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A novel fused porphyrinoid undergoes supramolecular assembly to form a persistently porous solution processable material for sensing of acetone vapour under high humidity using a membrane-type surface stress sensor.

Abstract Lithium-ion capacitors (LICs) are next-generation electrochemical storage devices that combine the benefits of both supercapacitors and lithium-ion batteries. Silicon materials have attracted attention for the development of high-performance LICs owing to their high theoretical capacity and low delithiation potential (~0.5 V vs. Li/Li+). However, sluggish ion diffusion has severely restricted the development of LICs. Herein, a binder-free anode of boron-doped silicon nanowires (B-doped SiNWs) on a copper substrate was reported as an anode for LICs. B-doping could significantly improve the conductivity of the SiNW anode, which could enhance electron/ion transfer in LICs. As expected, the B-doped SiNWs//Li half-cell delivered a higher initial discharge capacity of 454 mAh g−1 with excellent cycle stability (capacity retention of 96% after 100 cycles). Furthermore, the near-lithium reaction plateau of Si endows the LICs with a high voltage window (1.5-4.2V), and the as-fabricated B-doped SiNWs//AC LIC possesses the maximum energy density value of 155.8 Wh kg−1) at a battery-inaccessible power density of 275W kg−1. This study provides a new strategy for using Si-based composites to develop high-performance LIC.

1. Introduction Atomic layer depositions (ALD) of Al2O3 films are very essential technique to realize next generation electronic devices thanks to their high-k properties [1]. However, ALD-Al2O3 films usually suffer blistering during thermal treatments, which have caused serious problems for decades in the field of device fabrication [2]. Many groups have studied the cause of this phenomenon, and various models have been proposed. such as, stress at the interface between Al2O3 and Si [3], diffusion of Si atoms at the interface[4], residual H2O in the film after the ALD process [5], and aggregation of hydrogen atoms at the Al2O3/Si interface [6], and so on. However, the actual mechanism has hitherto remained unclear due to a lack of conclusive evidence. Here, in this study, we have tried to reveal the origin of this phenomenon using spectroscopic measurements [7]. As a result, we have succeeded in directly identifying the gas inside the blisters, which can be a concrete evidence to reveal the roots of a phenomenon that has long been obscured. 2. Experimental Procedure In the experiment, (100) oriented Si substrates with resistivity of 0.1-0.5 W∙cm were carried out. After cleaning the substrates by acetone, sulfuric-acid hydrogen-peroxide mixture solution, and hydrofluoric acid solution, all the substrates were loaded into ALD chamber which was heated up to 300oC. Then, Al2O3 layer with ~108 nm thickness was deposited on the substrates with conventional thermal ALD process using trimethylaluminum (TMA) and H2O as precursor gasses. After deposition, samples were annealed in rapid thermal annealing (RTA) furnace for 5 min with 400 – 1000 oC at N2 ambient. Finally the samples were characterized by laser microscopy, field emission scanning electron microscopy (FE-SEM), spectroscopic ellipsometry, and Raman spectroscopy. 3. Results and Discussions Figs. 1(a) and 1(b) show typical microscopic image of sample before, and after RTA (500oC, 5 min), respectively. We can clearly see that several blisters appear by annealing the samples, while there was no such sign before annealing. From the microscopic observations, we have summarized density of blisters as a function of RTA temperature in Fig. 2. Here, we can clearly see that by increasing RTA temperature, blister density increases, which is largely consistent with a previous result reported by O. Beldarrain et al, where 400-cycle Al2O3 layers were grown at 200 oC. To discuss the origin of the blister, we have conducted cross-sectional SEM observations of the formed blisters. Fig. 3 shows a typical SEM image of a blister after annealed at 500oC. The cross-sectional SEM observations clearly show that the blisters are completely hollow underneath. The surface of the flat Si substrate can also be seen under the blister, indicating that the upper Al2O3 film has completely delaminated from the interface between Si and Al2O3. From these results, we have speculated that blistering of Al2O3 after annealing is due to outgassing from the Al2O3/Si interface. Here, we came up with an idea that by identifying the gas inside the blisters, we can clarify the cause of this phenomenon. To identify the content inside blisters, Raman spectroscopy was carried out. The 532 nm wavelength laser used for Raman measurements can pass completely through Al2O3, making it possible to measure the gas inside without destroying the blisters. Fig. 4 shows a typical result of the Raman measurement of a blister of a sample after RTA (500oC). Here, as a result, characteristic spectra with peaks at positions ~4126, ~4144, ~4156, and ~4162 cm-1 were successfully observed. These four peaks can be assigned as peaks due to the difference in the rotational-quantum-number (J) of H2 as shown in Fig. 4, which is typical spectra of free H2 gas. These results provide evidence that blister formation is caused by the generation of hydrogen gas from the Al2O3/Si interface, a finding that is of great importance in clarifying the physics of blister formation mechanisms. In the presentation, we will also present details on the physics of hydrogen gas generation and methods to suppress blister formation. [References] [1] R. Zhang, et al., IEEE Trans. Electron Devices 59, 335-341, (2012). [2] G Dingemans, et al., J. Vac. Sci. Technol. A, 30, 040802, (2012). [3] J. Thurn., et al., J. Mater. Sci. 39, 4799, (2004) [4] M. Broas, et al., Appl. Phys. Lett. 111, 141606, (2017) [5] O. Beldarrain, et al., J. Vac. Sci. Technol. A, 31, 01A128 (2013) [6] D. G. Xie, et al., Nat. Mater., 14, 899, (2015). [7] R. Matsumura, et al., accepted to ACS Applied Materials & Interfaces, https://doi.org/10.1021/acsami.1c20660 Figure 1

