To study chemical functional groups on surfaces of diamond‐like carbon (DLC) films, a highly sensitive infrared reflection‐absorption spectroscopic technique, immersion infrared reflection‐absorption ...spectroscopy (IRRAS), is applied in the present study. The method employs (i) a conventional attenuated total reflection (ATR) accessory with a Ge crystal as an immersion medium and (ii) an aluminum underlayer beneath the 50–70 nm thick DLC film. Sensitivity, selectivity, and quantifiability of the method can be enhanced by chemical derivatization (CD), coupling chemical moieties with strong characteristic vibrational bands to specific functional groups on the DLC surface. The method is applied to amorphous sputtered carbon films (a‐C) to demonstrate that electrophilic groups, most probably epoxy groups, are formed during aging under ambient conditions.
Highly sensitive immersion infrared reflection‐absorption spectroscopy, ImIRRAS, is applied to study ultrathin amorphous carbon films (a‐C), using a Ge crystal as an immersion medium and an Al underlayer. Chemical derivatization with amines or hydrazines reveals that electrophilic groups, most probably epoxide groups, are formed during the aging of a‐C films under ambient conditions.
Atmospheric‐pressure plasma‐enhanced film deposition with single‐filament dielectric‐barrier discharges (DBDs) in argon was investigated using allyltrimethylsilane (ATMS) as a precursor. Nonionic ...deposition in the discharge zone is largely precluded by a rapid cross‐flow of the source gas, containing between 50 and 2000 ppm of ATMS. The performed experimental studies show a surprisingly large deposited film mass per transferred elementary charge between 220 and 540 amu. Film growth experiments, mass‐spectrometric studies, and kinetic considerations led to the conclusion that the deposition process is a cationic surface polymerization, initiated by ions produced in the DBD by energy transfer from long‐lived excited Ar species and propagated by addition of ATMS monomer molecules.
Cationic surface polymerization is proposed to be the dominating mechanism of thin film deposition from allyltrimethylsilane (ATMS)‐Ar mixtures in single‐filament dielectric‐barrier discharges. The reaction is periodically initiated by chemisorbed cations produced in transient microdischarges. Chain propagation by addition of ATMS molecules is eventually finished by the following microdischarge with opposite polarity.
A simplified chemical‐kinetic model was applied to Ar‐H2O dielectric‐barrier discharges (DBDs), presuming that dissociation processes are only due to energy transfer from excited Ar species. Good ...agreement was obtained between the densities of HO, H2, and O2 and experimental data from the literature, whereas a discrepancy for H2O2 could not be explained. The model is useful for designing DBD reactors and process development. Steady‐state densities of H atoms increase with decreasing fractions of
x
H
2
O which should be kept below 0.1% to obtain a large zone of virtually constant and large H‐atom density in the DBD reactor, whereas the HO density is hardly affected by
x
H
2
O. O2 contaminations must be kept well below 100 ppm in to attain maximum H‐atom densities.
A dielectric‐barrier discharge (DBD) in an Ar/H2O mixture is an efficient source of H atoms and HO radicals. The temporal evolution of discharge‐gap‐averaged species densities, including O, O2, O3, HO, HO2, H2O, and H2O2, in an Ar/H2O gas stream passing through the DBD is modeled using the simplifying assumption that dissociation processes are only due to reaction with excited Ar species, summarized in the model as a single “lumped species” Ar*. Results of the calculation, which are in good agreement with several experimental data taken from the literature, may be used to derive guidelines for reactor design and process development.
Purpose
To evaluate pix2pix and CycleGAN and to assess the effects of multiple combination strategies on accuracy for patch‐based synthetic computed tomography (sCT) generation for magnetic resonance ...(MR)‐only treatment planning in head and neck (HN) cancer patients.
Materials and methods
Twenty‐three deformably registered pairs of CT and mDixon FFE MR datasets from HN cancer patients treated at our institution were retrospectively analyzed to evaluate patch‐based sCT accuracy via the pix2pix and CycleGAN models. To test effects of overlapping sCT patches on estimations, we (a) trained the models for three orthogonal views to observe the effects of spatial context, (b) we increased effective set size by using per‐epoch data augmentation, and (c) we evaluated the performance of three different approaches for combining overlapping Hounsfield unit (HU) estimations for varied patch overlap parameters. Twelve of twenty‐three cases corresponded to a curated dataset previously used for atlas‐based sCT generation and were used for training with leave‐two‐out cross‐validation. Eight cases were used for independent testing and included previously unseen image features such as fused vertebrae, a small protruding bone, and tumors large enough to deform normal body contours. We analyzed the impact of MR image preprocessing including histogram standardization and intensity clipping on sCT generation accuracy. Effects of mDixon contrast (in‐phase vs water) differences were tested with three additional cases. The sCT generation accuracy was evaluated using mean absolute error (MAE) and mean error (ME) in HU between the plan CT and sCT images. Dosimetric accuracy was evaluated for all clinically relevant structures in the independent testing set and digitally reconstructed radiographs (DRRs) were evaluated with respect to the plan CT images.
