Sputtered Neutral Mass Spectrometry Research Articles

Electrodeposition of ternary compounds for novel PV application and optimisation of electrodeposited CdMnTe thin-films

Growth of polycrystalline CdMnTe ternary compound thin films has been carried out using cathodic electrodeposition technique at different cathodic potentials. The range of the cathodic potentials used in this work has been chosen according to the cyclic voltammogram results. The CdMnTe thin films were electroplated from electrolyte containing CdSO4, TeO2 and MnSO4 in an acidic aqueous medium. Glass/fluorine-doped tin oxide (FTO) substrates have been used to electrodeposit the semiconductor layers. The structural, compositional, morphological, optical and electrical properties of the CdMnTe thin films were studied using X-ray diffraction (XRD), Sputtered neutral-mass spectroscopy (SNMS), Scanning electron microscopy (SEM), UV–Vis spectroscopy and Photo-electro-chemical (PEC) cell measurements respectively. The primarily grown as-deposited (AD) layers went through two different post-growth surface treatment conditions- heat-treated in air in the presence of CdCl2 (CCT) and heat-treated in air in the presence of GaCl3 (GCT). Results from the XRD indicated the polycrystalline nature of the electrodeposited films. The electroplated films have cubic crystal structures and the preferred orientation was found to be along the (111) plane of CdMnTe. Inclusion of Mn has been qualitatively observed using SNMS measurement. The optical energy bandgaps of the thin films were found to be varying between ~ 1.90 and ~ 2.20 eV. Though all the layers after post-treatment showed p-type electrical conduction, both p and n-type conductivity were obtained at different cathodic potentials for as-deposited materials. Comparison of the deposited layers to other electrodeposited ternary compounds has also been discussed.

Improvement of ionization yield in sputtered neutral mass spectrometry using pulsed infrared and ultraviolet lasers

A new laser ionization method for sputtered neutral mass spectrometry (SNMS), which the authors call “dual-laser SNMS,” was developed to increase the ionization probability and improve sensitivity. In this technique, pulsed IR and UV lasers irradiated sputtered atoms simultaneously, while the additional UV laser pulse enhanced the ionization process. The useful yields of the target elements increased by 10%–20% compared to using the IR irradiation alone, and the yield increased with increasing UV power. In addition, there was little correlation between the ionization potential and the ratio of the ionization enhancement. Therefore, dual-laser SNMS was effective for the analysis of elements with higher ionization potential.

Matrix and element dependences of useful yield in Si and SiO2 matrices using laser-ionization sputtered neutral mass spectrometry

The element and/or material dependence of the useful yield in laser-ionization sputtered neutral mass spectrometry (SNMS) using a high-photon-flux laser was investigated. Useful yields obtained from Si, B, As, and O in Si and SiO2 matrices using both secondary ion mass spectrometry (SIMS) and SNMS were compared, and the possibility of the accurate analysis of impurities in multilayers was investigated in terms of tunnel ionization. The behavior of atoms released from the surface by ion bombardment was calculated, and it was considered that the flying speed of sputtered atoms depends on the mass and that this causes the elemental difference in the fractions of laser-irradiated atoms. In the case of SNMS, excluding O, whose ionization probability is considered to be much lower than for the other elements, the useful yields of Si, B, and As are within 1 order of magnitude in both the Si and SiO2 matrices, and the difference between the matrices for each element is within a factor of two. These differences are much smaller than in the result of SIMS. It was confirmed that the distribution of B in a SiO2/Si stacked layer can be analyzed more accurately by SNMS than by SIMS. SNMS with a high-photon-density laser is considered to be effective for the analysis of more than one element in multilayers.

High-mass heterogeneous cluster formation by ion bombardment of the ternary alloy Au7Cu5Al4

The ternary alloy Au7Cu5Al4 was irradiated with 0.1–10 keV Ar+ and the surface composition analyzed using laser sputter neutral mass spectrometry. Ejected clusters containing up to seven atoms, with masses up to 2000 amu, were observed. By monitoring the signals from sputtered clusters, the surface composition of the alloy was seen to change with 100 eV Ar+ dose, reaching equilibrium after 10 nm of the surface was eroded, in agreement with TRIDYN simulation and indicating that the changes were due to preferential sputtering of Al and Cu. Ejected gold containing clusters were found to increase markedly in intensity while aluminum containing clusters decreased in intensity as a result of Ar sputtering. Such an effect was most pronounced for low energy (<1 keV) Ar+ sputtering and was consistent with TRIDYN simulations of the depth profiling. The component sputter yields from the ternary alloy were consistent with previous binary alloy measurements but showed greater Cu surface concentrations than expected from TRIDYN simulations.

