Direct Milling Research Articles

Processing of silicon nanostructures by Ga+ resistless lithography and reactive ion etching

Ga^+ resistless lithography and subsequent reactive ion etching (RIE) with SF6 and C4F8 as process gases have been applied to fabricate silicon nanostructures with main emphasis on arrays of pillar type structures usable as nanoelectrodes. The strongly reduced etching rate of silicon areas implanted with Ga by focused ion beam (FIB) irradiation compared to unaffected silicon is investigated in dependence on the implanted dose and compared to literature. A certain dose range is found to result in an optimum masking effect whilst obtaining very smooth surfaces after RIE. As is demonstrated surfaces implanted with lower doses exhibit high roughnesses after RIE. Thus, patterning of 3D structures due to greyscale Ga^+ resistless lithography seems questionable. Depending on the RIE process parameters, however, for a given FIB mask pattern the lateral dimension of the final nanostructures can be varied in a wide range enabling very small pillar diameters or line widths due to underetching. Such structures exhibit aspect ratios well above 10 and lateral dimensions of slightly below 20nm as demonstrated within this work. First results for the removal of the Ga implanted masking layer are presented, too. Finally, the potential and performance of Ga^+ resistless lithography compared to the fabrication of nanoelectrode structures by direct FIB milling is critically discussed.

Microstructures induced microwave resonance peak shift of Co/Al2O3 nanocomposites prepared by ball milling

Microstructures play an important role in materials’ functional performances. In this work, the microstructures including interfaces induced microwave resonance peak shift of Co/Al2O3 nanocomposites is studied. Nanosized Co/Al2O3 composites were successfully fabricated via direct ball milling. The hcp and fcc Co phases coexist for a long milling duration and the interface effect is prominent in the nanocomposites. The measured relative complex permittivity of the Co/Al2O3 nanocomposite–paraffin wax mixture indicates that a high electrical resistivity and a dielectric loss exist in the Co/Al2O3 nanocomposites. The dielectric loss mainly arises from the polarization of the metal/insulator interfaces. The imaginary part of the relative complex permeability of the mixture exhibits a broad resonance peak centered at 8.3GHz which originates from the natural resonance of Co. In comparison to the reported value 6.5GHz, the shift of the resonance peak to higher frequency can be attributed to the surface anisotropy induced by prominent interface effects, which was confirmed by NMR. The position of the resonance peak results from the competition between the surface anisotropy and the dipolar coupling interaction of the Co grains. The calculated reflection loss curves show that the reflection loss value of the Co/Al2O3 nanocomposite–paraffin wax mixture can reach −10dB in a broad frequency range. The improved microwave characteristics are closely related to the microstructures, and can be tailored by controlling the content of Co and the thickness of the sample.

The influence of reactive milling on the structure and magnetic properties of nanocrystalline MnFe2O4

Abstract Nanocrystalline manganese ferrites (MnFe2O4) have been synthesized by direct milling of metallic manganese (Mn) and iron (Fe) powders in distilled water (H2O). In order to overcome the limitation of wet milling, dry milling procedure has also been utilized to reduce crystallite size. The effects of milling time on the formation and crystallite size of wet milled MnFe2O4 nanoparticles have been investigated. It has been observed that single phase 18.4 nm nanocrystalline MnFe2O4 is obtained after 24 h milling at 400 rpm. Further milling caused deformation of the structure as well as increased crystallite size. With the aim of reducing the crystallite size of 18.4 nm, MnFe2O4 sample dry milling has been implemented for 2 and 4 h at 300 rpm. As a result, the crystallite size has been reduced to 12.4 and 8.7 nm, respectively. Effects of the crystalline sizes on magnetic properties were also investigated. Magnetization results clearly demonstrated that crystallite size has much more effect on the magnetic properties than average particle size.

High-Tc Josephson junctions fabricated by focused ion beam direct milling

High-Tc Josephson junctions were successfully fabricated by focused ion beam (FIB) direct milling. The characteristics of the junction barrier were carefully controlled by tuning the thickness of the link region. The optimal remaining thickness for the YBCO is about 70–80 nm even though the YBCO thicknesses are different. The temperature-dependence of the critical current provides good evidence of the superconductor–normal–superconductor weak link of the junctions. Although the flux-flow behavior increasingly dominates at lower temperatures, the voltage–current shows resistively shunted junction-like characteristics at temperatures close to Tc. The Shapiro steps of a single junction irradiated with microwaves were measured, revealing strong Josephson effects in ion-damaged junctions. This method will be of great benefit to nanoSQUIDs for the detection of spin systems.

