Ar Ion Etching Research Articles

The COCAE Detector: An Instrument for Localization—Identification of Radioactive Sources

The COCAE project develops an instrument for localization and identification of radioactive sources. For the localization task it will exploit the Compton scattered photons within its detecting layers. It is based on pixilated Cd(Zn)Te matrices in a stacked configuration. Progress has been achieved in all the components necessary for this technology. CdZnTe crystals have been grown of up to 75 mm in diameter. A wafer level pixelization process has been tested and its results will be presented. Angular resolution for directional identification of the order of 6 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> requires energy resolution better than 5%. For this reason we have investigated planar metal-p-n diodes fabricated by using laser-induced solid phase doping and Schottky diodes created by Ar-ion etching of the Cd(Zn)Te surfaces before deposition of Ni electrodes. The energy resolution achieved is better than 1% FWHM @662 KeV. The development of a pixel CMOS readout integrated circuit has been undertaken. It outputs in digital format address, energy and time information for the pixels which have collected charge above a given threshold. Simulation studies of the minimum detection limits, of the Compton sequencing algorithms, of the angular resolution and of the reconstruction of the radioactive source position have been performed. Experiments with a precursor setup using an existing hybrid detector are underway.

Influence of dot size and annealing on the magnetic properties of large-area L1-FePt nanopatterns

Hard magnetic L10-FePt nanopatterns composed of a regular arrangement of single-domain nanodots with out-of-plane texture and dot sizes between 40 nm and 100 nm have been fabricated over an area of 4 mm2 from continuous epitaxially grown L10-Fe51Pt49 films by ultraviolet nanoimprint lithography combined with inductively coupled plasma reactive Ar-ion etching. Whereas the dot size within the dot size range investigated according to superconducting quantum interference device (SQUID) magnetometry has been found to have no significant influence on the magnetic properties, the magnetic properties and magnetization reversal mechanism significantly depend on the structural morphology and shape of the nanodots which change during a post-annealing process at elevated temperatures according to high-resolution TEM investigations from crown-shaped dots with a gradually deteriorated surface region of several nm to curved dots of pure L10-FePt. The different morphology of the nanodots results for the as-etched state in smaller coercivity values (1.30 T – 1.66 T at RT) and a less strong temperature dependence of the coercivity in the temperature range of 40 K – 350 K compared to the post-annealed state (4.37 T – 4.56 T at RT). As the morphology of the as-etched dots has been found to resemble the morphology of a phase graded composite particle magnetization reversal can be attributed to a domain wall induced process (microstructural parameter α &amp;lt; 0.15). In contrast, for the post-annealed dots of pure L10-FePt magnetization reversal takes place by a uniform nucleation process (microstructural parameter α &amp;gt; 0.79).

Large-area hard magnetic L10-FePt nanopatterns by nanoimprint lithography

Large-area hard magnetic L10-FePt nanopatterns with out-of-plane texture were fabricated by using a top-down approach.For the fabrication process, ultraviolet nanoimprint lithography (UV-NIL) in combination withinductively coupled plasma reactive Ar-ion etching was used. By this technique a continuousL10-Fe51Pt49 film was nanostructured into a regular arrangement of nanodots over an area of 4 mm2. The dot dimension and distribution was specified by the stamp, resultingin a dot size of 60 nm and a periodicity of 150 nm. For the large-scaleL10-FePt nanopatterns, huge coercivities up to 4.31 T could be achieved. By means of magneticforce microscopy it could be verified that the nanodots were magnetically decoupled fromeach other and occurred in the single-domain state with perpendicular magnetization.

The impact of etching during microfabrication on the microstructure and the electrical conductivity of gadolinia-doped ceria thin films

Gadolinia-doped ceria, Ce0.8Gd0.2O1.9−x (CGO), thin films deposited by spray pyrolysis and annealed to different degree of crystallinity between 0% and 95% are exposed to different etchants and etching methods. The attack of the etchants on the CGO thin films is analyzed with respect to changes in microstructure and in-plane electrical conductivity. It is found that amorphous CGO films are dissolved in hydrochloric acid after elongated etching times. Hydrofluoric acid severely attacks CGO thin films after already short times of exposure (1min), more intense the less crystalline the thin film is. Ar ion etching smoothens the surface of the CGO thin films without considerable removal of material. No microstructural attack of NaOH, CHF3/O2 and SF6/Ar is found. The electrical conductivity is in general only affected when microstructural changes are severe. Therefore, it is concluded that CGO thin films can be well used as functional layers in micro-fabricated devices and that micro-fabrication is, with the exception of hydrofluoric, not harmful for the electrical properties of crystalline CGO thin films.

