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Cracks are formed along the photolithographically pre-determined lines with extremely high yield and repeatability, when Cu clusters are introduced between planarized Au thin films sequentially deposited on a PET substrate. These clusters act as nanometer-sized spacers preventing the formation of contiguous metallic bond between the adjacent Au layers which will render prepatterned-cracking impossible. While the effective gap width is initially zero in the optical sense from microwaves all the way to the visible, outer-bending the PET substrate allows the gap width tuning into the 100 nm range, with the stability and controllability in the ranges of 100 s and Angstrom-scale, respectively. It is anticipated that our wafer-scale prepatterned crack technology with an unprecedented mixture of macroscopic length and Angstrom-scale controllability will open-up many applications in optoelectronics, quantum photonics and photocatalysis.

Objective To identify the factors affecting anger in post-traumatic stress disorder (PTSD) patients who underwent Clinician-Administered PTSD Scale (CAPS) and Minnesota Multiphasic Personality Inventory-2 (MMPI-2).Methods We retrospectively reviewed patients who underwent CAPS and MMPI-2 at Veteran Health Service Medical Center, Seoul, Korea. Based on the CAPS score, the patients were divided into the PTSD group (n=46) and the trauma exposed without PTSD group (n=29). After checking the correlation between anger, CAPS, and MMPI-2 scales, logistic regression analysis was performed to identify the risk factors for clinically relevant symptoms.Results The PTSD group showed significant differences in schizophrenia-related symptoms, ideas of persecution, aggressiveness, psychoticism, and anger scales compared to the trauma-exposed without PTSD group. There was a significant correlation between anger, CAPS, and MMPI-2 except masculinity/femininity, disconstraint, and MacAndrew Alcoholism-Revised. In particular, anger has been shown to have a substantial connection with paranoia, schizophrenia-related symptoms, ideas of persecution, aberrant experiences, and psychoticism. Multiple regression analysis identified that the only significant risk factor for anger was the negative emotionality/neuroticism scale (odds ratio=1.152, p

Absorbers for long-wavelength infrared (LWIR) are designed to have a reduced geometry fitted to a gold cross antenna and numerically studied. Compared to the square membrane geometry widely used in conventional microbolometers, the reduced geometry results in smaller thermal capacities of the vanadium dioxide (VO2) and silicon nitride (Si3N4) layers. However, near-field focusing by the cross antenna leads to a high LWIR absorption. Calculations show that the temperature change per incident energy increases with a decrease in the arm width, and the reduced absorber surpasses the square geometry for all incident angles and polarizations. The antenna-based reduced absorber studied here could serve as an alternative geometry for high-performance microbolometers.

One critical factor for bolometer sensitivity is efficient electromagnetic heating of thermistor materials, which plasmonic nanogap structures can provide through the electric field enhancement. In this report, using finite element method simulation, electromagnetic heating of nanorod dimer antennas with a nanogap filled with vanadium dioxide (VO2) was studied for long-wavelength infrared detection. Because VO2 is a thermistor material, the electrical resistance between the two dimer ends depends on the dimer’s temperature. The simulation results show that, due to the high heating ability of the nanogap, the temperature rise is several times higher than expected from the areal coverage. This excellent performance is observed over various nanorod lengths and gap widths, ensuring wavelength tunability and ultrafast operating speed, thereby making the dimer structures a promising candidate for high sensitivity bolometers.

Two-dimensional (2D) materials are promising candidates for building ultrashort-channel devices because their thickness can be reduced down to a single atomic layer. Here, we demonstrate an ultraflat nanogap platform based on atomic layer deposition (ALD) and utilize the structure to fabricate 2D material-based optical and electronic devices. In our method, ultraflat metal surfaces, template-stripped from a Si wafer mold, are separated by an Al2O3 ALD layer down to a gap width of 10 nm. Surfaces of both electrodes are vertically aligned without a height difference, and each electrode is ultraflat with a measured root-mean-square roughness as low as 0.315 nm, smaller than the thickness of monolayer graphene. Simply by placing 2D material flakes on top of the platform, short-channel field-effect transistors based on black phosphorus and MoS2 are fabricated, exhibiting their typical transistor characteristics. Furthermore, we use the same platform to demonstrate photodetectors with a nanoscale photosensitive channel, exhibiting higher photosensitivity compared to microscale gap channels. Our wafer-scale atomic layer lithography method can benefit a diverse range of 2D optical and electronic applications.

