Search

The role of a self-assembled monolayer obtained by vacuum deposition of 4-aminopyridine (4-AP), a small organic molecule having amine and pyridine groups, as a metal nucleation inducer and adhesion promoter was verified, and the applicability was evaluated. 4-AP deposited to an extremely thin thickness effectively changed the substrate surface properties, increasing the nucleation density of silver (Ag) more than 3 times and eventually forming a more transparent, low-resistance Ag thin film. The optical transmittance of the Ag thin film, which was less than 60% when 4-AP was not applied, could be increased to about 77% by simply applying 4-AP, and the electrical resistance could be lowered from 37 to 14 Ω/square at the same time. Transmittance could be further improved to higher than 90% by depositing an antireflection layer for use as a transparent Ag electrode. It was also verified that 4-AP not only serves as a nucleation inducer but also contributes to improving interfacial adhesion. The Ag transparent electrode using 4-AP provided the improved performance of the organic light-emitting device due to higher transmittance, lower resistance, and surface roughness. Small organic molecules including functional groups that can be vacuum deposited, such as 4-AP, are expected to be used as surface pretreatment materials for various depositions because they can be easily patterned and can efficiently modify the surface even with extremely thin thickness.

The synthesis of uniform low-defect graphene on a catalytic metal substrate is getting closer to the industrial level. However, its practical application is still challenging due to the lack of an appropriate method for its scalable damage-free transfer to a device substrate. Here, an efficient approach for a defect-free, etchant-free, wrinkle-free, and large-area graphene transfer is demonstrated by exploiting a multifunctional viscoelastic polymer gel as a simultaneous shock-free adhesive and dopant layer. Initially, an amine-rich polymer solution in its liquid form allows for conformal coating on a graphene layer grown on a Cu substrate. The subsequent thermally cured soft gel enables the shock-free and wrinkle-free direct mechanical exfoliation of graphene from a substrate due to its strong charge-transfer interaction with graphene and excellent shock absorption. The adhesive gel with a high optical transparency works as an electron doping layer toward graphene, which exhibits significantly reduced sheet resistances without optical transmittance loss. Lastly, the transferred graphene layer shows high mechanical and chemical stabilities under the repeated bending test and exposure to various solvents. This gel-assisted mechanical transfer method can be a solution to connect the missing part between large-scale graphene synthesis and next-generation electronics and optoelectronic applications.

The adsorption of peptides and proteins on hydrophobic solid surfaces has received considerable research attention owing to their wide applications to biocompatible nanomaterials and nanodevices, such as biosensors and cell adhesion materials with reduced nanomaterial toxicity. However, fundamental understandings about physicochemical hydrophobic interactions between peptides and hydrophobic solid surfaces are still unknown. In this study, we investigate the effect of secondary structures on adsorption energies between peptides and hydrophobic solid surfaces via experimental and theoretical analyses using surface-assisted laser desorption/ionization-time-of-flight (SALDI-TOF) and molecular dynamics (MD) simulations. The hydrophobic interactions between peptides and hydrophobic solid surfaces measured via SALDI-TOF and MD simulations indicate that the hydrophobic interaction of peptides with random coil structures increased more than that of peptides with an α-helix structure when polar amino acids are replaced with hydrophobic amino acids. Additionally, our study sheds new light on the fundamental understanding of the hydrophobic interaction between hydrophobic solid surfaces and peptides that have diverse secondary structures.

