Removal Of Surface Contaminants Research Articles

Laser Surface Cleaning in Air: Mechanisms and Applications

Surface contaminations are removed by laser irradiation with pulse output and short wavelength in ambient air. It is a dry cleaning process to remove surface contaminations without using ultrasonic cleaning requiring carbon fluorochloride and other organic solvents. The mechanisms of laser cleaning may include laser photodecomposition, laser ablation and surface vibration due to the impact of the laser pulse. Examples of cleaning metal surfaces and magnetic head sliders show that this cleaning process could be widely used in various industrial applications.

Elemental Palladium by XPS

X-ray photoelectron spectroscopy (XPS) spectra of elemental palladium (Pd) are presented. The specimen is a polycrystalline foil and was analyzed after chemical cleaning and ion-sputtering to remove surface contamination. The spectra were collected with a Surface Science Instruments SSX-101 M-Probe ESCA instrument using monochromatized Al Kα x rays. Spectra include a survey scan and the Pd 3d, 3p, 3s, 4s, 4p, and valence band regions. Also included are the Pd MNN and MNV Auger transitions.

X-ray photoelectron spectroscopy analysis of aluminum and copper cleaning procedures for the Advanced Photon Source

The Advanced Photon Source (APS), presently under construction, will produce x rays of unprecedented brightness. The storage ring where the x rays will be produced will be constructed from an extruded 6063 aluminum alloy, while transition pieces (flanges, etc.) will be made from a 2219 aluminum alloy. In addition, cooled photon absorbers will be placed in strategic locations throughout the ring to intercept the majority of the unused high power-density radiation. These will be made of either CDA-101 (OFHC) copper or glidcop (a dispersion strengthened copper alloy). Before any of these components can be assembled they must be cleaned to remove surface contaminants so that the ultrahigh vacuum (<0.1 nTorr) necessary for successful operation can be achieved. Many recipes for cleaning aluminum and copper exist; however, most of them involve the use of chemicals that present safety and/or environmental concerns. We have undertaken an x-ray photoelectron spectroscopy study of the effects of a variety of commercially available cleaners on the surface cleanliness of aluminum and copper. Several important results have been identified in this study. A simple alkaline detergent in an ultrasonic bath cleans aluminum alloys as effectively as the more aggressive cleaning solutions. The detergent can be used at 65 °C to clean the 6063 alloy and at 50 °C to clean the 2219 alloy. A citric acid based cleaner was found to be effective at cleaning copper, although the surface oxidizes rapidly. To date, we have been unable to find a universal cleaning procedure, i.e., one that is optimal for cleaning both Al and Cu.

Removal of surface contamination after reactive ion etching of silicon dioxide

Reactive Ion Etching (RIE) during semiconductor device fabrication can cause surface and near-surface damage or contamination which may degrade electrical performance. We have investigated methods of removing this damage and contamination prior to further device processing. Using X-ray photoelectron spectroscopy we have analysed the surface residue remaining after a CHF 3-based RIE process used for the removal of thermal oxide on Si substrates. The dry etched wafer surface was studied before and after wet chemical cleaning or UV/O 3 exposure. Surface morphology was investigated using atomic force and scanning optical microscopy. Thickness of thermal oxides grown upon dry etched and subsequently treated wafer surfaces were measured. The results indicate the formation of a modified Si surface region underlying a residue layer formed during the RIE process. We report an investigation of the composition and oxidation behaviour as a function of depth through this near-surface region. This was performed by chemical depth profiling using a sequence of room temperature UV/O 3 oxidation and dilute HF oxide removal steps.

A practical excimer laser-based cleaning tool for removal of surface contaminants

A laser-cleaning tool capable of removing surface contaminants such as submicron-sized particulates and organic films has been constructed and implemented in practical use. An industrial-grade KrF excimer laser is utilized to irradiate the solid surface to be cleaned. The nanosecond-pulsed laser irradiation, shortly after the deposition of a thin liquid film on the surface, induces explosive vaporization of the liquid and removal of particulates (steam cleaning). The ultraviolet (UV) irradiation also causes ablative photodecomposition of organic film contaminants on the surface (dry cleaning). Hence, cleaning can best be done with the combination of these two laser-cleaning modes. The excimer laser cleaning tool is constructed with an aim toward practical use: It includes a computer-controlled laser beam scanning system and a stable liquid film deposition unit, providing a cleaning rate of over 200 cm /min. Semiconductor, metal, and ceramic sample surfaces, contaminated with 1-/spl mu/m sized alumina particles and micron-thick epoxy films, are tested by laser cleaning. The effectiveness of laser cleaning is compared with ultrasonic technique. The cleaning strategy and the probability of thermal damage due to laser cleaning are discussed. >

Detailed in-situ monitoring of film growth: application to TiSi 2 chemical vapor deposition