SNMS investigations of thermally sprayed coatings

Abstract Surface protective coatings are commonly used in order to protect the bulk materials against corrosion and high temperature oxidation. The present publication discusses the morphology of high-velocity oxygen fuel (HVOF) sprayed MCrAlY coatings obtained from CoNiCrAlY particles (8 wt.-% Al) before and after electron beam (EB) treatment. The latter process was applied in order to achieve a homogeneous and refined structure free of pores and oxides. The microstructure and phase modification of the coatings before and after the EB remelting were characterized by scanning electron microscopy (SEM) and X-ray diffraction technique. Using the sputtered neutral mass spectrometry (SNMS) technique, the element contents (O, N, Co, Ni, Cr, Al, Y) of the coating in as sprayed and after EB irradiation were examined. Experiments have shown that while the Co concentration remains practically unchanged, significant changes in Cr, Ni, Al and Y concentrations occurred. Also, the N and O contents are lower compared to those of the as sprayed coatings.

High sensitivity sputter neutral mass spectrometry – Sputtering of neutral mixed clusters from gold–aluminum alloys

We have used the surface sensitivity of laser sputter neutral mass spectrometry to make measurements of clusters sputtered from AuAl alloys surfaces with high dynamic range. Polycrystalline AuAl4 and Au4Al were bombarded with 15keV Ar+ at 60° incidence, and the resulting secondary neutral yield distributions were measured using laser postionization mass spectrometry. Neutral clusters containing up to 28 atoms were observed and exhibited an odd–even variation in signal dependent on the stability of the photoion. Clusters sputtered from Au4Al were gold rich compared to the substrate and the yield of neutral clusters containing n atoms, Yn, was found to follow a power in n, i.e. Yn∝n−δ, where the exponent δ was approximately 3.4.

Imaging of Polycyclic Aromatic Hydrocarbons by Means of Sputtered Neutrals Mass Spectrometry Using a Diode-pumped Solid-State Laser

Laser post-ionization of sputtered molecules by pulsed Ga focused ion-beam (Ga-FIB) bombardment was examined for the detection and imaging of polycyclic aromatic hydrocarbons (PAHs) on particles. As model samples, pyrene and pelyrene adsorbed on TiO2, blended regents of pyrene and n-heneicosan were used. The TiO2 particle size was selected to be several micro-meters. Laser light and Ga-FIB were synchronized with each other. The repetition rate synchronized with Ga-FIB was 1 kHz for pyrene analysis and 2 kHz for perylene, respectively. The laser wavelength was set to 266 nm. The wavelength was a generated fourth harmonic of a Nd:YAG DPSS (diode-pumped solid-state) micro-chip laser (UV microchip laser). By using a UV microchip laser, laser-SNMS (laser post-ionized sputtered neutral mass spectrometry) analysis and imaging were performed. The imaging of pyrene (m/z = 202, C16H10) and perylene (m/z = 252, C20H12) has been successful. Both the scanning ion microscopy image of TiO2 and the PAHs image in laser-SNMS analysis were well-fitted with each other.

Composition modifications and heat treatment procedures for increasing the emissivity of alumina surface scales on FeCrAl alloys

The oxidation limited lifetime of thin-walled FeCrAlY heating elements is governed by the depletion of the aluminium reservoir from the bulk alloy as a result of scale growth, whereby the lifetime is known to strongly decrease with increasing temperature. The present investigation aims at obtaining a heating element lifetime extension by increasing the emissivity of the growing alumina scales because this would allow using a lower heating element temperature without decreasing the usable heat output. For this purpose, the oxidation mechanisms of a Zr doped FeCrAlY alloy as function of time, temperature, composition and component thickness were investigated using a combination of experimental techniques such as thermogravimetry, optical microscopy, scanning electron microscopy, transmission electron microscopy, focused ion beam technique, sputtered neutrals mass spectrometry and glow discharge optical emission spectroscopy. The emissivity of the oxide scales was determined by measuring the reflectivity of oxidised specimens as a function of wavelength and correlated with the oxide scale morphologies as a function of initial alloy composition and pretreatment procedure. The results showed that an increased emissivity of the alumina scales as a result of a change in oxide morphology (i.e. wavy scaleyalloy interface and incorporation of the Zr-oxide precipitates across the oxide scale) can be obtained by suitable Zr-doping of the alloy. The emissivity value during long term exposure at high temperatures is, however, adversely affected by depletion of Zr in the bulk alloy, especially in thin components. Pretreatment of the alloys in a H2–H2O containing atmosphere (low pO2) resulted in an increased emissivity, probably due to an increased Fe (and Cr) content in the outer part of the alumina scale.