Precise measurements of the mobility anisotropy along high-symmetry crystal axes in black phosphorus (BP) MOSFETs are reported. Locally back-gated BP MOSFETs with 13-nm HfO2 dielectric and channel length ranging from 0.3 to 0.7 $\mu \text{m}$ are fabricated. A single BP flake of a uniform thickness is exfoliated and etched along armchair (AC) and zigzag (ZZ) crystal axes, and the orientations are confirmed using optical and transmission electron microscopy analyses. The hole and electron mobilities along each direction are extracted using the transfer length method. The AC-to-ZZ hole mobility ratio is found to increase from 1.4 (1.5) to 2.0 (2.9) as the sheet concentration increased from $5.1\times 10^{\textsf {11}}$ to $1.9\times 10^{\textsf {12}}$ cm−2 at room temperature (77 K). The room-temperature electron mobility anisotropy is found to be similar to that for holes with an AC-to-ZZ mobility ratio increasing from 1.4 to 2.1 from $5.1\times 10^{\textsf {11}}$ to $1.9\times 10^{\textsf {12}}$ cm−2 though electrons showed only a very weak temperature dependence. A Boltzmann transport model is used to explain the concentration- and temperature-dependent mobility anisotropies which can be well described using a charge center scattering model.

We report high performance, orientation-controlled, and locally back-gated black phosphorus (BP) n-MOSFETs and p-MOSFETs with titanium and permalloy contacts, respectively. Devices with channel length ranging from 0.3 to $0.7~\mu \text{m}$ are analyzed. Armchair-oriented BP p-MOSFETs (n-MOSFETs) display 3.5 times (1.5 times) higher maximum current compared with zigzag devices. Saturated transconductance values up to 4.8 times (1.6 times) higher for BP p-MOSFETs (n-MOSFETs) oriented along the armchair direction compared with the zigzag direction are observed. Using this orientation control and contact engineering, n-MOSFETs with transconductance of $110~\mu \text{S}/\mu \text{m}$ and p-MOSFETs with contact resistance as low as 0.31 $\text{k}\Omega \cdot \mu \text{m}$ are demonstrated.

A high spatial resolution, cyclical thinning method for realizing black phosphorus (BP) heterostructures is reported. This process utilizes a cyclic technique involving BP surface oxidation and vacuum annealing to create BP flakes as thin as 1.6 nm. The process also utilizes a spatially patternable mask created by evaporating Al that oxidizes to form Al2O3, which stabilizes the unetched BP regions and enables the formation of lateral heterostructures with spatial resolution as small as 150 nm. This thinning/patterning technique has also been used to create the first-ever lateral heterostructure BP metal oxide semiconductor field-effect transistor (MOSFET), in which half of a BP flake was thinned in order to increase its band gap. This heterostructure MOSFET showed an ON/OFF current ratio improvement of 1000× compared to homojunction MOSFETs.

The effect of thickness, temperature, and source-drain bias voltage, V(DS), on the subthreshold slope, SS, and off-state properties of black phosphorus (BP) field-effect transistors is reported. Locally back-gated p-MOSFETs with thin HfO2 gate dielectrics were analyzed using exfoliated BP layers ranging in thickness from ∼4 to 14 nm. SS was found to degrade with increasing V(DS) and to a greater extent in thicker flakes. In one of the thinnest devices, SS values as low as 126 mV/decade were achieved at V(DS) = -0.1 V, and the devices displayed record performance at V(DS) = -1.0 V with SS = 161 mV/decade and on-to-off current ratio of 2.84 × 10(3) within a 1 V gate bias window. A one-dimensional transport model has been utilized to extract the band gap, interface state density, and the work function of the metal contacts. The model shows that SS degradation in BP MOSFETs occurs due to the ambipolar turn on of the carriers injected at the drain before the onset of purely thermionic-limited transport at the source. The model is further utilized to provide design guidelines for achieving ideal SS and meet off-state leakage targets, and it is found that band edge work functions and thin flakes are required for ideal operation at high V(DS). This work represents a comprehensive analysis of the fundamental performance limitations of Schottky-contacted BP MOSFETs under realistic operating conditions.

