Comparison of ion beam sputtered chromium and iridium films for electron microscopy applications

The structure and composition of thin, conductive metallic films of chromium and iridium that are typical of the coatings used for electron microscopy is described. The purpose of this study was to determine the grain size and composition of the films deposited, with thicknesses of 1 nm, 2.5 nm, and 5 nm, onto amorphous carbon films using ion beam sputtering with argon as the sputtering gas. A comparison between chromium films deposited under conditions of liquid nitrogen (LN) trapping or of no trapping revealed slight differences in their microstructure. As expected, the grain size of the films increased with the thickness, and the average grain sizes varied between 10 and 25 nm. Grain size was also found to depend on the source of ion beam energy; the correlation between grain size and beam energy was more pronounced in the iridium films than in the chromium films. This effect was greater when the deposition chamber was not LN trapped. As the ion beam energy increased from 18 W to 24 W, there was a corresponding increase in grain size in some of the films. Although transmission electron diffraction analysis indicated the presence of about 5% chromium oxide in the chromium films, no oxide was detected in the iridium films.     

Specimen coating for high resolution scanning electron microscopy

Thin conducting films, produced by evaporation or soft vacuum sputtering generally show cracks and grain formation, when examined under high resolution scanning electron microscopy (SEM). These artefacts can obscure surface features of coated specimens or cause confusion in the interpretation of micrographs. No such structures have been observed in films produced by ion beam deposition. Ion beam deposition equipment is described in which a cold cathode saddle field ion source, operating at low pressure (15mPa), produces a 2 mm diameter beam of energetic ions (5 keV) and neutrals. With the beam directed onto a target at 30° to glancing incidence, the sputtered material coats the specimens, which are held in a planetary system for good coverage. Conditions favouring fine grain growth are a high nucleation density and low energy transfer to the substrate by thermal conduction or radiation or by particle or photon radiation. These conditions are satisfied by ion beam deposition but evidently not by evaporation or soft vacuum sputtering. With the specimen stationary, sharp shadowing is obtained because the target acts almost as a point source, because of the small diameter of the beam and because there is little scatter at the operating pressure.     

Application of ion beam sputtering for high-resolution electron microscopy

Ion beam sputtering for high-resolution electron microscopy has basically provided miscellaneous operational features such as atomic shadowing, uncoated observation, and etching of biological specimens coupled with tungsten sputter coating and thinning of solid materials. Based on the power-potential law of Lindhard for ionic impact phenomena on metal surfaces, the universal yield-energy relationship has been derived. Thereby the sputtering deposition rate with reference to the sputtering removal rate was obtained as a function of sputtering yield, and the most important angular distribution of sputtering yield could be measured by using the hemicylindrical specimen stage. Evidence is presented to show that ion beam sputtering has become one of the most powerful tools for high-resolution electron microscopy.     

A source of gas, vapor, metal, and carbon ions based on a low-pressure hollow-cathode discharge

A compact source of gas, vapor, metal, and carbon ions based on a cold-hollow-cathode reflective discharge has been developed, in which a 6-mm-diameter flat target (Cu, Mo, W, C) is installed on the bottom of the cold cathode insulated from it. The density of the ion flow from cathode plasma reaches 100 mA/cm² at an accelerating voltage of up to 10 kV and a discharge current of 0.2-0.5 A. Vapors produced during ion sputtering of the target are ionized in the cathode and anode cavities. A beam containing ions of the plasma-producing gas and vapor is extracted throug h the channel in the reflector cathode. A fraction of the vapor of the sputtered target, the flow of which is sufficient for growing layers at a rate of ∼0.03 nm/s at a distance of 10 cm from the emission channel under the action of an ion beam, is extracted together with ions. The fraction of metal ions in the extracted beam is 0.05-0.10. The total current of the ion beam is 20-30 mA.     

负偏压对DLC薄膜结构和摩擦学性能的影响

采用离子束溅射沉积镀膜法制备了DLC薄膜,研究了偏压对薄膜性能的影响。通过原子力显微镜(AFM)和拉曼光谱对DLC薄膜的表面形貌以及内部结构进行了分析表征。并用UTM-2摩擦磨损仪对其摩擦学性能进行了测试。结果表明,利用离子束溅射沉积制备的DLC薄膜具有良好的减摩抗磨性能。随着偏压的增加薄膜的摩擦因数先减小后增加,在-150 V偏压时,薄膜的摩擦学性能最好。     

