NH4OH Treatment Research Articles

Improvement of the Oxidative Desulfurization Performance Using MoO3/CuO‐Modified Hierarchical HY Zeolite

AbstractThe presence of sulfur compounds in the chemical industry poses significant environmental and economic problems, including endangering human and animal lives and damaging equipment. For this purpose, hierarchical HY zeolite (Hie‐Y) with a SiO2/Al2O3 molar ratio 10 was successfully synthesized through sequential desilication‐dealumination using NH4OH treatment. A weak alkaline media with surfactant cetyltrimethylammonium bromide (CTAB) facilitates mesoporosity formation and preserves the zeolite structure. Metal oxide (CuO, MoO3) ‐ hierarchical HY zeolite nanocomposites have been prepared by one or a combination of 3 methods: 1) ion exchange, 2) precipitation, and 3) calcination. The obtained catalysts were characterized using XRD, FT‐IR, FESEM, UV‐Vis, EDS, and BET techniques. The formation of a hierarchical structure is associated with structure preservation, but partial destruction occurs based on the entering Cu in the zeolite pores. These catalysts have been studied in the oxidative desulfurization (ODS) reaction. Several parameters, including temperature, catalyst amount, DBT concentration, and reaction time, were evaluated in ODS using the Taguchi Design of Experiments. Catalytic activity order was obtained as Y<Hie‐Y<Hie‐Y/CuO<Hie‐Y/MoO3<Hie‐Y/MoO3/CuO. Results indicate an activity increase for the Hie‐Y/MoO3/CuO hierarchical structure owing to synergistic effects of secondary mesoporosity and metal oxides. The catalyst was recoverable and reused for five consecutive runs with preservation of catalytic activity.

Impact of NH4OH treatment on the ion exchange and pore characteristics of a metakaolin-based geopolymer.

We investigated the viability and influence of NH4OH post-synthetic treatment on the pore characteristics of geopolymers. Geopolymers are a class of materials with amorphous aluminosilicate three-dimensional frameworks, regarded as amorphous analogues of zeolites. Similar to zeolites, when geopolymers are used in catalysis or adsorption applications, post-synthetic treatments such as ion exchange with NH4 + salts (e.g., NH4Cl and NH4NO3) and desilication (using strong bases such as NaOH) are necessary to introduce active sites and modify their pore structure, respectively. Recently, it has been shown that treatment with NH4OH combines these two steps, in which acidic sites are introduced and the pore structures of zeolites are modified simultaneously. Considering the increasing interest in geopolymers in catalysis and adsorption applications, understanding the impact of such treatment on the structure of geopolymers is needed. Our diffuse reflectance infrared Fourier-transform spectra show that NH4 + exchanges Na+ in the geopolymer, and laser diffraction with scanning electron microscopy images show that the particle size of the powdered geopolymer decreases after NH4OH treatment. N2 sorption isotherms and 129Xe and 1H NMR measurements revealed information about the changes in pore structures: micropores were larger than mesopores and inborn mesopores increased in diameter, thereby reducing the surface area to volume ratio. However, pore accessibility and pore connectivity were not altered by NH4OH treatment. Since solid-state NMR and X-ray fluorescence revealed desilication, these changes in particle size and pore characteristics are considered to be due to desilication caused by NH4OH treatment.

Switchable hydrophilic/hydrophobic antibacterial fibrous composites for biomedical application

In this study, novel pH responsive hydrophilic/hydrophobic breathable Janus fibrous composites were fabricated with N-halamine quaternary ammonium salt/polyhydroxybutyrate inside and pH sensitive polymer/polycaprolactone outside. After HCl treatment, the fibrous membrane shows well hydrophilicity and breathability, which is helpful for cell growth and proliferation, further accelerating wound healing. Moreover, the membrane has prominent antibacterial efficiencies, which can activate 99.95% of S. aureus and 99.99% of E. coli O157:H7 within 30 min. Notably, this membrane displays excellent hemostasis performance. After further NH4OH treatment, the membrane transforms different wettability and thus reduce bacterial adhesion by its hydrophobicity. Similarly, one side of membrane has hemostasis property, while another side possesses anticoagulant properties with high contact angle of blood, which can prevent blood permeate. Besides, the cell viability test illustrates that no pronounced toxicity to cells is observed. Therefore, the adjustable hydrophilic/hydrophobic material highly extends the application of Janus membrane as wound healing dressing.

