The heat-assisted magnetic recording (HAMR) head–disk interface is a unique operating environment that combines nanoscale spacings, high shear rates, high-temperature gradients, and high optical fluxes in a mass-produced device. One of the greatest challenges is to develop materials for the head–disk interface that enable the required head–media spacing while also providing reliability. Traditional head–disk interface materials, engineered and optimized for conventional magnetic recording hard-disk drives, are challenged to provide the needed performance at the high temperatures that HAMR involves. We review some of the primary materials used in conventional magnetic recording, how high temperatures challenge their performance, and some of the current understanding and strategies to develop a reliable HAMR head–disk interface.

We have deposited dense and pinhole-free thin films of SiO2, Al2O3 and ITO at room temperature via ion beam sputtering. The SiO2 films were found to be of similar quality as thermal oxide with a resistivity greater than 1015 Ω·cm and breakdown field in excess of 7 MV/cm. The Al2O3 films were part of a Pt- Al2O3-Pt vertical tunnel junction and were kept extremely thin, from 2 nm to 4 nm. The current-voltage characteristics of these junctions indicated a breakdown field in excess of 20 MV/cm, roughly twice that achieved by ALD films. This breakdown voltage was found to be independent of junction area, strongly suggesting the absence of pinholes in the film. The ITO films were 50 nm to 100 nm thick. As deposited, they are fully transparent with an electrical resistivity of 5x10-4 Ω·cm.

Over the last few years, significant improvements in sources, columns, detectors, control software, and accessories have enabled a wealth of new focused ion beam applications. In addition, modeling has provided many insights into ion-sample interactions and the resultant effects on the sample. With the knowledge gained, the community has found new ion-beam induced chemistries and ion-beam sources, allowing extending nanostructure fabrication and material deposition to smaller dimensions and better control for direct write and patterning. Insignificant proximity effects in resist-based ion beam lithography, combined with the availability of sub-nm ion spot sizes, opens the way to sub-10 nm structures and dense patterns. Additionally, direct-write ion beam nanomachining can process multilevel structures with arbitrary depths in one single process step, with all the information included in a single standard design file, thus enabling fabrication applications not achievable with any other technique.

This article reviews recent developments and applications of two beam systems (focused ion beam [FIB] and scanning electron microscope [SEM]) for in situ characterization and manipulation of material at the micro- and nanoscale. In these applications, the sample may be manipulated, ion milled, mechanically or electrically excited, and its temperature varied from above room temperature to cryogenic levels. FIB-SEM instruments offer new opportunities for in situ characterization by enabling localized exposure of surface layers within the high vacuum microscope chamber environment (especially in conjunction with cryogenic cooling of the bulk sample), through experiments that require either highly accurate material removal or localized material addition through beam-induced gas deposition, and by using micro- and nano-manipulation technologies for probing or positioning. This article describes the current state of the art of this experimental methodology and provides case studies in the areas of cryogenic, electrical, and mechanical characterization.

We report on the preparation and characterization of crystalline bismuth oxide thin films via Biased Target Ion Beam Deposition method. A focused blue laser (405nm) is used to write an array of dots in the bismuth oxide thin film and demonstrate clear and circular recording marks in form of “bubbles” or “little volcanos” (FWHM ∼500nm). Results indicate excellent static recording characteristics, writing sensitivity and contrast. The recording mechanism is investigated and is believed to be related to laser-induced morphology change.

ITO samples were sputtered at room temperature by ion assisted dual ion beam sputtering using atomic or molecular oxygen. The electrical properties appear to depend on the oxygen flow rate during deposition and the resistivity decreases for samples sputtered at a higher oxygen flow rate (1-5 sccm). The resistivity is lowest at an oxygen flow rate of 4 sccm. The average absorption in the visible part of the spectrum also decreases as a function of the oxygen flow rate and is lower for samples sputtered with atomic oxygen. The figure of merit, i.e. the ratio of the conductivity versus the average absorption in the visible range, increases for higher oxygen flow rates and is typically 20-60% higher for samples sputtered using an atomic oxygen assist beam.

Electrical and Optical measurements were carried out on permalloy oxide (PyO) thin films made by reactive dual ion beam sputtering at room temperature. VSM measurements at room temperature and 15 Kelvin did not reveal any magnetic moment in 120 nm thick films. The optical refraction and extinction spectra from 200-1000 nm were determined from ellipsometry measurements using a Cody-Lorentz model and provided in a reproducible method to determine the film thickness of PyO films on different substrate materials. PyO is transparent above 700 nm and is strongly absorbing below 500 nm. The resistivity values of PyO samples sputtered at room temperature depend on the oxygen flow rate and is approximately 4E3 Ohm cm for films prepared at 10 sccm. The resistivity of PyO decreases as a function of temperature. The dielectric constant is strongly frequency dependent, decreasing from 500 at 500 Hz to 10 at 1 MHz.

