Removal Of Surface Contaminants Research Articles

Influence of primary electron incident angle and electron bombardment on the secondary electron yield of laser-treated copper

Electron cloud is a persistent problem in operating modern accelerators. It might be eliminated by reducing the secondary electron yield (SEY), which is a property of the material of vacuum chambers. In the present study, the SEYs of oxygen-free copper samples are dramatically mitigated by grooving their surfaces with a laser-etching technique. Such mitigation is realized by trapping incident primary electrons and their induced secondary electrons in the grooves. The SEYs of the laser-etched samples are dependent on the geometrical characteristics of the grooves and the incident angles of the primary electrons, i.e., reducing the incident angle can lead to a reduction in the SEY. Electron bombardment of the grooved surface with an electron dose of 2 × 10−2 C mm−2 will further reduce its maximum SEY from 1.15 to 0.98, which might be attributed to the formation of Cu2O and graphite-like C—C bonds and the removal of surface contaminants.

Oxide-water interaction and wetting property of ceria surfaces tuned by high-temperature thermal aging

The high transmittance, environmentally robust, and unique interaction with water make lanthanide series rare-earth oxides promising for various applications such as next-generation self-cleaning coatings. However, the underlying mechanism of the anomalous hydrophobicity in lanthanide oxides remains controversial due to the lack of molecular-level studies in a well-controlled environment, which greatly limits the possibility to engineer their wettability for broader technical applications. Here, we systematically studied the mechanism that governs the wetting behaviors of ceria films by in-situ X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and water contact angle measurements under the environmentally controlled conditions. It was found that the hydrophobicity of ceria was mainly contributed by the adsorbed hydrocarbon, and the wettability could be enhanced on cleaner ceria surfaces with more degree of hydroxylation. Based on the significant dependence of wetting property on surface contamination, we further developed an in-situ annealing method to significantly improve the water-splitting performance of ceria powders by removing hydrocarbon contamination. These results suggest that the removal of surface contamination by high-grade oxidation is the key factor to facilitate the water dissociation of ceria films, providing new insights into the control of their wetting property and design of high-performance devices based on ceria films.

Surface and subsurface characterization of laser-interference structured Ti6Al4V

Ti6Al4V specimens were exposed to high-energy laser pulses of 1.24 J/cm2 fluences per pulse using a two-beam optical configuration to attain laser-interference. In addition to the formation of periodic surface textures by laser-interference, scanning electron microscope (SEM) images demonstrated several microstructural changes on the surface processed. Moreover, the surface and subsurface of Ti6Al4V specimens were characterized for the as-received and laser-interference processed conditions using x-ray photoelectron spectroscopy (XPS) and electron energy dispersive spectroscopy (EDS). The XPS data showed that this laser technique is effective at removal of surface contaminants for Ti6Al4V. The XPS analysis also revealed the formation of an oxy-nitride layer on the laser treated material. The microstructure analysis indicates that grain refinement, dendrite and twin structures were found near the surface due to laser processing.

Degradation of Temminck's pangolin (Smutsia temminckii) scales with a keratinase for extraction of reproductive steroid hormones

Hormone monitoring in keratinous tissues has become increasingly popular. The insoluble keratin materials are generally pulverised before hormone extraction; however, this is difficult for thicker keratin structures like baleen plates or hooves. A new method, involving the use of keratinase, allows enzymatic digestion of keratin and hormone analysis in the resulting suspension. Pangolins are unique mammals covered in keratinous scales, which are one of the reasons these animals are extensively trafficked. This study aimed to investigate the suitability of Temminck's pangolin scales as hormone matrix for quantifying reproductive steroids. A protocol was developed to digest scales with a keratinase before measuring hormone concentrations. This method can be used to investigate the reproductive endocrinology of Temminck's pangolins but may also be extended to the other extant pangolin species.•Keratinase digests Temminck's pangolin scales and reproductive steroid metabolite concentrations are measurable in the resulting suspension.•Isopropanol is an ideal washing solvent for scales to remove surface contaminants and scale sample mass should be standardised to allow comparisons.•Any section of a scale and scales from any pangolin body region can be used as samples for hormone quantification.

