Thermal Etching Research Articles

Oriented thermal etching of hollow carbon spheres with delicate heat management for efficient solar steam generation

Hollow carbon spheres (HCSs) with controllable morphology and structure have received considerable attention in the field of energy conversion and storage. Herein, monodispersed HCSs with cavity sizes tuned from 100 nm to 800 nm and shell thickness from 450 nm to 50 nm were successfully synthesized through a unique template-free thermal-etching method. It was evidenced that the dynamically controllable synthesis of HCSs was attributed to the “inside-out” oriented thermal oxidation etching of carbon spheres (CSs) induced by the differentiated “core-shell” chemical structures. Comparing to CSs, the obtained HCSs exhibited much increased efficiency for solar-driven interfacial steam generation (SISG), reaching as high as 88.9%, which outperforms most of the previously reported carbon-based materials. It was then demonstrated that the rational heat management for both photothermal and thermal-evaporation conversion is essential to achieve satisfying SISG efficiency. Depending on the increasing cavity sizes, HCSs presented gradual increases in both photothermal conversion and thermal-evaporation performances, mainly attributed to the improved light absorption and the delicate heat management, respectively. However, the further increase in cavity size resulted in excessive heat loss and presented decreased thermal-evaporation performance. This work provides an alternative and promising approach to the reasonable design of hollow nanostructures with delicate heat management for efficient SISG as well as other solar energy conversion applications.

2D Graphitic Carbon Nitride for Energy Conversion and Storage

AbstractGraphitic carbon nitride (g‐C3N4) have attracted great attention in the field of energy conversion and storage due to its unique layered structure, tunable bandgap, metal‐free characteristic, high physicochemical stability, and easy accessibility. 2D g‐C3N4 nanosheets have the features of short charge/mass transfer path, abundant reactive sites and easy functionalization, which are beneficial to optimizing their performance in different fields. However, the reviews of the comprehensive applications of 2D g‐C3N4 for energy conversion and storage are rare. Herein, this review first introduces the physicochemical properties of bulk g‐C3N4 and g‐C3N4 nanosheets, and then summarizes the synthetic strategies of 2D g‐C3N4 nanosheets in detail, such as thermal oxidation etching, chemical exfoliation, ultrasonication‐assisted liquid phase exfoliation, chemical vapor deposition, and others. Emphasis is focused on the rational design and development of 2D g‐C3N4 nanosheets for the diversified applications in energy conversion and storage, including photocatalytic H2 evolution, CO2 reduction, electrocatalytic H2 evolution, O2 evolution, O2 reduction, alkali‐metal ion batteries, lithium‐metal batteries, lithium–sulfur batteries, metal‐air batteries, and supercapacitors. Finally, the current challenges and perspectives of 2D g‐C3N4 nanosheets for energy conversion and storage applications are discussed.

Modelling the Growth and Etch of Thin Film Metal Oxides

HfO2 and ZrO2 are two high-k materials that are crucial in semiconductor devices. Atomic level control of material processing is required for fabrication of thin films of these materials at nanoscale device sizes. Atomic layer deposition (ALD) and thermal atomic layer etching (ALE) allow fabrication of ultra-thin films for semiconductor device processing. ALD is a well-known metal oxide thin film deposition technique in which metal and oxygen containing precursors are added sequentially to the reactor to ensure self-limiting precursor adsorption and reaction to enable a high level of control over film thickness. Thermal ALE, which is a relatively modern technique, uses self-limiting fluorination (using hydrogen fluoride exposure) and subsequent ligand exchange reactions at elevated temperatures to remove up to a monolayer of the metal oxide material. This modern approach for controlled etching is the reverse of ALD and removes only the fluorinated layer.Given that it is difficult to investigate ALD and ALE reactions directly using experimental techniques, first-principles-based atomic-level simulations using density functional theory (DFT) can give deep insights into the precursor chemistry and the reactions that drive the deposition and etch of different materials. This contribution presents first principles density functional theory modelling to examine the growth and etch of thin films of HfO2 and ZrO2. Concerning the ALD reaction, the adsorption mechanism of precursors TDMAHf and TDMAZr are studied at the bare and hydroxylated surfaces of HfO2 and ZrO2 respectively. Stable OH coverages of 0.50 ML and 0.63 ML on the surfaces of HfO2 and ZrO2 were found respectively. Ligand loss from the metal precursor can be achieved by protonation from the OH terminated surface of both metal oxides. Concerning the ALE reaction, HF exposures on the surfaces of HfO2 and ZrO2 are studied. HF coverages ranging from 1.0 ± 0.3 to 17.0 ± 0.3 HF/nm2 are investigated and a mixture of molecularly and dissociatively adsorbed HF molecules is present at higher coverages. Theoretical etch rates of -0.61 ± 0.02 Å /cycle for HfO2 and -0.57 ± 0.02 Å /cycle ZrO2 were calculated using maximum coverages of 7.0 ± 0.3 and 6.5 ± 0.3 M-F bonds/nm2 respectively (M = Hf, Zr).

