Atomic Force Microscopy Phase Images Research Articles

Assessment of compatibility of dextran/PEMA blends by thermal, topologic and viscoelastic analysis

In this study, the compatibility of polymer blends of dextran (DEX) and poly(ethylene-alt-maleic anhydride) (PEMA) was evaluated with their enhanced thermal and dynamic mechanical properties as well as structural and topological properties. Blends were prepared in various ratios via solution casting method. The effects of composition and dispersion on interactions, thermal, viscoelastic and topological properties of the blends were investigated using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), atomic force microscopy (AFM) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray diffraction (XRD) analysis. TGA results indicated that blends exhibited higher thermal stability than the individual polymers, with residue percentages increasing from 13.57 % and 11.43 % for DEX and PEMA, respectively, to 27.42 %–16.86 % for the blends at 605 °C. DMA results showed that all blends remained intact at higher temperatures compared to the polymers, with higher Tg values due to the H-bonding interactions confirmed by ATR-FTIR. AFM phase imaging enabled the visualization of miscibility distinctions, revealing that the 30/70 DEX/PEMA blend had a uniform phase distribution and minimal phase shifts, suggesting improved miscibility. In contrast, other blends exhibited more heterogeneous miscibility. These findings highlight that DEX/PEMA blends, with their enhanced thermal and dynamic mechanical properties, have significant potential for various applications.

The evolution of morphology and structure of spin-coated Zinc Acetate thin films and their impact on ZnO film morphology

The deposition of ZnO thin films using sol-gel technology is a straight forward and widely used method for fabricating ZnO films with diverse morphologies and tunable electrical and optical properties. Notably, the preparation of ZnO compact layers from a zinc acetate and monoethanolamine (ZA:MEA) solution via spin-coating has gained popularity due to its simplicity. The pretreatment of spin-coated ZA:MEA films significantly impacts the morphology and structure of the resulting ZnO films. While the effects of preheating and its rate on ZnO precursor films have been extensively studied, the morphological and structural evolution of ZA:MEA films immediately after spin-coating and its subsequent impact on the final ZnO film have not been previously explored. In this study, we present the topography and phase composition of as-grown ZA:MEA films using atomic force microscopy (AFM). We conduct an in-situ investigation of the morphological evolution of ZA:MEA films. Our results reveal that as-grown ZA:MEA films possess an inhomogeneous structure. AFM phase image shows two distinct domains in the ZA:MEA films. Over time, we observe the growth of crystals in both vertical and perpendicular directions. ZA:MEA film aged for at least 20 h develops arrays of vertically oriented crystals throughout the film covered with sheet-like crystals forming on the film surface. This temporal evolution in the morphology and structure of ZA:MEA films significantly influences the morphology of the final ZnO film.

Systematic root cause analysis of ceria-induced defects during chemical mechanical planarization and cleaning

As semiconductor devices become smaller, having ultra-smooth and flawless surfaces is crucial. The manufacturing of advanced devices requires strict conditions to avoid defects. These defects can lead to device failure and reliability problems. This paper presents a detailed study of defects related to ceria on SiO2 surfaces after post-chemical mechanical planarization (CMP) cleaning processes. The focus is on uncovering the primary causes of these defects, which are believed to appear in various forms: remnants, small fragments, and cerium-modified layers. The investigation found no traces of ceria remnants in atomic force microscopy phase images, suggesting they might have been eliminated during cleaning. Yet, small ceria particle fragments were detected on the SiO2 films. These fragments, likely created during polishing, adhere strongly to the SiO2, resisting removal by brush scrubbing. Moreover, the research revealed a cerium-modified layer on the SiO2 surface, formed by the chemical interaction between ceria particles and SiO2 films during polishing. Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) mapping showed Ce atoms in areas without visible ceria particles, confirming this layer's presence. The insights from this study provide a deeper understanding of ceria-related defects in the semiconductor manufacturing process, offering valuable information for improving residue removal and surface cleaning in post-CMP processes.

