Dinesh K. Sood

Ion implantation based selective synthesis of silica nanowires on silicon wafers

A new method for selective growth of silica nanowires on silicon wafers is demonstrated by using ion implantation through a mask. Pd ions are implanted into Si (100) to form nanoclusters of Pd. The nanoclusters get activated and act as catalyst silicide seeds for nanowire growth, when heated in an open tube quartz furnace, using Ar as carrier gas. Silica nanowires grow selectively only on the implanted region. The vapor-liquid-solid model of nanowire formation is shown to be valid. This method facilitates controlled localized and directed bottom-up growth of silica nanowires and may enable applications such as in on-chip optoelectronics, biosensors, microantennae, and metallic nanotubes.

Modification of tribomechanical properties of commercial TiN coatings by carbon ion implantation

Abstract Physical vapour deposited commercial TiN coatings of about 2 μm thickness on high speed steel substrates were implanted at room temperature with 95 keV carbon ions at nominal doses between 1 × 10 17 and 8 × 10 17 ions cm −2 . An ultra-microhardness apparatus (UMIS-2000) was used to measure hardness, and a pin-on-disc machine (CSEM tribometer) with a sapphire ball was used to measure wear, friction and adhesion. Carbon implantation induced a significant improvement in ultra-microhardness, friction coefficient and wear properties. The surface microhardness increases monotonically by up to 115% until a critical dose φ crit is reached. Beyond this dose the hardness decreases, but remains higher than that of unimplanted sample. A lower friction coefficient and a longer transition period towards a steady state condition were obtained by implantation. Proton elastic scattering (PES) measurements show loss of nitrogen after implantation by up to 27%. Rutherford backscattering (RBS) analysis indicated that some implanted carbon has diffused out from the implanted region towards the TiN surface. The changes in tribomechanical properties are discussed in terms of radiation damage and possible second phase formation.

Young's modulus measurements of silicon nanostructures using a scanning probe system: a non-destructive evaluation approach

Nanomechanical silicon cantilever beam test structures were fabricated from silicon-on-insulator wafers using electron beam lithography. A scanning probe system in the form of an atomic force microscope was used to measure their mechanical properties in a non-destructive evaluation approach. It is important to note that, despite the nanometer size of the silicon cantilever beams in the [100] direction, Youngs modulus remained unchanged from the bulk value: 179 GPa. We believe that the fabrication processes did not induce any major structural modifications to the basic building blocks of silicon. Hence the Youngs modulus was measured to be the same as that of the bulk silicon, which is important for designing predictable structures at nanometer scale.

A novel technique for fabrication of metallic structures on polyimide by selective electroless copper plating using ion implantation

Abstract The successful use of palladium ion implantation into polyimide to seed an electroless plated film of copper on the polyimide surface is reported. Polyimide (Hitachi PIX 3400) was implanted with palladium ions to doses of 1.5 × 10 15 − 1.2 × 10 17 ions cm −2 using a MEVVA ion implanter. The implanted ions acted as sites for nucleation of copper film. A copper film was then deposited on implanted polyimide using a commercial electroless plating solution. The ion energy was kept low enough to facilitate a low critical ‘seed’ threshold dose that was measured to be 3.6× 10 16 Pd ions cm −2 . Test patterns were made using polyimide to study the adaptability of this technique to form thick structures. Plated films were studied with optical microscopy, Rutherford Backscattering Spectrometry (RBS) and Profilometry. The adhesion of films was qualitatively assessed by a ‘scotch tape test’. The film growth (thickness) was observed to be linear with plating time. A higher implantation dose led to greater plating rates. The adhesion was found to improve with increasing dose.

Prototype feedback-controlled bidirectional actuation system for MEMS applications

We have successfully developed a one degree-of-freedom microsuspension system, with active position control, as a paradigm of a micromagnetic bearing. This system integrates an electromagnetic actuator, a position sensor, and a feedback control system that provides active position control. This paper discusses the design and fabrication details of the microelectromechanical system (MEMS) components: the beam mass structure integrated with a drive coil and metallized targets, spacer plate, and sensor coils. It also discusses their integration with millimagnets and electronics. Noncontact magnetic bearings based on this principle have the potential of overcoming the tribo-physical issues associated with active MEMS devices.