高能离子束辅助沉积制备钛纳米膜

用离子束溅射沉积和高能离子束辅助沉积方法制备了具有择尤性的钛纳米薄膜,并采用原子力显微镜、X射线衍射仪和俄歇电子谱仪研究了试样表面预处理、离子束流和温度等离子束工艺参数对钛薄膜结构的影响。结果表明：离子束溅射沉积的钛膜在[002]和[102]晶向上呈现出明显的择尤生长现象,并分别在该两个晶向上表现出纳米晶型和非纳米晶型结构;当用高能离子束辅助沉积时,[102]晶向择尤生长现象消失,且钛膜的结构对束流变化较为敏感,束流较低时,钛膜为纳米结构且择尤生长现象减弱,而束流增加时晶粒长大,择尤生长现象叉增强。另外钛膜容易受到氧的污染,并随辅助离子强度增加而增强。     

TEM-, SEM- and STEM-studies of sputter-coated cytoskeletons

A technique for sputter coating of cytoskeletons from detergent extracted cells is described. The method allows their study in high resolution TEM, SEM and STEM. The use of cytoskeletons is also a valuable model system for the evaluation of metal coating techniques, allowing studies of deposited metal on fine filamentous structures of varying thicknesses. Pt and W were sputtered at 1 to 5 nm, and comparisons were made with reference to contrast and granularity. Both metais gave good topographical contrast, but Pt showed a coarse structure and a greater decorating tendency than W. The method provides a simple system for studies of the three-dimensional cytoskeletal organization, without the use of cumbersome replica-techniques.     

时间监控离子束溅射沉积光学薄膜的厚度修正

通过单层和多层膜的实验模拟,研究了离子束溅射沉积速率和沉积时间的关系。在溅射镀膜的初始阶段,对于Ta2O5,沉积速率随时间增加而增大;对于SiO2,沉积速率随时间先显著地增加,随后逐渐地减小。结果表明,通过对高、低折射率各层的监控时间进行补偿,即可实现光学薄膜厚度的精确监控。     

Thermal stability of Ti and Pt nanowires manufactured by Ga+ focused ion beam

Ti and Pt nanowires have been produced by ultra high‐vacuum molecular beam epitaxy deposition of Ti thin films and focused ion beam (FIB) deposition of Pt thin films, followed by cross‐sectional FIB sputtering to form electron‐transparent nanowires. The thermal stability of the nanowires has been investigated by in situ thermal cycling in a transmission electron microscope. Epitaxial single crystal Ti nanowires on (0001)Al₂O₃ substrates are microstructurally stable up to 550–600 °C, above which limited dislocation motion is activated shortly before the Ti‐wires oxidize. The amorphous FIB‐deposited Pt wires are stable up to 580–650 °C where partial crystallization is observed in vacuum. Faceted nanoparticles grow on the wire surface, growing into free space by surface diffusion and minimizing contact area with the underlying wire. The particles are face‐centred cubic (fcc) Pt with some dissolved Ga. Continued heating results in particle spheroidization, coalescence and growth, retaining the fcc structure.     

Rationale for the application of thin,continuous metal films in high magnification electron microscopy

Various metal films of different thicknesses were deposited on to a particle test specimen and their effects on topographic contrast generation and specimen preservation were determined. Tobacco mosaic virus adsorbed on to thin carbon supports or silicon chips was imaged in TEM or high resolution SE-I SEM at a magnification of 350,000×. Tantalum films of 1–2 nm (average mass) thickness produced best contrasts and prevented volume loss of the particles from electron beam damage. Excessively thick films of 5–10 nm thickness blanketed fine structures and caused severe volume losses. Discontinuous 2 nm thick films of gold or platinum decorated the surfaces, caused a loss in topographic contrasts and induced very high volume losses. Thin continuous metal films were necessary to generate high topographic contrast and to prevent volume loss from beam damage by providing sufficient mechanical stability for small topographic features and increased thermal conductivity of the specimen surface.     

基于离子束溅射Ta2O5薄膜的紫外吸收膜技术

为获得高性能紫外激光薄膜元件,急需研制紫外高反射吸收薄膜,实现吸收损耗的精确测量。本文采用离子束溅射技术,通过调控氧气流量实现了具有不同吸收的Ta_2O_5薄膜的制备。以Ta_2O_5薄膜作为高折射率材料,设计了355nm的紫外高反射吸收薄膜。采用离子束溅射沉积技术,在熔融石英基底上制备了355nm的吸收薄膜,对于A=5%的紫外吸收光谱,在355nm的透射率、反射率和吸收率分别为0.1%,95.0%和4.9%;对于A=12%的紫外吸收光谱,在355nm的透射率、反射率和吸收率分别为0.1%,87.4%和12.5%。实验结果表明,采用离子束溅射沉积技术,可以实现不同吸收率的355nm高反射吸收薄膜的制备,对于基于光热偏转测量技术的紫外光学薄膜弱吸收测量仪的定标具有重要的意义。     

