Wei-Kan Chu

New uses of ion accelerators

1. Ion-Excited X-Ray Analysis of Environmental Samples.- I. Introduction.- II. General Considerations for Ion Beam Analysis of Environmental Samples.- III. Formalism and Optimization.- IV. The UCD/ARB Aerosol Analysis System.- A. The Primary Ion Beam.- B. Detection of X-Rays.- C. Data Acquisition and Reduction.- D. System Calibration.- E. Target Preparation and Matrix Effects.- F. Estimation of Analytical Costs.- G. Validation of System Operations.- V. Ion-Excited X-Ray Analysis Programs.- Appendix (Forward Scattering).- Acknowledgments.- References.- 2: Material Analysis by Nuclear Backscattering.- A. Introduction.- General Comments on Nuclear Backscattering.- Appendix (Numerical Examples).- References.- B. Applications.- I. Introduction.- II. Ion Implantation.- III. Thin Films: Growth and Deposition.- IV. Thin Film Reactions: Interdiffusion and Compound Formation.- V. Bulk Effects: Composition, Diffusion and Solubility.- VI. Concluding Remarks.- Acknowledgments.- References.- Formalism.- 1. Three Basic Concepts in Backscattering.- A. Backscattering Kinematic Factor Mass ? Analysis.- B. Differential Scattering Cross Section ? Quantitative Analysis.- C. Energy Loss ? Depth Analysis.- 2. Depth Scale in Backscattering Analysis [S].- A. Depth Scale in Backscattering Analysis.- B. Surface Approximation.- C. Linear Approximation.- 3. Height of an Energy Spectrum.- A. Surface Approximation for Spectrum Height.- B. Thick Target Yield.- C. Backscattering Yield of a Thin Film.- 4. Applications of Backscattering from Elemental Targets.- A. Surface Contamination and Ion Implantation.- B. Doping Level of a Bulk Sample.- C. Film Thickness Measurement and dE/dx Measurements.- D. Yield Formula and dE/dx Measurements.- E. Differential Scattering Cross Section Measurement.- 5. Application of Backscattering to Compound Targets.- A. Thin Film Analysis.- B. Thick Compound Targets.- C. Analysis on Composition Varying Continuously with Depth.- Appendix 1. Notations.- Appendix 2. Formulae.- Appendix 3. Sources for dE/dx Information.- References.- 3: Material Analysis by Means of Nuclear Reactions.- Charged Particle Activation Analysis.- Charged Particle Activation Analysis - Examples.- Prompt Radiation Analysis.- Nonresonant Nuclear Reactions - Gamma Rays Observed.- Nonresonant Nuclear Reactions - Nuclear Particles Observed.- Resonant Nuclear Reactions.- Summary.- Acknowledgment.- References.- 4: Lattice Location of Impurities in Metals and Semiconductors.- I. Introduction.- II. Impurity Detection.- III. The Channeling Technique.- 1. Channeling Concept.- 2. Experimental Technique.- IV. Lattice Location Analysis.- V. Examples.- 1. Substitutional Impurities.- 2. Nearly Substitutional Impurities.- 3. Interstitial Impurities.- 4. High Impurity Concentrations.- 5. Radiation-Induced Change in Impurity Sites.- VI. Summary of the Literature on Channeling Lattice Location Data.- VII. Limitations.- VIII. Conclusions.- References.- 5: Ion Implantation in Metals.- Historical Perspective.- Friction and Wear.- Corrosion.- 1. Oxides with Anion Defects.- 2. Oxides with Cation Defects.- Ion Backscattering.- Titanium and Stainless Steel.- Zirconium.- Aluminum.- Copper.- Aqueous Corrosion.- Practical Applications in Corrosion.- Electrochemistry and Catalysis.- Implantation Metallurgy.- Equipment for the Ion Implantation of Metals.- Conclusions.- References.- 6: Ion Implantation in Superconductors.- Definition of the Superconducting Parameters.- Influence of Radiation Damage on the Superconducting Properties.- a. Non-Transition Metals.- b. Transition Metals.- c. Transition Metal Alloys.- d. Superconductors with A-15 and NaCl-Structure.- e. Transition Metal Layer Compounds.- f. Quantitative Estimation of Damage in Superconductors.- Influence of Implanted Ions on the Superconducting Transition Temperature.- a. Magnetic Impurities in Non Transition Metals.- b. Pd-, Pd-Noble Metal Alloy, -Hydrogen System.- c. Ion Implanted Transition Metal Systems.- d. Aluminum Based Ion Implanted Systems.- Application to Superconducting Devices.- Conclusions.- References.- 7: Ion-Induced X-Rays from Gas Collisions.- 1. Introduction.- 2. Collision Models.- 2.1. Survey of Models.- 2.2. Coulomb Ionization.- 2.3. The Molecular-Orbital Model.- 3. Measurements of Inner-Shell Excitations.- 3.1. Introduction.- 3.2. Theory of Energy-Loss Measurements.- 3.3. X-Ray and Electron Emission.- 3.4. Typical Apparatus-Ionization and Inelastic Energy Loss.- 3.5. Scattered- Ion-X-Ray/Electron Coincidence Apparatus.- 4. Discussion of Typical Data.- 4.1. Ionization States.- 4.2. Inelastic Energy Loss.- 4.3. Electron Emission Cross Sections.- 4.4. Fluorescence Yield Effects.- 4.5. X-Ray-Scattered-Ion Coincidence Data.- 4.6. X-Rays from Highly Stripped Fast Ion Beams.- 5. Summary.- References.- 8: Ion-Induced X-Rays in Solids.- 1. Introduction.- 2. Accelerators and Target Chambers.- 2.1. Ion Sources.- 2.2. Target Chambers.- 3. The Detection and Analysis of X-Rays.- 3.1. The Gas Flow Proportional Counter.- 3.2. The Si(Li) Detector.- 3.3. The X-Ray Crystal or Grating Spectrometer.- 4. The Use of Protons and Helium Ions to Generate X-Rays from Solid Targets.- 4.1. Current Areas of Fundamental Interest.- 4.2. Applications.- 5. The Use of Heavy Ions to Generate X-Rays from Solid Targets.- 5.1. General Background.- 5.2. Physical Processes.- 5.3. Applications.- 6. Conclusions.- References.- Author Index.

