Etching Mechanism of Ti_(3)C_(2)Cl_(2) MXene Phases by CuCl_(2)-Lewis Molten Salt Method

We described a method for obtaining fluorine-free Ti_(3)C_(2)Cl_(2)MXene phases by melting copper in CuCl_(2)instead of aluminum in Ti_(3)AlC_(2).XRD results show that when molten salt CuCl_(2)etches Ti_(3)AlC_(2),it forms an intermediate product Ti_(3)CuC_(2),and then reacts with Ti_(3)CuC_(2)to obtain Ti_(3)C_(2)Cl_(2).The reaction of Ti_(3)AlC_(2)and CuCl_(2)at a temperature of 800℃for 2 h to obtain Ti_(3)C_(2)Cl_(2)with an optimal lamellar structure is shown in SEM results.The pseudopotential plane-wave(PP-PW)method is used to calculate on the electronic structure.The etching mechanism is investigated by the total energies of each substance.The chemical reaction of Ti_(3)AlC_(2)and CuCl_(2)will first become Ti_(3)CuC_(2)and Cu,and then become Ti_(3)C_(2)Cl_(2)during the Lewis acid etching process,which are consistent with the experimental results.

Recent Advances and Perspectives of Lewis Acidic Etching Route:An Emerging Preparation Strategy for MXenes

Since the discovery in 2011,MXenes have become the rising star in the field of two-dimensional materials.Benefiting from the metallic-level conductivity,large and adjustable gallery spacing,low ion diffusion barrier,rich surface chemistry,superior mechanical strength,MXenes exhibit great application prospects in energy storage and conversion,sensors,optoelectronics,electromagnetic interference shielding and biomedicine.Nevertheless,two issues seriously deteriorate the further development of MXenes.One is the high experimental risk of common preparation methods such as HF etching,and the other is the difficulty in obtaining MXenes with controllable surface groups.Recently,Lewis acidic etching,as a brand-new preparation strategy for MXenes,has attracted intensive attention due to its high safety and the ability to endow MXenes with uniform terminations.However,a comprehensive review of Lewis acidic etching method has not been reported yet.Herein,we first introduce the Lewis acidic etching from the following four aspects:etching mechanism,terminations regulation,in-situ formed metals and delamination of multi-layered MXenes.Further,the applications of MXenes and MXene-based hybrids obtained by Lewis acidic etching route in energy storage and conversion,sensors and microwave absorption are carefully summarized.Finally,some challenges and opportunities of Lewis acidic etching strategy are also presented.

Etching characteristics and surface modification of InGaSnO thin films under Cl_(2)/Ar plasma

Indium gallium tin oxide(IGTO)thin films have the potential for high mobility and lowtemperature processing,which makes them suitable for applications such as display backplanes and high-voltage switching devices.However,very few studies have investigated the plasmaetching characteristics of IGTO and changes in its properties after etching.In this study,the etching characteristics of IGTO were investigated using Cl_(2)/Ar plasma,and changes in surface properties were analyzed.Results showed that the etch rate increased with an increase in the proportion of Cl_(2),with the highest etch rate observed at 69 nm min^(-1)in pure Cl_(2)plasma with a gas flow rate of 100 sccm.Furthermore,increased radio-frequency power caused a rise in the etch rate,while a process pressure of 15 m Torr was optimal.The primary etching mechanism for IGTO thin films under Cl_(2)plasma was a chemical reaction,and an increased work function indicated the occurrence of defects on the surface.In addition,the etching process reduced the surface roughness of Cl_(2)-containing plasma,whereas the etching process in pure Ar plasma increased surface roughness.This study contributes to a better understanding of the plasmaetching characteristics of IGTO and changes in its properties after etching,providing valuable insights for IGTO-based applications.