Magnetic anisotropy and magnetization reversal of (Ga,Mn)As dot-array

The present article describes the magnetic anisotropy and magnetization reversal of (Ga,Mn)As dot-arrays with 1 μm and 200 nm in diameter fabricated by electron-beam lithography and Ar ion etching. The magnetization reversal mode is due to the magnetization rotation in the dot-arrays fabricated in the present study; they probably have a single-domain structure. The microfabrication of the (Ga,Mn)As dot-arrays modifies magnetic anisotropy through the relaxation of strain in the dots as previously reported; the 200-nm-dot-array exhibits magnetically isotropic features. The cubic anisotropy constant of the 200-nm-dot-array is estimated to be reduced by approximately a tenth of that of the (Ga,Mn)As epitaxial film by the calculation from the measured M-H loops based on a phenomenological model related to magnetic energy.

Incomplete oxidation in back channel of GaInZnO thin-film transistor grown by rf sputtering

Thin-film transistors (TFT's) may have a low-quality back channel in addition to the high-quality main channel. The presence of the back channel can deteriorate TFT turn-off characteristics. We studied properties of the back channel in bottom-gate GaInZnO TFT's grown by rf sputtering. X-ray photoelectron spectroscopy (XPS) results confirmed existence of low-quality oxide in the back channel. We observed that 200 °C annealing increased binding energies of metals and oxygen on the surface. This energy increase can be explained as a result of tighter bonding between metals and oxygen. When the top surface of GaInZnO was removed by Ar etching, XPS did not show such energy increase after the annealing. XPS also showed that the top surface has significantly higher In concentration compared to the bulk.

Adaption of graded Cr/CrN-interlayer thickness to cemented carbide substrates' roughness for improving the adhesion of HPPMS PVD films and the cutting performance

High Power Pulsed Magnetron Sputtering (HPPMS) techniques jointly with the deposition of a graded Cr/CrN-nanointerlayer on cutting inserts can increase the film adhesion and consequently the tool life. These improvements depend on the roughness of the employed cemented carbide substrates. The investigations described in the present paper intend to explain the effect of Cr/CrN-interlayer thickness and substrate roughness on the coating adhesion and cutting performance. To attain various roughnesses, the applied cemented carbide inserts were superficially treated. These treatments were grinding at a medium roughness level, or grinding with subsequent polishing for enhancing the surface integrity and finally, in all cases, micro-blasting by fine Al 2O 3 grains. After Ar-ion etching, graded Cr/CrN adhesive layers with different thicknesses were deposited by HPPMS technology on the variously pretreated substrates. Subsequently, an approximately 3 μm thick (Ti,Al)N film was deposited by HPPMS PVD on all used inserts. Rockwell C indentations and inclined impact tests were performed to assess qualitatively and quantitatively the films' adhesion. The cutting performance of the coated tools was investigated in milling of 42CrMo4 QT. FEM supported calculations of the developed stresses during the material removal process contributed in explaining the obtained tool wear results. In these calculations, the adhesion, dependent on the substrate roughness characteristics and on the adhesive interlayer thickness, was taken into account. The results revealed that the effectiveness of HPPMS adhesive graded Cr/CrN-nanointerlayer strongly depends on the substrate surface integrity and on the interlayer thickness. Thus, the film adhesion and consequently the cutting performance can be significantly improved if the interlayer thickness is adapted to the substrate roughness.

Molecular dynamics simulations of the sputtering process of silicon and the homoepitaxial growth of a Si coating on silicon

Molecular dynamics simulations of the sputtering process of silicon by Ar atoms in the low energy range, 20eV–1000eV, were performed using the IMD software package and the commercial software Materials Explorer 4.0 from Fujitsu Ltd. with the combination of the Tersoff potential and the Ziegler–Biersack–Littmrk (ZBL) potential in order to get more insight into the sputter process itself and to extract data comparable to experiments. The analysis of the sputter yield as a function of argon impact energy, surface impact coordinate and of crystal orientation was performed. These simulation results were compared with experimental values as determined by Ar ion etching in a microwave plasma and measurement of the etch depth and etch time. A good agreement between experiments and simulations was found. Physical parameters such as binding energy of the Si (001) surface, vacancy energy and vacancy migration energy were also determined in order to explain the simulation results of the sputter process. Finally, the coating process of a silicon substrate by Si atoms was simulated using the Si sputter results as input parameters.