In this study, green indium phosphide (InP) quantum dots (QDs) were synthesized using a tris(dimethylamino)phosphine ((DMA)3P) phosphorus source and applied to electroluminescent quantum light-emitting diodes (QLEDs). The (DMA)3P precursor is safer and more cost-effective than the conventional tris(trimethylsilyl)phosphine. The emission peak of the InP QDs was shifted to the green region from the red by replacing the conventional zinc precursor ZnCl2 with ZnI2. The surface reaction rate was limited using ZnI2 in the core formation step, yielding small-sized QDs to achieve green emission. In addition, with the optimal ZnSeS intermediate shell and outer shell, the maximum quantum yield of 67.5% with a narrow full width at half maximum of 46 nm was achieved for the (DMA)3P-based green-emitting InP@ZnSeS/ZnS QDs. QLEDs were demonstrated with the (DMA)3P-based green InP QDs, and their efficiency was maximized by optimizing the Mg doping ratios in the electron transport layer (ETL) of ZnMgO. The maximum external quantum efficiency of 1.68% and current efficiency of 4.79 cd/A were achieved with an optimal doping ratio of 12.5% ZnMgO for the (DMA)3P-based green InP QLEDs. This study demonstrates that safer (DMA)3P phosphide source-based green InP QDs are effective in achieving low-cost InP QLEDs.

In this study, multishelled InP-based quantum dots (QDs) were synthesized using a phosphorus source tris(dimethylamino)phosphine [(DMA)3P] and were applied to solution-processed QD light-emitting d...

The effect of organic solvents on the crystalline structure of the hole-transporting poly(3-hexylthiophene) (P3HT) layer of perovskite solar cells (PSCs) was investigated in this study. UV–visible ...

In this study, the Gaussian mixture model (GMM) was modified and implemented to determine the real-time endpoint of SiO2 plasma etching using optical emission spectrum analysis. Optical emission spectroscopy (OES) signals were collected from the SiO2 plasma etching processes, and the modified GMM was applied to SiO2 etching with relative areas of 8.0, 4.0, and 1.0 %. Consequently, the sensitivity of OES signals was improved by ~5.5 times, and the sensitivity factor of the modified GMM was increased by approximately two times, compared with those of the modified K-means cluster analysis (another clustering technique). In addition, 60 peaks related to the reactants were selected out of 6144 signals to improve the sensitivity of the modified GMM with full-spectrum wavelengths. The modified GMM analysis using the 60 reactant-related peaks exhibited a higher sensitivity (~1.4 times) than that with 6144 full-spectrum OES signals. Thus, the modified GMM can be a suitable and effective clustering technique for etching endpoint detection.

Quinary Zn-Mg-Ga-Cl-O nanoparticles were synthesized for the electron transport layer (ETL) of green InP-based quantum dot light emitting diodes (QLEDs) to achieve band alignment and charge balance. These nanoparticles were synthesized by simple hydrolysis reactions in the solution phase. The band gap of Zn-Mg-Ga-Cl-O increased to 3.85 eV, which exceeded that of ZnO by 0.3 eV. The energy gap between the conduction bands of Zn-Mg-Ga-Cl-O and InP-based quantum dots changed from 0.78 eV to −0.17 eV. Electron transport in green InP-based QLEDs was reduced, and the charge balance was improved by Zn-Mg-Ga-Cl-O compared with that by ZnO and Zn-Mg-O. Green InP-based QLEDs with a Zn-Mg-Ga-Cl-O ETL exhibited a maximum luminance of 3270 cd/m2. The maximum external quantum efficiency (EQE) and power efficiency of the QLEDs with a Zn-Mg-Ga-Cl-O ETL were 3.8% and 19.6 lm/W, respectively, which were 9.5 times and 9.24 times higher than those of the QLEDs with a ZnO ETL. The maximum EQE and power efficiency were achieved at 2.5 V and 170 cd/m2.

The synthesis of uniform low-defect graphene on a catalytic metal substrate is getting closer to the industrial level. However, its practical application is still challenging due to the lack of an appropriate method for its scalable damage-free transfer to a device substrate. Here, an efficient approach for a defect-free, etchant-free, wrinkle-free, and large-area graphene transfer is demonstrated by exploiting a multifunctional viscoelastic polymer gel as a simultaneous shock-free adhesive and dopant layer. Initially, an amine-rich polymer solution in its liquid form allows for conformal coating on a graphene layer grown on a Cu substrate. The subsequent thermally cured soft gel enables the shock-free and wrinkle-free direct mechanical exfoliation of graphene from a substrate due to its strong charge-transfer interaction with graphene and excellent shock absorption. The adhesive gel with a high optical transparency works as an electron doping layer toward graphene, which exhibits significantly reduced sheet resistances without optical transmittance loss. Lastly, the transferred graphene layer shows high mechanical and chemical stabilities under the repeated bending test and exposure to various solvents. This gel-assisted mechanical transfer method can be a solution to connect the missing part between large-scale graphene synthesis and next-generation electronics and optoelectronic applications.