Photoluminescence, thermoluminescence, and cathodoluminescence of optimized cubic Gd2O3:Bi phosphor powder

Cubic Gd2 − xO3:Bix phosphor powders were prepared with a combustion method and the effect of different annealing temperatures and dopant concentration on the photoluminescence (PL), thermoluminescence (TL), and cathodoluminescence (CL) were investigated. A single-phase cubic crystal structure with the Ia3¯ space group was formed. The average crystallite size increased and decreased, respectively, with an increased annealing temperature and an increased Bi3+ doping concentration. Absorption bands at 250, 275, and 315 nm were observed due to 4f-4f transitions of the Gd3+ ions and at 260, 335, and 375 nm due to the excitation of Bi3+ ions. The emission was obtained from two centers associated with the substitution of the Gd3+ ions with Bi3+ ions at the two different sites in the crystal lattice of Gd2O3 (with a point symmetries C2 and S6). The TL glow curves of the UV-irradiated samples showed a low temperature peak at about 364 K and a high temperature peak at 443 K for all the samples. The surface and CL stability during electron irradiation was monitored. The CL emission of the Gd2O3:Bi was stable after removal of surface contaminants. The phosphor might be usable for solid state lighting and displays due to its broad blue-green emission.

Inducing upwards band bending by surface stripping ZnO nanowires with argon bombardment

Metal oxide semiconductors such as ZnO have attracted much scientific attention due their material and electrical properties and their ability to form nanostructures that can be used in numerous devices. However, ZnO is naturally n-type and tailoring its electrical properties towards intrinsic or p-type in order to optimise device operation have proved difficult. Here, we present an x-ray photon-electron spectroscopy and photoluminescence study of ZnO nanowires that have been treated with different argon bombardment treatments including with monoatomic beams and cluster beams of 500 atoms and 2000 atoms with acceleration volte of 0.5 keV–20 keV. We observed that argon bombardment can remove surface contamination which will improve contact resistance and consistency. We also observed that using higher intensity argon bombardment stripped the surface for nanowires causing a reduction in defects and surface OH– groups both of which are possible causes of the n-type nature and observed a shift in the valance band edge suggest a shift to a more p-type nature. These results indicate a simple method for tailoring the electrical characteristic of ZnO.

Pathogenesis of Molar Hypomineralisation: Aged Albumin Demarcates Chalky Regions of Hypomineralised Enamel.

Molar hypomineralisation (MH) is becoming globally recognised as a significant public health problem linked to childhood tooth decay. However, with causation and pathogenesis unclear after 100 years of investigation, better pathological understanding is needed if MH is to become preventable. Our studies have implicated serum albumin in an extracellular pathomechanism for chalky enamel, opposing longheld dogma about systemic injury to enamel-forming cells. Hypothesising that chalky enamel arises through developmental exposure to serum albumin, this study used biochemical approaches to characterise demarcated opacities from 6-year molars. Addressing contradictory literature, normal enamel was found to completely lack albumin subject to removal of surface contamination. Querying surface permeability, intact opacities were found to lack salivary amylase, indicating that “enamel albumin” had become entrapped before tooth eruption. Thirdly, comparative profiling of chalky and hard-white enamel supported a dose-response relationship between albumin and clinical hardness of opacities. Moreover, albumin abundance delineated chalky enamel from white transitional enamel at opacity borders. Finally, addressing the corollary that enamel albumin had been entrapped for several years, clear signs of molecular ageing (oxidative aggregation and fragmentation) were identified. By establishing aged albumin as a biomarker for chalky enamel, these findings hold methodological, clinical, and aetiological significance. Foremost, direct inhibition of enamel-crystal growth by albumin (here termed “mineralisation poisoning”) at last provides a cogent explanation for the clinical presentation of demarcated opacities. Together, these findings justify pursuit of an extracellular paradigm for the pathogenesis of MH and offer exciting new prospects for alleviating childhood tooth decay through medical prevention of MH.

