CO2 Aerosol Research Articles

Unambiguous detection of mesospheric CO2 clouds on Mars using 2.7 μm absorption band from the ACS/TGO solar occultations

Mesospheric CO2 clouds are one of two types of carbon dioxide clouds known on Mars. We present observations of mesospheric CO2 clouds made by Atmospheric Chemistry Suite (ACS) onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter (TGO). We analyzed 1663 solar occultation sessions of Thermal InfraRed (TIRVIM) and Middle InfraRed (MIR) channels of ACS covering more than two Martian years that contain spectra of 2.7 μm carbon dioxide ice absorption band. That allowed us to unambiguously discriminate carbon dioxide ice aerosols from mineral dust and water ice aerosols, not relying on the information of atmospheric thermal conditions. CO2 clouds were detected in eleven solar occultation observations at altitudes from 39 km to 90 km. In five cases, there were two or three layers of CO2 clouds that were vertically separated by 5–15 km gaps. Effective radius of CO2 aerosol particles is in the range of 0.1–2.2 μm. Spectra produced by the smallest particles indicate a need for a better resolved CO2 ice refractive index. Nadir optical depth of CO2 clouds is in the range 5 × 10−4–4 × 10−2 at both 2.7 μm and 0.8 μm. Asymmetrical diurnal distribution of detections observed by ACS is potentially due to local time variations of temperature induced by thermal tides. Two out of five cases of carbon dioxide cloud detections made by the TIRVIM instrument reveal the simultaneous presence of CO2 ice and H2O ice aerosols. Temperature profiles measured by the Near InfraRed (NIR) channel of ACS are used to calculate CO2 saturation ratio S at locations of carbon dioxide clouds. Supersaturation S > 1 is detected in only 6 out of 19 cases of CO2 cloud layers; extremely low values of S < 0.1 are found in 9 out of 19 cases.

Coronavirus disease 2019 and laparoscopic surgery in resource-limited settings.

During the coronavirus disease 2019 (COVID-19) pandemic, the use of laparoscopy has been discouraged by the Intercollegiate General Surgery because of its potential for aerosol generation and infection. In contrast, the Society of American Gastrointestinal and Endoscopic Surgeons and the European Association of Endoscopic Surgery recommend continuing to use laparoscopy but with devices to filter released CO2 aerosol particles. However, commercially available systems are costly and may not be readily available. Herein, we describe a custom-made system to safely remove surgical smoke and CO2 , as well as a case of laparoscopic cholecystectomy in which we used it. The patient had had multiple episodes of biliary pancreatitis and required urgent cholecystectomy during the COVID-19 pandemic. Although India was in complete lockdown, it was decided to operate with precaution. A system was designed using underwater seal chest tube drainage and an electrostatic membrane filter with a viral retention function greater than 99.99%. The system was connected to an extra port for continuous controlled egression of CO2 pneumoperitoneum. A regular four-port cholecystectomy was performed at an intra-abdominal pressure of 12 mm Hg. The gas flow rate was 10 L/min. CO2 for pneumoperitoneum, surgical aerosol, and effluents passed through the system before collecting in the suction apparatus. The exchange of operating instruments through the ports was kept to a minimum. It was done after the abdomen was temporarily desufflated using this system. The system we designed appears safe and is cost-effective. In resource-limited settings, it will be handy in patients requiring laparoscopic surgery both during and after the COVID-19 pandemic.

A Novel Cleaning Approach to Remove the Carbon Contaminant from Ru Surface of EUV Mask