Isotherm and kinetic investigations of sawdust-based biochar modified by ammonia to remove methylene blue from water

Chemical industry effluent may pose significant environmental risks to both human health and the economy if it is not properly managed. As a result, scientists and decision-makers are paying increasing attention to developing a sustainable, low-cost wastewater treatment technique. This work aims to investigate the adsorption of Methylene Blue (MB) dye present in water using biochar derived from sawdust modified by boiling in an ammonia solution (SDBA). The properties of SDBA were characterized by BET, SEM, XRD, BJH, FT-IR, DTA, EDX and TGA analyses. The presence of –OH and –NH groups in SDBA was confirmed by FTIR, which proved that the NH4OH treatment of biochar successfully added nitrogen groups on its surface. The influence of pH (2 to 12), MB dye initial concentration (20 to 120 mg/L), adsorbent dosage (0.5 to 4.0 g/L) and contact time (0 to 180 min) on the adsorption process has been investigated. The adsorption of MB dye is more favorable at basic pH, with optimum adsorption at pH 8. Using a starting concentration of 20 mg/L of MB dye and a 4.0 g/L SDBA dose, the maximum percent clearance of MB dye was 99.94%. Experimental results were fitted to the Freundlich (FIM), Tempkin (TIM) and Langmuir (LIM) isotherm models (IMs). The FIM fitted the equilibrium data well, with a 643.74 mg/g Qm. Various error function models were used to test the data obtained from IMs. According to Error Function results, experimental data showed that it fits better for LIM and FIM. Kinetic studies indicated that the MB dye adsorption procedure followed pseudo-second-order (PSOM) kinetics based on film diffusion (FDM), pseudo-first-order (PFOM) and intra-particle diffusion models (IPDM). MB dye sorption on the SDBA involved electrostatic interaction, surface participation, hydrogen bond and π–π interactions. The adsorption mechanism of MB dye by SDBA was proposed as physical adsorption via the electrostatic attraction process. SDBA is an effective adsorbent in removing MB dye from water. Six adsorption–desorption cycles of the MB dye were run through the regeneration of SDBA with only a minimal amount of adsorption capacity loss, demonstrating the reusability of manufactured SDBA.

Characterization of Wet Chemical Atomic Layer Etching of InGaAs

In this work, we characterized the wet chemical atomic layer etching of an InGaAs surface by using various surface analysis methods. For this etching process, H2O2 was used to create a self-limiting oxide layer. Oxide removal was studied for both HCl and NH4OH solutions. Less In oxide tended to remain after the HCl treatment than after the NH4OH treatment, so the combination of H2O2 and HCl is suitable for wet chemical atomic layer etching. In addition, we found that repetition of this etching process does not impact on the oxide amount, surface roughness, and interface state density. Thus, nanoscale etching of InGaAs with no impact on the surface condition is possible with this method.

Surface modification of activated carbon via HCl or NH4OH treatment to enhance the removal of Cr(VI) from aqueous solution

Surface modification of activated carbon via HCl or NH4OH treatment to enhance the removal of Cr(VI) from aqueous solution

Fabrication of pH-responsive hydrophobic/hydrophilic antibacterial polyhydroxybutyrate/poly-ε-caprolactone fibrous membranes for biomedical application