Technical use of compact micro-onde devices

Due to the very small size of a COMIC (Compact MIcrowave and Coaxial) device [P. Sortais, T. Lamy, J. Me?dard, J. Angot, L. Latrasse, and T. Thuillier, Rev. Sci. Instrum. 81, 02B31 (2010)] it is possible to install such plasma or ion source inside very different technical environments. New applications of such a device are presented, mainly for industrial applications. We have now designed ion sources for highly focused ion beam devices, ion beam machining ion guns, or thin film deposition machines. We will mainly present new capabilities opened by the use of a multi-beam system for thin film deposition based on sputtering by medium energy ion beams. With the new concept of multi-beam sputtering (MBS), it is possible to open new possibilities concerning the ion beam sputtering (IBS) technology, especially for large size deposition of high uniformity thin films. By the use of multi-spots of evaporation, each one corresponding to an independent tuning of an individual COMIC ion source, it will be very easy to co-evaporate different components.     

Structure analysis of sputter-coated and ion-beam sputter-coated films: a comparative study

Gold, platinum and tungsten films were deposited by low energy input (7 mA, 450 V), or high deposition rate (80 mA, 1500 V), diode sputter coating and by ion beam sputter coating. Film structures on Formvar coated grids and on the surface of coated erythrocytes, resin embedded, sectioned, and recorded at high magnification in a TEM were compared using computer-assisted measurements and analysis of film thickness and grain size. The average grain size of the thinnest gold and platinum films was relatively independent of the mode or rate of deposition but as the film thickness increased, significant differences in grain size and film structure were observed. Thick platinum or gold films deposited by low energy input sputter coating contained large grain size and electron transparent cracks; however, more even films with narrower cracks but larger grain size were produced at high deposition rates. Ion beam sputter coated gold had relatively large grain size in 10 nm thick films, but beyond this thickness the grains coalesced to form a continuous film. Platinum films deposited by ion beam sputter coating were even and free of electron transparent cracks and had a very small grain size (1–2 nm), which was relatively independent of the film thickness. Tungsten deposition either by low energy input or ion beam sputter coating resulted in fine grained even films which were free of electron transparent cracks. Such films remained granular in substructure and had a grain size of about 1 nm which was relatively independent of film thickness. Tungsten films produced at high deposition rates were of poorer quality. We conclude that thick diode sputter coated platinum and gold films are best deposited at high deposition rates provided the specimens are not heat sensitive, the improvement in film structure being more significant than the slight increase in grain size. Thick diode or ion beam sputter coated gold films should be suitable for low resolution SEM, and thin discontinuous gold films for medium resolution SEM. Diode sputter coated platinum should be suitable for medium resolution SEM and ion beam sputter coated platinum for medium and some high resolution SEM. 1–5 nm thick tungsten films, deposited by low energy input or ion beam sputter coating should be suitable for high resolution SEM, particularly where contrast is of less importance than resolution.     

EVAPORATION OF LOW-VAPOR PRESSURE METALS USING A CONVENTIONAL MINI ELECTRON BEAM EVAPORATOR

In this article, the evaporation of niobium, ruthenium, and titanium using a conventional mini electron-beam evaporator (Tectraé-flux) is described. These metals require high temperatures for evaporation due to their high melting points, low vapor pressures, and large bond energies between atoms. Usually, a high-power electron-beam evaporator with a power exceeding 600 W is used in order to grow films of these metals. However, evaporation conditions for deposition using a mini electron-beam evaporator of low power (600 W at 2 kV) were obtained. Film thicknesses between 2 nm and 12 nm were obtained and the films were characterized with different analytical techniques. In the case of ruthenium, a comparison between the evaporation achieved when using a graphite crucible or a metal rod as a target is presented. The quality of the deposited films was ascertained by Auger electron spectroscopy. Niobium and titanium film's thickness and quality were determined by X-ray reflectivity and atomic force microscopy. Theoretical values of vapor pressure as a function of temperature were calculated for niobium, ruthenium, and titanium using the Clausius-Clapyeron equation to compare their evaporation behaviors.     