Interfacial properties and formation of a Schottky barrier at the CdS/PEDOT : PSS hybrid junction

The behaviour of a hybrid heterojunction (HJ) of an inorganic semiconductor cadmium sulfide (CdS) single crystal (102 Ω cm) and an organic conducting polymer poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonic acid) (PEDOT : PSS) has been studied using electrical and photoelectrical measurements as well as ultraviolet photoelectron spectroscopy (UPS) with in situ Ar ion etching. Photovoltaic data and current–voltage characteristics demonstrated that the HJ is a Schottky diode with an electron barrier height ca φb = 0.5 eV. The estimates based on the energy balance at the interface allowed us to assert on the presence of an interfacial dipole with an energy offset of −0.3 eV. A dipole barrier of the same magnitude was also clearly revealed from the UPS measurements directly.

Characterization of thin and ultrathin transparent conducting oxide (TCO) films and TCO‐Si interfaces with XPS, TEM and ab initio modeling

AbstractInterfaces play an important role in solar cell heterostructures, especially when film thicknesses decrease. In this work, we use XPS, transmission electron microscopy (TEM) and density functional theory (DFT) to study both the film and the film–Si interface of electron beam deposited indium tin oxides (ITO) and pulsed laser deposition (PLD) deposited ZnO on p‐Si (100). Vacuum evaporation of ITO resulted in a film that contained elemental Sn and In which oxidized after annealing at 300 °C for 30 min. Ar etching of the HF‐treated Si substrate in the PLD deposition chamber caused an increase of the interfacial oxide thickness independently of the deposition temperature as a result of Ar etching‐induced dangling bonds. Deposition as well as annealing at elevated temperature also increases the interfacial oxide thickness for both ITO‐Si and ZnO‐Si systems. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Analysis Of Corrosion Products Formed By Edge Corrosion Of Residual Coated Steel Sheets

The object of this study is to clarify the mechanism and difference of edge corrosion behaviors of prepainted Zn and 55%-Zn coated steels, from the EPMA analysis of corrosion products of prepainted metallic coated steels. Cross section of two kinds (Zn and 55%Al-Zn coating) of prepainted metallic coated steel sheets exposed in Miyako-jima (Subtropical marine area) and Choshi (Moderate marine) are analyzed. Samples for cross section analysis were prepared by a new technique using Ar ion etching. Corrosion of both samples started at the edge of metal coating layer, and proceeded to inner area gradually. In the case of corrosion of Zn coating layer, corrosion progresses almost uniformly from the edge. In the case of corrosion of 55%Al-Zn coating layer, the tendency with which the Zn-rich part of the eutectic phase corrodes selectively.

Functional plasmonic antenna scanning probes fabricated by induced-deposition masklithography

We have fabricated plasmonic bowtie antennae on the apex of silicon atomic-forcemicroscope cantilever tips that enhance the local silicon Raman scattering intensity by∼4 × 104 when excited near the antenna resonance. The antennae were fabricated using anovel method, induced-deposition mask lithography (IDML), capable of creatinghigh-purity metallic nanostructures on non-planar, non-conducting substrates withhigh repeatability. IDML involves electron-beam-induced deposition of a W orSiOx hard mask on the material to be pattered, here a 20 nm Au film, followed by Arion etching to remove the mask and the unmasked gold, leaving a chemicallypure Au bowtie antenna. Antenna function and reproducibility was confirmed bycomparing Raman spectra for excitation polarized parallel and perpendicularto the antenna axis, as well as by dark-field spectroscopic characterization ofresonant modes. The field enhancement of these plasmonic AFM antennae tips wascomparable with antennae produced by electron-beam lithography on flat substrates.

