W. W. R. Araújo

Low cost ion implantation technique

We describe an approach to ion implantation in which the plasma and its electronics are held at ground potential and the ion beam is formed and injected energetically into a space held at high negative potential. The technique allows considerable savings both economically and technologically, rendering feasible ion implantation applications that might otherwise not be possible for many researchers and laboratories. Here, we describe the device and the results of tests demonstrating Nb implantation at 90 keV ion energy and dose about 2 × 1016 cm−2.

Spontaneous wrinkling of soft matter by energetic deposition of Cr and Au

Wrinkling of stiff thin films deposited on compliant substrates is an effect that has been broadly investigated. However, wrinkling consequent to metal ion implantation has been less studied. In the work described here, we have explored the sub-micron wrinkling phenomena that spontaneously occur when metal ions (Au and Cr) are implanted with energy of a few tens of electron volts (49 eV for Au and 72 eV for Cr) into a compliant material (PDMS). This very low energy ion implantation was performed using a Filtered Cathodic Vacuum Arc technique, a process often referred to as energetic deposition or energetic condensation. For comparison, Au and Cr depositions with similar doses were also done using a sputtering technique (with lower particle energy of approximately 2 eV), and no wrinkle formation was then observed. In this way, we can discuss the role of ion energy in wrinkle formation. Depth profiles of the implanted material were calculated using the Tridyn computer simulation code for each metal, for sev...

Cell adhesion and growth on surfaces modified by plasma and ion implantation

In this study, we show and discuss the results of the interaction of living CHO (Chinese Hamster Ovary) cells, in terms of adhesion and growth on glass, SU-8 (epoxi photoresist), PDMS (polydimethylsiloxane), and DLC (hydrogen free diamond-like carbon) surfaces. Glass, SU-8, and DLC but not PDMS showed to be good surfaces for cell growth. DLC surfaces were treated by oxygen plasma (DLC-O) and sulfur hexafluoride plasma (DLC-F). After 24 h of cell culture, the number of cells on DLC-O was higher than on DLC-F surface. SU-8 with silver implanted, creating nanoparticles 12 nm below the surface, increased significantly the number of cells per unit area.

Isotropic and anisotropic wrinkling of diamond-like carbon films on polydimethylsiloxane substrates

We describe experimental results about the spontaneous wrinkling of diamond-like carbon films over the thickness range 2 nm–58 nm, grown on polydimethylsiloxane (PDMS) substrates with a 5 nm gold film deposited as adhesion layer. Using Atomic Force Microscopy data with suitable processing, we explore both isotropic and anisotropic wrinkling, the latter done by creating trench structures on PDMS substrates. We show new non-predictable results based on the known literature.

Environmental effects in kelvin force microscopy of modified diamond surfaces

We have explored the effects of atmospheric environment on Kelvin force microscopy (KFM) measurements of potential difference between different regions of test polycrystalline diamond surfaces. The diamond films were deposited by microwave plasma‐assisted chemical vapor deposition, which naturally produces hydrogen terminations on the surface of the films formed. Selected regions were patterned by electron‐beam lithography and chemical terminations of oxygen or fluorine were created by exposure to an oxygen or fluorine plasma source. For KFM imaging, the samples were mounted in a hood with a constant flow of helium gas. Successive images were taken over a 5‐h period showing the effect of the environment on KFM imaging. We conclude that the helium flow removes water molecules adsorbed on the surface of the samples, resulting in differences in surface potential between adjacent regions. The degree of water removal is different for surfaces with different terminations. The results highlight the importance of taking into account the atmospheric environment when carrying out KFM analysis.

Gold nanoparticle formation in diamond-like carbon using two different methods: Gold ion implantation and co-deposition of gold and carbon

We describe work in which gold nanoparticles were formed in diamond-like carbon (DLC), thereby generating a Au-DLC nanocomposite. A high-quality, hydrogen-free DLC thin film was formed by filtered vacuum arc plasma deposition, into which gold nanoparticles were introduced using two different methods. The first method was gold ion implantation into the DLC film at a number of decreasing ion energies, distributing the gold over a controllable depth range within the DLC. The second method was co-deposition of gold and carbon, using two separate vacuum arc plasma guns with suitably interleaved repetitive pulsing. Transmission electron microscope images show that the size of the gold nanoparticles obtained by ion implantation is 3–5 nm. For the Au-DLC composite obtained by co-deposition, there were two different nanoparticle sizes, most about 2 nm with some 6–7 nm. Raman spectroscopy indicates that the implanted sample contains a smaller fraction of sp3 bonding for the DLC, demonstrating that some sp3 bonds ar...

A high voltage pulse power supply for metal plasma immersion ion implantation and deposition

We describe the design and implementation of a high voltage pulse power supply (pulser) that supports the operation of a repetitively pulsed filtered vacuum arc plasma deposition facility in plasma immersion ion implantation and deposition (Mepiiid) mode. Negative pulses (micropulses) of up to 20 kV in magnitude and 20 A peak current are provided in gated pulse packets (macropulses) over a broad range of possible pulse width and duty cycle. Application of the system consisting of filtered vacuum arc and high voltage pulser is demonstrated by forming diamond-like carbon (DLC) thin films with and without substrate bias provided by the pulser. Significantly enhanced film∕substrate adhesion is observed when the pulser is used to induce interface mixing between the DLC film and the underlying Si substrate.

On the influence of PDMS (polydimethylsiloxane) substrate surface energy in wrinkling of DLC (diamond-like carbon) thin films

We have explored the influence of surface energy of the PDMS (polydimethylsiloxane) substrate on the wrinkling of diamond-like carbon thin films. The surface energy of PDMS can be tuned by exposure to oxygen plasma or by shallow-implantation of gold. The result is an increase in the wrinkling wavelength and amplitude. By means of a tri-layer wrinkling model, we discuss whether the major contribution to the wavelength variation is via the surface energy of the substrate or via the mechanical properties of the interface layer resulting from the surface treatment. We conclude that the surface energy of the substrate is an important property that must be considered in order to provide a complete description of wrinkling phenomena.We have explored the influence of surface energy of the PDMS (polydimethylsiloxane) substrate on the wrinkling of diamond-like carbon thin films. The surface energy of PDMS can be tuned by exposure to oxygen plasma or by shallow-implantation of gold. The result is an increase in the wrinkling wavelength and amplitude. By means of a tri-layer wrinkling model, we discuss whether the major contribution to the wavelength variation is via the surface energy of the substrate or via the mechanical properties of the interface layer resulting from the surface treatment. We conclude that the surface energy of the substrate is an important property that must be considered in order to provide a complete description of wrinkling phenomena.

Cell growth on 3D microstructured surfaces.

Chinese Hamster Ovary (CHO) cell cultures were grown on surfaces lithographed with periodic 3D hexagonal microcavity array morphology. The range of microcavity size (inscribed circle diameter) was from 12 μm to 560 μm. CHO cells were grown also on flat surfaces. The characterization was performed with respect to cell growth density (number of nuclei per unit area) by fluorescence optical microscopy and evaluated by correlation function analysis. We found that optimum microcavity radius was 80 μm, concerning to the maximum cell growth density, being even greater than the growth density on a flat (unstructured) substrate of the same material. This finding can be important for optimization of biotechnological processes and devices.