Ion beam lithography for direct patterning of high accuracy large area X-ray elements in gold on membranes

X-ray elements like Fresnel zone plates (FZPs) are challenging objects for nanofabrication, as they require high accuracy, high aspect ratio and large area structures. In most cases they are fabricated with electron beam lithography (EBL) based techniques plus plasma or wet etching, which deliver routinely zone plates with outermost zone widths down to 25 nm and aspect ratios of 5:1. In this work we present a complementary resistless technique based on ion beam lithography (IBL) using direct milling with a focused Gallium beam and advanced process control. A zone plate of 100 μm diameter and 100 nm outermost zone widths has been produced in a 500 nm thick gold layer on a Si3N4 membrane. To achieve the desired resolution we developed a 15 h low current milling process including high accuracy automated drift correction on a mark outside the 500 × 500 μm membrane window. In addition first results of X-ray imaging with the zone plate are presented. To the best of our knowledge this is the first ion beam fabricated zone plate which has proven its functionality for X-ray imaging.

Study of the Plasmon Talbot Effect of Metallic Nanolenses Induced by Linearly Polarized Illumination

The plasmon Talbot effect of metallic nanolenses was studied theoretically and experimentally for the linearly polarized incident beam case. To demonstrate this self-imaging-based focusing property of the metallic nanolenses, a plasmonic nanolens with five periodic concentric through rings on Al film supported on quartz substrate was numerically studied firstly by the use of rigorous finite-difference and time-domain algorithm. To further demonstrate its working performance experimentally, it was fabricated by means of a focused ion beam direct milling technique. A near-field scanning optical microscope (NSOM) was then employed for the optical characterization of its focusing property. The experimental results indicate that the NSOM probing-based results are in agreement with the theoretical calculation results in general.

Direct and Transmission Milling of Suspended Silicon Nitride Membranes With a Focused Helium Ion Beam

Helium ion milling of suspended silicon nitride thin films is explored. Milled squares patterned by scanning helium ion microscope are subsequently investigated by atomic force microscopy and the relation between ion dose and milling depth is measured for both the direct (side of ion incidence) and transmission (side opposite to ion incidence) regimes. We find that direct-milling depth varies linearly with beam dose while transmission-milling depth varies with the square of the beam dose, resulting in a straightforward method of controlling local film thickness.

Preparation of nanostructured nickel aluminate spinel powder from spent NiO/Al2O3 catalyst by mechano-chemical synthesis

In this paper, the possibility of mechano-chemical synthesis, as a single step process for preparation of nanostructured nickel aluminate spinel powder from NiO/Al2O3 spent catalyst was investigated. Powder samples were characterized in terms of composition, morphology, structure, particle size and surface area using complementary techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential thermal analysis (DTA) and volumetric adsorption of nitrogen. It was found that formation of spinel was possible after 60h of milling with no heat treatment. Additionally, influence of mechanical activation on the heat treatment temperature was discussed. It was observed that heat treatment of 15h milled sample at 1100°C is enough to produce nickel aluminate spinel. A product of direct mechanical milling showed higher value of surface area (42.3m2/g) and smaller crystallite size (12nm) as compared to the heat treated product.

Maximal reduction of steps for iron casting one-of-a-kind parts

The direct milling of sand blocks could be a feasible technique when rapid casting is necessary. Avoiding the use of a wood pattern, this technology aims at one-of-a-kind pieces or art pieces, where only one prototype or component is required, but lead times are required to be much reduced. This technology becomes a pattern-less one, reducing production stages, times and costs. The key of the procedure is to achieve enough tool life when milling with carbide tools, avoiding the risk of sand destruction or surface damage during the free-form milling process. For this purpose, in this paper a special study of tool wear is presented. Moreover, other problems and difficulties are taken into account, such as, machine protection, sand quality or the optimum milling strategies. Two examples of unique parts are also presented in this work. Following the proposed methodology, the reduction of time and cost for the rapid reproduction of one-of-a-kind pieces or for very short batches is economically and technologically feasible.

