Auger Electron Spectroscopy Measurements Research Articles

Co-deposition of bismuth-nitrogen films on MgO (001) by molecular beam epitaxy

We attempted to grow a thin film of BiN by co-deposition of bismuth and nitrogen on rock-salt structure MgO (001) substrates. Furthermore, we studied the effect of variation of the growth temperature and the nitrogen to bismuth flux ratios on sample growth. For the samples grown and conditions used, we do not find strong evidence for the formation of a bulk Bi-N alloy. Even for very high nitrogen to bismuth flux ratio, we observed only bismuth and no nitrogen using bulk Rutherford back-scattering spectroscopy measurements, and only 1%–2% nitrogen was seen through surface Auger electron spectroscopy measurements. The in-plane lattice measurements show that the resulting Bi (110) samples are strained, which is presumably caused by lattice mismatch between the sample and the substrate when grown without any buffer layer. The use of a high-temperature buffer layer helps to release strain in the sample but only along one axis. Measurements of the atomic layer spacing using x-ray diffraction and also scanning tunneling microscopy confirm the Bi (110) thin film sample structure.

Surface chemical states and structures of epitaxial Mg2Sn thermoelectric thin films

Abstract Evaluation of the surface chemical states and structures of thermoelectric thin films is vital for the successful fabrication and operation of microscale thermoelectric devices incorporating such films. The chemical states and structures present in the surface layers of epitaxially grown Mg2Sn thermoelectric thin films were evaluated by Auger electron spectroscopy and reflection high-energy electron diffraction measurements. An oxide layer about 5 Å thick was shown to form on the surface of epitaxially grown Mg2Sn thermoelectric thin films on exposure to air, giving meaningful insights into potential ways of improving the microfabrication of thin-film-based miniaturized thermoelectric devices.

Drop-Dry Deposition of SnO2 Using a Complexing Agent and Fabrication of Heterojunctions with Co3O4.

The drop-dry deposition (DDD) is a simple chemical technique of thin film deposition, which can be applied to metal oxides. The deposition solution is an aqueous solution including a metal salt and an alkali. However, some metal ions react spontaneously with water and precipitate. This work is the first attempt to use complexing agents in DDD to suppress the precipitation. SnO2 thin films are fabricated using DDD with Na2S2O3 as a complexing agent and via annealing in air. The results of the Auger electron spectroscopy measurement show that the O/Sn composition ratio of the annealed films approached two, indicating that the annealed films are SnO2. The photoelectrochemical measurement results show that the annealed films are n-type. Co3O4/SnO2 heterojunction is fabricated using p-type Co3O4 films which are also deposited via DDD. The heterojunction has rectification and photovoltaic properties. Thus, for the first time, a metal oxide thin film was successfully prepared via DDD using a complexing agent, and oxide thin film solar cells are successfully prepared using only DDD.

Characterization of pulsed laser deposited La2O2S:Eu3+ thin films and effect of coating with graphene oxide layers

Surface coatings have been widely used to improve phosphor characteristics for the purpose of increasing luminescence intensity and protecting against degradation. In this study, an uncoated La2O2S:Eu3+ thin film is compared to films coated by graphene oxide, as prepared or annealed in an inert or reducing atmosphere. The characteristic red emission of Eu3+ ions was observed for all samples and attributed to 5D0-7F2 transitions, while no luminescence associated with graphene oxide was observed. The luminescence intensity from the as-coated sample and the one annealed in an inert Ar atmosphere was less, compared to the uncoated film, whereas the coated sample annealed in a reducing atmosphere (Ar/H2) had emission, which was of similar intensity to the uncoated sample. Its degradation, and that of the uncoated sample, were studied by recording Auger electron spectroscopy and cathodoluminescence measurements, simultaneously. During electron irradiation, the surface of the uncoated sample was converted to a much more luminescent layer as C and S were gradually removed from the surface. Auger electron spectroscopy measurements of the coated sample showed that even initially, it had almost no S on the surface. The loss of S was attributed to annealing in Ar/H2, where H2S gas may be produced as the phosphor was converted into La2O3. This La2O3 subsequently formed La(OH)3 due to its hydroscopic nature. Unlike the uncoated sample, from which C due to unintentional contamination was fairly easily removed from the surface, C on the surface of the coated sample became less but was resistant to removal, which was associated with the formation of CHLaO3 at the surface as suggested by x-ray diffraction. Although coating with graphene oxide did not result in chemically stable La2O2S:Eu3+ thin films, the cathodoluminescence intensity of both the uncoated and graphene oxide coated samples annealed in reducing atmosphere increased during electron beam exposure (with no change in the form of the emission spectra) so that such films may have potential cathodoluminescence applications.

