Low-Temperature Centimeter-Scale Growth of Layered 2D SnS for Piezoelectric Kirigami Devices.

Tin monosulfide (SnS) is a promising piezoelectric material with an intrinsically layered structure, making it attractive for self-powered wearable and stretchable devices. However, for practical application purposes, it is essential to improve the output and manufacturing compatibility of SnS-based piezoelectric devices by exploring their large-area synthesis principle. In this study, we report the chemical vapor deposition (CVD) growth of centimeter-scale two-dimensional (2D) SnS layers at temperatures as low as 200 °C, allowing compatibility with processing a range of polymeric substrates. The intrinsic piezoelectricity of 2D SnS layers directly grown on polyamides (PIs) was confirmed by piezoelectric force microscopy (PFM) phase maps and force-current corroborative measurements. Furthermore, the structural robustness of the centimeter-scale 2D SnS layers/PIs allowed for engraving complicated kirigami patterns on them. The kirigami-patterned 2D SnS layer devices exhibited intriguing strain-tolerant piezoelectricity, which was employed in detecting human body motions and generating photocurrents irrespective of strain rate variations. These results establish the great promise of 2D SnS layers for practically relevant large-scale device technologies with coupled electrical and mechanical properties.

Colloidal Ag2Se intraband quantum dots.

With the emergence of the Internet of Things, wearable electronics, and machine vision, the exponentially growing demands for miniaturization, energy efficiency, and cost-effectiveness have imposed critical requirements on the size, weight, power consumption and cost (SWaP-C) of infrared detectors. To meet this demand, new sensor technologies that can reduce the fabrication cost associated with semiconductor epitaxy and remove the stringent requirement for cryogenic cooling are under active investigation. In the technologically important spectral region of mid-wavelength infrared, intraband colloidal quantum dots are currently at the forefront of this endeavor, with wafer-scale monolithic integration and Auger suppression being the key material capabilities to minimize the sensor's SWaP-C. In this Feature Article, we provide a focused review on the development of sensors based on Ag2Se intraband colloidal quantum dots, a heavy metal-free colloidal nanomaterial that has merits for wide-scale adoption in consumer and industrial sectors.

Peel-and-Stick Integration of Atomically Thin Nonlayered PtS Semiconductors for Multidimensionally Stretchable Electronic Devices.

Various near-atom-thickness two-dimensional (2D) van der Waals (vdW) crystals with unparalleled electromechanical properties have been explored for transformative devices. Currently, the availability of 2D vdW crystals is rather limited in nature as they are only obtained from certain mother crystals with intrinsically possessed layered crystallinity and anisotropic molecular bonding. Recent efforts to transform conventionally non-vdW three-dimensional (3D) crystals into ultrathin 2D-like structures have seen rapid developments to explore device building blocks of unique form factors. Herein, we explore a "peel-and-stick" approach, where a nonlayered 3D platinum sulfide (PtS) crystal, traditionally known as a cooperate mineral material, is transformed into a freestanding 2D-like membrane for electromechanical applications. The ultrathin (∼10 nm) 3D PtS films grown on large-area (>cm2) silicon dioxide/silicon (SiO2/Si) wafers are precisely "peeled" inside water retaining desired geometries via a capillary-force-driven surface wettability control. Subsequently, they are "sticked" on strain-engineered patterned substrates presenting prominent semiconducting properties, i.e., p-type transport with an optical band gap of ∼1.24 eV. A variety of mechanically deformable strain-invariant electronic devices have been demonstrated by this peel-and-stick method, including biaxially stretchable photodetectors and respiratory sensing face masks. This study offers new opportunities of 2D-like nonlayered semiconducting crystals for emerging mechanically reconfigurable and stretchable device technologies.

High-Performance Oxide-Based p-n Heterojunctions Integrating p-SnOx and n-InGaZnO.

The fabrication of oxide-based p-n heterojunctions that exhibit high rectification performance has been difficult to realize using standard manufacturing techniques that feature mild vacuum requirements, low thermal budget processing, and scalability. Critical bottlenecks in the fabrication of these heterojunctions include the narrow processing window of p-type oxides and the charge-blocking performance across the metallurgical junction required for achieving low reverse current and hence high rectification behavior. The overarching goal of the present study is to demonstrate a simple processing route to fabricate oxide-based p-n heterojunctions that demonstrate high on/off rectification behavior, a low saturation current, and a small turn-on voltage. For this study, room-temperature sputter-deposited p-SnOx and n-InGaZnO (IGZO) films were chosen. SnOx is a promising p-type oxide material due to its monocationic system that limits complexities related to processing and properties, compared to other multicationic oxide materials. For the n-type oxide, IGZO is selected due to the knowledge that postprocessing annealing critically reduces the defect and trap densities in IGZO to ensure minimal interfacial recombination and high charge-blocking performance in the heterojunctions. The resulting oxide p-n heterojunction exhibits a high rectification ratio greater than 103 at ±3 V, a low saturation current of ∼2 × 10-10 A, and a small turn-on voltage of ∼0.5 V. In addition, the demonstrated oxide p-n heterojunctions exhibit excellent stability over time in air due to the p-SnOx with completed reaction annealing in air and the reduced trap density in n-IGZO.

