Ion Milling Techniques Research Articles

High quality YBa2Cu3O7−δ films with controllable in-plane orientations grown on yttria-stabilized zirconia substrates

The pulsed-laser deposition (PLD) technique was used to grow high TC superconducting YBa2Cu3O7−δ (YBCO) films on both virgin and ion-bombarded yttria-stabilized zirconia (YSZ) substrates. To pattern high TC films for device applications, the ion milling technique is often used to turn virgin YSZ substrates into ion-bombarded substrates. Multilayered processes require the growth of high TC films on these ion-bombarded substrates. The purpose of this work was to investigate the growing conditions for these two kinds of substrate surfaces. We found that high quality 0° in-plane orientation films can be grown on either substrate when the growth temperature is about 810°C. The thin film grown at this temperature has TC of about 90.3K and JC of about 4×106Acm−2 at 77K. On virgin substrates, the in-plane orientations of YBCO films grown within the temperature range of 790–730°C exhibit a mixture of 0° and 45° domains. As the growth temperature decreases, the dominant orientation shifts gradually from 0° to 45°. On the other hand, on ion-bombarded YSZ substrates, the in-plane orientation of YBCO films grown within the same temperature range shows that the 45° domain is more prominent. Furthermore, 9° subpeaks appear around the 0° peak on ion-bombarded YSZ substrates. At a lower growth temperature of around 690°C, only the 45° domain exists on the virgin substrate, while a small amount of 0° domain is present with the majority of 45° domain on the ion-bombarded substrate. The TC and JC of the films grown at around 690°C on virgin substrates are as good as films grown at high temperatures, despite the difference in the in-plane orientations.

Large-area fabrication of periodic Fe nanorings with controllable aspect ratios in porousalumina templates

Highly uniform Fe nanoring arrays in porous anodic alumina templates are fabricated byphysical vapour deposition and grazing ion milling techniques. The nanorings haveaspect ratios ranging from 0.8 to 4, depending on the deposition conditions. Theouter diameter of the individual nanorings, and the area density and distributionpatterns are completely determined by the template used. Selected-area electrondiffraction reveals that these nanorings have a polycrystalline microstructure. Thenanoring fabrication method demonstrated here can be extended to other materials.

Effect of antiphase boundaries on electrical transport properties of Fe3O4 nanostructures

Fe 3 O 4 nanowires have been fabricated based on Fe3O4 thin films grown on α-Al2O3 (0001) substrates using the hard mask and ion milling technique. Compared with thin films, the Fe3O4 nanowire exhibits a slightly sharper Verwey transition but pronounced anisotropic magnetoresistance properties in the film plane at low magnetic field. Detailed bias-dependence study of both the conductance and magnetoresistance curves for both the thin films and nanowires suggests that the electrical conduction in magnetite near and above the Verwey transition temperature is dominated by a tunneling mechanism across antiphase boundaries.

ＣＰＰ‐ＧＭＲおよび鏡面散乱効果によるＧＭＲ効果の高性能化

A CPP (Current perpendicular to Plane)-GMR and a specular reflection effect have investigated for an improvement of GMR effect. Structures of films for CPP-GMR were Si/Cu(30nm)/Ta(5nm)/NiFe/CoFe/Cu/CoFe/IrMn/Ta/SiO2(20nm)/AlO(150nm)/Al(200nm) spin valve. The samples were prepared by RF/DC magnetron sputtering system with 10 cathodes. The GMR size is a few mm square. A contact hole was fabricated in a SiO2 layer using Ion milling and Photo lithography technique. A size of holes which were observed by SEM was much smaller than that of mask. Although the resistance of samples decreased with increasing the thickness of an under electrode, the GMR effect was not obtained. Therefore, the samples have the under electrode of 30 nm thick and their resistance is a few Ω. When the Cu layer thickness between two magnetic layers was varied, the change of resistance had a maximum value at 5 nm. AΔR(A is the size of the contact hole, which is regarded as the element area, and ΔR is the change of resistance.) was calculated 0.7 mΩμm2 from the dependence of the relationship between the resistance change and the inverse of A. The resistance change increased with increasing a pinned layer thickness and had a peak value with increasing a free layer thickness. For the total magnetic layer thickness, the resistivity change was obtained the maximum value at 14 nm thick. The specular reflection effect was also investigated for the improvement of the MR ratio. The thin oxidation layer prepared in the pined CoFe layer using a natural oxidation technique. When the CoFe layer was oxidized at the pressure of 0.026 and 0.065 Pa for about 5 minutes, MR ratio increased from 3.5 % to 6 %. The exchange coupling field between the antiferromagnetic layer and the pined layer did not decreased in this conditions.

