Surface modification of polytetrafluoroethylene by Ar+ irradiation for improved adhesion to other materials

A surface of thin square polytetrafluoroethylene (PTFE) samples (1 × 1 × 0.2 cm³) was irradiated with Ar⁺ at 1 keV with varying ion dose from 5 × 10¹⁴ to 1 × 10¹⁷ ions/cm² with and without an oxygen environment. The irradiated surface of the samples was examined by scanning electron microscopy (SEM) for surface textural changes and x-ray photoelectron spectrometry (XPS) for changes in chemical structure. A wettability test was conducted on the irradiated surface of PTFE samples by water droplets. A Scotch ™ tape adhesion test, after a thin film of Cu or Al was evaporated on the irradiated surface, and a tensile test after irradiated samples were glued to sample holders by an adhesive glue (Crystal Bond) was also run. The SEM micrographs showed increasing roughness with fiber forest-like texture with increasing ion dose. The Ar⁺ with an O₂ environment produced finer and denser fiber forest-like texture than that without O₂. The high-resolution XPS spectra showed decreased intensity of the F1s peak and formation of the O1s peak when irradiated with the O₂ environment. The increase of the O1s peak may be attributed to the reaction of oxygen atoms and the free radicals created by Ar⁺ bombardment. The wettability of water droplets on the irradiated surfaces was found to be inversely proportional to the surface roughness. Adhesion tests were conducted on 2000 Å thick Al or Cu film. Full detachment of the metal films was observed when PTFE samples were not modified. Partial detachment of the Al film occurred when PTFE was irradiated without the O₂ environment, regardless of ion dose. No detachment of the film occurred when PTFE was irradiated with the O₂ environment with the ion dose exceeding 1 × 10¹⁶ ions/cm². Partial detachment of Cu film was observed with or without the O₂ environment when the ion dose was 5 × 10¹⁴ ions/cm². No detachment occurred with or without the O₂ environment when the ion dose was 1 × 10¹⁵ ions/cm² or greater. The tensile test showed that adhesion of an adhesive cement (Crystal Bond) to the irradiated PTFE samples increased significantly with increasing ion dose up to 1 × 10¹⁶ ions/cm². Possible mechanisms for the improved adhesion are given. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1913–1921, 1997     

Surface treatment of CFRP composites by Ar+ irradiation to improve bonding strength between aluminum and CFRP composites

The effect of surface treatment of carbon fiber reinforced plastic (CFRP) composites on the T-peel strength and the shear strength between CFRP and aluminum panels was studied. The surface of the composite panel was treated with Ar⁺ irradiation under oxygen environment. The optimal Ar⁺ ion dose was determined by measuring the changes of contact angle and surface energy as a function of ion dose. T-peel tests and SLS tests were performed using irradiated CFRP/aluminum specimens and unirradiated CFRP/aluminum specimens to determine the treatment effect by Ar⁺ irradiation under oxygen environment on the T-peel strength and shear strength of CFRP/aluminum composites. The results showed that contact angle on the surface of the composite panel was reduced from ∼80° to ∼8° and the surface energy increased from 31 ergs/cm² to 72.4 ergs/cm² with an ion dose of 10¹⁷ ions/cm². T-peel strength and shear strength are significantly affected by the surface treatment of composite panel. T-peel strength and shear strength improved 650% and 56%, respectively, when the treatment was made with an ion dose of 10¹⁶ ions/cm². SEM examination showed that the improvement of bonding strength was attributed to the uniform spread and fracture of epoxy adhesive.     

Improving adhesion between thin chromium film and polyimide substrate by Ar+ irradiation

Ar⁺ irradiation and annealing at an elevated temperature are used to improve the adhesion of deposited Cr thin films by vacuum evaporation onto polyimide (PI) substrates. The Ar⁺ ions of 50 and 200 keV and various Ar⁺ doses ranging from 1 × 10¹³ to 2 × 10¹⁶ ions/cm² are chosen for the experiments, after many preliminary trials. The surface analyses are conducted employing Rutherford Backscattering Spectroscopy (RBS), Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), and Scanning electron microscopy (SEM). Ar⁺ irradiation produces an interfacial layer of about 100 Å (10 nm) thick in which Cr particles and PI molecules are physically mixed and chemically bonded. The chemical bonds of Cr? O and a trace of Cr?C are observed by XPS and FTIR. Impact-wear tests are also conducted in order to determine the effects of the Ar⁺ irradiation on the wear property of a Cr/PI system. A significant increase in the property is observed and the increase appears to be a function of the degree of adhesion of the Cr film to the PI substrate.     