Preparation of clean MgO surface by oxygen plasma: Comparison with standard substrate cleaning procedures

Different surface preparation methods for cleaning MgO, a widely used substrate in oxide epitaxy, are summarized and compared. We find that in situ surface preparation methods are preferable to ex situ preparation methods. We show that the complete removal of hydroxide, carbonate, and adventitious carbon from the MgO surface can be achieved via oxygen plasma exposure at 200 °C without high temperature annealing. Using this process, an atomically flat surface with root mean square roughness values of ∼0.1 nm is demonstrated. Surfaces treated thus also exhibit sharp RHEED streaks indicating good crystalline order of the surface. We also show that high temperature annealing of MgO, either by itself or following other ex situ cleaning methods, such as solvent cleaning, is a reasonably effective method for the removal of surface contaminants, enabling one to achieve a surface roughness of ∼0.2 nm. We show that wet etching or other ex situ cleaning methods alone without annealing cannot eliminate all surface contaminants and may even worsen the surface roughness significantly.

Ar/N2 Plasma Induced Metastable CuxNy for Cu-Cu Direct Bonding

Metal-metal bonding is a promising semiconductor bonding technique, which has been widely developed to establish vertically electrical connections, provide mechanical support, and form hermetical sealing. In this work, we report Ar/N2 plasma induced metastable CuxNy for Cu-Cu die-die bonding performed in ambient environment. Surface characterization is performed on the Cu surface both before and after plasma exposure, revealing that the plasma induced CuxNy surface remains in “activated” state for up to 6 hours compared to the regular Cu surface. Subsequently, the dies are bonded. The bonding quality is assessed for mechanical bonding strength, hermeticity, and electrical conduction. The results support successful bonding with the desired properties. This reported bonding technology can be applied for high-throughput 3D integration and CMOS-MEMS packaging. Introduction Microelectromechanical systems (MEMS) packaging requires both mechanical and electrical connections in addition to hermetical sealing, therefore 3D integration is a promising solution [1]. Metal diffusion (thermocompression) bonding, eutectic alloy bonding, and solid-liquid interdiffusion bonding are popular bonding methods [2]. The latter two bonding methods, which are based on solder materials, may be plagued by inter-metallic compound (IMC) reliability issue. On the other hand, metal diffusion bonding, such as Cu-Cu, is absent of IMC issue. However, Cu is prone to rapid oxidation. To overcome this issue, Cu surface treatments such as specialized chemical mechanical polishing (CMP), chemical treatment, surface assembled monolayer (SAM), and plasma activation, have been reported. Among these methods, plasma activation is favorable as the process does not leave behind any residue. In this work, we report on the time-dependent evolution of the Ar/N2 plasma induced CuxNy layer and its application for Cu-Cu die-die bonding performed in ambient environment. Cu-Cu Die-Die Bonding Si wafers were firstly patterned and deposited with 10 nm thickness of Ti as adhesion layer, followed with 100 nm thickness of Cu via electron-beam evaporation. Afterwards, the wafers were diced into small dies with dimensions of 5 mm × 7 mm. Thereafter, the Cu surface of the diced dies was exposed to Ar/N2 plasma. During the plasma process, Ar plasma was firstly applied to remove surface contaminants and copper oxides, N2 plasma was subsequently applied on the Cu surface to form an ultra-thin layer of CuxNy for passivating the Cu surface and achieving low temperature bonding. Finally, the “activated” dies were immediately pre-bonded in ambient environment in clean room (18 ºC and 40% humidity) and were annealed at 300 ºC for a duration of 30 min. Results and Observation The evolution of water contact angle (θ) with time variation for both the non-activated and Ar/N2 plasma activated Cu surface is shown in Figure 1. Compared to that of the non-activated Cu surface (~60º), the water contact angle of the Ar/N2 plasma activated Cu surface (~10º) is lower initially, signifying that the activated surface is more hydrophilic. Subsequently, the water contact angle of the Ar/N2 plasma activated Cu surface increases gradually until it is comparable to that of the non-activated Cu surface. The results show the metastability and degradation of CuxNy layer, revealing that the CuxNy layer remains in an “activated” state for up to 6 hours post plasma exposure. In addition, the mechanical bonding strength, hermeticity, and electrical conduction of the bonded dies are shown in Figures 2(a) and 2(b), 2(c), and 2(d), respectively. The results show that the dies are bonded successfully with the desired properties. Conclusion In this work, Ar/N2 plasma activated Cu-Cu die-die bonding in ambient environment was conducted. Surface analysis revealed that the plasma induced metastable CuxNy surface is more hydrophilic than the non-activated Cu surface and the plasma activated Cu surface remains in an “activated” state for a duration of 6 hours after plasma exposure. In addition, the mechanical bonding strength, hermeticity, and electric conduction of the bonded dies were determined, the results show that the dies were bonded together successfully. This bonding technology can be applied for high-throughput 3D integration and CMOS-MEMS packaging. Acknowledgement Authors acknowledge funding support from A*STAR (A18A4b0055) under the “Nanosystems at the Edge” program.