(Invited) Novel Chemistries for Layer-by-Layer Etching of 2D Semiconductor Coatings and Organic-Inorganic Hybrid Materials

Here we report two new advances in atomic layer etching (ALEt) that extend our range of capabilities in nanoscale device fabrication. Semiconductor device manufacturing is limited by our ability to precisely deposit and remove thin film layers at the various levels of multistep device fabrication processes. Consequently, innovations in atomic layer deposition (ALD) and etching methods are essential. ALD-based methods have matured significantly and are now used extensively in semiconductor fabs. Recently, there has been an intense focus on developing ALEt methods. In particular, thermal ALEt has been shown to precisely remove ALD inorganic thin films selectively and on complex structures. These capabilities have opened new possibilities for nanoscale device design. Here, we report a new thermal etching process similar to ALEt for removing hybrid inorganic-organic layers that we call molecular layer etching (MLEt). This MLEt process uses vapor phase lithium organic salts in combination with trimethyl aluminum to perform layer-by-layer etching of molecular layer deposition (MLD) coatings.Ultra-thin layers of two dimensional (2D) transition metal dichalcogenide (TMD) semiconductors can exhibit exceptional electrical, optical, magnetic, mechanical and chemical properties. This allows the exploration of internal quantum degrees of freedom of electrons and their potential application in optoelectronic, energy, and sensor devices. Among the various 2D-TMDs, MoS2 has shown exciting material properties and this has stimulated the exploration of a variety thin film synthesis methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and solution based methods. In addition, the ALD community is investigating ALD methods for MoS2 growth. Here we report the thermal ALEt of ALD MoS2 thin films. We believe the successful combination of both ALD and ALEt of MoS2 and other TMDs can pave the way to control the synthesis of 2D-TMD layers over large areas. Combining ALD and ALEt will allow MoS2 interface engineering and enable MoS2 integration into the large-scale manufacturing of future complex device structures.

Sulfur doping and structure defect functionalized carbon nitride nanosheets with enhanced photocatalytic degradation activity

Carbon nitride (C3N4) is a promising semiconductor photocatalytic material to treat residual pollutants in water. However, the limited visible light absorption and severe recombination of photoinduced carriers restrict the further development of C3N4 photocatalyst. Herein, sulfur doping and structure defect simultaneous functionalized C3N4 nanosheets (SCN-T) were prepared by convenient copolymerization of dicyandiamide and thioacetamide followed by thermal oxidation etching process. The SCN-T can not only harvest more visible light due to sulfur doping by lifting the valence band and conduction band, but also exhibit stronger reduction ability originated from combined effect of doping and exfoliation, higher separation and transfer efficiency and prolonged average lifetime of photoinduced carriers than pristine bulk C3N4 because of defect and sheet structures. The photocatalytic activity of the SCN-T was evaluated by performing the degradation experiments of Rhodamine B (RhB) and tetracycline hydrochloride (TC-HCl), and the results show that SCN-T exhibits a significant enhanced photocatalytic degradation activity. The degradation rate constants for RhB and TC-HCl over the SCN-T are 4.95 times and 2.07 times that of pristine bulk C3N4, respectively. The work provides valuable information for the activity optimization on the basis of composition and structural properties.