An experimental approach for monitoring chemical vapor deposition is described that combines in-situ, real-time monitoring of deposition rate and gas composition together with transfer capabilities into ultrahigh vacuum for Auger analysis. This approach has been applied in the specific case of TiSi 2 low-pressure deposition on Si using TiCl 4 and SiH 4. In the early stages of growth, Si for the growing film is supplied directly from the substrate. In later stages, Si arrives through SiH 4 adsorption. The primary gas phase reaction products are H 2, HCl, SiH 3Cl and the radical species SiCl 2. Removing surface contamination from the substrate is not sufficient to promote film nucleation; surface defects are apparently required as well. Steady-state multiplicity in the reaction rate is observed near 700°C for large SiH 4:TiCl 4 ratios.

Critical discussion of relevant physical issues surrounding the weeping of nuclear-waste casks

Spent fuel casks have arrived at fuel disposal sites on numerous occasions with removable external surface contamination levels in excess of regulatory limits, although preshipment surveys indicated much lower contamination levels. This phenomenon is called “weeping” and a conceptual model has been proposed here to describe the same. A passive, vitreous oxide film having M-O and M-OH bonds is believed to form on the SS 304 cask surface which incorporates the pool-borne radio-nuclides into its network structure during cask-loading in the spent fuel pool. Reordering and crystallization of the film takes place some time after the cask has been removed from the pool, decontaminated and shipped. The incorporated nuclides are thus able to migrate through the more defective, crystalline film to the film exterior, leading to a “weeping” phenomenon. The model successfully takes into account the effect of various factors which are known to influence weeping, e.g., humidity and temperature of the environment, cask exposure to sunlight, and its surface roughness.

Isolation of Salmonella from Ovaries and Oviducts from Whole Carcasses of Spent Hens

Spent hens containing hard-shelled eggs were obtained to study the influence of sample collection and sample preparation methodology on the detection of Salmonella in ovaries. Four hundred eighteen birds from 19 flocks were collected, and the carcasses were opened aseptically within 8-12 hours of collection. A sample set containing hard-shelled egg, ovary, and oviduct section were collected from each carcass, and surface contaminants were removed from ovaries with polyoxyethylene ether. Three of 19 flocks (15.8%) and six of 407 ovary samples were positive for Salmonella; two oviduct samples were positive (0.5%). No eggs were Salmonella-positive. Single and multiple serotypes were detected in ovaries. Results indicated that Salmonella recovery rates can be significantly affected by speed in processing samples after collection, by cleanliness of the tissue-collection environment (laboratory vs. slaughter plant), and by removal of surface contaminants.

Optical second harmonic generation studies of the nature of the oxide-covered and clean c(4 × 4) and (2 × 4) reconstructed GaAs(001) surfaces

We report the application of the “epioptic” technique of optical second harmonic generation (SHG) to the study of surface chemical processes occurring at the technologically important (001) surfaces of the non-centrosymmetric compound semiconductor GaAs. SHG has been used to monitor the thermal removal of surface contamination from an GaAs(001) substrate mounted in a conventional molecular beam epitaxy (MBE) chamber. Rotational anisotropy plots of the reflected SH signal recorded at near-normal incidence indicate that the oxide layer is not fully disordered and possesses some structural anisotropy, i.e. some preferred net surface orientation. In addition the rotational anisotropy plots were observed to change in both intensity and apparent phase between the oxide-covered surface and the clean reconstructed surfaces. Following heating to 850 K under the background As 2 flux present in the chamber, the SH signal from the clean, reconstructed surface was approximately 5 × weaker than that observed for the contaminated surface and was subsequently found to be insensitive to the reconstruction change between the (2 × 4) and c(4 × 4) surfaces, in agreement with theoretical predictions for surfaces having 2mm and 4mm symmetry, respectively. These data are discussed in terms of the difficulties encountered when attempting to observe a surface SH response from a non-centrosymmetric substrate. The sensitivity of the technique towards the thin oxide overlayer suggests that for overlayers which are likely to possess net oriented in-plane dipoles due to the structural mismatch with the substrate, an SH response may be observed in preference to a bulk response when a normal incidence geometry is employed.