The clinical microbial infection has been a common syndrome and a serious threat to patients, and the biodegradable biomaterials with antibacterial property attracted increasing attention to replace traditional biomaterials including packaging and bandages. In this study, we generated fibrous membranes with biodegradable polyester polyhydroxybutyrate and poly-ε-caprolactone (PHB/PCL) by electrospinning, and synthesized containing N-halamine quaternary ammonium salt (HQAS) as antibacterial agent. Dimethylaminoethyl methacrylate (DMAEMA) as pH-responsive hydrophobic agent was grafted onto PHB/PCL fibrous membranes by in situ polymerization. The hydrophilic and the hydrophobic membranes were obtained with HCl and NH4OH treatments, respectively. On one hand, the membrane manifested prominent antimicrobial efficacy against E. coli O157:H7 (ATCC 43895) and S. aureus (ATCC 6538) when the surface was hydrophilic after further treatment by HCl solution, and the membrane had prominent thrombogenicity with 60.6% of BCI. On the other hand, after further treatment by NH4OH solution, the membrane showed poor antibacterial efficacy against E. coli O157:H7, while the membrane surface exhibited excellent hydrophobicity with an average contact angle of 134oand self-cleaning properties to reduce bacterial adhesion. In addition, the pH-responsive hydrophilic/hydrophobic membranes showed good stability and durability towards UVA light exposure and storage. Therefore, these pH-responsive hydrophilic/hydrophobic antibacterial membranes may have great potential for application in biomedical materials.

Immobilization and activation of cobalt-amine catalyst on NH4OH-treated activated carbon for ethylene dimerization

Catalytic dimerization of ethylene (C2H4) to butene (C4H8) utilizes homogenous catalysts composed of transition metal molecular complexes in the presence of a co-catalyst or Ni, Rh or Cr supported heterogeneous catalysts. Recently, a heterogeneous cobalt catalyst supported on NH4OH-treated carbon (Co/NC) has gained attention. However, the structure of the active site, the identity of the active phase, the role of NH4OH treatment and the effect of thermal activation have remained elusive. Herein, in situ Raman spectroscopy showed the absence of crystalline cobalt oxide phases, such as CoO or Co3O4, in the working catalyst. An intense Raman band at 810 cm−1 was detected in the as-synthesized catalyst, which corresponds to μCo-peroxo species formed via auto-oxidation of the [Co(NH3)x]2+ sites during the drying step. UV–vis DRS absorbance bands at ∼286, 340 and 560 nm indicated that a mixture of octahedral Co3+ and Co2+ is present in the as-synthesized catalyst. During thermal treatment in inert atmosphere, the 265 and 810 cm−1 Raman bands diminished signifying the reduction of μCo-peroxo sites, with the oxidation of some NH3 ligands to N2O(g), indicated by an IR doublet at ∼2225 cm−1. UV–vis DRS during thermal treatment corroborated the reduction of Co3+ to Co2+, with Co2+ sites coordinated in a tetrahedral fashion, as indicated by a new absorbance band at ∼600−700 nm. The presence of the immobilized pseudo-tetrahedral [Co(NH3)x]2+ molecular complexes active for dimerization is proposed as an alternative to previous reports that attribute olefin dimerization activity to crystalline cobalt oxide phase in this catalyst. Steady-state catalytic test results at 1 bar, 80 °C, 5.0 % C2H4 at 10 sccm, 0.3 g catalyst show that model catalyst containing crystalline cobalt oxides (Co/C) exhibited similar initial butene productivity to the [Co(NH3)x]2+ containing Co/NC catalyst, but suffered sharper deactivation due to the irreversible olefin deposition on Co3+ sites.

Phyllosilicate mineral dissolution upon alkaline treatment under aerobic and anaerobic conditions

The dissolution of phyllosilicate minerals exposed to high-pH environments was studied to quantify the influence of alkaline treatments and variable redox conditions on clay dissolution including incongruent dissolution phenomena. The objective of this research was to systematically quantify mineral dissolution with variable alkaline treatments and redox conditions for the first time. This study is focused on the dissolution of phyllosilicate minerals (illite, muscovite, and montmorillonite) under anaerobic and aerobic conditions using comparative solutions (sodium hydroxide and ammonium hydroxide) at similar hydroxide concentration. Our batch data show that there is a rapid decrease in aluminum dissolution (<240 h) and slow increase in silica dissolution over time (up to 1440 h). This trend was particularly evident for montmorillonite for which the greatest dissolution was observed with ammonium hydroxide treatment, likely due to intercalation of the polyatomic cation ammonium into the mineral's expandable layers. When comparing alkaline treatments, the strong base sodium hydroxide dissolved more of the mica minerals, illite and muscovite, likely due to ion-pairing between the silicate tetrahedra [SiO4]n- and Na+ cations in solution compared with weak base NH4OH treatment. In addition, the decreasing redox changes in the absence of oxygen were similar, although the sodium hydroxide treatment had greater variability. For all investigated phyllosilicates, the calculated aqueous aluminum and silicon ratios over time were significantly different from the minerals' stoichiometric ratios. As a result, we conclude that incongruent dissolution occurred and suggest formation of secondary precipitates. Understanding the potential for clay mineral alterations from interaction with alkaline solutions has implications for in situ remediation, mining operations, and waste interactions within the subsurface. This research shows that incongruent dissolution in phyllosilicate minerals occurs and will likely lead to secondary precipitation which may have long term physical and chemical impacts in the subsurface.

