Growth of GaN Nanowires on Epitaxial GaN

We report experiments on the formation of GaN nanowires on epitaxial GaN using thin layers of Ni. GaN covered with Ni shows roughening that is strongly dependent on the thickness of the Ni layer and the annealing conditions. With the initial Ni thickness of 0.8 nm we observe formation of Ni-filled antidots. These act as nucleation sites in the growth of GaN nanowires, allowing for the preparation of nanowires with an average diameter as small as 30 nm. Dense and well-oriented nanowires are formed by pulsed metallorganic chemical vapor deposition at 750°C. The size of the Ni features determines the diameter of the GaN nanowires, resulting in good control over the formation process.     

Catalyst-Free Direct Vapor-Phase Growth of Hexagonal ZnO Nanowires on <Emphasis>α</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The evolution of ZnO nanowires has been studied under supersaturation of Zn metal species with and without a ZnO thin-film buffer layer on α-Al₂O₃ deposited by the pulsed laser ablation technique. The nanowires had diameters in the range of 30 nm to 50 nm and lengths in the range of 5 μm to 10 μm with clear hexagonal shape and [000[`1]] [000\bar{1}] , [10[`1]1] [10\bar{1}1] , and [10[`1]0] [10\bar{1}0] facets. X-ray diffraction (XRD) measurements indicated crystalline properties for the ZnO nanostructures grown on pulsed laser deposition (PLD) ZnO nucleation layers. The optical properties were analyzed by photoluminescence (PL) and cathodoluminescence (CL) measurements. The ZnO nanowires were found to emit strong ultraviolet (UV) light at 386 nm and weak green emission as observed by PL measurements. The stoichiometry of Zn and O was found to be close to 1 by x-ray photoelectron spectroscopy (XPS) measurements. The process-dependent growth properties of ZnO nanostructures can be harnessed for future development of nanoelectronic components including optically pumped lasers, optical modulators, detectors, electron emitters, and gas sensors.     

The excellent spontaneous ultraviolet emission of GaN nanostructures grown on silicon substrates by thermal vapor deposition

In this study, GaN nanostructures were grown on p-Si (111) substrate by thermal chemical vapor deposition (TCVD). Ga vapor directly reacted with NH₃ solution in N₂ carrier gas flow of 2 L/min at different temperatures (950–1050 °C). The influence of NH₃ solution and growth temperature on the morphology, structure, optical and photoresponse properties of GaN nanostructures was investigated. Scanning electron microscopy images showed that the densities of the NWs varied with increasing temperature. The use of NH₃ solution and increased growth temperature improved the crystalline quality of GaN nanostructures. The photoluminescence (PL) spectra of nanostructures displayed a near band-edge (NBE) emission at around 363–367 nm. Higher growth temperature (1050 °C) resulted in a strong NBE emission with no yellow emission peak. With +5 V applied bias, the NWs metal–semiconductor–metal UV photodetector exhibited a high photocurrent of 1.6×10⁻³ A. The photocurrent to dark current contrast ratio was 120.     

Rational Design of Multifunctional Integrated Host Configuration with Lithiophilicity-Sulfiphilicity toward High-Performance Li–S Full Batteries

High-energy-density Li–S batteries are considered one of the next-generation energy storage systems, but the uncontrolled Li-dendrite growth in Li metal anodes and the shuttling of polysulfides in S cathode severely impede the commercial development of Li–S batteries. Herein, a conductive composite architecture that is made up of bio-derived N-doped porous carbon fiber bundles (N-PCFs) with co-imbedded cobalt and niobium carbide nanoparticles is employed as a multifunctional integrated host for simultaneously addressing the challenges in both Li anodes and S cathodes. The implantation of Co and NbC nanoparticles bestows the N-PCFs matrix with synergistically enhanced degree of graphitization, electrical conductivity, hierarchical porosity, and surface polarization. Theoretical calculations and experimental results show that NbC with specific lithiophilic and sulfiphilic features can synchronously regulate the Li and S electrochemistry by realizing homogeneous lithium deposition with suppressed Li-dendrite growth and exerting catalytic effects for promoting the polysulfide conversion together with fast Li₂S nucleation. Hence, the assembled Li–S full batteries exhibit a superb rate capability (704 mAh g⁻¹ at 5 C) and cycling life (≈82.3% capacity retention after 500 cycles) at a sulfur loading over 3.0 mg cm⁻², as well as high reversible areal capacity (>6.0 mAh cm⁻²) even at a higher sulfur loading of 6.7 mg cm⁻².     