Metal nanoparticles that can couple light into tightly confined surface plasmons bridge the size mismatch between the wavelength of light and nanostructures are one of the smallest building blocks of nano-optics. However, plasmonic nanoparticles have been primarily studied to concentrate or scatter incident light as an ultrasmall antenna, while studies of their intrinsic plasmonic light emission properties have been limited. Although light emission from plasmonic structures can be achieved by inelastic electron tunneling, this strategy cannot easily be applied to isolated single nanoparticles due to the difficulty in making electrical connections without disrupting the particle plasmon mode. Here, we solve this problem by placing gold nanoparticles on a graphene tunnel junction. The monolayer graphene provides a transparent counter electrode for tunneling while preserving the ultrasmall footprint and plasmonic mode of nanoparticle. The tunneling electrons excite the plasmonic mode, followed by radiative decay of the plasmon. We also demonstrate that a dielectric overlayer atop the graphene tunnel junction can be used to tune the light emission. We show the simplicity and scalability of this approach by achieving electroluminescence from single nanoparticles without bulky contacts as well as millimeter-sized arrays of nanoparticles.

High carrier mobility and tunability in graphene enable fundamental studies for plasmonics and various applications. Despite its versatility, however, single-layer graphene (SLG) suffers from poor coupling efficiency to electromagnetic waves, presenting a major challenge for photonic applications. Compared with visible or infrared radiation, terahertz (THz) waves exhibit higher absorption in SLG due to Drude-like intraband transitions, but the wavelength-to-SLG size mismatch becomes even more dramatic. Here, we experimentally demonstrate 99% extinction of THz wave transmission when SLG covers the openings of 2-nm-wide (≈λ/1 000 000) slits through a metal film. By resonantly coupling THz waves through annular nanogaps, the extremely localized fields lead to near-perfect extinction and strong absorption in SLG. Atomic-layer lithography is used to produce these nanometer-wide, millimeter-long gaps over an entire 4-in. wafer. Furthermore, by integrating these devices with an ionic liquid, enhanced intraband absorption in the SLG leads to 80% modulation of THz waves with an operational voltage as low as 1.5 V.

We have investigated the extraordinary optical transmission of terahertz waves through an array of nanogaps with varying dimensions and periodicities, and used this platform to demonstrate terahertz sensing of a thin film of single-walled carbon nanotubes. We have used atomic layer lithography to fabricate periodic arrays of nanogap loops that have a gap size of 2 nm and a loop length of 100 μm (aspect ratio of 50 000). These sub-mm-scale loops of nanogaps can sustain terahertz electromagnetic resonances along the contour. We have characterized the transmission of terahertz waves through the nanogap arrays and investigated the influence of inter-gap electromagnetic coupling as the array periodicity shrinks from 100 μm to 4 μm. While the gaps occupy only 0.1% of the surface area, we have measured an amplitude (|E|) transmittance of over 50% due to the strong and broadband field enhancement inside the nanogaps. The absolute transmission through the 2 nm gaps along the rectangular loops can be boosted up to 25%, while it is only 1% for annular gaps with the same perimeter. Furthermore, the extremely tight field confinement and strong field enhancement near the 2 nm gap lead to 43% extinction of THz waves in a 10 nm-thick film of single-walled carbon nanotubes over the gaps. On the other hand, THz extinction by the same nanotube film on a bare glass substrate is only 2%. These nanogaps pave the way toward developing sensitive terahertz detectors for biological and chemical targets.

With strong light-matter interaction in their atomically thin layered structures, two-dimensional (2D) materials have been widely investigated for optoelectronic applications such as photodetectors and photovoltaic devices. Depending on the aim of optoelectronic applications, different device structures have been employed. Lateral phototransistor structures have been employed for high optical gain, while vertical photodiode structures have been employed for fast response and low power operation. Herein, we demonstrate a multimodal photodetector platform based on 2D materials, combining both a phototransistor and a photodiode and taking the corresponding desirable characteristics from each structure within a single device. In this platform, a multilayered transition-metal dichalcogenide flake is transferred on top of metal electrodes, and a transparent gate electrode is employed. The channel region of the flake between electrodes operates as a phototransistor providing a high gain mode, while the electrode region in the same flake operates as a vertical Schottky photodiode providing a fast response mode. These modes can be dynamically selected by controlling the drain voltage and gate voltage.

We report a successful development of a floating electrode-based DNA sensor with controllable responses. Here, metallic floating electrodes were fabricated to form Schottky barriers between carbon nanotubes and the floating electrodes. We showed that the sensor response could be enhanced by increasing the number of floating electrodes. We also analyzed the response of the sensors based on the Langmuir isotherm theory.

