Chemical bonding in native oxides of GaAs, before and after etching, is detected by X-Ray Photoelectron Spectroscopy (XPS). It is correlated with surface energy engineering (SEE), measured via Three Liquid Contact Angle Analysis (3LCAA), and oxygen coverage, measured by High Resolution Ion Beam Analysis (HR-IBA).

Before etching, GaAs native oxides are found to be hydrophobic with an average surface energy, γT, of 33 ± 1 mJ/m2, as measured by 3LCAA. After dilute NH4OH etching, GaAs becomes highly hydrophilic and its surface energy, γT, increases by a factor 2 to a reproducible value of 66 ± 1 mJ/m2. Using HR-IBA, oxygen coverage on GaAs is found to decrease from 7.2 ± 0.5 monolayers (ML) to 3.6 ± 0.5 ML. The 1.17 ratio of Ga to As, measured by HR-IBA, remains constant after etching.

XPS is used to measure oxidation of Ga and As, as well as surface stoichiometry on two locations of several GaAs(100) wafers before and after etching. The relative proportions of Ga and As are unaffected by adventitious carbon contamination. The 1.16 Ga:As ratio, measured by XPS, matches HR-IBA analysis. The proportions of oxidized Ga and As do not change significantly after etching. However, the initial ratio of As2O5 to As2O3, within the oxidized As, significantly decreases after etching from approximately 3:1 to 3:2.

Absolute oxygen coverage, as a function of surface processing, is determined within 0.5 ML by HR-IBA. XPS offers insight into these modifications by detecting electronic states and phase composition changes of GaAs oxides. The changes in surface chemistry are correlated to changes in hydro-affinity and surface energies measured by 3LCAA.

Interaction of GaAs with sulfur can be immensely beneficial in reducing the deleterious effect of surface states on recombination attributes. Bonding of sulfur on GaAs is also important for developing novel molecular devices and sensors, where a molecular channel can be connected to GaAs surface via thiol functional group. However, the primary challenge lies in increasing the stability and effectiveness of the sulfur passivated GaAs. We have investigated the effect of single and double step surface passivation of n-GaAs(100) by using the sulfide and fluoride ions. Our single-step passivation involved the use of sulfide and fluoride ions individually. However, the two kinds of double-step passivations were performed by treating the n-GaAs surface. In the first approach GaAs surface was firstly treated with sulfide ions and secondly with fluoride ions, respectively. In the second double step approach GaAs surface was first treated with fluoride ions followed by sulfide ions, respectively. Sulfidation was conducted using the nonaqueous solution of sodium sulfide salt. Whereas the passivation steps with fluoride ion was performed with the aqueous solution of ammonium fluoride. Both sulfidation and fluoridation steps were performed either by dipping the GaAs sample in the desired ionic solution or electrochemically. Photoluminescence was conducted to characterize the relative changes in surface recombination velocity due to the single and double step surface passivation. Photoluminescence study showed that the double-step chemical treatment where GaAs was first treated with fluoride ions followed by the sulfide ions yielded the highest improvement. The time vs. photoluminescence study showed that this double-step passivation exhibited lower degradation rate as compared to widely discussed sulfide ion passivated GaAs surface. We also conducted surface elemental analysis using Rutherford Back Scattering to decipher the near surface chemical changes due to the four passivation methodologies we adopted. The double-step passivations affected the shallower region near GaAs surface as compared to the single step passivations.

Electrophoretic deposition enables the rapid deposition of single wall carbon nanotube films at room temperature. An accurate, reproducible film thickness can be obtained by controlling electric field strength, suspension concentration, and time. To investigate the electrical and mechanical properties of such films, we recorded electric resistance and Young’s modulus using I-V characterization and a nanoindenter, respectively. The measured resistivity of the films varied from 2.14 × 10-3 to 7.66 × 10-3 Ω·cm, and the Young’s modulus was 4.72 to 5.67 GPa, independent of film thickness from 77 to 134 nm. These results indicated that the mechanical and electrical properties of film are comparable with previously reported methods such as layer by layer deposition even though we achieved much higher deposition rates. We also measured the film mass density which is usually unrecorded even though it is an important parameter for MEMS/NEMS device actuation. The film density was found with conventional thickness measurement and Rutherford backscattering spectrometry. It varied from 0.12 to 0.54 g/cm3 as the film thickness increased. This method could be extended to applications of CNT films for flexible electronics or high frequency RF MEMS devices.

