Surface morphology analysis of natural single crystal diamond chips bombarded with Ar ion beam

We have studied the surface morphology of natural single crystal diamond chips machined by 0.5-3.0 keV Ar⁺ ion beam irradiation at ion incidence angles of 0°, 30°, 45°, 60°, and 80° with ion doses from 3.4 × 10¹⁸ ions/cm² to 6.8 × 10¹⁸ ions/cm². The surface of diamond chips machined with 0.5 and 1.0 keV Ar⁺ ion beam, at angles of ion incidence from 0° to 45° can be made smooth. Results show that the machined surface at ion dose of 6.8 × 10¹⁸ ions/cm² and beam energy of 0.5 and 1.0 keV become ultra-smooth (surface roughness SR = 0.1 nm rms) compared with unprocessed surface (SR = 0.15-2.1 nm rms). Results also confirm the ripple formation on diamond surface at ion incidence angles of 60°-80° by 0.5-3.0 keV Ar⁺ ion beam. Therefore, the technique of smoothing by choosing ion beam irradiation parameter can be applicable to nano-finishing of diamond tools without ripple formation. This technique can also be applicable in mass production if the diamond surface is mechanically pre-finished.     

Transmission functions of an energy-mass spectrometer and energy spectra vs. emission angle data for silicon secondary ions

Results of a computer simulation of the propagation of ions through an energy mass analyzer comprising 90° and 180° spherical deflectors, transport lenses, and a quadrupole mass spectrometer are reported, which give the apparatus function of the analyzer for two operating modes. These functions were used to improve the experimental energy spectra for silicon secondary ions Si⁺, Si²⁺, and Si₂⁺ measured under 10 keV Ar ion bombardment of a silicon surface. The observed shift of energy spectra maxima with angle of emission was explained in terms of the concept of a local electron excitation in the collision cascade region. This model, developed earlier for metals, was shown to adequately describe the principal regularities of the secondary ion emission from semiconductors.     

SIMS and GDMS depth profile analysis of hard coatings

Rapid development in hard coating technology calls for simple construction depth profile analysers. Here we present results of depth profile analysis of a set of Ar arc plasma deposited TiN, CrN layers. The results are obtained with the use of recently constructed simple glow discharge mass spectrometer (GDMS) and compared with secondary ion mass spectrometer (SIMS). In SIMS (SAJW-05 model) we apply 5 keV Ar⁺ ion beam of about 100 μm in diameter. Digitally controlled spiral scanning of primary ion beam is performed over 1.6 mm² area. Secondary ions are extracted from the central part due to an “electronic gate” and analysed by quadrupole mass spectrometer QMA-410 Balzers (16 mm rods).GDMS analyses are performed on SMWJ-01 glow discharge prototype spectrometer. To supply discharge in 1 hPa argon we use 1.5 kV DC voltage. The analysed sample works as a cathode in a discharge cell. Area of the analysis is ∼4 mm² due to the use of secondary cathode—high purity tantalum diaphragm. Sputtered atoms are ionised, next extracted into the analytical chamber and finally analysed by the quadrupole mass analyser SRS-200 (6 mm rods).The results show that the use of simple construction GDMS analyser allows obtaining similar or even slightly better depth resolution than it can be obtained in the SIMS spectrometer. Application of glow discharge analysis opens new possibilities in direct quantitative depth profile analysis of hard coatings.     

Quadrupole-based glow discharge mass spectrometer: Design and results compared to secondary ion mass spectrometry analyses

A design of quadrupole-based glow discharge mass spectrometer is briefly presented. A glow discharge occurs when a DC voltage (up to 3 kV) is applied between two electrodes in a cell filled with Ar at ∼1 hPa pressure. In this configuration, the sample acts as the cathode, and its surface (∼12 mm²) is sputtered by impacting Ar ions. The sputtered neutral atoms are ionised downstream in the plasma, and are extracted through a diaphragm to an energy filter and quadrupole spectrometer (6 mm rods) in high vacuum. The processes of sputtering and ionisation are separated, therefore reducing matrix effects.Preliminary results of elemental analysis of stainless steel, chromium-vanadium steel, Al-Mg-Cu and Armco alloys are presented. These results are compared to secondary ion mass spectrometry (SIMS) results obtained for the same set of samples using a 5 keV Ar⁺ ion beam and a quadrupole mass analyser (16 mm rods). The glow discharge mass spectrometry (GDMS) results allowed us to find SIMS relative sensitivity factors (RSF) for the analysed materials. Simple design and quick analysis time makes the new GDMS analyser an attractive tool in material technology.     