Oscillatory rheology of chitosan and calcium chloride crosslinked pectin blend filmogenic solutions and atomic force microscopy of film surface topography

This work examines the synergistic interaction between chitosan (CS) and calcium crosslinked pectin (CP) in aqueous solution by small-amplitude oscillatory shear measurements at selected CS/CP blend ratios (1:1, 1:2, 1:3, and 1:4) and compares the surface morphology of cast films of those blends using atomic force microscopy (AFM). A 2% (w/v) pectin solution concentration could not produce a film, which was improved with the addition of 0.18 M calcium chloride solution, and the corresponding dynamic moduli increased by 3 log cycles. The mechanical rigidity of the blends increased with increasing CP contents. The complex viscosity (η*) decreased with increasing temperature due to molecular mobility at higher temperatures and the breaking of the junction between CS and CP. The applicability of the Cole-Cole plot to selected blend ratios demonstrated that only the CS/CP ratio of 1:3 best fitted and established the well-miscibility between the polymers. AFM phase imaging further illustrates the distribution of CS and CP particles in the blended films and provides complementary information to the topography image, revealing the variations in the surface properties of the films. AFM proves to be a powerful tool for investigating microstructural changes in polymer blends and complementing rheological measurements.

Examination of Polymer Blends by AFM Phase Images

Atomic force microscopy (AFM) belongs to the high-resolution surface morphology investigation methods. Since it can, in many cases, be applied in air, samples can more easily be inspected than by a scanning electron microscope (SEM). In addition, several special modes exist which enable examination of the mechanical and other physical parameters of the specimen, such as friction, adhesion between tip and sample, elastic modulus, etc. In tapping mode, e.g., phase imaging can be used to qualitatively distinguish between different materials on the surface. This is especially interesting for polymers, for which the evaluation by energy-dispersive X-ray spectroscopy (EDS) is mostly irrelevant. Here we give an overview of phase imaging experiments on different filaments used for 3D printing by fused deposition modeling (FDM). Furthermore, the acrylonitrile butadiene styrene (ABS), especially different poly(lactide acids) (PLAs) with special features, such as thermochromic or photochromic properties, are investigated and compared with SEM images.

Microstructural and Mechanical Characterization of Al Nanocomposites Using GCNs as a Reinforcement Fabricated by Induction Sintering

High-energy ball milling is a process suitable for producing composite powders whose achieved microstructure can be controlled by the processing parameters. Through this technique, it is possible to obtain a homogeneous distribution of reinforced material into a ductile metal matrix. In this work, some Al/CGNs nanocomposites were fabricated through a high-energy ball mill to disperse nanostructured graphite reinforcements produced in situ in the Al matrix. To retain the dispersed CGNs in the Al matrix, avoiding the precipitation of the Al4C3 phase during sintering, the high-frequency induction sintering (HFIS) method was used, which allows rapid heating rates. For comparative purposes, samples in the green and sintered state processed in a conventional electric furnace (CFS) were used. Microhardness testing was used to evaluate the effectiveness of the reinforcement in samples under different processing conditions. Structural analyses were carried out through an X-ray diffractometer coupled with a convolutional multiple whole profile (CMWP) fitting program to determine the crystallite size and dislocation density; both strengthening contributions were calculated using the Langford-Cohen and Taylor equations. According to the results, the CGNs dispersed in the Al matrix played an important role in the reinforcement of the Al matrix, promoting the increase in the dislocation density during the milling process. The strengthening contribution of the dislocation density was ~50% of the total hardening value, while the contribution by dispersion of CGNs was ~22% in samples with 3 wt. % C and sintered by the HFIS method. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to analyze the morphology, size, and distribution of phases present in the Al matrix. From the analyses carried out in AFM (topography and phase images), the CGNs are located mainly around crystallites and present height profiles of 1.6 to 2 nm.

Physical Properties and Shifting of the Extracellular Membrane Vesicles Attached to Living Bacterial Cell Surfaces.