Selective electroless copper plating on silicon seeded by copper ion implantation

Abstract We report on the successful use of copper (self) ion implantation into silicon to seed the electroless plating of copper on silicon (100) surfaces. Copper ions were implanted into silicon to doses of 5 × 1014−6.4 × 1016 ions cm-2 using a metal vapour vacuum arc ion implanter at extraction voltages of 10 kV and 20 kV. A copper film was then deposited onto implanted silicon using a commercial electroless plating solution. The ion energy was kept low enough to facilitate a low critical ‘seed’ threshold dose which was measured to be 2 × 1015 Cu ions cm-2. Test patterns were made using polyimide to study the adaptability of this technqiue to forming thick structures. Plated films were studied with Rutherford backscattering spectrometry, scanning electron microscopy (SEM), profilometry, energy-dispersive X-rays and Auger electron spectroscopy. The adhesion of films was estimated by a ‘Scotch tape test’. The adhesion was found to improve with increasing dose. However, high internal stress. Detailed examinations of the top and bottom of the film establish that delamination takes place at the amorphous-crystalline interface of the implanted silicon. SEM results show that the films grow first as isolated islands which become larger and eventually coalesce into a continuous film as the platingtime is increase.

Post-deposition treatments of hard coatings Part II: Ion beam treatments of TiN and related coatings

Abstract This paper presents an overview of the current state of the art on the effects of ion implantation treatments using nitrogen, argon and carbon on the tribological and structural properties of TiNx films. Data obtained by the authors and by other groups are discussed. Where available, data from similar treatments of related coatings (TiC and ZrN) are also presented. Improvements in tribological properties, in particular wear and adhesion, appear to be a general feature of implanted TiN coatings, irrespective of species and implantation parameters. However, ultramicrohardness of implanted films increases or decreases under various conditions, indicating that a number of different mechanisms contribute to wear improvements under various implantation regimes. Another common feature of implanted films is the observation that the treatment causes changes in the colour of the films, which vary with implanted species and dose. These changes are attributed to changes in stoichiometry induced by the beam in the upper layers of the films, and to changes in the surface texture.

The effect of carbon ion implantation on the nucleation of diamond on Ti-6Al-4V alloy

Abstract The heterogeneous nucleation of diamond particles during the early stages of diamond film formation on non-diamond substrates is not well understood. In this work, we used ion implantation as a pretreatment process, to control the nucleation of diamond particles. The well known surgical alloy Ti-6Al-4V (“mirror” polished) was used as the substrate. Carbon ions at 30 keV energy were implanted at room temperature into masked regions on the samples, up to doses of 1×1016-7×117 ions cm-2. At the high doses, carbon concentrations up to 80 at.% were generated as shown by Rutherford backscattering spectrometry (RBS). After ion implantation, diamond depositions were conducted at MRL utilizing a Toshiba microwave chemical vapour deposition (CVD) system. Operating conditions were 12 kPa total system pressure, 1% methane in hydrogen at a total flow of 100 standard cm3 min-1, substrate temperature of 1000 °C, deposition time 5 h. The deposited films were studied by scanning electron microscopy, microfocus Raman scattering and RBS. The results indicate (a) a reduction in nucleation density up to 8 times with increasing ion dose, (b) near perfect diamond particles (Raman scattering) and (c) large internal stresses leading to partial flaking when the film becomes continuous. The role of a possible “carbided layer” formed by ion implantation is discussed.

Design and fabrication of a micro magnetic bearing

A micro magnetic bearing actuator has been designed using electromagnets. In this design, the rotor position is actively controlled in the radial directions and passively supported in the axial direction. A micro position sensor, along with a proportional plus derivative (PD) control system, constitutes the feedback network, which ensures that the rotor is actively suspended in the radial directions. The circular stator has four control coils which are sandwiched between two stator end plates. The diameter of the stator and rotor are 2.1 and 2.6 mm respectively, while the thickness is fixed at 250 µm. The air gap between the stator and rotor has been fixed at 10 µm. The stator and rotor plates were fabricated using Permalloy electroplating, while the control coils of the stator were hand-wound using conventional coil winding techniques. The bearing components were assembled using normal micro assembly techniques. The details of the fabrication and assembly techniques employed for the micro bearings are presented, along with the test results.

Structural investigation of low energy ion beam deposited diamond-like films☆

Abstract Diamond-like films were deposited by ion beam deposition using various CH 4 H 2 gas mixtures and beam voltages of 1000 V and below. The films have been examined by Fourier transform infrared spectroscopy (FTIR) and Raman microprobe spectroscopy. Both FTIR and Raman spectra indicate an increase in the sp2 content of these films for high hydrogen content in the deposition gas. Raman spectroscopy also indicates an increase in the sp2 order with beam voltage for low hydrogen content. These results suggest that there are two competing mechanisms controlling the film structure. For films deposited with low hydrogen content in the deposition gas the structure is beam voltage (ion energy) dependent, whereas for high hydrogen contents there is no clear beam voltage (energy) dependence.