The Effect of Copper and Ceria Additions on the High Temperature Oxidation of Nickel

In this study, the effects of alloying with Cu and external doping with CeO2 on the oxidation of nickel were evaluated. The materials studied were pure Ni, Ni-5wt% Cu, and Ni with the surface doped with CeO2 by pulsed laser deposition (PLD). The oxidation kinetics were measured using thermogravimetric analysis (TGA). The oxidation microstructures were observed by scanning electron microscopy (SEM) compositional analysis was performed with energy dispersive x-ray analysis (EDS) and sputtered neutrals mass spectrometry (SNMS). Phase identification was performed using X-ray diffraction (XRD). The Cu additions had a negligible effect on the oxidation kinetics but Cu was found to be present in the outer portions of the scale in significant concentrations. Doping with CeO2 resulted in a significant decrease in the NiO growth rate. The scales on doped Ni grew primarily inward whereas those on the undoped Ni grew primarily outward. Deposition of the CeO2 dopant onto Ni with a thin, preformed NiO layer produced a similar reduction in the subsequent NiO growth rate. This suggests that the poisoned interface model, proposed by Pieraggi and Rapp, does not describe the effect of the CeO2 dopant. Mechanisms are presented to attempt to describe the above observations.

Chemical characterisation of evaporated In2Sx buffer layers in Cu(In,Ga)Se2 thin‐film solar cells with SNMS and SIMS

AbstractFor the series production of Cu(In,Ga)Se2 (CIGS)‐based thin‐film solar cells it is desirable to replace the thin CdS buffer layer between absorber and transparent front contact by non‐toxic, low‐absorbing semiconductors. In2S3, deposited by atomic layer deposition, has already been qualified as an alternative buffer material. In this work, results of indium sulphide buffer layers deposited by thermal evaporation are presented. Pressed powders with different compositions and morphology were used for evaporation at about 720 °C, resulting in different layer compositions and cell performances. The composition of the initial powder material and of the pellets after the deposition steps was determined by XRF. The deposited In2SxOy buffer layers and the buffer/absorber interface region were analysed by SIMS and sputtered neutral mass spectrometry (SNMS) depth profiling.Fine‐grained pressed In2S3 powder evaporates rather homogeneously during the entire deposition run, resulting in nearly stoichiometric In2S3 layers. S and Cl are evaporated preferentially from pellets of coarse‐grained, S‐poor In2S2.4 powder containing 2 at% Cl, leading to excess S and high Cl concentrations in the first deposited layer. The subsequent layers are S‐poor and the In/S ratios continue to increase. In all interface regions additional amounts of Se, In, and Ga are detected, which could be attributed to the Cu‐poor defect layer on top of the CIGS absorbers. The best solar cell performance with efficiences of about 13% was achieved with the S‐rich buffer layers. Stoichiometric In2S3 or S‐poor layers yield lower efficiences between 8 and 11%. Copyright © 2008 John Wiley & Sons, Ltd.

Microarea analysis of iron and phosphorus by resonance photoionization sputtered neutral mass spectrometry

A resonance-multiphoton-ionization sputtered neutral mass spectrometry (SNMS) instrument for submicron microarea analysis was developed. The laser system for producing resonance ionization in this SNMS consists of two yttrium aluminum garnet (YAG) lasers and three dye lasers. A combination of these laser beams, which makes available a maximum of four colors from the dye lasers and YAG lasers, can be simultaneously focused above a sample. The primary-ion-beam optical system, which uses a liquid-metal ion source, was developed specifically for this instrument. This system provides an ion-beam current density of more than 8A∕cm2 at a beam diameter of about 30nm. The depth profile of iron in a submicrometer microarea on a silicon wafer was obtained at a useful yield of about 5%, and the lateral profile of phosphorus in a rectangle area about 1400×500nm2 was obtained at useful yield of about 0.2%.