Midwavelength Infrared p-n Heterojunction Diodes Based on Intraband Colloidal Quantum Dots.

As an emerging member of the colloidal semiconductor quantum dot materials family, intraband quantum dots are being extensively studied for thermal infrared sensing applications. High-performance detectors can be realized using a traditional p-n junction device design; however, the heavily doped nature of intraband quantum dots presents a new challenge in realizing diode devices. In this work, we utilize a trait uniquely available in a colloidal quantum dot material system to overcome this challenge: the ability to blend two different types of quantum dots to control the electrical property of the resulting film. We report on the preparation of binary mixture films containing midwavelength infrared Ag2Se intraband quantum dots and the fabrication of p-n heterojunction diodes with strong rectifying characteristics. The peak specific detectivity at 4.5 µm was measured to be 107 Jones at room temperature, which is an orders of magnitude improvement compared to the previous generation of intraband quantum dot detectors.

Scalable Van der Waals Two-Dimensional PtTe2 Layers Integrated onto Silicon for Efficient Near-to-Mid Infrared Photodetection.

In recent years, there has been increasing interest in leveraging two-dimensional (2D) van der Waals (vdW) crystals for infrared (IR) photodetection, exploiting their unusual optoelectrical properties. Some 2D vdW materials with small band gap energies such as graphene and black phosphorus have been explored as stand-alone IR responsive layers in photodetectors. However, the devices incorporating these IR-sensitive 2D layers often exhibited poor performances owing to their preparation issues such as limited scalability and air instability. Herein, we explored wafer-scale 2D platinum ditelluride (PtTe2) layers for near-to-mid IR photodetection by directly growing them onto silicon (Si) wafers. 2D PtTe2/Si heterojunctions exhibited wavelength- and intensity-dependent high photocurrents in a spectral range of ∼1-7 µm, significantly outperforming stand-alone 2D PtTe2 layers. The observed superiority is attributed to their excellent Schottky junction characteristics accompanying suppressed carrier recombination as well as optical absorbance competition between 2D PtTe2 layers and Si. The direct and scalable growth of 2D PtTe2 layers was further extended to demonstrate mechanically flexible IR photodetectors.

Vertically Stacked Intraband Quantum Dot Devices for Mid-Wavelength Infrared Photodetection.

Intraband quantum dots are degenerately doped semiconductor nanomaterials that exhibit unique optical properties in mid- to long-wavelength infrared. To date, these quantum dots have been only studied as lateral photoconductive devices, while transitioning toward a vertically stacked structure can open diverse opportunities for investigating advanced device designs. Here, we report the first vertical intraband quantum dot heterojunction devices composed of Ag2Se/PbS/Ag2Se quantum dot stacks that bring the advantage of reduced dark conductivity with a simplified device fabrication procedure. We discuss the improvement in the colloidal synthesis of Ag2Se quantum dots that are critical for vertical device fabrication, identify an important process that determines the mid-wavelength infrared responsivity of the quantum dot film, and analyze the basic device characteristics and key detector performance parameters. Compared to the previous generation of Ag2Se quantum dot-based photoconductive devices, approximately 70 times increase in the mid-wavelength responsivity, at room temperature, is observed.

High-performance thermoelectric silver selenide thin films cation exchanged from a copper selenide template.

Over the past decade, Ag2Se has attracted increasing attention due to its potentially excellent thermoelectric (TE) performance as an n-type semiconductor. It has been considered a promising alternative to Bi-Te alloys and other commonly used yet toxic and/or expensive TE materials. To optimize the TE performance of Ag2Se, recent research has focused on fabricating nanosized Ag2Se. However, synthesizing Ag2Se nanoparticles involves energy-intensive and time-consuming techniques with poor yield of final product. In this work, we report a low-cost, solution-processed approach that enables the formation of Ag2Se thin films from Cu2-x Se template films via cation exchange at room temperature. Our simple two-step method involves fabricating Cu2-x Se thin films by the thiol-amine dissolution of bulk Cu2Se, followed by soaking Cu2-x Se films in AgNO3 solution and annealing to form Ag2Se. We report an average power factor (PF) of 617 ± 82 µW m-1 K-2 and a corresponding ZT value of 0.35 at room temperature. We obtained a maximum PF of 825 µW m-1 K-2 and a ZT value of 0.46 at room temperature for our best-performing Ag2Se thin-film after soaking for 5 minutes. These high PFs have been achieved via full solution processing without hot-pressing.

