Low-energy Oxygen Ion Bombardment Research Articles

Amendment the surface structure and optical properties of Makrofol LT by low energy oxygen ion bombardment

Ion beam bombardment is a powerful technique to improve the surface properties of polymeric materials without changing the bulk properties. Herein, Makrofol LT films were bombarded with low energy of oxygen ions at different fluences ranging from 11 × 1017 to 44 × 1017 ions/cm2. X-ray diffraction, FTIR spectroscopy, surface-roughness tester, ultraviolet–visible spectroscopy, and Fluorescence spectroscopy were used to examine the change in the structure, chemical functional groups, alteration in surface roughness parameters, and photo-physical properties. The obtained results evidenced that the ordering and disordering structure of bombarded Makrofol LT films were influenced by ion beam irradiation according to the ion fluence. The FTIR spectroscopy of functional group examination revealed the possibility of the presence of sp2-carbon clusterization and amorphization. The surface roughness parameters increase as the ion fluences increase. Optical measurements exhibit a shift of absorption-edge towards the visible zone that correlated to the surface damage and the creation of CC bonds. The fluorescence spectra exhibit that the yield intensities decrease with increasing ion fluences. This refers to improvement in the radiative-recombination rate relative to non-radiative recombination. This is attributable to the growth of clusters, the increase of density states of the surface, and the increase in the surface roughness of the bombarded samples.

Suppression of self-organized surface nanopatterning on GaSb/InAs multilayers induced by low energy oxygen ion bombardment by using simultaneously sample rotation and oxygen flooding

Time of flight secondary ion mass spectrometry (ToF-SIMS) is a well-adapted analytical method for the chemical characterization of concentration profiles in layered or multilayered materials. However, under ion beam bombardment, initially smooth material surface becomes morphologically unstable. This leads to abnormal secondary ion yields and depth profile distortions. In this contribution, we explore the surface topography and roughening evolution induced by O2+ ion bombardment on GaSb/InAs multilayers. We demonstrate the formation of nanodots and ripples patterning according to the ion beam energy. Since the latter are undesirable for ToF-SIMS analysis, we managed to totally stop their growth by using simultaneously sample rotation and oxygen flooding. This unprecedented coupling between these two latter mechanisms leads to a significant enhancement in depth profiles resolution.

Oksidacija molibdena z nizkoenergetskim kisikovim ionskim obstreljevanjem

Oksidacija molibdena z nizkoenergetskim kisikovim ionskim obstreljevanjem

Formation of self-organized nano-surfaces on III–V semiconductors by low energy oxygen ion bombardment

Pattern formation on surfaces of III–V compound semiconductors GaAs, GaSb, and InSb by O2+ ion sputtering was studied. For GaAs, a ripple pattern was observed under a 2-keV primary beam energy for two ion fluences, i.e., 3.1×1018 ions/cm2 and 5.4×1018 ions/cm2. The pattern wavelengths were 175nm and 200.2nm. A bubble-like structure was observed on the GaSb surface bombarded with 1-keV and 2-keV oxygen ions. In the case of InSb, several pyramidal structures with sub-micrometer dimensions were observed when the ion energy was 1keV. When the ion energy was increased to 2keV, the pyramidal structures acquired micrometer dimensions and a ripple pattern with a wavelength of 246nm was observed in the surrounding area.

Electronic structure of nitinol surfaces oxidized by low-energy ion bombardment

We have studied the electronic structure of nitinol exposed to low-energy oxygen-ion bombardment, using x-ray photoemission spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. XPS spectra reveal a gradual transformation of nitinol surfaces into TiO2 with increased dose of implanted oxygen. No oxidation of Ni atoms has been detected. NEXAFS spectra around O K-edge and Ti L2,3-edge, reflecting the element-specific partial density of empty electronic states, exhibit features, which can be attributed to the creation of molecular orbitals, crystal field splitting, and the absence of long-range order, characteristic of the amorphous TiO2. Based on these results, we discuss the oxidation kinetics of nitinol under low-energy oxygen-ion bombardment.

