Effective removal of Ga residue from focused ion beam using a plasma cleaner

Samples prepared using the focused ion beam (FIB) inevitably contain the surface damage induced by energetic Ga+ ions. An effective method of removing the surface damage is demonstrated using a plasma cleaner, a device which is widely used to minimize the surface contamination in scanning transmission electron microscopy (STEM). Surface bombardment with low-energy Ar+ ions was induced by biasing the sample immersed in the plasma source, so as to etch off the surface materials. The etch rates of SiO2, measured with a bias voltage of 100-300 V, were found to vary linearly with both the time and bias and were able to be controlled from 1.4 to 9 nm/min. The removal of the Ga residue was confirmed using energy dispersive spectroscopy (EDS) after the plasma processing of the FIB-prepared sample. When the FIB-prepared sample was processed via plasma etching for 10 min with a bias of 150 V, the surface Ga damage was completely removed.     

湿法化学刻蚀技术处理抛光熔石英元件

为了提高熔石英元件的抗激光损伤能力,采用基于氢氟酸刻蚀的湿法化学技术去除元件内的激光损伤诱因。利用不同的氢氟酸溶液处理经氧化铈抛光的熔石英元件,并对元件的刻蚀速率、表面洁净度、粗糙度、透过率和激光损伤性能进行评价。研究结果表明,与传统的静态刻蚀相比,在质量分数为6%的氢氟酸刻蚀溶液中引入能量密度约为0.6 W/cm^2的兆声能量对元件的溶解速率和激光损伤性能没有明显的提升作用;化学刻蚀产生的沉积物对元件表面粗糙度和透过率均有不利影响,且沉积物比例与所用的刻蚀液成分和浓度密切相关;经质量分数6%或12%的纯氢氟酸溶液刻蚀(5±1)μm深度后,熔石英元件的激光损伤阈值相比于未刻蚀元件提升了约1.9倍;熔石英元件的激光损伤性能与表面粗糙度和透过率之间不是简单的线性关系,但激光损伤阈值较理想的元件(>20 J/cm^2@3ns)往往具有较光滑的表面,即表面粗糙度<2 nm,由此可以确定有利于熔石英元件激光损伤性能的刻蚀条件,并获得元件表面粗糙度的控制指标。     

Imaging of fullerene-like structures in CNx thin films by electron microscopy; sample preparation artefacts due to ion-beam milling

The microstructure of CN(x) thin films, deposited by reactive magnetron sputtering, was investigated by transmission electron microscopy (TEM) at 200kV in plan-view and cross-sectional samples. Imaging artefacts arise in high-resolution TEM due to overlap of nm-sized fullerene-like features for specimen thickness above 5nm. The thinnest and apparently artefact-free areas were obtained at the fracture edges of plan-view specimens floated-off from NaCl substrates. Cross-sectional samples were prepared by ion-beam milling at low energy to minimize sample preparation artefacts. The depth of the ion-bombardment-induced surface amorphization was determined by TEM cross sections of ion-milled fullerene-like CN(x) surfaces. The thickness of the damaged surface layer at 5 degrees grazing incidence was 13 and 10nm at 3 and 0.8keV, respectively, which is approximately three times larger than that observed on Si prepared under the same conditions. The shallowest damage depth, observed for 0.25keV, was less than 1nm. Chemical changes due to N loss and graphitization were also observed by X-ray photoelectron spectroscopy. As a consequence of chemical effects, sputtering rates of CN(x) films were similar to that of Si, which enables relatively fast ion-milling procedure compared to carbon compounds. No electron beam damage of fullerene-like CN(x) was observed at 200kV.     