Titanium (Ti) is the material of choice for orthopaedic applications because it is biocompatible and encourages osteoblast ingrowth. It was shown that the biocompatibility of Ti metal is due to the presence of a thin native sub-stoichiometric titanium oxide layer which enhances the adsorption of mediating proteins on the surface [1]. The present studies were devised to evaluate the adhesion, survival, and growth of cells on the surface of new engineered nano-crystal films of titanium and titanium oxides and compare them with orthopaedic-grade titanium with microcrystals. The engineered nano-crystal films with hydrophilic properties are produced by employing an ion beam assisted deposition (IBAD) technique. IBAD combines physical vapor deposition with concurrent ion beam bombardment in a high vacuum environment to produce films (with 3 to 70 nm grain size) with superior properties. These films are “stitched” to the artificial orthopaedic implant materials with characteristics that affect the wettability and mechanical properties of the coatings.

To characterize the biocompatibility of these nano-engineered surfaces, we have studied osteoblast function including cell adhesion, growth, and differentiation on different nanostructured samples. Cell responses to surfaces were examined using SAOS-2 osteoblast-like cells. We also studied a correlation between the surface nanostructures and the cell growth by characterizing the SAOS-2 cells with immunofluorescence and measuring the amount alizarin red concentration produced after 7 and 14 days. The number of adherent cells was determined by means of nuclei quantification on the nanocrystalline Ti, TiO2, and microcrystalline Ti and analysis was performed with Image J. Our experimental results indicated that nanocrystalline TiO2 is superior to both nano and microcrystalline Ti in supporting growth, adhesion, and proliferation. Improving the quality of surface oxide, i.e. fabricating stoichiometric oxides as well as nanoengineering the surface topology, is crucial for increasing the biocompatibility of Ti implant materials.

This paper addresses the application of engineered nanocrystalline ultrahydrophilic titanium oxide films to artificial orthopaedic implants. Titanium (Ti) is the material of choice for orthopaedic applications and has been used for over fifty years because of its known bio-compatibility. Recently it was shown that biocompatibility of Ti metal is due to the presence of a thin native sub-stoichiometric titanium oxide layer [1] which enhances the adsorption of mediating proteins on the surface thus enhancing cell adhesion and growth [2,3,4]. Improving the quality of surface oxide, i.e. fabricating stoichiometric oxides as well as nanoengineering the surface topology that matches the dimensions of adhesive proteins, is crucial for the increase of protein adsorption [2] and, as a result, the biocompatibility of Ti implant materials. We have fabricated ultrahydrophilic nano-crystalline transparent films of anatase phase of titania (TiO2) by ion beam assisted deposition (IBAD) processes in an ultrahigh vacuum system. Source material was 99.9% pure rutile TiO2. Various ion beam conditions were used to produce these coatings with different grain sizes (4 to 70 nm) that affect the wettability, roughness, and the mechanical and optical properties of the coating [5]. Our biological experiments have shown that biocompatibility of these ultrahydrophilic nanoengineered TiO2 coatings are superior to commonly used orthopaedic titanium and even hydroxyapatite.

We designed and produced pure cubic zirconia (ZrO2) ceramic1 coatings by an ion beam assisted deposition (IBAD) with nanostructures comparable to the size of proteins. Our ceramic coatings exhibit high hardness and a zero contact angle with serum. In contrast to hydroxyapatite (HA), nano-engineered zirconia films possess excellent adhesion to all orthopaedic materials. Cell adhesion and proliferation experiments were performed with a bona fide mesenchymal stromal cell line (OMA-AD). Our experimental results indicate that the nano-engineered cubic zirconia is superior in supporting growth, adhesion, and proliferation. Since cell attachment is mediated by adhesive proteins such as fibronectin (FN), to elucidate why cells attach more effectively to our nanostructures, we performed a comparative analysis of adsorption energies of FN fragment using quantum mechanical calculations and Monte Carlo (MC) simulation both on smooth and nanostructured surfaces. We have found that a FN fragment adsorbs significantly stronger on the nanostructured surface than on the smooth surface2.

