Homogeneous Depth Research Articles

Channeled implantation with a parallel scanned ion beam

Direct axial channeling, with the major crystal axis aligned with the incident ion beam, can produce deep penetration of dopants at modest ion energies. In addition, damage levels are significantly reduced. When the ion beam is scanned parallel over the wafer, this deep penetration can be achieved at every location on the wafer, provided the change of the angle of incidence across the wafer is small compared to the critical angle for channeling. Also, if implants in a random direction are done, the implant will be random all across the wafer, resulting in a homogeneous dopant depth profile. Si wafers of up to 150 mm have been implanted under channeling and random conditions. Dopant and lattice damage profiles were measured with Rutherford backscattering and SIMS. The reproducibility and applicability of the axial channeling implant technique are discussed.

Laser implantation of impurity atoms into silicon and gallium-arsenide single crystals

Sn and Fe have been incorporated into the bulk of silicon single crystals by means of an irradiation of thin metallic surface layers of these elements with light pulses from a Nd-glass laser. Analogously, Sn has been implanted into gallium-arsenide single crystals and furthermore, a successful implantation of Sn into GaAs has been achieved by an irradiation from the backside of the sample. Depth profiles of the implants have been determined by Rutherford backscattering analysis. The state of the impurity atoms has been studied by conversion-electron Mössbauer spectroscopy. The surface topography of Sn-implanted silicon was analyzed by scanning electron microscopy. The dependence of the number of implanted impurity atoms and their depth profiles on the laser power density and the thickness of the deposited surface layer has been investigated. The fraction of atoms implanted from the surface layer decreases with increasing layer thickness. For a given layer thickness, the implanted fraction reaches a maximum for a certain laser power density. The impurity atoms can be implanted to a depth of several thousand angstroms with nearly homogeneous depth profiles for suitably chosen conditions. The concentrations exceed the solid solubilities by orders of magnitude. These findings are consistent with a qualitative model for the implantation process assuming a detailed balance between an evaporation of the metallic surface layers and the incorporation of the impurity atoms into the bulk by diffusion in a molten substrate layer. After the recrystallization, as inferred from the Mössbauer spectra, Sn is found on substitutional lattice sites in silicon and on substitutional Ga sites in GaAs, whereas Fe in silicon precipitates in agglomerates. Upon thermal annealing, the depth profiles relax towards more homogeneous distributions. No segregation of Sn from the supersaturated solution is indicated; however, drastic changes in the Fe Mössbauer spectra after annealing indicate that a fraction of these atoms may occupy well-defined lattice sites, whereas the majority remains in agglomerates.

Quantitative approach of Auger electron spectrometry: I. A formalism for the calculation of surface concentrations

We describe a formalism leading to a quantization of Auger spectrometry without resorting to standards. An element of the matrix is choosen as a reference and the other species have their Auger signals expressed in terms of the Auger signal of that reference by means of a sensitivity coefficient α. The intensity of an Auger signal is interpreted as the sum of the contributions given by every atomic layers of the sample, each of them being characterized by an attenuation coefficient k, closely related to the escape depth of the Auger electrons. We derive a formalism which allows us to determine the elemental composition of the atomic layers. Homogeneous sample, heterogeneous sample, multiphase sample, surface segregation and depth profiling have been considered.

Use of X-ray Scattering in Absorption Corrections for X-ray Fluorescence Analysis of Aerosol Loaded Filters

Two methods are described for computing multielement x-ray absorption corrections for aerosol samples collected in IPC-1478 and Whatman 4l filters. The first relies on scatter peak intensities and scattering cross sections to estimate the mass of light elements (Z < l4) in the sample. This mass is used -with the measured heavy element (Z ≥l4) masses to iteratively compute sample absorption corrections. The second method utilizes a linear function of ln(μ) vs. ln(E) determined from the scatter peak ratios and estimates sample mass from the scatter peak intensities. Both methods assume a homogeneous depth distribution of aerosol in a fraction of the front of the filters, and the assumption is evaluated with respect to an exponential aerosol depth distribution. Penetration depths for various real, synthetic and liquid aerosols were measured.

A Numerical Model for Circulation in a Homogeneous World Ocean

The results for two steady-state models of the world's ocean circulation are presented. The first model is of a homogeneous constant depth ocean with natural coastline geography. The second model, in addition, incorporates realistic sea floor topography. The flow fields indicate that in the constant depth ocean a coefficient of body friction R=1.5×10−6 see−1 is required to produce the observed Circumpolar Transport. For this model the magnitude of the Circumpolar Current is approximately proportional to the inverse of the friction parameter whereas in the variable depth model the effect of the frictional processes on the circumpolar circulation is of minor importance. The circulation is primarily determined by the sea floor topography, and the transport of the Circumpolar Current is small (∼16×1012 gm sec−1). The gyres in the ocean basins, however, are of magnitudes comparable with the constant depth model.

How faithfully will the geostrophic currents represent the existing ocean currents?

It is widely recognized that the geostrophic flows computed by the dynamic method of Bjerknes and collaborators represent the actual currents pretty faithfully. However, what would be the reason that a geostrophic current derived by only retaining the terms of Coriolis and the pressure gradient forces in the hydrodynamical equations agrees so closely with the actual ocean current of the same area? In this attempt was assumed an imaginative ocean of homogeneous water and uniform depth on a rotating earth but with neither continent nor islands. The average wind distribution observed along several meridians over the Pacific Ocean was assumed to prevail in this sea throughout with no variation in east-west direction. Taking the curvature of the earth surface, rotation of the earth, Coriolis forces, pressure gradients and the horizontal and vertical eddy viscosity into account, the equations of motion were solved and velocity components were derived for all latitudes. A comparison of the east-west components thus obtained with the corresponding components of the geostrophic flows, reveals that they agree well in higher latitudes but there appears a remarkable disagreement in lower latitudes. This means that a special care must be taken in replacing the existing currents with the geostrophic flows at lower latitudes.

A review of a number of cases treated by radium in the year 1924

1. Rodent ulcers respond favourably to treatment by radium. One application is usually sufficient, and the cosmetic results are very good. 2. The combined applications of radium and X-Rays are more beneficial than one or other of them alone in the treatment of uterine and oral carcinoma, when a rapid intensive local effect is required as well as a diffuse effect to destroy metastases. 3. For prophylactic post operative irradiation “Deep Therapy” is preferable to radium, because X-Rays are more diffuse in their action, and a more homogeneous depth dose can be obtained with them than with the amount of radium which is ordinarily available.