Chemical etching in processing cortical bone specimens for scanning electron microscopy

Transverse and longitudinal sectioning of undecalcified cortical bone is a commonly employed technique for investigating the lamellar structure of the osteons. Since a flat surface is required, the specimen has to be grinded and then polished. Whereas the smear of debris and inorganic/organic deposits left by these treatments cannot be removed by ultrasonication alone, a chemical treatment of the specimen surface with either a basic or an acid etching solution is currently employed. A further effect of the latter can be the enhancement of the lamellar bone pattern. The kind of etching solution, its pH, the concentration of etchants, and the contact time significantly affect the sectioned surface when it is observed with scanning electron microscopy (SEM). The etching procedures can severely influence the obtained images. Homogeneous cortical bone specimens were sampled from the first metatarsal of two fresh human subjects. One or two cut surfaces were exposed to different acid and basic solutions in bonded conditions. Considering the type of chemical agents, the solution pH, and the exposure time of the specimens, the effects of several etching media have been investigated and compared. Strong etching, either acid or basic produced surface decalcification and severe damage of the collagen matrix, compromising any morphological or morphometric analysis. Weak acid etching (for example citric and acetic acid), even though causing distinctive alteration of the sample, enhanced the visibility of the lamellar pattern, while the polyphosphate treatment of the surface decalcified a thin layer matrix, ensuring a good visibility of fibrils and avoiding rough distortions. Microsc. Res. Tech. 77:653–660, 2014. © 2014 Wiley Periodicals, Inc.     

Surface quality improvement of EDMed Ti–6Al–4V alloy using plasma etching and TiN coating

This paper seeks to improve the surface quality of electrical discharge machining (EDM) Ti–6Al–4V using plasma etching treatment and TiN coating. The EDM parameter setting is optimized firstly based on grey-Taguchi method. Four EDM parameters, including current (A), voltage (V), pulse duration (μs), and duty factor (%), are selected for multiple performance of lower electrode wear rate (EWR), higher material removal rate (MRR), and better surface roughness (SR). An orthogonal array, signal-to-noise (S/N) ratios, and analysis of variance (ANOVA) are used to analyze the effects of these EDM parameters. Normality tests show that all the distributions fit normality assumption with p?=?0.276, 0.688, and 0.663, respectively. The EDM process is stable over time monitored by Shewhart control charts. It is observed that there is an EDM damaged layer on the surface consisting of debris, microcracks, molten drops, and solidified metals by scanning electron microscopy. The plasma etching and TiN coating are employed to improve surface quality of the EDMed Ti–6Al–4V alloys. The results demonstrate that using the oxygen plasma etching treatment, the damaged phenomena are decreased, and the mean SR value is reduced from Ra?=?2.91 to Ra?=?2.50 μm. In addition, when the plasma-treated alloy is coated with Ti buffer/TiN coating by physical vapor deposition, the surface morphology exhibits less defects and a better surface finish. The mean SR values are further reduced from Ra?=?2.50 μm to Ra?=?1.48 μm (for 740 nm TiN film) and Ra?=?0.61 μm (for 1450 nm TiN film), respectively.     

Design of a scanning probe microscope with advanced sample treatment capabilities: An atomic force microscope combined with a miniaturized inductively coupled plasma source

We describe the design and performance of an atomic force microscope (AFM) combined with a miniaturized inductively coupled plasma source working at a radio frequency of 27.12 MHz. State-of-the-art scanning probe microscopes (SPMs) have limited in situ sample treatment capabilities. Aggressive treatments such as plasma etching or harsh treatments such as etching in aggressive liquids typically require the removal of the sample from the microscope. Consequently, time consuming procedures are required if the same sample spot has to be imaged after successive processing steps. We have developed a first prototype of a SPM which features a quasi in situ sample treatment using a modified commercial atomic force microscope. A sample holder is positioned in a special reactor chamber; the AFM tip can be retracted by several millimeters so that the chamber can be closed for a treatment procedure. Most importantly, after the treatment, the tip is moved back to the sample with a lateral drift per process step in the 20 nm regime. The performance of the prototype is characterized by consecutive plasma etching of a nanostructured polymer film.     

Metallization and Ar‐O plasma effects on dental enamel roughness evaluated with SEM and MeX™ for 3D reconstruction