Evaluation of glancing angle X-ray diffraction and MeV 4He backscattering analyses of silicide formation

Nickel and palladium silicide films have been used in an evaluation of MeV 4He backscattering, the Read X-ray camera and the Seemann-Bohlin X-ray diffractometer. Identical samples of untextured, textured and epitaxial crystalline layers have been studied by all three techniques. Backscattering spectrometry techniques give concentration ratios and and silicide layer thicknesses. Glancing angle X-ray diffraction is required for positive phase identification and structural analysis. The Seemann-Bohlin diffractometer is capable of quantitative structural analysis; however, the Read camera is adequate in phase identification of silicide formation.

Line-shape extraction analysis of silicon oxide layers on silicon by channelling effect measurements☆

Abstract A technique of line-shape extraction has been developed and applied to find the number of Si atoms and O atoms per square centimeter of anodically grown and thermally oxidized silicon oxide layers. Back-scattering and channelling effect measurements with 0.3-2.0 MeV 4He+ ions were used. The thicknesses of the silicon oxide investigated ranged from native oxide thickness to 1500 A. For all thicknesses the composition was found to be silicon-rich, with the number of Si atoms per square centimeter equal to one-half the number of oxygen atoms per square centimeter plus (0.8-1) × 1016 Si/cm2. We propose that the oxide layer is stoichiometric SiO2 with a silicon-rich transition region between the oxide layer and the crystal substrate. The presence of such a transition region at the interface should be considered when evaluating the composition of dielectric layers on semiconductors.