Design and milling manufacture of polyurethane custom contoured cushions for wheelchair users

The design of custom contoured cushions manufactured in flexible polyurethane foams is an option to improve positioning and comfort for people with disabilities that spend most of the day seated in the same position. These surfaces increase the contact area between the seat and the user. This fact contributes to minimise the local pressures that can generate problems like decubitus ulcers. The present research aims at establishing development routes for custom cushion production to wheelchair users. This study also contributes to the investigation of Computer Numerical Control (CNC) machining of flexible polyurethane foams. The proposed route to obtain the customised seat began with acquiring the user's contour in adequate posture through plaster cast. To collect the surface geometry, the cast was three-dimensionally scanned and manipulated in CAD/CAM software. CNC milling parameters such as tools, spindle speeds and feed rates to machine flexible polyurethane foams were tested. These parameters were analysed regarding the surface quality. The best parameters were then tested in a customised seat. The possible dimensional changes generated during foam cutting were analysed through 3D scanning. Also, the customised seat pressure and temperature distribution was tested. The best parameters found for foams with a density of 50kg/cm(3) were high spindle speeds (24000 rpm) and feed rates between 2400-4000mm/min. Those parameters did not generate significant deformities in the machined cushions. The custom contoured cushion satisfactorily increased the contact area between wheelchair and user, as it distributed pressure and heat evenly. Through this study it was possible to define routes for the development and manufacturing of customised seats using direct CNC milling in flexible polyurethane foams. It also showed that custom contoured cushions efficiently distribute pressure and temperature, which is believed to minimise tissue lesions such as pressure ulcers.

A direct-write, resistless hard mask for rapid nanoscale patterning of diamond

We introduce a simple, resist-free dry etch mask for producing patterns in diamond, both bulk and thin deposited films. Direct gallium ion beam exposure of the native diamond surface to doses as low as 10 16 cm −2 forms a top surface hard mask resistant to both oxygen plasma chemical dry etching and, unexpectedly, argon plasma physical dry etching. Gallium implant hard masks of nominal 50 nm thickness demonstrate oxygen plasma etch resistance to over 450 nm depth, or 9:1 selectivity. The process offers significant advantages over direct ion milling of diamond including increased throughput due to separation of patterning and material removal steps, allowing both nanoscale patterning resolution as well as rapid masking of areas approaching millimeter scales. Retention of diamond properties in nanostructures formed by the technique is demonstrated by fabrication of specially shaped nanoindenter tips that can perform imprint pattern transfer at over 14 GPa pressure into gold and silicon surfaces. This resistless technique can be applied to curved and non-planar surfaces for a variety of potential applications requiring high resolution structuring of diamond coatings.

Experimental Study of Indirect Phase Tuning-Based Plasmonic Structures for Finely Focusing

Three types of indirect phase tuning-based plasmonic structures with subwavelength circular grooves/slits and/or central apertures corrugated on Au film supported by glass substrate: depth modulation, width modulation, and hybrid depth-width modulation, were put forth in this paper. They were investigated experimentally by means of nanofabrication and near-filed scanning optical microscope characterization. The plasmonic structures were fabricated using the technique of focused ion beam direct milling. Our experimental results demonstrated that all of the phase tuning-based structures have focusing functions. Both the width and depth modulation-based structures can realize beam focusing and produce an elongated depth of focus. Moreover, after comparison among these three structures, we found that the width modulation-based structure has the best focusing performance.

DNA-functionalized solid state nanopore for biosensing

The possible use of nanopores for single DNA molecules biosensing has been demonstrated,but much remains to do in order to develop advanced engineered devices with enhancedstability, and controlled geometry and surface properties. Here we present morphologicaland electrical characterization of solid state silicon nitride nanopores fabricated by focusedion beam direct milling and chemically functionalized by probe oligonucleotides, with thefinal aim of developing a versatile tool for biosensing and gene expression profiling.

Experimental investigation of superfocusing of plasmonic lens with chirped circular nanoslits

A plasmonic lens with metallic chirped circular nanoslits corrugated on Au film supported on quartz substrate for the purpose of superfocusing was put forth and fabricated by means of focused ion beam direct milling technique. Topography of the lens was imaged using an atomic force microscope. After that a near-field scanning optical microscope was employed for optical characterization of focusing performance of the lens. Our experimental results verify the focusing performance and further demonstrate that they are in agreement with the theoretical calculation results. Focusing performance is significantly improved in comparison to that of the non-chirped lens. The lenses are possible to be used for the applications of bioimaging, detection, and inspection in submicron scale resolution.