In this study, synthesis and characterization of rutile-Titanium dioxide (TiO2) thin films using pulsed DC Magnetron Sputtering at room temperature, along with the fabrication and characterization of MIM capacitors have been discussed. XPS and RBS data show that the films are stoichiometric and have compositional uniformity. The influence of electrode materials on electrical characteristics of the fabricated MIM capacitors has been studied. The Al/TiO2/Al based capacitors show low capacitance density (9 fF/μm2) with low dielectric constant (K=25) and high EOT (3.67 nm) due to low dielectric constant TiO2 phase formation on Al/Si substrate. On the other hand, Ru/TiO2/Ru based capacitors show high capacitance density (49 fF/μm2) with high dielectric constant (K=130) and low EOT (0.7nm) values at high frequency (100 KHz) due to high dielectric constant phase (rutile) formation of TiO2, on Ru/Si substrate. Raman spectra confirm that the films deposited on Ru/Si substrate show the rutile phase.

Thin films of Transition Metal Oxides (TMOs) were deposited by reactive sputtering of pure transition metal targets in Argon-Oxygen gas mixture at elevated substrate temperature for efficient energy consumption. The atomic composition and thickness of the TMO films was determined by Rutherford Backscattering Spectroscopy (RBS). Optical transmittance and reflectance spectrum of the films on quartz substrate was measured with thin film measuring system at room temperature and slightly elevated temperature. The surface morphology and structure of the TMO films was determined with Atomic Force Microscope (AFM).

An experimental set up has been designed to suppress electron currents generated during energetic ion irradiation to obtain accurate current integration for Heavy Ion Rutherford Backscattering Spectroscopy (HIRBS) measurements of heavy element concentrations and target depth profiles. A combination of an electron trap to suppress any electrons ejected from beam collimators and slits, and a biased aluminum mesh to suppress any secondary electrons ejected from the target was used. Two samples that produce cleanly interpreted spectra have been used as targets to check the accuracy of the system for 3.0 and 4.5 MeV O+2 projectile ions. Details of the experimental set up and data are presented.

In this work, we study the effects of implanted hydrogen ions on defect formation and impurity redistribution in ZnO crystals implanted with silver ions. Hydrogen was first implanted at room temperature in ZnO with energy of 30 keV to a dose of 2 × 1016 /cm2. The ZnO samples with and without prior H implantation were implanted with Ag ions at four different energies, 30, 75, 150, and 350 keV, to doses 3.3×1013, 4.2×1013, 8.3×1013 and 3.4×1014 /cm2, respectively, resulting in a uniform concentration profile of Ag from the surface to depth ~ 150 nm. These samples were annealed at temperatures 850-1050°C for 30 minutes in an oxygen gas flow. The distribution of Ag atoms, either aligned or nonaligned along the crystalline directions, were measured by Rutherford backscattering (RBS) combined with ion channeling. Following Ag ion implantation, the damage level in the ZnO lattice, measured along the <10-11> crystalline direction is higher in the sample without H ion implantation than the sample with H. Lattice damage was found to recover faster in the sample without H implantation than the sample with H, e.g., for Zn signals, the normalized RBS yield χmin for the without H-implanted sample dropped from 27.5% following Ag implantation to 4.3% after annealing at 1050 ˚C, whereas the Zn χmin value for the sample with H implant decreased from 17.6% following Ag implantation to 5.3% after annealing at 1050 ˚C. On the other hand, the χmin values for the Ag dopants before annealing in the H-implanted sample are the same in the sample without H. Post-Ag-implantation annealing resulted in much higher χmin values for Ag in the sample with H implant. For the as-implanted samples, 26.6% of the implanted Ag atoms are on substitutional sites in the sample with H, as compared to 30.3% of the implanted Ag being on the substitutional sites in the sample without H. After annealing at 1050 ˚C, the fraction of substitutional Ag is 73.7% in the H-implanted sample, in contrast to the fraction of 61.6% for substitutional Ag in the sample without H implant. Similar to other oxide crystals, H ion implantation and thermal annealing can result in the formation of nanocavities in the ZnO lattice. We discuss these findings in the context of the effects of nanocavities on formation and annihilation of point defects as well as on impurity diffusion and trapping in ZnO crystals.