Reversible structural transition of two-dimensional copper selenide on Cu(111)

Structural engineering opens a door to manipulating the structures and thus tuning the properties of two-dimensional materials. Here, we report a reversible structural transition in honeycomb CuSe monolayer on Cu(111) through scanning tunneling microscopy and Auger electron spectroscopy (AES). Direct selenization of Cu(111) gives rise to the formation of honeycomb CuSe monolayers with one-dimensional moiré structures (stripe-CuSe), due to the asymmetric lattice distortions in CuSe induced by the lattice mismatch. Additional deposition of Se combined with post annealing results in the formation of honeycomb CuSe with quasi-ordered arrays of triangular holes (hole-CuSe), namely, the structural transition from stripe-CuSe to hole-CuSe. Further, annealing the hole-CuSe at higher temperature leads to the reverse structural transition, namely from hole-CuSe to stripe-CuSe. AES measurement unravels the Se content change in the reversible structural transition. Therefore, both the Se coverage and annealing temperature play significant roles in the reversible structural transition in CuSe on Cu(111). Our work provides insights in understanding of the structural transitions in two-dimensional materials.

Unraveling the Highly Complex Nature of Antimony on Pt(111)

AbstractUnderstanding the growth behavior of group‐V elements on metal surfaces provides valuable information that can shed light on the feasibility of tailoring atomically thin monoelemental 2D polymorphs composed of pnictogens on these metallic substrates. Here, by combining scanning tunneling microscopy (STM), low energy electron diffraction and Auger electron spectroscopy measurements under ultra‐high vacuum conditions, a wide variety of Sb reconstructions on single‐crystal Pt(111) are identified and characterized. At Sb coverage of ≈0.2 ML, STM data are compatible with a scenario in which Sb atoms are randomly embedded into the topmost layer of Pt, in a substitutional configuration and without establishing a periodic structure. This disorder is robust against thermal annealing and quenching. Increasing the surface coverage and whether or not the sample is annealed, different well‐ordered Sb phases are formed. The Sb structures synthesized at room temperature without any heating process are best interpreted as surface alloys that involve only the first atomic layer. In contrast, experimental evidence points towards the development of multilayer alloy phases for the annealed samples.

Electronic coupling between the unoccupied states of the organic and inorganic sublattices of methylammonium lead iodide: A hybrid organic-inorganic perovskite single crystal

Organic-inorganic halide perovskites have been intensively re-investigated due to their applications, yet the opto-electronic function of the organic cation remains unclear. Through organic-selective resonant Auger electron spectroscopy measurements on well-defined single crystal surfaces, we find evidence for electronic coupling in the unoccupied states between the organic and inorganic sub-lattices of the prototypical hybrid perovskite, which is contrary to the notion based on previous studies that the organic cation is electronically inert. The coupling is relevant for electron dynamics in the material and for understanding opto-electronic functionality.

A novel method to determine Ga profile in CIGS thin film compound via focused ion beam modification

Ga profile is a critical design in CIGS thin film solar cells to enhance device performance. Many techniques have been exploited to determine Ga profiles including secondary ion mass spectroscopy (SIMS), Auger electron spectroscopy (AES), Raman depth profiling and Energy-dispersive X-ray spectrometry in a scanning electron microscope (SEM-EDX) etc. These techniques, when considering deployment in a manufacturing environment, are either time-consuming or expensive. Herein, a novel method is developed in this work to obtain Ga profiles by analyzing the Ga nanodots formed on CIGS cross-section under Focused Ion Beam (FIB) modification. A model of the formation of the Ga nanodots has been established and a mathematical method has been developed to process their depth distribution. Good agreement has been reached between the developed method and AES measurement. This method provides the fast-growing CIGS industry a fast, precise and cost-effective way to determine Ga profiles to realize process monitoring.

Surface Characterization of MoS2 Atomic Layers Mechanically Exfoliated on a Si Substrate.

