Auger Depth Profiling Measurements Research Articles

Self-organization of mesoscopic silver wires by electrochemical deposition.

Long, straight mesoscale silver wires have been fabricated from AgNO3 electrolyte via electrodeposition without the help of templates, additives, and surfactants. Although the wire growth speed is very fast due to growth under non-equilibrium conditions, the wire morphology is regular and uniform in diameter. Structural studies reveal that the wires are single-crystalline, with the [112] direction as the growth direction. A possible growth mechanism is suggested. Auger depth profile measurements show that the wires are stable against oxidation under ambient conditions. This unique system provides a convenient way for the study of self-organization in electrochemical environments as well as for the fabrication of highly-ordered, single-crystalline metal nanowires.

Observation of sulfur on the surface of giant aurothiol nanoclusters.

We report the study of aurothiol nanoclusters using high-resolution electron microscopy, energy loss spectroscopy, X-ray photoelectron spectroscopy, Auger spectroscopy, and microscopy. It is concluded that the sulfur atoms are located on the surface of the gold nanoparticles in both (100) and (111) microfacets. The X-ray photoelectron spectroscopy data show that there is a Au-Au bond as well as a Au-S bond. Auger depth profile measurements made by sputtering of the nanoparticles corroborates that the sulfur is located on the surface of the nanoparticle. Quantitative Auger analysis indicates a ratio Au/S between approximately 1.79 and 1.98.

Optical and structural properties of sol-gel SiO2 layers containing cobalt

SiO 2 coatings containing cobalt were prepared using the sol-gel method and the Si to Co nominal atomic ratio in the coatings was varied from 1.3 to 7.1. The structure and optical properties of the coatings, heat-treated in air at 300 and 500 °C, were characterized using optical, x-ray diffraction, and Auger depth profile measurements. The optical transmission data in the UV-visible range, in samples with low cobalt concentrations, show only the absorption bands associated with the tetragonal Co2+, regardless of the heat treatment temperature. Coatings with a larger amount of Co treated at 300 °C show absorption bands associated with both tetragonal and octahedral Co2+. When these coatings are heat treated at 500 °C, most of the cobalt migrates to the free surface of the coatings, where it is oxidized by the atmospheric oxygen and forms a top layer of Co3O4. The thickness of the cobalt oxide layer depends on the heat treatment temperature and on the Co concentration. To describe the absorption bands of both tetragonal and octahedral Co, the Lorentz oscillator model was used to represent the complex effective dielectric function of the SiO2 cobalt doped layers. The frequency dependence of the optical constants, in the UV-visible range for the top cobalt oxide layer, was obtained with a Jellison–Modine model.

Formation of a Co3O4 Top Layer in SiO2 Cobalt Containing Coatings Sol-gel Obtained

ABSTRACTSiO2 coatings containing cobalt were prepared on glass substrates using the sol-gel method. It has been found that in coatings with a Si to Co ratio of 1.3, a layer of Co3O4 is formed at the free surface of the coating upon thermal annealings in air. The properties of the coatings were studied using optical, x-ray and Auger depth profile measurements. The thermal annealings in the temperature range of 300 to 500 oC, in steps of 50 oC, were performed for 10 min. Some samples were subjected to an isothermal annealing at 400 °C for different times from 10 to 210 min. From the x-ray diffraction patterns the cubic spinel structure of Co3O4 was detected after the thermal treatments. The optical reflection and transmission spectra for each annealing temperature and annealing time, are described with an air-Co3O4-SiO2:Co2+-substrate system. From this, the cobalt oxide thickness was obtained as a function of the annealing temperature and annealing time. From the Arrhenius plots, in the temperature range studied, it was found that the activation energy for the growth of the cobalt oxide layer is 0.41 eV. The layer thickness follows a parabolic behavior with time, which suggests a diffusion-controlled process. The Auger depth profiles obtained from a sample annealed at 500 °C confirm the optical model used.