Although Helium Ion Microscopy (HIM) was introduced only a few years ago, many new application fields are budding. The connecting factor between these novel applications is the unique interaction of the primary helium ion beam with the sample material at and just below its surface. In particular, the HIM secondary electron (SE) signal stems from an area that is very well localized around the point of incidence of the primary beam. This makes the HIM well-suited for both high-resolution imaging as well as high resolution nanofabrication. Another advantage in nanofabrication is the low ion backscattering fraction, leading to a weak proximity effect. The lack of a quantitative materials analysis mode (like EDX in Scanning Electron Microscopy, SEM) and a relatively low beam current as compared to the SEM and the Gallium Focused Ion Beam are the present drawbacks of the HIM.

Bending tests of Diamond-Like Carbon (DLC) nanopillars fabricated by Focused Ion-Beam assisted Chemical Vapor Deposition (FIB-CVD) were carried out in a scanning electron microscope (SEM) to investigate their mechanical behavior. Special attention was paid on the effect of the specimen size. The nanopillars with nano-sized diameter and micro-sized length were grown using spot irradiation without scanning FIB. The diameter of the nanopillars was changed in the range of 100 ~ 1000 nm by changing the magnitude of defocusing FIB.

In the bending tests, brittle fracture was observed for the nanopillars with diameter of 1000 nm. On the contrary, large deformation without brittle fracture was confirmed in the specimens with diameter of 300 nm. In addition, the pillar recovered its original shape after unloading without any permanent deformation even after the large deformation.

Transmission electron microscope (TEM) analysis revealed that the pillars had uniform amorphous structures regardless of the diameters if the FIB was defocused during processing. In addition, similar gallium (Ga) content and sp2/sp3 fraction were observed in both specimens. These results indicate that difference in microstructures cannot be the reason for that in mechanical behavior. In other words, it must be caused by the intrinsic size effect on the mechanical properties of DLC fabricated by FIB-CVD process.

Influence of processing condition on mechanical and structural properties of diamond-like carbon (DLC) by focused ion-beam chemical vapor deposition (FIB-CVD) method was investigated. The DLC specimens were produced under conditions of varying supplied amount of material gas and probe current of FIB. Volume determination results of DLC structures indicated that a deposition rate was increased with both the amount of gas and the probe current. To evaluation of mechanical property, indentation hardness was measured by a nano-indentation tester. From evaluation of mechanical property, it was found that the indentation hardness was sensitive to the processing condition, showing in the range of 8-13 GPa. The hardness of DLC structures was seemed to be lower when etching process higher contributed for formation process. Crystallographic structure of DLC remained amorphous even though the mechanical properties varied widely. Results of hydrogen concentration measurement indicated that increase of hydrogen concentration might lead to decrease of hardness.

The growth of epitaxial semiconductor nanostructures and films at low temperatures is important for semiconductor technology because it allows the possibility of monolithically integrating different high-performance single-crystalline semiconductor structures directly onto low cost technologically important substrates. At sufficiently low temperatures this can enable, for example, Si or Ge device fabrication on flexible substrates such as plastics. We have studied the reduced-temperature liquid-mediated growth of Ge nanostructures and films on crystalline template layers on non-single-crystalline substrates in a low-pressure chemical vapor deposition (LPCVD) system. The heteroepitaxial process is implemented by the Au seeded vapor-liquidsolid (VLS) catalytic growth technique with germane below 400 ºC. Crystalline template layers were prepared with ion-beam-assisted-deposition (IBAD) texturing and electron-beam evaporation on glass substrates. A thin layer of e-beam evaporated Au forms the catalyst layer, upon which we grew Ge films at 386 ºC. Scanning electron microscopy and x-ray diffraction results indicated that both Ge islands and nanowires grew heteroepitaxially on the crystalline template layers on glass substrates with good alignment over large areas.

In this paper, we present the possibility of nano-scale patterning on surfaces of 3-D micro structures by means of block copolymer self assembly. We succeeded in forming vertical cylinders on the surfaces of the 3-D micro structures using dip-coat process with Au deposition instead of random copolymers. The material of 3-D structures fabricated by FIB-CVD was diamond-like carbon (DLC) due to selecting phenanthrene as a gas source. Since the surface energy of DLC is low, instead of PS-r-PMMA polymer brush, 100 nm-thick Au films were coated on the surfaces of 3-D structures. PS-b-PMMA (PS:PMMA = 50 kg/mol:21 kg/mol) was dip-coated on the Au coated surfaces and annealed. First, we prepared DLC 60° angled slope with size of 2.5 by 3 μm2. As a result, the vertical cylinders were formed in a similar way regardless of the places, i.e., top, middle and bottom on the slopes. vertical cylinders were formed regularly and densely on the entire slope. In order to investigate the effect of slope angle, we prepared 3-D micro structures with different angled slopes such as 70, 80 and 90°. There was no slope angle specific difference, and vertical cylinders were also formed on each slope.