In recent years, germanium (Ge) has attracted a lot of attention for the development of next generation devices due to its higher carrier mobilities compared with silicon (Si) and its compatibility for complementary metal-oxide-semiconductor (CMOS) applications. It is widely known that Ge is an indirect-band semiconductor like Si. However, by introducing tensile strain, the 136 meV difference between direct and indirect gaps can be reduced. Furthermore, in the case of 0.2-0.3% tensile strained Ge, n-type doping in the order of 1019 cm-3 were expected to be resulted in quasi direct-band light emission around 1550 nm wavelength. [1] The realization of this tensile strained n-Ge is promising for the integration of light sources on next generation Ge-based devices. Here, we focused on n-type Ge deposition using molecular beam epitaxy (MBE) method and have succeeded in realizing highly Sb-doped epitaxial n-Ge films by modulating the deposition temperatures. [2] Moreover, we have recently reported the crystallization of amorphous Ge by high-speed continuous wave laser annealing (CWLA), which more importantly also resulted in the introduction of 0.55-0.62% tensile strain. [3] In this study, we applied the similar annealing technique for crystallization of Sb-doped Ge toward the realization of tensile strained n-type Ge films. Sb-doped poly-crystalline Ge films with high Sb concentration (approximately 1019 cm-3) and thickness of about 100 nm were deposited on quartz substrate by molecular beam deposition at 450ºC substrate temperature. Then, 300 nm of SiO2 capping layer was deposited by sputtering in room temperature, such that the sample structure become that shown in Fig.1(a). The samples then annealed in the CWLA system equipped with Nd:YVO4 solid state laser with wavelength of 532 nm as the light source, which scan laser light at the speed (vscan) of 800 m/min. Also, the laser is focused to 20 μm diameter and shifted at 5 μm to scan the samples. Here, the laser power (Elaser) was changed from 300 to 1000 mW. After laser annealing, the capping layer were removed then the samples were characterized by micro-Raman spectroscopy. The annealed sample surface shows brighter contrast compared to the as-deposited samples, as shown in Fig.1(b) and (c), which indicate the structural change of Ge layer. Raman spectra measured at surface of annealed Ge layers are summarized in Fig.2. Here, Ge-Ge peak around 300.2 cm-1 confirmed on the samples, indicating the crystallization of the Ge layers. This peak is not shifted in low Elaser but largely shifted in high Elaser at up to -2.4 cm-1 for undoped and -3.6 cm-1 for the Sb-doped Ge films. This difference could be explained by the liquid phase recrystallization after Ge layer melted in high Elaser (≥600 mW). During recrystallization process, tensile strain is accumulated upon cooling as the tensile strain amount (0.43-0.63%) is agree with the thermal expansion value of Ge between solidification temperature and room temperature (-0.60%). This mechanism is similar to the crystallization of amorphous Ge films on quartz substrates in our previous work. [3] These results show the successful crystallization of tensile strained n-Ge layer by the CWLA method. This finding will be useful for the growth of Ge-based films and a promising step toward the development of CMOS-integrated optoelectronics. Further investigation of the annealing conditions and its relations with the properties of Sb-doped Ge films will be discussed in the main presentation. References Liu, J., Kimerling, L. C. & Michel, J. Semicond. Sci. Technol. 27, (2012). Saputro, R.H., Matsumura, R. & Fukata, N. Cryst. Growth & Des. 21, 6523–6528 (2021). Matsumura, R. & Fukata, N. ECS J. Solid State Sci. Technol. 9, 063002 (2020). Figure 1

