Hee Jun Shin

Conformational characteristics of β-glucan in laminarin probed by terahertz spectroscopy

We measured the binding-state-dependent power absorptions, refractive indices, and dielectric constants of triple-stranded helices (TSHs) and single-stranded helices (SSHs) β-glucans in laminarin using terahertz time-domain spectroscopy (TDS). The SSH β-glucan was obtained from a TSH β-glucan laminarin by a chemical treatment with NaOH solution. The power absorption of TSH β-glucan increased more rapidly than that of the SSH β-glucan with the frequency increment. The refractive index and dielectric constants of TSH β-glucan were also larger than those of the SSH β-glucan. This result implies that terahertz-TDS is a very effective method in classifying the conformational state of β-glucans.

Nanoparticle contrast agents for Terahertz medical imaging

We show in this study that nanoparticle composites can be used as contrast agents to enhance the sensitivity of terahertz medical imaging. The terahertz reflection signal increases by nearly 50 % for the sample with nanoparticles upon near infrared laser beam irradiation. This is due to the hyperthermia effect induced by surface plasma polaritons. This technique facilitates cancer diagnosis with a micron resolution.

Transient Carrier Cooling Enhanced by Grain Boundaries in Graphene Monolayer

Using a high terahertz (THz) electric field (ETHz), the carrier scattering in graphene was studied with an electric field of up to 282 kV/cm. When the grain size of graphene monolayers varies from small (5 μm) and medium (70 μm) to large grains (500 μm), the dominant carrier scattering source in large- and small-grained graphene differs at high THz field, i.e., there is optical phonon scattering for large grains and defect scattering for small grains. Although the electron-optical phonon coupling strength is the same for all grain sizes in our study, the enhanced optical phonon scattering in the high THz field from the large-grained graphene is caused by a higher optical phonon temperature, originating from the slow relaxation of accelerated electrons. Unlike the large-grained graphene, lower electron and optical phonon temperatures are found in the small-grained graphene monolayer, resulting from the effective carrier cooling through the defects, called supercollisions. Our results indicate that the carrier mobility in the high-crystalline graphene is easily vulnerable to scattering by the optical phonons. Thus, controlling the population of defect sites, as a means for carrier cooling, can enhance the carrier mobility at high electric fields in graphene electronics by suppressing the heating of optical phonons.

Unsaturated Drift Velocity of Monolayer Graphene

We observe that carriers in graphene can be accelerated to the Fermi velocity without heating the lattice. At large Fermi energy | EF| > 110 meV, electrons excited by a high-power terahertz pulse ETHz relax by emitting optical phonons, resulting in heating of the graphene lattice and optical-phonon generation. This is owing to enhanced electron-phonon scattering at large Fermi energy, at which the large phase space is available for hot electrons. The emitted optical phonons cause carrier scattering, reducing the drift velocity or carrier mobility. However, for | EF| ≤ 110 meV, electron-phonon scattering rate is suppressed owing to the diminishing density of states near the Dirac point. Therefore, ETHz continues to accelerate carriers without them losing energy to optical phonons, allowing the carriers to travel at the Fermi velocity. The exotic carrier dynamics does not result from the massless nature, but the electron-optical-phonon scattering rate depends on Fermi level in the graphene. Our observations provide insight into the application of graphene for high-speed electronics without degrading carrier mobility.

Binding-state-dependent characteristics of β-glucans in laminarin studied by terahertz time-domain spectroscopy

We measured the frequency dependent power absorption, refractive index of single-stranded helix (SSH) and triple-stranded helix (TSH) β-glucan in laminarin by terahertz time-domain spectroscopy (THz-TDS), and the two states were compared.

Probing the conformation-dependent properties of β-glucan in laminarin by Terahertz time-domain spectroscopy

β-glucans are polysaccharides distributed in various plants such as fungi, algae and mushrooms. β-glucans have been studied for their anti-tumor properties as they activate the immune responses of human cells such as natural killer cell (NK-cell), T-cell or macrophage [1]. β-glucans are combined as a triple-stranded helix (TSH) structure by the intermolecular hydrogen bonds between the O-H molecules. The correlation between the immune activities and structures of β-glucans has also been studied because the single-stranded helix (SSH) β-glucans can be denatured from the TSH by a chemical treatment and they are known to have different immune properties [2].

Optical Properties of Laminarin Using Terahertz Time‐Domain Spectroscopy (abstract)

Terahertz spectroscopy is important in the study of biomolecular structure because the vibration and rotation energy of large molecules such as DNA, proteins, and polysaccharides are laid in terahertz regions. Terahertz time‐domain spectroscopy (THz‐TDS), using terahertz pulses generated and detected by femto‐second pulses laser, has been used in the study of biomolecular dynamics, as well as carrier dynamics of semiconductors. Laminarin is a polysaccharide of glucose in brown algae. It is made up of β(1–3)‐glucan and β(1–6)‐glucan. β‐glucan is an anticancer material that activates the immune reaction of human cells and inhibits proliferation of cancer cells. β‐glucan with a single‐strand structure has been reported to activate the immune reaction to a greater extent than β‐glucan with a triple‐strand helix structure. We used THz‐TDS to characterize the difference between single‐strand and triple‐strand β‐glucan. We obtained single‐strand β‐glucan by chemical treatment of triple‐strand β‐glucan. We measur...

Terahertz Characteristics of Liquid D2O in H2O (abstract)

D2O used in nuclear power generation is very slightly different from H2O. Deuterium (D) is the isotope of hydrogen (H) and has one more neutron than H. D2O is heaver than H2O by about 11% and its melting and boiling points are 3.81° C and 101.42° C, respectively. Moreover, D2O is toxic. It is harmful for human body if it replaces more than approximately 25–50% of a human’s body water. So, knowledge of the properties of D2O included in H2O is necessary. The confinement energy and hydrogen bonding energy of large molecules are in the terahertz frequency region (2∼10 THz, 3∼66 cm−1). Particularly, the polar molecules such as H2O and D2O react to this frequency region well because the time of hydrogen relaxation motion is subpicosecond. Terahertz time‐domain spectroscopy (THz‐TDS) using terahertz pulses has been used in the study of ultrafast dynamics of hydrogen bonds in biomolecules and carriers in semiconductors. We obtained the refractive index and power absorption of H2O and D2O at room temperature. The results show that the refractive index and power absorption of H2O are larger than for D2O.D2O used in nuclear power generation is very slightly different from H2O. Deuterium (D) is the isotope of hydrogen (H) and has one more neutron than H. D2O is heaver than H2O by about 11% and its melting and boiling points are 3.81° C and 101.42° C, respectively. Moreover, D2O is toxic. It is harmful for human body if it replaces more than approximately 25–50% of a human’s body water. So, knowledge of the properties of D2O included in H2O is necessary. The confinement energy and hydrogen bonding energy of large molecules are in the terahertz frequency region (2∼10 THz, 3∼66 cm−1). Particularly, the polar molecules such as H2O and D2O react to this frequency region well because the time of hydrogen relaxation motion is subpicosecond. Terahertz time‐domain spectroscopy (THz‐TDS) using terahertz pulses has been used in the study of ultrafast dynamics of hydrogen bonds in biomolecules and carriers in semiconductors. We obtained the refractive index and power absorption of H2O and D2O at room temperature. The ...