Caesium sites coordinated in Boron-doped porous and wrinkled graphitic carbon nitride nanosheets for efficient charge carrier separation and Transfer: Photocatalytic H2 and H2O2 production

This study reports the synthesis of a highly efficient visible-light-driven photocatalyst for hydrogen evolution and H2O2 production by manipulating the electronic band structure and surface properties of g-C3N4. Boron and caesium co-doped g-C3N4 porous and wrinkled nanosheets were nobly synthesized by using recrystallization of melamine in water in the presence of boric acid and CsCl followed by calcination and thermal etching. The prepared nanosheets showed an extremely porous and wrinkled structure with high surface area and edge sites. The optimized B, Cs co-doped g-C3N4 nanosheets exhibited a stable hydrogen evolution rate of 1,120 μmolg-1h−1 in the presence of triethanolamine, which is 7.7 times higher than that of the bulk. Moreover, this optimized structure showed a greatly increased hydrogen peroxide production rate of 113 μmolg-1h−1 compared to that (19 μmolg-1h−1) of the bulk GCN-B. Meanwhile, the optimized structure showed a high photooxidation ability toward RhB oxidation. This outstanding improvement in photocatalytic performance is attributed to the enhanced charge carrier mobility in the π-conjugated structure and increased accessible reaction sites for photocatalytic reactions originated from the synergetic effect of co-doping and formation of the porous and wrinkled nanosheets.

SEraMic: A semi-automatic method for the segmentation of grain boundaries

The SEraMic method, implemented in the SEraMic plugin for Fiji or ImageJ software, was developed to calculate a segmented image of a ceramic cross section that shows the grain boundaries. This method was used to accurately and automatically determine grain boundary positions and further assess the grain size distribution of monophasic ceramics, metals, and alloys. The only required sample preparation is polishing the cross section to a mirror-like finish. The SEraMic method is based on at least six backscattered electron scanning electron microscopy images of a unique region of interest with various tilt angles ranging from -5° to +5°, which emphasises the orientation contrasts of the grains. Because the orientation contrast varies with the incident beam angle on the sample, the set of images contains information related to all the grain boundaries. The SEraMic plugin automatically calculates and builds a segmented image of the grain boundaries from the set of tilted images. The SEraMic method was compared with classical thermal etching methods, and it was applied to determine the grain boundaries in various types of materials (oxides, phosphates, carbides, and alloys). The method remains easy to use and accurate when the average grain diameter is greater than or equal to 0.25 μm.

Formation of colloidal solutions of silicon nanoparticles in ethyl alcohol with ultra-short laser pulses

The study of surface morphology of a silicon target after laser exposure, the formation and study of nanoparticles, obtained by laser ablation by ultrashort infrared pulses, were conducted. The material was processed using a yttrium aluminum garnet laser (LS-2134D) with a wavelength of 1064 nm, generating in a two-pulse mode (pulses are separated by a time interval of 3 μs, pulse duration is 10 ns, pulse repetition rate is 10 Hz, single pulse energy ~ 0.05 J). Alcohol solutions of silicon nanoparticles were obtained by laser ablation. It is shown that an ensemble of particles of different sizes (from 20 nm to 2.5 μm) is formed, which have no faceting. Using the method of scanning electron microscopy, the features of the morphology of the surface of the crater of polycrystalline silicon, which is in ethyl alcohol during pulsed laser processing in the double pulse mode, have been established. It is shown that the structure of the crater consists of silicon grains separated from each other by grooves; the material evaporates along the grain boundaries, and wide thermal etching grooves are formed. These results can be used to create solar cells.