Heavily doped n-type Ge crystals are essential for Ge-based electronics and optical applications. In this report, we describe the mechanism of dopant redistribution via out-diffusion and re-evapora...

Formic acid (HCOOH) is an important intermediate in chemical synthesis, pharmaceuticals, the food industry, and leather tanning and is considered to be an effective hydrogen storage molecule. Direct contact with its vapor and its inhalation lead to burns, nerve injury, and dermatosis. Thus, it is critical to establish efficient sensing materials and devices for the rapid detection of HCOOH. In the present study, we introduce a chemical sensor based on a quartz crystal microbalance (QCM) sensor capable of detecting trace amounts of HCOOH. This sensor is composed of colloidal phenyl-terminated carbon nitride (Ph-g-C3N4) quantum nanoflakes prepared using a facile solid-state method involving the supramolecular preorganization technology. In contrast to other synthetic methods of modified carbon nitride materials, this approach requires no hard templates, hazardous chemicals, or hydrothermal treatments. Comprehensive characterization and density functional theory (DFT) calculations revealed that the QCM sensor designed and prepared here exhibits enhanced detection sensitivity and selectivity for volatile HCOOH, which originates from chemical and hydrogen-bonding interactions between HCOOH and the surface of Ph-g-C3N4. According to DFT results, HCOOH is located close to the cavity of the Ph-g-C3N4 unit, with bonding to graphitic carbon and pyridinic nitrogen atoms of the nanoflake. The sensitivity of the Ph-g-C3N4-nanoflake-based QCM sensor was found to be the highest (128.99 Hz ppm-1) of the substances studied, with a limit of detection (LOD) of HCOOH down to a sub-ppm level of 80 ppb. This sensing technology based on phenyl-terminated attached-g-C3N4 nanoflakes establishes a simple, low-cost solution to improve the performance of QCM sensors for the effective discrimination of HCOOH, HCHO, and CH3COOH vapors using smart electronic noses.

Direct photocatalytic oxidation of methane to liquid oxygenated products is a sustainable strategy for methane valorization at room temperature. However, in this reaction, noble metals are generally needed to function as cocatalysts for obtaining adequate activity and selectivity. Here, we report atomically dispersed nickel anchored on a nitrogen-doped carbon/TiO2 composite (Ni-NC/TiO2) as a highly active and selective catalyst for photooxidation of CH4 to C1 oxygenates with O2 as the only oxidant. Ni-NC/TiO2 exhibits a yield of C1 oxygenates of 198 μmol for 4 h with a selectivity of 93%, exceeding that of most reported high-performance photocatalysts. Experimental and theoretical investigations suggest that the single-atom Ni-NC sites not only enhance the transfer of photogenerated electrons from TiO2 to isolated Ni atoms but also dominantly facilitate the activation of O2 to form the key intermediate •OOH radicals, which synergistically lead to a substantial enhancement in both activity and selectivity.

Schottky junction photovoltaic devices were successfully assembled by using nanowire shaped graphene sheets grown on-site onto nano-imprint lithography silicon nanowires (SiNWs). Graphene formation was accomplished by rapid CVD synthesis on nickel catalysts deposited on SiNWs. The graphene remains on the SiNWs after the underlying metal catalyst is wet etched, forming a graphene-Si 3D-junction. The SiNWs substrate contributes light trapping qualities while the NW-shaped graphene increases the carrier collecting area compared to flat graphene resting on SiNWs. Complicated graphene transfer procedures could be avoided, and the process is capable of being scaled up. Simple SiNW-based devices improved the power conversion efficiency (PCE) and ease of fabrication compared to equivalent planar-type controls and could reach a PCE up to 2.19% without doping, or 3.83% after p-type doping with AuCl3. High recombination losses likely limited device performance in this simple system, necessitating future improvements in graphene quality and interface engineering.

