Q

Quantum computer
Quantum computers were developed with the aim of dramatically improving computing capability by superimposing two or more different states quantum mechanically and processing signals in one go. Although it is very difficult to ensure that it does not break down during the computation while superimposed quantum mechanically, the unique spin structure of the surface of the topological insulator is considered to be useful in creating a quantum computer that is resistant to disturbances.
Quantum dot
When a granular structure that is about the size of the de Broglie wavelengths of electrons (several nm – 20nm) is created, mainly in semiconductors, the electrons are sealed into that domain. When the direction of the confinement is one-dimensional, it is known as a quantum well structure. When the direction is two-dimensional, it is known as a quantum wire. When it is sealed in from all directions, that is, three-dimensionally, it is known as a quantum dot. A quantum dot has specific electrical properties, and is therefore expected to be applied to areas such as single-electron transistors, quantum teleportation, and quantum computers. By changing the size of the quantum dot, it is also possible to control the band gap energy and to change the light absorption and wavelength of the light emitted. For that reason, it is also expected to be utilized for quantum dot solar cells and quantum dot lasers.
Quantum effect
This includes the quantum size effect and tunneling effect, and a nanometer order structure has been discovered for both. When the diameter of nanoparticles is reduced to roughly the wavelength of the de Broglie wavelengths of electrons (several nm – 20nm), the electrons are sealed into that domain, and adopt discrete energy levels. Furthermore, as the degree of freedom of electron movement is extremely restricted, that kinetic energy increases. Consequently, as the particle size becomes smaller, the band gap energy increases. This phenomenon is known as the quantum size effect. Through the quantum size effect, it is possible to control light absorption and emission wavelength in a semiconductor nanocrystal through the particle diameter. On the other hand, the tunneling effect refers to the phenomenon that takes place in a micro structure wherein, at a certain probability, particles pass through an energy domain (potential barrier) that normally cannot be crossed. For example, when a thin layer of insulating material (barrier) is placed between two types of metals or semiconductors and pressure is applied to both ends, the insulating layer becomes extremely thin, reaching the nanometer (nm) level. When this happens, an electric current will flow as a result of the tunneling effect.
Quantum mechanics
Quantum mechanics is a theory that describes the physical phenomena of atoms and the micro-world of its constituent elements, such as electrons and nuclei.

R

Rashba effect
This phenomenon emerges in two-dimensional systems such as surfaces and the surface junctions of semiconductors. Electrons that are subjected to the influence of this effect will have a two-dimensional vertical spin direction with respect to the direction of the momentum. Normally in the Rashba effect the same number of upward and downward spins are present. Therefore, although the total sum of spins for the entire matter is zero, the number of electrons for the spin facing a specific direction will increase when an electric field is applied, and a spin current will flow. If we were able to elucidate this spin behavior and control the spin, there would be greater potential for application in the uncovering of new quantum phenomena and the development of spintronics elements. For that reason, vigorous efforts are being put into research in this field both in Japan and overseas.
Redox cycle
A redox cycle in electrochemical measurement refers to the phenomenon wherein oxidation and reduction reactions are successively brought about in the measured substance, and the obtained signal is amplified by increasing the volume of the measured substance that reacts on the electrodes.