Surface reaction on polyvinylidenefluoride (PVDF) irradiated by low energy ion beam in reactive gas environment

Polyvinylidenefluoride (PVDF) was irradiated by a keV Ar⁺ ion in O₂ environment for improving adhesion between PVDF and Pt, and reaction between PVDF and the ion beam has been investigated by X‐ray photoelectron spectroscopy (XPS). The adhesion test between Pt and the modified PVDF was carried out by boiling test, in which the specimens were kept in boiling water for 4 h. Two failure modes (buckling up due to weak adhesion and crack formation due to strong adhesion) of Pt films have been observed in the system. Contact angle of PVDF was reduced to 31 from 75° by the irradiation of 1 × 10¹⁵ Ar⁺ ions/cm² with oxygen flow rate of 8 sccm. The surface of the irradiated PVDF became more rough as ion dose increased. The improved adhesion mechanism and identification of newly formed chemical species have been confirmed by Carbon 1s and Fluorine 1s X‐ray photoelectron core‐level spectra. The main reaction occurred at the irradiated PVDF surface is an ion‐beam‐induced oxidation accompanied with preferential sputtering of fluorine. Newly formed chemical species at interface are regarded as ester and carboxyl groups. Adhesion of the Pt–PVDF interface was improved by ion irradiation in O₂ environment. This improvement is originated from the presence of carbon—oxygen bonds on the irradiated PVDF surface. Comparison of failure modes on the irradiated PVDF at various conditions after the boiling test shows that adhesion of Pt film is largely affected by the product of ion‐assisted reaction. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 41–47, 1999     

Surface characterization of polymers modified by keV and MeV ion beams

The present work deals with two different surface modification techniques for altering the surface properties of polymers: plasma treatment and ion implantation. Polymer foils were exposed in an inductively-coupled r.f. (13.56 MHz) plasma system with and without applying a negative high voltage pulse to the sample stage. The influence of low pressure plasmas of oxygen, nitrogen, or argon on the chemical composition, topography, and wettability of polymer surfaces was studied in detail. Etch rates of poly(ethylene terephthalate) for different plasma parameters were monitored. The polymer surface was also modified by a high energy ion beam process. Polyimide films were implanted with different ion species such as Ar⁺, N⁺, C⁺, He⁺, and O⁺ at doses from 1 × 10¹⁵ to 1 × 10¹⁷ ion/cm². Ion energy was varied from 10 to 60 keV for the plasma source ion implantation (PSII) experiment. Polyimide samples were also implanted with 1 MeV hydrogen, carbon, and oxygen ions at a dose of 1 × 10¹⁴ ion/cm². Depending on the ion energy, dose, and ion species, the surface resistivity of the film was reduced by several orders of magnitude. A study on the plasma-treated and ion beam-treated polymer surfaces was performed using TOF-SIMS, XPS, SEM, AFM, and water contact angle measurements.     

Ion-induced electron emission (IIEE) from undoped and B-doped diamond films induced by 1–10 KeV H+ and Ar+

A newly developed experimental system enables measurements of IIEE at a very low ion flux (10⁵ ions/s cm²) avoiding the fast emission degradation caused by high ion fluxes (usually applied 10¹⁰–10¹³ ions/s cm²). The method overcomes the difficulty of measurement of reliable ion-induced secondary electron emission (IIEE) yield, associated with fast degradation of the IIEE yield. We report on the investigation of the IIEE from hydrogenated undoped and B-doped diamond films as a function of (i) moderate heating in vacuum prior to the measurements, (ii) H⁺ and Ar⁺ energy in the range of 1–10 KeV, and (iii) film thickness and microstructure. An IIEE yield (γ) enhancement was typically detected when the films were heated to 300 °C in vacuum. In the B-doped diamond film heated to 300 °C, γ rose nearly linearly from ∼ 20 to ∼ 100 electrons/ion, for 1 to 10 KeV Ar⁺ ions, respectively. The values of γ obtained with H⁺ showed a more moderate, nonlinear increase from ∼ 8 electrons/ion at 1 KeV up to ∼ 90 electrons/ion at 10 KeV. In heated undoped diamond films of different thicknesses the measured values of γ were similar for all the studied films and somewhat lower than in B-doped film: from ∼ 10–16 to 60–70 electrons per 1 to10 KeV Ar⁺, respectively, and from 14–26 to 50–60 electrons per 1 to10 KeV H⁺, respectively. The experimental results were interpreted using TRIM calculations.     