A reliable hydrophobic/superoleophilic fabric filter for oil–water separation: hierarchical bismuth/purified terephthalic acid nanocomposite

In the present work, we developed a simple, eco-friendly, and cost-effective approach to fabricate a recyclable hydrophobic/superoleophilic fabric filter using bismuth nanostructures and purified terephthalic acid (PTA)-based resin. First, different morphologies of bismuth nanostructures such as dendritic, hierarchical, flower and cactus-like were prepared by a facile one-step galvanic displacement method. Afterwards, the coating composition of Bi/PTA mixtures was applied on the surface of fabric filters by a simple hand brushing route. The results indicated that the water and oil contact angles of the modified hydrophobic-superoleophilic fabric filter were about 135° and 0°, respectively. The various oil/water mixtures can be successfully separated by a facile gravity-driven filtration using the as-coated hydrophobic filter with the separation efficiency above 93% and repeatability for at least 10 times. Also, the improved hydrophobic filter showed excellent self-cleaning performance for the removal of surface contaminants. The advantages of scalable production, high efficiency, cost-effective, time saving, sustainable and excellent reusability for the prepared hydrophobic-superoleophilic filter make it to be a potential candidate for oil/water separation and self-cleaning applications.

Assessing Hair Decontamination Protocols for Diazepam, Heroin, Cocaine and Δ9-Tetrahydrocannabinol by Statistical Design of Experiments.

Prior to toxicological analysis, hair as a matrix requires pre-treatment measures including decontamination, homogenization and extraction. Decontamination is performed to differentiate between drug present from superficial deposition and drug incorporated from systemic distribution following ingestion. There are many methods for decontamination of hair samples, mostly developed by empirically using a traditional "one factor at a time" approach, in which one independent variable at a time is changed to observe the effect on the dependent variable. The goal of the present work was to compare the efficacy of decontamination protocols using statistical "design of experiments" (DoE), which allows for analysis of multiple variables and interactions within a single experiment. Decontamination parameters included identity of aqueous and organic wash solutions, number of sequential aqueous and organic washes, order of aqueous and organic washes, and duration of each wash. DoE studies were completed to identify optimal decontamination conditions for four abused drugs with varying physiochemical properties. For this purpose, drug-free human hair was externally contaminated with diazepam, heroin, cocaine or Δ9-tetrahydrocannabinol. Each analyte was found to have a unique set of decontamination conditions that were most effective. These included three 30-min washes with methanol followed by three with 1% sodium dodecyl sulfide for diazepam, three 30-s washes with dichloromethane followed by one with water for heroin, one 30-s wash with 1% sodium dodecyl sulfate followed by three with dichloromethane for cocaine and three 30-min washes with water followed by one with methanol for Δ9-tetrahydrocannabinol. The results provide proof-of-principle for a DoE approach to identify effective parameters for hair decontamination for a physicochemically diverse group of drugs. The major advantage of DoE is to elucidate combinations of parameters that result in effective removal of surface contamination, a goal that would be challenging to accomplish using a one factor at a time approach.

