Ga Focused Ion Beam Research Articles

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.

Development of a high lateral resolution TOF-SIMS apparatus for single particle analysis

A novel TOF-SIMS apparatus was designed and constructed aiming at single small particle analysis. The apparatus consisted of high lateral resolution TOF-SIMS part and SEM function for seeking analytical target. A pulsed Ga-focused ion beam (FIB) was also newly developed for this purpose based on state-of-the art ion optics. Secondary ion yield of Al was 1.8 × 10 −2 which is high enough small area analysis, and mass resolution was also acceptable for element analysis. The most prominent feature, lateral resolution, was demonstrated to be 40 nm in actual mapping of an IC cross-section. As an application aerosol particles were analyzed individually.

Controlled fabrication of nanopores using a direct focused ion beam approach with backface particle detection

We report a direct, ion drilling technique that enables the reproduciblefabrication and placement of nanopores in membranes of different thickness.Using a 30 keV focused Ga ion beam column combined with an in situ,back face, multi-channelplate particle detector, nanopores are sputtered inSi3N4 and W/Si3N4 to have diameters as small as 12 nm. Transmission electron microscopy shows that focusedion beam-drilled holes are near-conical with the diameter decreasing from entry to exitside. By monitoring the detector signal during ion exposure, the drilled hole width can beminimized such that the exit-side diameter is smaller than the full width at half-maximumof the nominally Gaussian-shaped incident beam. Judicious choice of the beam definingaperture combined with back face particle detection allows for reproducible exit-side holediameters between 18 and 100 nm. The nanopore direct drilling technique does not requirepotentially damaging broad area exposure to tailor hole sizes. Moreover, this techniquesuccessfully achieves breakthrough despite the effects of varying membrane thickness,redeposition, polycrystalline grain structure, and slight ion beam current fluctuations.

Enhanced growth of anodic alumina nanochannels on Ga-ion pre-irradiated aluminum

Exposure of an Al substrate to energetic Ga ions is found to result in enhanced growth rate of its nanochannels during a subsequent anodization process. Depending on the ion dose, the nanochannels in the pre-irradiated area exhibit different lengths. This interesting phenomenon is exploited by scanning a Ga focused ion beam over the desired area to facilitate the fabrication of arrays of anodic alumina nanochannels with custom-designed super-structure, which is based on the variation of channel length in different areas.

Correlation between ion beam parameters and physical characteristics of nanostructures fabricated by focused ion beam

We report a study of the physical characteristics of the pillars of C, Pt and W grown by 10–30keV Ga focused ion beam (FIB) as a function of Ga ion flux, and present a quantitative analysis of the elements using energy-dispersive analysis of X-rays (EDAX). All the FIB grown pillars exhibit a rough morphology with whisker like protrusions on the cylindrical surface and broadening of the base as compared to the nominal size. For a constant fluence, the height of the pillar initially increases and then reduces after going through a maximum as a function of ion flux in all the cases. The compositional analysis shows good metallic quality for Pt structures but reveals significant contamination of Ga in C and Ga and C in W structures at higher ion fluxes. Explanation to all these observations has been sought in the light of secondary ion and electron effects and the different processes involved which lead to the FIB induced deposition.

Measuring the effects of some laser parameters on the surface and near surface region of laser treated cast iron cylinder bore

The environmental and polluting materials emission standards in Europe are going to be always stricter, so in order to keep up with them, one of the largest European automotive manufacturers performs a laser treatment on the cylinder bores of their combustion engines. In this article the laser treated layers of cast iron cylinder bores with lamellar graphite are investigated with a FISCHERSCOPE^\unhbox \voidb@x \hbox \textregistered HM2000 XY microhardness measurement system and with a FEI Nova Nanolab 600 SEM/FIB dual beam scanning electron microscope (SEM), equipped with focused Ga-ion beam source. Four samples treated by two different laser sources in three configurations were investigated.

Nanoporous structure formations on germanium surfaces by focused ion beamirradiations

The formation of porous structures of nanometre size (nanoporous structures) ongermanium (Ge) surfaces by focused ion beam (FIB) irradiations was investigated usingvarious FIB conditions such as ion species, irradiation energies, total fluences, fluence rates,and incident angles. FIB-irradiated regions were observed using a scanning electronmicroscope and an atomic force microscope. It is found that, using a focused Ga ion beam(Ga FIB) at an energy of 100 keV, the irradiated Ge surface swelled up to ion fluence of2 × 1017 cm−2 with nanoporous structures and then was etched for larger fluences. The shape of swollennanoporous structures depended on the fluence rate and the incident angle of the Ga FIB.However, such porous structures were observed neither for low-energy (15–30 keV) FIBirradiations using Si and Au ions nor for high-energy (200 keV), heavy ion (Au) irradiation.These observations might be helpful in discussing the formation mechanisms of thenanoporous structures on Ge surfaces by ion beam irradiations. Fabrication of patternedstructures at selected regions on the Ge surface was demonstrated without using anymasks.