The kinetics of sputtered deposited carbon on silicon: a phenomenological model

A phenomenological model based on the rate equations for the carbon sputter deposition on Si surface is proposed. The processes of carbon adsorption, formation of SiC and transition from sp² to sp³ sites induced by low energy ion bombardment are included. The calibration of the model was performed with the experimental results. The amorphous carbon films were deposited by magnetron sputtering of graphite with Ar⁺ ions. The energy of ions bombarding the growing film was varied by applying a bias voltage on the substrate. It is shown that the non-monotonous kinetics of film growth is determined by the variations of surface composition at different stages of growth.     

Sharpening of CVD diamond coated tools by 0.5−10 keV Ar ion beam

CVD diamond coated tungsten carbide tools have been used for cutting and drilling of soft materials such as aluminum and copper alloys. However, it is very difficult to obtain a tool having a sharp tip of the order of sub-μm by mechanical abrasive polishing methods. Therefore, we applied ion beam processing for sharpening the cutting edge of diamond coated tungsten carbide tools. Result shows that it is possible to obtain a 20-80 nm order tip width of a CVD diamond coated knife processed by a 0.5-10 keV Ar⁺ ion beam, and the sharpening speed of a tip of the knife depends on the ion beam energy. Namely, a tip width of a knife processes by a 1.0 keV Ar⁺ ion beam at an ion dose of 2.7 × 10²⁰ ions/cm² becomes 20 nm, and a tip width of a knife processed by a 10 keV Ar⁺ ion beam at an ion dose of 5.4 × 10¹⁹ ions/cm² becomes 40 nm. However, a facet with an apex angle in the range of 60-100° was formed on the cutting edge of a knife with an initial apex angle of 55°, and we found that the facet angle can be controlled by choosing ion beam energy of 0.5-10 keV. Moreover, results show that the processed knife machined by a 0.5 keV Ar⁺ ion beam has very smooth rake and flank faces, and also has a small line edge roughness of the cutting edge compared to those of the sharpened knife by a 1.0-10 keV Ar⁺ ion beam.     

Adhesion enhancement in Fe-Al2O3 and Cu-Al2O3 metal-ceramic systems induced by ion beam mixing

The ion beam mixing technique is well adapted to treat metal-ceramic interfaces under low temperature and non-equilibrium conditions. Using this technique, we have mixed Cu-Al₂O₃ and Fe-Al₂O₁ interfaces in order to improve the adhesion. Cu and Fe metallic layers having thicknesses of less than ~ 100 nm were deposited on optical grade polished surfaces of sapphire substrates. Ion beam mixing experiments were performed at room temperature with xenon, krypton, argon, and neon ions of various energies and fluences ranging from 10¹⁵ to 4 x 10¹⁶ ions per cm². A linear increase of adhesion with ion mixing was observed for all the ions and systems studied. A strong dependence of adhesion on the energy transfer, controlled by the nature and energy of the incident ions, was observed, allowing us to optimize the adhesion enhancement in the particular case of the Nebombarded Fe-Al₂O₃ interface. The microstructural and chemical effects induced at the interface during the ballistic phase of the mixing process responsible for the adhesion enhancement were characterized by high resolution transmission electron microscopy and associated measurements using X-ray photoelectron (XPS) and Auger electron spectroscopy (AES) as well as conversion electron Mössbauer spectrometry (CEMS). The presence of a non-equilibrium phase formed at the interface in a thin layer (3-5 nm), containing the atoms displaced in the nuclear collision cascades during the short-time ballistic phase of the mixing process, was detected and is responsible for the metal-ceramic adherence.     