Mo disulfide overlayers with the thickness exceeding 1.77 nm were obtained on Si substrates through mechanical exfoliation. The resulting Mo disulfide flakes were then analyzed ex situ using combination of Auger electron spectroscopy (AES), elastic-peak electron spectroscopy (EPES) and scanning electron microscopy (SEM) in order to characterize their surface chemical composition, electron transport phenomena and surface morphology. Prior to EPES measurements, the Mo disulfide surface was sputter-cleaned and amorphized by 3 kV argon ions, and the resulting S/Mo atomic ratio varied in the range 1.80–1.88, as found from AES measurements. The SEM images revealed single crystalline small-area (up to 15 μm in lateral size) Mo disulfide flakes having polygonal or near-triangular shapes. Such irregular-edged flakes exhibited high crystal quality and thickness uniformity. The inelastic mean free path (IMFP), characterizing electron transport, was evaluated from the relative EPES using Au reference material for electron energies E = 0.5–2 keV. Experimental IMFPs, λ, determined for the AES-measured surface compositions were approximated by the simple function λ = kEp, where k = 0.0289 and p = 0.946 were fitted parameters. Additionally, these IMFPs were compared with IMFPs resulting from the two methods: (i) present calculations based on the formalism of the Oswald et al. model; (ii) the predictive equation of Tanuma et al. (TPP-2M) for the measured Mo0.293S0.551C0.156 surface composition (S/Mo = 1.88), and also for stoichiometric MoS2 composition. The fitted function was found to be reasonably consistent with the measured, calculated and predicted IMFPs. We concluded that the measured IMFP value at 0.5 keV was only slightly affected by residual carbon contamination at the Mo disulfide surface.

Effect of microstructure on the passive behavior of selective laser melting-fabricated Hastelloy X in NaNO3 solution

The electrochemical dissolution characteristics of nickel-based alloys produced by selective laser melting (SLM) have received considerable attention in electrochemical machining (ECM). However, the passive behavior of Hastelloy X (HX) during ECM has not been systematically investigated so far. This study aimed to investigate the effect of microstructures on the passive behavior of SLM-fabricated HX, and compare it with that of wrought HX. The findings indicated that the XOY plane (perpendicular to build direction) with the refined microstructure exhibited a superior corrosion resistance. Compared to the wrought plane (the cross-sectional plane), the finer grain size, denser sub-grain boundaries, and dislocations all contributed to the formation of a more stable and thicker passivation film on the XOY plane of SLM HX in 10 wt% NaNO3 solution. An analysis of the Auger electron spectroscopy and X-ray photoelectron spectroscopy measurement results showed that a comparatively thick outer layer existed in the passivation film.

Formation of ordered anodic alumina nanofibers during aluminum anodizing in oxalic acid at high voltage and electrical power

In this study, we modified the synthesis modes of aluminum anodizing in an aqueous solution of oxalic acid and suggested quick, one-step and convenient method for porous alumina surface modification to increase largely its surface area. Anodic alumina nanofibers consisting of pure aluminum oxide were formed by high field anodizing with evolving of Joule heating of aluminum foil of 60 and 100 μm thickness in 0.3 M aqueous solution of oxalic acid. It was shown that nanofibers formed on the surface of the films for an anodizing voltage of 90 V and a power range of 13.5–31.5 W cm−2. The thickness of the Al foil has proved to be responsible for the formation of the alumina nanofibers, which cannot be obtained in the same electrolyte and for similar current densities on 25 μm thick aluminum foil. We could show that during anodizing of 60 μm thick Al foil, regardless of anodic current density value, alumina nanofibers uniformly covered the entire surface of the films. However, during 100 μm Al foil anodizing, the pores were etched and the nanofibers partially dissolved and separated from the surface with increasing anodizing current density. Auger electron spectroscopy measurements showed that porous anodic alumina containing carbon impurities was obtained during anodizing of the 25 μm Al foil. Alternatively, the surface of the nanofibers formed on 60 and 100 μm Al foil consisted of pure alumina.

The influence of the atomic scale interface roughness on the GMR effect in Fe/Cr multilayers

In this study, we analysed Fe/Cr multilayers that had been modified by Bi, In, and Pb surfactants. Their structure, morphology and interface roughness were investigated using low-energy electron diffraction, Auger electron spectroscopy (AES), X-ray reflectivity and conversion electron Mössbauer spectroscopy (CEMS). The magnetic and magnetotransport properties of the multilayers were studied by measuring the Kerr effect and four-point magnetoresistance, respectively.We observed that the Bi surfactant caused a slight interface smoothening while the introduction of In and Pb surfactants had a negative influence on the epitaxial growth of Fe and Cr, which were associated with an increase of interface roughness. These changes did not destroy the layer continuity, which was confirmed by AES measurements. The magnetic measurements revealed an antiferromagnetic coupling of the Fe layers for the as-deposited sample as well as for the Bi and Pb-modified multilayers and its partial reduction for the In-modified sample. We observed that the increase of interface roughness that had originated from atom intermixing resulted in a reduction of the giant magnetoresistance. In these investigations in which CEMS studies were used, we were able to distinguish between the interface roughness that was caused by atom intermixing and interface corrugation.