Optical second harmonic generation studies of the nature of the oxide-covered and clean c(4 × 4) and (2 × 4) reconstructed GaAs(001) surfaces

We report the application of the “epioptic” technique of optical second harmonic generation (SHG) to the study of surface chemical processes occurring at the technologically important (001) surfaces of the non-centrosymmetric compound semiconductor GaAs. SHG has been used to monitor the thermal removal of surface contamination from an GaAs(001) substrate mounted in a conventional molecular beam epitaxy (MBE) chamber. Rotational anisotropy plots of the reflected SH signal recorded at near-normal incidence indicate that the oxide layer is not fully disordered and possesses some structural anisotropy, i.e. some preferred net surface orientation. In addition the rotational anisotropy plots were observed to change in both intensity and apparent phase between the oxide-covered surface and the clean reconstructed surfaces. Following heating to 850 K under the background As 2 flux present in the chamber, the SH signal from the clean, reconstructed surface was approximately 5 × weaker than that observed for the contaminated surface and was subsequently found to be insensitive to the reconstruction change between the (2 × 4) and c(4 × 4) surfaces, in agreement with theoretical predictions for surfaces having 2mm and 4mm symmetry, respectively. These data are discussed in terms of the difficulties encountered when attempting to observe a surface SH response from a non-centrosymmetric substrate. The sensitivity of the technique towards the thin oxide overlayer suggests that for overlayers which are likely to possess net oriented in-plane dipoles due to the structural mismatch with the substrate, an SH response may be observed in preference to a bulk response when a normal incidence geometry is employed.

Atomically flat gold films grown on hot glass

The results of a scanning tunneling microscope (STM) study of the morphology of Au films thermally evaporated onto heated glass substrates are presented. Au films of thickness 20–80 nm were evaporated onto Corning glass cover slips at temperatures of 20–465 °C. Before the evaporation, the glass substrates were prebaked at 300–400 °C for 12 h to remove surface contamination. Grain size and surface roughness of the films have been measured, and the best results were obtained with Au films 80 nm thick evaporated onto 300 °C substrates. These films have 250-nm-diam grains with large, atomically flat tops exhibiting step-free terraces as large as 200×200 nm2. These results are comparable to the best reported results for Au grown on heated mica and show that epitaxial growth is not required for the production of films with large atomically flat regions. This study of Au on glass was motivated by failed attempts to produce flat films of gold on mica using recipes in the literature. Possible reasons for the poor results with mica are discussed.

Low energy electron diffraction and cyclic voltammetry studies of flame-annealed platinum single crystals

Low energy electron diffraction (LEED) and cyclic voltammetry were used to examine the surface structure of flame-annealed platinum (100), (110), and (111) electrodes. Well-defined LEED patterns were obtained for these surfaces but only after heat treatment in vacuo at 400°C in order to remove surface contaminants. The cyclic voltammograms correspond to those expected for these low index platinum surfaces from prior studies.

Detecting Removable Surface Contamination

Although surveying for radioactive contamination by wiping surfaces is the norm, this practice can be highly variable and may be inefficient for detecting low-energy beta emitters. Relying on wipe testing may likewise be an inefficient use of personnel and may seriously underrepresent the amount of contamination present. In general practice, it is better to clean and, where applicable, renew surfaces regularly as part of standard operating protocols and work practices.

Advances in remote plasma-enhanced chemical vapor deposition for low temperature In situ hydrogen plasma clean and Si and Si1-xGex epitaxy

Remote plasma-enhanced chemical vapor deposition (RPCVD) is a low temperature growth technique which has been successfully employed inin situ remote hydrogen plasma clean of Si(100) surfaces, silicon homoepitaxy and Si1- xGex heteroepitaxy in the temperature range of 150–450° C. The epitaxial process employs anex situ wet chemical clean, anin situ remote hydrogen plasma clean, followed by a remote argon plasma dissociation of silane and germane to generate the precursors for epitaxial growth. Boron doping concentrations as high as 1021 cm−3 have been achieved in the low temperature epitaxial films by introducing B2H6/He during the growth. The growth rate of epitaxial Si can be varied from 0.4A/min to 50A/min by controlling therf power. The wide range of controllable growth rates makes RPCVD an excellent tool for applications ranging from superlattice structures to more conventional Si epitaxy. Auger electron spectroscopy analysis has been employed to confirm the efficacy of this remote hydrogen plasma clean in terms of removing surface contaminants. Reflection high energy electron diffraction and transmission electron microscopy have been utilized to investigate the surface structure in terms of crystallinity and defect generation. Epitaxial Si and Si1-xGex films have been grown by RPCVD with defect densities below the detection limits of TEM (~105 cm-2 or less). The RPCVD process also exploits the hydrogen passivation effect at temperatures below 500° C to minimize the adsorption of C and 0 during growth. Epitaxial Si and Si1-xGex films with low oxygen content (~3 × 1018 cm-3) have been achieved by RPCVD. Silicon and Si/Si1-xGex mesa diodes with boron concentrations ranging from 1017 to 1019 cm-3 in the epitaxial films grown by RPCVD show reasonably good current-voltage characteristics with ideality factors of 1.2-1.3. A Si/Si1-xGex superlattice structure with sharp Ge transitions has been demonstrated by exploiting the low temperature capability of RPCVD.In situ plasma diagnostics using single and double Langmuir probes has been performed to reveal the nature of the RPCVD process.