Electrical and Structural Properties of Ar+ Implanted Nylon-6 Films

The changes in the structural and electrical properties of nylon-6 films after implantation with an inert gas ion such as Ar⁺, with energy of 285keV and at different dose rates (10¹⁴ to 10¹⁷ ions cm^-2), have been investigated. The conductivity, calculated using the projected range as the thickness of the implanted layer, increases by about four to five orders of magnitude for a dose rate of 5×10¹⁵ ions cm^-2. This is the result of the formation of dangling bonds and free radicals due to implantation. The concentration of free radicals at room temperature measured using an electron spin resonance spectrometer shows that it is proportional to the dose rate up to a certain value, beyond which irradiation-induced damage sets in. The Fourier transform infra-red absorption spectra of the samples indicate certain structural changes due to ion implantation. © of SCI.     

Development of edge state on graphite surface induced by Ar+ irradiation studied using near-edge X-ray absorption fine structure spectroscopy

We have studied the electronic structure of the surface of graphite irradiated by Ar⁺ ions with various kinetic energies using in situ near-edge X-ray absorption fine structure spectroscopy in order to verify the appearance of an edge state over a macroscopic area and the variation of the edge state feature by severely damaging a sample. The disruption of the π bonding network of graphite is manifested by the reduction of the intensity of the π¹ peak upon Ar⁺ irradiation. The increase of the lower energy shoulder of the π¹ peak can be clearly attributed to the edge state of π-electron origin at vacancies. High energy Ar⁺ irradiation strongly induces an amorphous-like structure at the surface where carbon atoms have a random coordination. As a consequence, sp³-hybridized carbon atoms become involved in bonding, resulting in the mixing of π and σ states that then broadens the observed π¹ peak. In addition, the reduction in concentration of π electrons that screen core holes results in a blue shift of the central π¹ peak energy. Moreover, the edge state, which is the signature of π conjugation, survives even at the severely damaged Ar⁺ irradiated graphite surface having an amorphous-like structure.     

Epitaxial growth of β-SiC on Si (100) by low energy ion beam deposition

Epitaxial β-silicon carbide (SiC) films on mirror-polished (100) Si substrates were deposited using low energy (150 eV) ion beam modification at different ion doses (1×10¹⁷/cm², 1×10¹⁸/cm², 1×10¹⁹/cm²). The Si substrates were exposed to a broad ion beam of hydrocarbon, argon, and hydrogen ions, generated in a Kaufman ion source. These ions reacted with the Si substrates and formed the epitaxial β-SiC films. Amorphous carbon films were generated on top of β-SiC films. Some voids were found with transmission electron microscopy (TEM) at the interface between the Si substrate and the β-SiC film. By studying the ion dose dependence of the quality and thickness of the SiC and amorphous carbon films, we suggest that the formation of the epitaxial β-SiC was driven by thermal diffusion of Si atoms in SiC and preferential etching of non-epitaxial SiC crystals by H ions.     

Free volume-limited diffusion in ion-modified polymers

Iodine diffusion in ion-modified polyethylene (PE) using the Rutherford Backscattering method (RBS) has been studied. PE was irradiated by N⁺, Ar⁺ and As⁺ ions with an energy of 150 keV and doses of 1 X 10¹³−1 × 10¹⁵ cm⁻². Iodine diffused in ion-modified PE from vapor at 90°C. Iodine's concentration profile changed its shape dramatically for ion doses over 1 × 10¹⁴ cm⁻² when it showed two maxima. A similar profile was exhibited by oxygen, which diffused in PE on implantation. Iodine's concentration dropped in the layer where the most significant polymer carbonization occurred. This range was found ahead of the implanted ions concentration. Iodine diffusion was most intensive for lower ion doses (≤1 × 10¹⁴ cm⁻²) while for higher doses it was substantially slower due to PE carbonization. The reason was the lower free volume in the PE carbonized layer as compared with the layer where the polymer's degradation was not reflected in such a significant increase in carbon content. © 1996 John Wiley & Sons, Inc.     