Cathodoluminescence degradation of Y2O3:Dy3+ nanophosphor for field emission displays

Cathodoluminescence (CL) degradation of Y2O3:Dy3+ nanophosphors prepared by the solution combustion method was explored for feasible applications in low voltage field emission displays (FEDs). Oxide materials are excellent candidates for FED fabrication due to their high melting points, chemical and radiation stability with long lifetimes, high color purity, and being environmentally friendly. Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) were used to monitor changes in the surface chemical composition and correlation fit with CL degradation. AES and CL spectroscopy (2 keV energy electrons and with a beam current of 15 μA) measurements were done in high vacuum (1.5 × 10−8 Torr) and oxygen pressures of 1 × 10−7 and 5 × 10−7 Torr. The Y2O3:Dy3+ nanophosphor showed strong yellow (572 nm) and relatively weaker blue (492 nm) CL emissions. These CL emissions increased as carbon (C) was depleted from the surface, and then it slightly decreased at a high electron dose in both the vacuum and oxygen atmospheres, for electron doses up to about 690 C/cm2. The C was depleted from the surface due to electron stimulated reactions. No significant change in the chemical state of Y 3d was observed with XPS high resolution spectra for the postirradiation sample. The change in the CL intensity was, therefore, attributed to the depletion of C from the surface.

Chemical bonding states and dopant redistribution of heavily phosphorus-doped epitaxial silicon films: Effects of millisecond laser annealing and doping concentration

We investigated the effect of millisecond (ms) laser annealing and doping concentration on the chemical bonding states and dopant behaviors of P-doped epitaxial Si (Si:P) layers grown on Si (1 0 0) substrates using high-resolution X-ray photoelectron spectroscopy (HR-XPS), secondary-ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) measurements. Our XPS results showed that the intensities of P 2p peaks for Si:P films were increased with P concentration and subsequent laser annealing. From the SIMS and AES measurement results, we found that P atoms were slightly accumulated at the near-surface region of the Si:P film by the laser annealing, while macroscopic P concentration being maintained in the whole Si:P films without significant diffusion of P atoms toward the Si (1 0 0) substrate. In addition, we performed ex-situ HF cleaning on the as-grown and laser-annealed Si:P films in order to precisely measure the change in chemical states and dopant distribution at the near-surface region. The intensities of the P 2p peak in the as-grown Si:P films were increased after the HF cleaning due to the removal of native oxide layers from the Si:P films. In contrast, the decrease in P 2p peak intensities was observed in the laser-annealed Si:P films after the HF cleaning, indicating the dopant loss from the near-surface region with native oxide removal.

Cathodoluminescence degradation of Bi doped La2O3 and La2O2S phosphor powders

Simultaneous cathodoluminescence (CL) and Auger electron spectroscopy (AES) measurements were performed on La2-xO3:Bix=0.002 and La2-xO2S:Bix=0.002 phosphor powders during long term exposure to an electron beam in order to assess the CL degradation and chemical changes on the surface. X-ray photoelectron spectroscopy (XPS) measurements were also made before and after CL degradation. After a small amount of initial CL degradation, the La2-xO3:Bix=0.002 sample remained stable under the electron beam and it may be suitable for use in field emission displays. However, the La2-xO2S:Bix=0.002 showed continuous and severe CL degradation and is not suitable for CL applications. During degradation AES measurements showed that there was a decrease in the surface concentration of S, suggesting the formation of a non-luminescent La2O3 surface layer which was responsible for degradation. However, some S remained on the surface and XPS spectra showed that a sulphate, possibly La2O2SO4, was present which may have contributed to the degradation.

Morphological, structural and room temperature optical properties of ZnO:Eu layers deposited by RF-Sputtering

The structural and optical properties of ZnO:Eu thin films deposited on silicon and glass substrates by the magnetron sputtering method have been studied by scanning electron microscopy, energy dispersive X-ray analysis, Auger electron spectroscopy, Raman spectroscopy and photoluminescence measurements. Intense red emission of Eu3+ dopant in ZnO films is issued by the band-to-band excitation and energy transfer from the host ZnO to europium ions.