Dendrite-Free Reverse Lithium Deposition Induced by Ion Rectification Layer toward Superior Lithium Metal Batteries

Considerable endeavors are developed to suppress lithium (Li) dendrites and improve the cycling stability of Li metal batteries in order to promote their commercial application. Herein, continuous zinc (Zn) nanoparticles-assembled film with homogenous nanopores is proposed as a modified layer for separator via a scalable method. The in situ formed LiZn alloy film during initial Li plating can serve as a Li⁺ ion rectification and lithiophilic layer to regulate the nucleation and reverse deposition of Li. When applied in Li|LiFePO₄ full cells with traditional carbonate-based electrolyte, the modified separator enables outstanding cycling stability of up to 350 cycles without capacity loss at a large rate of 5 C (3.4 mA cm⁻²) and a remarkable reversible capacity of 144 mAh g⁻¹ after 120 cycles at a commercial mass loading as high as 19.72 mg cm⁻². The excellent electrochemical performances are ascribed to the dendrite-free reverse Li deposition induced by modified layer by means of its lithiophilic property for regulating homogeneous Li nucleation on the separator as well as its well-distributed nanopores for homogenizing Li⁺ ion flux and enhancing electrolyte wetting.     

Water-Surface-Mediated Precise Patterning of Organic Single-Crystalline Films via Double-Blade Coating for High-Performance Organic Transistors

Application-oriented growth of patterned organic semiconductor (OSC) thin films with a single domain is a nonnegotiable requirement for the manufacturing of high-performance organic electronic devices. However, the prevalent selective-wetting patterning method remains a challenge in controlling the density of nucleation events in microscale spaces, resulting in thin films with high grain boundary density and no preferential orientation spherulites. Herein, a simple double-blade-coating printing technique using a combination of wetting-patterned substrates to produce an array of highly crystalline OSC thin films is developed. Specifically, the approach confines the OSC crystallization on a molecular-flat water surface in specific areas, enabling a significant reduction in the number of nuclei. Consequently, patterned 2,7-dioctyl[1]benzothieno[3,2-b] benzothiophene (C₈-BTBT) thin films comprising single-crystal domains are achieved with an exceptionally high yield of 62.5%. The organic field-effect transistor array developed from such patterns of C₈-BTBT single-crystalline films exhibits an excellent average mobility of 11.5 cm² V⁻¹ s⁻¹ which is 12.5-fold higher compared to that of the reference sample fabricated via conventional single-blade coating. It is believed that this approach can be widely applied to other soluble organic materials, thereby opening up opportunities for fabricating multicomponent integrated electronics.     

Growth behaviors of platinum-assisted GaN nanostructures in vapor–liquid–solid mechanism

This article reports the investigation of the growth behaviors of platinum-catalyzed GaN nanostructures grown via chemical vapor deposition method by manipulating growth temperature and ammonia flow rate. Morphological observation revealed the tapering behavior of GaN nanostructures at high growth temperatures and high ammonia flow rates in which the GaN nanowires were observed to be grown from the surface of GaN microcrystal structures. Growth mechanism of the tapering effect was discussed. X-ray diffraction showed the synthesized GaN nanostructures are of wurzite structure with no existence of impurities and found that GaN nanostructures grown at 1050 °C under ammonia flow rate of 250 sccm possessed the highest degree of crystallinity. Raman measurement exhibited no peak shift in E₂(high) while a redshift in A₁(LO) mode with rising growth temperatures, indicating the decreased of carrier concentration in the GaN nanostructures.     

