Wet Chemical Method Research Articles

Colloidal substrate-facilitated synthesis of gold nanohelices

Helical nanostructures have unique optical and mechanical properties, yet their syntheses had always been quite challenging. Various symmetry-breaking mechanisms such as chiral templates, strain-restriction and asymmetric ligand-binding have been developed to induce the helical growth at nanoscale. In this work, with neither chiral ligands nor templates, gold (Au) nanohelices were synthesized via a facile wet-chemical method, through an asymmetric Active Surface Growth facilitated by colloidal silica nanoparticles (NPs). The one-dimensional growth followed the Active Surface Growth, which employs a thiolated ligand to direct continuous deposition of Au at the interface, known as the active surface, between the Au nanostructures and the silica NPs – the colloidal substrates. More importantly, the colloidal substrates are crucial for the helical growth, as the diameter of the obtained nanohelices was found proportional to the size of the colloidal substrates. We propose that the nanoscale size and the curvature of the silica NPs would reduce the size of anchoring point between Au nanowires and the substrates, causing partial blockage of the active surface by the substrate and divergence of the activity on the active surface towards Au deposition. The subsequent inequivalent deposition, and the dynamic shifting of the blockage lead to the asymmetric growth and the formation of nanohelices. Factors that would affect the asymmetric Active Surface Growth were also identified and discussed, including the reduction kinetics, substrate treatment and the type and concentration of the ligand. In particular, variation of the size of the active surfaces would change the degree of the surface inequivalence, and thus affect the yield of the nanohelices.

Mechanical characteristics and antibacterial activity against Staphylococcus aureus of sustainable cellulosic paper coated with Ag and Cu modified ZnO nanoparticles

In this study, zinc oxide (ZnO) nanoparticles were prepared and modified using a wet chemical method with different concentrations of Ag and Cu nanoparticles. The objective was to improve the mechanical, optical, and antibacterial properties of the coated paper by using the prepared pigments. The long-term antimicrobial effects of the coated paper were evaluated over 25 years. The successful synthesis of a hexagonal structure of ZnO nanoparticles decorated with spherical Ag and Cu nanoparticles ranging from 20 to 50 nm was confirmed using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). By increasing the concentrations of Ag and Cu from 0.01% to 1.0%, the mechanical properties of the coated paper were enhanced. The tensile strength reached a maximum of 6.77 kN/m and 7.03 kN/m, elongation increased to 1.69% and 1.70%, tensile energy absorption improved to approximately 77 and 80 J/m2, and burst strength rose to 218 and 219 kPa, respectively. The use of Ag-modified ZnO maintains the optical properties, while Cu-modified ZnO reduces brightness and whiteness without affecting opacity. The antimicrobial inhibition activity was improved with higher silver (Ag) and copper (Cu) content. The formulations containing 1% Ag/ZnO and 1%Cu/ZnO showed long-lasting antibacterial effects against gram-positive Staphylococcus aureus bacteria. Even after 25 years of aging, they maintained inhibition rates of 92.2% and 62.2%, respectively. The molecular docking and GeneMANIA analysis revealed the potential of ZnO, Ag-modified ZnO, and Cu-modified ZnO nanoparticles to disrupt the S. aureus cell wall biosynthesis pathway by targeting the MurA enzyme and associated cell wall synthesis genes.

Enhanced adhesion strength of copper deposited epoxy composite films for chip substrates by tuning copper oxide and internal stress

Copper oxides and internal stress have an obvious influence on adhesion strength of copper deposited polymer composites. However, the effect of the evolution behavior of copper oxides and internal stress on adhesion force of chip substrates is no clear and rare far. Herein, the copper deposited epoxy-phenolic/silica composite film with different desmear time was fabricated by using wet chemistry and electrochemistry methods. The chemical structure, surface roughness, morphology, surface chemical state, crystal structure and adhesion strength of copper and epoxy resin substrate were characterized by scanning electron microscope (SEM), interference microscope, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The adhesion strength of samples is increased from 3 N/cm to 4.7 N/cm. The effect of the evolution behavior of copper oxides and internal stress on adhesion strength of copper deposited epoxy resin composite films at the interfaces was systematically investigated, the mechanisms and reason of increasing adhesion strength and interfacial adhesion failure for copper deposited epoxy resin composite substrates were revealed. This work will provide a guidance in theory and experiment to enhance interfacial adhesion force of epoxy resin composite films for advanced substrate in the future.