The sp2-rich hydrogenated amorphous carbon (a-C:H) is widely adopted as hard masks in semiconductor-device fabrication processes. The ion-enhanced etch characteristics of sp2-rich a-C:H films on ion density and ion energy were investigated in CF4 plasmas and O2 plasmas in this work. The etch rate of sp2-rich a-C:H films in O2 plasmas increased linearly with ion density when no bias power was applied, while the fluorocarbon deposition was observed in CF4 plasmas instead of etching without bias power. The etch rate was found to be dependent on the half-order curve of ion energy in both CF4 plasmas and O2 plasmas when bias power was applied. An ion-enhanced etching model was suggested to fit the etch rates of a-C:H in CF4 plasmas and O2 plasmas. Then, the etch yield and the threshold energy for etching were determined based on this model from experimental etch rates in CF4 plasma and O2 plasma. The etch yield of 3.45 was observed in CF4 plasmas, while 12.3 was obtained in O2 plasmas, owing to the high reactivity of O radicals with carbon atoms. The threshold energy of 12 eV for a-C:H etching was obtained in O2 plasmas, while the high threshold energy of 156 eV was observed in CF4 plasmas. This high threshold energy is attributed to the formation of a fluorocarbon layer that protects the a-C:H films from ion-enhanced etching.

Globally, perovskite solar cells (PSCs) represent a third-generation photovoltaic technology that is being increasingly implemented and commercialized. However, the biological impacts of leachates from PSCs are poorly understood. Therefore, the aim of this study was to investigate the ecotoxicity of PSC leachates compared with that of commercial Si-based solar cell (SBSC) leachates. We performed leaching assessments and aquatic bioassays using internationally recommended test species and measured and compared the ecotoxicity of PSC and SBSC leachates. As a result of the leaching analyses, Si, Pb, and Al were found to be the most leached elements from broken PSCs and SBSCs. The bioassays indicated that polycrystalline SBSC (p-Si) and monocrystalline SBSC (m-Si) leachates were more toxic to fish embryos than the PSC leachates and that water fleas were sensitive to m-Si leachates, but less sensitive to PSC and p-Si leachates. In addition, principle component analyses indicated that the ecotoxicity of solar cell leachates was related to either the Pb or Si content. This is the first comparative study of the potential ecotoxicity of PSC and SBSC leachates in aquatic ecosystems, and the results of which can be used in the environmentally safe commercialization of solar cells.

Acrylate groups were introduced on quantum dots (QD) via ligand exchange followed by nucleophilic reaction. The QDs were then polymerized with other multi-functional acrylic monomers in this study. Two acrylate groups were introduced at the end of an elongated ligand and the ligands with two acrylate groups were fully coordinated on the entire surface of the QD. This ligand modification scheme made the QDs highly reactive and also compatible with common organic solvents. No decrease in the quantum yield of the QDs was observed after ligand modification and the adduction reaction. The acrylate functional groups in the QDs were verified by 1H NMR and FT-IR. The prepared QDs with a terminal acrylate group were reacted with trimethylolpropane triacrylate and 1,6-hexanediol diacrylate to form micrometer scale beads via suspension polymerization. The diameter of the spherical beads was in the range of 80–150 μm and QDs 13 nm in diameter were found to be evenly dispersed in the polymer beads. The QD-polymer beads were applied to color conversion layers (CCL) on a blue light emitting diode (LED). The QD-polymer beads showed a 50% reduction over 72 h from the initial optical efficiency, while the QD embedded in the PMMA matrix (QD-PMMA) was reduced by 50% for 14 h.