Growth behavior and improved water–vapor-permeation-barrier properties of 10-nm-thick single Al2O3 layer grown via cyclic chemical vapor deposition on organic light-emitting diodes

We have investigated the growth behavior and water vapor permeation barrier properties of cyclic chemical vapor deposition (C-CVD)-grown 10-nm-thick single layer of Al₂O₃. Al₂O₃ layers grown by C-CVD showed a high density of 3.298 g/cm³ and were amorphous without grain boundaries. A deposition rate of 0.46 nm/cycle was obtained. The C-CVD system was self-limiting, as in the case of atomic layer deposition, which enables precise control of the thickness of the Al₂O₃ layer. A water vapor transmission rate of 1.51 × 10⁻⁵ (g/m²)/day was obtained from a Ca degradation test performed at 85 °C and 85% relative humidity. Moreover, the performance of organic light-emitting diodes, passivated by a C-CVD-grown 10-nm-thick Al₂O₃ single layer, was not affected after 24,000 h of turn-on time; this is strong evidence that C-CVD-grown Al₂O₃ layers effectively prevent water vapor from diffusing into the active organic layer.     

Controlling aggregation and crystallization of solution processed diketopyrrolopyrrole based polymer for high performance thin film transistors by pre-metered slot die coating process

The organic semiconductors have attracted much attention for plastic electronics due to their good solution processability, low temperature deposition, and compatible with large-area printing technology. The charge transport properties of polymer based field effect transistors are limited by their amorphous domains and weakly interaction between polymer chains. In this study, antisolvent like methanol is introduced to promote polymer chain aggregation, and slot die coating is used to finely tune the film morphology. The effects of anti-solvent introduction and slot die coating process on the device performance, e.g. charge transport, surface morphology, and solid state packing, were investigated in details. By optimizing the antisolvent ratio and polymer chain aggregation, the charge transport properties of the polymer devices were observed to be significantly improved. An average charge carrier mobility of 3.76 cm² V⁻¹ s⁻¹ and a maximum mobility of 4.10 cm² V⁻¹ s⁻¹ were achieved under optimized conditions. The controlling the aggregation degree by combining the mixed solvent system and slot die coating technique provides a convenient and practical approach to achieve high performance polymer field effect transistor.     

Strain-Invariant,Highly Water Stable All-Organic Soft Conductors Based on Ultralight Multi-Layered Foam-Like Framework Structures

Soft and flexible conductors are essential for the development of soft robots, wearable electronics, electronic tissue, and implants. However, conventional soft conductors are inherently characterized by a large change in conductance upon mechanical deformation or under alternating environmental conditions, e.g., humidity, drastically limiting their application potential. This work demonstrates a novel concept for the development of strain-invariant, highly elastic and highly water stable all-organic soft conductors, overcoming the limitations of previous strain-invariant soft conductors. For the first time, thin film deposition technologies are combined in a three-dimensional fashion, resulting in micro- and nano-engineered, multi-layered (<50 nm), ultra-lightweight (< 15 mg cm⁻³) foam-like framework structures based on Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and Polytetrafluoroethylene (PTFE), characterized by a highly strain-invariant conductivity (≈184 S/m) between 80% compressive and 25% tensile strain. Both the initial electrical and mechanical properties are retained during long-term cycling, even after 2000 cycles at 50% compression. Furthermore, the PTFE thin film renders the framework structure highly hydrophobic, resulting in stable electrical properties, even when immersed in water for a month. Such innovative multi-scaled and multi-layered functional materials are of interest for a broad range of applications in soft electronics, energy storage and conversion, sensing, water and air purification, as well as biomedicine.     

Contact-Barrier Free,High Mobility,Dual-Gated Junctionless Transistor Using Tellurium Nanowire

The gate-all-around nanowire transistor, due to its extremely tight electrostatic control and vertical integration capability, is a highly promising candidate for sub-5 nm technology nodes. In particular, the junctionless nanowire transistors are highly scalable with reduced variability due to avoidance of steep source/drain junction formation by ion implantation. Here a dual-gated junctionless nanowire p-type field effect transistor is demonstrated using tellurium nanowire as the channel. The dangling-bond-free surface due to the unique helical crystal structure of the nanowire, coupled with an integration of dangling-bond-free, high quality hBN gate dielectric, allows for a phonon-limited field effect hole mobility of 570 cm² V⁻¹ s⁻¹ at 270 K, which is well above state-of-the-art strained Si hole mobility. By lowering the temperature, the mobility increases to 1390 cm² V⁻¹ s⁻¹ and becomes primarily limited by Coulomb scattering. The combination of an electron affinity of ≈ 4 eV and a small bandgap of tellurium provides zero Schottky barrier height for hole injection at the metal-contact interface, which is remarkable for reduction of contact resistance in a highly scaled transistor. Exploiting these properties, coupled with the dual-gated operation, we achieve a high drive current of 216 μA μm⁻¹ while maintaining an on-off ratio in excess of 2 × 10⁴. The findings have intriguing prospects for alternate channel material based next-generation electronics.     