Galvanomagnetic transport properties of nitrogenated (La,Sr)MnO3-δ and LaMnO3-δ

Epitaxial thin films of nitrogenated La0.65Sr0.30MnO3 were grown on MgO(100) substrates by pulsed laser deposition (PLD). The nitrogenation was achieved by a continuous nitrogen flow in the PLD chamber with pressures of up to 0.12 mbar. The chemical analysis of the samples regarding the exchange of oxygen by nitrogen was achieved by time of flight secondary ion mass spectrometry, sputtered neutral mass spectrometry (SNMS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and yielded a content of incorporated nitrogen ranging from 0.6% to 3.8%. Without nitrogenation the electrical resistivity of La0.65Sr0.30MnO3 exhibited a metal–insulator (MI) transition at about 180 K. The magnetoresistance (MR) effect (ΔR/R(0)) was about -50% at the transition temperature. Our nitrogen contents affected the MI transition so as to completely disappear and resulted in a resistivity increase of more than three orders of magnitude as well. By carefully reoxidizing the samples with subsequent heat treatments in air the MI transition reappeared at lower temperatures and we found a continuously enhanced MR ratio for decreasing temperatures. MR ratios of more than -99% were observed for a magnetic field of 10 T. The results are interpreted as a percolation phenomenon of ferromagnetic–metallic domains within an antiferromagnetic–semiconducting matrix.

Oxygen Effects in Plasma Nitriding of Ferrous Alloys

In this paper, we study the oxygen effect in low energy nitrogen implanted stainless steel AISI 316 at different oxygen partial pressures and temperatures. The samples were studied by photoemission electron spectroscopy (XPS) and sputtered neutral mass spectrometry (SNMS). Increasing the oxygen partial pressure during nitriding decreases the nitrogen content in the material depth. Surface oxidation induces phase segregation. The presence of oxygen forms CrOχ on the top most layer of the sample and, subsequently, a nickel layer appears at approximately 9–10 nm beneath the surface. Moreover, the surface oxidation reaction of metal elements depends more strongly on the oxygen atoms landing on the surface rather than on the temperature process. At higher temperatures, on the other hand, the NOχ species are degraded.

The role of SiO2 barrier layers in determining the structure and photocatalytic activity of TiO2 films deposited on stainless steel

Abstract TiO 2 thin films were deposited using two different precursor systems, and their photocatalytic activities studied in the context of the feasibility of self-cleaning added value steel products. SiO 2 layers deposited using flame-assisted CVD were investigated as possible barrier layers to prevent diffusion of substrate components in to the TiO 2 films. The films were characterized by X-ray photoelectron spectroscopy (XPS), sputtered neutral mass spectrometry (SNMS), Raman spectroscopy and scanning electron microscopy (SEM). Photo-activity was characterised by the UV-induced destruction of stearic acid layers. On bare steel growth using titanium tetraisopropoxide yielded anatase, while growth with titanium tetrachloride (with ethyl acetate) yielded rutile. In contrast, on silica coated steels both precursor systems yielded anatase exclusively. The diffusion of components originating from the steel substrates was shown to have a deleterious effect on the photoactivities of the TiO 2 thin films, with this effect being more influential at higher deposition temperatures. However, the presence of the SiO 2 barrier layers significantly reduced ion diffusion into the TiO 2 film and consequently also improved the photocatalytic activity of the samples. While the SiO 2 coated samples gave rise to anatase growth, there is evidence that the thickness of the SiO 2 coating has a direct effect on TiO 2 morphology.

Iron nitrocarburising in flowing post-discharge: Evolution of the compound layer

In this work, the monitoring of mass increase during post-discharge nitrocarburising treatments by sample controlled thermogravimetry (SCTG) is presented. For the first time, a thermobalance is mounted on a post-discharge reactor to study the kinetics of the compound layer growth by following carbon and nitrogen uptakes. Pure iron specimens are successfully nitrocarburised in N 2–H 2–CH 4 post-discharge. The treatments lead to a compound layer composed by a dual phase: a γ′-Fe 4(N,C) sublayer beneath a ε-Fe 2(N,C) 1− x layer. The monitored mass gain exhibits an incubation time due to the nucleation step of only 100 s before a parabolic mass increase. Iron nitrocarbide layers synthesised at 853 K in post-discharge were investigated by optical microscopy, X-ray diffraction (XRD) analysis and Sputtered Neutral Mass Spectroscopy (SNMS). The carbon concentration in the substrate does increase after treatment despite it remains lower than necessary to avoid the growth of the γ′-phase.