Bacterial cells release nanometer-sized extracellular membrane vesicles (MVs) to deliver cargo molecules for use in mediating various biological processes. However, the detailed processes of transporting these cargos from MVs to recipient cells remain unclear because of the lack of imaging techniques to image nanometer-sized fragile vesicles in a living bacterial cell surface. Herein, we quantitatively demonstrated that the direct binding of MV to the cell surface significantly promotes hydrophobic quorum-sensing signal (C16-HSL) transportation to the recipient cells. Moreover, we analyzed the MV-binding process in the Paracoccus denitrificans cell surface using high-speed atomic force microscopy phase imaging. Although MV shapes were unaltered after binding to the cell surface, the physical properties of a group of single MV particles were shifted. Additionally, the phase shift values of MVs were higher than that of the cell's surfaces upon binding, whereas the phase shift values of the group of MVs were decreased during observation. The shifting physical properties occurred irreversibly only once for each MV during the observations. The decreasing phase shift values indicated alterations of chemical components in the MVs as well, thereby suggesting the dynamic process in which single MV particles deliver their hydrophobic cargo into the recipient cell. IMPORTANCE Compared to the increasing knowledge about MV release mechanisms from donor cells, the mechanism by which recipient cells receive cargo from MVs remains unknown. Herein, we have successfully imaged single MV-binding processes in living bacterial cell surfaces. Accordingly, we confirmed the shift in the MV hydrophobic properties after landing on the cell surface. Our results showed the detailed states and the attaching process of a single MV into the cell surface and can aid the development of a new model for MV reception into Gram-negative bacterial cell surfaces. The insight provided by this study is significant for understanding MV-mediated cell-cell communication mechanisms. Moreover, the AFM technique presented for nanometer-scaled mapping of dynamic physical properties alteration on a living cell could be applied for the analyses of various biological phenomena occurring on the cell surface, and it gives us a new view into the understanding of the phenotypes of the bacterial cell surface.

Direct Observation and Semiquantitative Analysis of Hierarchical Structures in Graft-Type Polymer Electrolyte Membranes Using the AFM Technique.

The structural features of a polymer electrolyte membrane (PEM), consisting of polystyrene sulfonic acid (PSSA) grafted onto poly(ethylene-co-tetrafluoroethylene) (ETFE), can be characterized semiquantitatively by atomic force microscopy (AFM). The cross-sectional AFM phase images are converted to the binarized image by fitting two Gaussian functions. The domains correspond to hydrophilic PSSA domains and hydrophobic ETFE crystalline and amorphous regions, respectively, at lower and higher phase shift values. The area fraction of PSSA domains was consistent with the volume fraction determined by the grafting degree (GD). The dependence of the radius and interdomain distance of the PSSA domains on the GDs of PEMs shows discontinuous features at the threshold GD (39%). The former slightly increased from 10 to 12 nm and significantly increased to 17 nm at a GD greater than 39%; the latter decreased from 140 to 54 nm with increases in GDs up to 39% but inversely increased to 78 nm at a GD of 46%. This discontinuous change in radius and interdomain distance should be caused by the fusion of adjacent PSSA domains to form a larger size and spacing and thus less connectivity between each large domain, thereby lowering the conductivity at GD greater than 39%. We were able to demonstrate the existence of an ion-conducting hydrophilic path with a radius of approximately 10 nm. Even though it has received little attention in the past, it is expected to enable the design of electrolyte membrane functions in the future.

Concentration‐Induced Phase Separation to Suppress Energy Transfer for High‐Temperature Ratiometric Sensing in Organic Films

AbstractEnergy transfer is usually applied in ratiometric thermometry, but it often decreases sensitivities due to much reduced distinguishment in the thermal responses of two different‐colored emitters. Herein, a feasible strategy to restrain energy transfer is utilized for achieving sensitive high‐temperature detection, simply by increasing the dopant concentration to induce microphase separation. Atomic force microscopy phase images reveal that this phase separation becomes dominant when the doping ratio reaches above 40%. This results in suppression of energy transfer, which is evidenced by systematic photophysical investigations. On this basis, by using heat‐resistant emitters, a series of inexpensive and easily prepared solid‐film organic high‐temperature ratiometric thermometers are developed. They exhibit a broad eye‐detective sensing range of 102–236 °C with the relative sensitivity (Sr) higher than 0.5% K−1 and the maximum temperature resolution attaining 0.39 K. Good reversibility and stability are also demonstrated in ambient atmosphere.