S

Scanning electrochemical microscope (SECM)
The concentration distribution of the types of electrochemical reactions on the surface of the test sample is oxidized/reduced using microeletrodes and subjected to two-dimensional imaging as a current value. This is applied to the evaluation of the corrosion process and the catalytic ability of metals, as well as the evaluation of the respiration rate of cells. In particular, as it is possible to carry out these measurements non-invasively, it is used in reproductive medicine to measure the respiration rate of an embryo in the early stages of pregnancy.
Scanning tunneling microscope (STM)
A probe with a sharp tip is brought close to the surface of the sample and voltage is applied between the probe and the surface of the sample so that a tunneling current flows between the two. This method of experiment is used to study surface shape and local electronic state through observation of the space distribution of this micro tunneling current.
Slurry
When fine solid particles are dispersed in liquid to take on a muddy state.
Spherical aberration correction device
Correction devices developed in recent years have enabled the elimination of spherical aberration in lenses, making it possible to concentrate a beam in a very small area. As a result, it has become possible to obtain electron microscopic images of a high resolution.
Spin
Spin refers to the property of magnets that is derived from rotation, and is a property possessed by electrons. There are possible two states for the direction of the rotational axis—upward and downward. This rotational axis faces various directions as a result of electromagnetic interaction in the matter. In common metals and semiconductors, the same number of electrons with upward spin and downward spin are present, which cancel each other out. However, in ferromagnetic matter (magnets), there is a large number of spin electrons facing a single direction., which generates strong magnetism.
Spin current
This refers to the flow of spin angular momentum. For example, electrons hold an electric charge that has a degree of electrical freedom, as well as spin angular momentum that has a degree of magnetic freedom. The flow of the former is known as electric current, and the flow of the latter is known as spin.
Spin-orbit interaction
Spin-orbit interaction is induced in consideration of the relativism effect through the force acting between the orbital angular momentum (revolution) and spin (rotation) of an electron. As electrons carry an electric charge, an electric current flows when there is orbital (revolutionary) momentum around the nucleus. This generates a magnetic field. On the other hand, as an electron has spin, an interaction takes effect between its magnetic property in terms of its upward and downward spin and the magnetic field arising as a result of orbital momentum. While spin-orbit interaction is present in all kinds of matter, its effect becomes more apparent with heavier atoms. There is much anticipation in the field of next-generation spintronics for the development of technology that harnesses this spin-orbit interaction.
Spin-resolved photoemission spectroscopy
This is a method of experiment that measures the energy, momentum, and spin of an electron that is emitted from a crystal through the external photoelectric effect produced by irradiating high-intensity ultraviolet light on the surface of a given matter. Through this method it is possible to directly determine how the direction and size of the spin of the electron in the matter are related to the energy and momentum of the electron. As the efficiency of detecting spin in an electron has to this day been very low, it has been difficult to determine the electron spin state to a high level of precision. However, through various efforts and improvements, Tohoku University has successfully developed an ultra-high resolution spin-resolved photoemission spectroscopy equipment with the highest resolution in the world.
Spin-Seebeck effect
This is the phenomenon wherein a spin current is generated by applying a temperature difference to a magnetic object. In the field of spintronics, the application of this effect as a highly-versatile spin current source is greatly anticipated. In addition, there is also the suggestion of a possibility for its application as thermoelectric conversion elements by combining it with the inverse spin-hall effect.
Spintronics
This refers to the field that conducts research and development into entirely new electron elements (transistors, diodes, etc.) that are operated using spin, which is the magnetic property of an electron. Signal processing is carried out by replacing the upward/downward state of electron spin with the electrical signals “0” and “1.” Electron spin offers quick response and generates very little thermal energy. Therefore spintronics elements that utilize electron spin are perceived as the strongest candidates for becoming next-generation electron elements with ultra-high speed and ultra-low power consumption.
Soft magnetism
A magnetic material with a small magnetic field and an easily-aligned direction of magnetization. The size of an external magnetic field where residual magnetization becomes zero is known as coercive force. As amorphous alloys have a random atomic arrangement, magnetocrystalline anisotropy is not observed. Generally, coercive force is small, and magnetic permeability is high.
Stress-strain curve
When an external force is applied on matter, an internal resistance (stress) is generated inside the matter against that external force, and strain occurs at the same time. The stress-strain curve shows the relationship between the stress and the strain.
Supercomputer
A supercomputer is a computer that runs dramatically faster than common computers and which has the ability to carry out simulation and numerical calculations for large-scale atomic structure models. Supercomputers are also used for weather forecasts.
Superconductivity (superconductor)
Superconductivity refers to the phenomenon wherein electrical resistance becomes zero, and a superconductor is a material that is in a state of superconductivity. A comparatively large number of materials enter a state of superconductivity when cooled to an extremely low temperature close to absolute zero (−273.15 ℃), but lose this superconductive property when the temperature rises. For that reason, a material that can become a superconductor at room temperature has not yet been found at this point in time. In the Japanese language, superconductivity is often written with the character for “conductivity.” However, particularly in the field of electrical engineering, it can also be written with the character for “electricity.” A superconductor is able to carry electricity without loss for long distances, and is a strong candidate for providing a solution to our energy problems. Therefore the search continues for a material that can become a superconductor even under higher temperatures.
Supercooling
This is the state in which even if liquids or gases are cooled to below a temperature where phase transition is usually expected to occur, they remain in their current phase. It refers to situations where, even if a liquid is cooled to below a temperature where the precipitation of the solute usually begins, the entire portion of the liquid remains in the liquid state. There are cases where water does not freeze when it is slowly cooled to 0℃; this situation is known as supercooling.
Superparamagnetism
This refers to the magnetic property shown by fine particles of a magnet. In these fine particles, the direction of the magnetization fluctuates thermally without any order, thereby resulting in magnetic randomness.
Supramolecule
This refers to a mass of molecules that come together through the weak interaction between multiple different molecules and ions. It exhibits different properties and functions from the original individual molecules.
Surface plasmon
This refers to the phenomenon wherein free electrons on a metal surface cause a collective vibration through an optical electric field. The phenomenon wherein the electric field and optical electric field caused by the vibration of the free electrons resonate is known as surface plasmon resonance. This is applied as the principle for driving sensors that are used to detect molecular adsorption, as well as to propose and validate various application functions.

T

Topological insulator
Depending on the electronic state inside the matter, it is possible to separate solids into metals, insulators (semiconductors), and superconductors. By incorporating the concept of topology into the analysis of the electronic state of matter, a new insulation material was proposed in 2005 that was markedly different from other insulators to date. An extremely strong electron-conducting pathway is generated against the scattering of impurities on the surface of a three-dimensional material and on the edges (sides) of a two-dimensional material. This conducting pathway is divided depending on whether the electron’s spin is facing upward or downward, and a control and spin response that could not be attained in any other material to date are now possible. Hence, both in Japan and overseas, vigorous efforts are being put into research in this field, which can potentially uncover new quantum phenomena and develop spintronics elements.
Toughness
Toughness indicates the tenacity of a matter, and refers to the size of its resistance.