A novel approach for quantitative determination of lignin content in tobacco via multiCP/MAS NMR spectroscopy

AbstractAs the main structural component of tobacco cell wall, lignin content is an important factor affecting the safety of tobacco smoking. However, it is time‐consuming to quantify lignin by conventional wet chemical analysis methods. In this work, a 13C multiCP/MAS NMR spectral analysis method for tobacco lignin was established. The multiCP/MAS NMR sequence was optimized for tobacco lignin. The optimized nuclear magnetic sequence parameters were 9 CP cycles of 1.5 ms, repolarization time of 0.7 s, and a total acquisition time of 130 min. Subsequently, TMSP was used as the internal standard substance to establish the working curve, and the correlation coefficient was 0.9946. The relative standard deviation (RSD, n = 5) was 3.26%. This method was applied to the determination of lignin content in different types of tobacco samples. The relative error in the determination of lignin content by this method did not exceed 4.46% compared to the results of the chemical method. The results showed that the 13C multiCP/MAS NMR spectral analysis method had the advantages of accuracy and rapidity, which provided a new technical means for the quantitative study of tobacco cell wall substances.

Preparation of Nonfouling Zwitterionic Coatings by Plasma-Enhanced Chemical Vapor Deposition under Ambient Pressure.

Nonspecific protein adsorption significantly impacts the performance of biomedical devices in both hemocompatibility and tissue compatibility. Polyzwitterionic coatings are a promising solution. However, conventional zwitterionic coatings always have to rely on sophisticated wet chemistry methods, leading to low controllability and high cost. In this work, zwitterionic coatings were prepared by nitrogen plasma-enhanced chemical vapor deposition (PECVD) of precursors for 90 s under ambient pressure followed by hydrolysis. The results showed that the PECVD-coated thermoplastic polyurethane (TPU), Tecoflex, effectively resists nonspecific protein adsorption, platelet adhesion, and bacterial adhesion without changing the mechanic properties of TPU. This approach simplified the zwitterionic coating process with highly controllability, showing a promising potential for the surface modification of biomedical devices.

Effect of temperature on the growth of Cupric and Cuprous Nanoparticles in a wet chemical synthesis

Cuprous oxide (Cu2O) and cupric oxide (CuO) particles were synthesized using a wet chemical surfactant free method at different synthesis temperatures from 25 °C to 60 °C. Morphology, size, and chemical composition of the prepared Cu2O particles were analyzed by FESEM, PXRD, and UV-vis. We discovered that the chemical composition of the Cu2O particles remained unaffected by the synthesis temperature. However, morphology and size of the particles showed a strong temperature dependency. This could be attributed to the temperature induced formation of CuO species from the copper hydroxide (Cu(OH)2) precursor which also functions as copper precursor for the Cu2O particle growth. The cupric oxide species was determined to be the main cause for the formation of micrometer sized particles, whereas with the Cu(OH)2 precursor species for the Cu2O particles nanocubes with smaller edge lengths as well as octahedrons were obtained.

Glucose electrooxidation on carbon supported NiAu electrocatalysts

NiAu/C nanomaterials are synthesised using a wet chemistry method with targeted Au atomic ratios of 10 %, 20 % and 30 %. Physicochemical characterisations indicate that the materials have mean compositions close to the nominal ones but ca. 20 at% Au richer in average than expected (Au ratios of 13.6 at%, 23.1 at% and 35.9 at%, respectively). The NiAu/C materials are composed of Au-rich spherical-like Janus particles of several tenths nm and of a phase of very small Ni-rich nanoparticles and Ni(OH2) clusters. The electrochemical measurements in a 0.1 M NaOH/0.1 M glucose electrolyte indicate that the NiAu20/C catalyst is the most active for the glucose oxidation reaction, leading to a mass activity at +0.6 V vs RHE >1.5 times higher than that with a pure Au/C catalyst, although the Au content is almost 5 times lower. The chronoamperometry measurements for 900 s at +0.6 V vs RHE confirm the activity gain with the NiAu20/C catalyst. The electrolysis measurement at a cell voltage of + 0.6 V for 6 h shows that the NiAu20/C catalyst is selective towards the production of gluconic acid, with a faradaic efficiency higher than 100 %, indicating the occurrence of a 1-electron reaction with anodic hydrogen coproduction. At +0.8 V, the faradaic efficiency is lower than 100 %, indicating the formation of other products than gluconic acid, but at a very low extent (not detectable by HPLC) guarantying a very high selectivity towards gluconic acid.