Highly-impermeable Al2O3/HfO2 moisture barrier films grown by low-temperature plasma-enhanced atomic layer deposition

Polymer substrates are essential components of flexible electronic applications such as OTFTs, OPVs, and OLEDs. However, high water vapor permeability of polymer films can significantly reduce the lifetime of flexible electronic devices. In this study, we examined the water vapor permeation barrier properties of Al₂O₃/HfO₂ mixed oxide films on polymer substrates. Al₂O₃/HfO₂ films deposited by plasma-enhanced atomic layer deposition were transparent, chemically stable in water and densely amorphous. At 60 °C and 90% relative humidity (RH) accelerated condition, 50-nm-thick Al₂O₃/HfO₂ had water vapor transmission rate (WVTR) = 1.44 × 10⁻⁴ g m⁻² d⁻¹, whereas single layers of Al₂O₃ had WVTR = 3.26 × 10⁻⁴ g m⁻² d⁻¹ and of HfO₂ had WVTR = 6.75 × 10⁻² g m⁻² d⁻¹. At 25 °C and 40% RH, 50-nm-thick Al₂O₃/HfO₂ film had WVTR = 2.63 × 10⁻⁶ g m⁻² d⁻¹, which is comparable to WVTR of conventional glass encapsulation.     

Consequences of twisting the aromatic core of N,N′-dimethylperylene-3,4,9,10-biscarboximide by chemical substitution for the electronic coupling and electric transport in thin films

Thin films of 1,6,7,12-tetrachloro-N,N^′-dimethylperylene-3,4,9,10-biscarboximide (Cl₄MePTCDI) prepared by physical vapor deposition (PVD) were compared to thin films of the unchlorinated N,N^′-dimethylperylene-3,4,9,10-biscarboximide (MePTCDI) to investigate the influence of a changed molecular structure on the electrical properties of the materials. The films were prepared on microstructured Si/SiO₂ substrates with interdigitated Au electrode arrays of 2 μm electrode distance or on quartz glass with electrode distances in the mm range. The films were investigated by conductance measurements, thermoelectric power, electric field effect, ultraviolet photoelectron spectroscopy (UPS) and atomic force microscopy (AFM). The thickness-dependence of the conductance measured during film growth (in situ) indicated a growth mode in islands (Volmer-Weber), which was confirmed by subsequent AFM. As expected, Cl₄MePTCDI was characterized as an organic n-type semiconductor. Charge transport occurred by a hopping mechanism as revealed by temperature-dependent thermopower and field-effect measurements. Effective electron mobilities at room temperature were found around 10⁻⁵ cm² V ⁻¹ s⁻¹ considerably lower than the values for MePTCDI. A rather constant concentration of mobile electrons of (1–2) × 10¹⁸ cm⁻³ was determined for both materials. The morphology of Cl₄MePTCDI islands indicated amorphous growth as opposed to crystals obtained for MePTCDI, as also revealed earlier by optical spectroscopy and the role of crystallinity in the electrical conduction is discussed.     

Nanoscale Film Thickness Gradients Printed in Open Air by Spatially Varying Chemical Vapor Deposition

Nanoscale films are integral to all modern electronics. To optimize device performance, researchers vary the film thickness by making batches of devices, which is time-consuming and produces experimental artifacts. Thin films with nanoscale thickness gradients that are rapidly deposited in open air for combinatorial and high-throughput (CHT) studies are presented. Atmospheric pressure spatial atomic layer deposition reactor heads are used to produce spatially varying chemical vapor deposition rates on the order of angstroms per second. ZnO and Al₂O₃ films are printed with nm-scale thickness gradients in as little as 45 s and CHT analysis of a metal-insulator-metal diode and perovskite solar cell is performed. By testing 360 Pt/Al₂O₃/Al diodes with 18 different Al₂O₃ thicknesses on one wafer, a thicker insulator layer (≈7.0 nm) is identified for optimal diode performance than reported previously. Al₂O₃ thin film encapsulation is deposited by atmospheric pressure chemical vapor deposition (AP-CVD) on a perovskite solar cell stack for the first time and a convolutional neural network is developed to analyze the perovskite stability. The rapid nature of AP-CVD enables thicker films to be deposited at a higher temperature than is practical with conventional methods. The CHT analysis shows enhanced stability for 70 nm encapsulation films.     

