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Here we report a synthetic pathway toward Au truncated octahedral dual-rim nanoframes wherein two functional facets are formed including (1) eight hot nanogaps formed by hexagonal nanoframes embracing core circular nanorings for near-field focusing and (2) six flat squares that facilitate the formation of well-ordered arrays of nanoframes through self-assembly. The existence of intra-nanogaps in a single entity enables strong electromagnetic near-field focusing, allowing single-particle surface-enhanced Raman spectroscopy. Then, we built "all-hot-spot bulk SERS substrates" with those entities, wherein the presence of truncated terraces with high homogeneity in size and shape facilitate spontaneous self-assembly into a highly ordered and uniform superlattice, exhibiting a limit of detection of attomolar concentrations toward 2-naphthalenethiol, which is 6 orders lower than that of monorim counterparts. The observed low limit of detection originates from the combined synergic effect from both inter- and intraparticle coupling in a superlattice, which we dubbed "all-hot-spot bulk SERS substrates".

Tip-enhanced Raman spectroscopy (TERS) has gained great attentions for sensitive characterization and super-resolution chemical imaging of various materials. The performance of TERS is mainly affected by the probe geometry, such as the diameter of the tip apex, surface roughness, etc. In this regard, the fabrication of a sharp apex from metal wire is the one of the most important factor for TERS experiments. Conventionally, the electrochemical etching is commonly used technique for fabricating those metallic probes. To avoid the surface defects, the pulsed bias was commonly employed in the electrochemical etching process. However, it would make the fabrication system to be complex and sophisticated. Here, we report an simple automated electrochemical etching systems using DC bias for the efficient fabrication of TERS probes. With our optimized condition for DC electrochemical etching, gold probes with a clean surface and a radius of curvature below 200 nm can be obtained with yield of 85%. The fabricated metallic probe is used to detect the brilliant cresyl blue (BCB) molecules on the gold film, and it is confirmed that the enhancement factor is about 3,400.

We investigate conducting characteristics of biochar derived from the pyrolysis of a paper at terahertz frequencies. Paper is annealed under temperatures ranging from 600 to 1000 °C to modify structural and electrical properties. We experimentally observe that the terahertz conductivity increases above 102 S/m as the annealing temperature increases up to 800 °C. From structural characterization using energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, we confirm that more graphitic biochars are produced in high annealing temperature, in agreement with the improvement of terahertz conductivity. Our results show that biochar can be a highly promising candidate to be used in paper-based devices operating at terahertz frequencies.

In this paper, we report that the beam profile of the near-infrared light from superluminescent diodes (SLDs) can be measured with a resolution below the diffraction limit by using the photothermal effect and scanning thermal microscopy (SThM). Due to the sub-diffraction resolution of SThM, the beam profile measured using SThM was much clearer than the beam profile obtained by using the knife-edge method. By stacking cross-sectional images of the optical beam profile obtained by using SThM, we were able to obtain successively the three-dimensional optical beam profile. Our novel method of using small probes to measure optical beam profiles is compatible with conventional microscopy systems and can potentially be used in various applications.

Surface plasmon resonance (SPR) devices are known to be able to detect traces of chemicals and can, therefore, be applied to a variety of applications. However, in order to define the sensitivity of such a device, one must obtain its minimum detectability. Nevertheless, the standard way to define the lower limit of detectability of an SPR device has not yet been established. In this paper, we propose a method to define the minimum detectability of SPR devices based on the 3σ rule. We measured the response of an SPR device by varying the concentrations of a single neutral analyte (ethylene glycol in deionized water). Then, we successfully obtained its lower limit of detectability, based on the measured data and the 3σ rule. Our method provides a standardized way to easily evaluate the quality of SPR devices.

Scanning thermal microscopy (SThM) enables to obtain thermal characteristic information such as temperature and thermal conductivity from the signals obtained by scanning a thermometer probe over a sample surface. Particularly, the precise control of the thermometer probe makes it possible to study near-field radiative heat transfer by measuring the near-field thermal energy, which implies that when light is used as a local heat source, photothermal energy can be detected from the optical near-field by approaching the probe in the near-field region. In this study, SThM is applied to generate sub-wavelength near-field optical image in the plasmonic grating coupler. Herein, by controlling the surface plasmon polariton generation, we show that the dominant component of SThM signal is from the optical response rather than the thermal response. The obtained near-field optical images have a spatial resolution of 40 nm and signal to noise ratio of up to 19.8. In addition, field propagation images in the Z-direction can be visualised with the precise control of the distance between the thermometer probe and the sample

Herein, we report unprecedented four-dimensional complex nanoparticles by embedding various kinds of three-dimensional polyhedral nanoframes within a single entity. This synthetic strategy is based on the selective deposition of metal atoms on high surface energy facets and subsequent growth into solid platonic nanoparticles, followed by the etching of inner metals, leaving complex nanoframes. Our synthetic routes are rationally designed and executable on-demand with a high structural controllability. Diverse Au solid nanostructures (octahedra, truncated octahedra, cuboctahedra, and cubes) evolved into complex multi-layered nanoframes with different numbers/shapes/sizes of internal nanoframes. We refer to the resulting four-dimensional complex nanoframes as “N-th nanoframes”. After coating the surface of the N-th nanoframes with plasmonically active metal (like Ag), the materials exhibited highly enhanced electromagnetic near-field focusing embedded within the internal complicated rim architecture.