We report on diffusion behavior for ion implanted indium and silver atoms in ZnO crystals. Both In and Ag ions were implanted at room temperature at 7-10° relative to c-axis to avoid channeling effects during implantation. In ions were implanted at four different energies (40, 100, 200, and 350 keV, respectively) and doses (4.20×1013, 6.70×1013, 8.10×1013 and 3.10×1014 /cm2, respectively), resulting in a total dose of 5 ×1014 /cm2. For another set of ZnO samples, Ag ions were implanted at energies 30, 75, 150, and 350 keV at doses 3.3×1013, 4.2×1013, 8.3×1013 and 3.4×1014 /cm2, respectively, to reach a total dose of 5×1014 /cm2. Both In and Ag implants resulted in a uniform concentration profile of the implanted dopants from surface to depth ~ 150 nm. The samples were annealed for 30 minutes at temperatures between 850-1050 °C in an oxygen gas flow. The distributions of In and Ag atoms, either aligned or nonaligned along the crystalline directions, were measured by Rutherford backscattering combined with ion channeling. The diffusivities for nonaligned (interstitial) and aligned (substitutional) dopants atoms were determined to vary with annealing temperature via the Arrhenius relationship. The diffusion activation energies (Ea) along the <10-11> direction for substitutional impurity atoms were lower than those for interstitial dopants atoms e.g., in the case of In, Ea ~ 1.52 eV for <10-11> aligned In atoms and Ea ~ 2.61 eV for interstitial In atoms between <10-11> atomic rows and in the case of Ag, Ea ~ 1.77 eV for the interstitial Ag atoms between the <10-11> atomic rows and 1.11 eV for <10-11> aligned Ag atoms. The diffusion activation energies showed a different trend for the two dopants as measured along the <0001> crystalline direction. For Ag implanted in ZnO, the activation energy of Ea ~ 0.91 eV for the aligned Ag atoms along <0001> direction and Ea ~ 1.55 eV were found for the interstitial Ag atoms, whereas in the case of In along the <0001> direction, the interstitial In was found to migrate with a higher activation energy (Ea ~ 1.78 eV) than the substitutional In (Ea ~1.42 eV). These results will be compared with first-principle calculations for understanding the energetics of defect formation and migration in both n- and p-type doping cases.

The influence of negative substrate bias on the chemical, electrical and mechanical properties of silicon carbide (SiC) thin films deposited onto (100) silicon substrate by dc magnetron cosputtering without external substrate heating is reported. These studies were performed by using the following techniques: Rutherford backscattering spectroscopy (RBS), profilometry, Raman spectroscopy, four-point probe method and nanoindentation. The results indicate that there is a good correlation between the substrate bias voltage and the argon incorporation into SiC film, namely, the SiC films deposited under substrate bias of –200 V and –300 V have higher argon content and higher elastic modulus and hardness than those deposited at 0 V. An opposite behavior was found for electrical resistivity: the SiC deposited at –300 V has resistivity of 0.45 Ω.cm whereas the deposited at 0 V has 7.0 Ω.cm.

