High Acceleration Voltage Research Articles

Ultra-smooth diamond-like carbon coatings with high elasticity deposited at low temperature by direct ion beam deposition

Diamond-like carbon (DLC) coatings were fabricated under high vacuum at low temperature using a direct ion beam deposition technique based on a Penning ion source. Post-acceleration and electrostatic scanning were applied to form adhesive and laterally homogenous coatings across 50mm using ion energies from 3.0 to 10.5kV. The deposition rate was set to 0.4nms−1 to prevent heating of the coating and substrate. Structural, physical and chemical analyses revealed the formation of atomically flat hydrogenated amorphous carbon (a-C:H) coatings with a sp3 content of typically 20%. RBS measurements show that coatings produced at high acceleration voltage have impurities of carbon in the near-surface region of the silicon substrate as well as silicon impurities in the DLC coating at the interface. The penetration depth of the impurities is energy dependent. Nanoindentation measurements provided hardness figures of up to 18GPa combined with high elasticity values of 90%. Hardness and elasticity values and the sp3 content were measured to be proportional to the acceleration energy. An interface layer was observed with transmission electron microscopy indicating atomic interlocking between the carbon coating and the silicon substrate. The results highlight the opportunity to produce a-C:H coatings with high elasticity by direct ion deposition at low temperature.

Single-crystal cubic boron nitride thin films grown by ion-beam-assisted molecular beam epitaxy

We investigated the formation of cubic boron nitride (c-BN) thin films on diamond (001) and (111) substrates by ion-beam-assisted molecular beam epitaxy (MBE). The metastable c-BN (sp3-bonded BN) phase can be epitaxially grown as a result of the interplay between competitive phase formation and selective etching. We show that a proper adjustment of acceleration voltage for N2+ and Ar+ ions is a key to selectively discriminate non-sp3 BN phases. At low acceleration voltage values, the sp2-bonded BN is dominantly formed, while at high acceleration voltages, etching dominates irrespective of the bonding characteristics of BN.

Stability of deflected-beam metal–insulator–metal tunneling cathodes under high acceleration voltage

Metal–insulator–metal (MIM) tunneling cathodes have advantageous features, such as areal electron beams and robustness to surface contamination. Therefore, they are suitable for field-emission displays. This paper reports the long-term stability of MIM tunneling cathodes in display panels operating under a high acceleration voltage (anode voltage). A preliminary life test was carried out using conventional display panels, which consisted of a phosphor-coated anode plate and a cathode plate having matrix-arrayed cathodes. The life test indicated that the pace at which cathodes degrade increases significantly when the acceleration voltage exceeds a few kilovolts. This high-voltage (HV)-induced degradation is presumably attributed to cathodes being bombarded by positive ions originating from residual gases. To suppress HV-induced degradation, the authors propose the concept of a deflected-beam cathode, in which electron beams are deflected so that the recoiling ions fail to hit the cathode. This concept was implemented by introducing deflector electrodes in the cathode plate, thereby forming an electron lens in each pixel. As 6-μm high scan lines were used as the deflector electrodes in this design, the deflected-beam cathodes could be fabricated only by modifying the pattern of the scan lines. The authors also present a simulation-based design procedure using an emitter-landing diagram, which facilitates analysis of the margins for the deflected-beam cathodes. The deflected-beam cathodes thus designed were incorporated into 3.8 cm-diagonal test panels to confirm the validity of the concept. The degree of beam deflection that was observed was in excellent agreement with the results obtained from simulation. A life test extending over a 20 000-h period demonstrated that the HV-induced degradation was suppressed with the deflected-beam MIM cathodes.