Interaction of potassium with Fe 3O 4(111) at elevated temperatures

The surface structures formed by the annealing of a potassium overlayer on Fe 3O 4(111) were investigated by low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). Annealing at 600–700°C in vacuum or 10 −6 mbar of oxygen resulted in well-ordered surface structures depending on the amount of potassium pre-deposited. As the K coverage increased, the surface transformed gradually from a (4×4) to a (2×2), and then, to a (1×1) structure relative to the original Fe 3O 4(111)-(1×1) surface. At low coverage, the (4×4) structure was formed by a long-range modulation of the surface with an ∼24 Å periodicity, which exhibited an internal 6 Å periodicity characteristic of the Fe 3O 4(111)-(1×1) surface. At mid-coverage, two sorts of (2×2) domains were observed, which were distinguished by the different diameter of protrusions forming an STM image. They were attributed to the different states of potassium in the top layer. These domains coexisted on the surface and were found in both oxidative and vacuum preparations. At high K coverage, the surface exhibited a (1×1) structure with a high density of vacancy defects. Auger depth-profile measurements confirmed the diffusion of potassium into the iron oxide bulk at elevated temperatures. The formation of a non-stoichiometric K 2O/K 2Fe 22O 34/Fe 3O 4(111) interface with a gradually decreasing potassium concentration with depth has been suggested.

Oxygen diffusion in silica glass prepared by the sol–gel method

The oxygen diffusion constants for SiO 2 coatings, prepared by the sol–gel method, were determined from Auger depth profile and Raman measurements. To do that, the coatings were deposited on copper substrates, and isothermally treated at various temperatures in air. The oxygen diffusion through the glass coating formed an oxide layer at the copper/SiO 2 interface. The treatment times, at a given temperature were maintained until the minimum thickness of the copper oxide layer formed at the copper/SiO 2 interface was detectable by Raman spectroscopy. This oxide layer thickness was determined from Auger depth profile measurements. The room temperature values for the diffusion constant and the activation energy were, 2.2×10 −15 cm 2/s and 0.5 eV, respectively.

Effect of power on interface and electrical properties of SiO2 films produced by plasma-enhanced chemical-vapor deposition

The effect of power on the electrical and interface properties of silicon dioxide films produced by direct plasma-enhanced chemical-vapor deposition, using nitrous oxide and silane with high helium dilution, has been investigated. Auger depth profiling measurements indicate that while the bulk of the films have no measurable impurities, the interface region contains about 1.6×1015 atoms/cm2 of nitrogen. In contrast to thermal oxides, there is no thick interface layer with a large intrinsic compressive stress. The interface-state densities of the films obtained from capacitance-voltage measurements on metal-oxide-semiconductor diodes increase with increasing plasma power, but these can be removed to some extent by high-temperature annealing at temperatures in the range 800–950 °C. The flatband voltage is relatively insensitive to plasma power. Thermal oxide samples have been subjected to the plasma processes and these also show evidence of plasma damage. A thin layer produced at the interface by a separate plasma oxynitridation process is shown to be incapable of protecting the Si/SiO2 interface from the plasma damage produced by subsequent high-power plasma deposition processes. The nature of the interface states is discussed.

Structural and Electrical Characterization of Si-Implanted TiN as a Diffusion Barrier for Cu Metallization

AbstractThe feasibility of Si-implanted TiN as a diffusion barrier between Cu and Si was investigated. Barrier effectiveness was evaluated via reverse leakage current of Cu/TixSiyNz/Si diodes as a function of post-deposition annealing temperature and time, and was found to depend heavily on the film composition and microstructure. TiN implanted with Si28, l0keV, 5xl016ions/cm2 formed an amorphous ternary TixSiyNz layer whose performance as a barrier to Cu diffusion exceeded that of unimplanted, polycrystalline TiN. Results from current-voltage, transmission electron microscopy (TEM), and Auger depth profiling measurements will be presented. The relationship between Si-implantation dose, TixSiyNz structure and reverse leakage current of Cu/TixSiyNz/Si diodes will be discussed, along with implications as to the suitability of these structures in Cu metallization.

Optical studies of InP/InAlAs/InP interface recombinations

We report on the photoluminescence characterization of a metalorganic vapour phase epitaxy grown InP/InAlAs/InP structure. The energy band alignment of the InAlAs/InP interface is of type II. The PL arising from the first grown interface (InAlAs grown on InP) is clearly seen at 1.2 eV. The localization was possible by scanning the laser beam on a angle-bevelled sample whose bevel crosses all the layers of the InP/InAlAs/InP structure. For the second interface, called the inverse interface (InP grown on InAlAs), a different PL behaviour is observed. The energy of the observed PL peak is 1.3 eV. It is very sensitive to the excitation power. From this behaviour, the Auger depth profiling measurements and the wedge transmission electron microscopy performed on this sample we conclude that this recombination does not originate from a type II interface band structure but from an InAsxP1-x layer located at the inverse interface. This intermediate layer originates from the higher incorporation coefficient of As compared to that of P.