N-doped porous carbon supported Ni catalysts derived from modified Ni-MOF-74 for highly effective and selective catalytic hydrodechlorination of 1,2-dichloroethane to ethylene

Metal-organic frameworks (MOFs) have received significant attention as promising precursors or sacrificial templates in the preparation of porous carbon supported catalysts. In this study, N-doped porous carbon supported Ni catalysts (denoted as Ni/NC) were prepared using furfuryl alcohol (FA) loaded Ni-MOF-74 as the precursor followed by NH4OH treatment and pyrolysis under N2 atmosphere. For comparison purpose, Ni catalysts supported on porous carbon (denoted as Ni/C) were also prepared by direct pyrolysis of Ni-MOF-74. The selective gas phase catalytic hydrodechlorination of 1,2-dichloroethane to ethylene was carried out to evaluate the catalytic performances of the catalysts. It was found that for Ni catalysts prepared at the same pyrolysis temperature, Ni particle sizes in Ni/NC catalysts were significantly smaller (20–40% smaller) than that of Ni/C. This reflected that pre-modification of Ni-MOF-74 using FA and NH4OH could effectively increase Ni dispersion in Ni catalysts derived from Ni-MOF-74. Moreover, Ni/NC had a markedly stronger ability to form spillover H2 owing to the enhanced metal-support interactions by N-doping. Accordingly, Ni/NC catalysts exhibited much higher catalytic activities than Ni/C catalysts. The turnover frequencies of Ni/NC catalysts were found to be 1.22–1.65 times higher than Ni/C catalysts. Increasing pyrolysis temperature led to decreased catalytic activities of both Ni/C and Ni/NC catalysts, due to the aggregation of Ni particles at higher treatment temperature. The findings from this study demonstrate that the MOF-mediated synthesis method offers a promising way to prepare Ni-based catalysts for catalytic hydrodechlorination of chlorinated hydrocarbons.

Comparison of methods for economic and efficient tick and Borrelia DNA purification

DNA purification is a critical step in the processing of samples for molecular diagnosis and/ or identification of pathogens via polymerase chain reaction (PCR). Especially when handling vectors like ticks, purifying the DNA always poses a challenge.In this study, we compared factors that may have an influence on DNA extraction namely commercially available DNA extraction kits vs alkaline hydrolysis for DNA extraction. The methods were applied to questing Ixodes (I.) ricinus ticks and Borrelia cultures of defined cell concentrations. A total of 69 questing I. ricinus ticks were collected. From 34 ticks, total DNA was extracted using a commercial DNA extraction kit. Thirty-five ticks were treated with 1.25% ammonium hydroxide (NH4OH). Six ticks from each batch were placed in 70% ethanol (EtOH) for one week prior to DNA extraction to see the effect of EtOH preservation on total DNA yield. DNA yield was estimated in field-collected ticks using conventional PCR targeting the Ixodes Cytochrome C oxidase (coi) gene and in cultured Borrelia isolates using quantitative real-time PCR (qPCR) targeting the FlaB encoding gene of Borrelia.Column DNA extraction yielded slightly better results than NH4OH treatment when tested in a PCR targeting a tick-specific coi gene (96% PCR-positive vs 86% PCR-positive results, respectively). EtOH preservation had a slightly negative effect on DNA yield and – again – slightly stronger PCR products were observed by commercial kit extraction. A Shapiro-Wilk test conducted revealed a significance-level of 90% for both the methods, indicating a normal distribution of the values generated by BioNumerics quantification. A two-sided t-test conducted revealed a significant (p < 0.01) mean difference between the methods. Similarly, qPCR on cultured specimen DNA of Borrelia burgdorferi sensu stricto (B. burgdorferi s.s.) (B31) with different concentrations revealed a better yield for kit extraction in comparison to NH4OH treatment; a difference of approximately 3 Ct-values was ascertained between extraction methods. A one-sided t-test showed a significant difference between the methods at lower concentration of Borrelia i.e. better extraction with a commercial kit at lower borrelial DNA concentration, while at higher concentration (106 cells per ml) the difference was not significant.