The surfaces of extreme ultraviolet (EUV) mask and optics are very vulnerable to carbon contamination during EUV lithography process. The top surface of EUV mask is coated with Ru capping layer to protect the mask substrate. Carbon contamination occurs on Ru surface when the EUV light of 13.5 nm interacts with the surface. The carbon contamination on mask surface is known to lose its reflectivity and change the critical dimension (CD). Thus, the removal of carbon contaminant from mask surface is required to maintain the integrity of EUV lithography process. Conventional cleaning methods such as SPM and UV cleaning are widely used for the removal of organic contaminants but can cause surface damages on EUV mask such as surface oxidation and etching of absorber pattern. In this study, a novel cleaning mechanism is proposed to remove carbon contaminant using a quaternary ammonium hydroxide solution and an organic solvent mixture solution. According to the SN2 (nucleophilic substitution) reaction, hydroxyl ions are ready to react with carbon atoms as nucleophiles. Also, polar aprotic solvents such as DMSO solvate cations to actively assist hydroxyl ion reactions. Therefore, a study on the removal of carbon contaminants was carried out using a mixture of quaternary ammonium hydroxide solution and polar aprotic solvent. There have been limited studies reported on organic solvent cleaning in a semiconductor process for removal of photoresist. However, physical cleaning such as megasonic and UV treatment were applied to the organic solvent cleaning process to improve organic removal. Few studies have also been carried out to remove the photoresist by applying an additional cleaning process such as CO2 aerosol, megasonic, and UV pretreatment to the organic solvent. So far no studies have been reported on the removal of carbon contaminants using quaternary ammonium hydroxide solution with an organic solvent. This study investigated the effect of cleaning solution on hydrocarbon film removal by using four kinds of quaternary ammonium hydroxide (TMAH, TEAH, TPAH and TBAH) as alkaline chemicals and DMSO and THF organic solvents as polar aprotic solvents. Instead of EUV carbon contaminant, a hydrocarbon film with similar properties to EUV carbon contaminant was prepared and evaluated using alkaline chemicals and organic solvents. The hydrocarbon film was effectively removed from Ru surface in the mixture of TBAH and THF. This is because of low polarity nature of both TBAH and THF. When DMSO used with quaternary ammonium hydroxide solution, hydrocarbon was also removed with longer process time. The carbon removal efficiency is improved and reduced the cleaning process time for TBAH+DMSO cleaning process with megasonic due to the easy lift-off of hydrocarbon film from Ru surface. The polarity of carbon contaminant and cleaning solution have to be considered for removal carbon contaminant from Ru surface.

Biofilm Removal Using Carbon Dioxide Aerosols without Nitrogen Purge.

Biofilms can cause serious concerns in many applications. Not only can they cause economic losses, but they can also present a public health hazard. Therefore, it is highly desirable to remove biofilms from surfaces. Many studies on CO2 aerosol cleaning have employed nitrogen purges to increase biofilm removal efficiency by reducing the moisture condensation generated during the cleaning. However, in this study, periodic jets of CO2 aerosols without nitrogen purges were used to remove Pseudomonas putida biofilms from polished stainless steel surfaces. CO2 aerosols are mixtures of solid and gaseous CO2 and are generated when high-pressure CO2 gas is adiabatically expanded through a nozzle. These high-speed aerosols were applied to a biofilm that had been grown for 24 hr. The removal efficiency ranged from 90.36% to 98.29% and was evaluated by measuring the fluorescence intensity of the biofilm as the treatment time was varied from 16 sec to 88 sec. We also performed experiments to compare the removal efficiencies with and without nitrogen purges; the measured biofilm removal efficiencies were not significantly different from each other (t-test, p > 0.55). Therefore, this technique can be used to clean various bio-contaminated surfaces within one minute.

Effects of Carbon Dioxide Aerosols on the Viability of Escherichia coli during Biofilm Dispersal.

A periodic jet of carbon dioxide (CO2) aerosols is a very quick and effective mechanical technique to remove biofilms from various substrate surfaces. However, the impact of the aerosols on the viability of bacteria during treatment has never been evaluated. In this study, the effects of high-speed CO2 aerosols, a mixture of solid and gaseous CO2, on bacteria viability was studied. It was found that when CO2 aerosols were used to disperse biofilms of Escherichia coli, they led to a significant loss of viability, with approximately 50% of the dispersed bacteria killed in the process. By comparison, 75.6% of the biofilm-associated bacteria were viable when gently dispersed using Proteinase K and DNase I. Indirect proof that the aerosols are damaging the bacteria was found using a recombinant E. coli expressing the cyan fluorescent protein, as nearly half of the fluorescence was found in the supernatant after CO2 aerosol treatment, while the rest was associated with the bacterial pellet. In comparison, the supernatant fluorescence was only 9% when the enzymes were used to disperse the biofilm. As such, these CO2 aerosols not only remove biofilm-associated bacteria effectively but also significantly impact their viability by disrupting membrane integrity.