Surface nanostructures on Nb-doped SrTiO3 irradiated with swift heavy ions at grazing incidence

A single crystal of SrTiO3 doped with 0.5 wt% niobium (Nb-STO) was irradiated with 200 MeV Au32+ ions at grazing incidence to characterize the irradiation-induced hillock chains. Exactly the same hillock chains are observed by using atomic force microscopy (AFM) and scanning electron microscopy (SEM) to study the relation between irradiation-induced change of surface topography and corresponding material property changes. As expected, multiple hillocks as high as 5–6 nm are imaged by AFM observation in tapping mode. It is also found that the regions in between the adjacent hillocks are not depressed, and in many cases they are slightly elevated. Line-like contrasts along the ion paths are found in both AFM phase images and SEM images, indicating the formation of continuous ion tracks in addition to multiple hillocks. Validity of preexisting models for explaining the hillock chain formation is discussed based on the present results. In order to obtain new insights related to the ion track formation, cross-sectional transmission electron microscopy (TEM) observation was performed. The ion tracks in the near-surface region are found to be relatively large, whereas buried ion tracks in the deeper region are relatively small. The results suggest that recrystallization plays an important role in the formation of small ion tracks in the deep region, whereas formation of large ion tracks in the near-surface region is likely due to the absence of recrystallization. TEM images also show shape deformation of ion tracks in the near-surface region, suggesting that material transport towards the surface is the reason for the absence of recrystallization.

A Single Shot of Vesicles.

Bacteria communicate through signaling molecules that coordinate group behavior. Hydrophobic signals that do not diffuse in aqueous environments are used as signaling molecules by several bacteria. However, limited information is currently available on the mechanisms by which these molecules are transported between cells. Membrane vesicles (MVs) with diverse functions play important roles in the release and delivery of hydrophobic signaling molecules, leading to differences in the dynamics of signal transportation from those of free diffusion. Studies on Paracoccus denitrificans, which produces a hydrophobic long-chain N-acyl homoserine lactone (AHL), showed that signals were loaded into MVs at a concentration with the potential to trigger the quorum sensing (QS) response with a "single shot" to the cell. Furthermore, stimulating the formation of MVs increased the release of signals from the cell; therefore, a basic understanding of MV formation is important. Novel findings revealed the formation of MVs through different routes, resulting in the production of different types of MVs. Methods such as high-speed atomic force microscopy (AFM) phase imaging allow the physical properties of MVs to be analyzed at a nanometer resolution, revealing their heterogeneity. In this special minireview, we introduce the role of MVs in bacterial communication and highlight recent findings on MV formation and their physical heterogeneity by referring to our research. We hope that this minireview will provide basic information for understanding the functionality of MVs in ecological systems.

Enhanced performance of high‐temperature proton exchange membrane by introducing 1,2, 4‐triazole‐ functionalized graphene oxide into polybenzimidazole

1,2,4-triazole is successfully grafted onto C═C bonds of graphene oxide surface with retained carboxylic acid, hydroxy, and epoxy groups. The structure of the resulting 1,2,4-triazole-doped graphene oxide (NGO) is proved by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy spectra. The polybenzimidazole (PBI)/NGO composite membranes (NGO content:0.5%, 1%, 3%, 5%) were also prepared and subjected to the absorption of various suitable amounts of phosphoric acid (PA). As expected, the composite membranes well maintained their superior mechanical properties (57-69 MPa) containing 2 PA molecules per PBI unit. The morphological characterization using the atomic force microscopy phase images and transmission electron microscopy analysis revealed a micro-phase separation, providing continuous ionic channels and ultimately enhancing the ionic conductivity. As a result, the maximum proton conductivity of 27 mS cm−1 is achieved for PBI/NGO-3 membrane (NGO content: 3%) at 160°C under anhydrous conditions, and the maximum power density of the cell using PBI/NGO-3 membrane is 254 mW cm−2. These composite membranes displayed great potential for high-temperature proton exchange membranes under anhydrous conditions. The scanning electron microscopy images further showed the condensed structures with the suitable quantity of NGO in the composite membranes due to the hydrogen bonding and acid–base interactions between NGO and PBI. This condensed structure improved the mechanical properties, enhanced thermal stability, and increased oxidative stability of the composite membranes. Additionally, the PBI/NGO/PA composite membranes exhibit high thermal decomposition temperature (Td[5%] higher than 284°C) and superior tensile strengths (greater than 55 MPa). Remarkably, the membranes demonstrated exceptional oxidative stability and could maintain less than 15% quantity loss for more than 200 hours in Fenton's reagent (3 wt% H2O2, 4 ppm Fe2+). Novelty statement The manuscript entitled “Enhanced Performance of High-Temperature Proton Exchange Membrane by Introducing 1,2,4-Triazole Functionalized Graphene Oxide into Polybenzimidazole” was written by Haiqiu Zhang In this work, 1,2,4-triazole is successfully grafted onto graphene oxide nanosheets by C═C bonds without damaging other groups, and condensed structure improved the oxidative stability effectively, meanwhile, with the low-acid-loaded quantity and gained higher proton conductivity under anhydrous condition.