Optimization of an electron beam lithography instrument for fast, large area writing at 10 kV acceleration voltage

Electron beam lithography (EBL) is a maskless lithography technique used in numerous applications for fabrication of ultrahigh-resolution photolithography masks. The main disadvantage of EBL is that it is time-consuming, requiring the pattern to be written in a successive fashion. Various approaches are used to lower the write time. Throughput-oriented EBL instruments used in industrial applications typically apply a very high acceleration voltage (≥50 kV). However, in many research environments, more cost-effective instruments are used. These tools are usually optimized for high-resolution writing and are not very fast. Hence, they are normally not considered very suitable for writing large-scale structures with high pattern densities, even for limited resolution applications. In this paper, the authors show that a carefully considered optimization of the writing parameters in an EBL instrument (Raith e_LiNE) can improve the writing time to more than 40 times faster than commonly used instrument settings. The authors have applied the optimization procedure in the fabrication of high-precision photolithography masks. Chrome photolithography masks, 15 mm in diameter with a write resolution of 200 nm, were routinely produced during overnight exposures (less than 9 h). The write time estimated by the instrument software for most commonly used settings was close to 14 days. A comparison with conventional chrome masks fabricated using a high-resolution (128 000 dpi) photolithography mask printer showed that our pattern definition is significantly better.

130 kV High-Resolution Electron Beam Lithography System for Sub-10-nm Nanofabrication

An electron beam lithography (EBL) system, CABL-UH, with a 130 kV high acceleration voltage has been developed that succeeded in minimizing beam size by minimizing Coulomb blur. This system has a short single-stage electron beam (EB) gun with an alignment function of two extractor centers to minimize Coulomb blur. This gun has also succeeded in thoroughly avoiding microdischarges. By adopting this EB gun and many other techniques, high resolution and long-term high stability have been achieved and an extremely fine pattern (4 nm line) has been delineated.

Controllable Shrinking and Shaping of Glass Nanocapillaries under Electron Irradiation

The ability to reshape nanopores and observe their shrinkage under an electron microscope is a powerful and novel technique. It increases the sensitivity of the resistive pulse sensing and enables to detect very short and small molecules. However, this has not yet been shown for glass nanocapillaries. In contrast to their solid-state nanopore counterparts, nanocapillaries are cheap, easily fabricated and in the production do not necessitate clean room facilities. We show for the first time that quartz nanocapillaries can be shrunken under a scanning electron microscope beam. Since the shrinking is caused by the thermal heating of the electrons, increasing the beam current increases the shrink rate. Higher acceleration voltage on the contrary increases the electron penetration depth and reduces the electron density causing slower shrinkage. This allows us to fine control the shrink rate and to stop the shrinking process at any desired diameter. We show that a shrunken nanocapillary detects DNA translocation with six times higher signal amplitudes than an unmodified nanocapillary. This will open a new path to detect small and short molecules such as proteins or RNA with nanocapillaries.

Spatial high resolution energy dispersive X-ray spectroscopy on thin lamellas

For conventional samples and measurement geometries the spatial resolution of energy dispersive X-ray spectroscopy is limited by a tear drop shaped emission volume to about 1 μm. This restriction can be substantially improved using thin samples and high acceleration voltage. In this contribution the spatial resolution of energy dispersive X-ray spectroscopy in a scanning electron microscope using thin lamella samples is investigated. At an acceleration voltage of 30 kV, an edge resolution down to Δdedge = 40 ± 10 nm is observed performing linescans across an interface, using an 80 nm thin sample prepared from a GaAs/AlAs-heterostructure. Furthermore, Monte-Carlo simulations of pure elements ranging from sodium to mercury are performed for different sample thicknesses. From the simulations we can derive a simple empirical formula to predict the spatial resolution as a function of sample thickness.

Improved durability of Pt/CNT catalysts by the low temperature self-catalyzed reduction for the PEM fuel cells

Long-term durability of catalysts is considered as the most critical issue to commercialize the fuel cell vehicles. In this study, we showed highly durable CNT-supported Pt catalysts treated by simple low temperature hydrogen bubbling (LTHB). Even at low temperature, the loss of the oxygen related functional groups which can accelerate the carbon corrosion and Pt agglomeration was observed by the effect of the catalytic cleavage of hydrogen molecules followed by the spillover and dehydration reaction. The 62.5% activity loss was observed in the commercial Pt/C catalyst but only 6.2% for Pt/CNT-R catalyst after high voltage acceleration test. Less agglomeration of Pt particles and loss of active surface area were observed than those of commercial Pt/C catalysts, which also contributed to the less increase in the electrochemical resistance of PT/CNT-R. The polarization resistance increased only 3% for Pt/CNT-R but as high as 700% for commercial Pt/C.