Bragg's rule study in binary metal alloys and metal oxides for MeV 4He+ ions

Abstract A self-consistent procedure for testing Braggs rule in solids is described and applied to 4 He + ions between 0.5 and 2.25 MeV for the binary metal systems Au-Ag, Au-Cu and Au-Al. The validity of the procedure is verified by numerical analysis. Braggs rule correctly predicts the energy loss in Au-Al and Au-Ag mixtures to within the 1% sensitivity of the experiment and to within 2% in Au-Cu alloys. We propose that Braggs rule is valid for all metal alloys. A second method has been applied to the oxides of iron and aluminum. This “yield ratio test” assumes that the composition of the target and the elemental stopping cross sections are known. The measured relative stopping powers in α-Fe 2 O 3 and Fe 3 O 4 are consistent with the use of Braggs rule and the available elemental stopping data. The relative stopping power in Al 2 O 3 differs by about 10% from the expected value.

Relative measurements of stopping cross section factors by back-scattering☆

From international conference on ion beam surface layer analysis; Yorktown Heights, NY (18 Jun 1973). A procedure for evaluating relative stopping cross section factors from the ratios of two heights in a single back-scattering spectrum is described. The method, which requires a two-layered target, is used to test the stopping cross sections of 1 to 2 MeV /sup 4/He/sup +/ ions incident on Au, Ag, Cu, Si and Al. The ratios of the heights of Au, Ag and Cu are consistent with published stopping cross section data. The Au--Al height ratio is within the errors quoted for the Au and Al stopping cross section measurements. The Al-- Si height ratio differs significantly from the expected value. It is also shown that the height ratio changes slightly as a function of the thickness of the surface layer. (auth)

Material Analysis by Nuclear Backscattering

Historically, the first use of ion backscattering for material analysis was by Geiger and Marsden1 (1909), whose effects were explained by the Rutherford2 atomic model (1911). This was followed immediately by suggestions of ion channeling in single crystals by Stark and Wendt (1912). Recently, the most widely publicized example of nuclear backscattering was the first atomic compositional analysis of the moon by Surveyor 5 (1967). This first soft-landing package contained a radioactive source of 5MeV α-particles which were backscattered from the moon’s surface and provided information on the elemental composition of the moon’s surface.4,5

Anomalous Annealing Behavior of Arsenic Implanted Silicon as a Function of Dose and Energy

Anomalous annealing behavior of damage in As implanted Si has been investigated by channeling effect measurements. Room temperature As implants with doses from 1014 to 2 × 1016cm-2 at energies ranging from 50 to 250 keV into Si were annealed over the range of 600°C to 1100°C. Anneal temperatures ≥ 950°C reduce the disorder for ion doses of 0.5 to 1 × 1016 cm-2 at energies between 50 and 250 keV. Anomalously high residual disorder was found for the intermediate doses of 2 × 1014 to 2 × 10/cm2 implanted above 100 keV. For this intermediate dose, annealing of implants performed at liquid nitrogen temperatures did not show significant reduction in this damage. However implants at 200° to 300°C indicate a lower amount of damage compared to the room temperature implants.

Enhanced Residual Disorder in Silicon from Recoil Implantation of Oxygen and Nitrogen by Arsenic Implants Through Dielectric Layers

Channeling effect measurements have been used to evaluate the enhanced residual disorder found in silicon after implantation of arsenic through thin oxide and nitride layers. The disorder is found to be a function of both the dielectric layer thickness and the arsenic dose. Measurements after anneal of the implants at 1000°C for 30 minutes indicate the amount of damage increases with As dose and dielectric layer thickness. Simulation of the “knock-on” implantation by oxygen or nitrogen implants allows the inference of the number of recoils as a function of As energy and layer thickness. For the case of a 480A SiO2 layer and 1016 As/cm2 implanted at 200 keV approximately 4 × 10l5/cm2 forward oxygen recoil atoms are produced. In general the residual damage for equivalent nitride layers was found to be approximately one-half that measured for oxide implants. Erosion of the films due to sputtering by the As implantation indicated that the number of atoms sputtered away is equivalent to 30–50A of SiO2 for a dose of 2 × 1016 As/cm2.