Colloidal-annealing of ZnO nanoparticles to passivate traps and improve charge extraction in colloidal quantum dot solar cells.

The popularity of colloidal quantum dot (CQD) solar cells has increased owing to their tunable bandgap, multiple exciton generation, and low-cost solution processes. ZnO nanoparticle (NP) layers are generally employed as electron transport layers in CQD solar cells to efficiently extract the electrons. However, trap sites and the unfavorable band structure of the as-synthesized ZnO NPs have hindered their potential performance. Herein, we introduce a facile method of ZnO NP annealing in the colloidal state. Electrical, structural, and optical analyses demonstrated that the colloidal-annealing of ZnO NPs effectively passivated the defects and simultaneously shifted their band diagram; therefore, colloidal-annealing is a more favorable method as compared to conventional film-annealing. These CQD solar cells based on colloidal-annealed ZnO NPs exhibited efficient charge extraction, reduced recombination and achieved an enhanced power conversion efficiency (PCE) of 9.29%, whereas the CQD solar cells based on ZnO NPs without annealing had a PCE of 8.05%. Moreover, the CQD solar cells using colloidal-annealed ZnO NPs exhibited an improved air stability with 98% retention after 120 days, as compared to that of CQD solar cells using non-annealed ZnO NPs with 84% retention.

Colloidal quantum dots for thermal infrared sensing and imaging.

Colloidal quantum dots provide a powerful materials platform to engineer optoelectronics devices, opening up new opportunities in the thermal infrared spectral regions where no other solution-processed material options exist. This mini-review collates recent research reports that push the technological envelope of colloidal quantum dot-based photodetectors toward mid- and long-wavelength infrared. We survey the synthesis and characterization of various thermal infrared colloidal quantum dots reported to date, discuss the basic theory of device operation, review the fabrication and measurement of photodetectors, and conclude with the future prospect of this emerging technology.

Paper Thermoelectrics: Merging Nanotechnology with Naturally Abundant Fibrous Material.

The development of paper-based sensors, antennas, and energy-harvesting devices can transform the way electronic devices are manufactured and used. Herein we describe an approach to fabricate paper thermoelectric generators for the first time by directly impregnating naturally abundant cellulose materials with p- or n-type colloidal semiconductor quantum dots. We investigate Seebeck coefficients and electrical conductivities as a function of temperature between 300 and 400 K as well as in-plane thermal conductivities using Angstrom's method. We further demonstrate equipment-free fabrication of flexible thermoelectric modules using p- and n-type paper strips. Leveraged by paper's inherently low thermal conductivity and high flexibility, these paper modules have the potential to efficiently utilize heat available in natural and man-made environments by maximizing the thermal contact to heat sources of arbitrary geometry.

Protein-directed self-assembly of a fullerene crystal.

Learning to engineer self-assembly would enable the precise organization of molecules by design to create matter with tailored properties. Here we demonstrate that proteins can direct the self-assembly of buckminsterfullerene (C60) into ordered superstructures. A previously engineered tetrameric helical bundle binds C60 in solution, rendering it water soluble. Two tetramers associate with one C60, promoting further organization revealed in a 1.67-Å crystal structure. Fullerene groups occupy periodic lattice sites, sandwiched between two Tyr residues from adjacent tetramers. Strikingly, the assembly exhibits high charge conductance, whereas both the protein-alone crystal and amorphous C60 are electrically insulating. The affinity of C60 for its crystal-binding site is estimated to be in the nanomolar range, with lattices of known protein crystals geometrically compatible with incorporating the motif. Taken together, these findings suggest a new means of organizing fullerene molecules into a rich variety of lattices to generate new properties by design.

Photovoltaic Performance of PbS Quantum Dots Treated with Metal Salts.

Recent advances in quantum dot surface passivation have led to a rapid development of high-efficiency solar cells. Another critical element for achieving efficient power conversion is the charge neutrality of quantum dots, as charge imbalances induce electronic states inside the energy gap. Here we investigate how the simultaneous introduction of metal cations and halide anions modifies the charge balance and enhances the solar cell efficiency. The addition of metal salts between QD deposition and ligand exchange with 1,3-BDT results in an increase in the short-circuit current and fill factor, accompanied by a distinct reduction in a crossover between light and dark current density-voltage characteristics.

Alternative Method of Retrocrural Approach during Celiac Plexus Block Using a Bent Tip Needle.