The effects of the PEDOT:PSS acidity on the performance and stability of P3HT:PCBM-based OSCs

The optical transmittance, electrical conductivity and morphology of PEDOT:PSS treated with ammonium hydroxide (NH4OH) have been investigated. Transmittance spectra of spun PEDOT:PSS layers were enhanced slightly as a result NH4OH treatment while surface of the films has exhibited variation in the roughness and an increase in the electrical conductivity. Improvement in the physical properties of PEDOT:PSS is shown to be the key factor in enhancing the power conversion effeciency (PCE) with values as high as 4% associated with high fill factor (FF) of 57%, open circuit voltage (VOC) of 0.64 V and larger short circuit current density (JSC) of 11 mA cm−2. Stabiltiy test of the devices has been carried out over a period of 2 months, when a device incorporating PEDOT:PSS with pH ~ 4 as the hole transport layer has shown an improved stability with a degredation in PCE in about 43% whereas JSC has decreased in about 20% compared to a device incorporating pristine PEDOT:PSS with PCE decreased in about 66% and JSC in about 50% over the stated period of test. These effects have been ascribed to the increased acidity of the hole transport layer.

Wet Pretreatment-Induced Modification of Cu(In,Ga)Se2/Cd-Free ZnTiO Buffer Interface.

We report a novel Cd-free ZnTiO buffer layer deposited by atomic layer deposition for Cu(In,Ga)Se2 (CIGS) solar cells. Wet pretreatments of the CIGS absorbers with NH4OH, H2O, and/or aqueous solution of Cd2+ ions were explored to improve the quality of the CIGS/ZnTiO interface, and their effects on the chemical state of the absorber and the final performance of Cd-free CIGS devices were investigated. X-ray photoelectron spectroscopy (XPS) analysis revealed that the aqueous solution etched away sodium compounds accumulated on the CIGS surface, which was found to be detrimental for solar cell operation. Wet treatment with NH4OH solution led to a reduced photocurrent, which was attributed to the thinning (or removal) of an ordered vacancy compound (OVC) layer on the CIGS surface as evidenced by an increased Cu XPS peak intensity after the NH4OH treatment. However, the addition of Cd2+ ions to the NH4OH aqueous solution suppressed the etching of the OVC by NH4OH, explaining why such a negative effect of NH4OH is not present in the conventional chemical bath deposition of CdS. The band alignment at the CIGS/ZnTiO interface was quantified using XPS depth profile measurements. A small cliff-like conduction band offset of -0.11 eV was identified at the interface, which indicates room for further improvement of efficiency of the CIGS/ZnTiO solar cells once the band alignment is altered to a slight spike by inserting a passivation layer with a higher conduction band edge than ZnTiO. Combination of the small cliff conduction band offset at the interface, removal of the Na compound via water, and surface doping by Cd ions allowed the application of ZnTiO buffer to CIGS treated with Cd solutions, exhibiting an efficiency of 80% compared to that of a reference CIGS solar cell treated with the CdS.