GaAs∕AlOx micropillar fabrication for small mode volume photon sources

Micropillar devices have shown promise as single photon sources for applications in quantum key distribution as well as single photon metrology and fundamental science. For higher temperature operation (77K), a high quality factor (Q) cavity and a small modal volume are necessary for enhanced spontaneous emission. Although high Q’s have been demonstrated, achieving small modal volumes is difficult due to the limited index contrast available from the lattice-matched Bragg layers of GaAs and AlGaAs. However, by wet thermal oxidation of AlGaAs or AlAs layers to amorphous aluminum oxide (AlOx), very high index contrast layers can be obtained. This allows for high reflectivity mirrors with fewer Bragg pairs, resulting in reduced mode volume from reduced penetration of the optical mode within the mirror pairs. The authors apply this method in a GaAs∕Al0.95Ga0.05As material system and describe a fabrication process for such devices, utilizing a BCl3:Cl2:Ar etch. Photoluminescence measurements of micropillars with three top and five bottom layers are demonstrated. They are measured to have Q’s of 200–400 for approximately 1–3μm diameters, respectively. These results indicate that high Q devices may be possible while simultaneously reducing the modal volume.

Nanoscale Friction Behaviors of Hierarchical Superhydrophobic Structure of Diamond-like Carbon Films with Various Humidity Conditions

Superhydrophobic double roughening structure of DLC film was prepared by 2.45 GHz surface wave-excited plasma CVD with the mixture of methane (CH4) and tetramethylsilane (TMS: Si(CH3)4) gases on the undulated DLC film by a series of plasma Ar etching, coating process and plasma Ar etching. Static wetting angle of water was observed that double roughening structure of DLC was superhydrophobicity such as wetting angle 161°. This approach also increased in air pockets easily trap among the needle-like posts. For the low friction at nanoscale, the surface wettability of the solid lubrication played a significant role, when the DLC film modified from flat to double roughening structure, the friction was constantly inner humidity conditions. Results generally showed that humidity had insignificant effect on the nanoscale friction at superhydrophobic DLC surface. The effect of the superhydrophobic double roughening DLC and friction were discussed with the following factors; the surface morphology affinity to needle-like shape, a reduction of the real area of contact, graphitization and easily occur to slip at small contact interface due to superhydrophobicity.

Microstructure and magnetic properties of perpendicular media with reduced grain size

A new approach to control the grain size of Co alloy oxide perpendicular media by means of Ar-ion etching is presented. Ar plasma was applied to the surface of a continuous Ru1 layer, on top of which a granular Ru2+SiO2 layer was subsequently deposited. It was found that etching time and high Ar-ion energy have a significant effect on the surface roughness of the seedlayer, which in turn have a great effect on microstructure and magnetic properties of the media. A granular Ru2+SiO2 layer with mean grain size of 3.9±0.7 nm was obtained, and its oxide boundary thickness decreased with the decreasing Ru grain size. As a result, the mean grain size of the magnetic layer was greatly reduced to 5.3±0.8 nm from 7.6±1.3 nm of a controlled sample without Ar-ion etching. The coercivity (Hc) of the media is 2.7 kOe, while Hc of the controlled sample is 4.8 kOe. The small CoPt grain size, the possible oxidization of metal grains, and the resultant increasing c-axis dispersion of the magnetic layer can explain the decreasing Hc and remanent magnetization (Mr) and increasing (Hn−Hc) values of the perpendicular MH loops.

Study of SrTiO 3 thin films grown by sputtering technique for tunnel barriers in quasiparticle injection contacts

High-quality, c-axis oriented YBa 2Cu 3O 7 − x /SrTiO 3/Au (YBCO/STO/Au) planar structures were fabricated in situ by direct current/radiofrequency inverted-cylinder magnetron sputtering on (001) STO oriented substrates. The sandwich-type structures were patterned to transistor dimensions by standard ultraviolet-photolithography and Ar etching. The current transport mechanism in the very thin STO barriers (2–30 nm) was examined by measuring the tunneling G as function of temperature ( T), and bias voltage ( V). It was found that resonant tunneling and hopping via a small number of localized states (LS) are responsible for electronic conduction in the insulating material. Elastic tunneling was observed for the case of a nominal 2 nm thick STO-barrier with an energy gap Δ ≈ 20 meV in the (001) direction of YBCO. On the other hand, inelastic hopping transport via n-LS dominated for STO barrier thickness d > 2 nm. G of the lowest-order hopping channel (hopping via two LS) exhibits the characteristic T and V dependences: G 2 hop( T) ∝ T 4/3, G 2 hop( V) ∝ V 4/3, respectively. Increasing the thickness of the STO barriers, hopping channels of higher order contribute more and more to the current transport as proven by measuring the T and V dependences. A crossover to variable range hopping behavior has been observed for junctions with thicker barriers ( d ≥ 20 nm) in the high- V or high- T regime. By fitting the experimental data to theoretical models, physical parameters of the LS could be determined. For instance, the value of the localization length or radius of the localized state was determined to be ~ 4.6 × 10 − 8 cm which corresponds to the lattice constant of the STO unit cell. A value of ~ 6 × 10 19 (eV) − 1 cm − 3 was calculated for the density of LS and the average barrier height was estimated as ~ 0.4 eV.