Floating Catalyst Chemical Vapor Deposition Patterning Nitrogen-Doped Single-Walled Carbon Nanotubes for Shape Tailorable and Flexible Micro-Supercapacitors

Micro-supercapacitors (MSCs) as high-power density energy storage units are designed to meet the booming development of flexible electronics, requiring simple and fast fabrication technology. Herein, a fast and direct solvent-free patterning method is reported to fabricate shape-tailorable and flexible MSCs by floating catalyst chemical vapor deposition (FCCVD). The nitrogen-doped single-walled carbon nanotubes (N-SWCNTs) are directly deposited on a patterned filter by FCCVD with designable patterns and facilely dry-transferred on versatile substrates. The obtained MSCs deliver an excellent areal capacitance of 3.6 mF cm⁻² and volumetric capacitance of 98.6 F cm⁻³ at a scan rate of 5 mV s⁻¹ along with excellent long-term cycle stability over 125 000 circles. Furthermore, the MSCs show good performance uniformity, which can be readily integrated via connection in parallel or series to deliver a stable high voltage (4 V with five serially connected devices) and large capacitance (5.1 mF with five parallel devices) at a scan rate of 100 mV s⁻¹, enabling powering the light emitting displays. Therefore, this method blazes the trail of directly preparing flexible, shape-customizable, and high-performance MSCs.     

MXene Functionalized,Highly Breathable and Sensitive Pressure Sensors with Multi-Layered Porous Structure

Breathable, flexible, and highly sensitive pressure sensors have drawn increasing attention due to their potential in wearable electronics for body-motion monitoring, human-machine interfaces, etc. However, current pressure sensors are usually assembled with polymer substrates or encapsulation layers, thus causing discomfort during wearing (i.e., low air/vapor permeability, mechanical mismatch) and restricting their applications. A breathable and flexible pressure sensor is reported with nonwoven fabrics as both the electrode (printed with MXene interdigitated electrode) and sensing (coated with MXene/silver nanowires) layers via a scalable screen-printing approach. Benefiting from the multi-layered porous structure, the sensor demonstrates good air permeability with high sensitivity (770.86–1434.89 kPa⁻¹), a wide sensing range (0–100 kPa), fast response/recovery time (70/81 ms), and low detection limit (≈1 Pa). Particularly, this sensor can detect full-scale human motion (i.e., small-scale pulse beating and large-scale walking/running) with high sensitivity, excellent cycling stability, and puncture resistance. Additionally, the sensing layer of the pressure sensor also displays superior sensitivity to humidity changes, which is verified by successfully monitoring human breathing and spoken words while wearing a sensor-embedded mask. Given the outstanding features, this breathable sensor shows promise in the wearable electronic field for body health monitoring, sports activity detection, and disease diagnosis.     

Very facile fabrication of aligned organic nanowires based high-performance top-gate transistors on flexible,transparent substrate

Aligned single-crystalline organic nanowires (NWs) show promising applications in flexible and stretchable electronics, while the use of pre-existing aligned techniques and well-developed photolithography techniques are impeded by the large incompatibility with organic materials and flexible substrates. In this work, aligned copper phthalocyanine (CuPc) organic NWs were grown on flexible and transparent poly(dimethylsiloxane) (PDMS) substrate via a grating-assisted growth approach. Furthermore, a simple yet efficient etching-assisted transfer printing (ETP) method was used to achieve CuPc NW array-based flexible top-gate organic field-effect transistors (OFETs) with a high mobility up to 2.0 cm² V⁻¹ s⁻¹, a small operating voltage within ±10 V, a high on/off ratio >10⁴, and excellent bend stability with bending radius down to 3 mm. It is expected that the high-performance organic NW array-based top-gate OFETs with exceeding bend stability will have important applications in future flexible electronics.     

