Occurrence of particle debris field during focused Ga ion beam milling of glassy carbon

To explore the machining characteristics of glassy carbon by focused ion beam (FIB), particles induced by FIB milling on glassy carbon have been studied in the current work. Nano-sized particles in the range of tens of nanometers up to 400 nm can often be found around the area subject to FIB milling. Two ion beam scanning modes - slow single scan and fast repetitive scan - have been tested. Fewer particles are found in single patterns milled in fast repetitive scan mode. For a group of test patterns milled in a sequence, it was found that a greater number of particles were deposited around sites machined early in the sequence. In situ EDX analysis of the particles showed that they were composed of C and Ga. The formation of particles is related to the debris generated at the surrounding areas, the low melting point of gallium used as FIB ion source and the high contact angle of gallium on glassy carbon induces de-wetting of Ga and the subsequent formation of Ga particles. Ultrasonic cleaning can remove over 98% of visible particles. The surface roughness (R_a) of FIB milled areas after cleaning is less than 2 nm.     

Simulation study and experiment on laser-ablation surface cleaning

A study of the ablation effects of an ultra-short pulsed Nd : YAG laser was carried out. Using a 21 μm Zn-coated carbon steel plate as the target, the relationship between ablation rate and laser fluence was investigated through computer simulation and experiment, and the optimal processing conditions were determined. The tendency of the scanning operation curve was confirmed and the data obtained were taken as a guide for the practical utilization of this technique. Finally, a decontamination factor was introduced and satisfactory cleaning was obtained.     

Enzymatic cleaning of ultrafiltration membranes fouled by protein mixture solutions

Compared to other typical cleaning agents, application of enzyme in cleaning of membranes fouled with protein solution promised the high cleaning efficiencies with lower environmental impact. This paper is focused on the mechanisms of protein removal by enzyme cleaning agent from the membrane surface by analysis hydraulic resistance, total protein removal using Lowry method, and membrane surface analysis using MALDI-MS and gel electrophoresis to estimate the foulant composition. Using single and binary protein solutions of bovine serum albumin and beta-lactoglobulin as the feed solution for filtration process, the experimental results indicate that optimum cleaning time and cleaning agent concentration is due to the competition between foulant removal and deposition of enzymes on the membrane during the cleaning process. The removal rate of different protein species in the fouling layer is varied, indicating that cleaning strategies can be tailor-made for fouling layer with different protein compositions.     

An erosion sensor based on a quartz crystal microbalance for quantitative determination of the cleaning efficiency in an ultrasonic vessel

The efficiency of ultrasonic cleaning vessels cannot be measured directly in an easy way. In the presented work, a sensor is developed which quantitatively measures the ablation of a test layer. The sensor element is a quartz crystal which is coated with a sacrificial layer. Small changes in mass of this layer can be measured by a frequency shift of the crystal oscillation. For measurements, a 10 MHz AT-cut quartz crystal was used in a cleaning vessel working at 44.9 kHz. To determine the frequency shift by the ablation of the test layer, the quartz crystal was driven by a frequency generator sweeping the frequency in the range of the resonance frequency and a characteristic frequency was determined. The test layer which was applied to the quartz crystal consisted of silica microparticles suspended in varnish. In a preliminary experiment using a commercial cleaner it could be shown that significant changes in resonance frequency by cavitation effect could be detected. The initial frequency shift of the sacrificial layer is reproducible within 10%. The test layer can be adapted to the conditions of the cleaning vessel. By changing the electrical input power of the vessel, a threshold in the cavitation erosion was found.     

Surface refinement and electronic properties of graphene layers grown on copper substrate: An XPS, UPS and EELS study

The present work focuses on the assessment of two surface treatment procedures employed under ultra high vacuum conditions in order to obtain atomically clean graphene layers without disrupting the morphology and the two dimensional character of the films. Graphene layers grown by chemical vapor deposition on polycrystalline Cu were stepwise annealed up to 750 °C or treated by mild Ar⁺ sputtering. The effectiveness of both methods and the changes that they induce on the surface morphology and electronic structure of the films were systematically studied by X-ray photoelectron spectroscopy, and electron energy loss spectroscopy. Ultraviolet photoelectron spectroscopy was employed for the study of the electronic properties of the as received sample and in combination with the work function measurements, indicated the hybridization of the C-π network with Cu d-orbitals. Mild Ar⁺ sputtering sessions were found to disrupt the sp2 network and cause amorphisation of the graphitic carbon. Annealing between 300 °C and 450 °C under ultra high vacuum proved to be an effective and lenient way for achieving an atomically clean graphene surface. At higher temperatures the rigid structure of graphene does not follow the expansion of the copper substrate leading to the graphene/Cu interface breakdown and possibly to further rippling of the graphene layers leaving bare areas of cooper substrate.     