Automatic electron beam alignment adjustment system and automatic filament current adjustment system for electron beam welder

Recently, the electron beam welders with high acceleration voltage (more than 100 kV) and high electrical power (more than 15 kW) have been reviewed the role of the high-energy electron beam density again, due to space or aircraft development or automobile industry desired high productivity and high accurate welding for saving energy. NEC group have supplied these electron beam welders. This time, the automatic alignment adjustment system of the electron beam orbit and the automatic adjustment system of filament current were developed and put to a practical use. As a result, the great effectiveness for the stability of welding quality was apparent.

Novel EBSD preparation method for Cu/Sn microbumps using a focused ion beam

We proposed a novel technique developed from focused ion beam (FIB) polishing for sample preparation of electron backscatter diffraction (EBSD) measurement. A low-angle incident gallium ion beam with a high acceleration voltage of 30 kV was used to eliminate the surface roughness of cross-sectioned microbumps resulting from mechanical polishing. This work demonstrates the application of the FIB polishing technique to solders for a high-quality sample preparation for EBSD measurement after mechanical polishing. ► The novel FIB technique of sample preparation is fast, effective and low-cost. ► It can enhance the process precision to the specific area of the sample. ► It is convenient for analyzing the metallurgy of the microbump in 3DIC packaging. ► The EBSD image quality can be enhanced by just using a common FIB instrument.

Characterization of Cu(In,Ga)Se2 films deposited by single-step electron beam evaporation for solar cell applications

CuInxGa(1−x)Se2 (CIGS) thin films have been prepared by a single step of electron beam evaporation of a mixed alloy power made of high purity elemental copper, indium, gallium and selenium. The crystalline quality of CIGS films increases with increasing the substrate temperature, and stoichiometric CuIn0.7Ga0.3Se2 with chalcopyrite phase and (112) preferential orientation can be obtained at a substrate temperature of 650°C. X-ray diffractometer (XRD), scanning electron microscope (SEM) and absorption spectroscopy are used to characterize the obtained films. CuIn0.7Ga0.3Se2 films evaporated at 650°C is found to have a bandgap of about ∼1.11eV. In addition, two different acceleration voltages (5kV and 10kV) for the electron gun are also compared and a high acceleration voltage is found to be crucial in order to obtain stoichiometric CIGS films without Cu-deficiency. Our results suggest that the single-step electron beam evaporation at a high acceleration voltage could be potentially applied for fabrication of CIGS thin solar cells.

New understanding of the initiation of material transfer and transfer layer build-up in metal forming—In situ studies in the SEM

The tribological mechanisms behind the initiation of material transfer and build-up of transfer layers in aluminium forming have been studied in situ in the SEM where a tip of aluminium is put into contact with a tool steel surface under controlled sliding contact conditions.By combining in situ observations with post-test high resolution FEG-SEM studies of the contacting surfaces we have shown that aluminium is immediately transferred onto the fine polished tool steel. It was also confirmed that the initial transfer occurs on a very fine scale and is localised to the surface irregularities presented by the slightly protruding carbonitrides. In contrast, the less protruding M6C carbides, as well as the martensitic steel matrix exhibit very little initial transfer.Intentionally made scratches (roughly 5μm wide and 2μm deep) across the tool surface immediately result in larger scale transfer, which grows upon further passages of work material causing a high coefficient of friction. The study illuminates the extreme value of combining the in situ technique with high-resolution scanning electron microscopy using low acceleration voltage as a mean to detect the very thin initial transfer layers. With the higher acceleration voltages normally used, the transferred aluminium becomes transparent and can hardly be detected.