Effect of ZnO on dielectric properties of Li-Al-Si photoetchable glasses as an interposer

In current three-dimensional (3D) radio frequency (RF) package field, the silicon interposer can’t entirely meet the needs of the package because of its non-negligible dielectric loss. Similarly, the application of through Glass vias (TGV) has restriction for the same reason. Therefore, this paper focuses on reducing dielectric loss of photoetchable glass (PEG), as well as the performance of TGV technology of PEG for packaging. The PEG was reduced in the dielectric loss by the addition of ZnO. The reduction in dielectric loss is due to changes in structure. The structure of PEG was analyzed through the XRD and the Raman spectroscopy. The dielectric performance was verified by the Impedance Analyzer. The result indicated dielectric loss obviously decreased to 0.0035 by ZnO doped and the reason primarily attributed to the decrease number of the Non-Oxygen-Bridge in the glass network and the structure is more stable. Through thermal processes and etching, the average diameter obtained around 75μm by TGV, and the aperture ratio of up to 25: 1, TGV density can reach 10000 / cm2.

Molecular Mechanism of Thermal Dry Etching of Iron in a Two-Step Atomic Layer Etching Process: Chlorination Followed by Exposure to Acetylacetone

Controlling thickness and morphology of transition-metal thin films used in magnetic random-access memory fabrication is a major challenge. Thermal dry etching has emerged as a method of choice for preparing the desired films; however, the mechanisms of the underlying surface processes are very difficult to assess. In this work, thermal dry etching of metallic iron by using sequential exposure to chlorine gas and 2,4-pentanedione (acetylacetone, acacH) was investigated. The mechanism of reacting acacH with chlorine-modified iron surface was studied by following the fragments desorbing from the surface in temperature-programmed desorption experiments in half-cycle processes that compared the chlorinated, oxidized, mixed (Cl and O), and clean (sputtered) iron films. In situ Auger electron spectroscopy and ex situ X-ray photoelectron spectroscopy of each sample after each etching step confirmed that the surface is activated by chlorine and then the chlorine-containing iron species are removed from the top layer of the sample, resulting in a metallic iron surface. No etching of clean (sputtered) surface was observed with acacH. The complete mechanism of acacH reaction with chlorinated iron samples is complicated, and etch products can contain both Fe2+ and Fe3+. However, a number of major conclusions, including the formation of surface intermediates and the final products of etching, primarily removal of Fe(acac)xCly, are inferred by comparing the results of these experiments with the computational investigation of selected surface processes using density functional theory calculations.

Thermal atomic layer etching: A review

This article reviews the state-of-the art status of thermal atomic layer etching of various materials such as metals, metal oxides, metal nitrides, semiconductors, and their oxides. We outline basic thermodynamic principles and reaction kinetics as they apply to these reactions and draw parallels to thermal etching. Furthermore, a list of all known publications is given organized by the material etched and correlated with the required reactant for each etch process. A model is introduced that describes why in the nonsaturation mode etch anisotropies may occur that can lead to unwanted performance variations in high aspect ratio semiconductor devices due to topological constraints imposed on the delivery of reactants and removal of reactant by-products.

Aluminium-assisted chemical etching for fabrication of black silicon

This paper investigates aluminium-assisted chemical etching (AACE) process to fabricate b-Si absorber for the first time. The AACE process combines deposition of a thin aluminium (Al) film with thickness of 12–30 nm on crystalline silicon (c-Si) wafers, followed by subsequent thermal annealing and wet chemical etching processes. The AACE process produces random nanopores on the b-Si surface. From the results, thicker Al thickness leads to lower depth of nanopores, lower surface coverage of nanopores on the b-Si and exhibits higher weighted average reflection (Ravg) within 300–1100 nm wavelength region. The b-Si fabricated by Al film of 12 nm thickness demonstrates the lowest Ravg (11.9%) and the highest broadband light absorption. The b-Si reveals nanopores with average depth of 200 nm and surface coverage of 45.1%. The findings from this work demonstrate the potential of the AACE process to produce b-Si with superior broadband light absorption, which is crucial for photovoltaic (PV) applications.