The MeX? software is a useful tool for tridimensional data collection for surface evaluation and could be relevant to evaluate the same specimen in different phases of the study, assuming repeated measures of dental enamel roughness. The aim of this study was to evaluate the influence of sample metallization for dental enamel roughness analysis with 3D images reconstructed using MeX? software from Scanning Electron Microscopy (SEM) images. The influence of 74.98% (%mol/mol) argon?oxygen plasma for carbon layer removal on surface roughness of the metallized specimen was also evaluated. Dental enamel specimens were prepared for SEM analysis with and without carbon metallization using conventional or environmental modes. Argon?oxygen plasma for carbon layer removal was used and surface roughness was re‐evaluated. Roughness obtained by SEM and MeX? reconstructed images, with or without metallization, did not differ. No significant alteration on surface roughness after carbon layer removal using plasma was found. SEM baseline evaluation using conventional mode without sample preparation and in environmental mode were not comparable. Roughness of enamel 3D images reconstructed with MeX? software from SEM images, with or without metallization was similar. The 74.98% (%mol/mol) argon?oxygen plasma removed the carbon layer with no effect on enamel roughness.     

A simple method for depositing thin films on the surface of transmission electron microscope specimens

Thin-film deposition on already thinned transmission electron microscope (TEM) samples is generally difficult as these samples are often small and fragile. To overcome this difficulty, we have developed a new method for depositing thin films of practically any material onto TEM samples using an ion-milling machine. This principle utilizes the fact that an ion-milling machine can be used not only for removal but also for deposition of materials. Fine-grained thin films were found to grow on TEM samples by this method.     

A comparison of EDS microanalysis in FIB-prepared and electropolished TEM thin foils

This paper reports the results of a fine-probe EDS microanalytical study of cellular precipitation in a Cu-Ti binary alloy. Compositional profiles across the solute depleted Cu-rich FCC lamellae and the Cu4Ti lamellae within isothermally formed cellular colonies were measured in a FEG-TEM from thin-foil specimens prepared by conventional electropolishing and by a technique using a Ga+ focused ion-beam (FIB). The Cliff-Lorimer ratio method, with an absorption correction, was employed to quantify the compositions. Two FIB samples were prepared with different orientations of the lamellae with respect to the ion-milling direction. The compositional profiles across the Cu-rich FCC lamellae and the Cu4Ti compound lamellae in both the FIB-prepared samples and the electropolished sample were, within experimental error, numerically equivalent. The composition of the Cu4Ti compound phase lamellae was very close to the ideal stoichiometric composition of 20 at % Ti. It is concluded that for this system, and for the specimen preparation procedures used in this study, the Ga+ ion-milling process has had no detectable effect on the chemistry changes across the interlamellar interface at the scale studied. These results indicate that the possible sources of chemical artifacts which include redeposition, preferential sputtering and ion-induced atomic migration can be minimized if several precautions are taken during milling in the FIB. Consistent with previous investigators, it was also found that the ion-milling process does introduce significant structural artifacts (e.g., dislocations) into the softer FCC Cu-rich phase compared with a specimen produced by conventional electropolishing.     

Measurement and estimation of temperature rise in TEM sample during ion milling

The actual temperature rise was measured during ion-milling process used in the transmission electron microscopy (TEM) sample preparation. Special probes were fabricated for the measurements, one with shielded, floating thermocouple mounted onto a 3mm grid to compute the thermal load at the sample, and the other, a bare probe with a polymer coating to measure the maximum temperature attained. The temperature measured in the most commonly used ion-milling system reached up to 295 degrees C when the typical milling conditions, 6keV ion-energy and an incident angle of 80 degrees, were used. Based on the temperature profiles that were obtained by the shielded probe, two unknown parameters, the amount of heat deposited by the energetic ions/neutrals to the sample and the thermal conductivities between the materials, were estimated and used to compute the temperature rise in commonly adopted materials. The calculation showed that the temperature of the glass sample reached more than 300 degrees C under typical ion-milling conditions. The calculated value was confirmed with the experimental result of the crystallization of an amorphous Si on the glass under the typical ion-milling condition, which gave the same extent as annealing at 350 degrees C.     