Precise control of CO2 electroreduction pathways over copper foil through regulating the microenvironment between morphology and crystal plane

Precisely regulating the reaction pathway to produce desired products is a major challenge in electrocatalytic carbon dioxide reduction (eCO2R). In this paper, the wet chemical method was used to adjust the microenvironment between surface morphology and crystal planes of copper-based catalyst to accurately modulate eCO2R pathway, and to achieve the switching between methane (CH4) and ethylene (C2H4) products. In high concentration acidic CuCl2 etching solution for 80 s (Cu-3.6M-80s), the surface of copper foil formed a nano-groove structure with exposed Cu (111), which exhibited remarkable selectivity towards CH4 production. In contrast, when subjected to a low concentration acidic CuCl2 etching solution for 60 s (Cu-1.8M-60s), the copper foil surface exhibited a nanosheet/cube structure exposing Cu (220) and CuCl (111), resulting in the main product switched from CH4 to C2H4 with 57.03 % at −1.0 V versus reversible hydrogen electrode. In-situ attenuated total reflectance infrared and density functional theoretical calculations demonstrated that the Cu-3.6M-80s effectively enriched proton donation and lowered the energy barrier for *CO hydrogenation, while the Cu-1.8M-60s enhanced coverage of *CO intermediates, thereby promoting subsequent C-C coupling. This study presented a promising strategy for modulating the local microenvironment of catalysts, enabling precise control eCO2R pathway to achieve distinct target products.

A comprehensive study of cytosine-ZnO interactions: Theoretical and experimental insights

This paper presents a comprehensive investigation of the adsorption of cytosine, a DNA base, on ZnO model clusters, specifically Zn2O2, Zn3O3, Zn4O4, Zn6O6, Zn8O8 ring (R) and cubic rocksalt. A density functional theory (DFT) method was used to simulate the adsorption of cytosine on ZnO (C/ZnO) clusters. The B3LYP/LanL2DZ method, which includes a correction for the dispersion contribution, was used. The calculated energy gap (Eg) for cytosine showed a strong dependence on the cluster size, highlighting variations corresponding to the dimensions of the clusters. The proposed physisorption mechanism involves the formation of an N...Zn bond between cytosine and the active Zn site on ZnO. In addition, experimental data, including microscopic and spectroscopic evidence, were integrated to further elucidate the interactions between cytosine and ZnO. A composite of C and ZnO was prepared by the wet chemical method and characterised by SEM, XRD and FT-IR analyses. The interaction of cytosine with ZnO nanoparticles was observed by UV–vis spectroscopy. The experimental results were then compared with those obtained from DFT calculations, taking into account the new insights into the cytosine-ZnO interactions. This comparison provided a holistic understanding of the system.

Digital Etching of Molybdenum Interconnects Using Plasma Oxidation

AbstractMolybdenum (Mo) has a high potential of becoming the material of choice for sub‐10 nm scale metal structures in future integrated circuits (ICs). Manufacturing at this scale requires exceptional precision and consistency, so many metal processing techniques must be reconsidered. In particular, present direct wet chemical etching methods produce anisotropic etching profiles with significant surface roughness, which can be detrimental to device performance. Here, it is shown that polycrystalline Mo nanowires can be etched uniformly using a cyclic two‐step “digital” method: the metal surface is first oxidized with isotropic oxygen plasma to form a layer of MoO3, which is then selectively removed using either wet chemical or dry isotropic plasma etching. These two steps are repeated in cycles until the intended metal recess is achieved. High uniformity of plasma oxidation defines the etching uniformity, and small metal recess per cycle (typically 1–2 nm) provides precise control over the etching depth. This method can replace wet etching where high etching precision is needed, enabling the reliable manufacturing of nanoscale metal interconnects.

Visible Light-Driven Photocatalysis and Antibacterial Performance of a Cu-TiO2 Nanocomposite.