Simple and effective cleaning method for RuO2 nanosheet films for flexible transparent conducting electrodes

A critical and practical issue in employing low dimensional nanomaterials as transparent conducting electrodes (TCEs) is the simple and effectual cleaning of the nanomaterials; the presence of contaminants increases the contact resistance at the interface region in practical applications. In this study, various cleaning methods are examined to remove surface contaminants on RuO2 nanosheets (NSs), which are the promising materials for TCEs. The Ar gas cluster ion beam (GCIB) sputtering technique can effectively remove organic surface contaminants, although it has critical drawbacks in the mass production. The simple deionized water treatment can provide satisfactory cleaning performance, which is comparable with that of the Ar GCIB sputtering method. Other methods such as solution-based treatments that use ethanol and chloroform and the heating method do not provide a comparable cleaning performance. The conductive atomic force microscopy demonstrates highly increased conductivity of water-cleaned RuO2 NS films at the nanoscale. This study proposes a practical method for the cleaning of RuO2-based nanomaterials for their application as TCEs and emphasizes their significance of the cleaning process to achieve a higher performance for TCEs based on low dimensional nanomaterials.

Removal of Surface Contamination by Atomic Hydrogen Annealing

Removal of Surface Contamination by Atomic Hydrogen Annealing

Extraction of thermally stable cellulose nanocrystals in short processing time from waste newspaper by conventional acid hydrolysis

Motivated by many exclusive and useful features of cellulose nanocrystals (CNC) and the underutilized resource of waste newspaper, this study aimed to extract CNC from waste newspapers by means of alkali and bleaching treatments followed by acid hydrolysis. The morphological structure of the obtained CNC was analysed by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) methods. The remarkable removal of surface contamination and the reduction in fiber diameter during alkali and bleaching treatment were observed and the nano-dimension of the extracted CNC was revealed with the average diameter of 12.3 ± 2.8 nm. Characterization of the extracted CNC showed a high whiteness index of 80%, and high transparency of about 80% of the light at 600 nm calculated for a 0.02 mm thick nanocellulose film. Fourier transform infrared spectroscopy (FTIR) indicated that lignin, hemicellulose and other coloring agents were successfully removed. A comparably high crystallinity index of 80.15% was calculated from x-ray diffraction data. Thermogravimetric analysis showed that the product had a typical maximum thermal degradation at 300 °C. The analysis results indicated the successful extraction of good CNC from waste newspaper with the shortest processing time ever reported for acid hydrolysis with conventional alkali and bleaching pretreatment. The findings also strongly support for further research of nanocomposites reinforced by CNC produced from waste newspaper.

Substrate protection and deprotection with salt films to prevent surface contamination and enable selective atomic layer deposition

Surface contamination can decrease surface reactivity, and removal of surface contaminants adds additional steps to a process. Here we demonstrate surface protection from contamination and one-sided atomic layer deposition (ALD) by means of protective, sacrificial, thermally evaporated NaCl layers. This approach allows clean silicon surfaces to be stored under ambient conditions for extended periods of time in a pristine state, and ALD to be performed selectively on one side of a planar material. For the ALD depositions, planar substrates are (i) selectively coated on one side with ca. 100 nm of NaCl by thermal evaporation, (ii) non-selectively coated using traditional ALD, and (c) rinsed with water to remove the NaCl layer. Water treatment removes the salt film and any ALD deposition on top of it. Salt film deposition, surface protection, and selective ALD are confirmed by X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). Selective, thermal ALD of alumina and ZnO are demonstrated, and protective salt films of different thicknesses (10, 50, and 100 nm) are investigated.

Mechanical cleaning of graphene using in situ electron microscopy

Avoiding and removing surface contamination is a crucial task when handling specimens in any scientific experiment. This is especially true for two-dimensional materials such as graphene, which are extraordinarily affected by contamination due to their large surface area. While many efforts have been made to reduce and remove contamination from such surfaces, the issue is far from resolved. Here we report on an in situ mechanical cleaning method that enables the site-specific removal of contamination from both sides of two dimensional membranes down to atomic-scale cleanliness. Further, mechanisms of re-contamination are discussed, finding surface-diffusion to be the major factor for contamination in electron microscopy. Finally the targeted, electron-beam assisted synthesis of a nanocrystalline graphene layer by supplying a precursor molecule to cleaned areas is demonstrated.