Mechanical desorption of immobilized proteins using carbon dioxide aerosols for reusable biosensors

Reusability of a biosensor has recently received considerable attention, and it is closely related with the effective desorption of probe molecules. We present a novel mechanical desorption technique to reuse biosensors by using periodic jets of carbon dioxide (CO2) aerosols (a mixture of solid and gaseous CO2), and demonstrate its feasibility by removing physically adsorbed and covalently bonded fluorescent proteins i.e., Escherichia coli fluorescein isothiocyanate antibody and bovine serum albumin (E. coli FITC–Ab and FITC–BSA) from silicon chips. The proteins on the chip surfaces were measured by fluorescent images before and after applying the aerosols. The removal efficiency of the aerosol treatment was measured for various concentrations (1–20μgmL−1) of E. coli FITC–Ab and FITC–BSA with two different removal cycles (5 and 11 cycles; each cycle: 8s). We observed high removal efficiencies (>93.5% for physically adsorbed Ab and >84.6% for covalently bonded Ab) at 11 cycle aerosol treatment. This CO2 aerosol treatment did not undermine re-functionalization, which was confirmed by the fluorescent images of FITC–Abs for fresh and reused chips. Desorption of the immobilized layers was validated by Fourier transform infrared and X-ray photoelectron spectroscopic analyses. We also conducted an experiment on the regeneration of E. coli sensing chips using this aerosol treatment, and the chips were re-used 5 times successfully. This mechanical desorption technique is a highly effective and novel strategy for reusable biosensors.

Removal of different-age biofilms using carbon dioxide aerosols

Many techniques to inactivate or remove biofilms in a wide variety of applications have been developed. Most of these techniques have been applied to biofilms at their initial stage of growth, since they are generally difficult to eradicate once established. The removal of established biofilms has received relatively little attention. In this paper, we report the effectiveness of periodic jets of carbon dioxide aerosols (a mixture of solid and gaseous CO2) to remove Escherichia coli (XL1-blue) biofilms of different ages (up to 3 weeks) on silicon surfaces. The biofilms were not immersed in liquids after growth/rinsing and were treated with the CO2 aerosols. The CO2 aerosols were generated by the adiabatic expansion of high-pressure CO2 gas through a nozzle. The surface area of the biofilms was measured from fluorescent images before and after applying the aerosols for 11, 20, and 30 cycles (each cycle: 8 sec), to compute the removal efficiency. The removal efficiencies decreased with increasing growth time and for the 3-week-old biofilms, they ranged from 91.5 to 99.6% within 4 min. This technique was highly effective for removing both fresh and old biofilms, but some of the biofilm debris such as growth media remained. Further, this CO2 aerosol technique was compared with other removal techniques.

Combined application of bacterial predation and carbon dioxide aerosols to effectively remove biofilms

This study evaluated predation with Bdellovibrio bacteriovorous and CO2 aerosol spraying to remove fluorescent Escherichia coli biofilms from silicon chips. Initial tests found that 7.5×105 viable E. coli cells were dispersed into the surrounding environment during aerosol treatment. The total number dispersed per test decreased to only 16 for predated biofilms. This is nearly 50,000-fold lower compared to untreated chips and 1000-fold lower compared to chips soaked in HEPES buffer only. Both scanning electron microscopy (SEM) and fluorescent microscopy analyses confirmed that predation alone did not completely eradicate the biofilm population. When used in conjunction with CO2 aerosols, however, no fluorescent signals remained and the SEM pictures showed a pristine surface devoid of bacteria. Consequently, this study demonstrates these two methods can be used with each other to significantly remove biofilms from surfaces while also significantly reducing the likelihood of human exposure to potential pathogens during their removal.

All Wet Photoresist Strip by Solvent Aerosol Spray

The introduction of metal gates and high-k dielectrics in FEOL and porous ULK dielectrics in BEOL presents severe issues [1] and leads to the requirement of new chemistries and processes. A major challenge in cleaning is the removal of photoresist (PR) in both FEOL and BEOL. In current semiconductor device fabrication flow, the photoresist strip process in FEOL is mostly achieved by applying a sequence of plasma ashing followed by a wet-clean step with sulfuric-peroxide mixture (SPM). But in general, ashing leads to strong oxidation or etching of silicon substrate. Hence, several approaches for ashless PR strip have been reported, such as hot SPM [2] and the combination of a pre-treatment using high velocity CO2 aerosol [3].