Focused ion beam based sputtering yield measurements on ZnO and Mo thin films

In order to facilitate the lateral structuring of solar cell multilayer structures, the ion beam sputtering behaviour of Mo and ZnO thin films deposited onto soda-lime glass and single crystalline Si substrates was studied. Prior to ion beam processing the layers were analyzed by Energy Dispersive X-Ray Spectrometry (EDS), X-Ray Diffractometry (XRD) and Rutherford Backscattering (RBS). In order to characterize the ion beam sputtering of the investigated layers, 2◊2 µm 2 fractions of the thin films were removed by a scanned 30 keV focused Ga + ion beam (FIB) in a dual beam system. SEM images taken during the milling process allowed continuous monitoring of the process without breaking the vacuum. The depth of the groove after removal of the layers was measured by Atomic Force Microscopy (AFM) and was plotted as a function of the ion dose. The sputtering depth has a dependence on the ion dose that is close to linear. The deviation from linearity is produced by heating effects at high beam currents. Sputtering yield values calculated from the experiments and simulations showed good agreement in the case of Mo but deviation was found in the case of ZnO. c 2007 Elsevier Ltd. All rights reserved.

Enhanced extrinsic magnetoresistance in [formula omitted] artificial grain boundaries induced by ion implantation

The resistance of polycrystalline divalent-ion-doped LaMnO 3 has been shown to be highly sensitive to low magnetic fields. To enable direct study of the properties of isolated grain boundaries, we developed a new method to form artificial boundaries in manganite thin films. Metal slits about 70 nm in width were printed by 30 KV focused Ga ion beam nanolithography on a 4 μ m La 2 / 3 Sr 1 / 3 MnO 3 bridge, and the materials in these slits were then irradiated by accelerated H 2 + ions. Using this method, magnetoresistance (MR) > 8 % and > 16 % were, respectively, obtained at 150 and at 10 K in a magnetic field of 1 T. This technique is very promising in terms of its simplicity and flexibility of fabrication and has the potential for high-density integration.

A study on maskless selective growth of Mg-doping p-type GaAs using low-energy focused ion beam

Maskless selective growth of Mg-doped GaAs films was performed by using a low-energy (30–200 eV) Mg–Ga focused ion beam (FIB) under the ambient of As 4 molecular beam. Under suitable As 4 pressure, all samples showed p-type and the carrier concentrations were around 10 17 cm −3. We achieved very high sticking coefficient of Mg ( k Mg of nearly 10 −1) compared with the result obtained at Molecular beam epitaxy (MBE) growth ( k Mg of nearly 10 −5). A p–n junction was formed on n +-type GaAs substrate by maskless selective growth. The diode showed typical I– V characteristics and the quality factor ( n-value) was approximately 1.75 for the sample grown at 60 eV. These results indicate that this method would be suitable for making maskless selective micro-device fabrication.

Focused ion beam etched nitride/air DBRs as cavity mirror facets of violet InGaN/GaN multiple‐quantum well laser diodes

We report on the demonstration of focused ion beam (FIB) etched nitride/air distributed Bragg reflector (DBR) gratings as cavity mirror facets of violet InGaN/GaN multiple quantum wells edge emitting laser diodes (LD). The nitride/air DBRs consisted of fifth order Bragg semiconductor wall and third order Bragg air gap with the depths around 1.2 micron to 1.5 micron were successfully achieved by focused Ga ion beam (FIB) milling as backside laser facets on GaN-based laser diodes. Under pulsed current injection at room temperature, sharp laser emissions were observed at the wavelength between 398 to 401 nm. The threshold currents of stripe and ridge lasers with nitride/air DBR mirror facets were found to be respectively lower than the related LDs with cleaved facets. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

NEXAFS study on carbon-based material formed by focused-ion-beam chemical-vapor-deposition

The coordination of carbon atoms in the carbon-based material formed by chemical-vapor-deposition of phenanthrene assisted by Ga-focused ion beam was investigated by the measurement of near-edge X-ray absorption fine structure spectra of the carbon K-edge over the excitation energy range 275–320 eV. Novel peak observed at 289.0 eV was assigned to the 1s→σ* transition of carbon neighboring to the residue gallium. The material formed by this method was found to be Ga-doped diamond-like carbon, that consists of a high sp 3 hybridized carbon.

Magneto-optical microscopy as a favourite tool to probe focused ion beam patterning atlow dose

Checking the effect of focused Ga ion beam (FIB) irradiation on a target at verylow dose is still a challenge. High-resolution magneto-optical microscopy andscanning electron microscopy (SEM) are used to investigate weakly irradiated trackspatterned by FIB on a Pt/Co(1 nm)/Pt ultrathin ferromagnetic film. The twotechniques give complementary results on surface film morphology and magnetism.Magneto-optical microscopy, linked to tiny ion rearrangements at interfaces, is found to bemore sensitive than SEM to detect damages after irradiation at very low dose.