Secondary ion emission from Ti and Si targets induced by medium energy Ar ion bombardment - Experiment and computer simulation

The paper presents experimental results of secondary ion energy distributions obtained for Ti and Si targets bombarded by 20-30 keV monoisotope Ar⁺ ion beam. The influence of the extraction voltages between target and a slit of the electrostatic energy analyzer entrance on the energy distributions of secondary ions was investigated. After optimization of the secondary ion extraction system, the mass spectra of secondary ions were also measured. The investigations were done using recently built experimental system. Experimental data are compared with the computer simulation results obtained using TRQR and SATVAL codes.     

Generation processes of super-high-energy atoms and ions in magnetron sputtering plasma

Energy distribution function (EDF) of ion species (Ar⁺, Kr⁺, Xe⁺) in a rare gas magnetron plasma is measured at a substrate position, 0.1 m away from the target surface, by energy-resolved mass spectrometry. The measured ion EDF contains, besides a bulk low-energy part (<10 eV), a tail part of super-high energy on an order of 100 eV, depending on the mass ratio of ion species to target material (tungsten, permalloy (80% Ni, 20% Fe)). A weak electric field in a diffusion region of magnetron plasma cannot accelerate slow bulk ions of ∼0.2 eV to such high energies. Origin of large kinetic energies is attributed to the backscattering process on the target surface where, e.g., Ar⁺ ions impinging on the target are neutralized and reflected as fast Ar atoms of the kinetic energy approximately given by a two-body collision model. Subsequently, a part of fast atoms may be converted to fast ions in three possible collision processes in the diffusion region: (i) electron impact ionization (ii) resonant charge exchange, and (iii) ionization of slow atoms by fast atoms. Among them, the third process is found to be dominant from Monte Carlo simulations where the backscattering process is evaluated by the TRIM code. Furthermore, when the target mass is larger than the bombarding ion mass, the substrate is bombarded by the super-high-energy atoms having a flux 2-4 orders of magnitude larger than the fast-ion flux.     

The influence of sputtering on FeSi

The effect of different (0.5, 2 and 4 keV) Ar⁺ energy ions on (a) the composition of an FeSi surface, (b) the oxidation of the FeSi surface after bombardment, and (c) the segregation of silicon after bombardment, has been monitored by Auger electron spectroscopy. Silicon was found to be preferentially sputtered by the Ar⁺ ions at all the different energies during bombardment. This effect was more pronounced at the 0.5 keV ion energy bombardment. There was a slight increase in the oxidation rate from the higher to the lower Ar⁺ ion energy at which the sample was sputtered before oxidation. The rate of silicon diffusion to the surface at 593 K after the sample had been sputtered, was lower when the sample had been sputtered by 0.5 keV ions than by 2 keV ions.     

In-situ analyses on the reactive sputtering process to deposit Al-doped ZnO films using an Al-Zn alloy target

The kinetic energies of generated ions were investigated during the reactive sputtering process to deposit Al-doped ZnO (AZO) films using an Al-Zn alloy target. The sputtering system was equipped with specially designed double feedback system to stabilise the reactive sputtering processes and analysis was performed with a quadrupole mass spectrometer combined with an energy analyser. Negative ions O⁻, O₂⁻, AlO⁻ and AlO₂⁻ with high kinetic energies corresponding to cathode voltage are generated at the partially oxidised target surface, after which some of the ions undergo subsequent charge exchange and/or dissociation. Positive ions O⁺, Ar⁺, Zn⁺ and Al⁺ with lower kinetic energies (around 10 eV) are generated by charge exchange of sputtered neutral O, Ar, Zn and Al atoms, respectively. As the target surface oxidises, cathode voltage decrease, the flux of high-energy negative ions increases and the electrical properties of the AZO degrade by ion bombardment as well as the AZO films that are deposited by conventional magnetron sputtering using an AZO target.     

The ion energy distributions and ion flux composition from a high power impulse magnetron sputtering discharge

The energy distribution of sputtered and ionized metal atoms as well as ions from the sputtering gas is reported for a high power impulse magnetron sputtering (HIPIMS) discharge. High power pulses were applied to a conventional planar circular magnetron Ti target. The peak power on the target surface was 1-2 kW/cm² with a duty factor of about 0.5%. Time resolved, and time averaged ion energy distributions were recorded with an energy resolving quadrupole mass spectrometer. The ion energy distributions recorded for the HIPIMS discharge are broader with maximum detected energy of 100 eV and contain a larger fraction of highly energetic ions (about 50% with E_i > 20 eV) as compared to a conventional direct current magnetron sputtering discharge. The composition of the ion flux was also determined, and reveals a high metal fraction. During the most intense moment of the discharge, the ionic flux consisted of approximately 50% Ti¹⁺, 24% Ti²⁺, 23% Ar¹⁺, and 3% Ar²⁺ ions.     