Specimen preparation for high-resolution transmission electron microscopy using focused ion beam and Ar ion milling

We have developed a focused ion beam (FIB)-Ar ion-milling technique for high-resolution transmission electron microscopy. A micrometresized specimen was mounted on a cross section of metal foil of a few micrometres thick, using FIB microsampling. Following this, a 2 degrees wedgeshaped part was made in the specimen using FIB. Finally, the specimen was milled using an Ar ion beam to remove the FIB-damaged layers. We applied the FIB-Ar ion milling technique to a CeO(2)/Gd(2)Zr(2)O(7) multilayer specimen, resulting in the crystal lattice fringes of both layers being clearly observable in comparison to a specimen finished using a Ga ion beam at an accelerating voltage of 10 kV.

TEM thin foil preparation for ceramic composites with multilayered matrix

A method for preparing thin foils for transmission electron microscopy (TEM) has been developed in the field of ceramic matrix composites (CMC). These composites belong to the last generation. They are developed for high temperature applications in oxidative environment (1350 °C). They possess a self-healing capability. Their design is based on a multilayered matrix. A refinement of the regular ion-milling technique was necessary to thin the samples and to proceed to a full observation of the inner matrix of the composite by TEM. In a regular CMC, the matrix is homogeneous and thereafter it has not to be fully inspected from the fiber to the surface. This sampling technique unable to thin the complete sequence of the different layers in the vicinity of large pores where the ion-milling technique is known to be very difficult. High resolution TEM as well as electron energy loss spectroscopy can be managed anywhere in the core sequence of the matrix.

Toward optical and superconducting circuit integration

The physics of the interaction between coherent light and superconductivity is a veryintriguing subject but the alignment of a laser beam with integrated superconductingsystems (thin films, striplines or tunnel junctions) has represented so far a real bottleneckfor the experimentalists. The integration of both junctions and waveguides onthe same chip surely represents a possible path around this difficulty. In thispaper we report on the combined integration of optical structures based on hybridchannel waveguides with superconducting Josephson junctions circuits. The opticalfilms are grown on silicon substrates by a spin-coating process using the hybridorganic/inorganic sol–gel route. The channel waveguides are deposited on a buffer layer andrealized by photolithographic and ion milling techniques. We find that the opticalbuffer is a good substrate for SIS Josephson junctions and circuitry based on theNb/Al–AlOx/Nb trilayer processing. The junctions produced present good current–voltagecharacteristics with critical current density of the order of1 kA cm−2, high subgap resistance and good uniformity. Our results show that the quality of theJosephson junctions is well preserved even when they are grown on the sol–gel buffer layer.

1.3 μm light amplification in dye-doped hybrid sol-gel channel waveguides

We report on light amplification of dye-doped hybrid channel waveguides in the near-infrared region. Films have been grown both on glass and silicon substrates by a spin-coating process that uses a hybrid organic/inorganic sol-gel route. Doped films have been obtained by incorporation of an organic dye (IR1051) emitting in the 1.1–1.3 μm spectral region. Active channel waveguides have been synthesized by photolitographic and ion-milling techniques. An optical gain of about 11 cm−1 was estimated by amplified spontaneous emission measurements. An estimation of the optical losses of the hybrid waveguides is also reported.

Switching behavior of cross contacting current perpendicular to plane giant magnetoresistance structure fabricated by two-step ion milling technique

A current perpendicular to plane giant magnetoresistance structure with a cross contact geometry was fabricated by a two-step ion-milling technique. Multilayer pillars with various layer structures and a lateral dimension down to 0.4 μm were embedded between orthogonal top and bottom electrodes. The microfabricated cross point structure minimizes the influence of electrode resistance in measurements of magnetoresistance in current perpendicular to plane geometry. Individual switching of Co layer was observed in a pillar with layer structure of [Co(10 nm)/Cu(4 nm)/Co(2 nm)/Cu(10 nm)]3 and lateral dimension of 0.4×2.0 μm2. Distinct three-step resistance change was observed for the rising part of the magnetoresistance (MR) curve, corresponding to the switching of Co(2 nm) layers. Somewhat complicated MR behavior in the falling part suggests the existence of a local minimum configuration during the switching of Co(10 nm) layers. The switching behavior of magnetic layers with interlayer dipole coupling was studied by micromagnetic simulations. Markedly different switching field of Co layers can be attributable to the variation of the dipole fields at each layer.