Combining Janus Separator and Organic Cathode for Dendrite-Free and High-Performance Na-Organic Batteries

The growth of Na-dendrites and the dissolution of organic cathodes are two major challenges that hinder the development of sodium-organic batteries (SOBs). Herein, a multifunctional Janus separator (h-BN@PP@C) by using an interfacial engineering strategy, is proposed to tackle the issues of SOBs. The carbon layer facing the organic cathode serves as a barrier to capture dissolved organic materials and enhance their utilization. Meanwhile, the h-BN layer facing the Na anode possesses high thermal conductivity and mechanical strength, which mitigates the occurrence of localized-temperature “hot spots” and promotes the formation of a NaF-enriched SEI, thereby suppressing dendrite growth. Consequently, the Janus separator enables a stable Na plating/stripping cycling for 1000 h at 3 mA cm⁻². Equipped with the Janus separator, organic cathodes including dibenzo[b,i]thianthrene-5,7,12,14-tetraone (DTT), pentacene-5,7,12,14-tetrone and Calix[4]quinone cathodes demonstrate high capacity and remarkable cycling performance. In particular, the DTT exhibits a bipolar co-reaction storage mechanism and achieves an ultrahigh capacity (≈342.6 mAh g⁻¹), long-term cycling stability (capacity decay rate of 0.15% per cycle over 550 cycles at 500 mA g⁻¹) and fast kinetics (1000 mA g⁻¹≈2.8 C). This study offers a straightforward, effective, and promising solution to address the challenges in SOBs.     

Atom Probe Tomography of Zinc Oxide Nanowires

Wide-bandgap zinc oxide (ZnO) semiconductors and nanowires have become important materials for electronic and photonic device applications. In this work, we report the growth of well-aligned single-crystal ZnO nanowire arrays on sapphire substrates by chemical vapor deposition and the development of atom probe tomography, an emerging nanoscale characterization method capable of providing deeper insight into the three-dimensional distribution of atoms and impurities within its structure. Using a metal-catalyst-free approach, the influence of the growth parameters on the orientation and density of the nanowires were studied. The resulting ZnO nanowires were determined to be single crystalline, with diameter on the order of 50 nm to 150 nm and length that could be controlled between 0.5 μm to 20 μm. Their density was on the order of high 10⁸ cm⁻² to low 10⁹ cm⁻². In addition to routine characterizations using scanning and transmission electron microscopy, x-ray diffraction, photoluminescence, and Raman spectroscopy, we developed the atom probe tomography technique for ZnO nanowires, comparing the voltage pulse and laser pulse modes. In-depth analysis of the data was carried out to determine the accurate chemical composition of the nanowires and reveal the incorporation of nitrogen impurities. The current–voltage characteristics of individual nanowires were measured to determine their electrical properties.     

High-Performance Photodetector and Angular-Dependent Random Lasing from Long-Chain Organic Diammonium Sandwiched 2D Hybrid Perovskite Non-Linear Optical Single Crystal

3D organic-inorganic metal halide perovskites are excellent materials for optoelectronic applications due to their exceptional properties, solution processability, and cost-effectiveness. However, the lack of environmental stability highly restricts them from practical applications. Herein, a stable centimeter-long 2D hybrid perovskite (N-MPDA)[PbBr₄] single crystal using divalent N1-methylpropane-1,3-diammonium (N-MPDA) cation as an organic spacer, is reported. The as-grown single crystal exhibits stable optoelectronic performance, low threshold random lasing, and multi-photon luminescence/multi-harmonic generation. A photoconductive device fabricated using (N-MPDA)[PbBr₄] single crystal exhibits an excellent photoresponsivity (≈124 AW⁻¹ at 405 nm) that is ≈4 orders of magnitudes higher than that of monovalent organic spacer-assisted 2D perovskites, such as (BA)₂PbBr₄ and (PEA)₂PbBr₄, and large specific detectivity (≈10¹² Jones). As an optical gain media, the (N-MPDA)[PbBr₄] single crystal exhibits a low threshold random lasing (≈6.5 µJ cm⁻²) with angular dependent narrow linewidth (≈0.1 nm) and high-quality factor (Q ≈ 2673). Based on these results, the outstanding optoelectronic merits of (N-MPDA)[PbBr₄] single crystal will offer a high-performance device and act as a dynamic material to construct stable future electronics and optoelectronic-based applications.