Liquid Phase Epitaxy of AlGaInP on GaAs Substrate Using AlGaAs Buffer Layer

AbstractLiquid phase epitaxial layers of AlGaInP were successfully grown on Al0.9Ga0.1 As buffer layer with varying aluminum melt composition. Epitaxial layers were characterised by using a scanning elelctron microscope, X‐ray diffraction, photoluminescence (PL) and Auger depth profile measurements. The shortest peak wavelength of PL spectra obtained in the samples was 630 nm at room temperature. It was found that the thickness of the AlGaInP layer is very small due to rapid change of aluminum in the melt composition.

Si-YBaCuO intermixing and reactive patterning technique

A novel Si-YBaCuO intermixing technique has been developed for patterning YBaCuO superconducting thin films on both insulating oxide substrates (MgO) and semiconductor substrates (Si). The electrical, structural, and interfacial properties of the Si-YBaCuO intermixed system have been studied using resistivity, x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy and Auger depth profiling measurements. The study showed that the reaction of Si with YBaCuO and formation of silicon oxides during a high temperature process destroyed superconductivity of the film and created an insulating film. On a MgO substrate, the patterning process was carried out by first patterning a silicon layer using photolithography or laser-direct-writing, followed by the deposition of YBaCuO film and annealing. For a silicon substrate, thin metal layers of Ag and Au were patterned as a buffer mask which defines the YBaCuO structures fabricated thereafter. Micron-sized (2-10 Μm) superconducting structures with zero resistance temperature above 77 K have been demonstrated. This technique has been used to fabricate current controlled HTS switches and interconnects.

A study of polycrystalline Cd(Zn, Mn)Te/Cds films and interfaces

Polycrystalline films of Cd1-xZnxTe (x = 0–0.4) and Cd1-xMnxTe (x = 0–0.25) were grown by MBE and MOCVD, respectively, on CdS/SnO2/glass substrates to investigate their feasibility for solar cell applications. The compositional uniformity and interface quality of the films were analyzed by x-ray diffraction, surface photovoltage, and Auger depth profile measurements to establish a correlation between growth conditions and lattice constant, atomic concentration, and bandgap of the ternary films. MBE-grown polycrystalline Cd1-xZnxTe films showed a linear dependence between Zn/(Cd + Zn) beam flux ratio, Zn concentration in the film, and the bandgap. Polycrystalline Cd1-xZnxTe films grown at 300° C showed good compositional uniformity in contrast to compositionally non-uniform Cd1-xMnxTe films grown by MOCVD in the temperature range of 420–450° C. The MBE-grown Cd1-xZnxTe interface also showed significantly less interdiffusion compared to the MOCVD-grown Cd1-xMnxTe/CdS interface, where preferential exchange between Cd from the CdS layer and Mn from the Cd1-xMnxTe film was observed. The compositional uniformity of MOCVD-grown polycrystalline Cd1-xMnxTe films grown on CdS/SnO2/glass substrates was found to be a strong function of the growth conditions as well as the Mn source.

Novel method of patterning YBaCuO superconducting thin films

A unique method of patterning YBaCuO thin films based on the inhibition of superconductivity by Si-YBaCuO intermixing has been developed. In the experiment, a thin Si film was first evaporated on a MgO substrate and subsequently patterned using laser direct-write etching. Multilayered YBaCuO thin films were then deposited by e-beam evaporation and annealed in a rapid thermal annealing system for 30–90 s at 980 °C. The YBaCuO film deposited on the silicon regions became insulating. Auger depth profiling measurements indicate that Si-YBaCuO intermixing had occurred in these areas. Between the insulating regions, narrow YBaCuO superconducting lines were formed. For both 10-μm-wide, 1-mm-long and 2.5-μm-wide, 80-μm-long lines, the Tc was observed above 76 K. The critical current density of the lines was measured to be 300 A/cm2 at 75 K. This patterning technique may be useful for fabrication of high Tc superconducting interconnects and devices.