Transition from silicene monolayer to thin Si films on Ag(111): comparison between experimental data and Monte Carlo simulation.

Scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low energy electron diffraction have been used to follow the growth of Si films on Ag(111) at various temperatures. Using a simple growth model, we have simulated the distribution of film thickness as a function of coverage during evaporation, for the different temperatures. In the temperature regime where multilayer silicene has been claimed to form (470–500 K), a good agreement is found with AES intensity variations and STM measurements within a Ag surfactant mediated growth, whereas a model with multilayer silicene growth fails to reproduce the AES measurements.

Formation and magnetic properties of InFeP:Ag nanorods fabricated with noble metal Ag using an ion milling method

The formation, including the density and height of the InFeP:Ag nanorods doped with noble metal Ag using an ion milling method, was preponderantly determined from transmission electron microscopy and x-ray diffraction analyses. We investigate, in particular, the enhanced ferromagnetism of the well-aligned InFeP:Ag nanorods. Auger electron spectroscopy and x-ray photoelectron spectroscopy measurements were carried out in order to investigate the incorporation of Ag and to verify the local chemical bonding of the InFeP:Ag nanorods. The variation of FWHM for the double-crystal x-ray rocking curve and triple-axis diffraction peaks demonstrates that noble metal Ag is incorporated into the InFeP:Ag nanorods. The noticeable ferromagnetic signature (M-H curve) of the InFeP:Ag nanorods is observed and Tc persists up to almost 350 K (3.9 × 10−4 emu g−1), as determined by temperature-dependence magnetization (M-T curve) measurements. This study suggests that the InFeP:Ag nanorods should be a potential candidate for the application of spintronic devices.

Comparing postdeposition reactions of electrons and radicals with Pt nanostructures created by focused electron beam induced deposition.

The ability of electrons and atomic hydrogen (AH) to remove residual chlorine from PtCl2 deposits created from cis-Pt(CO)2Cl2 by focused electron beam induced deposition (FEBID) is evaluated. Auger electron spectroscopy (AES) and energy-dispersive X-ray spectroscopy (EDS) measurements as well as thermodynamics calculations support the idea that electrons can remove chlorine from PtCl2 structures via an electron-stimulated desorption (ESD) process. It was found that the effectiveness of electrons to purify deposits greater than a few nanometers in height is compromised by the limited escape depth of the chloride ions generated in the purification step. In contrast, chlorine atoms can be efficiently and completely removed from PtCl2 deposits using AH, regardless of the thickness of the deposit. Although AH was found to be extremely effective at chemically purifying PtCl2 deposits, its viability as a FEBID purification strategy is compromised by the mobility of transient Pt–H species formed during the purification process. Scanning electron microscopy data show that this results in the formation of porous structures and can even cause the deposit to lose structural integrity. However, this phenomenon suggests that the use of AH may be a useful strategy to create high surface area Pt catalysts and may reverse the effects of sintering. In marked contrast to the effect observed with AH, densification of the structure was observed during the postdeposition purification of PtCx deposits created from MeCpPtMe3 using atomic oxygen (AO), although the limited penetration depth of AO restricts its effectiveness as a purification strategy to relatively small nanostructures.

Effect of surface preparation on the corrosion resistance of friction stir linear lap welded AZ31B-H24

ABSTRACTThe effect of surface preparations on the atmospheric (continuous NaCl salt fog) corrosion resistance of bare (uncoated) linear friction stir lap welded magnesium (Mg) alloy AZ31B-H24 joints was investigated. The surface preparations evaluated included as-received (as-welded for the weld zones), mechanically abraded and acid-cleaned. Electrochemical potentiodynamic polarisation, X-ray photoelectron spectroscopy and Auger electron spectroscopy measurements were made to elucidate the link between the surface preparation and the relative corrosion resistance observed across the microstructural zones of the joints. Heavy metal surface contamination of the as-received material, rather than the air-formed oxide or differences in alloy grain size resulting from variations in thermo-mechanical processing history, was found to be the controlling factor affecting the corrosion mode observed and, in turn, the relative corrosion resistance across the joint. Removal of the heavy metal contamination changed the corrosion mode from pit-like to filament-like, which in turn homogenised the corrosion resistance across the joint in the continuous salt fog exposure.