G. K. Hubler

Stand-off detection of trace explosives via resonant infrared photothermal imaging

We describe a technique for rapid stand-off detection of trace explosives and other analytes of interest. An infrared (IR) laser is directed to a surface of interest, which is viewed using a thermal imager. Resonant absorption by the analyte at specific IR wavelengths selectively heats the analyte, providing a thermal contrast with the substrate. The concept is demonstrated using trinitrotoluene and cyclotrimethylenetrinitramine on transparent, absorbing, and reflecting substrates. Trace explosives have been detected from particles as small as 10 μm.

Effects of thermal annealing on the refractive index of amorphous silicon produced by ion implantation

Precise infrared reflection measurements of the refractive index of silicon show that there are two well‐defined optical states of amorphous silicon produced by ion implantation. One is the as‐implanted amorphous state which is the high refractive index state produced by high fluence implantation of Si or P ions into Si samples. The other state, which has a refractive index intermediate between the as‐implanted and crystalline values, is induced by thermal annealing and is thermally stable until epitaxial recrystallization occurs.

High‐fluence implantations of silicon: Layer thickness and refractive indices

Refractive‐index measurements are given for amorphous Si produced by ion implantation. Reflection interference measurements in the frequency range 250≲ν≲ 7600 cm−1 were made for several Si samples implanted with P‐ion fluences between 1.0×1016 and 10×1016 ions/cm2 and ion energies between 0.20 and 2.7 MeV and for Si implants of 1.0×1016 and 3.0×1016 ions/cm2 and an ion energy of 0.30 MeV. The interference measurements were computer analyzed by using a model in which the damaged layer has a refractive index nD and extinction coefficient kD, and the substrate has a refractive index ns and ks=0. The optical constants of the two regions are smoothly connected by a transition region approximated by a half‐Gaussian curve of standard deviation σD. The finite‐width transition region is necessary for fitting the data. Excellent fits are obtained for literature values of ns and kD with the chi‐square being ?10−5. The value of kD has little effect on the analysis. Within the experimental accuracy a single curve for ...

Fundamentals of ion‐beam‐assisted deposition. I. Model of process and reproducibility of film composition

An ion‐beam‐assisted‐deposition (IBAD) system is under development to fabricate Si1−x Nx films for optical devices. Reproducible film composition requires characterization of the relationship between the incorporated nitrogen atom fraction x and the real time experimental measurable quantities. In this paper a simple model is presented which relates the film composition x to the measured beam current density JF , the vapor impingement rate Q, and the chamber pressure p. Effects included in the model are reflection of energetic particles, sputtering from the film surface, and charge exchange neutralization of the ions. Each term in the model is examined as a potential source of both systematic and random deviations of the data from the model. Data on film composition as a function of the nitrogen ion current to deposition rate ratio are presented for several sets of ion source voltages and chamber pressures. It is shown that by modifying the deposition system so as to minimize the identified sources of err...

Electrical and structural characterization of implantation doped silicon by infrared reflection

Abstract A physical model is presented for calculating infrared reflection interference spectra from ion implanted and annealed crystalline materials. The utility of the method is illustrated by presenting best fit spectra for a silicon sample implanted with 2.7 MeV phosphorous to a fluence of 1.74 × 1016 ions/cm2 and isothermally annealed at 500°C. Non-linear least-squares fitting of reflection data yields structural and electrical information about the implanted region with reasonable precision. The physical quantities determined are (i) the depth of the amorphous layer produced by implantation both before and during isothermal annealing, the thickness of the recrystallized material, and the widths of any transition regions, (ii) the dielectric properties of the amorphous and recrystallized material, and (iii) the characteristics of the free carrier plasma which yield the carrier density profile, the mobility near the carrier density maximum, and the carrier activation efficiency. Up to nine fitti...