Plasma plume characteristics and properties of pulsed laser deposited diamond-like carbon films

Pulsed laser deposition is a unique technique for the deposition of hydrogen-free diamond-like carbon films. During deposition, amorphous carbon is evaporated from a solid target by a high-energy KrF laser, ionized, and ejected as a plasma plume. The plume expands outwards and deposits the target material on a substrate. The plasma properties of the plume determine the quality of the thin films deposited on the substrate. These plume properties include ion density, ion flow speed, electron temperature, and plume peaking parameter. In this research, a triple Langmuir probe is used to determine various plasma properties of the plume created from the pulsed laser ablation of amorphous graphite as a function of laser energy density and laser spot size on the target. A thin diamond-like carbon film is deposited and analyzed with electron energy-loss spectroscopy to determine the sp3/sp2 fraction. A special preparation technique was used to prepare the thin film for analysis to prevent the damage that may be caused by conventional ion milling techniques.

Visualization of vacancy type defects in the RP/2 region of ion implanted and annealed silicon

Recently, a strong metal gettering in Si after ion implantation and annealing has been detected at depths between the surface and the mean projected ion range R P ( R P/2 effect), indicating the presence of residual defects therein. These defects are ascribed to excess vacancies generated in the R P/2 region by the ion implantation process. So far, the defects at R P/2 have been considered to be too small to be visible by transmission electron microscopy (TEM). We show that the crucial point for visualization of the vacancy-type defects at R P/2 by TEM is the specimen preparation technique. The very widely used conventional ion-milling technique for TEM specimen preparation introduces damage on the surface of the XTEM specimen, which blurs the original defect structure at R P/2 and obscures it from visualization. Only TEM specimens prepared by cleaving reveal cavities at R P/2. Minimum damage production caused during the preparation of the TEM specimen allows the imaging of the cavities at R P/2.

Microwave Properties of Parallel Plate Capacitors based on (Ba,Sr)TiO3 Thin Films Grown on SiO2/Al2O3 Substrates

ABSTRACTBa0.7Sr0.3TiO3 (BST) single and quadruple layer capacitors with Pt electrodes were fabricated together on polycrystalline alumina substrates with a SiO2-based multicomponent amorphous buffer layer (SiO2/Al2O3). This paper presents the results of the characterization of these capacitors, to demonstrate their suitability for application as decoupling (high value) capacitors and as components in tunable RF applications (e.g., phase shifters and filters). BST films of different compositions, (Ba0.7Sr0.3)TiO3 and (Ba0.5Sr0.5)TiO3, were grown by metal-organic decomposition (MOD) and RF magnetron reactive sputtering. The capacitance density of 90–140 nm thick BST films was in the range of 20 to 70 fF/μm 2. Parallel plate capacitors with areas from 16 μm2 to 2.25 mm2 were fabricated using photolithography and ion milling techniques. For large capacitors (0.125 to 2.25 mm2), capacitance and tanδ were measured at low frequencies (1 KHz - 1 MHz) using an LCR meter. Smaller capacitors (16 μm2 to 3600 μm2) were additionally characterized in the frequency range of 50 MHz - 20 GHz. In such case, capacitance, tanδ and equivalent series resistance (ESR) were extracted from two port scattering parameters obtained using a vector network analyzer (VNA). The relationship between dielectric loss, tunability and calculated figure of merit vs. BST composition and deposition temperature was outlined. In addition, loss and ESR at high frequencies was investigated. The typical achieved leakage current density of sputtered BST films for 2.25 mm2 capacitors fabricated on SiO2/Al2O3 was 7.3×10-9 A/cm2 at 300 kV/cm (65 fF/μm2), about 2 times lower than for (Ba0.7Sr0.3)TiO3 films deposited by MOD (1.4×10-8 A/cm2 at 300 kV/cm, 34.5 fF/μm2). Furthermore, the tunability of (Ba0.7Sr0.3)TiO3 deposited by both methods on SiO2/Al2O3 was ∼60% at 350 kV/cm.

Site-specific cross-sectioning of carbon nanotube-to-metal junctions for high spatial resolution chemical and structural analysis

AbstractIn this study, we have demonstrated successful site-specific cross-sectioning of carbon-nanotube - metal junctions which provided samples suitable for high resolution transmission electron microscopy and electron energy loss spectroscopy. For the cross-sectioning, we have suggested a modified technique based on combination of the Focused Ion Beam (FIB) lift-out and the conventional Ar+ ion milling techniques. Electron-transparent cross-sections of multiwall carbon nanotubes showing no significant surface amorphization or Ga contamination (typical artifacts of conventional FIB lift-out technique) were obtained. High-resolution transmission electron microscopy and electron energy loss spectroscopy of a multi-wall carbon nanotube cross-section have been carried out.