Effect of Surface Preparation on the Residual Oxide Thickness and Material Loss of In-Ga-As Epi Layer

Si-based complementary metal-oxide-semiconductor (CMOS) is facing physical limitation resulting from the scaling down of devices. In addition, several issues such as short channel effect and increase in the leakage current become critical. In order to solve those problems in the Si-based CMOS, introduction of a new channel material for the transistor such as III-V compound semiconductors and Ge can be one of the solutions due to their high electron mobilities [1, 2]. Among the III-V compound semiconductors, InGaAs is receiving an attention for improving device performance because it has electron mobility as high as 11400 cm2/Vs [3]. However, it is known that III-V semiconductors are not as robust as Si against the wet chemistries. Therefore, in order to introduce InGaAs as a new channel material, surface preparation of InGaAs in wet chemical processes should be controlled. In the current study, we investigated the effect of various wet chemical treatments on the InGaAs surface. In order to study surface reaction of InGaAs such as oxidation and etching, undoped epitaxial InGaAs (100) on InP:Fe wafers were used. InGaAs samples were dipped in the solutions such as HCl, HCl/H2O2 mixture (HPM), NH4OH, and NH4OH/H2O2 (APM). The chemical state of InGaAs surface was observed by X-ray photoelectron spectroscopy (XPS) and the oxide thickness and etching rate of InGaAs were measured by transmission electron microscopy (TEM) and spectroscopic ellipsometry. The chemical states (Ind35/2, Ga3d and As3d) of InGaAs surface after HCl, HPM, deionized water, NH4OH and APM are shown in Fig. 1. It is first observed that the oxidation states in In3d, Ga3d and As3d (In2O3, Ga2O3 and As2O3) decreased after HCl treatment as compared to as-received InGaAs surface, while they increased after NH4OH treatment. On the other hand, significant increases in oxidation states of InGaAs were observed after the treatment of HPM or APM, which suggests that oxidation of InGaAs surface is accelerated by H2O2 in aqueous solutions. It is also noted that InGaAs surface was also oxidized after deionized water treatment. Although E-pH diagram is based on the theoretical calculations of thermodynamical equilibrium in a single metal-water system, based on each E-pH diagram of In, Ga and As, it is expected that InGaAs surface can be dissolved in both acidic and basic solution [4]. Therefore, from the fact that the XPS oxidation states of the InGaAs surface after basic treatment were larger than in acidic solution as shown in Fig. 1, it is suggested that dissolution of the oxidized InGaAs layer is dominant in acidic solution, while it is a rate limiting step in the basic solution. Those findings imply that further increase in the oxidant concentration in acidic solution (HCl or HPM) will accelerate overall etching kinetics of InGaAs, while its impact in the basic solution is smaller. The effect of process sequence on the residual oxide thickness on InGaAs surface was investigated and the results are shown in Fig. 2. The oxide thickness was obtained by ellipsometry and TEM measurements, and the results are relatively well matched each other as shown in Figs. 2(a) and (b). It is here noted that a significant increase in the oxide thickness was observed with 1/1/100 HPM (1HPM) as compared to 1/0.1/100 HPM (0.1HPM) in either HF-last or HPM-last process, which suggests a higher concentration of H2O2 in HPM solution produced an increased oxide thickness on InGaAs surface. The amount of material loss of InGaAs epi layer during each sequence is also given in Fig. 2(a). As expected from the observation of XPS spectra, once 1/1/100 HPM (1HPM) is introduced in the wet processes, the loss of InGaAs was much larger due to active and balanced surface oxidation and etching, as compared to 1/0.1/100 HPM (0.1HPM) process. Based on those results, it is concluded that the concentration of H2O2 in HPM solution is one of key factors to determine the residual oxidation and overall etching rate of InGaAs layer, which strongly suggests that the concentration of H2O2 especially in HPM process should be optimized at the surface preparation of InGaAs semiconductor.

XPS Study of the Chemical Surface Engineering on Ultra-Thin Inaln Layers: Evaluation of Thermal Stability to Oxygen Exposure