The oxidation and diffusion of Molybdenum layer sputter-deposited on 2μm CVD diamond grown on silicon substrate has been studied. The Mo layer was protected by refractory metal silicide barrier layer. The samples were annealed in air ambient at 500°C over 30 hours. The oxidation of the samples was monitored with Rutherford Backscattering Spectroscopy (RBS). The effect of reactive sputtering of refractory silicide target in argon-nitrogen gas mixture (5% nitrogen by flow rate) on the barrier characteristics was investigated. The sheet resistivity of the barrier layer on SiC substrates as a function of annealing time in air at 500°C is reported. The surface structure and morphology of the refractory silicide films was determined with X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).

Embedded Si nano-particles of average size around 5nm were synthesized in an amorphous Si matrix by two stage ion implantation processes. It has been observed that amorphous Si (a-Si) layers were recrystallized using 50 MeV Au ions with enhanced regrowth rate with activation energy in the range of 0.29 eV. During the crystallization process Si nanocrystals were formed in the a-Si layers due to sudden quenching of the molten tracks created by MeV Au ions. The recrystalizations were confirmed by Rutherford backscattering spectrometry-Channeling (RBSC) technique. The structural modification and nanocluster creation that emerged during recrystallization process was observed in high-resolution transmission electron microscopy and photoluminescence (PL) spectroscopy. The PL emission was observed over a broad band of 2.8 – 3.4 eV and centered at 3.25 eV. The Si nano-crystal formation can be explain by a mechanism combining the melting within the ion tracks by thermal spike process and the subsequent recrystallization nucleated from the crystalline sides at the interface.

Due to the low absorption coefficient of silicon in the bulk of the solar spectrum, the majority of silicon-based photovoltaic cells are at least 300 micrometers thick, limiting their economic feasibility. To achieve cost parity with conventional sources of energy, silicon-based photovoltaics have begun to move towards thinner substrates, on the order of a few micrometers; such thinner cells necessitate the use of light-trapping methods to increase the optical path length. Much research has begun investigating the use of trapped electromagnetic waves, or surface plasmons, to increase light scattering and interband carrier transition rates in the surrounding material. In one scheme, plasmonic modes can be supported through polarization of metallic nanoparticles. Past research has focused on the deposition of silver nanoparticles on the surface, and has shown that light absorbance can be increased markedly for certain bandwidths. Here, the relevant mechanism is increased lateral light scattering, which tends to guide the light into directions that are then totally internally reflected. When such metallic nanoparticles are polarized by incoming radiation, in addition to increased light scattering, the electric field in the vicinity of the nanoparticle is highly magnified. Such high fields can increase the carrier transition rates, and therefore the absorbance, in the surrounding silicon by orders of magnitude. The enhancement however decreases rapidly with the radial distance and is virtually diminished by 10 nm from the nanoparticle surface. Deposition on the surface of the solar cell, therefore, cannot exploit this effect, being isolated from the silicon by the passivating layer. It has been suggested that instead, such particles might be embedded into the silicon itself. To that end, we have developed a method to create subsurface silver nanospheres, using a combination of ion implantation, thermal deposition, and subsequent thermal annealing. By tailoring the implantation parameters, we can localize the layer of nanospheres and even create various bands at various depths. Through Rutherford backscattering and secondary ion mass spectroscopy characterization, we have found that the Ag has indeed annealed into the desired location. To ensure that the Ag has agglomerated to nanoparticles, we have confirmed this with TEM images and selected area diffraction patterns that indicate that such nanoparticles are indeed bulk phase silver and have diameters of 20-35 nanometers. This method can help realize more efficient surface plasmon-enhanced Si-based photovoltaics.