Spectroscopic Investigation of Quantum Confinement Effects in Ion Implanted Silicon-on-Sapphire Films

Crystalline Silicon-on-Sapphire (SOS) films were implanted with boron (B⁺) and phosphorous (P⁺) ions. Different samples, prepared by varying the ion dose in the range 10¹⁴–5 × 10¹⁵ and ion energy in the range 150–350 keV, were investigated by the Raman spectroscopy, photoluminescence (PL) spectroscopy and glancing angle x-ray diffraction (GAXRD). The Raman results from dose dependent B⁺ implanted samples show red-shifted and asymmetrically broadened Raman line-shape for B⁺ dose greater than 10¹⁴ ions cm⁻². The asymmetry and red shift in the Raman line-shape is explained in terms of quantum confinement of phonons in silicon nanostructures formed as a result of ion implantation. PL spectra shows size dependent visible luminescence at ∼1.9 eV at room temperature, which confirms the presence of silicon nanostructures. Raman studies on P⁺ implanted samples were also carried out as a function of ion energy. The Raman results show an amorphous top SOS surface for sample implanted with 150 keV P⁺ ions of dose 5 × 10¹⁵ ions cm⁻². The nanostructures are formed when the P⁺ energy is increased to 350 keV by keeping the ion dose fixed. The GAXRD results show consistency with the Raman results.     

Effect of oxides on the adhesion of Cu films deposited onto stainless steel by electron shower and thermal evaporation methods

When Cu films were deposited by thermal evaporation onto stainless steel substrates at 30°C, the oxygen gas in the vacuum chamber (1.5 x 10^-3 Torr) caused the adhesion of Cu films to increase from 3 to 5 MPa. Moreover, it increased further from 13 to 16 MPa when deposited at 300°C. The Cu film was not peeled off when deposited by the electron shower method and the epoxy resin failed (20 MPa), and this was independent of the addition of oxygen gas. As the chemical shift of Cu 2_p3/2 was observed at the interface between the Cu film and the substrate when oxygen gas was added, it is concluded that the adhesion is mainly determined by the chemical bonding, such as CuO and Cu₂O. The depth profile of Cu 2_p3/2 measured by X-ray photoelectron spectroscopy (XPS) using Ar etching showed apparent thermal diffusion of Cu into the substrate. But the Ar etching rate was decreased by Cu oxides at the interface. The amount of oxides depended on the substrate temperature and the deposition method for Cu film. Therefore, the depth profile of Cu measured by XPS did not represent the thermal diffusion of Cu into the substrate correctly. When the etching rate was modified, the diffusion of Cu was almost the same for different samples deposited at the same temperature, and the effect of the thermal diffusion on the adhesion was small. The adhesion on hydrated [Cr(OH)₃.0.4H₂O] and hydroxide [Cr(OH)₃] surfaces was lower than that on the oxide (Cr₂O₃) surface. In other words, the pretreatment of the substrates was very important to the adhesion.     

Influence of 27Al+ ion mixing on the adhesion and interfacial chemistry of Ni films on polyimide and polyester

In order to evaluate the influence of ion chemistry on ion-induced interfacial chemistry and thin film adhesion, 30 nm Ni films on polyester (PET) and polyimide (PI) substrates were implanted with various doses (1-10 x 10¹⁶ Al/cm²) of 50 keV ²⁷Al⁺. The ion-induced interfacial chemistry and adhesion were then examined using X-ray photoelectron spectroscopy (XPS) and scratch testing, respectively. The implantation induced extensive interfacial mixing in both types of specimens. In addition, the implanted Al reacted with oxygen in the polymer substrates to form interfacial Al₂O₃ and Al-O-C layers in the Ni/PET and Ni/PI specimens, respectively. Despite the ion-induced interfacial mixing and compound formation, the scratch testing indicated that no significant adhesion enhancement was produced by the ²⁷ Al⁺ ion mixing. The absence of adhesion enhancement was attributed to the absence of complete chemical bonding between the Ni films and the polymer substrates. Criteria for the selection of an effective reactive ion for adhesion enhancement in a given film/substrate system are discussed.     