Results
The cross‐validated MAEs for the whole‐HN region using pix2pix and CycleGAN were 66.9 ± 7.3 vs 82.3 ± 6.4 HU, respectively. On the independent testing set with additional artifacts and previously unseen image features, whole‐HN region MAEs were 94.0 ± 10.6 and 102.9 ± 14.7 HU for pix2pix and CycleGAN, respectively. For patients with different tissue contrast (water mDixon MR images), the MAEs increased to 122.1 ± 6.3 and 132.8 ± 5.5 HU for pix2pix and CycleGAN, respectively. Our results suggest that combining overlapping sCT estimations at each voxel reduced both MAE and ME compared to single‐view non‐overlapping patch results. Absolute percent mean/max dose errors were 2% or less for the PTV and all clinically relevant structures in our independent testing set, including structures with image artifacts. Quantitative DRR comparison between planning CTs and sCTs showed agreement of bony region positions to <1 mm.
Conclusions
The dosimetric and MAE based accuracy, along with the similarity between DRRs from sCTs, indicate that pix2pix and CycleGAN are promising methods for MR‐only treatment planning for HN cancer. Our methods investigated for overlapping patch‐based HU estimations also indicate that combining transformation estimations of overlapping patches is a potential method to reduce generation errors while also providing a tool to potentially estimate the MR to CT aleatoric model transformation uncertainty. However, because of small patient sample sizes, further studies are required.
Room-temperature growth of oxide layers on aluminum in highly diluted mixtures of oxygen with argon (O
2
molar fractions 20 ppm ≤
x
O
2
≤ 500 ppm, partial pressures 2 Pa ≤
p
O
2
≤ 50 Pa) flowing ...through a dielectric-barrier discharge (DBD) reactor is studied, including oxidation in the pre- and post-discharge regions (PrD, PoD) adjacent to the main DBD. Three different mechanisms of plasma-enhanced oxidation were found to prevail, depending on the location of the sample: (1) In the close PrD region, up to 1 cm upstream from the discharge, accelerated growth of Al
2
O
3
is due to the irradiation of the sample surface by highly energetic (9.8 eV) argon excimer radiation in the presence of O
2
. (2) In the remote PoD, a few cm downstream from the DBD, oxidation can largely be attributed to oxygen atoms, with number densities typically between 1 and 5 × 10
14
cm
−3
. Here, analysis in terms of Cabrera–Mott (CM) theory results in CM potentials between − 1.5 and − 2.1 V. (3) In the DBD itself both O atoms and VUV photons generally play an important role but, under special conditions, an additional oxidation mode can be identified, characterized by a much larger limiting thickness: While, in general, oxide growth by O atoms and/or VUV photons virtually stops at thicknesses
X
between 5 and 6 nm, much thicker oxide films can be achieved in the downstream region of the main DBD, with thicknesses growing with the length of the DBD zone. Tentatively, we attribute this observation to negative oxygen ions O
m
−
(1 ≤ m ≤ 3) accumulating in the gas while passing the reactor. Any direct electrical effects of the discharge process on the oxidation can probably be neglected.
The short residence time of Ar–HMDSO (Ar–hexamethyldisiloxane) gas mixtures rapidly flowing across atmospheric‐pressure, glow‐type, single‐filament dielectric barrier discharges is utilized to ...accomplish thin‐film deposition via a purely ionic route. A comparison of thin‐film volumes obtained from profilometry, on the one hand, and from the transferred charge, on the other hand, enables to evaluate the mass of the ions contributing to the film growth. For HMDSO fractions at the lower end of the studied range of molar fractions, 50 ppm, pentamethyldisiloxanyl cations (Me3SiOSiMe2+, PMDS+), generated from the monomer via Penning ionization by Ar(1s) species, are mainly responsible for film formation. For HMDSO fractions growing beyond 1,000 ppm, ionic oligomerization processes by reactions of PMDS+ with HMDSO molecules result in a 2.5‐fold increase of the average deposited ion mass.
The short gas residence time in atmospheric‐pressure, glow‐type, single‐filament dielectric barrier discharges in a crossflow of Ar–HMDSO (Ar–hexamethyldisiloxane) mixtures results in a purely ionic film deposition. For small fractions of HMDSO, Me3SiOSiMe2+ ions, generated by Penning ionization, are the main film‐forming species. With increasing monomer fractions, ionic oligomerization products from reactions of HMDSO with pentamethyldisiloxanyl cations gain importance for film growth.
