Reduction Of Carbon Contamination Research Articles

Mid-infrared transparent Y2O3-MgO composites with wide transmittance range and weak absorption peaks via the reduction of carbon contamination and agglomerations

Y2O3-MgO composites are promising for mid-infrared windows and domes in harsh environments. However, the insufficient transmittance range (the transmittance >30 % only in ∼2–7 μm) and strong absorption peak (the transmittance <32 % at 7.0 μm) of Y2O3-MgO composites severely limit their application range because of agglomerations and carbon contamination from organics in the raw materials, currently. In this study, utilizing carbon-free raw materials and high molecular motions, the reduction of carbon contamination and agglomerations within the as-synthesized nanopowers was achieved via the modified co-precipitation synthesis. A highly mid-infrared transparent (the maximum transmittance of 79 % at 6.0 μm) Y2O3-MgO composite with wide transmittance range (the transmittance >30 % in 2.2–9.7 μm) and weak absorption peaks (the transmittance ≈68.57 % at 7.0 μm) was fabricated by the hot-pressing sintering method using the as-obtained nanopowders in the absence of exogenous dopants. And the modified co-precipitation synthesis is a method with great potential for the development of mid-infrared transparent Y2O3-MgO composites with wide transmittance range and weak absorption peaks.

Defect Engineering to Achieve Wake‐up Free HfO2‐Based Ferroelectrics

Wake‐up effect is still an obstacle in the commercialization of hafnia‐based ferroelectric thin films. Herein, the effect of defects, controlled by ozone dosage, on the field cycling behavior of the atomic layer deposited Hf0.5Zr0.5O2 (HZO) films is investigated. A nearly wake‐up free device is achieved after reduction of carbon contamination and oxygen defects by increasing the ozone dosage. The sample which is grown at 30 s ozone pulse duration shows about 97% of the woken‐up Pr at the pristine state whereas that grown below 5 s ozone pulse time shows a pinched hysteresis loop, that underwent a large wake‐up effect. This behavior is attributed to the increase in oxygen vacancy and carbon concentration in the films deposited at insufficient O3 dosage, which is confirmed by X‐ray photoelectron spectroscopy (XPS). The X‐ray diffraction (XRD) scan shows that the increase in ozone pulse time yields the reduction of tetragonal phase; therefore, the dielectric constant reduces. The I–V measurements reveal the increase in current density as the ozone dosage decreases, which might be due to the generation of oxygen vacancies in the deposited film. Finally, the dynamics of wake‐up effect is investigated, and it appears to be explained well by the Johnson–Mehl–Avrami–Kolmogoroff model, which is based on structural phase transformation.

Improved pretreatment method for the isolation and decontamination of pyrogenic carbon for radiocarbon dating using hydrogen pyrolysis

Abstract Pyrogenic carbon (charcoal, black carbon, elemental carbon) is one of the most common materials used for radiocarbon dating of terrestrial samples. However, exogenous carbon contamination can compromise the accuracy of radiocarbon ages. This study presents the results of two chemical pretreatments prior to hydrogen pyrolysis (hypy) as improved protocols for the isolation and decontamination of pyrogenic carbon, i) a simple acid-oxidation step (A-Ox/hypy) and ii) acid-base-acid (ABA/hypy). The A-Ox/hypy protocol uses HNO3 and H2O2, while ABA/hypy uses HCl and NaOH. Both pretreatments remove labile and inorganic carbon before hypy, decreasing the potential for in situ production of pyrogenic carbon during the hypy reaction. The effectiveness of each protocol was directly measured on charcoal artificially produced at 350 °C, 450 °C and 550 °C from radiocarbon-free wood, and exposed to environmental contamination for 1–3 yrs. The results show a >94% reduction in carbon contamination for the 450 °C and 550 °C charcoal samples occurred using A-Ox/hypy, but this treatment was less effective for the 350 °C charcoal. A >99% reduction in carbon contamination in all charcoal samples examined occurred using ABA/hypy. The A-Ox/hypy protocol was further tested on cave guano sediments, which had previously reported erroneous dates following simple organic solvent extraction followed by ABA pretreatment. Effective decontamination was achieved using A-Ox/hypy on the guano, which corrected a radiocarbon age reversal. Overall, ABA/hypy effectively decontaminated the charcoals and was a more efficient pretreatment for charcoal than A-Ox/hypy, however resulting in larger sample mass loss. Therefore, ABA/hypy is the recommended protocol for older (>30,000 14C yr BP) charcoal or sediment samples, or where date accuracy is imperative, while A-Ox/hypy represents an improved protocol for the quick and cost-effective measurement of younger samples (

Reduction of carbon contamination during the melting process of Czochralski silicon crystal growth