Site-specific cross-sectioning of carbon nanotube-to-metal junctions for high spatial resolution chemical and structural analysis

ABSTRACTIn this study, we have demonstrated successful site-specific cross-sectioning of carbon-nanotube - metal junctions which provided samples suitable for high resolution transmission electron microscopy and electron energy loss spectroscopy. For the cross-sectioning, we have suggested a modified technique based on combination of the Focused Ion Beam (FIB) lift-out and the conventional Ar+ ion milling techniques. Electron-transparent cross-sections of multiwall carbon nanotubes showing no significant surface amorphization or Ga contamination (typical artifacts of conventional FIB lift-out technique) were obtained. High-resolution transmission electron microscopy and electron energy loss spectroscopy of a multi-wall carbon nanotube cross-section have been carried out.

1/f noise of Bi2Sr2CaCu2Oy intrinsic Josephson junctions

We have measured the low-frequency voltage noise properties across mesa stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2Oy (BSCCO) single crystals as a function of bias voltage. The BSCCO mesas with area of 160×40 μm2 were fabricated on the surface of cleaved BSCCO single crystals using standard photolithography and Ar ion-milling techniques. The measured noise voltage spectrum density SV(f ) had a 1/f dependence on frequency. The magnitude of the 1/f noise spectra was found to increase monotonically with the branch number in the I–V characteristic at fixed bias current, and no anomalously enhanced 1/f noise was observed.

Manufacturing issues of thin film NiTi microwrapper

Manufacturing issues related to a thin film NiTi shape memory alloy (SMA) microactuator (i.e. microwrapper) have been investigated using both wet and dry etching techniques. Results show that wet etching the amorphous film produces a cleaner pattern than the crystallized film. Transformation temperatures are not affected by the pre-exposure of the NiTi film to air before crystallization. However, this process produces breakage in the NiTi film at sacrificial layer steps. This is believed to be due to residual stresses developed between the film and substrate during sputtering. The film breakage is overcome by dry etching the film with an ion-milling technique. Curvature in the microwrapper arms is induced using either a bi-layer material (i.e. polyimide and NiTi) or a functionally gradated NiTi film. Results show that when heated the microwrapper arms flatten due to shape memory effect and curl up to form a cage-like structure when cooled.

In-Situ Ion Milling in the Transmission Electron Microscope (TEM) Outlook to a New Preparation Technique

Abstract Recent developments in transmission electron microscopy put high demands on specimen preparation. in general the imaging quality is not limited by the performance of the microscope but by the quality of the specimen. in order to achieve a spatial resolution of 0.1 nm in HRTEM undamaged samples with a thickness below 10 nm are required. in energy filtering analytical electron microscopy (EFTEM), a constant specimen thickness over large areas and very low contamination is needed. Conventional ion-milling techniques for TEM specimen preparation are essentially blind. Thus, it is left to chance whether the specimen detail of interest is suitable for TEM-imaging (many specimen areas are too thick). Another problem is the reaction of the specimen with the atmosphere during the transfer from the preparation stage to the microscope, which makes it very difficult to obtain the clean specimen surfaces that are needed in analytical EFTEM. Especially in high-resolution electron microscopy and electron holography the formation of amorphous oxidation and contamination layers on otherwise crystalline materials may seriously reduce the quality of high resolution images of the crystal structure.

Formation of nano-scale icosahedral quasicrystalline phase in amorphous Zr60Ni25Ti15 alloy