Comparison of YBa/sub 2/Cu/sub 3/O/sub 7/ films grown by solid-state and vapor-phase epitaxy

Epitaxial films of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) have been grown on single-crystal SrTiO/sub 3/ and MgO substrates by two different routes using RF and DC magnetron cosputtering. In the first case, amorphous oxide films were deposited at a substrate temperature of 400 degrees C and the crystalline film grew by solid-state epitaxy in an in situ postanneal at approximately 850 degrees C. In the second case, a substrate temperature of 600-650 degrees C was used which was sufficient to crystallize the film as it was deposited from the vapor phase. Reaction with the substrate was less for the films grown by vapor-phase epitaxy-even when they were annealed at 850 degrees C-as shown by the transition temperatures of very thin films, Auger depth profile measurements, in situ XPS analysis, and transmission electron microscopy. XPS was used to show that segregation of Ba at the free surface can occur in either type of film. The relative merits of each growth process are discussed for microwave applications and tunnel junction fabrication. >

Use of Si-YBaCuO Intermixed System for Patterning of Superconducting Thin Films

AbstractA Si-YBaCuO intermixed system has been formed using rapid thermal annealing (RTA) of Cu/BaO/Y2O2/Si layered structures, which were deposited on MgO substrates by electron-beam evaporation. The electrical and structural properties of the Si-YBaCuO system have been analyzed by resistivity, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy and Auger depth profiling measurements. It was found that Si mixed with YBaCuO during annealing, thus creating an insulating film. This effect has been used to pattern YBaCuO films. The patterning process was carried out on an underlying silicon layer, rather than the YBaCuO film itself, using conventional photolithography or laser etching. After YBaCuO film deposition and RTA, the patterned region became superconducting separated by Si-YBaCuO intermixed areas. Micron-sized line features with Tc's above 77 K have been demonstrated.

Auger depth profiling and preferential sputtering of platinum nickel silicide

Auger depth profiling measurements are presented of platinum nickel silicide films grown on n-Si and on n+-Si by annealing a sputter-deposited Pt0.4Ni0.6 alloy layer at 500 °C for 20 min in N2. Quantification of the profiles is achieved by calibration with standards. The silicide composition varies with depth and at the interface is PtxNi1−xSi with x≪1. Also, total sputtering yields and preferential sputtering coefficients are given for 2 keV, 45°, Ar+ bombardment of the elements and their binary and ternary silicides. The amount of preferential sputtering is practically independent of projectile energy (0.5–5 keV) and of substituting Xe+ for Ar+. However, its variation with composition complicates the quantitative analysis of nickel.

Bilayer silicide formation during the interaction of thin chromium, nickel and platinum films with silicon

Silicide formation in the Si/Ni/Cr and Si/Pt/Cr tertiary systems was investigated. NiSi and PtSi formation was found to take place at about 350 °C, whilst subsequent CrSi 2 growth on top of these silicides started at approximately 440 °C for NiSi and 500 °C for PtSi. The CrSi 2 formation was found to be linear with time, indicating a reaction-limited process. In both cases the silicide phases stayed well separated, with no evidence of tertiary compound formation. The growth rate of CrSi 2 on epitaxial PtSi was found to be nearly 30% slower than that on non-epitaxial PtSi, whilst the activation energy for CrSi 2 formation on NiSi and PtSi was found to be the same, namely 1.8±0.2 eV for both Si〈100〉 and Si〈111〉 substrates. Auger depth profile measurements indicated that the observed delay times before CrSi 2 formation started to take place, and the large difference in the temperature at which CrSi 2 starts to grow on NiSi and PtSi, could probably be ascribed to oxygen contamination.

Determination of the depth resolution in Auger depth profiling measurements

The depth resolution Δ z of the Auger depth profiling method was studied in multilayer thin films comprising alternate layers of nickel and molybdenum or of cobalt and molybdenum. The composition-depth profiles of several interfaces located at different depths within the same film were compared. Thus changes which depended on the sputtering depth z could be distinguished from effects which were independent of z. According to a statistical theory the profiles of the interfaces can be described by a gaussian error function. An empirical formula Δz = αz 1 2 + β was determined from the width of the profiles. The first term agrees with the statistical theory and the constant term is explained by the roughness of the interface. The order of magnitude of β (≈ 3 nm) suggests that the depth resolution in the films is not limited by the escape depth of the Auger electrons (⩽ 1.5 nm). The relative depth resolution Δz z improves with increasing sputtering depth.