Surface morphology of polycrystalline diamond films etched by Ar+ beam bombardment

Polycrystalline diamond films etched by Ar⁺ beam bombardment were investigated by scanning electron microscopy and Raman spectroscopy. In an ion sputtering apparatus, an etching rate of 14 m C^–1 was obtained when 10 kV-accelerated Ar⁺ ions penetrated with an angle of 15–30° from the normal. A number of cavities were created on the surface treated at low incidence angle. In contrast, micro-prominence was seen under the condition of high incidence angle. The degree of surface roughness on etched films was also changed with the incidence angle of the beam. A relatively smooth surface appeared after the treatment with an incidence angle of 15°. Raman spectroscopy revealed that the physical etching of diamond is effective in obtaining high quality surface of polycrystalline diamond films.     

Metastable C3H5 produced by electron impact of propane

Metastability of C₃H₅²⁺ ions formed by electron impact ionization of propane was monitored with the help of a magnetic mass spectrometer of reversed geometry (BEE geometry). In the present paper, we report decay reactions resulting in C₃H₄⁺+H⁺, and C₃H₃⁺+H₂⁺. We observed fragment ions which are formed with high kinetic energy. Mass analyzed ion kinetic energy (MIKE) scan technique in the third field free region of the mass spectrometer was applied to identify the fragment ions and determine their kinetic energy release (KER). An average KER of 1.6±0.3 eV for the first reaction and 0.67±0.15 eV for the second reaction are reported.     

Secondary ion emission of Fe-Ni alloys in the temperature range including the Curie point

The temperature dependence of secondary ion emission was investigated for Fe-Ni ferromagnetic alloys with different Curie points T_c and elemental composition: 35% Ni 65% Fe (T_c=240°C), 40% Ni 60% Fe (T_c=360°C), and 50% Ni 50% Fe (T_c=530°C). The alloy 79% Ni 16% Fe 5% Mo (T_c=345°C) was also studied. The spatial distribution of Ni⁺ and Fe⁺ secondary ions emitted from the (1 1 1) face of invar and permalloy single crystals was shown to be anisotropic with pronounced ion-yield maximum for both components in the 〈1 1 0〉 directions. The shape of the energy distribution of Ni⁺ and Fe⁺ ions was found to be virtually identical for all the alloys under investigation with a most probable energy at 7 eV and a width at half-maximum of 12 eV. The temperature dependence of the Ni⁺ and Fe⁺ emission has a maximum near the Curie point of the investigated alloys and another maximum at the Curie point of nickel which may indicate the precipitation of nickel into microscopic islands on the surface as a result of heating and sputtering. Auger analysis of the surface composition in the surface layers showed a variation in concentration of oxygen and carbon atoms when Fe-Ni alloys pass from the ferromagnetic to the paramagnetic state and this must affect also the secondary ion emission of alloy components.     

Optical investigation of nitrogen ion implanted bulk ZnO

Nitrogen ions were implanted into melt-grown ZnO (0001) substrates and subsequently annealed at 800 °C under an oxygen ambient. The photoluminescence spectrum of N⁺-implanted ZnO excited by a He-Cd laser exhibited donor-acceptor pair (DAP) transition emission at 385 nm with a full width at half maximum of 30 nm at 10 K. The DAP emission is associated with the acceptor energy of nitrogen in ZnO, calculated to be 170 meV. Defect-related red emission at about 610 nm observed in N⁺-implanted ZnO was due to the residual damage from the implantation step because it was also observed in Ar⁺-implanted ZnO but not in un-implanted ZnO annealed at 800 °C under the same oxygen ambient.     

Ion-induced self-organized dot and ripple patterns on Si surfaces

The evolution of the surface topography during low-energy Ar⁺ ion beam erosion of silicon surfaces is studied. Depending on ion-beam parameters, a variety of nanostructured patterns with a very narrow size distribution can be developed on the surface. By rotating the sample, ordered nanodots are formed for ion energies ?300 eV at normal and oblique ion incidence angles with respect to the surface normal. Dots evolving at oblique ion incidence of 75° show a very high degree of ordering with a mean dot size λ∼30 nm. Without sample rotation at near normal ion incidence angle (∼15°), remarkably ordered ripple structures develop with a wavelength λ∼45 nm. The degree of ordering and size homogeneity of these nanostructures increases with erosion time eventually leading to the most ordered self-organized patterns on Si surfaces reported so far.     

Development and application of highly charged ion source

The interaction of slow highly charged ions (HCIs) with solid surfaces is useful for ‘nanoprocess’; the modification, activation, machining and analysis in nanometer scale. An electron beam ion source ‘Kobe EBIS’ has been developed for the application of HCIs to nanoprocesses. The ion source produces ion beams of Ar^q+ (q ≤ 12) HCI in the nanoampere range. The ion source was applied to irradiate samples in order to investigate the structural or electric modification effect of HCIs with high fluence on the topmost layers of sample surfaces.     