Recent efforts in investigating the mechanism of ion beam assisted deposition (IBAD) of biaxially textured thin films of magnesium oxide (MgO) template layers have shown that the texture develops suddenly during the initial 2 nm of deposition. To help understand and tune the behavior during this initial stage, we pre-deposited thin layers of MgO with no ion assist prior to IBAD growth of MgO. We found that biaxial texture develops for pre-deposited thicknesses < 2 nm, and that the thinnest layer tested, at 1 nm, resulted in the best qualitative RHEED image, indicative of good biaxial texture development. The texture developed during IBAD growth on the 1.5 nm pre-deposited layer is slightly worse and IBAD growth on the 2 nm pre-deposited layer produces a fiber texture. Application of these layers on an Al2O3 starting surface, which has been shown to impede texture development, improves the overall quality of the IBAD MgO and has some of the characteristics of a biaxially texture RHEED pattern. It is suggested that the use of thin (<2 nm) pre-deposited layers may eliminate the need for bed layers like Si3N4 and Y2O3 that are currently thought to be required for proper biaxial texture development in IBAD MgO.

We describe our efforts to control the grain boundary alignment in polycrystalline thin films of silicon by using a biaxially textured template layer of CaF2 for photovoltaic device applications. We have chosen CaF2 as a candidate material due to its close lattice match with silicon and its suitability as an ion beam assisted deposition (IBAD) material. We show that the CaF2 aligns biaxially at a thickness of ~10 nm and, with the addition of an epitaxial CaF2 layer, has an in-plane texture of ~15°. Deposition of a subsequent layer of Si aligns on the template layer with an in-plane texture of 10.8°. The additional improvement of in-plane texture is similar to the behavior observed in more fully characterized IBAD materials systems. A germanium buffer layer is used to assist in the epitaxial deposition of Si on CaF2 template layers and single crystal substrates. These experiments confirm that an IBAD template can be used to biaxially orient polycrystalline Si.

We examined crystalline-texture evolution during ion-beam-assisted deposition (IBAD) of MgO thin films. We have demonstrated for the first time that in-plane crystalline texturing in IBAD of MgO scales with deposition rate. At high ion currents an in-plane texture full width at half-maximum (FWHM) of 10° can be achieved in less than 1 s, and 6° in 2.2 s. MgO texture further improves with thickness of a homoepitaxial layer deposited on top. We have developed an empirical quantification of the texture evolution in both IBAD and homoepitaxial layers. The best texture attained thus far in the MgO layer on polished Hastelloy tape has an in-plane FWHM of 1.6°. The high deposition rates demonstrated here make high-throughput manufacturing of IBAD textured templates a practical and cost-effective concept.

Ion-beam induced etching and deposition rates are proportional to the flux of recoils reaching the surface. Based on this finding we propose an improved algorithm for etching and deposition simulations. In this algorithm the recoil flux at each point on the surface is calculated by summing up the recoil fluxes originating from ions impinging on any other surface point. The latter are determined by interpolation in tables calculated by binary collision simulations. For concave surfaces a correction to this algorithm is proposed. Fluxes calculated by this model are in good agreement with binary collision simulations of collision cascades in the same 2-d structure. Consistent with experimental findings, the model predicts that deposited pillars are broader than the ion beam, while etched trenches do not show such broadening. The pillar broadening is related to the lateral straggling of the recoils.

The use of an ion beam assist during the concurrent deposition of cubic materials can result in the growth of crystallographically oriented thin films. A model system, magnesium oxide (MgO), has been successfully used as a biaxially textured template film and develops texture in a different manner from that of other well-studied materials, like yttria-stablized zirconia. Here, we present data on the initial nucleation of biaxial texture in this model system using a novel in-situ quartz crystal microbalance (QCM) substrate combined with in-situ reflected high-energy electron diffraction (RHEED). Temporal correlation of mass uptake with the RHEED images of the growing surface can be used to elucidate the mechanism of texture development in these films. Experimental data shows that the initially polycrystalline MgO film develops biaxial crystallographic texture at a thickness of ˜2 nm, regardless of the ion-to-molecule ratio. RHEED images show the onset of texture occurs quickly and is somewhat analogous to a solid phase re-crystallization process with crystallite sizes of ˜3 to 4 nm. Imaging with transmission electron microscopy has corroborated these observations. Changes in the ion-to-molecule ratio can influence the crystallite size and affect the nucleation density of these films. Growth of these films on various substrates changes the sticking coefficient of the MgO and influences the nucleation density and film growth mode as well. This opens the possibility of using MgO and other materials to develop biaxially textured crystallites with a narrow, specified size distribution for nanoscale applications.