Silver and gold nanostructures were fabricated by thermal deposition followed by laser annealing on novel type substrates - diamond abrasive films and scratched quartz plates. The morphology and optical properties of the nanostructures were studied and they were applied for surface-enhanced Raman spectroscopy of the insecticide Karate Zeon 5 CS (lambda-cyhalothrin). The limit of detection of about ≈50 µM was estimated.

A gold nanoparticle-decorated graphene oxide (GO-AuNP) hybrid material was prepared by using the chemical reduction method. The obtained results showed that the AuNPs of about of 15 nm are well bound on the surface of GO. The GO-AuNP hybrid material was used for transparent conductive film (TCF) and organic/inorganic hybrid solar cells. The TCF based on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) containing GO-AuNPs was fabricated at room temperature. The obtained results show that the TCF containing 0.5 wt% GO-AuNPs has a high transmittance of 69.7% at 550 nm, a low sheet resistance of 50.5 Ω □

In recent years, Ge-based semiconductor materials has attracted a lot of attention for its possibility of higher mobility channel formation, toward next-generation complementary metal-oxide-semiconductor (CMOS) transistors. For this material to reach its potential, formation and optimization of p-n junction, which is the fundamental structure for a practical device, need to be investigated. In most cases, dopant ions are injected to form dopant-enriched films at the semiconductor interface, followed by annealing with various possible techniques1. However, crystal damages caused by high implantation energy makes it difficult to recrystallize and activate the dopant atoms. In this research, in-situ doping of Sb in epitaxial Ge layers grown on crystalline p-Ge substrates were studied, aiming a vertical p-n diode with higher Sb doping while maintaining good crystal quality. Formation of highly doped n-Ge is one of the most crucial challenges, as it was reported that uniform doping distribution across the layers are difficult to be achieved, which potentially deteriorate the crystallinity of the n-Ge layer2,3. Therefore, a study to overcome the doping problems in n-Ge, can lead to wider application of Ge-based devices. The p-Ge substrates were treated by ultrasonic cleaning in Acetone followed by a diluted-HF dip and de-ionized water rinse. The cleaned substrate then loaded into molecular beam epitaxy (MBE) chamber (base pressure of 10-8 Pa) and subjected to thermal cleaning at 450 ºC for 10min. Subsequently, Ge film were homo-epitaxially grown on the p-Ge substrate using the Knudsen cell (K-cell) that heated around 1100 ºC to maintain a fixed 0.2 Å/s deposition rate. At the same time Sb source was evaporated by heating the Sb K-cell (Tdop.: 325-400 ºC) for the in-situ doping deposition. Here, the depositions of Sb-doped Ge layer were performed on the p-Ge substrate at fixed temperature of 450 ºC. The Sb contents in the epitaxial layer were quantitatively evaluated by the secondary ion mass spectrometry (SIMS), and a reflection high-energy electron diffraction (RHEED) system equipped on the MBE chamber was used to monitor the epitaxial growth during depositions. Moreover, the crystal quality also characterized by the Raman spectroscopy method. After the deposition of 100 nm Sb-doped Ge layer, the samples then used to form vertical p-n diode structures using a conventional lithography method as shown in Fig. 1. The depth profiles obtained by SIMS measurements shows that high amount of Sb atoms (>1019 cm-3) was incorporated into the epitaxial Ge layer (Fig 2(a)). It also shows that Sb atomic concentrations vary with the Sb K-cell temperatures (Tdop.), in which higher temperature (Tdop.: 400 ºC) resulted in higher Sb concentration. The epitaxial growth of Sb-doped Ge layer was observed using the RHEED system, which resulted in a streaky pattern of the diffracted electron beam as seen in the inset of Fig. 2(b). The crystallinity of the epitaxial layer also matched with the results obtained by of Raman measurement shown in Fig.2(b). A strong Ge-Ge phonon peak at similar position to the reference crystalline Ge (at 300.2 cm-1) was obtained for both Tdop.: 325 ºC and 400 ºC samples. This result indicates the growth of Ge crystals with high crystallinity despite the high Sb content. Fig. 2(c) shows rectifying properties for vertical p-n junctions using these samples, where the current obtained at forward bias is much higher than that obtained at reverse bias (ION >> IOFF ). Interestingly, this p-n diode rectifying behavior was also improved (higher ION /IOFF ratio) with the increase of dopant concentrations. The relation between Sb concentration and electrical properties can be explained by the dopant activation rate in the Sb-doped Ge layer, because higher amount of Sb atoms increases the electron doping density. This result clearly shows that highly doped n-Ge layer was formed on the top of p-Ge. This can be expected a useful method for the formation of next-generation vertical transistors where n+-Ge is utilized in source/drain formation. Further investigation about the growth conditions and its relations with electrical properties of the vertical p-n diodes will be discussed in the main presentation. References Sgourou, E. N., Panayiotatos, Y., Vovk, R. V., Kuganathan, N. & Chroneos, A. Diffusion and dopant activation in germanium: Insights from recent experimental and theoretical results. Appl. Sci. 9, (2019). Yurasov, D. V. et al. Antimony segregation in Ge and formation of n-type selectively doped Ge films in molecular beam epitaxy. J. Appl. Phys. 118, (2015). Sawano, K. et al. Ultrashallow Ohmic contacts for n-type Ge by Sb δ -doping. Appl. Phys. Lett. 97, 2008–2011 (2010). Figure 1