Patchable electrodes are attractive for applications in optoelectronic devices because of their easy and reliable processability. However, development of reliable patchable transparent electrodes (TEs) with high optoelectronic performance is challenging; till now, optoelectronic devices fabricated with patchable TEs have been exhibiting limited performance. In this study, Ag nanowire (AgNW)/poly(methyl methacrylate) (PMMA) patchable TEs are developed and the highly efficient transparent quantum dot light-emitting diodes (QLEDs) using the patchable TEs are fabricated. AgNWs with optimized optoelectronic properties (figure of merit ≈ 3.3 × 10

In this research, a flowable chemical vapor deposition (FCVD) process was developed to planarize particle-scattered surfaces for thin film encapsulation by atomic layer deposition (ALD). Nanometer-thick ALD layers are known to have good barrier properties owing to the conformal deposition of the films and their high density, but those barrier properties are vulnerable to degradation because of surface particles on the substrates. In this study, FCVD silicon oxide layer was applied to particlescattered surfaces as a planarization interlayer. Flowable silicon oxide thin films were deposited with tetrabutoxysiline and O₂ in an inductively coupled plasmas reactor. The chemical bonding structure of the flowable silicon oxide was verified with Fourier transform infrared spectroscopy. To confirm the planarization effect, particles 2 μm in diameter were intentionally spread on the substrates by electrospray processing and nanometer-thick Al₂O₃ layers were deposited on top of the planarization interlayers. With the flowable silicon oxide interlayer and the same particle density on flexible substrates, the water vapor transmission rate was reduced to 1.2×10-3 g/(m² day) from 2.0×10-3 g/(m² day). The flowable silicon oxide layers are thus demonstrated to be effective interlayers to reduce the influence of particle contamination for ALD barrier films.

Vertically oriented graphene (VG) with three-dimensional architecture has been proved to exhibit unique properties, and its particular morphology has been realized by researchers to be crucial for its performance in practical applications. In this study, we investigated the morphology evolution of VG films synthesized by the plasma-enhanced chemical vapor deposition process, including porous graphene film, graphene wall, and graphene forest. This study reveals that the morphology of VG is controlled by a combination of the deposition and etching effects and tailored by the growth conditions, such as plasma source power and growth time and temperature. The plasma source power relates to the number of branches of VG, and the growth temperature relates to the thickness of each VG flake, whereas the growth time determines the height of VG. Finally, the electrochemical properties of VG films along with morphology evolution are investigated by fabricating as VG-based supercapacitor electrodes.

Tailored-ZnMgO layers result in green-emitting InP based quantum dot light emitting diodes (QLEDs) with a maximum luminance of 13 900 cd m-2 and an external quantum efficiency (EQE) of 13.6%. This is the first report of green-emitting InP based QLEDs that exceed an EQE of 10% and a luminance of 13 000 cd m-2.

This study presents the feasibility of the use of hexafluoroisopropanol (HFIP) as a substitute to perfluorocarbon (PFC) for the plasma etching of SiO2 to confront the continuous increase in demand for PFC emission reduction. SiO2 etching is conducted in HFIP/Ar and C4F8/Ar plasmas, respectively, and its characteristics are compared. The SiO2 etch rates in the HFIP/Ar plasma are higher compared with those in the C4F8/Ar plasma. The thickness of the steady-state fluorocarbon films formed on the surface of SiO2 are lower in the HFIP/Ar plasma compared with in the C4F8/Ar plasma. Higher SiO2 etch rates and thinner fluorocarbon films in the HFIP/Ar plasma are attributed to the oxygen atoms in HFIP, which generate oxygen radicals that react with the fluorocarbon films to turn into volatile products. Due to the higher dissociation of C-F bonds in CF4 compared with in HFIP, the etch rates of SiO2 in the C4F8/Ar plasma increase more rapidly with the magnitude of the bias voltage compared with those in the HFIP/Ar plasma. The etch profiles of the 200 nm diameter SiO2 contact holes with an aspect ratio of 12 show that fairly anisotropic SiO2 contact hole etching was achieved successfully using the HFIP/Ar plasma.

