Fundamentals

The atomic force microscope (AFM) is a spin-off from the scanning tunneling microscope (STM), designed with the intention to measure the topography of nonconductive samples. It surpasses the limitations of conventional optics and is an extremely accurate and versatile instrument enabling investigations of surface topography, tip-sample interaction forces, and magnetic surface phenomena (-> MFM).

MFM is a technique derived from AFM, in which an etched silicon cantilever/tip combined with optical deflection detection is used to precisely measure local forces such as those caused by van der Waals or Coulomb interaction. MFM uses cantilevers with very low spring constant K and with magnetic coatings (typically NiCr or cobalt), sensitive to the magnetic interaction between tip and sample.

Kelvin Probe Force Microscopy (KPFM), also known as Surface Potential Microscopy, is a non-contact mode AFM technique capable of imaging local variations in the Work Function of a sample. The work function is defined as the binding energy of the outermost electron of a given material with regards to the vacuum level. Since KPFM uses a probe (AFM tip) with its own work function, overlapping with the sample’s work function, KPFM yields information about the difference between the two, called contact potential difference.

Multiferroic materials have attracted significant attention recently due to their possible applications as magnetoelectronic devices, such as electrically tuneable spin valves or tunnel magnetoresistance sensors (TMR). Especially thin films of multiferroics in composite devices are of interest as electrically tuneable tunnel barriers and in potential storage applications. Due to their natural domain sizes, it is important to understand their behavior at the nanoscale.

Conducting/conductive-tip atomic force microscopy is another variant of AFM, which uses conductive cantilevers and a bias voltage on the sample to measure the resulting current through the tip and sample interface. As the tip is in contact with the sample only locally, the measured resistance is dominated by the local resistance of the sample. Typically, the tip is brought into contact with the sample surface, and then scanned across it with a bias voltage applied.

After decades of evolution in magnetic imaging, combining the sensitivity needed to detect single electron or nuclear spins with a spatial resolution of a few nanometers may soon get within reach of current state-of-the-art instrumentation: optically detected magnetic resonance (ODMR) is commonly considered to be the most promising candidate to achieve this goal by using the unique properties of single nitrogen-vacancy (NV) centers in diamond.

Confocal microscopy is the most common instrumental technique in quantum optics to investigate semiconductor quantum dots, single molecules, color centers in diamond, photonic crystals, nanowires, quantum wells, 2D layered materials (graphene, chalcogenides) and many more. Often, the quantum nature of light emission requires cryogenic temperatures for the samples under investigation.

Historically, the Indian scientist C. V. Raman discovered in 1928 the - what was later called Raman - effect by demonstrating inelastic scattering of monochromatic light by highly viscous fluids. Only two years later, Raman was awarded the Nobel prize for his achievement. The Raman effect occurs if light impinges on a molecule and interacts with its electronic bonds. The spontaneous Raman effect is described as a three-level event, in which an incident photon first excites the molecule from ground state to a virtual state.

While the free-beam based attoCFM I offers a maximum amount of flexibility, its fiber-based counterparts attoCFM II and attoCFM III offer ultimate long-term stability onto the sample, and back up to the detector.

Transmission experiments in confocal microscopy sometimes also require filtering and shaping of the optical beam, and hence free-beam access instead of purely fiber-based can have quite some advantages in terms of flexibility.

SGM utilizes the ability of an AFM tip to influence the electrostatic properties of a sample locally. By applying voltage to the scanning tip, the tip acts as a movable electrical gate that can modify electrostatic potential for electrons in the sample and thus enables exploring electronic and transport properties at the nanoscale