Fluorometric quantification of biological molecules is a key feature used in many biosensing studies. Fluorescence resonance energy transfer (FRET) using highly fluorescent quantum dots offers highly sensitive detection of the in-proximity wide variety of analyst molecules. In this contribution, we report the use of carbon quantum dots (CDs) for the ultrasensitive optical biosensing of cancer antigen 125 (CA-125) in the early malignant stage. This approach is based on monitoring the quenching of CDs luminescence at 535 nm by CA-125 after excitation at 425 nm and pH 10. The calibration of this method was performed in the concentration range of CA-125 from 0.01 to 129 U ml−1 (R2 = 0.99) with a detection limit of 0.66 U ml−1, which matches remarkably with the standard chemiluminometric method in control and real patient samples. The sensing mechanism for cancer antigen 125 assessment was discussed on the basis of fluorescence quenching of CDs and time-resolved photoluminescence spectroscopy. The current method is easy, sensitive, cost-effective and provides a wide range of validity, which helps in overcoming the limitations of high cost and time consumption exhibited by many other traditional clinical assays for CA-125 quantification.

Vertical-oriented silicon nanowire (SiNW) arrays with shaped smooth, nanodot-, or NW-structured surfaces offer many desirable advantages for advanced device applications. In this study, these functionalized SiNW formations were simplified by ex situ preparation of an aluminum (Al) catalyst along with optimization of the substrate temperature and time during vapor-liquid-solid chemical vapor deposition as a one-step process. SiNW-based photovoltaic cells were demonstrated with minimized NW surface defects through NW surface modification, opening a new path for the development of versatile Al-catalyzed SiNWs as a material of choice for on-chip integration in future nanotechnologies.

Chromophores that generate singlet oxygen (

The release of untreated industrial wastewater creates a hazardous impact on the environment. In this regard, the development of an environmentally friendly catalyst is of paramount importance. Here, we report a highly efficient and reusable core-shell TiN/SiO2/Cr-TiO2 (TSCT) photocatalyst that is composed of SiO2-cladded titanium nitride (TiN) nanoparticles (NPs) decorated with Cr-doped TiO2 NPs for the removal of organic contaminants from water. The TiN NPs serve as the main light absorber component with excellent visible-light absorption along with Cr-TiO2 NPs. The TSCT shows remarkable improvement in the photodecomposition of methylene blue (MB) over Cr-TiO2 and TiO2 NPs. An efficient structural design is proposed by adopting calcium alginate beads (P-Marimo beads) as a transparent scaffold for supporting our TSCT, which floats nature on the water surface and realizes easy handling as well as excellent reusability for multipurpose water purification. Surprisingly, our TSCT is found to keep its catalytic activity even after the illumination is turned off. Our proposed P-Marimo-encapsulated TSCT can be utilized as an excellent green photocatalyst with high photocatalytic performance, good recyclability, and easy handling.