Large magnetoresistance in La2∕3Ca1∕3MnO3 thin films induced by metal masked ion damage technique

We have developed a simple process to obtain large magnetoresistance (MR) in perovskite manganite thin films by a combination of focused ion beam milling and 120keV H2+ ion implantation. Metal slits about 70nm in width were printed by 30kV focused Ga ion beam nanolithography on a 4μm track, and the materials in these slits are then irradiated by the accelerated H2+ ions. Using this method, in a magnetic field of 5T we can get a MR>60% over a 230K temperature scope, with a maximum value of 95% at around 70K. This technique is very promising in terms of its simplicity and flexibility of fabrication and has potential for high-density integration.

Comparison of FIB-CVD and EB-CVD growth characteristics

We evaluated the growth characteristics of amorphous carbon (source gas: C 14H 10) fabricated by focused-ion-beam (FIB) and electron-beam (EB) chemical-vapor-deposition (CVD) in the same apparatus environment. All experiments were carried out in a Ga FIB and SEM composite system. It is confirmed that there are some differences in the surface appearance of pillars fabricated by FIB-CVD and EB-CVD. The rate at which an FIB-CVD pillar grows is about 100 times faster than that of an EB-CVD pillar. We found FIB-CVD wiring has electrical conductor properties with a resistivity of 380 Ω cm, and EB-CVD wiring has electric-insulator properties. Furthermore, we demonstrated by fabricating spring-shape features that FIB-CVD is superior to EB-CVD for making 3D structures.

Maskless fabrication of nanogap electrodes by using Ga-focused ion beam etching

We develop maskless fabrication methods using sputter etching with Ga-focused ion beams (FIBs) to obtain nanogap electrodes with high reproducibility. This method is based on in situ monitoring of etching steps by measuring current through patterned electrode films. The etching steps are terminated electrically at a predetermined current level. In the present experiment, 30-keV Ga FIBs with beam size of ~12 nm is irradiated, and the effect of film structures and monitoring current is investigated to obtain reliable fabrication methods. We find that electrode gaps much narrower than the beam size can be reproducibly fabricated. The controllability of the fabrication steps is significantly improved by using triple-layered films consisting of a thin Ti top, an Au electrode, and a bottom Ti adhesion layer. The minimum gap width achieved is ~3 nm, and the fabrication yield reached ~90% for ~3- to 6-nm-wide gaps. Most of the fabricated nanogap electrodes show high insulating resistance ranging from 1 G to 1 T.

Artificial domain structures realized by local gallium focused Ion-beam modification of Pt∕Co∕Pt trilayer transport structure

We demonstrate that a high-resolution Ga focused ion beam can be used to introduce artificial domain structures in Pt(1.6nm)∕Co(0.5nm)∕Pt(3.5nm) trilayer transport structures. We have used thin SiO2 overlayers to control the effective energy and dose of Ga ions at the Pt∕Co interface. The extraordinary Hall effect (EHE) was used to characterize the magnetic properties of the patterned films. Using 30keV Ga ions and SiO2 overlayer thicknesses in the range of 0–24nm, we achieve complete control of the coercive field of our Pt∕Co∕Pt trilayer structures. The magnetization reversal mechanism for an artificial domain of size of 3×0.5μm2 is investigated using EHE.

Effects of the artificial Ga‐nitride/air periodic nanostructures on current injected GaN‐based light emitters

In this report, III-nitride/air deeply etched one-dimensional (1D) distributed Bragg reflector (DBR) stacks and two-dimensional (2D) photonic octagonal quasi-crystals (8PQCs) were formed on the GaN-based light emitters by focused Ga ion beam (FIB) milling. The effects of these 1D and 2D GaN/air periodic nanostructures on the properties of the GaN-based light emitters were studied by the measurements of microscopic optical reflection, flourescence, electrical luminescence and current-voltage characteristics. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Maskless fabrication of nanoelectrode structures with nanogaps by using Ga focused ion beams

Maskless fabrication techniques of nanoelectrode with nanogaps are investigated, which use sputter etching technique by Ga focused ion beam (FIB). The etching steps are reliably controlled in situ by monitoring a current fed to the films. 30 keV Ga FIB with a beam size of 12 nm is irradiated on double layer films consisting of 10–30 nm thick Au top conducting layer and 1–2 nm thick Ti bottom adhesion layer to form nanowires and gaps. The films are deposited on a silicon substrate on which 200 nm of oxide has been thermally grown and patterned to define 5–7 μm wide strips by photolithography and Ar sputter etching. By the present techniques nanogaps with a width much smaller than a beam diameter are fabricated. The minimum gap width of ∼3 nm and the highest gap resistivity of ∼80 GΩ are obtained.

Maskless selective growth and in situ beryllium-doping of GaAs grown by low-energy focused ion beam

Maskless selective growth of Be-doped GaAs films was performed by using a low-energy (30–200 eV) Be–Ga focused ion beam (FIB) with the irradiation of As 4 molecular beam simultaneously. As a result, the selective p-type films of GaAs were grown successfully. Moreover, it was found that irradiation damages could be minimized and the surface morphology was improved by using the low-energy FIB. A p–n junction was formed on n +-type GaAs substrate by maskless selective growth for the first time. The I–V characteristics of the sample confirmed successful p–n structure formation. These results indicate this method would be suitable for making maskless selective micro-device fabrication.