The ability to control the tribological and electrical properties of graphene is critical to the fabrication of micro- and nanoelectromechanical systems (MEMS/NEMS) devices. Due to its high energy, electron beam irradiation has been widely used to adjust the local electrical properties of the graphene, such as inducing local defects or n-type doping. However, whether electron beam irradiation can affect the local tribological properties of wrinkled graphene has not been investigated yet. In this research, we demonstrated that the lateral force signal and the work function of the wrinkled monolayer graphene were affected by the electron beam irradiation. By using Kelvin-probe force microscopy (KPFM) and Raman spectroscopy, we measured the local electrical properties of the wrinkled monolayer graphene and confirmed that the electron-beam exposed area was changed as n-doped graphene. We compared the lateral force signal with surface potential data and concluded that the n-type doping induced by electron beam affected the tribological characteristics. Characterization of the electron-beam exposed wrinkled graphene provides a physical insight that the electrical and tribological characteristics of wrinkled graphene are correlated.

We demonstrated the extraordinary transmission of light through a freestanding Au thin film with a 7×7 subwavelength aperture array and double slits. Firstly, we observed the dependence of the change in the light transmission through a plasmonic structure on the pitch size of the aperture array. Also, we fabricated a freestanding Au thin film to avoid the effects of absorption and reflection of the substrate. We perforated the 7×7 subwavelength hole array on the Au film for extraordinary optical transmission caused by the electric field enhancement from the structures. Additionally, we designed a hybrid structure composed of 7×7 subwavelength apertures and double slits to enhance the transmission of the light. The normalized-to-area transmission of the hybrid structures was approximately five times greater than that of the structures without double slits.

In non-contact atomic force microscopy, a feedback loop is used to maintain the set-point frequency relative to the force between the specimen and the cantilever. The quality factor of the cantilever affects the sensitivity of feedback loop. Therefore, the fabrication of a high-quality-factor cantilever to improve the scan speed of non-contact atomic force microscopy is highly desirable. Here, we optimized the thickness of the non-contact atomic force microscope’s cantilever to maximize the quality factor with a high resonant frequency. These maximized values reached about 1200 and 530 kHz, respectively. The corresponding scan rate was more than 0.12 mm/s, indicating that the cantilever can be used in high-speed non-contact atomic force microscopy.

Plasmon-mediated polymerization has been intensively studied for various applications including nanolithography, near-field mapping, and selective functionalization. However, these studies have been limited from the near-infrared to the ultraviolet regime. Here, we report a resist polymerization using intense terahertz pulses and various nanoantennas. The resist is polymerized near the nanoantennas, where giant field enhancement occurs. We experimentally show that the physical origin of the cross-linking is a terahertz electron emission from the nanoantenna, rather than multiphoton absorption. Our work extends nano-photochemistry into the terahertz frequencies.

Advances in photolithographic processes have allowed semiconductor industries to manufacture smaller and denser chips. As the feature size of integrated circuits becomes smaller, there has been a growing need for a photomask embedded with ever narrower patterns. However, it is challenging for electron beam lithography to obtain

We present a new method for sorting directionally-oriented microparticles in a microfluidic channel. During the process of injecting the microparticles into a microfluidic channel, directionally-oriented microparticles are disordered, floating freely in the solution. In order to arrange microparticles where proper directional orientation is required, two sorting methods can be used with respect to the microparticle's rotation and flip. For sorting microparticles based on their rotation, we used a lean wedge shaped fin on the microparticles and a Y-shaped railed microfluidic channel containing a groove on the top of the channel. For sorting according to flip, we used two grooves on the top and bottom of the microfluidic channel, and rectangular fins on the microparticles. Thus, we have demonstrated simple direction-oriented fluidic assembly, allowing for two plane orientation of prefabricated microparticles injected into a microfluidic channel.

In view of the clinical importance of angiotensin-converting enzyme (ACE) as a major marker for cardiovascular diseases, we investigated insertion/deletion (I/D) polymorphism of the ACE gene in Koreans. Genotype frequencies were examined by polymerase chain reaction in 171 patients with coronary artery disease (CAD) and 120 healthy subjects. Allele frequencies of ACE polymorphism in Koreans were not significantly different between patient and control groups. In addition, association between ACE genotypes and the number of stenosed coronary arteries was not detected. ACE genotypes in the CAD group were not associated with body mass index and plasma lipid levels. Thus, our results suggest that, at least in Koreans, I/D polymorphism of the gene is unlikely to be a useful marker for CAD subjects. However, the I allele frequency of Koreans (0.58) was higher than that of Caucasian populations (0.47) but lower than that of Samoan (0.91) and Yanomami (0.85) populations. Here, we discuss the clinical and ethnic importance of ACE polymorphism.