Singlet oxygen sensitization involving a class of hemiquinonoid-substituted resorcinarenes prepared from the corresponding 3,5-di-t-butyl-4-hydroxyphenyl-substituted resorcinarenes is reported. Based on variation in the molecular structures, quantum yields comparable with that of the well-known photosensitizing compound meso-tetraphenylporphyrin were obtained for the octabenzyloxy-substituted double hemiquinonoid resorcinarene reported herein. The following classes of compounds were studied: benzyloxy-substituted resorcinarenes, acetyloxy-substituted resorcinarenes and acetyloxy-substituted pyrogallarenes. Single crystal X-ray crystallographic analyses revealed structural variations in the compounds with conformation (i.e., rctt, rccc, rcct) having some influence on the identity of hemiquinonoid product available. Multiplicity of hemiquinonoid group affects singlet oxygen quantum yield with those doubly substituted being more active than those containing a single hemiquinone. Compounds reported here lacking hemiquinonoid groups are inactive as photosensitizers. The term ‘fuchsonarene’ (fuchson + arene of resorcinarene) is proposed for use to classify the compounds.

We show here that MOF-5, a sample Zn-based MOF, can uniquely transform into distinct zinc oxide nanostructures. Inspired by the interconversion synthesis of zeolites, we converted MOF-5 into nanocrystalline ZnO. We found the conversion of MOF-5 into ZnO to be tunable and straightforward simply by controlling the treatment temperature and choosing an appropriate structure-directing agent (SDA). Refined X-ray diffraction (XRD) patterns showed that a synthesis temperature of 180 °C (sample ZnO-180) was optimal for achieving high crystallinity. We examined ZnO-180 with high-resolution transmission electron microscopy (HRTEM), which confirmed that the samples were made of individual crystallites grown along the c-axis, or the (001) direction, thus exposing lower energy surfaces and corroborating the XRD pattern and the molecular dynamics calculations. Further investigations revealed that the obtained ZnO at 180 °C has a superior photocatalytic activity in degrading methylene blue to other ZnO nanostructures obtained at lower temperatures.

Herein, the effect of nanostructured silicon and gold nanoparticles (AuNPs) on the power conversion efficiency (PCE) of an n-type silicon/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (n-Si/PEDOT:PSS) hybrid solar cell was investigated. The Si surface modified with different nanostructures including Si nanopyramids (SiNPs), Si nanoholes (SiNHs) and Si nanowires (SiNWs) was utilized to improve light trapping and photo-carrier collection. The highest power conversion efficiency (PCE) of 8.15% was obtained with the hybrid solar cell employing SiNWs, which is about 8%, 20% and 40% higher compared to the devices using SiNHs, SiNPs and planar Si, respectively. The enhancement is attributed to the low reflectance of the SiNW structures and large PEDOT:PSS/Si interfacial area. In addition, the influence of AuNPs on the hybrid solar cell's performance was examined. The PCE of the SiNW/PEDOT:PSS hybrid solar cell with 0.5 wt% AuNP is 8.89%, which is

Silicon (Si) films were deposited on low-cost graphite substrates by the electrochemical reduction of silicon dioxide nanoparticles (nano-SiO2) in calcium chloride (CaCl2), melted at 855 °C. Cyclic voltammetry (CV) was used to analyze the electrochemical reduction mechanism of SiO2 to form Si deposits on the graphite substrate. X-ray diffraction (XRD) along with Raman and photoluminescence (PL) results show that the crystallinity of the electrodeposited Si-films was improved with an increase of the applied reduction potential during the electrochemical process. Scanning electron microscopy (SEM) reveals that the size, shape, and morphology of the Si-layers can be controlled from Si nanowires to the microcrystalline Si particles by controlling the reduction potentials. In addition, the morphology of the obtained Si-layers seems to be correlated with both the substrate materials and particle size of the feed materials. Thus, the difference in the electron transfer rate at substrate/nano-SiO2 interface due to different applied reduction potentials along with the dissolution rate of SiO2 particles during the electrochemical reduction process were found to be crucial in determining the microstructural properties of the Si-films.

A new method of introducing nanopores with spongy morphology during fabrication of size and pitch controlled flexible silicon microwires (SiMWs) in wafer scale is presented using nanosphere lithography technique in addition to metal catalyzed electroless etching technique by varying concentration of oxidant and introducing surfactant or co-solvents to the etching solution. For achieving self-assembled monolayer closed-pack pattern of SiO2 microparticles in wafer-scale simple spin coating process was used. The effect of variation of the etchant, oxidant and surfactant on the morphology and optical properties of SiMWs were studied. By simply controlling the diameter of SiO2 microparticles and concentration of H2O2 the size of the MWs as well as the introduction of pores could be controlled in wafer-scale. Average reflectance suppressed to below 8% in the broad spectral range of 400-800 nm for these porous, spongy and flexible SiMW arrays in wafer scale. The mechanism behind this formation of spongy, porous and flexible nature of the SiMWs is also demonstrated for a better understanding of the etching process., Comment: 22 pages 10 Figures