Molten salt assisted fabrication of Fe@FeSA-N-C oxygen electrocatalyst for high performance Zn-air battery

Non-noble-metal-based electrocatalysts with superior oxygen reduction reaction (ORR) activity to platinum (Pt) are highly desirable but their fabrications are challenging and thus impeding their applications in metal-air batteries and fuel cells. Here, we report a facile molten salt assisted two-step pyrolysis strategy to construct carbon nanosheets matrix with uniformly dispersed Fe3N/Fe nanoparticles and abundant nitrogen-coordinated Fe single atom moieties (Fe@FeSA-N-C). Thermal exfoliation and etching effect of molten salt contribute to the formation of carbon nanosheets with high porosity, large surface area and abundant uniformly immobilized active sites. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image, X-ray absorption fine spectroscopy, and X-ray photoelectron spectroscopy indicate the generation of Fe (mainly Fe3N/Fe) and FeSA-N-C moieties, which account for the catalytic activity for ORR. Further study on modulating the crystal structure and composition of Fe3N/Fe nanoparticles reveals that proper chemical environment of Fe in Fe3N/Fe notably optimizes the ORR activity. Consequently, the presence of abundant FeSA-N-C moieties, and potential synergies of Fe3N/Fe nanoparticles and carbon shells, markedly promote the reaction kinetics. The as-developed Fe@FeSA-N-C-900 electrocatalyst displays superior ORR performance with a half-wave potential (E1/2) of 0.83 V versus reversible hydrogen electrode (RHE) and a diffusion limited current density of 5.6 mA cm−2. In addition, a rechargeable Zn-air battery device assembled by the Fe@FeSA-N-C-900 possesses remarkably stable performance with a small voltage gap without obvious voltage loss after 500 h of operation. The facile synthesis strategy for the high-performance composites represents another viable avenue to stable and low-cost electrocatalysts for ORR catalysis.

Thermal atomic layer etching of germanium-rich SiGe using an oxidation and “conversion-etch” mechanism

The thermal atomic layer etching (ALE) of germanium-rich SiGe was demonstrated using an oxidation and “conversion-etch” mechanism with oxygen (O2) or ozone (O3), hydrofluoric acid (HF), and trimethylaluminum [TMA, Al(CH3)3] as the reactants. The crystalline germanium-rich SiGe film was prepared using physical vapor deposition and had a composition of Si0.15Ge0.85. In situ spectroscopic ellipsometry was employed to monitor the thickness of both the SiGe film and the surface oxide layer on the SiGe film during thermal ALE. Using a reactant sequence of O2-HF-TMA, the etch rate of the SiGe film increased progressively with temperatures from 225 to 290 °C. At 290 °C, the SiGe film thickness decreased linearly at a rate of 0.57 Å/cycle with a surface oxide thickness of 18–19 Å. This etch rate was obtained using reactant pressures of 25, 0.2, and 0.4 Torr and doses of 1.5, 1.0, and 1.0 s for O2, HF, and TMA, respectively. The TMA and HF reactions were self-limiting and the O2 reaction was reasonably self-limiting at 290 °C. Using an O3-HF-TMA reaction sequence, the SiGe ALE etch rate was 0.42 Å/cycle at 290 °C. This etch rate was obtained using reactant pressures of 15, 0.2, and 0.4 Torr and dose times of 0.5, 1.0, and 1.0 s for O3, HF, and TMA, respectively. The O3, TMA, and HF reactions were all self-limiting at 290 °C. Atomic force microscopy images revealed that thermal ALE with the O2-HF-TMA or O3-HF-TMA reaction sequences did not roughen the surface of the SiGe film. The SiGe film was etched selectively compared with Si or Si3N4 at 290 °C using an O2-HF-TMA reaction sequence. The etch rate for the SiGe film was >10 times faster than Si(100) or Si3N4 that was prepared using low-pressure chemical vapor deposition. This selectivity for the SiGe film will be useful to fabricate Si nanowires and nanosheets using SiGe as the sacrificial layer.