Ultrastructural comparison of ion beam and radiofrequency plasma etching effects on biological tissue sections

Three dry etching techniques (Ar+ ion beam, O₂+ ion beam, O₂ radiofrequency electrodeless discharge) were compared with respect to preferential etching and damage to the ultrastructure of glutaraldehyde-fixed Epon-embedded frog skeletal muscle sections. SEM and TEM studies were performed on both unstained and stained (osmium tetroxide, uranyl acetate) sections. Etching effects were observed to differ for the various ion beam or plasma etching techniques. Whereas selective retention of electron dense structures (e.g. Z lines, nuclear heterochromatin) was observed for oxygen plasma etching, preferential etching of these components was observed using O₂+ ion beam bombardment. Selectively etched Z lines and etch-resistant nucleoli were observed for both reactive (O₂+) and inert (Ar+) ion beam sputtering after sufficiently high ion doses. The above suggest that selective etching under keV ion beam irradiation is related more to physical sputtering processes (momentum transfer) than to the chemical reactivity of the incident ion. Heavy metal post-fixation and staining had no qualitative effect on the nature of the selective etching phenomena. The above findings are significant in that they potentially influence both electron and ion microprobe measurements of etched biological specimens.     

Use of membrane filters and osmium tetroxide etching in the preparation of sperm for scanning electron microscopy

A new method was developed which is suitable for the preparation of mammalian sperm for scanning electron microscopy under either laboratory or field conditions. Samples of ejaculates from humans, two ferret species, and epididymal sperm from the African elephant were diluted in Millonig phosphate buffer and then fixed in glutaraldehyde solution. A small sample of the fixed sperm suspension was diluted in the same buffer, withdrawn with a syringe, and injected very slowly onto either a cellulose acetate or a polycarbonate membrane filter. This step was essential to concentrate the dilute sperm samples. During the various dilution steps most of the granular prostatic secretions were lost. However, a protein-like sheath, which remained attached to most sperm, obscured the surface features and had to be removed for SEM studies. It was removed by prolonged fixation/etching in 1% osmium tetroxide. Membrane filters containing sperm on their surfaces then were dehydrated, dried by the critical point drying method, and sputter coated with gold. Polycarbonate filters were superior to cellulose acetate filters in producing a flat and homogeneous background.     

Ion milling of materials science specimens for electron microscopy: A review

Ion bombardment to perforation is a common technique in the materials sciences by which thin specimens can be prepared for transmission electron microscopy. The process is not without complication and involves radiation damage to the specimen and tends not to preserve the initial specimen topology. Some of the more important facets of the ion-milling process, pertinent to such specimen preparations, are described.     

Frictional Behavior of Polyurethane Modified by Carbon Coatings Synthesized in Dual-Frequency Plasma

A method for changing the surface properties of polymeric materials is by plasma treatment and, in particular, the modification by carbon coatings synthesized using plasma techniques. This article presents the tribological properties of carbon coatings produced on polyurethane substrates by a dual-frequency plasma technique. The analyses were made in terms of placement of the samples in the reactor and the number of modification steps. The samples were characterized by atomic force microscopy and friction tests, which were performed using a ball-on-disc tribometer. The chemical structure of the produced coatings was analyzed with the use of Raman spectroscopy. The obtained results show that the best tribological properties were characteristic of carbon coatings produced on samples placed onto the water-cooled electrode without preliminary ion etching in an argon atmosphere. The modifications decreased the coefficient of friction from 1.2, characteristic of unmodified polyurethane, to a value of about 0.38. The wear rate was reduced from 16.8 × 10^?5 to a value of 4 × 10^?9 mm³/Nm. Based on analysis of the wear tracks it was determined that for the proposed combination of a ZrO₂ ball versus a polyurethane disc modified with a diamond-like carbon (DLC) layer the dominant mechanism of wear is friction; however, in extreme cases, when the DLC coating is worn out, characteristic debris can be observed.     

Fabricating nanostructures through a combination of nano-oxidation and wet etching on silicon wafers with different surface conditions

This study investigates the surface conditions of silicon wafers with native oxide layers (NOL) or hydrogen passivated layers (HPL) and how they influence the processes of nano-oxidation and wet etching. We also explore the combination of nano-oxidation and wet etching processes to produce nanostructures. Experimental results reveal that the surface conditions of silicon wafers have a considerable impact on the results of nano-oxidation when combined with wet etching. The height and width of oxides on NOL samples exceeded the dimensions of oxides on HPL samples, and this difference became increasingly evident with an increase in applied bias voltage. The height of oxidized nanolines on the HPL sample increased after wet etching; however, the width of the lines increased only marginally. After wet etching, the height and width of oxides on the NOL were more than two times greater than those on the HPL. Increasing the applied bias voltage during nano-oxidation on NOL samples increased both the height and width of the oxides. After wet etching however, the increase in bias voltage appeared to have little effect on the height of oxidized nanolines, but the width of oxidized lines increased. This study also discovered that the use of higher applied bias voltages on NOL samples followed by wet etching results in nanostructures with a section profile closely resembling a curved surface. The use of this technique enabled researchers to create molds in the shape of a silicon nanolens array and an elegantly shaped nanoscale complex structures mold.     