A Cu-TiO2 nanomaterial with unique antibacterial and photocatalytic properties is introduced in this study. Cu-TiO2 nanocomposites were obtained using an adapted direct current magnetron sputtering apparatus, where TiO2 anatase nanoparticles (NPs) were used as the substrates and copper as the sputtering target. The obtained powder was characterized by physical and chemical methods. Copper was deposited on TiO2 NPs for 30 and 60 min, resulting in two samples with different copper contents of 3 and 5 wt %, respectively. The photocatalysis test evaluated the degradation of rhodamine B (RhB) dye under a specific wavelength (405 nm LED) and a complete degeneration occurred in 120 min, ∼ 33% faster when compared to pristine TiO2. The antibacterial assays were performed for Escherichia coli and Staphylococcus aureus in dark and visible-light conditions, using a 405 nm LED and a wide-spectrum white LED, reaching an inactivation of 99.9999% for both bacteria. The magnetron sputtering is an ecofriendly way to form heterojunctions with photocatalytic and bactericidal properties in the absence of wet chemical methods or residues. This work may open new pathways for enhancing the fungicidal and virucidal activities of nanocomposites under the action of visible light.

Crystallographic characterization of gypsum synthesized from marine wastes (Babylonia japonica, Olive sayana, and Conasprella bermudensis)

This study focused on the synthesis of gypsum nanocrystals using conventional wet chemical precipitation method from marine mollusks like Babylonia Japonica, Olive Sayana, and Conasprella bermudensis. Different characterization techniques like Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDX) were used to confirm the formation of the nanocrystals. XRD data assessed various structural parameters, including the dimension of the unit cell, crystallinity index, specific surface area, lattice parameters, dislocation density, and macrostrain. The Rietveld refinement study did not reveal the formation of alternate phases, and the predicted lattice parameters, Full Width at Half Maximum (FWHM), and X-ray density contradicted the actual data. The synthesized gypsum displayed crystallite dimension within the acceptable range of <200 nm, as calculated using various XRD models and equations. Additionally, the values for strain (2 × 10−4 to 4 × 10−4), stress (−1 × 107 to 2 × 107 N/m2), and energy density (2.87 × 102 to 2.16 × 103 J/m3) were also estimated for the synthesized samples. The preferential growth calculation indicateed stable phase formation of gypsum along the (0 2 0) and (0 4 0) planes. Furthermore, The study compared the properties of gypsum, including pH, conductivity, and potential difference (PD), in soil extraction and an aqueous medium.

NIR spectroscopy prediction model for capsaicin content estimation in chilli: A rapid mining tool for trait-specific germplasm screening

Chilli is a widely produced crop, highly valued for its capsaicin content, a key economic trait. Traditional wet chemistry methods for estimating capsaicin are time-taking and laborious, while non-destructive methods like NIRS coupled with chemometrics, offer efficient alternatives, simplifying and accelerating biochemical assessments. This study is the first to develop and validate and tested for applicability of NIRS-based prediction model for capsaicin content in Indian chilli germplasm using MPLS regression. Various mathematical treatments were performed, and the most suited model was selected based on high RSQexternal, RPD and lower SEP values in the external validation set, indicating strong prediction accuracy and minimal error. The model achieved high RSQexternal value of 0.808, RPD value of 2.088 and low SEP value of 3.415 for capsaicin content, demonstrating excellent prediction performance. A paired sample t-test p-value of 0.757 (p > 0.05) showed non-significant difference between wet lab and predicted values, confirming the model’s accuracy. The applicability of the model was validated on fresh harvest germplasm the following year, showing a higher reliability score of 0.949, further confirming model’s reliability. This model would aid in high-throughput, accurate screening of chilli germplasm for capsaicin, accelerating chilli crop improvement programs and the development of new high-capsaicin varieties.