Scanning electron microscopic examination of ultrasonic and effervescent methods of surface contaminant removal from complete dentures

Dentures were examined by scanning electron microscopy to evaluate removal of surface contaminants such as plaque, calculus, microflora, and cigarette smoke. Ten complete dentures were obtained during patient appointments and prepared for SEM examination. Samples from 10 control surfaces, 10 surfaces cleaned with effervescent cleansers, and 10 surfaces ultrasonically cleaned were photographed at ×5000. One photograph of each sample was evaluated in random order by five judges for a total of 150 observations. Photographs were compared with one of a clean denture sample. Statistical analysis of the results validated the superiority of the ultrasonic method for cleaning dentures.

I n s i t u cleaning of silicon substrate surfaces by remote plasma-excited hydrogen

We have demonstrated a low-temperature cleaning technique for removing both carbon and oxygen from a Si surface. It uses a combination of ex situ wet chemical clean and an in situ remote rf plasma-excited hydrogen clean in an ultrahigh vacuum chamber. Since a remote rf plasma is used, there is insignificant plasma damage or other deleterious effects on surface morphology. A combination of in situ Auger and RHEED analysis has been used to confirm the removal of surface contaminants and the reconstruction of the Si surface. From mass spectroscopy studies, we believe that the hydrogen cleaning is due to a chemical etching of the Si by atomic hydrogen produced by the plasma. This clean is compatible with UHV processing and yields Si substrates that can be used for successful very low temperature (220–400 °C) Si homoepitaxy by remote plasma-enhanced chemical vapor deposition.

Outgassing and desorption of the stainless‐steel beam tubes after different degassing treatments

Chemical cleaning, vacuum firing, glow discharge cleaning, and in situ bakeout have become standard practice for lowering the outgassing rate and removing surface contaminants in the ultrahigh vacuum systems of particle accelerators and storage rings. This paper presents the work done with the thermal outgassing of several long stainless‐steel (304LN and 316L) beam chambers with areas of more than 1×104 cm2 . They were measured between 20 and 500 °C after vacuum firing, glow discharge cleaning, or reactive gas (nitric oxide) cleaning. Outgassing rates of low 10−13 and low 10−14 Torr 1/s cm2 were achieved for H2 and CO, respectively, with vacuum firing alone. The outgassing of H2 in this temperature range is consistent with that due to bulk diffusion with an enthalpy of 9±1 kcal/mole. The photon stimulated desorption of the chamber surface after the above treatments were also studied by exposure to an intense photon beam at the National Synchrotron Light Source. The effectiveness and merits of reactive gas cleaning in removing the surface contaminants in large vacuum systems are compared to those of vacuum firing and glow discharge cleaning.

Adhesive Bonding

The main advantage of adhesive bonding over other jointing methods is that it gives a continuous bond instead of localised point contacts. This results in a structure with a more uniform stress distribution and greater stiffness. Other advantages include lower process temperatures than with welding or brazing and the ability to join several components together in one operation. Adhesives are generally of two types Structural adhesives set by a chemical reaction and include anaerobics, cyanoacrylates, toughened acrylics, polyurethanes, and epoxies. Non-structural adhesives set by a physical change and include hot melts, plastisols, rubber-based adhesives, polyvinyl acetates, and pressure sensitive adhesives. Most structural adhesives are strongest in shear, compression and tension but relatively weak under peel and cleavage. Joints should ideally be designed so that the loading stresses will be directed along the lines of greatest strength, ie peel stresses should be minimised. If this is not possible one of the new generation of toughened adhesives should be used. It is usually desirable to prepare the surfaces for bonding by the removal of surface contaminants, generally by solvent degreasing plus abrasion. Two-part adhesives must be correctly proportioned and thorouhly mixed prior to application.

Oxidation of cold copper films with oxygen radicals

The oxidation of cold copper films in vacuum using a flux of oxygen radicals is reported. Also atomic hydrogen can be usefully employed to remove surface contaminants and to reduce the oxide controllably.

Fluorinated Diamond Films, Slabs, and Grit

AbstractDiamond powders, single crystal diamonds (slabs and naturally occurring stones), and CVD diamond films have been fluorinated via direct fluorination and plasma techniques at a variety of temperatures and reaction times. Infrared, ESCA, and mass spectrometric studies verify that the diamond surfaces are altered by fluorination and that fluorine is attached to the surface to some degree in most instances. Based on spectra obtained using the FT-IR techniques of DRIFTS and ATR, the fluorine appears to have an effect on the diamond surfaces at relatively low temperatures in short reaction times by the removal of surface contaminants. A relatively high temperature (600ºC) or long reaction time at slightly lower temperatures is needed to attach a significant number of fluorine atoms onto the diamond surface. Once fluorinated, the diamonds show enhanced resistance to further oxidation. The outward appearance of the diamonds remains unchanged even at fluorination temperatures nearing 800ºC.