Differential contrast imaging of secondary electron signals in cryo-field-emission scanning electron microscopy

Low-temperature scanning electron microscopy (LTSEM) is limited in resolution and image quality by charging of frozen hydrated samples and collection deficiencies of secondary electron signal contrasts. We measured and corrected both effects using differential hysteresis processing (DHP) of LTSEM images, scanned at 15-bit from 5×4 inch Polaroid negatives. Bulk charging produced a major contrast component equal to 44–87% of the intensity range of the image. The strong charging contrast reduced the local high-resolution signal contrasts to an unrecognizable level. Segmentation and imaging of the unaffected surface contrasts produced high-quality images of high contrast from metal-coated samples as well as from uncoated samples. The differential contrast imaging can be used for control of the sequential etching of ice from the non metal-coated sample as well as improved LTSEM imaging of the finally coated sample.     

电感耦合等离子体(ICP)深刻蚀的模型与模拟

为对交替复合深刻蚀过程进行工艺仿真,本文利用鞘层近似模型,以离子辅助刻蚀和直接粒子刻蚀的组合来实现交替复合深刻蚀过程中的刻蚀步骤,辅以各向同性钝化过程,对电感耦合等离子体深刻蚀（硅片）进行了建模.本文采用单一的二维廓线＂线算法＂模型实现对刻蚀材料的区分,进而实现了对电感耦合等离子体深刻蚀的二维模拟和三维带状显示.其优点是相比元胞及混合模型算法统一,运行效率高、速度快,且模拟结果与实验相比较为理想.     

Manufacturing process of copper microgrooves utilizing a novel optical fiber-based laser-induced etching technique

A new approach for the fabrication of copper microgrooves with near triangular cross-sectional profile is introduced. For manufacturing the microgrooves, a laser-induced thermochemical etching technique based on an optical fiber as an optical waveguide and machining tool is proposed, which significantly reduced the complexity of a conventional laser etching set up. It is explained that the possible problem of fiber damage during laser etching with the proposed method can be solved by appropriately controlling the gap between the sample surface and fiber tip. The fabrication of copper microgrooves with 100 ∼ 300 μm in depth and 100 ∼ 150 μm in width is accomplished with the proposed technique. The grooves fabricated in the optimal process condition have smooth surfaces and clear edge. The angle of triangular groove is measured to be in the range of 30 ∼ 50 degree and the aspect ratio of grooves is about 1 ∼ 2. The overall etching results such as etch width, depth, and aspect ratio variation are reported in detail with respect to process variables.     

Electron backscatter diffraction applied to lithium sheets prepared by broad ion beam milling

Due to its very low hardness and atomic number, pure lithium cannot be prepared by conventional methods prior to scanning electron microscopy analysis. Here, we report on the characterization of pure lithium metallic sheets used as base electrodes in the lithium‐ion battery technology using electron backscatter diffraction (EBSD) and X‐ray microanalysis using energy dispersive spectroscopy (EDS) after the sheet surface was polished by broad argon ion milling (IM). No grinding and polishing were necessary to achieve the sufficiently damage free necessary for surface analysis. Based on EDS results the impurities could be characterized and EBSD revealed the microsctructure and microtexture of this material with accuracy. The beam damage and oxidation/hydration resulting from the intensive use of IM and the transfer of the sample into the microscope chamber was estimated to be <50 nm. Despite the fact that the IM process generates an increase of temperature at the specimen surface, it was assumed that the milling parameters were sufficient to minimize the heating effect on the surface temperature. However, a cryo‐stage should be used if available during milling to guaranty a heating artefact free surface after the milling process. Microsc. Res. Tech., 78:30?39, 2015. © 2014 Wiley Periodicals, Inc.