The development of a rapid and sensitive detection method for well-known, yet abused, antibiotics has been an important issue for food safety and environmental protection. This paper presents a simple and sensitive method for the specific or family-selective detection of antibiotics using carbon nanotube (CNT)-based sensors. Herein, CNT-based sensor transducers were functionalized with the single-chain variable-fragment (scFv) of antibodies that can selectively bind to a specific antibiotic or the certain family of antibiotics. Our CNT-based sensors functionalized with A2 scFv or F9 scFv exhibited the specific detection of enrofloxacin or the family-selective detection of fluoroquinolone-based antibiotics, respectively, in a real-time manner. This simple but efficient strategy can be utilized for various applications in the fields of food safety and environmental protection.

Recently, carbon nanotube (CNT)-based devices have been extensively utilized for various cellular applications, including neural-signal amplifi cation, [ 1 , 2 ] cancer therapeutics, [ 3 ] and tissue engineering. [ 4 ] For those applications, it is often crucial to control the location and direction of cell growth on CNTs while mimicking an in-vivo-like cellular environment to retain in-vivo-like cellular activity. Several research groups have reported that bulk CNT substrates can support cell adhesion, growth, and differentiation. [ 5–8 ] CNT patterns were also reported to induce the selective growth of neurons and human mesenchymal stem cells (hMSCs). [ 9 , 10 ] However, the effects of CNTs on cells are still controversial and the underlying mechanism for selective cell adhesion and growth is still obscure. In this Communication, we report a study of the role of extracellular matrix (ECM) proteins, such as fi bronectin (FN), in CNT–cell interactions and propose FN–CNT hybrid nanostructures as an effi cient means for cell-growth control. In this work, we fi rst investigated the adhesion properties and conformational change of FNs on the CNTs via immunofl uorescence and force-spectroscopy study. FNs exhibited a strong affi nity to CNTs and maintained a high binding capability to biomolecules even after being adsorbed onto the CNTs. Moreover, the results of our force-spectroscopy-based protein-unfolding experiment confi rm that FNs maintained their native structures on the CNTs. FN–CNT hybrid nanostructures had a stronger affi nity to cells than conventional surfaces, such as FN-coated glass. Importantly, cells formed focal adhesion and grew selectively on the FN–CNT hybrid nanostructures, indicating that the selective growth of cells on

We have developed a wide contact structure for low-noise nanochannel devices based on a carbon nanotube (CNT) network. This low-noise CNT network-based device has a dumbbell-shaped channel, which has wide CNT/electrode contact regions and, in effect, reduces the contact noise. We also performed a systematic analysis of structured CNT networks and established an empirical formula that can explain the noise behavior of arbitrary-shaped CNT network-based devices including the effect of contact regions and CNT alignment. Interestingly, our analysis revealed that the noise amplitude of aligned CNT networks behaves quite differently compared with that of randomly oriented CNT networks. Our results should be an important guideline in designing low-noise nanoscale devices based on a CNT network for various applications such as a highly sensitive low-noise sensor.

Although advanced devices based on nanotubes (NTs) and nanowires (NWs) are drawing much attention, devices based on a single NT or NW are not suitable for general manufacturing purposes, as it is still extremely difficult to control the electronic properties, growth and alignment of individual NTs or NWs on an industrially reliable scale. An alternative strategy for implementing NTs or NWs in real-world devices is the use of NT- or NW-network-based structures containing a number of NTs or NWs. Herein, we review the recent progress in NT/NW-network-based integrated devices. The technology for NW/NT-network-based devices is supported by massive integration methods, such as directed assembly, printing and directed growth, and devices based on NW/NT networks display several unique properties, such as percolating conduction and scaling behaviors, that differentiate them from individual NT/NW-based devices. A variety of applications are possible for NT/NW networks, including transistors and sensors, all of which offer unique characteristics for use in integrated nanoelectronics.

Herein, wereport a method to control the adhesion and shape of MSCsusing monolayered CNT patterns. As a proof of concept, wepatterned various 1D nanostructures, including CNTs andNWs, on substrates, and MSCs were subsequently culturedand observed on the patterned substrates. In this work, self-assembled monolayer (SAM) patterns were first used todirect the assembly of single-walled CNTs (swCNTs) andmulti-walled CNTs (mwCNTs) on solid substrates. A self-limiting mechanism ensured the assembly of only a singlelayer of CNTs, without significant change of surface morphol-ogy. Importantly, the MSCs exhibited preferential growth onCNT patterns, and the cell culture results suggested that theCNT patterns did not have a harmful effect on the MSCs.Further, we demonstrated the growth of MSCs on swCNTpatterns between electrodes. These results clearly show thatCNT patterns have enormous potential as a new platform forbasic research and applications using stem cells.Figure 1 shows a schematic diagram depicting our experi-mental procedure for directed MSC growth. First, a non-polarSAM of 1-octadecanethiol (ODT) was patterned, while leav-ing some bare Au regions (Fig. 1A). SAM patterning on Aucan be achieved using dip-pen nanolithography (DPN)

