Question: Hermann Grimmeiss is a German-Swedish physicist who focused his research on studies of the emission of electrons or other free carriers when light is shone onto a what?
Context: Photoemission Electron microscopy (PEEM, also called photoelectron microscopy, PEM) is a widely used type of emission microscopy.  PEEM utilizes local variations in electron emission to generate image contrast.  The excitation is usually produced by UV light, synchrotron radiation or X-ray sources.  PEEM measures the coefficient indirectly by collecting the emitted secondary electrons generated in the electron cascade that follows the creation of the primary core hole in the absorption process.  PEEM is a surface sensitive technique because the emitted electrons originate from a very shallow layer.  In physics, this technique is referred to as PEEM, which goes together naturally with low-energy electron diffraction (LEED), and low-energy electron microscopy (LEEM).  In biology, it is called photoelectron microscopy (PEM), which fits with photoelectron spectroscopy (PES), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The photoelectric effect is the emission of electrons or other free carriers when light is shone onto a material.  Electrons emitted in this manner can be called "photo electrons".  The phenomenon is commonly studied in electronic physics, as well as in fields of chemistry, such as quantum chemistry or electrochemistry. The quantum-confined Stark effect (QCSE) describes the effect of an external electric field upon the light absorption spectrum or emission spectrum of a quantum well (QW).  In the absence of an external electric field, electrons and holes within the quantum well may only occupy states within a discrete set of energy subbands.  Only a discrete set of frequencies of light may be absorbed or emitted by the system.  When an external electric field is applied, the electron states shift to lower energies, while the hole states shift to higher energies.  This reduces the permitted light absorption or emission frequencies.  Additionally, the external electric field shifts electrons and holes to opposite sides of the well, decreasing the overlap integral, which in turn reduces the recombination efficiency (i.e. fluorescence quantum yield) of the system. Thermionic emission is the thermally induced flow of charge carriers from a surface or over a potential-energy barrier.  This occurs because the thermal energy given to the carrier overcomes the work function of the material.  The charge carriers can be electrons or ions, and in older literature are sometimes referred to as "thermions".  After emission, a charge that is equal in magnitude and opposite in sign to the total charge emitted is initially left behind in the emitting region.  But if the emitter is connected to a battery, the charge left behind is neutralized by charge supplied by the battery as the emitted charge carriers move away from the emitter, and finally the emitter will be in the same state as it was before emission. Low-energy electron microscopy, or LEEM, is an analytical surface science technique invented by Ernst Bauer in 1962, however, not fully developed (by Ernst Bauer and Wolfgang Telieps) until 1985.  LEEM is a technique used by surface scientists to image atomically clean surfaces, atom-surface interactions, and thin (crystalline) films.  In LEEM, high-energy electrons (15-20 keV) are emitted from an electron gun, focused using a set of condenser optics, and sent through a magnetic beam deflector (usually 60˚ or 90˚).  The “fast” electrons travel through an objective lens and begin decelerating to low energies (1-100 eV) near the sample surface because the sample is held at a potential near that of the gun.  The low-energy electrons are now termed “surface-sensitive” and the near-surface sampling depth can be varied by tuning the energy of the incident electrons (difference between the sample and gun potentials minus the work functions of the sample and system).  The low-energy elastically backscattered electrons travel back through the objective lens, reaccelerate to the gun voltage (because the objective lens is grounded), and pass through the beam separator again.  However, now the electrons travel away from the condenser optics and into the projector lenses.  Imaging of the back focal plane of the objective lens into the object plane of the projector lens (using an intermediate lens) produces a diffraction pattern (low-energy electron diffraction, LEED) at the imaging plane and recorded in a number of different ways.  The intensity distribution of the diffraction pattern will depend on the periodicity at the sample surface and is a direct result of the wave nature of the electrons.  One can produce individual images of the diffraction pattern spot intensities by turning off the intermediate lens and inserting a contrast aperture in the back focal plane of the objective lens (or, in state-of-the-art instruments, in the center of the separator, as chosen by the excitation of the objective lens), thus allowing for real-time observations of dynamic processes at surfaces.  