In this study, a cyclic isotropic plasma atomic layer etching (ALE) process was developed for aluminum oxide that involves fluorination with NF3 plasma and ligand exchange with trimethylaluminum (TMA). The isotropic plasma ALE consists of two steps: fluorination and removal. During the fluorination step, the Al2O3 surface was fluorinated to AlOFx with NF3 plasma at 100 °C. The formation of the AlOFx layer was confirmed by x-ray photoelectron spectroscopy analysis, and the atomic fraction of fluorine on the surface was saturated at 25% after 50 s of plasma fluorination. The depths of the fluorinated layers were in the range of 0.79–1.14 nm at different plasma powers. In the removal step, the fluorinated layer was removed by a ligand exchange reaction with TMA at an elevated temperature range of 250–480 °C. The etch per cycle (EPC) was 0.20–0.30 nm/cycle and saturated after 30 s in the temperature range of 290–330 °C. No etching was observed below 250 °C, and the EPC increased in the temperature range of 250–300 °C during the removal step with the ligand exchange reaction and reached the maximum at 300 °C. Then, the EPC was significantly reduced at high temperatures, possibly due to TMA decomposition. The fluorine atomic fraction on the surface was reduced to 14% after the removal. In conclusion, Al2O3 was successfully etched at the atomic scale by the cyclic plasma ALE process. The average surface roughness of Al2O3 was reduced from 8.6 to 5.3 Å after 20 cycles of etching.

Supplemental data

Supplemental data

In this Letter, red-emitting multi-shelled indium phosphide (InP) quantum dots (QDs) were synthesized using the safe phosphorus precursor tris(dimethylamino)phosphine ( ( D M A ) 3 P ). The long-chain ligands of oleylamine (OAm) in the ( D M A ) 3 P phosphide source-based InP QDs were partially exchanged with short-chain ligands of phenethylamine (PEA) in the core formation process, and the resulting InP QDs were applied to quantum dot light-emitting diodes (QLEDs). The short-chain ligands of PEA with the π -conjugated benzene ring improved the charge transport and electrical conduction of the QLEDs with ( D M A ) 3 P phosphide source-based InP QDs. The PEA-engineering of InP QDs improved their maximum quantum yield from 71% to 85.5% with the full-width at half-maximum of 62 nm. Furthermore, the maximum external quantum efficiency of QLEDs with the PEA-engineered InP QDs improved from 1.9% to 3.5%, and their maximum power efficiency increased from 2.8 to 6.0 lm/W. This Letter demonstrates that engineering the core formation process with the short-chain ligands of PEA provides an efficient and facile way to improve the charge transport and electrical conduction in ( D M A ) 3 P phosphide source-based InP QLEDs for electroluminescent devices.

FT-IR spectra, 1H NMR spectra, Summary of TRPL data and device performance

In this study, we developed effective carbon-rich Al2O3 interlayers for flexible moisture barrier films. The carbon-rich Al2O3 films were deposited with excessive supply of trimethylaluminum (TMA) precursor. The five-layer structure was made with alternate layers of low-carbon Al2O3 and carbon-rich Al2O3 and the water vapor transmission rate (WVTR) of 3.3 × 10 −4 g/(m2·day) was demonstrated. The WVTR of the multilayer films is reduced by 36% compared to 25 nm thick single Al2O3 barrier film. The WVTR of the five-layer film shows increase of 86% after 1,000 bending at a 1.5 cm radius, while single Al2O3 thin films increased by 367%.

In this study, nanoscale-thickness Al2O3 layers for moisture barrier films were developed by a spatially resolved remote plasma atomic layer deposition process. The effect of various process parameters was investigated on the atomic concentration of Al2O3 films including the substrate temperature, plasma power, and scanning speed of the substrates. Carbon components were identified as major impurities in the films and is reduced at high temperature, high plasma power and low speed. Optimum conditions are maximum temperature of 80 °C to prevent plastic substrate deformation, a maximum plasma power of 150 W without surface damage and maximum speed of 125 mm/sec to maintain a low carbon contents. The water vapor transmission rate (WVTR) of 3.2 × 10 −4 g/(m2·day) was achieved with 30 nm-thick film in optimum condition.