Facile synthesis of Cu2O nano-microspheres anode for lithium-ion batteries

Transition metal oxide anode materials exhibit high theoretical specific capacities and can meet the energy density requirements through reasonable design. In this work, a facile wet-chemical method to fabricate Cu2O nano-microspheres anode for lithium-ion batteries with controllable size varied from 0.4 ∼ 1.2 μm is introduced, which basically using copper acetate as copper precursor and ascorbic acid as reducing agent. The solvent composition (DI water only or DI water:Ethanol = 1:1), solution alkalinity (amount of NaOH input), and synthesis temperature are investigated as factors affecting the size and morphology of Cu2O nano-microspheres. The samples are characterized by X-ray diffraction, transmission electron microscope and scanning electron microscope. Nanoparticle cluster structure is observed in the reaction product with the bi-solvent system. With the optimized synthesis condition, the prepared Cu2O anode (size of ∼ 455 ± 41 nm) delivers an initial discharge capacity of 539 mAh/g at a current density of 0.5C, 100 cycles of cyclic discharge at 0.5C with a capacity retention rate of 84.73 %. At the current density of 2C, the specific capacity is 347 mAh/g. Even at a large current density of 5C, the specific capacity is still as high as 219 mAh/g, indicating good rate capability.

An experimental and theoretical investigation of the enhanced effect of Ni atom-functionalized MXene composite on the mechanism for hydrogen storage performance in MgH2

The deposition of ultrafine single-atom nickel particles on Nb2C (MXene) was successfully achieved using a wet chemistry method to synthesize Ni@Nb2C composite. This study explored the effect of Ni@Nb2C on the hydrogen absorption and desorption properties of MgH2 through theoretical calculations and experimental investigations. Under the catalytic action of Ni@Nb2C, the initial dehydrogenation temperature of MgH2 was reduced by 121°C, with approximately 4.26 wt.% of H2 desorbed at 225°C in 100 min. The dehydrogenation activation energy of the MgH2 + Ni@Nb2C composite dropped to 86.7 kJ∙mol−1, a reduction of 60.5 kJ∙mol−1 compared to pure MgH2. Density functional theory calculations indicated that the incorporation of Ni@Nb2C enhanced the performance of MgH2 performance by improving interactions among Nb2C, Ni, Mg, and H atoms. In the Ni@Nb2C + MgH2 system, the lengths of Mg-H bonds (1.91–1.99 Å) were found to be longer than those observed in pure MgH2 (1.71 Å). The dehydrogenation energy for this system (1.08 eV) was lower than that for Nb2C (1.52 eV). These findings suggest that the synergistic effect of Ni and Nb2C significantly enhances the hydrogenation/dehydrogenation kinetics of MgH2, thereby introducing a novel approach for catalytic modification of solid hydrogen storage materials through synergistic actions.

Binder-free tin (IV) oxide coated vertically aligned carbon nanotubes as anode for lithium-ion batteries

Despite the tremendous potential of tin oxide (SnO2) as an anode material, irreversible capacity loss due to the sluggish kinetics and structural pulverization as a result of the substantial volume alteration during redox reactions limits its use in lithium-ion batteries. The typical layered design of an electrode consisting of binder and conductive additive can lower the practical capacity of high-capacity electrode materials. We synthesized a binder and conductive additive-free, self-standing core-shell vertically-aligned carbon nanotubes (VACNTs)-SnO2 anode (SnO2-VACNTs) on 3D nickel foam using plasma-enhanced chemical vapor deposition and wet chemical method. The SnO2-VACNTs exhibited excellent cyclability with a specific capacity of 1512 mAh g−1 at 0.1 A g−1 after 100 cycles and 800 mAh g−1 at 1 A g−1 after 200 cycles. The ultra-fine SnO2 particles (<5 nm) shortened the Li+ diffusion paths into the bulk electrode and alleviated the volume alteration by lowering the strains during the redox reactions. Also, proper inter-tube distance between individual SnO2-VACNTs buffered the volume instability and offered better electrolyte accessibility. Direct connection of VACNTs with the current collector ensured an uninterrupted electron conducting path between the current collector and active material, thus offering more efficient charge transportation kinetics at the electrode/electrolyte interfaces.

Kinetic Insights into Solar-Assisted Fabrication and Photocatalytic Performance of CoWO4/NCW Heterostructure

This work studies the kinetic model for the solar-driven fabrication of CoWO4/NCW heterostructure photocatalysts and investigates their enhanced photocatalytic degradation activity. The synthesis of CoWO4/NCW, its characterization, and the kinetic aspects of photocatalytic degradation under solar light. New nanocomposite prepared from Nano cellulose (NCW) by hydrolysis cotton waste (CW) by nitric acid and cobalt tungstate (CoWO4) prepared from sodium tungstate and cobalt chloride by wet chemical method and characterized through XRD, FTIR, EDX, and FE-SEM analyses. The composite's performance in organic oxidation from refinery wastewater (RWW) was evaluated under solar light. The high removal ratio was 97.4% for organic pollutants (OP) in refinery wastewater. The results indicate that the heterostructure exhibits improved photocatalytic performance compared to individual components, which kinetics model was the best to represent the photocatalytic degradation of organic pollutants from oily wastewater over the heterostructure CoWO4/NCW catalyst. Add future applications of this finding in the relevant industries. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Uniform PtCoRuRhFe high-entropy alloy nanoflowers: Multi-site synergistic signal amplification for colorimetric assay of captopril.