Such phenomena include (but are not limited to): tomography, phase transitions, adsorption, reaction, segregation, thin film growth, etching, strain relief, sublimation, and magnetic microstructure.  These investigations are only possible because of the accessibility of the sample; allowing for a wide variety of in situ studies over a wide temperature range. An opto-electric nuclear battery is a device that converts nuclear energy into light, which it then uses to generate electrical energy.  A beta-emitter such as technetium-99 or strontium-90 is suspended in a gas or liquid containing luminescent gas molecules of the excimer type, constituting a "dust plasma."  This permits a nearly lossless emission of beta electrons from the emitting dust particles.  The electrons then excite the gases whose excimer line is selected for the conversion of the radioactivity into a surrounding photovoltaic layer such that a lightweight, low-pressure, high-efficiency battery can be realised.  These nuclides are relatively low-cost radioactive waste from nuclear power reactors.  The diameter of the dust particles is so small (a few micrometers) that the electrons from the beta decay leave the dust particles nearly without loss.  The surrounding weakly ionized plasma consists of gases or gas mixtures (such as krypton, argon, and xenon) with excimer lines such that a considerable amount of the energy of the beta electrons is converted into this light.  The surrounding walls contain photovoltaic layers with wide forbidden zones as e.g. diamond which convert the optical energy generated from the radiation into electrical energy. Gas-discharge lamps are a family of artificial light sources that generate light by sending an electric discharge through an ionized gas, a plasma.  Typically, such lamps use a noble gas (argon, neon, krypton, and xenon) or a mixture of these gases.  Some include additional substances, like mercury, sodium, and metal halides, which are vaporized during startup to become part of the gas mixture.  In operation, some of the electrons are forced to leave the atoms of the gas near the anode by the electric field applied between the two electrodes, leaving these atoms positively ionized.  The electrons ejected from these atoms flow onto the anode, while the cations thus formed are accelerated by the electric field and flow towards the cathode.  Typically, after traveling a very short distance, the ions collide with neutral gas atoms, which transfer their electrons to the ions.  The atoms, having lost an electron during the collisions, ionize and speed toward the cathode while the ions, having gained an electron during the collisions, return to a lower energy state while releasing energy in the form of photons.  Light of a characteristic frequency is thus emitted.  In this way, electrons are relayed through the gas from the anode to the cathode.  The color of the light produced depends on the emission spectra of the atoms making up the gas, as well as the pressure of the gas, current density, and other variables.  Gas discharge lamps can produce a wide range of colors.  Some lamps produce ultraviolet radiation which is converted to visible light by a fluorescent coating on the inside of the lamp's glass surface.  The fluorescent lamp is perhaps the best known gas-discharge lamp. A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.  The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation".  The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow.  A laser differs from other sources of light in that it emits light "coherently".  Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography.  Spatial coherence also allows a laser beam to stay narrow over great distances (collimation), enabling applications such as laser pointers. Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum, i.e., they can emit a single color of light.  Temporal coherence can be used to produce pulses of light as short as a femtosecond. Hermann Grimmeiss (August 19, 1930), is a German-Swedish physicist.  He became the first professor of solid-state physics at Lund University in 1965, and he held his post until his retirement in 1996.  He became an important part of the Department of Physics and focused his research on electrical and photoelectric studies of semiconductor defects.  He was elected as a member of the Royal Swedish Academy of Engineering Sciences in 1977 and the Royal Swedish Academy of Sciences in 1978. Optical Gain is the most important requirement for the realization of a semiconductor laser because it describes the optical amplification in the semiconductor material.  This optical gain is due to stimulated emission associated with light emission created by recombination of electrons and holes.  While in other laser materials like in gas lasers or solid state lasers, the processes associated with optical gain are rather simple, in semiconductors this is a complex many-body problem of interacting photons, electrons, and holes.  Accordingly, understanding these processes is a major objective as being a basic requirement for device optimization.  This task can be solved by development of appropriate theoretical models to describe the semiconductor optical gain and by comparison of the predictions of these models with experimental results.
Answer: material