We developed an olfactory-nanovesicle-fused carbon-nanotube-transistor biosensor (OCB) that mimics the responses of a canine nose for the sensitive and selective detection of hexanal, an indicator of the oxidation of food. OCBs allowed us to detect hexanal down to 1 fM concentration in real-time. Significantly, we demonstrated the detection of hexanal with an excellent selectivity capable of discriminating hexanal from analogous compounds such as pentanal, heptanal, and octanal. Furthermore, we successfully detected hexanal in spoiled milk without any pretreatment processes. Considering these results, our sensor platform should offer a new method for the assessment of food quality and contribute to the development of portable sensing devices.

Carbon nanotube (CNT) networks on solid substrates have recently drawn attention as a means to direct the growth and differentiation of stem cells. However, it is still not clear whether cells can recognize individual CNTs with a sub-2 nm diameter, and directional nanostructured substrates such as aligned CNT networks have not been utilized to control cell behaviors. Herein, we report that human mesenchymal stem cells (hMSCs) grown on CNT networks could recognize the arrangement of individual CNTs in the CNT networks, which allowed us to control the growth direction and differentiation of the hMSCs. We achieved the directional growth of hMSCs following the alignment direction of the individual CNTs. Furthermore, hMSCs on aligned CNT networks exhibited enhanced proliferation and osteogenic differentiation compared to those on randomly oriented CNT networks. As a plausible explanation for the enhanced proliferation and osteogenic differentiation, we proposed mechanotransduction pathways triggered by high cytoskeletal tension in the aligned hMSCs. Our findings provide new insights regarding the capability of cells to recognize nanostructures smaller than proteins and indicate their potential applications for regenerative tissue engineering.

We have developed a method to monitor the activities of human taste receptor protein in lipid membrane using carbon nanotube transistors, enabling a “bioelectronic super-taster (BST)”, a taste sensor with human-tongue-like selectivity. In this work, human bitter taste receptor protein expressed in E. coli was immobilized on a single-walled carbon nanotube field effect transistor (swCNT-FET) with the lipid membrane. Then, the protein binding activity was monitored using the underlying swCNT-FET, leading to the operation as a BST device. The fabricated BST device could detect bitter tastants at 100 fM concentrations and distinguish between bitter and non-bitter tastants with similar chemical structures just like a human tongue. Furthermore, this strategy was utilized to differentiate the responses of taster or non-taster types of the bitter taste receptor proteins.

Researchers have made extensive efforts to mimic or reverse-engineer in vivo neural circuits using micropatterning technology. Various surface chemical cues or topographical structures have been proposed to design neuronal networks in vitro. In this paper, we propose a carbon nanotube (CNT)-based network engineering method which naturally mimics the structure of extracellular matrix (ECM). On CNT patterned substrates, poly-L-lysine (PLL) was coated, and E18 rat hippocampal neurons were cultured. In the early developmental stage, soma adhesion and neurite extension occurred in disregard of the surface CNT patterns. However, later the majority of neurites selectively grew along CNT patterns and extended further than other neurites that originally did not follow the patterns. Long-term cultured neuronal networks had a strong resemblance to the in vivo neural circuit structures. The selective guidance is possibly attributed to higher PLL adsorption on CNT patterns and the nanomesh structure of the CNT patterns. The results showed that CNT patterned substrates can be used as novel neuronal patterning substrates for in vitro neural engineering.

The behaviour of cells can be controlled by various microenvironments such as nanostructured cell-culture substrates with controlled nanotopography and chemical properties. One of promising substrates for controlled cell growth is a solid substrate comprised of synthetic one-dimensional nanostructures such as polymer nanofibers, carbon-based nanotubes/nanofibers, and inorganic nanowires. Such nanotube/nanowire structures have a similar dimension as extracellular matrix fibers, and their nanotopography and chemical properties can be easily controlled, which expands their possible applications in controlling the growth and differentiation of cells. This paper provides a concise review on the recent applications of solid substrates based on synthetic nanowires/nanotubes for controlled cell growth and differentiation.