Tsukazaki Laboratory


Material development using thin film technology

     In this division, we are interested in “Thin Film Chemistry and Material Science” for material synthesis and “Interfacial Properties and Solid-State Physics” for observation of interesting phenomena.

     Thin films are, as the name implies, the solid consisting of many atoms stacking as a layered form. There are some classifications such as amorphous, polycrystalline, and single-crystalline, depending on the way the atoms are packed. By applying a state-of-the art thin film technique, the thickness of thin films can be well regulated ranging from a few nanometers to several hundred nanometers. (1 nanometer is 10-9 meters, and the atomic radius is about 0.01~0.1 nanometer.)

     Thin films, together with the large bulk materials that we imagine as solids, are the subject of basic research and fundamental applied research in various research fields, including solid-state chemistry, materials science, condensed-matter physics, electronics, and quantum science. In recent years, these research fields seem to be closely connected through the promotion of collaborative research and the development of fusion research fields. Experimental samples as measurement targets are indispensable for the advancement of experimental physics research. From this point of view, we believe that thin film research can promote collaborative research with many research groups. We value the challenge of creating new research targets of thin films and heterostructures in the field of basic research.

     All thin films face to the surface and interface. An interface is the boundary between a solid and a solid or a solid and a liquid. On the other hand, the boundary between a solid and the atmosphere or vacuum is called a surface.

     Thin-film synthesis technology, which attempts to arrange atoms in a regular pattern, was developed in the 20th century.

     In addition, measurement techniques (e.g., x-ray diffraction and transmission electron microscopy for structural analysis) have been developed rapidly.

     In recent years, it has become possible to create a single layer of atoms in a precise arrangement and to observe that layer.

     Thin films and interfaces produced in this way are used in a wide variety of devices, such as arithmetic and memory devices.

     Generally, when used as a device, it has many interfaces by layering many layers of thin films. By understanding and controlling the characteristics of each interface, we can take advantage of its functions.

Exploration of low-temperature quantum phenomena

     At -273.15oC (0 K), the vibrations of atoms are suppressed and the physical properties that are governed by small energy scales become more pronounced. The energy of thermal fluctuation near room temperature is about 24.8 meV at around 300 K (26.85oC). Since the band gap of silicon Si, a typical semiconductor that supports modern society, is about 1.1 eV, the energy of thermal fluctuation at room temperature corresponds to about 1/44 of the Si band gap. Because the effect of thermal fluctuation is small, it can be used in devices that operate at room temperature. Since it would be troublesome if the operating characteristics of semiconductors are affected by these thermal fluctuations, it is important to consider the band gap and energy in the selection of materials and the design of devices.
     For example, the stability of macroscopic quantum states such as superconductivity and the quantum Hall effect may also be discussed in terms of energy. At higher measurement temperatures, thermal fluctuations can cause the superconducting state to cease to exist, or the quantum Hall state to cease to exist. Therefore, low temperatures are suitable for observing characteristic quantum phenomena. Measuring the temperature dependence of a physical property is expected to provide information related to the energy of the electronic structure associated with that property value. The sample is often cooled in the apparatus by supplying refrigerants. Commonly used refrigerants are liquid nitrogen and liquid helium. Recently, cryogen-free instruments that do not use such liquid refrigerants are also on the rise. In our laboratory, we can perform electrical measurements in the temperature range 2 ~ 400 K using equipment that supplies liquid nitrogen and liquid helium. In addition, we can measure resistance down to about 0.1 K using a special technique. When the sample is cooled and its electrical conduction properties are measured, it is possible to observe phenomena such as the transition to superconductivity and zero resistance, or the Hall resistance showing quantized plateau under a low- temperature with magnetic field. Other interesting phenomena, such as electron tunneling and quantum interference effects, can also be observed. Knowing the properties not only at room temperature but also at low temperatures and higher temperatures than room temperature may also be important for future use of the devices and for applications in harsh environments such as space.
     Recent research topics in our laboratory include observations of superconductivity in oxides and iron-based compounds, anomalous Hall and Nernst effects in topological materials, and quantum phenomena in high-mobility electron systems. We aim to develop new devices by taking advantage of the features of thin films and flexible interface formation. We also fabricate field-effect devices and multilayer structures, and study the control of such quantum states at low temperatures by the application of external electric and magnetic fields. Since the study of physical properties of thin films and multilayered devices may lead to future applications of such devices depending on their uses, we conduct our research while studying a wide range of topics from the fundamentals to the applications.