III-V nitride materials combine unique properties such as a direct and tuneable band gap from n-IR (InN, 0.7 eV) to n-UV (AlN, 6.2 eV). Among the electronic devices, AlGaN/GaN and InAlN/GaN device structures are commonly developed for HEMT (high electron mobility transistors). The strong advantage of InxAl1-xN is a spontaneous high polarization leading to an extremely high carrier density in 2DEG (about 3.5 x 1013 cm-2). Moreover, the near lattice matched composition with GaN is achieved for x = 0.17 - 0.20, leading to a strain-free heterojunction which drastically reduce the structural defects [1]. As a high difference is encountered in growth temperature between InN (600°C) and AlN (1100°C), the main difficulty resides in making a high crystalline quality and a good homogeneity of InAlN layers [2]. Nevertheless, MOCVD gives excellent composition uniformity and good device performance for ultra thin-layers (from 7 to 9 nm thickness). III-V nitride materials are known to be chemically stable at working temperature and poorly reactive to air exposure. Nevertheless, higher annealing temperatures (more than 800°C) are needed during engineering when ohmic contact is performed. Such materials request high performances and little variations on the surface chemistry can harm the quality of 2DEG. Moreover, InAlN/GaN structure shows a lower thermal stability compared to AlGaN/GaN devices [3]. Only few studies describe the thermal stability of InAlN layers [4]. Some workers show a better thermal stability for a slower rate of growth in MOCVD [5], whereas others focus on an ohmic contact annealing at a lower temperature of 600°C to 650°C [6]. In this work, we choose to study by XPS the chemical surface engineering on InAlN ultra-thin layers at higher temperature, from 850°C to 950°C, under O2 rich and Ar atmosphere, in order to detect the possible degradation mechanisms usually running through the HEMT elaboration process. XPS characterizations lead us to an accurate analyze on the major effects of the thermal treatments. The table Figure 1 (a) shows that the O2 thermal treatment at 850°C drastically increase the oxygen content and decrease the nitrogen content, justifying the formation of an ultra-thin oxide layer on surface. After the O2 thermal treatment, carbon content is very low, around 6 at%, showing layers with a very few contamination. The additional Ar thermal treatment at 850°C has practically no impact on the layer. Concerning the InAlN matrix, an important chemical change is observed at high energy (404 eV) in the N1s band. Figure 1 (b) shows the evolution of the N1s peak for InAlN as-grown layer, and layers annealed 850°C and 950°C under O2 rich atmosphere for 1 min. Area ratios shows an evolution in the proportion of the additional N1s peak at 404 eV from 32% for the annealing at 850°C to 56% for the annealing at 950°C. The very strong gap of 6.7 eV, observed between the later and the N1s peak at 397.3 eV accredited to InAlN, is attributed to interstitial N2 molecules trapped in the structure [7]. Enlargement of the N1s band at 397.3 eV can also be seen. This effect could be attributed to N-N bonded defect in structures [8]. The aging of the samples shows that the N2 interstitial molecules are slowly decreased after 2 months and almost totally gone after 1 year. Unlike this evolution, N-N defects still present inside the matrix even after 1 year of aging justifying that those defects are deeply incorporated inside the InAlN layer. To our knowledge, this unusual behavior was not reported before on InAlN layers. Indeed, the surface modification using physical process such as N2 plasma or chemical solution process such as NH4OH treatment will be also getting into details.

Effect of Surface Preparation on the Residual Oxide Thickness and Material Loss of InGaAs Layer

Indium gallium arsenide (InGaAs) can be introduced as a new channel material for improving device performance due to its high electron mobility. Surface preparation of InGaAs in wet chemical processes should be controlled because InGaAs is not as robust as Si against the wet chemistries. In this work, oxidation and etching behavior on InGaAs surface were investigated for acidic and basic treatments. It was observed that the oxidation states decreased after HCl treatment as compared to as-received InGaAs surface, while they increased after NH4OH treatment. The oxidation states increased after addition of H2O2 in both acidic and basic solutions. It is suggested that dissolution of the oxidized InGaAs layer is dominant in acidic solution, while it is a rate limiting step in the basic solution. Therefore, the concentration of oxidant such as H2O2 in acidic solution is important factor to determine residual oxidation and overall etching rate of InGaAs layer.

Effect of NH4OH Treatment on Plasma‐Assisted InP/Al2O3/SOI Direct Wafer Bonding

The effect of NH4OH treatment on InP/Al2O3/SOI direct wafer bonding is investigated. The atomic force microscope (AFM) and water contact angle (CA) results reveal a decrease in root‐mean‐square (RMS) surface roughness and CA of the NH4OH‐treated InP wafer. X‐ray photoelectron spectroscopy (XPS) analysis is carried out to ascertain the chemical composition of the bonding surfaces. It is found that NH4OH treatment followed by plasma activation increases the content of oxides on the surface of InP wafer. Based on these results, it is concluded that NH4OH treatment helps increase hydrophilicity and contact area of the bonding surface, thus contributing to the success of plasma‐assisted InP/Al2O3/SOI wafer bonding.