The precipitation of icosahedral quasicrystalline phases (I-phase) from Zr-based amorphous alloys was reported initially by Koster et al. [1]. Recently, much attention has been paid to amorphous Zr–Al–TM– M (TM = Co, Ni, Cu, M = Ag, Pd, Au, or Pt) system [2–4] and Zr–TM–M system [5–7] for the formation of I-phases from amorphous phases by crystallization. A typical alloy composition for the Zr–Al–TM–M system is Zr65Al7.5Ni10Cu12.5M5. In these alloys, noble metals (Pd, Pt, Au and Ag) are added to the wellknown good metallic glass former Zr65Al7.5Ni10Cu17.5 [8] in order to stabilize I-phases. For the Zr–TM– M system, the noble metals also play an important role in the formation of I-phases. It is noticed that most of the above amorphous alloys exhibit a large supercooled liquid region, Tx(=Tx − Tg), where Tx and Tg are the crystallization and glass transition temperature, respectively. Such a large supercooled region means good glass-forming ability for an amorphous alloy. It also seems that the addition of noble metals is essential for the formation of I-phases in these Zr-based amorphous alloys. For example, no icosahedral phase was observed in the Zr70(Ni, Cu)30 amorphous alloy, while I-phases could be acquired in the quaternary, ternary, and even binary Zr70(Ni, Cu, Pd)30 amorphous alloys [7]. In order to determine the possibility of getting an I-phase from a Zr-based amorphous alloy without a significant supercooled liquid region and noble metals, a study was undertaken on the formation of a nano-scale I-phase in amorphous Zr60Ni25Ti15 alloy. The Zr60Ni25Ti15 alloy ingot was prepared by arc melting a mixture of pure Zr, Ni and Ti. From the alloy ingot, a ribbon with a cross section of 0.03 × 1 mm2 was produced by a single roller melt-spinning method in an argon atmosphere. Annealing of the specimen was performed in a differential scanning calorimetry (DSC) at a heating rate of 0.67 K/s. The microstructure was examined by a transmission electron microscope (TEM). The sample for TEM observation was prepared by the ion milling technique. The XRD pattern of the melt-spun Zr60Ni25Ti15 ribbon is shown in Fig. 1. The existence of a broad peak indicates the formation of an amorphous state. It is very clear that the as-quenched ribbon only contains a single amorphous phase. The DSC curve of the melt-spun Zr60Ni25Ti15 ribbon is shown in Fig. 2. We can see from this figure that the crystallization proceeds through two Figure 1 XRD patterns of the Zr60Ni25Ti15 ribbon: (a) melt-spun, (b) annealed to 685 K, and (c) annealed to 900 K at a heating rate of 0.67 K/s and then cooled rapidly in the DSC cell.

Superconducting properties of YBa2Cu3O7 step-edge Josephsonjunctions prepared on CeO2-buffered sapphire substrates

Step-edge Josephson junctions in the c-axis oriented YBa2Cu3O7 films were fabricated on the CeO2-bufferedsapphire substrates. The step angles were controlled in the wide range of20-75° by an Ar ion milling technique. The I-V curves ofjunctions fabricated on the 35° step with the film thickness to thestep height ratio of about 0.8 exhibited a resistively shunted junction-likebehaviour with an ICRN product of about 250 µV and a criticalcurrent density of about 2×104 A cm-2 at 77 K. Thecritical currents of the step-edge junctions increased approximately linearlywith decreasing temperature but the normal resistance remained almostconstant. All the samples of the step-edge Josephson junctions satisfied ascaling behaviour of ICRN∝(JC)0.5, and a dc SQUID made out ofthose junctions exhibited a typical voltage modulation in an applied magneticfield.

Microstuctural Characterization of Water-Rich Boehmite (AlO(OH)): TEM Correlation of Apparently Divergent XRD and TGA Results

An understanding of the solid-phase thermodynamics and aqueous speciation of aluminum is critical to our ability to understand and predict processes in a wide variety of geologic and industrial settings. Boehmite (AlO(OH)) is an important phase in the system Al2O3-H2O that has been the subject of a number of structural and thermodynamic studies since its initial synthesis [1] and discovery in nature [2]. Unfortunately, it has long been recognized that thermogravimetric analysis (TGA) of both synthetic and natural boehmite samples (that appear well crystallized by powder XRD methods) yields significant excess water - typically losing 16-16.5 wt. % on heating as compared with a nominal expected weight loss of 15.0 wt. % [3,4]. The boehmite used in our experiments was synthesized hydrothermally from acid-washed gibbsite (Al(OH)3) at 200°C. Powder XRD and SEM examination showed no evidence of the presence a contaminant phase. The TGA patterns do not suggest that this is due to adsorbed water, so a structural source is likely. We therefore undertook to examine this material by TEM to clarify this phenomenon.Boehmite is orthorhombic (a = 0.0285nm, b = 0.1224nm and c = 0.0365nm, Amam). The crystals were tabular with major surfaces normal to <010>. Simple powder dispersals onto holey carbon films typically resulted in b-axis orientations parallel to the electron beam. To view other orientations, specimens were mulled in M-Bond epoxy, pressed between plates of single-crystal Si (aligning the boehmite tablets parallel to the Si plates) while the epoxy cured. Electron transparent thin foils normal to the silicon plates were produced by argon ion milling techniques. Sample stability in the electron beam was dramatically improved by cooling to −140°C using an 2 cold stage.