Stimuli-responsive delivery systems for cancer therapy have been increasingly used to promote the on-demand therapeutic efficacy of anticancer drugs and, in some cases, simultaneously generate heat in response to a stimulus, resulting in hyperthermia. However, their application is still limited due to the systemic drawbacks of intravenous delivery, such as rapid clearance from the bloodstream and the repeat injections required for sustained safe dosage, which can cause overdosing. Here, we propose a gold (Au)-coated nanoturf structure as an implantable therapeutic interface for near-infrared (NIR)-mediated on-demand hyperthermia chemotherapy. The Au nanoturf possessed long-lasting doxorubicin (DOX) duration, which helps facilitate drug release in a sustained and prolonged manner. Moreover, the Au-coated nanoturf provides reproducible hyperthermia induced by localized surface plasmon resonances under NIR irradiation. Simultaneously, the NIR-mediated temperature increase can promote on-demand drug release at desired time points. For in vivo analysis, the Au nanoturf structure was applied on an esophageal stent, which needs sustained anticancer treatment to prevent tumor recurrence on the implanted surface. This thermo- and chemo-esophageal stent induced significant cancer cell death with released drug and hyperthermia. These phenomena were also confirmed by theoretical analysis. The proposed strategy provides a solution to achieve enhanced thermo-/chemotherapy and has broad applications in sustained cancer treatments.

In this study, we synthesized mesoporous titanium dioxide (TiO2) nanoparticles and applied them to organic light-emitting diode (OLED) devices to improve the device efficiency by promoting light scattering in the device. Silver nanowire (AgNW) electrode was utilized as transparent anode for the OLEDs, because the AgNW anode integrated with a TiO2 scattering layer can be easily formed using a transfer process. When the mesoporous TiO2 nanoparticles were utilized, the OLED efficiency was improved by about 30% as compared with the case of amorphous TiO2 nanoparticles. This is because the refractive index and surface area of the mesoporous nanoparticles are larger than those of the amorphous ones, thereby further promoting the scattering of the light generated in the OLED device.

Due to the vulnerability of organic optoelectronic devices to moisture and oxygen, thin-film moisture barriers have played a critical role in improving the lifetime of the devices. Here, we propose a hexagonal boron nitride (hBN) embedded Al2O3 thin film as a flexible moisture barrier. After layer-by-layer (LBL) staking of polymer and hBN flake composite layer, Al2O3 was deposited on the nano-laminate template by spatial plasma atomic layer deposition (PEALD). Because the hBN flakes in Al2O3 thin film increase the diffusion path of moisture, the composite layer has a low water vapor transmission ratio (WVTR) value of 1.8 × 10−4 g/m2 day. Furthermore, as embedded hBN flakes restrict crack propagation, the composite film exhibits high mechanical stability in repeated 3 mm bending radius fatigue tests.

Hydrogenated amorphous carbon (a-C:H) films were deposited using inductively coupled C2H2 plasma, and the effect of process parameters on the sp2/sp3 hybridization ratio of the films was investigated. The sp2/sp3 ratio was deduced from the intensity ratios of the D and G peaks (ID/IG) observed in Raman spectra. The ion density in the C2H2 plasma was determined using an ion probe, and the relative density of CH and H radicals was quantified using optical actinometry. A high ID/IG ratio was observed at high substrate temperatures, and the high sp2/sp3 ratio is attributed to the loss of hydrogen atoms at high temperatures. A high ID/IG ratio was also observed with high plasma power and low pressure. The ID/IG ratio of the a-C:H films increased with increasing ion density in the C2H2 plasmas generated under various conditions, but decreased with the relative density of CH radicals. Ions remove hydrogen atoms from a-C:H films, and CH radicals introduce hydrogen atoms into a-C:H films. The etching resistance of a-C:H films was also investigated, wherein the etch rates of the a-C:H films decreased by 83.3% in the CF4 plasma and by 70.2% in the O2 plasma when the sp2/sp3 ratio was increased from 0.97 to 1.62.