Peter C.T. Ha

Surface-enhanced Raman characteristics of Ag cap aggregates on silicon nanowire arrays

A convenient nanotechnique is used to place analyte molecules between closely spaced silver-capped Si nanowires for investigating surface-enhanced Raman scattering (SERS). It is revealed that the SERS intensity (or sensitivity) is closely related to the etching time used to prepare the Si nanowires from wafer. As the etching leaves the nominal spacing between the nanowires unaffected, the observed effect can be explained based on different gaps between the Ag particles due to the different lengths of the Si nanowires. Large SERS intensity for short etching times can be elucidated in terms of the rigidity of the nanowires and the smaller SERS intensities for longer etching times can be explained by considering the bending of nanowires and the agglomeration of the Ag caps due to gravity and van der Waals forces.

Electronic conductance of ion implanted and plasma modified polymers

The authors used the plasma immersion ion implantation and deposition technique to modify polyethylene terephthalate (PET) and by using conductive atomic force microscope, the spatial distribution of ∼10nm size titanium nanoclusters embedded in PET matrices were observed. The I-V plots showed typical metal-semiconductor junction conductivity between the conductive tip and the surface. In addition, the authors also measured the temperature dependent conductivity and fitted it well to the Mott law, which implied that the conductance arose from electron hopping process. Such technique to create the surface structure of metal/polymer nanocomposites may open an alternative way for plastic nanoelectronics.

Structure and wetting properties of metal polymer nanocomposites

Polystyrene thin films of thickness 180-200 nm are modified by plasma immersion ion implantation and deposition (PIII&D) technique together with titanium filtered cathodic vacuum arc. The surface structure of modified films turns into a metal polymer nanocomposite where Ti nanoclusters of spatial size 10 - 20 nm are embedded in polystyrene matrices. Such structural formation is the interplay between ion sputtering and ion diffusion effect. The wetting properties of this nanocomposite, such as contact angle aging effect and hysteresis are investigated. The changes in various properties are believed to be due to structure of polymer nanocomposites as well as the basic principles of ion polymer interaction.

Anti-corrosion properties of nitrogen and oxygen plasma-implanted nickel-titanium shape memory alloy

Nickel-titanium shape memory alloys (NiTi) have potential applications as orthopedic implants but out-diffusion of harmful Ni from the NiTi substrate during prolonged use inside a human body is a serious issue and the problem must be solved before the materials can be more widely used in orthopedics. In this work, we produce TiN and TiOx barrier layers by plasma immersion ion implantation (PIII) and study the effects of different working voltages (20kV, 30kV, and 40kV). The corrosion resistance of the plasma-treated materials is found to be much improved and the optimal processing windows are described in this paper.

XPS studies on aluminum ions modified polyimide with the PIII technique

Polyimide samples modified by aluminum (Al) ions produced by filtered cathodic vacuum arc (FCVA) with plasma immersion ion implantation (PIII) technique, under ambient argon and oxygen gases (flow rate Ar:O2=2:1) were investigated by x-ray photoelectron spectroscopy (XPS). The working pressure was about 8×10−4 Torr and the plasma density was estimated to be 109 ions∕cm3. The applied bias voltages were varied from 5 to 12.5 kV but with fixed frequency at 900 Hz and duty time of 15μs. For 1 min process time, C 1s and O 1s spectra for modified samples clearly indicated that the carbonyl group (C=O) was largely destroyed by incident Al ions while Al 2p spectra suggested Al atoms remain inside polyimide matrices in the form of C-O-Al complexes. For a 5 min process time, when the ion fluence became large, both C 1s and O 1s spectra suggested a structure of “aluminum oxide-mixed layer-polyimide” and Al 2p spectra confirmed that most Al atoms were bonded to oxygen atoms on the top surface. These XPS results revea...

