Glossary

Scanning Capacitance Microscopy (SCM)

Distinct operation mode of an AFM, where local differences in the surface capacity are recorded. The probe is scanning at a certain height with a modulated voltage applied simultaneously.

Scanning Electron Microscopy (SEM)

A focussed electron beam is scanning the area under investigation. The electrons interact with the surface atoms resulting in backscattered electrons, secondary electrons, auger electrons and x-rays. Topographical information is predominantly provided by the secondary electrons, whereas chemical information can be concluded from the auger electrons and x-rays. To prevent local charging effects a conductive sample is required. In the case of isolating samples a thin layer of gold or carbon is evaporated initially.

Scanning force microscopy (SFM)

Synonym for AFM

Scanning Near Field Optical Microscopy (SNOM)

A scanning probe microscope where light is used to obtain local information about topography and optical properties. In conventional light microscopy the resolution is limited approximately to the half of the wavelength of the incident light. In order to circumvent this restriction the optical nearfield (or evanescent field) is used in combination with a nanosized light source (e.g. a tapering fibre).

Scanning probe microscopy (SPM)

Generic name for different scanning microscopes, where a local probe collects surface or topography related information through a specific interaction between this probe and the surface under investigation. This interaction can be the tunnel current for STM or the force or damping of an oscillation in the case of an AFM for example.

Scanning probe nanolithography (SPN)

Generic name for lithographic techniques based on scanning probe microscopes. This can be a scanning tunneling microscope (STM) and the associated lithography is based on a pulsed bias voltage or an atomic force microscope (AFM) combined with a force or voltage based surface modifying technique for example.

Scanning Thermal Microscope

Basically an atomic force microscope with an integrated thermal sensor to detect local variations in the thermal properties (heat conductivity).

Scanning Tunneling Microscope (STM)

A scanning probe technique where a local metallic probe is scanning a conductive surface. The topographic information is deduced from the tunnel current which runs between probe and sample without mechanical contact. The electron shells, or clouds, surrounding the atoms on the surface produce irregularities that are detected by the probe and mapped by a computer into an image.

Self-Assembly

Spontaneous aggregation of molecules or other particles to complex and ordered systems. Referred to as Self-Assembled Monolayers (SAM) in the case of quasi two-dimensional aggregating systems. Although Self-Assembly and Self-Organisation are very similar, the term Self-Assembly is normally used for systems where covalent bonds are involved whereas Self-Organisation points to weakly interacting systems as they can be found for example in biological systems.

Self-Organisation

General term for weakly interacting systems where order is spontaneously increased (so called dissipative structures). An example are biological systems where complex and ordered structures are formed from comparatively simple building blocks (e.g. lipids in cell membranes). See also Self-Assembly.

Semiconductor

A semiconductor is a substance, usually a solid chemical element or compound, that has a conductivity between a metal and an isolator (e.g. Silicon, Germanium). It's conductivity is adjustable (doping) making it a good medium for the control of the electrical current.

SIMS (Secondary Ion Mass Spectrometry)

Chemical analysis of surfaces by identifying the masses of desorbed ions. Desorption is achieved by sputtering with a focused ion beam (e.g. Ar) and the detection is done by a mass spectrometer, whereas positive or negative secondary ions can be collected in two steps. Depth profiles can be obtained by a longer sputtering time and or a higher bombardment energy.

Single-walled carbon nanotubes (SWNT)

see nanotubes

Soft lithography

Generic term for a class of lithographic techniques to produce structures on the microscopic and nanoscopic scale. The most common method are Microcontact Printing (µCP), Micromolding in Capillaries (MIMIC), Microtransfer Molding (TM) and Replica Molding. All techniques use a stamp made of PDMS (Polydimethylsiloxane) for the structure transfer, in the case of µCP, the stamp is wetted by an ink, which forms a self-assembled monolayer when pressed on a sample surface. In a final step this structured monolayer is used as a resist against etching. With this method structures of several 10 nm in width can be produced.

Spin coating

A method to obtain coatings with defined thickness in a huge range (from several nanometers up to millimetres). The coating material is dissolved in a solvent and dropped on the surface which is mounted on a spinning plate. The solvent evaporates and a homogeneous layer is left on the surface. The coating thickness is adjusted by the spin speed, the spin time and the viscosity of the liquid.

SQUID (Superconducting Quantum Interference Device)

Detecting ultra-small changes in magnetic fields. A SQUID is built up from one or more Josephson junctions using a subtle quantum mechanical effect on the supercurrent or the tunneling current running between the two superconductors in the presence of an external magnetic field. A SQUID is able to detect a change in the magnetic field in the order of fT (femtotesla) which is much smaller than the magnetic field of the earth. SQUID's are in use to measure the magnetic fields of mammalian brains for example. See also "Josephson effect".

Substrate

A solid material carrier where other material can adsorb or surface reactions take place.

Superconductor

A material which conducts electricity without loss below a certain temperature. At this so called critical temperature the electrical resistance drops to zero. Generally, the critical temperature is below -250 degrees centigrade and an enormous cooling capacity is required. Certain materials show superconductivity at higher temperatures (High Temperature Superconductors, HTS) and might be useful for future developments and applications.

Superlattices

The surface atoms of a crystal may rearrange spontaneously with a different symmetry from that of the bulk structure. This reconstruction process is caused by the surface free energy. An example can be found on silicon surfaces named as Si(111) 7x7. The reconstruction depends on the crystallographic orientation (here denoted as 111 and the symmetry of the superstructure is given by the two following digits). Superlattices are sometimes referred to as superstructures.

Superposition (quantum mechanical)

A principle from quantum mechanics. An object on the molecular or atomic scale can be in two or more states simultaneously. The object can be in state A and in state B rather than A or B, for example, whereas A and B can be the energy or location etc. When the energy or location is measured the system has to choose state A or B depending on their probability.

Surface tension

The ratio of the work needed to increase the surface area of a liquid and the surface area itself. The molecules in the surface layer attract each other resulting in the phenomenon of surface tension. Work has to be done against this attractive forces to increase the surface area. On the other hand energy or work is released when the surface area is decreased. Since a sphere has the smallest area for a fixed volume all droplets tend to be round.

Surfactant

A surface active agent. Surfactants adsorb easily on surfaces and in the case of a liquid as substrate they reduce the surface tension. Detergents or cleaning agents are prominent examples. They reduce the surface tension of the water resulting in a better cleaning ability or wetting property.

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