The catalyst-free formation of silicon (Si) and germanium (Ge) core-shell and core-double shell nanowires (NWs) was studied for use as building blocks of high electron (hole) mobility transistors (HEMTs). Vertically aligned p-type Si (p-Si)/intrinsic Ge (i-Ge) core-shell NWs and p-Si/i-Ge/p-Si core-double shell NWs with uniform diameters were formed by combining nanoimprint lithography, Bosch etching, and chemical vapor deposition. The boron (B) doping process was used to prepare p-Si NWs. The hole gas accumulation could be reliably detected from the i-Ge shell region in the p-Si/i-Ge core-shell NW and p-Si/i-Ge/p-Si core-double shell NW arrays through the Fano resonance effect, showing that core-shell NW heterostructures can suppress impurity scattering and act as high-mobility transistor channels. This provides the possibility for the future creation of vertical high-speed transistors.

Ge1-xSnx nanowires (NWs) have been a focus of research attention for their potential in realizing next-generation Si-compatible electronic and optoelectronic devices. To control the growth of NWs and increase their Sn content, the growth mechanism needs to be understood. The use of Au-Sn alloy catalysts instead of Au catalysts allows an easier understanding of Ge1-xSnx NW growth, and the effects of Sn at different concentrations in catalysts on growth direction, Sn incorporation, and crystallinity of Ge1-xSnx NWs can be clarified. High Sn content in Au-Sn alloy catalysts favors ⟨110⟩-oriented NW growth and high Sn incorporation in NWs. The higher Sn content in Au-Sn alloy catalysts also improves the crystallinity of NWs.

Vacancies have been demonstrated to be significant for CO2 reduction reaction (CO2RR) over ZnS, but anion vacancies were easily refilled with oxygen species and could work as both H2 and CO evoluti...

Photocatalytic CO2 reduction reaction (CO2RR) on a heterogeneous catalyst offers the possibility for CO2 abatement and emerges as a promising avenue for renewable carbonaceous fuels production at ambient temperature and pressure using solar light as the sole energy input. Here, we report a newly aqueous colloidal comprised of monodispersed Ni-doped ZnS (ZnS:Ni) nanocrystals as excellent visible-light-responsive photocatalysts for CO2RR into formate. The wavelength-dependent quantum yield shows a significant contribution of Ni doping for visible light activity. A high selectivity (>95%) of HCOOH production and remarkable quantum efficiency of 59.1% at 340 nm and 5.6% at 420 nm are obtained over ZnS:Ni (0.1%) colloidal nanocrystals modified by Cd2+. The proper balance between sulfur vacancies and extended visible light absorption of the constructed colloidal ZnS:Ni nanocrystals contributes to the prominent performance for CO2RR. However, excessive doping of Ni does not guarantee an increase of photocatalytic CO2RR due to a diminish of sulfur vacancies. The regulation of sulfur vacancies by Ni doping and their interplay on photocatalytic CO2RR activity are presented and discussed. This work provides an in-depth insight of the role of dopant on vacancy modulation in photocatalyst beyond light absorption and a guidance for design of the potential photocatalyst for CO2RR.

The combination of organic dyes with quantum dots (QDs) in solar cells can lead to more improvement in photovoltaic performance for such types of solar cells. Due to the quantum confinement, the photoluminescence (PL) of QDs can be tuned to match the absorption spectra of applied organic dyes. Herein, we introduce a new hybrid solar cell based on monomethine cyanine dye co-sensitized by CdS and CdTe/CdS core shell. The cyanine dye tends to aggregate on the surface of colloidal QDs due to electrostatic attraction followed by energy and electron transfer from QDs to cyanine dye. Electrophoretic deposition method was carried out to assist the cyanine dye loading on the surface of TiO2 thin film and the highest power conversion efficiency was 0.89% in case of cyanine dye co-sensitized by CdTe/CdS with open circuit voltage of 0.78 V and a photocurrent of 1.80 mA/ cm2.