Micro-patterning of NdFeB and SmCo magnet films for integration into micro-electro-mechanical-systems

The integration of high-performance RE-TM (NdFeB and SmCo) hard magnetic films into micro-electro-mechanical-systems (MEMS) requires their patterning at the micron scale. In this paper we report on the applicability of standard micro-fabrication steps (film deposition onto topographically patterned substrates, wet etching and planarization) to the patterning of 5–8 μm thick RE-TM films. While NdFeB comprehensively fills micron-scaled trenches in patterned substrates, SmCo deposits are characterized by poor filling of the trench corners, which poses a problem for further processing by planarization. The magnetic hysteresis loops of both the NdFeB and SmCo patterned films are comparable to those of non-patterned films prepared under the same deposition/annealing conditions. A micron-scaled multipole magnetic field pattern is directly produced by the unidirectional magnetization of the patterned films. NdFeB and SmCo show similar behavior when wet etched in an amorphous state: etch rates of approximately 1.25 μm/min and vertical side walls which may be attributed to a large lateral over-etch of typically 20 μm. Chemical–mechanical-planarization (CMP) produced material removal rates of 0.5–3 μm/min for amorphous NdFeB. Ar ion etching of such films followed by the deposition of a Ta layer prior to film crystallization prevented degradation in magnetic properties compared to non-patterned films.

Element-specific hard X-ray micro-magnetometry of magnetic modifications in Co–Pt dots fabricated by ion etching

We developed a micro-magnetometry with a 2.5 μm spatial resolution based on micro X-ray magnetic circular dichroism (XMCD) technique in order to study magnetic properties of dot arrays for bit-patterned media. This micro-magnetometer was applied to the magnetic characterization of Co–Pt dot arrays fabricated by ion beam etching. As the dot size became small, the intensity of XMCD drastically decreased for dots fabricated by Ga-focused ion beam. This suggested that the dot edges were damaged magnetically by implantation of Ga ions. The damaged width of the dot edge was estimated to be about 13 nm from the decrease in XMCD intensities. This damaged edge width agreed with the ion-implanted area estimated by Monte-Carlo simulation. The less-damaged effect of Ar ion etching was verified by the XMCD measurement of Co–Pt dots with diameter of 20 and 70 nm. It was concluded that ions with inertness, lower energy and smaller atomic number should be used to fabricate dot arrays with an areal density of 1 Tbit/in 2.

NiMnGa nanostructures produced by electron beam lithography and Ar-ion etching

The technologies of electron beam lithography, dry etching and systems integration are investigated to fabricate a series of Ni-Mn-Ga double-beam structures designed with decreasing critical dimensions of 10 μm, 1 μm and 400 nm. Ni-Mn-Ga thin films of 1 μm thickness are deposited by magnetron sputtering and heat-treated in free-standing condition after selective removal of the substrate. Differential scanning calorimetry and electrical resistance measurements on the films show the characteristic features of martensitic transformation above room temperature. First optical beam deflection experiments demonstrate the magnetic and thermal actuation performance of the double-beam structures.

Etching Damage Analysis of a Co/Pt Multilayer Patterned Medium Using the Grazing Incidence X-Ray Reflectivity Technique

A Co/Pt patterned medium was fabricated by an Ar ion etching process through a self-assembled polymer mask with a diameter of 40 nm, and its etching damage was investigated by using the grazing incidence x-ray reflectivity (GIXR) technique. This method is effective for investigating the changes in the morphology of surface and interface. It was found that the surface roughness was increased from 0.5 nm to 3.8 nm by the etching process, while the roughness of the multilayer structure was not changed. Large roughness at the surface is due to the lack of a dot structure as a result of the over-etching condition. The lack of significant damage to the internal multilayer structure is consistent with the lack of significant degradation in the magnetic characteristics. Ar ion etching is found to be robust for fabricating patterned medium with little damage even in the over-etching condition.