Preparation of a Biofunctionalized Surface on Titanium for Biomedical Applications: Surface Properties, Wettability Variations, and Biocompatibility Characteristics

This study developed a promising approach (low-temperature plasma polymerization with allylamine) to modify the titanium (Ti) surface, which helps the damaged tissue to heal faster. The Ti surface was first cleaned by argon (Ar) plasma, and then the functional amino-groups were coated on the Ti surface via plasma polymerization. The topography characteristics, wettability, and optimal plasma modification parameters were investigated through atomic force spectroscopy, secondary ion mass spectroscopy, and response surface methodology (RSM). Analytical results showed that the formation of a porous surface was found on the Ar plasma-modified Ti surfaces after Ar plasma modification with different parameters. The Ar plasma modification is an effective approach to remove surface contaminants and generate a porous topography on the Ti surface. As the Ti with Ar plasma modification was at 100 W and 190 m Torr for 12 min, the surface exhibited the maximum hydrophilic performance. In the allylamine plasma modifications, the contact angle values of the allylamine plasma-modified Ti surfaces varied between 70.15° and 88.26° in the designed parameters. The maximum concentration of amino-groups (31.58 nmole/cm2) can be obtained from the plasma-polymerized sample at 80 W and 150 mTorr for 22 min. Moreover, the cell response also demonstrated that the allylamine plasma-modified Ti sample with an optimal modification parameter (80 W, 22 min, and 150 mTorr) possessed great potential to increase cell adhesion ability. Thus, the optimal parameters of the low-temperature plasma polymerization with allylamine can be harvested using the RSM design. These data could provide new scientific information in the surface modification of Ti implant.

The use of titanium dioxide nanotubes as photoanodes for chloride oxidation

In recent years, significant attention has been given to the development of photoelectrochemical materials capable of producing high current densities under illumination for a range of applications. Titanium dioxide nanotubes (TiNTs) have emerged as a favourable nanomaterial due to a reduced rate of recombination coupled with the ability to generate stable and high photocurrents. To date however, there have been no reports on the use of TiNTs for the photoelectrochemical production of chlorine, a powerful disinfectant, under UV light. The work reported here describes the construction of TiNTs for chlorine generation under low power UV-Light Emitting Diode (UV-LED) irradiation. Linear sweep voltammetry has shown TiNTs to be active for chlorine generation, achieving an average faradaic yield of ~60%, which was found to be significantly higher when compared to sol-gel electrodes (~40%). Furthermore, the impact of electrode conditioning was evaluated, demonstrating improved performance after removing surface contaminants.

A Process towards Eliminating Cytotoxicity by Removal of Surface Contamination from Electrical Discharge Machined Nitinol

Abstract Electrical discharge machining (EDM) of biocompatible nitinol combines superelasiticity, high accuracy of fabrication and miniaturization capabilities, thus presenting a promising base material for flexible medical instruments in minimally invasive surgery. In order to remove cytotoxic surface contamination which is caused by brass wire in the standard EDM process, the effectiveness of a hydrofluoric acid and nitric acid based chemical etching process was tested. Here, Energy-dispersive X-ray spectroscopy proved the purity of the surface after etching, while cytotoxicity experiments showed great improvement in the reaction of human fibroblasts, shifting cell vitality to non-cytotoxic levels.

Investigation of a cleaning procedure for silicon spheres used in the realization and dissemination of the redefined kilogram via combined spectroscopic and gravimetric measurements

The new definition of the SI kilogram requires new methods of realizing this unit. The X-ray crystal density method is a primary realization method and uses silicon spheres. The spheres get cleaned before each measurement, in order to remove surface contaminations and thus reduce their uncertainty contribution to the realization. Therefore, cleaning is an inherent part of the realization and dissemination of the kilogram. A cleaning method for silicon spheres is investigated, concerning its suitability as a part of the realization of the redefined kilogram. Six silicon spheres were used to determine the repeatability of the established cleaning method. Measurements of the spheres' mass and the quantification of their surface layer mass after cleaning were carried out in several cycles resulting in 29 mass and surface measurements. The repeatability of the cleaning method applied shows a standard deviation in the order of two micrograms for both the mass and the surface layer. The cleaning method therefore sufficiently fulfils these requirements.