A study on backstreaming positive ions on a high power negative ion source for fusion

Future magnetic-confinement nuclear fusion experiments will be using neutral beam injection (NBI) systems for plasma heating that are based on sources for negative hydrogen ions as opposed to the positive ions mostly used to date. An unavoidable effect in negative NBI (NNBI) systems is the creation of positive ions in the acceleration region due to collisions between the fast negative ions and the neutral background gas. These positive ions are accelerated back into the ion source. At the high extracted ion current densities from NNBI sources and the high acceleration voltages—1 MeV in the case of ITER—the resulting heat load on the backplate of the source and the sputtering rates of the backplate material can be substantial. In this work, sputtering probes and a simple 1D calculation were employed to estimate the flux density of the backstreaming ions in the rear part of the ion source at the long pulse NNBI testbed MANITU (20 kV extraction voltage). It was found that the flux of backstreaming ions is approximately between 0.8 and 2.5% of the flux of negative ions extracted from the source. Experiment and theory are in fair agreement.

KEK digital accelerator

The High Energy Accelerator Research Organization KEK digital accelerator (KEK-DA) is a renovation of the KEK 500 MeV booster proton synchrotron, which was shut down in 2006. The existing 40 MeV drift tube linac and rf cavities have been replaced by an electron cyclotron resonance (ECR) ion source embedded in a 200 kV high-voltage terminal and induction acceleration cells, respectively. A DA is, in principle, capable of accelerating any species of ion in all possible charge states. The KEK-DA is characterized by specific accelerator components such as a permanent magnet X-band ECR ion source, a low-energy transport line, an electrostatic injection kicker, an extraction septum magnet operated in air, combined-function main magnets, and an induction acceleration system. The induction acceleration method, integrating modern pulse power technology and state-of-art digital control, is crucial for the rapid-cycle KEK-DA. The key issues of beam dynamics associated with low-energy injection of heavy ions are beam loss caused by electron capture and stripping as results of the interaction with residual gas molecules and the closed orbit distortion resulting from relatively high remanent fields in the bending magnets. Attractive applications of this accelerator in materials and biological sciences are discussed.

FIB-SEM cathodoluminescence tomography: practical and theoretical considerations

Focused ion beam-scanning electron microscope (FIB-SEM) tomography is a powerful application in obtaining three-dimensional (3D) information. The FIB creates a cross section and subsequently removes thin slices. The SEM takes images using secondary or backscattered electrons, or maps every slice using X-rays and/or electron backscatter diffraction patterns. The objective of this study is to assess the possibilities of combining FIB-SEM tomography with cathodoluminescence (CL) imaging. The intensity of CL emission is related to variations in defect or impurity concentrations. A potential problem with FIB-SEM CL tomography is that ion milling may change the defect state of the material and the CL emission. In addition the conventional tilted sample geometry used in FIB-SEM tomography is not compatible with conventional CL detectors. Here we examine the influence of the FIB on CL emission in natural diamond and the feasibility of FIB-SEM CL tomography. A systematic investigation establishes that the ion beam influences CL emission of diamond, with a dependency on both the ion beam and electron beam acceleration voltage. CL emission in natural diamond is enhanced particularly at low ion beam and electron beam voltages. This enhancement of the CL emission can be partly explained by an increase in surface defects induced by ion milling. CL emission enhancement could be used to improve the CL image quality. To conduct FIB-SEM CL tomography, a recently developed novel specimen geometry is adopted to enable sequential ion milling and CL imaging on an untilted sample. We show that CL imaging can be manually combined with FIB-SEM tomography with a modified protocol for 3D microstructure reconstruction. In principle, automated FIB-SEM CL tomography should be feasible, provided that dedicated CL detectors are developed that allow subsequent milling and CL imaging without manual intervention, as the current CL detector needs to be manually retracted before a slice can be milled. Due to the required high electron beam acceleration voltage for CL emission, the resolution for FIB-SEM CL tomography is currently limited to several hundreds of nm in XY and up to 650 nm in Z for diamonds. Opaque materials are likely to have an improved Z resolution, as CL emission generated deeper in the material is not able to escape from it.