Deposition of SiO 2 films by low-energy ion-beam induced chemical vapor deposition using hexamethyldisiloxane

Room-temperature preparation of silicon dioxide films with smooth surfaces and small carbon was achieved by low-energy ion beam induced chemical vapor deposition (IBICVD) with a bubbling system for hexamethyldisiloxane (HMDSO). When prepared using bubbled HMDSO and assisted O 2 gas under irradiation of 150 eV Ar ions, the film contained carbon of 0.2% and the root mean square of the surface roughness of the film was 2.0 nm. However, when prepared using the bubbled HMDSO under irradiation of 150 eV oxygen ions, the film contained carbon less than 0.1%, and the surface roughness was 0.25 nm. It is considered that low-energy oxygen ion bombardment promotes not only chemical reaction and dissociation of HMDSO but also reactive ion beam etching on the film surface.

Comparison of surface morphologies of SiO 2 films prepared by ion-beam induced chemical vapor deposition and ion-beam assisted deposition

The surface topographies of silicon dioxide films prepared by low-energy ion-beam induced chemical vapor deposition (IBICVD) and ion-beam assisted deposition (IBAD) were studied using an atomic force microscopy (AFM). In the case of IBICVD, when prepared using bubbled hexamethyldisiloxane (HMDSO) and assisted O 2 gas under irradiation of 150 eV Ar ions, the root mean square (RMS) of the surface roughness of the film was 2.0 nm. However, when prepared using the bubbled HMDSO under irradiation of 150 eV oxygen ions, the RMS deduced to 0.25 nm. In the case of IBAD, when deposited using evaporated silicon monoxide under irradiation of 150 eV oxygen ions, the RMS was 0.20 nm. As a reference, the RMS of fused silica was changed from original 0.70–0.40 nm after irradiated of 150 eV oxygen ions. It is concluded that low-energy oxygen ion bombardment not only promotes chemical reaction and dissociation of precursor but also leads to a smooth surface due to reactive ion beam etching on the film surface.

On the migration behavior of metal impurities in Si during secondary ion mass spectrometry profiling using low-energy oxygen ions

Secondary ion mass spectrometry (SIMS) was used to investigate the segregation of several metal impurities in Si under low-energy oxygen ion bombardment. Our results suggested that both the segregation of Ca, Cr, and Ta at the SiO2/Si interface, and the antisegregation of Ti, Hf, and Zr into the oxide were thermodynamically driven. The migration behavior of Ca indicates that CaO, having a higher heat of formation than Si, was most probably formed under oxygen bombardment. Sharper in-depth profiles were obtained for Ti, Zr, and Hf (metals with lower heat of oxide formation than Si) by bombarding at angles of incidence for which a stoichiometric surface oxide is formed. The effect of impurity diffusivity is demonstrated through SIMS measurements at elevated temperatures (∼350–380 °C) for Cr, Zr, Ta, and Ti.

Structures and electrical properties of barium strontium titanate thin films grown by multi-ion-beam reactive sputtering technique

The structure and electrical properties of multi-ion beam reactive sputter (MIBERS) deposited barium strontium titanate (BST) films were characterized in terms of Ba/Sr ratio, substrate temperature, annealing temperature and time, film thickness, doping concentration, and secondary low-energy oxygen ion bombardment. Films deposited onto unheated substrates, followed by annealing at 700 °C showed lower dielectric constant (<200), compared to a dielectric constant of about 560 for those deposited at elevated temperatures, probably due to reduced voids. Two types of microstructures (type I and type II) were observed depending on the incipient phase of the as-grown films, which also led to two types of time domain dielectric response, Curie-von Schweidler and Debye type, respectively. The current-voltage (I-V) characteristics of type II films doped with high donor concentration showed a bulk space-charge-limited conduction (SCLC) with discrete shallow traps embedded in a trap-distributed background at high electric fields. The I-V characteristics of bombarded films deposited at higher substrate temperatures showed promising results of lower leakage currents and trap densities.

Direct observation of the etching of damaged surface layers from natural diamond by low-energy oxygen ion bombardment

The interaction of oxygen ions with diamond surfaces is reported. Using electron energy loss spectroscopy (EELS), we found that 200 eV oxygen ion bombardment removed surface damaged layers (non-sp3 bonded), recovering diamond EELS features in the surface region, Higher-energy oxygen ion bombardment does not produce surfaces as ideal as the 200 eV case. The oxygen surface concentration after the 200 eV oxygen ion irradiation, examined using Auger electron spectroscopy, was determined to be ∼1×1015 cm−2.