Optimization of etching parameters of a fluorinated polyimide using the RIBE technique

A parametric study of etching a new type of fluorinated polyimide (6FDA-ODA) has been carried out. This kind of material was especially elaborated for plasma etching (reactive ion etching, RIE); its behaviour was tested with the reactive ion beam etching (RIBE) technique which uses an (O⁺) reactive ion beam and allows independent control of the ion energy and current density of the beam. Etch rates were measured as a function of energy (E), current density (J) and incident angle (θ) of the beam with the sample normal. These rates were shown to present a maximum value (1000Åmin^-1) for an energy flux of about 3Wcm^-2 (E=6keV and J=0·5mAcm^-2) and decreased when θ increased. These results were then compared with etching rates obtained with chemically inert ions (Ar⁺): in this case, etching rates were five times lower than those measured with O⁺ ions. © 1998 Society of Chemical Industry     

Increase the current density and reduce the defects of ZnO by modification of the band gap edges with Cu ions implantation for efficient,flexible dye-sensitized solar cells (FDSSCs)

Flexible dye-sensitized solar cells (FDSSCs) have good potential in future photovoltaic technology. The spin coating method deposited the ZnO films on indium-tin-oxide-coated polyethylene terephthalate (ITO-PET) flexible plastic substrates. These films are implanted with Cu-ions with 1 × 10¹³ ions/cm², 1 × 10¹⁴ ions/cm², and 1 × 10¹⁵ ions/cm². All the films have a hexagonal structure. The film irradiated with 1 × 10¹⁴ ions/cm² showed high crystallinity and crystallite size. Important optical properties like bandgap energy (E_g), band edges, refractive index, extinction coefficient, and dielectric constants are measured by UV–Vis spectroscopy. Bandgap energy decreases, and the refractive index increases at the fluence of Cu ions. The maximum decrease in E_g is observed at the 1 × 10¹⁴ ions/cm² dose. Photoluminescence spectra suggest that defects-related emission peaks are decreased at 1 × 10¹⁴ ions/cm² Cu ions fluency. J-V measurements have significantly improved photovoltaic performance compared to pristine ZnO-based solar cells. The highest efficiency (2.30%) is observed at a 1 × 10¹⁴ ions/cm² dose. The efficiency increase is related to improving the charge transfer ratio and shifting the fermi level toward the conduction band.     

The Adhesion of Evaporated Copper to Dow Cyclotene 3022®, Determined by Microscratch Testing

The mechanical integrity, stability, and strong interfacial adhesion between Cu, a high conductivity metal, and Dow Cyclotene 3022^®, a low permittivity polymer, are important for their application in future high-speed microelectronic devices. In the present study, Cu was deposited by both evaporation and sputtering, and various Cyclotene surface modifications were carried out. These modifications included low pressure N₂ plasma and Ar⁺ treatments and the use of a Ti interlayer. The adhesion was evaluated by use of the microscratch test, and complemented by an adhesive tape peel test and XPS. The N₂ plasma treatment was found to lead to a dramatic increase in adhesion, which was influenced to a minor extent by the adhesion promoter that was used at the Cyclotene/Si substrate interface. This significant Cu/Cyclotene adhesion enhancement is interpreted in terms of the chemical groups present at the Cyclotene surface and the bonds formed on Cu deposition.     

Nonlinear optical properties of poly‐ortho‐toluidine films implantated by N+ ions with different energy

This article reports experimental work on the effect of N⁺ ion implantation on third‐order nonlinear optical properties of POT films. Using K₂Cr₂O₇ as oxidizing agent, poly‐ortho‐toluidine (POT) was synthesized in 1 M hydrochloric. The POT films were prepared by spin‐coating method and then implantated by N⁺ ions (15–30 KeV) at a dose 1.9 × 10¹⁶ ions/cm². The films were characterized by FT‐IR spectroscopy, visible spectroscopy and SEM, their third‐order nonlinear optical susceptibility (χ⁽³⁾) were also examined by a degenerate four‐wave mixing (DFWM) system at 532nm. Compared to pristine POT films, the optical band gap obtained from visible spectra decreased from 3.58 to 3.48 eV when the energy was 30 KeV. Also, The χ⁽³⁾ value of implantated POT films increased from 3.31 × 10⁻¹⁰ esu to 4.04 × 10⁻⁹ esu when the implantated energy was 25 KeV. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers