AES, EELS and TRIM investigation of InSb and InP compounds subjected to Ar ions bombardment

The interaction of ions with matter plays an important role in the treatment of material surfaces. In this paper we study the effect of argon ion bombardment on the InSb surface in comparison with the InP one. The Ar⁺ ions, accelerated at low energy (300 eV) lead to compositional and structural changes in InP and InSb compounds. The InP surface is more sensitive to Ar⁺ ions than that of InSb. These results are directly inferred from the qualitative Auger electron spectra (AES) and electron energy loss spectroscopy (EELS) analysis. However, these techniques alone do not allow us to determine with accuracy the disturbed depth in Ar⁺ ions of InP and InSb compounds. For this reason, we combine AES and EELS with the simulation method TRIM (transport and range of ions in matter) to show the mechanism of interaction between the ions and the InP or InSb and hence determine the disturbed depth as a function of Ar⁺ energy.     

Studying the effect of oxygen content on the electron structure of Nd<Subscript>1.85</Subscript>Ce<Subscript>0.15</Subscript>CuO<Subscript>4</Subscript> by means of photoelectron spectromicroscopy

Changes in the electron structure of the surface layer of Nd_1.85Ce_0.15CuO₄ (NCCO) epitaxial films, which were caused by variation of the oxygen content and modification of the crystal structure of samples as a result of Ar⁺ ion etching and annealing, have been studied by means of photoelectron spectromicroscopy. A method is proposed for the cleaning the surface of oxygen-containing superconductors, which includes sequential stages of deep ion etching, high-temperature annealing in an oxygen-containing atmosphere (for the structural recovery and saturation with oxygen), a short-term ion etching (for the removal of an adsorbed layer of the oxidizer), and the final vacuum annealing of radiation-induced effects. The application of this procedure to NCCO films allowed an electron structure to be obtained, which was identical to that inherent in the surface of single crystals cleaved in situ in the measurement chamber.     

X-ray photoelectron spectroscopic studies of black silicon for solar cell

The black silicon has been produced by plasma immersion ion implantation (PIII) process. The microstructure and optical reflectance are characterized by field emission scanning electron microscope and spectrophotometer. Results show that the black silicon appears porous or needle-like microstructure with the average reflectance of 4.87% and 2.12%, respectively. The surface state is investigated by X-ray photoelectron spectroscopy (XPS) technique. The surface of the black silicon is composed of silicon, carbon, oxygen and fluorine element. The formation of Si_xO_yF_z in the surface of black silicon can be proved clearly by the O 1s, F 1s and Si 2p XPS spectra. The formation mechanism of the black silicon produced by PIII process can be obtained from XPS results. The porous or needle-like structure of the black silicon will be formed under the competition of SF_x⁺ (x ≤ 5) and F⁺ ions etching effect, Si_xO_yF_z passivation and ion bombardment.     

The unexpected formation of Au-Si by the resonance neutralization of Ar during the low energy bombardment of Au nanoparticles on c-Si

Nanoscale Au layers, with irregular porosities, have been formed by the low energy Ar⁺ bombardment of Au nanoparticles that were sputter-deposited onto native oxide-covered Si surfaces. High-resolution field emission scanning electron microcopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) have been used to characterize the formation and evolution of the nanoporous layer. Under Ar⁺ bombardment, the Au nanoparticles that were initially deposited were observed to flatten and spread across the native oxide surface, without diffusing, finally coalescing at their edges to form a nanoporous film having irregular pore dimensions. XPS showed that this evolution was accompanied by the loss of Au as a result of sputtering. The formation of such porous films necessitates strong interfacial bonding to avoid the lateral diffusion of the Au nanoparticles, and their ultimate coalescence into larger nanoparticles.We demonstrated that Ar⁺ beam bombardment invariably caused the formation of Au^δ+-Si^δ− bonding, rather than the expected Au^δ−-Si^δ+ bonding, and we explain this to be due to the resonance neutralization of the Ar⁺ beam on impacting the Au layer. We also reveal that the presumed formation of AuSi_x is not quantifiable by XPS, due to the superposition of the chemical shift of the Au nanoparticles with that of the quantum size effect, during Au loss on sputtering.     

The lowest electronic states of Ne2 +, Ar2 + and Kr2 +: comparison of theory and experiment

Non-relativistic configuration interaction (CI) ab initio calculations using large basis sets have been carried out to determine the potential curves of the first electronic states of Ne₂ ⁺, Ar₂ ⁺ and Kr₂ ⁺. The spin—orbit interaction was treated assuming that the spin—orbit coupling constant is independent of the internuclear separation (R). For Ar₂ ⁺, calculated dissociation energies and equilibrium separations are in good agreement with experimental results. The calculations for Ne₂ ⁺ suggest that the lowest vibrational level of the I(1/2u) ground state observed by threshold photoelectron spectroscopy by Hall et al. [1995, J. Phys. B: At. molec. opt. Phys., 28, 2435] and assigned to either ν = 0 or ν = 2 actually corresponds to ν = 4. The calculations also predict the I(1/2g) state of Ne₂ ⁺ and Ar₂ ⁺ to possess a double-well potential and that of Kr₂ ⁺ to be repulsive at short range and to only possess a single shallow well at large internuclear separation. The ab initio calculations provide an explanation for the observation made by Yoshii et al. [2002, J. chem. Phys., 117, 1517] that Kr₂ ⁺ and Xe₂ ⁺ dissociate after photoemission from the II(1/2u) state to the I(1/2g) state whereas Ar₂ ⁺ does not.     

Investigation of epitaxial Nd1.85Ce0.15CuO4 − y film surface by low energy electron diffractometry

The surface of epitaxial Nd_1.85Ce_0.15CuO_{4 ? y} (001) (NCCO) film has been studied by low energy electron diffractometry (LEED) and photoelectron spectroscopy. Ar⁺ ion etching of a surface with subsequent annealing in oxygen at atmosphere pressure has been found to lead to the ordered structure restoration of surface layers with the symmetry type and lattice parameters corresponding to the NCCO phase. Annealing in vacuum at temperatures close to the boundary of thermodynamic phase stability results in the formation of epitaxial Ce_0.5Nd_0.5O_1.75 phase on a surface that is indicated in the LEED pattern as additional spots corresponding to the surface lattice (√2 × √2)R45°.     

Tuning of ripple patterns and wetting dynamics of Si (100) surface using ion beam irradiation

Ripple patterns on Si (100) surface have been fabricated using 200 keV Ar⁺ oblique ion beam irradiation. Dynamical evolution of patterns is studied for the fluences ranging from 3 × 10¹⁷ ions/cm² to 3 × 10¹⁸ ions/cm². AFM study reveals that the exponential growth of roughness with stable wavelength of ripples up to higher fluence values is lying in the linear regime of Continuum models. Stylus Profilometer measurement was carried out to emphasize the role of sputtering induced surface etching in ripple formation. Rutherford Backscattering Spectroscopy shows the incorporation of Ar in the near surface region. Observed growth of ripples is discussed in the framework of existing models of surface patterning. Role of ion beam sputtering induced surface etching is emphasized in formation of ripples. In addition, the wetting study is performed to demonstrate the possibility of engineering the hydrophilicity of ripple patterned Si (100) surface.     

Effect of Ar+ irradiation on the electrical conductivity of BaCe0.9Y0.1O3−δ

The effects of 10 keV Ar⁺ ion irradiation on the electrical characteristics of BaCe_0.9Y_0.1O_2.95 subject to fluences of 0, 1.0 × 10¹⁷, 5.0 × 10¹⁷ and 1.0 × 10¹⁸ ions/cm² at room temperature, has been investigated using elastic recoil detection analysis (ERDA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and alternating current (AC) impedance measurements. It was confirmed from the ERDA results that the hydrogen concentration near the surface increased with increase of Ar⁺ ion fluence. This increase may be associated with the increasing quantities of hydrogen generated by interaction between oxygen vacancies, formed by irradiation, and H₂O from exposure to air. SEM images showed clearly that the number of surface defects due to modification increased with increasing fluence. In addition, the size of the defects showed a tendency to increase with increasing fluence. From the results of XPS analyses, providing information on the electronic states on the surface, it was evident that with increase in the Ar⁺ ion fluence, the quantity of excess oxygen, such as hydroxide, increased in the oxygen 1s XPS spectrum. In addition, it was indirectly found, from decomposition of the Ce 3d, spectrum that the concentration of oxygen vacancies increased with fluence, since the percentage of Ce³⁺ also increased. Accordingly, the surface modification led to the formation of more oxygen vacancies and a greater hydrogen concentration on the surface, since the H₂O interacted with some of them. From the results of the DC conductivity and AC impedance measurements, the proton conductivity was shown to predominate over the temperature range from 473 K to 823 K. It was concluded that the increase in these protons and vacancies generated from surface modification contributed to the increase of proton conductivity.     

Structural characteristics and morphology of SmxCe1−xO2−x/2 thin films

Effect of the deposition temperature (200 and 500 °C) and composition of Sm_xCe_1−xO_2−x/2 (x = 0, 10.9–15.9 mol%) thin films prepared by electron beam physical vapor deposition (EB-PVD) and Ar⁺ ion beam assisted deposition (IBAD) combined with EB-PVD on structural characteristics and morphology/microstructure was investigated. The X-ray photoelectron spectroscopy (XPS) of the surface and electron probe microanalysis (EPMA) of the bulk of the film revealed the dominant occurrence of Ce⁴⁺ oxidation state, suggesting the presence of CeO₂ phase, which was confirmed by X-ray diffraction (XRD). The Ce³⁺ oxidation states corresponding to Ce₂O₃ phase were in minority. The XRD and scanning electron microscopy (SEM) showed the polycrystalline columnar structure and a rooftop morphology of the surface. Effects of the preparation conditions (temperature, composition, IBAD) on the lattice parameter, grain size, perfection of the columnar growth and its impact on the surface morphology are analyzed and discussed.     

Sheath and electron density dynamics in the normal and self-pulsing regime of a micro hollow cathode discharge in argon gas

A microplasma is generated in the microhole (400 μm diameter) of a molybdenum-alumina-molybdenum sandwich (MHCD type) at medium pressure (30–200 Torr) in pure argon. Imaging and emission spectroscopy have been used to study the sheath and electron density dynamics during the stationary normal regime and the self-pulsing regime. Firstly, the evolution of the microdischarge structure is studied by recording the emission intensity of the Ar (5p[3/2]₁–4s[3/2]₁)_{1}) line at 427.217 nm, and Ar⁺ (4p′ ²P_3/2–4s′ ²D_5/2)_{5/2}) line at 427.752 nm. The maximum of the Ar⁺ line is located in the vicinity of the sheath-plasma edge. In both regimes, the experimental observations are consistent with the position of the sheath edge calculated with an ionizing sheath model. Secondly, the electron density is recorded by monitoring the Stark broadening of the H_b_\beta-line. In the self-pulsing regime at 150 Torr, the electron density reaches its maximum value of 4 × 10¹⁵ cm^-3, a few tens of ns later than the discharge current maximum. The electron density then decays with a characteristic decay time of about 2 μs, while the discharge current vanishes twice faster. The electron density in the steady-state regime is two orders of magnitude lower, at about 6–8 × 10¹³ cm^-3.     

Atomic excitations in sputtering studied with the use of composite targets

Atomic excitation phenomena in sputtering have been studied with the following combinations of projectile and target. (i) Be, B, Mg, Al, and Si bombarded with 80 keV Ar⁺ at UHV as well as with the target chamber backfilled with oxygen. (ii) Mg bombarded with 80 keV O⁺, F⁺, Ne⁺, Na⁺ Cl⁺, and Ar⁺. (iii) MgO, MgF₂, MgCl₂, MgSO₄, and several alkali halides bombarded with 80 keV Ar⁺ at UHV. Results are discussed. It is concluded that the excited-state formation takes place as electron tunneling at a fairly large separation between the target surface and the particle being sputtered. It is suggested with composite targets containing a metal element that excitation takes place predominantly at locations of the target surface where the work function is low, due to a thin, metallic surface layer, and that production of ground-state, positive secondary ions mainly takes place at target surface regions with high work function. For semiconductors, the changes caused by presence of oxygen are related to the change of the bonds in the solid from being of covalent nature to being fractionally ionic.     

Shallow surface etching of organic and inorganic compounds by electrospray droplet impact

The electrospray droplet impact (EDI) was applied to bradykinin, polyethylene terephthalate (PET), SiO₂/Si, and indium phosphide (InP). It was found that bradykinin deposited on the stainless steel substrate was ionized/desorbed without the accumulation of radiation products. The film thickness desorbed by a single collisional event was found to be less than 10 monolayers. In the EDI mass spectra for PET, several fragment ions were observed but the XPS spectra did not change with prolonged cluster irradiation. The etching rate for SiO₂ by EDI was measured to be ∼0.2 nm/min. The surface roughness of InP etched by EDI was found to be one order of magnitude smaller than that etched by 3 keV Ar⁺ for about the same etching depths. EDI is capable of shallow surface etching with little damage left on the etched surface.     

The effect of sub-band gap photon illumination on the properties of GaN layers grown on Si(111) by MBE

Nanostructured GaN layers are fabricated by laser-induced etching processes based on heterostructure of n-type GaN/AlN/Si grown on n-type Si(111) substrate. The effect of varying laser power density on the morphology of GaN nanostructure layer is observed. The formation of pores over the structure varies in size and shape. The etched samples exhibit dramatic increase in photoluminescence intensity compared to the as-grown samples. The Raman spectra also display strong band at 522 cm⁻¹ for the Si(111) substrate and a small band at 301 cm⁻¹ because of the acoustic phonons of Si. Two Raman active optical phonons are assigned h-GaN at 139 and 568 cm⁻¹ due to E2 (low) and E2 (high), respectively. Surface morphology and structural properties of nanostructures are characterized using scanning electron microscopy and X-ray diffraction. Photoluminance measurement is also taken at room temperature by using He–Cd laser (λ = 325 nm). Raman scattering is investigated using Ar⁺ Laser (λ = 514 nm).     

Exploration of large amplitude motions in the Ca+Ar2 complex

ABSTRACT

We present a theoretical study of the ground electronic state potential of the Ca⁺Ar₂ complex and of its photoabsorption spectra, simulated at temperatures ranging between 20 and 220?K. These calculations exploit a Monte-Carlo (MC) method, based on a one-electron pseudo-potential approach. A pairwise additive potential fitted to coupled cluster ab initio points, is used to model the Ca⁺Ar₂ complex. Our study shows that the most stable form of Ca⁺Ar₂ is a bent C_2v structure, whereas the linear isomer is located at around 90?±?10?cm^?1 above in energy. The analysis of the photoabsorption spectra establishes that a structural transition from bent Ca⁺Ar₂ to linear ArCa⁺Ar occurs at T～100?K. Trends in binding energies of both isomers, bond lengths and bond angles are also discussed. Molecular orbital overlaps provide an explanation for the order of stability between the bent and linear structures.     

Photoluminescence detection of impurities introduced in silicon by dry etching processes

We report on a photoluminescence study of silicon samples subjected to different dry etching processes. Several luminescence lines, known from defects produced by high-energy irradiation, manifest damage of the crystalline material. Noble gas ion beam etching (using Ne⁺, Ar⁺, Kr⁺, and Xe⁺) with ion energies as low as 400 eV produces characteristic luminescence lines which correspond to defects within a 200–300 Å thick surface layer. Incorporation of carbon during CF₄ reactive ion etching produces the familiar G-line defect. The G-line photoluminescence intensity in our samples is directly correlated with the substitutional carbon concentration, as determined by infrared absorption measurements before the etch process; we therefore suggest that a simple method to determine the substitutional carbon concentration in a crystalline silicon sample is a standard dry etching process and a comparison of the resulting G-line photoluminescence intensity to a calibrated sample. The sensitivity of this method seems to be better than 10¹⁴ carbon atoms/cm³.     

Surface morphology and composition of c-, a- and m-sapphire surfaces in O2 and H2 environments

This paper reports that monitoring the composition of the c(0 0 0 1), a(11–20) and m(10–10) sapphire surfaces is essential for a proper interpretation of the surface morphologies obtained after annealing at 1253 and 1473 K in ArH₂ or ArO₂ atmospheres. Our experimental investigations, which have used Auger electron spectroscopy (AES) and atomic force microscopy (AFM) on the surfaces of 99.99% pure sapphire wafers, have led to the following original conclusions: (i) Calcium segregates at the c-surface of sapphire both under ArO₂ and ArH₂. (ii) Potassium adsorption enhances the kinetics of step-bunching on the c-surface under ArO₂. (iii) The step edges on the a-surface may develop a comb-like morphology made of parallel strips along the [10–10] direction. (iv) At 1253 K, clean m-surfaces may be stable. (v) Under ArH₂, alumina surface diffusion is much slower than under ArO₂ for all surface orientations, the surface concentration of impurities is low, and the Al–O ratio of the AES signals at the surface is significantly larger.     

等离子体增强化学气相沉积法制备立方氮化硼薄膜过程中的表面生长机理

利用感应耦合等离子体增强化学气相沉积法以Ar，He，N₂和B₂H₆为反应气体制备了高纯立方氮化硼薄膜.用四极质谱仪对等离子体状况进行了系统的分析，发现B₂H₆完全被电离而N₂只是部分被电离.H₂和过量的N₂在等离子体中生成大量中性的H原子和活化的N^*₂，它们与表面的相互作用严重地阻碍了立方 关键词： 立方氮化硼薄膜 等离子体 质谱     

Synthesis and characterization of porous silicon layers for 1D photonic crystal application

In this paper, we studied the optical and physical properties of electrochemically prepared porous silicon layers. The atomic force microscopy analysis showed that the etching depth, pore diameter and surface roughness increase as the etching time increased from 30 to 50 mA/cm². By tuning two current densities J₁ = 50 mA/cm² and J₂ = 30 mA/cm², two samples of 1D porous silicon photonic crystals were fabricated. The layered structure of 1D photonic crystals has been confirmed by scanning electron microscopy measurement which showed white and black strips of two distinct refractive index layers. Finally, the measured reflectance spectra of 1D porous silicon photonic crystals were compared with simulated results.     

Sputtering of A 3 B 5 materials (GaP, GaAs, GaSb, InP, and InSb) by 2-to 14-keV N 2 + ions

Investigations of the general characteristics and distinctive features of sputtering of A ³ B ⁵ materials (GaP, GaAs, GaSb, InP and InSb) under bombardment with N ₂ ⁺ ions have been carried out. From the experimental data, dependences of the sputtering yield of these materials on the incidence angle and ion energy have been obtained and the surface relief patterns produced by target etching have been studied. It has been shown that the dependence on energy of the sputtering yield for GaP, GaAs, and InP can be adequately described by the Haffa-Switkovski formula for binary materials and Yudin’s approximation for elemental targets. Sputtering of GaSb and InSb proceeds in the surface layer recrystallization mode, and the sputtering yield agrees with calculations based on Onderlinden’s model. From a comparison of the experimental and calculated dependences, the surface bonding energies have been determined.     

Electron energy loss spectra from polycrystalline Cr and Cr2O3 before and after surface reduction by Ar bombardment

Electron energy loss spectra (ELS) have been obtained from polycrystalline Cr and Cr₂O₃ before and after surface reduction by 2 keV Ar⁺ bombardment. The primary electron energy used in the ELS measurements was systematically varied from 100 to 1150 eV in order to distinguish surface versus bulk loss processes. Two predominant loss features in the ELS spectra obtained from Cr metal at 9.0 and 23.0 eV are assigned to the surface and bulk plasmon excitations, respectively, and a number of other features arising from single electron transitions from both the bulk and surface Cr 3d bands to higher-lying states in the conduction band are also present. The ELS spectra obtained from Cr₂O₃ exhibit features that originate from both interband transitions and charge-transfer transitions between the Cr and O ions as well as the bulk plasmon at 24.4 eV. The ELS feature at 4.0 eV arises from a charge-transfer transition between the oxygen and chromium ions in the two surface layers beneath the chemisorbed oxygen layer, and the ELS feature at 9.8 eV arises from a similar transition involving the chemisorbed oxygen atoms. The intensity of the ELS peak at 9.8 eV decreases after Ar⁺ sputtering due to the removal of chemisorbed oxygen atoms. Sputtering also increases the number of Cr²⁺ states on the surface, which in turn increases the intensity of the 4.0 eV feature. Furthermore, the ELS spectra obtained from the sputtered Cr₂O₃ surface exhibit features characteristic of both Cr⁰ and Cr₂O₃, indicating that Ar⁺ sputtering reduces Cr₂O₃. The fact that neither the surface- nor the bulk-plasmon features of Cr⁰ can be observed in the ELS spectra obtained from sputtered Cr₂O₃ while the loss features due to Cr⁰ interband transitions are clearly present indicates that Cr⁰ atoms form small clusters lacking a bulk metallic nature during Ar⁺ bombardment of Cr₂O₃.