Showing papers by "Jong Hyun Ahn published in 2017"

Graphene-Based Three-Dimensional Capacitive Touch Sensor for Wearable Electronics

Abstract: The development of input device technology in a conformal and stretchable format is important for the advancement of various wearable electronics. Herein, we report a capacitive touch sensor with good sensing capabilities in both contact and noncontact modes, enabled by the use of graphene and a thin device geometry. This device can be integrated with highly deformable areas of the human body, such as the forearms and palms. This touch sensor detects multiple touch signals in acute recordings and recognizes the distance and shape of the approaching objects before direct contact is made. This technology offers a convenient and immersive human–machine interface and additional potential utility as a multifunctional sensor for emerging wearable electronics and robotics.

Stretchable Active Matrix Inorganic Light-Emitting Diode Display Enabled by Overlay-Aligned Roll-Transfer Printing

Abstract: An active matrix-type stretchable display is realized by overlay-aligned transfer of inorganic light-emitting diode (LED) and single-crystal Si thin film transistor (TFT) with roll processes. The roll-based transfer enables integration of heterogeneous thin film devices on a rubber substrate while preserving excellent electrical and optical properties of these devices, comparable to their bulk properties. The electron mobility of the integrated Si-TFT is over 700 cm2 V−1 s−1, and this is attributed to the good interface between the Si channel and the thermally grown SiO2 insulator. The light emission properties of the LED are of wafer quality. The resulting display stably operates under tensile strains up to 40%, over 200 cycles, demonstrating the potential of stretchable displays based on inorganic materials.

Local Strain Induced Band Gap Modulation and Photoluminescence Enhancement of Multilayer Transition Metal Dichalcogenides

Abstract: The photocarrier relaxation between direct and indirect band gaps along the high symmetry K−Γ line in the Brillion zone reveals interesting electronic properties of the transition metal dichalcogenides (TMDs) multilayer films. In this study, we reported on the local strain engineering and tuning of an electronic band structure of TMDs multilayer films along the K−Γ line by artificially creating one-dimensional wrinkle structures. Significant photoluminescence (PL) intensity enhancement in conjunction with continuously tuned optical energy gaps was recorded at the high strain regions. A direct optical band gap along K–K points and an indirect optical gap along Γ–K points measured from the PL spectra of multilayer samples monotonically decreased as the strain increased, while the indirect band gap along Λ–Γ was unaffected owing to the same level of local strain in the range of 0%–2%. The experimental results of band gap tuning were in agreement with the density functional theory calculation results. Local s...

Highly Sensitive, Gate-Tunable, Room-Temperature Mid-Infrared Photodetection Based on Graphene–Bi2Se3 Heterostructure

Abstract: Broadband detection of mid-infrared (IR) photons extends to advanced optoelectronic applications such as imaging, sensing, and telecommunications. While graphene offers an attractive platform for broadband visible/IR photodetection, previous efforts to improve its responsivity, for example, by integrating light-absorbing colloids or waveguide or antenna fabrication, were achieved at the cost of reduced photon detection bandwidth. In this work, we demonstrate room-temperature operation of a novel mid-IR photodetector based on a graphene–Bi2Se3 heterostructure showing broadband detection and high responsivity (1.97 and 8.18 A/W at mid- and near-IR, respectively), in which simultaneous improvement of the spectral range and responsivity is achieved via exploiting broadband absorption of mid-IR and IR photons in a small-band-gap Bi2Se3 topological insulator and efficient hot carrier separation and strong photogating across the Bi2Se3/graphene interface. With sufficient room for further improvement by interface...

Damage mitigation in roll-to-roll transfer of CVD-graphene to flexible substrates

Abstract: Roll-to-roll (R2R) transfer of a chemical vapor deposition (CVD) graphene is an inevitable step for large scale and high throughput manufacturing of graphene transparent electrodes on flexible substrates. The damages on graphene induced by high contact pressure of nip rolls during the roll transfer degrade the electrical properties of the transferred graphene on flexible substrates. In this study, we developed a damage mitigation method for the roll transfer of graphene. By analyzing scanning electron microscope (SEM) images of the damages on the transferred graphene, three types of failure modes were classified, and the corresponding failure mechanisms were revealed using the surface morphology and the finite element analyses. Based on the understanding of the failure mechanisms, the graphene transfer with a width of 400 mm was realized at a speed of 1000 mm min−1 using an R2R transfer machine with the capability of nip force control. The high electrical conductivity and uniformity of the roll-transferred graphene demonstrates the scalability and the productivity of the developed roll transfer technology.

Thickness-Dependent Phonon Renormalization and Enhanced Raman Scattering in Ultrathin Silicon Nanomembranes

Abstract: We report on the thickness-dependent Raman spectroscopy of ultrathin silicon (Si) nanomembranes (NMs), whose thicknesses range from 2 to 18 nm, using several excitation energies. We observe that the Raman intensity depends on the thickness and the excitation energy due to the combined effects of interference and resonance from the band-structure modulation. Furthermore, confined acoustic phonon modes in the ultrathin Si NMs were observed in ultralow-frequency Raman spectra, and strong thickness dependence was observed near the quantum limit, which was explained by calculations based on a photoelastic model. Our results provide a reliable method with which to accurately determine the thickness of Si NMs with thicknesses of less than a few nanometers.

Method for healing defect of conductive layer, method for forming metal-carbon compound layer, 2D nano materials, transparent electrode and method for manufacturing the same

Abstract: Provided are method for healing defect of conductive layer, method for forming metal-carbon compound layer, 2D nano materials, and transparent electrode and method for manufacturing the same. According to an embodiment of present invention, the method for healing defect of conductive layer comprises: forming a conductive layer on a first metal substrate; contacting the first metal substrate with a salt solution containing a second metal in an ionic form, and forming a second metal particle at least in a portion of a conductive area, the second metal having greater reduction potential than a first metal.

Characteristic analysis of axial flux permanent magnet machines with double-sided rotor and soft magnetic composites core using analytical method

Abstract: The axial flux permanent magnet (AFPM) machines are widely applied in various industrial settings in recent years, because of high energy density, high efficiency and compact construction as compared with other conventional radial flux permanent magnet (RFPM) machines.

Strain engineering in MgO magnetic tunnel junctions

Abstract: The material and interface engineering of magnetic tunnel junctions (MTJ) is the key for the future of spin transfer torque based random access memories (STT-RAM).

Iron loss analysis and reduction techniques of magnetic geared permanent magnet motors

Abstract: This paper presents the iron loss analysis of magnetic geared permanent magnet motors (MGPM), and suggests iron loss reduction techniques.