Realization of Vertical Silicon Nanowire Networks with an Ultra High Density Using a Top–Down Approach

In this paper, we demonstrate the top-down fabrication of vertical silicon nanowires networks with an ultra high density (4 x 10(10) cm(-2)), a yield of 100%, and a precise control of both diameter and location. Firstly, dense and well-defined networks of nanopillars have been patterned by e-beam lithography using a negative tone e-beam resist Hydrogen SylsesQuioxane (HSQ). A very high contrast has been obtained using a high acceleration voltage (100 kV), very small beam size at a current of 100 pA and a concentrated developer, 25% Tetramethylammonium Hydroxide. The patterns were transferred by reactive ion etching. Using chlorine based plasma chemistry and low pressure, etching anisotropy was guaranteed while avoiding the so-called 'grass effect'. This approach enabled the production of vertical silicon nanowires networks with a 20 nm diameter and a pitch of 30 nm. Lastly, the self-limited oxidation phenomenon in 1D structure has been used to perfectly control the shrinking of NWs and to obtain a Si surface free of defects induced by reactive ion etching. The silicon nanowires networks have been tapered by wet oxidation (850 degrees C) down to a diameter of 10 nm with a high aspect ratio 11.

Designing of electrode for high energy charged particle acceleration

Vacuum insulation plays an important role in charged particle acceleration. We are making one compact size neutron generator in our lab. For this purpose the deuterium ions are formed in a penning ion source and extracted along the axis of the electrode arrangement. For neutron generation from D-T reaction, the deuterium ions are to be accelerated up to ~ 100KeV to the tritium target. After extraction of the ions from the ion source, the ions pass through the acceleration electrode. For high acceleration voltage, selecting the shape of the electrode is important. The plane geometry leads to high electric field at the edge whereas a curved geometry reduces this effect. The study of the physical processes at the electrode surface due to ion interaction is crucial. In this presentation, we will present the designing of the electrode for our purpose and discuss the issues related to the physical process at the surface of the electrode

Chromatic correction: a revolution in electron microscopy?

When the development of correctors started in the 1970s, chromatic correction was already the main goal. The first corrector that could improve the resolution of an electron microscope was a chromatic corrector for a scanning electron microscope. Within the last three decades, the development of transmission electron microscopes (TEMs) was to a large extent driven by the attempt to improve the resolution in the presence of chromatic aberration. The major technical developments were high acceleration voltages, highly excited objective lenses with short focal length and field emission guns. Meanwhile, chromatic correction has reached the TEM world. Now, the question arises as to whether chromatic correction will make some of the aforementioned developments obsolete for high-resolution TEM, thereby opening up new imaging possibilities, which are nowadays prevented by instrument constraints. We show some examples for a 0.1 nm resolution TEM with unconventional microscope designs: very low voltages, far-field objective lenses and inexpensive electron guns.

Proximity Effect Correction for Mask Writing Taking Resist Development Processes into Account

In this paper, a proximity effect correction method for mask fabrication with taking into account resist development processes is proposed. The idea of our method is that the figure size of a developed resist is determined using a suitable function of exposure dose and the normalized deposited energy by backscattering electrons, under the assumption of high acceleration voltage electron beam mask writing. This suitable function should be determined empirically to include the effects of resist development process, and is called development process function in this paper. Methods of deriving the development process function, proximity effect correction equation, and optimum correction dose from the equation are proposed. To check the accuracy of our method, a sample model of development process function is introduced under the condition that the conventional threshold model has an intrinsic error of 8 nm. The method proposed in this paper is found to be able to suppress the correction error of this sample model to less than 1 and 0.2 nm by two and three iterations, respectively. The method proposed in this paper is expected to provide high accuracy proximity effect correction in future mask fabrication.

Crystallographic Damage to Mn-Ir Antiferromagnets by Ion Beam Etching

The etching damage caused by ion beam etching with a low energy from 100 to 425 eV to manganese (Mn) - iridium (Ir) antiferromagnets was investigated by fluorescent x-ray analysis and a way of precise grazing incidence-controlled x-ray diffraction. Two kinds of damage were observed: one was an increase in iridium content, which increased as the etching depth (detched) increased. The other kind of damage was a lattice strain. IBE at a higher acceleration voltage (Vacc) and larger detched caused expansion of the in-plane MnIr(220) spacing near the etched surface; the out-of-plane MnIr(202) spacing remained constant. A smaller detched limited the lattice strain. The depth at which the lattice strain occurred was about 12 nm from the surfaces etched with various Vacc's and to various detched's. The causes of these two types of damage might be the same, i.e., preferential etching of Mn atoms at the surface.