{001} facets dominated anatase TiO_2 : Morphology, formation/etching mechanisms and performance

Controllable growth of anatase TiO2 crystals with exposed high reactive crystal facets has aroused great attention in the fields of science and technology due to their unique structure-dependent properties. Recently, much effort has been paid to synthesize anatase TiO2 crystals with exposed high reactive {001 } facets. Herein, we review the recent progress in synthesizing {001 } facets dominated anatase TiO2 crystals with different morphologies by various synthetic methods. Furthermore, our review is mainly focused on the formation/etching mechanisms of {001 } facets dominated anatase TiO2 crystals based on our and other studies. The extensive application potentials of the anatase TiO2 crystals with exposed { 001 } facets have been summarized in this review such as photocatalysis, photoelectrocatalysis, solar energy conversion, lithium ion battery, and hydrogen generation Based on the current studies, we give some perspectives on the research topic. We believe that this comprehensive review on anatase Ti02 crystals with high reactive {001 } facets can further promote the relative research in this field.

Patterning two-dimensional semiconductors with thermal etching

The controllable synthesis of complicated nanostructures in advanced two-dimensional(2D)semiconductors,such as periodic regular hole arrays,is essential and remains immature.Here,we report a green,facile,highly controlled synthetic method to efficiently pattern 2D semiconductors,such as periodic regular hexagonal-shaped hole arrays(HHA),in 2D-TMDs.Combining the production of artificial defect arrays through laser irradiation with anisotropic annealing etching,we created HHA with different arrangements,controlled hole sizes,and densities in bilayer WS_(2).Atomic force microscopy(AFM),Raman,photoluminescence(PL),and scanning transmission electron microscopy(STEM)characterization show that the 2D semiconductors have high quality with atomical clean and sharp edges as well as undamaged crystals in the unetched region.Furthermore,other nanostructures,such as nanoribbons and periodic regular triangular-shaped 2D-TMD arrays,can be fabricated.This kind of 2D semiconductors fabrication strategy is general and can be extended to a series of 2D materials.Density functional theory(DFT)calculations show that one WS_(2)molecule from the edges of the laser-irradiated holed region exhibits a robust etching activation,making selective etching at the artificial defects and the fabrication of regular 2D semiconductors possible.

Visually monitoring the etching process of gold nanoparticles by KI/12 at single-nanoparticle level using scattered-light dark-field microscopic imaging

Real-time monitoring of reaction processes is helpful for understanding the reaction mechanisms. In this study we investigated the etching mechanism of gold nanopartides （AuNPs） by iodine on a single-nanopartide level because AuNPs have become important nanoprobes with applications in sensing and bioimaging fields owing to their specific localized surface plasmon resonance （LSPR） properties. By using a scattered-light dark-field microscopic imaging （iDFM） technique, the in situ KI/I2-treated etching processes of various shapes of AuNPs, including nanospheres （AuNSs）, nanorods （AuNRs）, and nanotrigonal prisms （AuNTs）, were monitored in real time. It was found that the scattered light of the different shapes of AuNPs exhibited noticeable color changes upon exposure to the etching solution. The scattering spectra during the etching process showed obvious blue-shifts with decreasing scattered intensity owing to the oxidation of Au atoms into [AuI2]-. Both finite-difference time-domain （FDTD） simulations and monitoring of morphological variations proved that the etching was a thermodynamic-dependent process through a chamfering mechanism coupled with layer-by-layer peeling, resulting in isotropic spheres with decreased particle sizes.

Controlled oxidative etching of gold nanorods revealed through in-situ liquid cell electron microscopy

Oxidative etching can be a powerful approach to modify the morphology of nanoscale materials for various applications.Unveiling of the etching mechanisms and morphological evolution during etching is critical.Using the liquid cell transmission electron microscopy,we investigate the etching behavior of gold nanorods under different electron beam dose rates:caseⅠ,3.5×10^9 Gy s^-1;caseⅡ,1.5×10^10 Gy s^-1;caseⅢ,4.5×10^10 Gy s^-1.The Au nanorod develops facets at the tips(caseⅠ)or adopts a transit ellipsoid shape and eventually dissolves(caseⅡ),depending on the dose rate.The rapid etching under an even higher dose rate(caseⅢ)may lead to the formation of Au3+ion-rich intermediates around the nanorod,which further accelerates the lateral etching and unexpectedly increases the aspect ratio of the nanorod.Our quantitative analysis shows that the critical size of the nanorod,below which the etching rate increases significantly with the reduction of nanorod size,may vary subject to the degree that the system is away from equilibrium.These results provide significant insights into the oxidative etching mechanisms and shed light on the rational design and synthesis of nanostructures.