Enhanced electrical properties of ferroelectric Pb(Zr0.5, Ti0.5)O3 thin films grown with low-energy oxygen ion assistance

Electrical properties pertinent to memory applications of ferroelectrics are systematically characterized for multi-ion-beam reactive sputter deposited Pb(Zr0.5, Ti0.5)O3 thin films. The processing dependence of electrical properties of the films offers an opportunity for property modification. Low-energy oxygen ion bombardment assistance is useful in this aspect. Under optimal bombardment conditions (ion/atom ratios between 1.0 and 1.3; ion/energies ranging from 60 to 80 eV), many electrical properties can be beneficially modified. Relative to the nonbombarded films, the bombarded films exhibit increases in remanent polarization and resistivity, and reductions in coercive field. Bombardment-enhanced properties also include switching characteristics, dielectric responses, switching endurance, polarization retention, dc current-voltage behavior, and time-dependent dielectric breakdown strength. The experimental results are explained in correlation to processing and structure of the films. The roles of preferential orientation, crystallinity, degree of imperfection, grain size, and grain boundaries of the films are emphasized.

Property modification of ferroelectric Pb(Zr,Ti)O3 thin films by low-energy oxygen ion bombardment during film growth

Low-energy oxygen ion bombardment is being used to enhance the electrical properties of multi-ion beam sputter deposited ferroelectric Pb(Zr,Ti)O3 thin films. The degree of (100) orientation, remnant polarization (Pr), coercive field (Ec), and dielectric constant (k) of the films were chosen to properly quantify the bombardment effect. It was found that these properties are strongly dependent on the ion beam flux and bombarding ion energy. The ion/atom ratios between 1.0 and 1.3 and the bombarding energies within the range of 60–80 eV are optimal to realize desirable property modification. Relative to the nonbombarding case, the bombardment could increase the Pr and k by up to 60% and 25%, respectively, and reduce the Ec by about 20%.

The effects of concurrent oxygen ion bombardment on ion beam sputtered Y 1Ba 2Cu 3O x thin films

We have investigated the effects of substrate ion bombardment and microwave electron cyclotron resonance (ECR) assisted processing on the microstructural and electrical properties of ion beam sputtered Y 1Ba 2Cu 3O x thin films. Substrate bombardment was performed using a Kaufman-type ion source or a microwave ECR gridless ion source. While substrate bombardment has been found to change the properties of the films, only in the case of ECR-assisted deposition was any sign of superconductivity observed in the as-deposited films. Results indicate that low energy oxygen ion bombardment, at low ambient pressures, simulates a high oxygen pressure ambient.

Growth mechanism of thin oxide films under low-energy oxygen-ion bombardment

Bombardment of silicon surfaces by low-energy oxygen ions has been investigated as a possible process for growing films of SiO2 at room temperature. Broad ion beams of energy 40–200 eV and variable oxygen content have been used to grow ultrathin oxides of extremely uniform thickness. The ion beam oxides are similar to thin thermal oxides in many respects—composition, chemical binding, optical, and electrical properties. The dependence of the thickness and quality of the oxide films on ion dose, ion energy, and substrate temperature have been investigated. The obtained thickness is observed to vary only slightly with increasing substrate temperature up to 650 °C which indicates nonthermal process kinetics. The ion-beam oxides reach a limiting thickness of 40–60 Å which is largely independent of ion dose and is also found to be insensitive to ion energy. The observed oxidation is explained on the basis of surface implantation and radiation-enhanced diffusion and reaction processes. Limited thicknesses are observed even when sputtering is negligible because of the decreasing effective penetration of the ions due to the swelling of the target which accompanies the conversion of Si to SiO2. Thus the film grows until the oxide–semiconductor interface moves beyond the current-ion penetration depth after which oxidation effectively stops. This model is equally applicable to high-energy, high-dose oxygen-ion implantation for production of buried oxides in silicon-on-insulator technology where it is observed that oxide growth occurs predominantly at the upper interface.

Carbon monoxide production in low energy oxygen ion bombardment of pyrolytic graphite and Kapton surfaces

We report the results of an investigation of the interaction of low energy oxygen ions with pyrolytic graphite and Kapton surfaces. CO molecules emitted from the surface as a result of the ion bombardment were detected by a mass spectrometer. Because the ion-induced signals were small compared to that arising from the CO background pressure in our vacuum system, the ion beam was modulated and the modulated component of the CO signal measured with a lock-in amplifier. The quantum yield (CO molecules emitted per incident oxygen ion) for graphite rose from 1.9 at 4.5 eV ion energy to 6.6 at 465 eV. Comparable yields were obtained for Kapton. The large size of our yields suggests contributions to the reaction process from the background O2 molecules in our vacuum system.