Preparation of g‐C3N4 Nanosheets/CuO with Enhanced Catalytic Activity on the Thermal Decomposition of Ammonium Perchlorate

AbstractThe thermal oxidation etching assisted g‐C3N4 nanosheets/CuO was prepared through a facile co‐precipitation strategy. In this work, the structure, morphology, and composition of g‐C3N4 (UCN, prepared by urea), g‐C3N4 nanosheets (TCN, prepared by thermal oxidation etching of UCN), g‐C3N4/CuO (UCN/CuO), g‐C3N4 nanosheets/CuO (TCN/CuO) were characterized via X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Furthermore, the catalytic effect of the obtained samples on the thermal decomposition of ammonium perchlorate (AP) was examined by thermal gravimetric analysis (TGA). As a result, in the case of 5 wt% TCN/CuO, the high decomposition temperature of AP decreased by 120.6 °C, which is much lower than that of UCN, TCN, CuO and UCN/CuO. In addition, the exothermic heat released from the decomposition of AP increased from 430.64 J g−1 to 2856.08 J g−1. This evident catalytic activity may be related to the synergistic effect of CuO and TCN. This work provides a novel strategy for the construction of composite catalyst for the thermal decomposition of AP, which is supposed to possess significant potential in the solid propellant field.

Impact of selective thermal etching in mixed H2/NH3 atmosphere on crystal quality of AlGaN/GaN heterostructures

We investigated the impact of selective thermal etching in a mixed hydrogen and ammonia atmosphere on the crystal quality and electrical characteristics of Ga- and N-polar AlGaN/GaN heterostructures. It was revealed that the etching rate of N-polar GaN is lower than that of Ga-polar GaN under our experimental conditions, and they showed a similar dependence on process temperature with almost the same activation energies. We demonstrated the use of a thin AlGaN layer as a selective etching stopper for both Ga- and N-polarity. The AlGaN stoppers exhibited a smooth surface after etching the GaN layer above them. As for the electrical characteristics, there was no significant degradation in the mobility of the two-dimensional electron gas. The results indicate that selective thermal etching is a promising technique for device fabrication and is especially suitable for precise GaN layer removal when GaN-based devices are fabricated with an epitaxial layer transfer technique.

Tailoring superficial morphology, defect and functional group of commercial carbon cloth for a flexible, stable and high-capacity anode in sodium ion battery

Developing a flexible hard carbon-based anode is very important for the flexible sodium ion battery. Here, a porous carbon cloth with lots of defects and C=O functional groups is prepared by combining the thermal etching with oxidation-exfoliation method. The partial graphitization and N and S codoping improve the conductivity and electrochemical properties. Multi-step modifications stabilize the defects, which is proved by in situ Raman and leads to the enhanced initial coulombic efficiency. Benefiting from the increased interlayer distance, C=O functional group, pore and defect, the Na+ adsorption (sloping region in discharging curve) plays an important role in Na+ storage process specially at high current density. In comparison with other hard carbon materials (0.40 V), the low midpoint voltages in sloping region of carbon cloth-derived electrodes (0.11 V) promote the energy density of full cell. The optimized electrode based on the total weight of electrode exhibits a high discharging capacity (0.983 mAh cm−2 at 0.2 mA cm−2 or 98.3 mAh g−1 at 20 mA g−1) and a long-term cycling performance (91.6% capacity retention after 1000 cycles at 0.6 mA cm−2). The high reversible capacity of coin-type full cell (≈0.515 mAh cm−2 at 0.2 mA cm−2) and the outstanding flexibility of pouch cell further reveal its potential.