XRF and SIMS/SNMS analyses of BaxSr1-xTiO3 dielectrics.

The development of analytical tools and procedures for process control is a prerequisite for the integration of high permittivity and/or ferroelectric materials in CMOS devices. The thickness and composition of perovskite oxide films were determined by wavelength dispersive X-ray fluorescence analysis (XRF) with special emphasis on the ratio of the group-II elements to the Ti content, and a precision of 0.5% was achieved for a typical film thickness of 20-30 nm. Secondary ion mass spectrometry (SIMS) and sputtered neutrals mass spectrometry (SNMS) was used for depth profiling to determine film homogeneity and elemental interdiffusion at hetero-interfaces. Examples are given for Ba(x)Sr(1-x)TiO(3) and SrTiO(x) thin films which were grown in a prototype MOCVD production tool. No interdiffusion was observed for films grown at 600 degrees C on Pt electrodes in contrast to films grown directly on Si.

H +, Na +, and K + ion sensing properties of sodium and aluminum coimplanted LPCVD silicon oxynitride thin films

Three different silicon oxynitride layers were fabricated by varying NH 3/N 2O flow rate ratios in low pressure chemical vapor deposition (LPCVD) process. Sodium and aluminum were then coimplanted by implanting sodium ions with the energy of 100 keV and dose of 5×10 16 cm −2 into an aluminum buffer layer on silicon dioxide and three different silicon oxynitride layers. The composition of the as-deposited silicon oxynitride layers was analyzed by sputtered neutral mass spectroscopy (SNMS). Sodium, potassium and pH-sensing properties of the layers were investigated on an electrolyte-isolator-silicon (EIS) structure using high frequency capacitance–voltage (HF-CV) measurements. Differences of pH, sodium and potassium sensing properties between the as-deposited silicon oxynitride layers and the coimplanted silicon oxynitride layers were investigated. The sodium and aluminum coimplanted layers showed better sodium and potassium sensitivity as well as a lower sensitivity towards hydrogen ions. The effect is more pronounced for higher oxygen concentration in the layers. On the other hand the stability of ion response of the layers, in contrast, is better for the higher nitrogen content of the layers.

Estimation of useful yield in surface analysis using single photon ionisation

Secondary ion mass spectrometry (SIMS), laser sputter neutral mass spectrometry (SNMS) and laser desorption photoionisation (LDPI) have been used to investigate the desorption of molecules from self-assembled monolayers of phenylsulphides. LDPI, using an F 2 excimer laser to single photon ionise gave the lowest fragmentation. A useful yield greater than 0.5% was found for analysis of diphenyldisulphide self-assembled monolayers. It is shown that using a free electron laser to postionise will lead, in the future, to analysis of many atoms and molecules with useful yields approaching 30%.

Energy distributions and excitation probability of nickel atoms sputtered from Ni 3Al, NiAl and Ni

The resonant electron tunnelling (RET) model for the sputtering of atoms in excited electronic states has been tested for Ni atoms sputtered from Ni, Ni 3Al and NiAl. Laser sputter neutral mass spectrometry using one-colour two-photon ionisation schemes has been used to measure the relative yields of atoms sputtered into the 3 F ground atomic state and the 3 D metastable state. It is found that more Ni atoms are sputtered into the excited state than the ground state, and that the energy distribution of sputtered atoms peaks at a higher energy for the excited state compared to the ground state, as found previously. In addition the relative population of the 3 D state is more pronounced for NiAl than for Ni 3Al or Ni. This is due to the increased interaction strength in NiAl, due to greater overlapping between the surface and atomic electronic structures.

MOCVD deposition of YSZ on stainless steels

Yttria stabilized zirconia was deposited on stainless steel using the metal–organic chemical vapor deposition (MOCVD) technique, from β-diketonate precursors. The variation of the evaporation temperatures of yttrium and zirconium precursor allowed to control the level of Y within the film. Over the temperature range 125–150°C, the Y content increased from 2.5 to 17.6at.%. X-ray diffraction (XRD) analyses evidenced tetragonal phase of zirconia when the Y content was below 8at.%, and cubic phase for higher concentration. Sputtered neutral mass spectrometry (SNMS) profiles confirmed that the control and stability of Y precursor temperature were of major importance to guarantee the homogeneity of the deposited films.