Phase, shape, and architecture of SF6 and SF6∕CO2 aerosol particles: Infrared spectra and modeling of vibrational excitons

Information on the phase, shape, and architecture of pure SF(6) and mixed SF(6)/CO(2) aerosol particles is extracted from experimental infrared spectra by comparison with predictions from quantum mechanical exciton calculations. The radius of the particles lies around 50 nm. The following extensions to our previous vibrational exciton model are included: (i) To account for the many degrees of freedom of degenerate vibrational bands of aerosol particles, we take a time-dependent approach to calculate infrared absorption spectra directly from the dipole autocorrelation function. (ii) In addition to the dipole-dipole interaction, dipole-induced dipole terms are included to account for the high polarizability of SF(6) and CO(2). We find SF(6) aerosol particles with a cubiclike shape directly after their formation and a change in the shape toward elongated particles with increasing time. Our microscopic model reveals that the cubic-to-monoclinic phase transition at 96 K found in the bulk cannot be observed with infrared spectroscopy because the two phases show almost identical spectra. Infrared spectra of two-component SF(6)/CO(2) particles with core-shell structure show characteristic split absorption bands for the shell. By contrast, homogeneously mixed SF(6)/CO(2) particles lead to broad infrared bands for both the core and the shell. The molecular origin of these various spectral features is uncovered by the analysis of the vibrational eigenfunctions.

Post Ion-Implant Photoresist Removal via Wet Chemical Cleans Combined with Physical Force Pretreatments

A combination of wet chemistry and high-velocity solid CO2 aerosol pre-treatment was used to remove ion-implanted resist from patterned Si structures. The top resist surface is modified by heavy ion-implantation forming a crust ~100nm thick. The aerosol treatment, which is aimed at breaking and partially removing the crusted top layer of implanted resist, produces circular openings in this surface, with diameters on the order of tens to hundreds of micrometers. No resist is detected by either optical microscopy or localized SEM inspection, after immersion in hot SPM mixture, on aerosol-pre-treated wafer fragments. In contrast, resist residue is still observed on similarly pre-treated specimens, after immersion in either N-methyl pyrrolidone or Microstrip2001{trade mark, serif}, even under ultrasonic agitation. Overall, the aerosol pre-treatment is a key step in reducing the amount of resist residue, for both aqueous-based and solvent-based wet cleaning. Full-wafer defect-count results, post aerosol treatment, are reported for poly-Si line widths down to 40 nm.

Investigation of the interaction between a hypersonic air stream and a carbon dioxide aerosol

A detailed investigation is made of the interaction between a hypersonic vibrationally excited donor gas and a carbon dioxide aerosol stream with a view to improving the energy characteristics of a gasdynamic CO2 laser. The analysis shows that rapid (within times shorter than the relaxation time of the upper active level) mixing of the evaporating aerosol and the vibrationally excited gas is possible as a result of this interaction. For a planar flow geometry with symmetrical aerosol injection, the transverse dimension of the active medium may be 20 cm for a hypersonic nozzle with a throat cross section ~1 mm high. The conditions under which there were no gas-dynamic perturbations in the mixing zone and the active medium was optically homogeneous were determined. A CO2 aerosol generator was developed with a solid particle size distribution function close to the optimal. An experimental investigation was made of the interaction between the streams using a system with a conical hypersonic nozzle for the air and perpendicular injection of the aerosol. The experimental results broadly agreed with the theoretical predictions. A CO2 laser radiation gain close to the calculated value was obtained in the excited air-carbon dioxide aerosol mixing zone.

Mie scattering and the Martian atmosphere

It has been suggested that the discrepancy between radio occultation determinations of the Martian atmospheric surface pressure (3.8 to 7 mb) and those deduced from optical polarization measurements and a simple Rayleigh atmosphere model (about 10 mb) are the results of sub-micron sized aerosols in the Martian atmosphere. Based on observed viewing angle dependence of the polarization of the Martian disk in the visual range, a Mie scattering analysis has been made utilizing the measured complex index of refraction of limonite and bulk solid CO2. The results of this study indicate that limonite aerosols alone are unsatisfactory to explain the viewing angle observations, whereas solid CO2 (and H2O ice) aerosol spheres, having a dominant particle radius range between 0.28 and 0.35 μ, could bring planetary and laboratory observations into compatibility. It is suggested, further, that solid CO2 aerosols could explain limb brightening in the blue spectral range. Various distributions of solid CO2 and H2O Mie particles with radii up to 0.35 μ show an opposition effect. However, the role of these aerosols in explaining the Mars opposition observations is very dependent on the optical properties of the underlying Mars surface material.