A high-pressure mass spectrometric study of ion-molecule reactions in a mixture of CF4 and He

Gas phase ion-molecule reactions of positive He⁺ ions produced from helium with neutral carbon tetrafluoride have been studied. The measurements were made with a quadrupole mass spectrometer with a high-pressure ion source. The fractional abundance I_i/∑I_i of dominant ions CF₃⁺, CF₂⁺ and helium ions has been determined as a function of the (1% CF₄ and 99% He) gas mixture pressure (in the range 1.33-31.92 Pa) and of the repeller electrode potential (ranging from 3 to 10 V).     

Ion bombardment of polyethylene—influence of polymer structure

Polyethylenes of various macromolecular and supermolecular structures were studied from the point of view of their susceptibility to an ion beam treatment. An influence of molecular weight (M_w), molecular weight distribution (M_w/M_n) and the degree of branching were compared within the set of low-density polyethylenes (LDPE) studied. An influence of the length of branches was compared between LDPE, linear low-density (LLDPE) and high-density (HDPE) polyethylenes. An influence of the degree of crystallinity and the morphology of a crystalline phase were compared for HDPE samples solidified under various thermal conditions and ultra-high molecular weight polyethylene (UHMWPE). Plate polymer targets ∼2 mm were bombarded with 100 keV He⁺ or 130 keV Ar⁺ ions (dose of 10¹⁴-10¹⁶ ions/cm²; ion energy stream density <0.1 μA/cm²), micromechanical properties of their surface layer (hardness, mechanical modulus and elastic recovery) determined and compared to the virgin materials.Ar⁺ ion beam bombardment generally lowers micromechanical properties of the polyethylenes, whereas He⁺ ion beam treatment makes them higher. The effect is the stronger the higher the molecular weight of polyethylene. However, a long chain branching adversely affects the modification. The degree of crystallinity facilitates an ion beam bombardment from the point of view of micromechanical properties of the materials, however, also the morphology of a crystalline phase was found to play a role.     

Ion sputtering rates of C, CrxCy, and Cr at different Ar ion incidence angles

To study the ion sputtering of a layered structure with different layer densities and ion sputtering yields a trilayer structure of C-graphite(46 nm)/Cr_xC_y(60 nm)/Cr(69 nm) was sputter deposited onto smooth silicon substrates. The ion sputtering rates of amorphous carbon, amorphous Cr_xC_y and polycrystalline Cr were determined by means of Auger electron spectroscopy depth profiling as a function of the angle of incidence of two symmetrically inclined 1 keV Ar⁺ ion beams in the range between 22° and 82°. The sputtering rates were calculated from the known thicknesses of the layers and the sputtering times necessary to remove the individual layers. It was found that the sputtering rates of C-graphite, Cr_xC_y carbide and Cr were strongly angle dependent. The experimental sputtering yields were in agreement with the theoretical results obtained by calculation of the transport of ions in solids, but the sputtering yields of C-graphite measured at ion incidence angles larger than 29° were smaller than the simulated ones.     

The absolute detection efficiency of vacuum electron multipliers,to keV protons and Ar+ ions

The single-ion detection efficiency of two types of electron multipliers is provided for incident energies reaching 10 keV. Absolute efficiencies above 90% were measured for a discrete dynode electron multiplier (DDEM), in response to Ar⁺ ions and protons, above an energy of 5 keV. The efficiency to detect protons is consistently higher than that of Ar⁺ ions, due to a higher secondary electron emission yield. For a channel electron multiplier we have measured a similar maximal detection efficiency for Ar⁺ ions; though strongly varying across the detector surface.     

Mixing in Au/Ge system induced by Ar<Superscript>+</Superscript> ion irradiation

Rutherford Backscattering Spectrometry (RBS) and Electrical Resistivity Measurements (ERM) were used to investigate the mixing of Au/Ge bilayer deposited onto glass substrate induced by Ar ions. Mixing was initiated by bombarding the sample with 400 keV ⁴⁰Ar⁺ beam with a fluence up to 1.2 × 10¹⁷ ions/cm² at a constant flux of 0.25 μA/cm². To assist the evaluation of the experimental results, all spectra were simulated using “RUMP” computer code. RBS results indicated that ion beam mixing led to a formation of AuGe₂ compound. The mixed region was noticed to increase with the gradual increase of Ar⁺ fluence. Results were also compared with current theoretical models used to describe the mixing process. The Bφrgesen thermal spike model was found to accurately predict the diffusion in Au/Ge interface. An increase in the electrical resistivity of the film was detected during Ar⁺ irradiation.