Applications of ion implantation for the improvement of localized corrosion resistance of M50 bearing steel

Abstract Pitting corrosion of M50 alloy steel bearings used in turbojet engines has been found to be a severe problem. The difficulty arises when salt-spray condensates accumulate in the engine lubricants of aircraft not in regular use. Ion implantation was applied to this problem because in the early stages of this work it was shown to be able to maintain both the dimensional stability and the contact fatigue lifetime of the M50 bearings. Qualitative tests, which simulated the geometry and thermal cycle conditions leading to pitting of the M50 bearing surface, were performed using oil containing 3 ppm NaCl. Initially it was found that chromium surface alloys containing 20–25% chromium substantially reduce the level of attack. Prior to further corrosion simulation tests, potentio-kinetic studies were carried out on M50 implanted with chromium, molybdenum and titanium in order to screen both the passivating tendency of the surface alloys formed and their resistance to localized forms of corrosion. Singular additions of chromium, molybdenum and titanium were found to increase the resistance of M50 to localized breakdown significantly. The highest resistance to localized breakdown was found for a multi-implantation of chromium and molybdenum.

Near infrared rugate filter fabrication by ion beam assisted deposition of Si (1− X ) NX films

The rugate filter employs a sinusoidal refractive index depth profile to produce high reflection in a narrow band of wavelengths. Fabrication relies on a continuously variable index of refraction in the wavelength regime of interest. The near IR refractive index of amorphous silicon-nitrogen films decreases continuously as the composition varies from pure silicon to stoichiometric silicon nitride (Si(3)N(4)). Ion implantation was found unsuitable as a fabrication method for rugate filters. Homogeneous and inhomogeneous films up to 5 microm in thickness have been produced by simultaneous deposition of electron beam evaporated silicon and of energetic nitrogen particles arising from an ion beam. The relative fluxes of beam and evaporant are found to determine the ratio of nitrogen to silicon in the films and therefore to determine the index. Single-band reflection filters of the rugate design of high peak optical density were fabricated under computer control using a quartz crystal oscillator shielded from the beam to monitor the silicon evaporation and three suppressed Faraday cups to monitor the ion beam current.

Amorphous silicon produced by ion implantation: Effects of ion mass and thermal annealing

Characterization of the two optical states of amorphous Si produced by ion implantation is extended to include electron paramagnetic resonance, fundamental absorption edge, and density measurements in addition to infrared reflection. It is found that the properties of the two a‐Si states are not dependent upon the mass of the incident ion (12C, 29Si, 31P, 120Sn) or upon the anneal temperature for 400 °≤TA≤600 °C. The dangling‐bond density drops about a factor of 2 when the a‐Si makes a transition between the two states. The absorption coefficient also drops by more than a factor of 5, but the density of the a‐Si does not change when the transition occurs. The transition between states was not completed at TA=300 °C, so the annealing mechanism may be temperature dependent.

Fundamentals of ion‐beam‐assisted deposition. II. Absolute calibration of ion and evaporant fluxes

A method is given to obtain an absolute calibration of the ion and evaporant fluxes in an ion‐beam‐assisted deposition system based upon a Kaufman ion source and an electron beam vapor source. The nitrogen‐ion silicon‐vapor material system is used for the calibration; Rutherford backscattering is used for measurement of composition and thickness of Si1−x Nx films deposited on C and Si substrates. It is shown that quantitative predictions of the ion‐to‐atom impingement ratio, film composition, and film thickness can be obtained when sputtering, reflection, charge exchange neutralization of the ions, and species content of the nitrogen beam are considered.

Binary collision cascade prediction of critical ion-to-atom arrival ratio in the production of thin films with reduced intrinsic stress

Abstract It is well established that ion beam assisted desposition produces thin films that are more dense and contain less intrinsic stress than films deposited without energy input from an ion beam. In some cases, a critical ion-to-atom arrival ratio has been measured, above which the stress is reduced. We have calculated this critical arrival ratio using the binary collision approximation to simulate collision cascades. Good agreement with data in the literature is obtained by making the assumption that each deposited atom must lie within the volume affected by an ion induced cascade. This model is simple to implement and should provide predictive capability for other covalently bonded systems.