these phenomena is the tunnel effect, which describes the ability of an electron to tunnel through a vacuum barrier from one electrode to the other. Since 1960 tunneling has been extensively studied experimentally. This led in 1981 to the first microscopic tool with which atoms could be observed in real space – the scanning tunneling microscopy. In addition to the atomic resolution imaging capability of STM, tunnel currents could be studied with this tool in a spectroscopy manner providing insight into the local density of state (LDOS) of material surfaces.

Introduction to Scanning Force Microscopy

(http://depts.washington.edu/nanolab/NUE_UNIQUE/Background/AFM.pdf)

Scanning Force Microscopy (SFM), also known as Atomic Force Microscopy (AFM), is today’s most prominent scanning probe method. It is a surface imaging technique that images both conductive and nonconductive surfaces by literally “feeling the surface”, i.e. measuring the force between a surface and an ultra sharp tip (typically 10 nm in radius).

AC - Scanning Force Microscopy

(http://depts.washington.edu/nanolab/NUE_UNIQUE/Background/AC-AFM.pdf)

Contact mode, non-contact mode, and intermittent-contact mode scanning probe microscopy (SPM) all use short range van der Waals forces to probe the topographic features of a sample. However, if we move the scanning probe further away from the surface (10-50 nm), we can examine longer range forces, such as electrostatic and magnetic forces. Intermittent-contact mode and electrostatic force microscopy (EFM) make use of the changes of the motion of an oscillating tip to produce images.

Non-Covalent Short-Range Interactions

(http://depts.washington.edu/nanolab/NUE_UNIQUE/Background/Interactions.pdf)

As technology moves more towards miniaturization in novel product developments, it is imperative to integrate interfacial interactions into design strategies. Consequently, interfacial forces have to be explored. Interfacial forces are on the order of 10^-6to 10^-10 N, strong enough, for instance, to freeze gears in micro-electrical mechanical systems (MEMS), to affect the stability of colloidal system, or to wipe out magnetically stored data information in hard drives. There are multiple ways of exploring the strength of interfacial interactions, one of which is by force spectroscopy, also known as force-displacement (FD) analysis. The FD analysis involves a nanometer sharp scanning force microscopy (SFM) tip that is moved relative to the sample surface in nanometer to micrometer per second, as illustrated at end of this document in Figure 10. Before we discuss FD analysis, we first discuss interaction forces, particularly weak interactions between molecules and solids.

Contact Mechanics and Aspects of Polymer Science and Rheology

(http://depts.washington.edu/nanolab/NUE_UNIQUE/Background/Contact_Mechanics.pdf)

Physical property measurements (e.g., mechanical properties, surface tension, friction, and phase and structural transition properties) involving scanning force microscopy (SFM) have been particularly successful for soft organic materials. Two science disciplines that have been of great value in analyzing SFM data are Contact Mechanics and Polymer Science and Rheology. Contact Mechanics focuses on the material responses to mechanical deformations at the surface, which involves besides the near surface material properties also the probe geometry, the local pressure and adhesion. More detailed insight into soft organic material responses to stresses on a macroscopic but also molecular scale is obtained from Polymer Science and Rheology.

Protein Surface Adsorption Kinetics

(WEB Address Under Construction)

One of the foremost challenges involving medical implants is to gain control over the adsorption kinetics of proteins. There are currently severe control limitations due to the body’s complex biochemical response mechanisms to foreign surfaces. The design of proper biomaterials and bioactive surfaces requires a fundamental understanding of the bio-response mechanism from the body and its ultimate effects at the interface of the material surface. Real time fluid-mode AFM imaging provides the opportunity to study the reaction kinetics of proteins, and thus, offers important input towards (a) the design of appropriate bio-compatible interfaces, but also (b) the engineering of genetically modified biomaterials (e.g., polypeptides).