We report here swift heavy ion (SHI) irradiation induced effects on structural and surface properties of III-nitrides. Tensile strained Al(1-x)InxN/GaN Hetero-Structures (HS) were realized using Metal Organic Chemical Vapour Despotion (MOCVD) technique with indium composition as 12%. Ion species and energies are chosen such that electronic energy deposition rates differ significantly in Al(1-x)InxN and are essential for understanding the ion beam interactions at the interfaces. Thus the samples were irradiated with 80 MeV Ni6+ and 100 MeV Ag7+ ions at varied fluence (1×1012 and 3 ×1012 ions/cm2) to alter the structural properties. Under this energy regime, the structural changes in Al(1-x)InxN would occur due to the intense ultrafast excitations of electrons along the ion path. We employed different characterization techniques like High Resolution X- ray Diffraction (HRXRD) and Rutherford back scattering spectrometry (RBS) for composition, thickness and strain. HRXRD and RBS experimental spectra have been fitted with Philip’s epitaxy SIMNRA code, which yields thickness and composition from compound semiconductors. The surface morphology of pristine and irradiated samples is studied and compared by Atomic Force Microscopy (AFM).

We have analyzed the degree of crystalline lattice recovery in samples implanted with Ti concentrations well above the Mott limit and subsequently Pulsed-Laser Melting (PLM) annealed by means of Raman spectroscopy and Rutherford Backscattering Spectroscopy (RBS). Since very recently, theoretical studies predicted Ti interstitial sites for the Intermediate Band (IB) formation, the knowledge of the Ti impurity lattice location after PLM annealing is an essential point that can be elucidated by means of RBS measurements. After PLM annealings, Raman and RBS measurements have shown a decrease in the lattice crystalline quality as implanted dose is increased, yielding a significantly improvement of the lattice quality at the highest energy density studied. The RBS channeling spectra show that after PLM annealings Ti impurities are mostly occupying interstitial lattice sites.

A new fabrication technique to prepare ultra-thin barrier layers for nano-scale Cu wires was proposed in our previous studies. Ti-rich layers formed at the Cu(Ti)/dielectric-layer interfaces consisted of crystalline TiC or TiSi and amorphous Ti oxides. The primary control factor for Ti-rich interface layer composition was the C concentration in the dielectric layers rather than the formation enthalpy of the Ti compounds. To investigate Ti-rich interface layer growth in Cu(Ti)/dielectric-layer samples annealed in ultra high vacuum, Rutherford Backscattering Spectrometry (RBS) was employed in the present study. Ti peaks were obtained only at the interface for all the samples. Molar amounts of Ti atoms segregated to the interface (n) were estimated from Ti peak areas. The n value was defined by n = Z·exp(-E/RT) · tm, where Z is a preexponential factor and E the activation energy for the reaction. The Z, E, and m values were estimated from plots of log n vs log t and log n vs 1/T. The m values are similar in all the samples. The E values for Ti atoms reacting with the dielectric layers containing carbon (except SiO2) tended to decrease with decreasing C concentration (decreasing k), while reaction rate coefficients (Z·exp(-E/RT)) were insensitive to C concentration in the dielectric layers. These factors lead to conclusion that growth of the Ti-rich interface layers is controlled by chemical reactions of the Ti atoms with the dielectric layers represented by the Z and E values, rather than diffusion in the Ti-rich interface layers.

Monolayer thin films of YbBiPt and YBiPt have been produced with 560 nm and 394 nm thick respectively in house and their thermoelectric properties were measured before and after MeV ion bombardment. The energy of the ions were selected such that the bombarding Si ions stop in the silicon substrate and deposit only electronic energy by ionization in the deposited thin film. The bombardment by 5.0 MeV Si ions at various fluences changed the homogeneity as well as reducing the internal stress in the films thus affecting the thermal, electrical and Seebeck coefficient of thin films. The stoichiometry of the thin films was determined using Rutherford Backscattering Spectrometry, the thickness has been measured using interferometry and the electrical conductivity was measured using Van der Pauw method. Thermal conductivity of the thin films was measured using an in-house built 3ω thermal conductivity measurement system. Using the measured Seebeck coefficient, thermal conductivity and electrical conductivity we calculated the figure of merit (ZT). We will report our findings of change in the measured figure of merit as a function of bombardment fluence.