Use of Atomic Force Microscopy (AFM) to monitor surface crystallization in caffeine-oxalic acid (CAFOXA) cocrystal compacts

Our objective was to monitor the surface crystallization in disordered caffeine-oxalic acid (CAFOXA) cocrystals following exposure to elevated water vapor pressure. This was accomplished using atomic force microscopy (AFM). Disorder was induced in the cocrystal particles by the common pharmaceutical unit operations of milling and compaction. The ‘activated’ solid, upon exposure to elevated water vapor pressure, had a high propensity to sorb water. This led to a rise in molecular mobility and the surface underwent rapid crystallization to form needle shaped crystals of CAFOXA. Using AFM height and phase imaging, we were able to directly visualize phase transformations on the compact surface. The milled compacts exhibited higher processing induced disorder than the unmilled compacts, thereby accelerating the surface recrystallization.

Abnormal Raman Characteristics of Graphene Originating from Contact Interface Inhomogeneity.

The Raman peak position shift rate per strain (RSS) coefficient of graphene is crucial for quantitative strain measurement by Raman spectroscopy. Despite its essential role, the experimentally measured RSS values are found to be highly scattered and many times significantly lower than the theoretical prediction. Here, using in situ Raman spectroscopy with a tensile test system, we resolve this controversy by examining the Raman characteristics of graphene derived from chemical vapor deposition (CVD) transferred on polymer substrates. Our experiments show that the Raman 2D-peak position of CVD graphene can shift nonlinearly with applied strain, in contrast to its intrinsically linear trait. More importantly, the resultant RSS coefficient at the steady state is much lower than the theoretical prediction. By analyzing atomic force microscopy (AFM) phase images and full width at half-maximum (FWHM) of Raman spectra, we attribute the abnormal behavior to nanometer-scale inhomogeneity of the graphene/substrate contact interface. Assisted by a simplified discrete interface slip model, we correlate the evolution of nanometer-scale inhomogeneity with that of the apparent Raman response. The theoretical model provides a useful tool for understanding and optimizing the contact interface behavior of various two-dimensional materials on substrates; the revealed mechanism is critical for correct interpretation of data obtained by Raman or any other spectroscopies based on homogenized laser signals.

Characterizing the coverage of anti-soiling coatings on photovoltaic modules

Anti-soiling coatings help protect solar modules against dust deposition. Tapping mode atomic force microscopy phase imaging can be used to ensure these coatings have ample coverage.

Characterization of reliability of anti-soiling coatings using tapping mode-AFM phase imaging

Power loss due to dust deposition on photovoltaic (PV) modules (also referred to as soiling) is a severe challenge to the economic viability of PV deployment in sunbelt countries like India and the Middle East. Anti-soiling coatings are nano/micrometer thick transparent coatings, which mitigate dust deposition on PV module. In this study, Tapping Mode Atomic Force Microscopy (TM-AFM) phase imaging was used to characterize the surface changes of four different commercial hydrophobic anti-soiling coatings as they were subjected to outdoor field exposure tests and three different indoor accelerated stress tests. The anti-soiling coatings were applied via manual spray coating method on solar glass substrates. The phase angle for not-coated glass shows a tight distribution around zero. The phase angle distribution of coated surface showed a larger spread. When the coatings were subjected to different environmental stressors, the phase angle distributions became tighter and, in some cases, collapsed to tight distributions around zero, indicating that the coatings were partly or completely removed from the glass surface. We demonstrate a correlation of the changes in surface coverage identified from phase angle distributions to contact angle and surface roughness, thus establishing TM-AFM phase imaging as a promising approach to characterize anti-soiling coatings subjected to environmental stress. While the analysis of the phase angle distribution is able to resolve the removal of the coating, contact angle and surface roughness cannot do so unambiguously.