BACKGROUND: This study sought to determine safe ranges of oblique angle, skin entry point and needle length by reviewing computed tomography (CT) scans and to evaluate the usefulness of a bent tip needle during celiac plexus block (CPB). METHODS: CT scans of 60 CPB patients were reviewed. Image of the uppermost margin of L2 vertebral body was used to measure the minimal and maximal oblique angles and the distances from the midline to skin puncture point. The imaginary needle trajectory distance was calculated by three-dimensional measurement. When the procedure was performed by using a 10° bent tip needle under a 20° oblique X-ray fluoroscopic view, the distance (GF/G'F) from the midline to the actual puncture site was measured. RESULTS: The imaginary safe oblique angle range was 26.4-34.2° and 27.7-36.0° on the right and left, respectively. The distance from the midline to skin puncture point was 6.1-7.6 cm on the right and 6.3-7.6 cm on the left. The needle trajectory distance at minimal angle was 9.6-11.6 cm on the right and 9.5-11.5 cm on the left. The distance of GF/G'F was 5.1-6.5 cm and 5.0-6.4 cm on the right and left, respectively. All imaginary parameters were correlated with BMI except for GF/G'F. All complications were mild and transient. CONCLUSIONS: We identified safe values of angles and distances using a straight needle. Furthermore, using a bent tip needle under a 20° oblique fluoroscopic view, we could safely perform CPB with smaller parameter values.

p-i-n Heterojunction solar cells with a colloidal quantum-dot absorber layer.

A quantum-dot (QD) p-i-n heterojunction solar cell with an increased depletion region is demonstrated by depleting the QD layer from both the front and back junctions. Due to a combination of improved charged extraction and increased light absorption, a 120% increase in the short-circuit current is achieved compared with that of conventional ZnO/QD devices.

Live bee acupuncture (Bong-Chim) dermatitis: dermatitis due to live bee acupuncture therapy in Korea.

Live bee acupuncture (Bong-Chim) dermatitis is an iatrogenic disease induced by so-called live bee acupuncture therapy, which applies the honeybee (Apis cerana) stinger directly into the lesion to treat various diseases in Korea. We present two cases of live bee acupuncture dermatitis and review previously published articles about this disease. We classify this entity into three stages: acute, subacute, and chronic. The acute stage is an inflammatory reaction, such as anaphylaxis or urticaria. In the chronic stage, a foreign body granuloma may develop from the remaining stingers, similar to that of a bee sting reaction. However, in the subacute stage, unlike bee stings, we see the characteristic histological "flame" figures resulting from eosinophilic stimulation induced by excessive bee venom exposure. We consider this stage to be different from the adverse skin reaction of accidental bee sting.

A histopathologic study of epidermoid cysts in Korea: comparison between ruptured and unruptured epidermal cyst.

BACKGROUND: An epidermoid cyst is a common epithelial-lined cyst. There have been many studies on epidermoid cysts, but few focused on ruptured epidermoid cyst and its histopathologic characteristics. OBJECTIVE: We evaluated the histopathologic differences between ruptured and unruptured epidermoid cysts, and their relationships. METHODS: We retrospectively examined 359 excision biopsy specimen diagnosed as epidermoid cyst from 1991 to 2011 at Department of dermatology at Daegu Catholic University Hospital. RESULTS: The mean cyst area was 38.89 mm(2) and the mean cyst area of the unruptured group was larger than that of the ruptured group. The mean wall thickness was 90.15 µm and was thicker in ruptured group than in unruptured group. The correlation between cyst diameter and wall thickness had statistically negative correlation in unruptured and in ruptured group. In ruptured group, the cystic size of the cases with rete ridge was smaller than that of without rete ridge. The cyst wall thickness of the cases with rete ridge was thicker than that of the cases without rete ridge. LIMITATIONS: For comparative evaluation of sizes, randomly shaped cysts are assumed to be perfectly elliptic. And only those with more than 3/4 cystic wall remaining were included in the subject. CONCLUSION: When comparing the ruptured and the unruptured cyst, the rupture of cyst had significant relationship with increased cyst diameter and area, increased wall thickness, more cyst contents, and more wall changes. Moreover, the presence of rete ridge in ruptured cystic wall is a valuable variable to recognize the duration of the rupture.

Bandlike transport in strongly coupled and doped quantum dot solids: a route to high-performance thin-film electronics.

We report bandlike transport in solution-deposited, CdSe QD thin-films with room temperature field-effect mobilities for electrons of 27 cm(2)/(V s). A concomitant shift and broadening in the QD solid optical absorption compared to that of dispersed samples is consistent with electron delocalization and measured electron mobilities. Annealing indium contacts allows for thermal diffusion and doping of the QD thin-films, shifting the Fermi energy, filling traps, and providing access to the bands. Temperature-dependent measurements show bandlike transport to 220 K on a SiO(2) gate insulator that is extended to 140 K by reducing the interface trap density using an Al(2)O(3)/SiO(2) gate insulator. The use of compact ligands and doping provides a pathway to high performance, solution-deposited QD electronics and optoelectronics.