Generation, incorporation, and accumulation of carbon (C) were investigated by transient global simulations of heat and mass transport during the melting process of Czochralski silicon (CZ-Si) crystal growth. Contact reaction between the quartz crucible and graphite susceptor was introduced as an extra origin of C contamination. The contribution of the contact reaction on C accumulation is affected by the back diffusion of C monoxide (CO) from the gap between the gas-guide and the crucible. The effect of the gas-guide coating on C reduction was elucidated by taking the reaction between the silicon carbide (SiC) coating and gaseous Si monoxide (SiO) into account. Application of the SiC coating on the gas-guide could effectively reduce the C contamination because of its higher thermochemical stability relative to that of graphite. Gas flow control on the back diffusion of the generated CO was examined by the parametric study of argon gas flow rate. Generation and back diffusion of CO were both effectively suppressed by the increase in the gas flow rate because of the high Péclet number of species transport. Strategies for C content reduction were discussed by analyzing the mechanisms of C accumulation process. According to the elucidated mechanisms of C accumulation, the final C content depends on the growth duration and contamination flux at the gas/melt interface.

Argon plasma treatment techniques on steel and effects on diamond-like carbon structure and delamination

We demonstrate alteration in diamond-like carbon (DLC) film structure, chemistry and adhesion on steel, related to variation in the argon plasma pretreatment stage of plasma enhanced chemical vapour deposition. We relate these changes to the alteration in substrate structure, crystallinity and chemistry due to application of an argon plasma process with negative self bias up to 600 V. Adhesion of the DLC film to the substrate was assessed by examination of the spallated fraction of the film following controlled deformation. Films with no pretreatment step immediately delaminated. At 300 V pretreatment, the spallated fraction is 8.2%, reducing to 1.2% at 450 V and 0.02% at 600 V. For bias voltages below 450 V the adhesion enhancement is explained by a reduction in carbon contamination on the substrate surface, from 59 at.% with no treatment to 26 at.% at 450 V, concurrently with a decrease in the surface roughness, R q, from 31.5 nm to 18.9 nm. With a pretreatment bias voltage of 600 V a nanocrystalline, nanostructured surface is formed, related to removal of chromium and relaxation of stress; X-ray diffraction indicates this phase is incipient at 450 V. In addition to improving film adhesion, the nanotexturing of the substrate prior to film deposition results in a DLC film that shows an increase in sp 3/sp 2 ratio from 1.2 to 1.5, a reduction in surface roughness from 31 nm to 21 nm, and DLC nodular asperities with reduced diameter and increased uniformity of size and arrangement. These findings are consistent with the substrate alterations due to the plasma pretreatment resulting in limitation of surface diffusion in the growth process. This suggests that in addition to deposition phase processes, the parameters of the pretreatment process need to be considered when designing diamond-like carbon coatings.

Etching of GaAs(100) with Aqueous Ammonia Solution: A Synchrotron-Photoemission Spectroscopy Study

Etching of the GaAs(100) surface with aqueous ammonia solution is studied by highly surface-sensitive synchrotron-radiation photoemission spectroscopy. It is shown that such treatment effectively removes the native oxide layer leaving the surface covered with elemental arsenic, as well as arsenic hydroxides AsOH and As(OH)3, gallium hydroxide GaOH, and gallium suboxide GaxO. After annealing of the surface at 500 °C, the arsenic and gallium hydroxides disappear, while the excess arsenic is dimerized. The residual carbon contamination prevents disappearance of gallium hydroxide and hinders dimerization of excess arsenic on annealing. Rinsing the etched surface with 2-propanol instead of water prior to annealing results in considerable reduction of carbon contamination after annealing.

Simultaneous Oxygen Plasma and Thermal Treatments of an ITO Surface to Improve the Electrical Characteristics of Organic Light-Emitting Diodes

The electrical characteristics of organic light emitting diodes (OLEDs) were improved by lowpower oxygen plasma processing of an indium tin oxide (ITO) surface at an elevated temperature of 500 ◦C in this work. ITO is widely used as a transparent electrode in light-emitting devices, and OLED device performance is sensitive to the surface properties of ITO. In this research, a simultaneously oxygen-plasma and thermally treated ITO surface showed better device performance than an oxygen-plasma-treated ITO surface in terms of current density, brightness, and power efficiency. OLED devices with the structure of ITO/TPD/Alq3/LiF/Al were fabricated, and the surface properties of ITO were investigated by using various characterization techniques. The work function of the modified ITO, as determined by using ultraviolet photoelectron spectroscopy (UPS), increased from 4.70 to 5.17 eV. An X-ray photoelectron spectroscopy (XPS) analysis showed an oxygen fraction change from 59.9 % to 70.1 % after the surface treatment. Based on the measurements, we conclude that hole injection is improved due to the high electronegativity of the oxygen adsorbed on the ITO surface. The XPS analysis also showed that the surface carbon composition decreased from 15.1 % to 4.67 % after the surface treatment. A reduction in carbon contamination is also attributed to the improvement in the electrical characteristics. Thus, we demonstrated that simultaneous oxygen plasma and thermal treatment is a proper way for improving the electrical characteristics of OLED devices.