NH₄OH Treatment for an Optimum Morphological Trade-off to Hydrothermal Ga-Doped n-ZnO/p-Si Heterostructure Characteristics.

Previous studies on Ga-doped ZnO nanorods (GZRs) have failed to address the change in GZR morphology with increased doping concentration. The morphology-change affects the GZR surface-to-volume ratio and the real essence of doping is not exploited for heterostructure optoelectronic characteristics. We present NH4OH treatment to provide an optimum morphological trade-off to n-GZR/p-Si heterostructure characteristics. The GZRs were grown via one of the most eminent and facile hydrothermal method with an increase in Ga concentration from 1% to 5%. The supplementary OH− ion concentration was effectively controlled by the addition of an optimum amount of NH4OH to synchronize GZR aspect and surface-to-volume ratio. Hence, the probed results show only the effects of Ga-doping, rather than the changed morphology, on the optoelectronic characteristics of n-GZR/p-Si heterostructures. The doped nanostructures were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, photoluminescence, Hall-effect measurement, and Keithley 2410 measurement systems. GZRs had identical morphology and dimensions with a typical wurtzite phase. As the GZR carrier concentration increased, the PL response showed a blue shift because of Burstein-Moss effect. Also, the heterostructure current levels increased linearly with doping concentration. We believe that the presented GZRs with optimized morphology have great potential for field-effect transistors, light-emitting diodes, ultraviolet sensors, and laser diodes.

Impact of Surface Treatment on Interface States of ALD Al2O3/GaN Interfaces

Two surface treatments of GaN, prior to atomic layer deposition (ALD) of Al2O3, were compared to investigate electronic and chemical interface properties: (1) HCl followed by HF and (2) NH4OH. Constant capacitance deep level transient and optical spectroscopies (CC-DLTS/CC-DLOS) and X-ray photoelectron spectroscopy (XPS) were used to study the impact of the surface treatments on the interface state density (Dit) and the chemical composition of the Al2O3/GaN interface, respectively. It was determined that the HCl/HF treatment resulted in 3–10 times higher Dit near the GaN conduction band, while the NH4OH treatment resulted in nearly 10 times higher Dit deeper in the GaN bandgap. XPS revealed that the HCl/HF treatment left residual adsorbed fluorine atoms at the interface and that the NH4OH treatment resulted in a higher concentration of carbon near the Al2O3/GaN interface. These results are discussed in relation to the relevant literature in attempt to understand the relationship between the chemical composition at the interface and the observed differences in Dit.

Chemically Roughened Solid Silver: A Simple, Robust and Broadband SERS Substrate.

Surface-enhanced Raman spectroscopy (SERS) substrates manufactured using complex nano-patterning techniques have become the norm. However, their cost of manufacture makes them unaffordable to incorporate into most biosensors. The technique shown in this paper is low-cost, reliable and highly sensitive. Chemical etching of solid Ag metal was used to produce simple, yet robust SERS substrates with broadband characteristics. Etching with ammonium hydroxide (NH4OH) and nitric acid (HNO3) helped obtain roughened Ag SERS substrates. Scanning electron microscopy (SEM) and interferometry were used to visualize and quantify surface roughness. Flattened Ag wires had inherent, but non-uniform roughness having peaks and valleys in the microscale. NH4OH treatment removed dirt and smoothened the surface, while HNO3 treatment produced a flake-like morphology with visibly more surface roughness features on Ag metal. SERS efficacy was tested using 4-methylbenzenethiol (MBT). The best SERS enhancement for 1 mM MBT was observed for Ag metal etched for 30 s in NH4OH followed by 10 s in HNO3. Further, MBT could be quantified with detection limits of 1 pM and 100 µM, respectively, using 514 nm and 1064 nm Raman spectrometers. Thus, a rapid and less energy intensive method for producing solid Ag SERS substrate and its efficacy in analyte sensing was demonstrated.