Uniform PtCoRuRhFe high-entropy alloy nanoflowers (HEANFs) were fabricated by a simple wet-chemical co-reduction method in oleylamine for quantitative colorimetric determination of captopril (CAP) based on multi-site synergistic signal amplification. Specifically, the peroxidase mimetic activity of the PtCoRuRhFe HEANFs was examined through catalysis of 3,3',5,5'-tetramethylbenzidine (TMB) oxidation, whose catalytic mechanism was investigated by electron paramagnetic resonance (EPR) spectroscopy. The role of the ·O2- was figured out during the catalytic procedure. Further, the oxidation of TMB (oxTMB) can be effectively reduced by CAP, accompanied by quickly transforming the solution color from blue to colorless. More importantly, the absorbance at 652nm is linearly related to the CAP concentration in a range 5.0-50.0mM with a low detection limit of 2.82mM. The method has been applied to the determination of CAP in human urine samples. It offers a simple and high-efficiency method for facile and visual detection of CAP in hospitals.

Investigation of the Effects of Cu and Fe/Cu Doping on ZnO Nanoparticles for Application as a Solid Electrolyte Battery

In this work, investigation is done on the effect of doping with copper (Cu) and iron/copper (Fe/Cu) on zinc oxide (ZnO) nanomaterials synthesized through a cost‐effective wet chemical precipitation method for application as a solid‐state electrolyte battery. The scanning electron microscope with energy dispersive X‐ray spectroscopy is used to investigate the morphology and elements presence in Cu and Fe/Cu‐doped ZnO nanoparticles. The X‐ray diffraction data illustrates that the crystallite sizes of pure ZnO, Cu–ZnO, and Fe/Cu–ZnO nanoparticles are 14.86, 13.35, and 10.66 nm, respectively, at the (101) plan calculated by Debye Scherrer's formula. The UV‐Vis absorption spectrum shows that the band gap energies of ZnO, Cu–ZnO, Fe–ZnO, and Fe/Cu–ZnO nanoparticles are identified as 3.382, 3.690, 3.5, and 3.465 eV, respectively. The electrical characterization revealed maximum impedance in Fe/Cu–ZnO nanoparticles with 400 Ω at 1 KHz frequency in comparison to other samples. The current–voltage (I–V) measurement shows that the current sensitivity and electrical conductivity are both enhanced for Fe/Cu–ZnO nanoparticles. Fe and Cu co‐doping improved the electrical characteristics of ZnO, and the Fe/Cu–ZnO nanoparticles are employed as a solid electrolyte in a battery, which achieved a high specific charge capacity of 657.85 mAh g−1.

Scanning electron microscopy imaging of multilayer-doped GaN: Effects of surface band bending, surface roughness, and contamination layers on doping contrast

Dopant profiling by a scanning electron microscope possesses great potential in the semiconductor industry due to its rapid, contactless, non-destructive, low cost, high spatial resolution, and high accuracy characteristics. Here, the influence of plasma and wet chemical treatments on doping contrast was investigated for a multilayered p-n GaN specimen, which is one of the most promising third-generation wide bandgap semiconductors. Angle-resolved x-ray photoelectron spectroscopy and atomic force microscope were employed to characterize the degree of surface band bending, surface roughness, gallium oxides, and hydrocarbons on the surface of GaN. N2 and air plasmas were unable to remove the surface contamination layers, although the degree of surface band bending was suppressed. In contrast, wet chemical methods offer superior capability in removing contamination layers; however, the surface roughness was increased to varying degrees. Notably, NH4F solution is capable of improving the doping contrast. The underlying mechanism was elucidated from the perspective of surface band bending, surface roughness, and contamination. The findings reported here will provide a feasible solution for effective characterization of semiconductor materials and devices.