Influence of ion source configuration and its operation parameters on the target sputtering and implantation process

In the work, investigation of the features and operation regimes of sputter enhanced ion-plasma source are presented. The source is based on the target sputtering with the dense plasma formed in the crossed electric and magnetic fields. It allows operation with noble or reactive gases at low pressure discharge regimes, and, the resulting ion beam is the mixture of ions from the working gas and sputtering target. Any conductive material, such as metals, alloys, or compounds, can be used as the sputtering target. Effectiveness of target sputtering process with the plasma was investigated dependently on the gun geometry, plasma parameters, and the target bias voltage. With the applied accelerating voltage from 0 to 20 kV, the source can be operated in regimes of thin film deposition, ion-beam mixing, and ion implantation. Multi-component ion beam implantation was applied to α-Fe, which leads to the surface hardness increasing from 2 GPa in the initial condition up to 3.5 GPa in case of combined N(2)-C implantation. Projected range of the implanted elements is up to 20 nm with the implantation energy 20 keV that was obtained with XPS depth profiling.     

Tribological properties of nickel-base nanocrystalline coatings sputter-deposited on austenitic stainless steel

500 nm-thick films are deposited on austenitic stainless steel by neutral (Ar⁺) or reactive (N⁺) ion beam sputtering of Ni or NiTi targets, with (or without) high energy 160 keV-Ar⁺ ion beam assistance. Most of the time the coatings are nanocrystalline and induce a large (excellent in some conditions) increase of the wear resistance. Only Ar⁺ ion beam sputtering of a NiTi target gives an amorphous deposit which does not improve the substrate tribological properties. The hardness and wear resistance of ion beam assisted films are larger than those obtained with non-ion beam assisted coatings. The presence of a hard TiN phase inside a ductile Ni phase, of grains with preferential orientation beneficial to slip, as well as film densification are the main factors which increase the wear resistance. The best results are obtained when the structure is composed of two phases, Ni and TiN. The TiN phase strengthens the already good tribological Ni properties and the Ni ductility induces mechanical accommodation during the friction process.     

射频磁控溅射法制备类金刚石薄膜的研究

采用射频磁控溅射法,纯Ar溅射石墨靶,制备出了类金刚石薄膜,并对薄膜沉积速率随各工艺参数的变化规律、薄膜结构以及光学性能进行了系统的研究。结果表明,沉积速率随射频功率、CH4流量和溅射气压的增大而增大;随温度的增大呈现先增大后小的趋势。结构分析发现,所制备的DLC薄膜是由sp2键镶嵌在sp3键基体中构成的。在3μm~5μm波段对Si衬底有明显的增透效果。     

阶段离子束辅助法制备基频减反膜

在研究阶段离子束辅助制备方式对薄膜性质影响的基础上,采用电子枪蒸发及离子束辅助沉积制备了氧化铪及氧化硅单层膜,采用阶段离子束辅助沉积及全程非离子束辅助沉积制备了基频减反膜。测量了所有样品的弱吸收、残余应力和激光损伤阈值。结果发现,相对电子枪热蒸发制备的样品,离子束辅助沉积的单层膜具有大的弱吸收、低的激光损伤阈值,且张应力减小,压应力增加;阶段离子束辅助沉积制备的减反膜剩余应力变小,弱吸收稍微增加,激光损伤阈值从10.91 J/cm²增加到18 J/cm²。分析表明,离子束辅助沉积在引入提高样品激光损伤阈值有利因素的同时,也引入 了不利因素,阶段离子束辅助沉积在引入有利因素的同时,有效减少了不利因素的引入,从而提高了样品的激光损伤阈值。     

Preparation of carbon films from evaporated fibers and rods at fore-vacuum pressure

Fore-vacuum (pressure ≥ 3 Pa) evaporation of carbon fibers and rods to thin films has been tested and the resulting thicknesses recorded. A modified sputter coater was used as a vacuum evaporator. The quality of the carbon films was evaluated by bright-field and dark-field electron microscopy. Although high-vacuum-evaporated carbon films are superior in quality, low-vacuum-evaporated carbon films were found fully acceptable for routine work in bright field, for both TEM and SEM purposes. Apart from being time-saving, the method presented has the obvious advantage, in SEM preparations, that carbon coating and metal sputtering can be carried out in the same unit without breaking the vacuum.     

High resolution shadowing for electron microscopy by sputter deposition.

The sputtering process by an ion beam well collimated and highly accelerated provides a valuable means of high resolution shadowing, replication of a fine object by a combination of pre-shadowing and deposition as well as a preparation of supporting films. High resolution shadowing and films with grains smaller than 1 nm can be obtained by argon ion-sputtering targets of tungsten and tungsten/tantalum alloy. The resolution of carbon replicas pre-shadowed with tungsten/tantalum is determined from the radius of curvature of replicated magnesium oxide crystal corners.