A high-efficiency (14.3%) solar cell using silicon nanopencils (SiNPs) was achieved by controlling surface carrier recombination and nanostructure morphology. Radial p-n junction nanopencils have several advantageous features that derive from their asymmetric structure, which enables excellent broad-band absorption and light trapping. The surface carrier recombination problem caused by plasma etching was solved using a chemical polish etching (CPE) method. The control of CPE treatment and SiNP morphology can reduce the surface recombination and increases the effective junction area. And bulk recombination was minimized by reducing the wafer thickness. These techniques have the potential to achieve low-cost and high-efficiency photovoltaic cells.

Mechanical resonators have wide applications in sensing bio-chemical substances, and provide an accurate method to measure the intrinsic elastic properties of oscillating materials. A high resonance order with high response frequency and a small resonator mass are critical for enhancing the sensitivity and precision. Here, we report on the realization and direct observation of high-order and high-frequency silicon nanowire (Si NW) resonators. By using an oscillating electric-field for inducing a mechanical resonance of single-crystalline Si NWs inside a transmission electron microscope (TEM), we observed resonance up to the 5th order, for both normal and parametric modes at ∼100 MHz frequencies. The precision of the resonant frequency was enhanced, as the deviation reduced from 3.14% at the 1st order to 0.25% at the 5th order, correlating with the increase of energy dissipation. The elastic modulus of Si NWs was measured to be ∼169 GPa in the [110] direction, and size scaling effects were found to be absent down to the ∼20 nm level.

The design of hydroxyapatite (HA) nanoarchitecture is critical for fabricating artificial bone tissues as it dictates the biochemical and the mechanical properties of the final product. Herein, we incorporated a simple hard-template approach to synthesise single crystal nanoplates of HA. We used the 2D graphitic nitride (g-C3N4) material to prepare an HA sol-gel under hydrothermal conditions. A new HA nanostructure was then formed during the calcination and removal of g-C3N4 at a higher temperature, which finally led to the production of nanoplates (thickness of ∼100 nm) while in lateral dimension the average size was in the micrometre scale. We characterised the synthesised HA nanoplates with XRD, TEM, and HRTEM. The theoretically predicted nanostructure construction based on Wulff's method is in full agreement with the experimental observations. We then prepared different weight ratios of HA and polylactic acid (PLA) composites for artificial 3D bone fabrication. The strong interaction between PLA and HA's (110) facet, which was the second most prevalent, resulted in the composite's mechanical robustness. After mechanical testing, an optimum ratio was selected for biological studies and 3D printing. Biological experiments demonstrated that the synthesised composite had excellent viability in vitro.

One-dimensional germanium (Ge)-related nanostructures including core–shell nanowires and nanotubes with high specific surface area show enhanced performance in energy storage and electronic devices, and their structural control is important for further improving their performance and stability. In this work, we fabricated vertically formed ZnO/Ge core–shell nanowires with different shell thicknesses. The dependence of morphology, crystallinity, and internal stress of the nanowires on the shell growth time and temperature was investigated. By applying the wet-etching method to the ZnO/Ge core–shell heterojunction nanowires, we demonstrated the Ge nanotube fabrication and stress relaxation in Ge after ZnO core removal.

Due to their novel physical properties, semiconductor nanowires are of great research interest. To realize novel devices that feature them, however, they need to be modified. One of the most well-known, important and effective functionalization techniques is impurity doping: this will be the key to the application of nanowires to metal oxide field-effect transistors, solar cells, sensors, and similar devices. To control doping and obtain superior properties, it is important to fine-tune the impurity doping process to a high level of precision. In this chapter, several doping methods such as ex situ, in situ, and surface doping are described. Each method has its own advantages and disadvantages for impurity doping of nanowire structures. The characterization of dopant atoms is also important to understand the status and behaviors of dopant atoms in nanowire structures and to control their properties.

The paper describes the preparation of advanced Ag and Au nanostructures via thermal deposition on three gradual grades of microabrasive processed (100) SiO2 substrates and the investigation of their morphology and optical properties. The quartz substrates were manually dry scratched in advance with three grades (0.1, 0.5, or 1 μm) of diamond supper-abrasive slurry coated on high precision polyester film. The deposition of Ag or Au was first applied, and then the films were laser annealed. The as-prepared nanostructures were used for surface-enhanced Raman spectroscopy analyses of neonicotinoid insecticide Mospilan 20 SP, which contains acetamiprid, in quantities much smaller than that usually applied in the agricultural medicine.