Conversion reactions in atomic layer processing with emphasis on ZnO conversion to Al2O3 by trimethylaluminum

Atomic layer processing such as atomic layer deposition (ALD) and thermal atomic layer etching (ALE) is usually described in terms of sequential, self-limiting surface reactions. This picture for ALD and thermal ALE leaves out the possibility that the metal precursor in ALD and thermal ALE can also convert the surface material to another new material. This perspective introduces the previous evidence for conversion reactions in atomic layer processing based on a variety of studies, including Al2O3 ALD on ZnO, growth of Zn(O,S) alloys, “self-cleaning” of III-V semiconductor surfaces, and thermal ALE of ZnO and SiO2. The paper then focuses on the reaction of Al(CH3)3 [trimethylaluminum (TMA)] on ZnO as a model conversion system. A variety of techniques are utilized to monitor ZnO conversion to Al2O3 using TMA at 150 °C. These techniques include FTIR spectroscopy, quadrupole mass spectrometry (QMS), x-ray reflectivity (XRR), gravimetric analysis, x-ray photoelectron spectroscopy (XPS), and quartz crystal microbalance (QCM) measurements. The various studies focus on ZnO conversion to Al2O3 for both hydroxyl-terminated and ethyl-terminated ZnO substrates. FTIR studies observed the conversion of ZnO to Al2O3 and provided evidence that the conversion is self-limiting at higher TMA exposures. QMS studies identified the volatile reaction products during the TMA reaction with ZnO as CH4, C2H4, C2H6, and Zn(CH3)2. The CH4 reaction product preceded the appearance of the Zn(CH3)2 reaction product. XRR investigations determined that the thickness of the Al2O3 conversion layer on ZnO limits at ∼1.0 nm at 150 °C after larger TMA exposures. A gravimetric analysis of the conversion reaction on ZnO nanoparticles with a diameter of 10 nm displayed a percent mass loss of ∼49%. This mass loss is consistent with an Al2O3 shell of ∼1 nm on a ZnO core with a diameter of ∼6 nm. XPS studies revealed that ZnO ALD films with a thickness of 2 nm were almost completely converted to Al2O3 by large TMA exposures at 150 °C. QCM investigations then measured the mass changes for lower TMA exposures on hydroxyl-terminated and ethyl-terminated ZnO films. More mass loss was observed on ethyl-terminated ZnO films compared with hydroxyl-terminated films, because TMA does not have the possibility of reacting with hydroxyl groups on ethyl-terminated ZnO films. The mass losses also increased progressively with temperatures ranging from 100 to 225 °C on both hydroxyl-terminated and ethyl-terminated ZnO films. The perspective concludes with a discussion of the generality of conversion reactions in atomic layer processing.

Coupled porosity and heterojunction engineering: MOF-derived porous Co3O4 embedded on TiO2 nanotube arrays for water remediation

Strive to develop the interaction and efficient co-catalysts is one of the vital projects in realizing hybrid photocatalytic systems for water remediation. In this work, p-type porous Co3O4 was embedded onto n-type vertical TiO2 nanotube via an in-situ thermal etching method. ZIF-67 was employed as the structural template for Co3O4, which then augmented the light harvesting ability of the resultant photocatalyst. Such improvement was prompted by the light reflecting and directing attributes of porous Co3O4. Therefore, a remarkable MB removal rate was attained under sunlight irradiation, with superoxide radical being identified as the major reactive species. Photoelectric properties evaluation also verified that the p-n heterojunction developed herein exhibits outstanding charges separation ability with low impedance, particularly under light irradiation. This work highlights the idea on coupling both porous and p-n heterojunction engineering in augmenting photoactivity of catalyst, while offering insights in such structure-mediating approach.

Optimized etching of porcelain and polycrystalline alumina with a glass phase

Chemical and thermal etching techniques are commonly used in ceramography to enhance microstructural features. While thermal etching works well for high purity ceramic systems, this technique may not be appropriate where glass is present. Porcelain and industrial alumina both contain a glass phase, typically 40−60 vol% and 4−30 vol%, respectively, and these glass chemistries are proposed to be similar. Chemical etching of porcelain is common, but the images published in the literature are frequently over-etched. When glass is present in the grain boundaries of alumina, thermal etching can cause the glass to disappear or to recrystallize, obscuring the microstructure. Because of this, it is proposed that both chemical and thermal etching are necessary to prepare an industrial alumina microstructure for grain size measurements. In addition, it was observed that chemical etching is sensitive to the residual stress in the glass phase, becoming more aggressive when there is residual tension in the glass.