A combination of two nuclear ion beam techniques, Rutherford Backscattering Spectrometry (RBS) and micro-Particle Induced X-Ray Emission (uPIXE) was tested to evaluate both diffusion profiles and radionuclide spatial distribution of radionuclides (RN) onto cement-based materials. The methodology was tested on a Spanish reference backfill concrete, used as engineering barrier in low-level radioactive waste repositories, using two elements (Cs and I) with different sorption behaviour onto the cement. The applicability and limitations of the selected methodology is discussed for both elements.

We have grown 100 periodic SiO2/SiO2+Ag multi-nano-layered systems where the SiO2+Ag layers were 7.26 nm and SiO2 buffer layer were 4 nm, total thickness is 563 nm. Using interferometer as well as in-situ thickness monitoring, we measured the thickness of the layers; using Rutherford Backscattering Spectrometry (RBS) measured the concentration and distribution of Ag in SiO2. The electrical conductivity, thermal conductivity and the Seebeck coefficient of the layered structure were measured at room temperature before and after bombardment by 5 MeV Si ions. The energy of the Si ions were chosen such that the ions are stopped in the silicon substrate and only electronic energy due to ionization is deposited in the layered structure. The electrical conductivity measured using Van der Pauw method. Thermal conductivity of the thin films was measured using an in-house built 3ω thermal conductivity measurement system. Using the measured Seebeck coefficient, thermal conductivity and electrical conductivity we calculated the figure of merit (ZT). We will report our findings of change in the figure of merit as a function of the bombardment fluence.

The Grolier Codex has been a controversial document ever since its late discovery in 1965. Because of its rare iconographical content and its unknown origin, specialists are not keen to assure its authenticity that would set it amongst the other tree known Maya codes in the world (Dresden, Paris Codex and Madrid Codex).

The document that has been kept in the Museo Nacional de Antropología in Mexico City, after its exposure in 1971 at the Grolier Club of New York, has been analyzed by a set of non-destructive techniques in order to characterize its materials including paper fibers, preparation layer and colors composition. The methodology included UV imaging, IR reflectography and optic microscopy examinations as well as Particle Induced X-ray Emission (PIXE) and Rutherford Backscattering Spectrometry (RBS) using an external beam setup for elemental analysis. All the measurements were carried out at 3MV Pelletron Accelerator of the Instituto de Física, UNAM. The aim of this work is to verify if the materials in the Grolier Codex match those found for other pre-Hispanic documents.

From the elemental composition we concluded that the preparation layer shows the presence of gypsum (CaSO4), color red is due to red hematite (Fe2O3) and black is a carbon-based ink. These results agree with previous analyses carried out by Scanning Electron Microscopy (SEM-EDX) on few samples. However, the presence of Maya Blue in the blue pigment cannot be assured. The examination using UV and IR lights shows homogeneity in the inks and red color but dark areas that contain higher amounts of K in the preparation layer. This paper discusses the results obtained for the UV-IR examinations and the elemental analysis. A comparison with other studies on pre-Hispanic and early colonial codex is presented.

Zinc oxide was considered to be substitute for indium tin oxide (ITO) as the transparent conductive oxide (TCO) films used in display industry according to indium is a rare and expensive metal. For the flexible display, the polymeric materials used as the flexible substrates are more bendable and lighter weight compared to the glass substrates used in flat panel display. However, the thermal sensitivity of polymer affects the properties of TCOs layers when it was deposited at room temperature. In this study, we doped the different ratio of indium oxide, magnesium oxide and aluminum oxide into zinc oxide to improve the properties of zinc oxide used as the TCOs films deposited by the sputtering method. The polyethylene terephthalate (PET) was used as the flexible substrate without thermal process and the glass was used as the comparison substrate with annealing. The light transmittance and the surface resistivity were measured. The chemical composition and the crystal structure were analyzed by using Rutherford backscattering spectrometry and X-ray diffraction measurement.