Deposition of hafnium oxide from Hf t-butoxide and nitric oxide

The high-κ stack consisting of an optional nitride interfacial layer and a HfO2 layer was studied. The result shows that nitride or oxynitride interfacial layers can be controllably formed down to a few angstroms. The growth of both interfacial layers is self-limited. The introduction of nitric oxide with hafnium t-butoxide during the high-κ deposition leads to smaller effective oxide thickness (EOT) and gate leakage current. EOTs below 1.0nm have been achieved with this combination of sources. The beneficial effect of nitric oxide can be explained in terms of reduced interfacial EOT, reduction of carbon contamination, and possibly a small trace amount of nitrogen incorporation.

Removal of oxygen and reduction of carbon contamination on (100) Cd0.96Zn0.04Te substrates

X-ray photoelectron and Auger electron spectroscopy as well as reflection high energy electron diffraction have been used to investigate the influence of heat treatment and sputtering on the oxygen and carbon contamination of the (100) Cd0.96Zn0.04Te surface. It was found that oxygen contamination can be completely eliminated from the surface at 300 degrees C in an ultra-high vacuum but not carbon. Heating at still higher temperatures decreases the carbon contamination only slightly while increasing the Zn to Cd ratio on the surface considerably. This affects the Cd0.96Zn0.04Te surface structure and hence subsequent molecular beam epitaxial growth. The authors have found that sputtering with argon ions at an incident angle ranging between 20 degrees and 60 degrees at temperatures between 200 and 250 degrees C can remove nearly all carbon contamination from the surface without destroying the (2*1) surface reconstruction.

Reduction of carbon contamination in triethylphosphorus OMVPE GaP layers by Pt/Al 2O 3 catalyst

The use of a Pt/Al 2O 3 catalyst during GaP growth using triethylphosphorus (TEP) OMVPE is presented. GaP layers are grown by atmospheric pressure OMVPE using TEP as a group-V source. Epilayers with mirror-like surface morphology are obtained with V/III ratio = 17 at 700°C. GaP growth was also conducted with a Pt/Al 2O 3 catalyst introduced into the growth reactor. We show that carrier concentration in GaP is decreased by about an order of magnitude through the use of the Pt/Al 2O 3 catalyst.

Removal of Fluorocarbon Residues on CF 4 / H 2 Reactive‐Ion‐Etched Silicon Surfaces Using a Hydrogen Plasma

A cleaning procedure based on a hydrogen plasma is described which removes most of the fluorocarbon passivation layer remaining on silicon surfaces exposed to reactive ion etching (RIE). Real time in situ ellipsometry performed during hydrogen plasma exposure of a reactive‐ion‐etched silicon surface showed removal of the bulk of this residue. The contamination layer thickness was reduced from 50Å to less than 10Å. X‐ray photoelectron spectroscopy of hydrogen‐plasma‐cleaned silicon showed an 80% reduction in carbon contamination and a 95% reduction in fluorine without appreciable oxidation of the surface. The contamination left after cleaning is a 10Å carbon film. Secondary ion mass spectrometry showed that hydrogen implantation into the silicon substrate during cleaning was negligible relative to the amount implanted during RIE. Continued exposure of the surface to the cleaning plasma resulted in a redeposition of contamination, the source of which is sputtered residue from the reactor walls that was deposited during RIE. Surface oxidation by residual water and oxygen desorbing from chamber surfaces may also take place during prolonged plasma cleaning.

Surface photochemical reactions for alkyl group elimination from precursors in OMVPE

Abstract Photo-irradiation, under conditions where direct photo-decomposition or photo-excitation of source precursors does not occur, can enhance alkyl group elimination from precursors in organometallic vapor phase epitaxy (OMVPE). For II–VI semiconductors such as ZnSe and ZnS, a significant increase in the growth rate with irradiation has been explained in terms of photocatalysis. For III–V semiconductors such as GaAs, the optical and electrical properties were improved. This may be attributed to a reduction in carbon contamination as found by secondary ion mass spectroscopy (SIMS). This phenomenon is promising not only for low temperature growth but also for the development of new group-V precursors for use as alternatives to the toxic hydrides.

Pyrolysis and Photolysis of Trimethylaluminum

A vapor-phase decomposition mechanism for the trimethylaluminum(TMA) used in an Al CVD was investigated by infrared spectroscopy. In pyrolysis, the annihilation of TMA was a first-order reaction and a CH3 radical was generated. The activation energy of the annihilation was about 0.4 eV. The generation mechanism of CH4 from the intermediates was investigated quantitatively. It is suggested that carbon contamination can be reduced by using an H2 carrier gas since the CH3 radical which causes such contamination is changed into CH4 by hydrogenation. In photolysis, the annihilation of TMA is a first-order reaction and C2H6 is generated by the coupling of two CH3 groups. The reduction of carbon contamination is also suggested because the generation of a CH3 radical is suppressed by the generation of C2H6.