Dielectric‐barrier discharges (DBDs) in Ar–N2 mixtures, with N2 fractions in 0.1–1% range, would be attractive alternatives to DBDs in pure N2 if energy‐transfer reactions between Ar(1s) atoms and N2 ...molecules were an efficient source of N atoms. Attempts to functionalize polyolefins in flowing postdischarges fed by such DBDs, as well as the search for the First Positive System in the emission spectrum, however, failed. Evidently, the energy‐transfer reactions do not produce N atoms. For Ar(1s3) and Ar(1s5) metastable states, this fact has already been reported in the literature. For Ar(1s2) and Ar(1s4) resonant states, a quantitative argument is derived in this paper: energy transfer from Ar(1s) atoms to N2 molecules is not an efficient source of N atoms.
Dielectric‐barrier discharges (DBDs) in Ar–N2 mixtures, with molar N2 fractions below 1%, would be attractive alternatives to DBDs in pure N2 if energy‐transfer reactions between Ar(1s) atoms and N2 molecules were an efficient source of N atoms. The failure of attempts to functionalize polyolefins in flowing postdischarges fed by such DBDs, however, showed that this energy transfer does not produce significant amounts of N atoms. For Ar(1s3) and Ar(1s5) metastable states, this had already been reported in literature. As shown here, the sum of rate coefficients for N2 dissociation by Ar(1s2) and Ar(1s4) resonant states is less than 2 × 10–13 cm3/s, nearly two orders of magnitude below the total quenching rates.
Atmospheric‐pressure dielectric barrier discharges (DBDs) in argon with admixtures of small amounts of hexamethyldisiloxane (HMDSO) have been analysed by means of numerical modelling. A ...time‐dependent, spatially one‐dimensional fluid‐Poisson model has been used, which takes into account the spatial variation of the discharge plasma between the plane‐parallel dielectrics covering the electrodes. Main features of the model, including the reaction kinetics for HMDSO, are given. Good agreement with related experimental studies of the ignition voltage for HMDSO amounts of up to 200 ppm and the temporal course of the discharge current for conditions typical of deposition experiments is obtained by the model calculations when assuming that 30% of the reactions of HMDSO with excited argon atoms, with a rate coefficient of 5.0 × 10−10 cm3/s, lead to the production of electrons due to Penning ionization. The modelling results for constant frequency f = 86.2 kHz and applied voltage Ua = 4 kV show that the electrical energy dissipated in the DBD decreases with an increasing amount of HMDSO and enable the determination of the energy absorbed per HMDSO molecule on the basis of their energy balance. The analysis of the plasma–chemical processes also makes clear that collision processes of HMDSO with excited argon atoms and molecules leading to neutral reaction products are essential for the formation of thin polymer films.
The electrical discharge characteristics of a large‐area experimental dielectric barrier discharge in argon–hexamethyldisiloxane mixtures containing up to about 1,600 ppm of the monomer is analysed ...by means of electrical measurements and numerical modelling. A time‐dependent, spatially one‐dimensional fluid model is employed, taking into account the spatial variation of the discharge plasma between the two plane‐parallel dielectrics covering the electrodes. Reasonable agreement between electrical measurements and modelling results is generally found for the gap voltages and discharge currents. Remaining differences between the measured and calculated electrical energy dissipated in the plasma per period are discussed.
Experimental results of the electrical characteristics obtained in a large‐area dielectric barrier discharge in argon–hexamethyldisiloxane mixtures at atmospheric pressure are compared with a corresponding modelling study. Measured and calculated results agree reasonably well, and certain differences in the electrical energy dissipated in the discharge per period are discussed from different viewpoints.
A dielectric‐barrier discharge (DBD) in an argon–water mixture is applied to plasma pretreatment (PP) of amorphous silica for subsequent vapor‐phase silanization (VS) in the same reactor. Comparison ...of amino‐silanization of silica fiber‐optic biosensor probes using a PP/VS sequence with strategies involving wet‐chemical pretreatment or silanization shows a considerable improvement in reproducibility by the completely dry process. Practical applicability is demonstrated by an immunoassay with human immunoglobulin G as analyte. Thanks to the advantages of shorter processing time, avoidance of washing steps, and improved reproducibility, PP/VS is highly promising for industrial use.
A dielectric‐barrier discharge in Ar–H2O provides H atoms and HO radicals—ideal for pretreatment of SiO2 for vapor‐phase silanization. SiO2‐fiber optical biosensor probes are amino‐silanized using a dry process providing the same group density as wet chemistry—with better reproducibility and avoiding chemical hazards. Process viability is demonstrated by immunoassay.
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