Structural and wetting properties of metal polymer nanocomposites

Polystyrene thin films of thickness 180-200 nm are modified by plasma immersion ion implantation and deposition (PIII&D) technique together with titanium filtered cathodic vacuum arc. The surface structure of modified films turns into a metal polymer nanocomposite where Ti nanoclusters of spatial size 10 - 20 nm are embedded in polystyrene matrices. Such structural formation is the interplay between ion sputtering and ion diffusion effect. The wetting properties of this nanocomposite, such as contact angle aging effect and hysteresis are investigated. The changes in various properties are believed to be due to structure of polymer nanocomposites as well as the basic principles of ion polymer interaction.

Passivation layer on polyimide deposited by combined plasma immersion ion implantation and deposition and cathodic vacuum arc technique

A thin passivation layer of aluminum oxide was deposited on polyimide by using the combined plasma immersion ion implantation and deposition (PIII&D) and cathodic vacuum arc technique. X-ray photoelectron spectroscopy C 1s spectra showed that the carbonyl bond (CO) and ether group (C–O–C and C–N–C) presented in pristine polyimide were damaged by implantation of aluminum ions and deposition of an aluminum oxide passivation layer. O 1s and Al 2p spectra confirmed the formation of a thin aluminum oxide passivation layer. This passivation layer can be implemented in aerospace engineering where polyimide may suffer degradation from fast atomic oxygen in the low-earth-orbit environment. To test the protection of this passivation layer to energetic oxygen ions, a plasma-enhanced chemical vapor deposition system was used to simulate the oxygen-ion irradiation, and the results showed that a higher weight occurred for passivated samples compared to pristine ones. X-ray diffraction showed that Al peaks were present...

Initial growth of conducting island-like structure on insulating polymer substrate

Using ultrasharp conductive tip atomic force microscopy (c-AFM), we have measured the current voltage (I-V) characteristics of titanium ions implanted into polystyrene thin film spin coated onto silicon substrate. The surface morphology and the electric current between the tip and sample have been obtained simultaneously on the nanometer scale. Initial island-like growths structures were observed and are comparable with implantation time while surface energy and thermodynamics theory allowing the initial stages of film growth to be explained. Our conductivity measurements showed that there are conducting channels, forming of conducting island-like structures surrounded by the pool of insulator polystyrene. The conducting channel or island-like structures on polymer substrate can be a good candidate for the future of nano-plastic-electronics devices.

Fabrication of embedded conductive layer in polymer by plasma immersion ion implantation

Plasma immersion ion implantation (PIII) offers an alternative to ion beam with the advantage of high implantation rate. However, problems inherent to the application of PIII to non-conducting materials such as polymers are due to surface charging. To overcome these difficulties and to have a controllable implantation depth, we sputtered a thin layer of gold before PIII is applied to the polymer substrate. The result is a controllable implantation dept and stronger adhesion between the metal-polymer interfaces. The extent of implantation depth can be correlated to tribological properties, electrical conductivity and Raman spectroscopy. While conductive AFM confirmed the conductivity of the embedded layer, the future applications, difficulties and limitations using this technique for fabrication of conductive embedded layer in polymers are also discussed.

Intrinsic Stress of DLC Film Prepared by RF Plasma CVD and Filteredcathodic ARC PVD

Summary form only given. Diamond-like carbon (DLC) films frequently exhibit poor adhesion strength and delaminate instantly due to high internal compressive stress , as high as 8.5 GPa generated in the film, thus resulting in the limitation of the film. Our recent experimental results suggest a functional relationship between the intrinsic compressive stress and the negative biasing voltage applied to the substrate. For the first time, we have obtained DLC compressive stress data as a function of DC bias voltage for films prepared from the C2H2 RF plasma and we compare them with data obtained from the cathodic arc. Although the deposition rate was different, the DLC deposition rate of the filtered cathodic arc being ~1 nm per sec. while the rate in the RF process is approximately 2 nm per min., a similar trend in the stress generation and the stress-relief region was observed in both methods of deposition. The motivation for this study was to establish a coating methodology for DLC that yields a high sp3:sp2 ratio and strong adhesion strength. Such a coating is expected to be hard but not easily delaminated, and would be useful when coated on to steel substrates such as industrial cutting tools, to enhance life performance and cost savings. The preliminary results showed that a thicker DLC film can be obtained by incorporating a lower stress, graphitic layer or a silicon layer.