Fabrication of complementary metal-oxide-semiconductor integrated nanomechanical devices by ion beam patterning

The authors present a novel approach to fabricate nanomechanical devices integrated into complementary metal-oxide-semiconductor (CMOS) circuits. It is based on focused ion beam patterning using two different processes: (i) ion-beam-induced deposition of tethraethoxysilane and (ii) direct exposure of silicon or polysilicon surfaces. In both cases, the irradiated areas sustain a reactive-ion etching process, acting as robust masks for defining nanomechanical devices with submicron resolution. These processes are compared, in terms of throughput, with direct milling of silicon and with patterning of thin aluminum layers. Compatibility with prefabricated CMOS circuits is studied and they found that the process is entirely compatible if the proper exposure conditions are used.

Rapid Manufacturing of Sand Molds by Direct Milling

Direct milling of sand molds is an important development in rapid manufacturing of sand molds. Direct milling is an effective method for manufacturing single or small batches of cast parts. This paper describes experimental investigations to find sand blocks with the appropriate strength, to describe wear patterns of different tools (high-speed steel (HSS), carbide, and polycrystalline diamond (PCD) tools), and to analyze sand mold cutting mechanisms. The results show that the PCD tool outperformes the other tools in terms of tool life. Average flank wear and micro-tipping are the dominant tool failure modes in the sand mold milling process. With a flank wear limit of 0.3 mm, the PCD tool works continuously for about 70 h under the experimental conditions. The experimental results show that the cutting mechanism for direct milling sand molds differs from metal cutting.

Characteristics of High-$T_{\rm c}$ Josephson Junction Fabricated by Focused Ion Beam and Ion Damage

A high-Tc Josephson junction and superconducting quantum interference devices (SQUIDs) were fabricated by focused ion beam (FIB) milling and 150 keV oxygen ion implantation. A single layer gold mask with a small aperture of 28-73 nm defined by direct milling with FIB, was used. The voltage versus current characteristics of high-Tc YBa2Cu3O7-x Josephson junctions were measured under microwaves. Shapiro steps were observed in the single junction. The voltage versus current and voltage versus magnetic field characteristics of a SQUID were measured.

Direct milling of polymethylmethacrylate for cranioplasty applications

The manufacturing of customized implants for cranioplasty applications has been recognized as a valuable alternative in order to reduce time and surgical costs and to produce better cosmetic results. Generally, the machining processes, in special milling, have been adopted as an intermediary step to manufacture a dedicated mold for casting the designed implant. In this work, we proposed the use of direct milling of simpler implants to shorten the process chain without compromising its dimensional quality. A set of computed tomography (CT) images were acquired from a dried human skull, vetorized, and further used to reconstruct a solid model. Such solid model was processed with computer-aided design (CAD) and computer-aided manufacturing systems to the machining planning. An acrylic implant was directly milled in a three-axis machining center and its external surface was measured with a coordinated measuring machine and compared with its corresponding in the original model (skull) and the digital ones (CT images and CAD). Based on the assessment of dimensional deviations, it is possible to affirm that direct milling can be considered the ultimate phase in the production of customized implants.

Total reflection mirrors fabricated on silica waveguides with focused ion beam

Efficient total reflection mirrors are fabricated on silica-based waveguides by direct milling with a focused ion beam. To reduce the excess losses of the mirrors, a two-step milling technique is employed that reduces the roughness of the mirror surface while maintaining a high milling rate. A focused ion beam is used to fabricate low-loss mirrors with small excess losses of about 1.0 dB.

Focused ion beam milling of photonic crystals in bulk silicon

Focused ion beam (FIB) direct milling was used to fabricate photonic crystals in bulk silicon. The milling requires the sidewalls as nearly perpendicular to the slab as possible and the top profile of the holes to be smooth. The re-deposition of milled material exaggerates the hole profiles. The effects on the sidewall profile and the top periphery due to the beam current, dwell time, and the extra boundary milling have been researched. It turns out that a combination of beam current, dwell time, and milling depth has optimized the sidewalls and top periphery of the holes.