“华光礁Ⅰ号”沉船出水瓷器“保护性损伤”量化评估的ICP-AES分析

目前,文物保护工作者已普遍认识到保护过程会对文物带来一定影响,产生“保护性损伤”。然而,关于“保护性损伤”的量化研究仍罕见报道。为探讨常用清洗试剂对“华光礁Ⅰ号”沉船出水瓷器的保护性损伤,本文利用ICP-AES测试了各步骤浸泡实验溶出液中的元素组成,发现浸泡液中Al,Fe,Mg三种元素的含量较高,且具有一定规律。利用这三种元素作为指标,对出水瓷器的保护性损伤进行了量化评估。研究结果表明,清洗能力强的试剂,对陶瓷本体的损伤也较大;保存较好的器物,所受“保护性损伤”更小;每种清洗剂都会对瓷器造成一定程度的损坏,连中性试剂(如H₂O)同样可以溶解出一定量胎体组分;而普遍认为的较为温和的清洗试剂在长时间浸泡陶瓷器时,对瓷器本体的损伤已非常接近强酸短时间浸泡的影响。故在此特别强调,在实际的文物保护过程中,应切实认识到各种清洗剂对陶瓷本体产生的损害,并同时考虑累积损伤。如此,方能安全有效的保护海洋出水瓷器。     

Reaction of cyanide ions with copper on Si surfaces and its use for Si cleaning

A Si cleaning method has been developed by use of potassium cyanide (KCN) dissolved in methanol. When silicon dioxide (SiO₂)/Si(1 0 0) specimens with 10¹⁴ atom/cm² order copper (Cu) contaminants are immersed in 0.1 M KCN solutions of methanol at 25 °C, the Cu concentration is reduced to below the detection limit of total X-ray fluorescence spectrometer of ∼3 × 10⁹ atoms/cm². X-ray photoelectron spectra show that the thickness of the SiO₂ layers is unchanged after cleaning with the KCN solutions. 10¹⁴ cm⁻² order Cu contaminants on the Si surface can also be removed below ∼3 × 10⁹ atoms/cm², without causing contamination by potassium ions. UV spectra show that Cu-cyano complex ions are formed in the KCN solutions after the cleaning. The main Cu species in the KCN solutions is ions with the concentration of []:[Cu⁺] = 1:1.6 × 10²³. Even when the KCN solutions are contaminated with 64 ppm Cu²⁺ ions in the solutions, which form ions, the cleaning ability does not decrease, showing that ions are not re-adsorbed. The KCN solutions can also passivate defect states such as Si/SiO₂ interface states, leading to the improvement of characteristics of Si devices.     

Transient removal of a contaminated fluid from a cavity

A numerical and experimental study of the time-dependent hydrodynamic removal of a contaminated fluid from a cavity on the floor of a duct is presented. The duct flow has a parabolic inlet velocity profile and laminar flows are considered in a Reynolds number range between 50 and 1600 based on the duct height. The properties of the contaminated cavity fluid are assumed to be the same as for the fluid flowing in the duct. Attention is focussed on the convective transport of contaminated fluid out from the cavity and the effect of duct flow acceleration on the cleaning process. Passive markers which are convected with the flow are used in the numerical simulation for the purpose of identifying the contaminated cavity fluid. It is shown that the cleansing of the cavity is more pronounced during the unsteady start-up of the duct flow and the rate of cleaning decreases as the flow reaches a steady state. The cleaning process is enhanced as the cavity aspect ratio is increased and as the duct Reynolds number increases. A ‘volumetric’ approach based on the spread of markers is shown to be useful in determining the fraction of the cavity that remains contaminated after steady conditions have been reached. The distribution of the contaminant in a cavity during the unsteady stage and after steady conditions are reached are identified using passive markers.     

Modeling of surface cleaning by cavitation bubble dynamics and collapse

Surface cleaning using cavitation bubble dynamics is investigated numerically through modeling of bubble dynamics, dirt particle motion, and fluid material interaction. Three fluid dynamics models; a potential flow model, a viscous model, and a compressible model, are used to describe the flow field generated by the bubble all showing the strong effects bubble explosive growth and collapse have on a dirt particle and on a layer of material to remove. Bubble deformation and reentrant jet formation are seen to be responsible for generating concentrated pressures, shear, and lift forces on the dirt particle and high impulsive loads on a layer of material to remove. Bubble explosive growth is also an important mechanism for removal of dirt particles, since strong suction forces in addition to shear are generated around the explosively growing bubble and can exert strong forces lifting the particles from the surface to clean and sucking them toward the bubble. To model material failure and removal, a finite element structure code is used and enables simulation of full fluid–structure interaction and investigation of the effects of various parameters. High impulsive pressures are generated during bubble collapse due to the impact of the bubble reentrant jet on the material surface and the subsequent collapse of the resulting toroidal bubble. Pits and material removal develop on the material surface when the impulsive pressure is large enough to result in high equivalent stresses exceeding the material yield stress or its ultimate strain. Cleaning depends on parameters such as the relative size between the bubble at its maximum volume and the particle size, the bubble standoff distance from the particle and from the material wall, and the excitation pressure field driving the bubble dynamics. These effects are discussed in this contribution.     

Ultrasonic cleaning of 3D printed objects and Cleaning Challenge Devices

We report our experiences in the evaluation of ultrasonic cleaning processes of objects made with additive manufacturing techniques, specifically three-dimensional (3D) printers. These objects need to be cleaned of support material added during the printing process. The support material can be removed by dissolution in liquids with or without ultrasonic cavitation.