Influence of microstructural variations on morphology and separation properties of polybutadiene-based polyurethanes.

Polybutadiene-based polyurethanes with different cis/trans/1,2-vinyl microstructure contents are synthesized. The phase morphology and physical properties of the polymers are investigated using spectroscopic analysis (FTIR and Raman), differential scanning calorimetry (DSC), X-ray scattering (WAXD and SAXS) and atomic force microscopy (AFM). In addition, their gas transport properties are determined for different gases at 4 bar and 25 °C. Thermodynamic incompatibility and steric hindrance of pendant groups are the dominant factors affecting the morphology and properties of the PUs. FTIR spectra, DSC, and SAXS analysis reveal a higher extent of phase mixing in high vinyl-content PUs. Moreover, the SAXS analysis and AFM phase images indicate smaller microdomains by increasing the vinyl content. Smaller permeable soft domains as well as the lower phase separation of the PUs with higher vinyl content create more tortuous pathways for gas molecules and deteriorate the gas permeability of the membranes.

Structural and optical properties of HDPE implanted with medium fluences silver ions

The implantation of high-density polyethylene (HDPE) has been conducted using Ag+ ions with energy of 60 keV, achieved fluences 1.5 and 10?1015 ions/cm2. Transmission electron microscopy (STEM) and field emission gun - scanning electron microscopy (FEG-SEM) showed the existence of nanoparticle clusters. X ray photoelectron spectroscopy (XPS) revealed the presence of silver in the sample surface region. The surface topography was studied by atomic force microscopy (AFM), while the surface composition uniformity was analyzed using phase imaging AFM. Optical characterization obtained by spectroscopic ellipsometry (SE) showed changes in refractive index, extinction coefficient and the optical band gap with the fluence of implanted ions.

Current timer switch in a GaAs-based nanowire coupled with polyoxometalate nanoparticle and conductive AFM tip

We demonstrate a current timer switch function in a GaAs-based nanowire electrostatically coupled with a polyoxometalate nanoparticle (POM NP) and a conductive atomic force microscopy (AFM) tip. The nanowire current associated with the charge state of the POM NP on the nanowire surface abruptly changed after several ten seconds from biasing the conductive tip. The current switch timing changed depending on the tip voltage. The timer switch function appeared when the tip approached the POM NP where the AFM phase image showed phase lag at high atmospheric humidity condition. We discuss the timer mechanism in terms of the configuration of the electromechanical potential of the cantilever and dynamic potential modulation by mobile ions and polarized molecules in the water-absorbed POM NP surface.

Improved Understanding of the Sulfidization Mechanism in Amine Flotation of Smithsonite: An XPS, AFM and UV–Vis DRS Study

Sulfidization is required in the amine flotation of smithsonite; however, the sulfidization mechanism of smithsonite is still not fully understood. In this work, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) were used to characterize sulfidized and unsulfidized smithsonite. The XPS and UV–vis DRS analyses showed that smithsonite sulfidization is a transformation of ZnCO3 to ZnS on the smithsonite surfaces. However, this transformation is localized, resulting in the coexistence of ZnCO3 and ZnS or in the formation of ZnS island structures on the sulfidized smithsonite surfaces. AFM height imaging showed that sulfidization can substantially change the surface morphology of smithsonite; in addition, AFM phase imaging demonstrated that sulfidization occurs locally on the smithsonite surfaces. Based on our findings, it can be concluded that smithsonite sulfidization is clearly a heterogeneous solid–liquid reaction in which the solid product attaches at the surfaces of unreacted smithsonite. Smithsonite sulfidization involves heterogeneous nucleation and growth of ZnS nuclei. Moreover, the ZnS might nucleate and grow preferentially in the regions with high reactivity, which might account for the formation of ZnS island structures. In addition, sphalerite-structured ZnS is more likely to be the sulfidization product of smithsonite under flotation-relevantconditions, as also demonstrated by the results of our UV–vis DRS analyses. The results of this study can provide deeper insights into the sulfidization mechanism of smithsonite.