Amplitude Of Surface Deformation Research Articles

Measurement of microscopic surface deformation due to low energy ion bombardment on Si(111)

A low energy electron diffraction spot profile analysis of the Si(111) surface, after argon ion bombardment at an elevated temperature, finds a continuous, low amplitude distribution of surface height, in addition to the atomic-step-and-terrace structure. With an amplitude of tenths of an Angstrom or less in height, correlated laterally over tens of Angstroms, this microscopic surface deformation is measured versus ion dose and for various sample temperatures during bombardment and annealing. For 230eV argon ion doses increasing in the range of 1015−1016cm−2 with the sample held at 580K and 800K, the amplitude of surface deformation, measured as the standard deviation wz of the continuous height distribution, increases steadily in the range 0.06−0.10Å. For higher ion doses in the range of 3×1016−1×1017cm−2, saturation-like behavior with wz≈0.14−0.15Å is measured at 800K. After an ion dose of 1017cm−2, the surface deformation shows a lateral correlation length of 20Å, implying an average lateral feature size of ≈40Å, slightly less than the average terrace width of ≈60Å. On the other hand, after the same ion dose at 300K followed by annealing at 800K, the surface deformation has a similar correlation length but a much smaller height amplitude of wz=0.06Å. It is notable that wz depends quite differently on sample preparation conditions overall, compared to the average terrace width and to the degree of (7×7) order indicated by diffraction intensities, both of which are found to evolve much more slowly with ion dose in conditions for which the height amplitude increased in the range of 0.06−0.14Å. The surface height deformation due to strain around buried, subsurface defects is estimated as a function of defect concentration using a simple, order-of-magnitude theoretical model, in which a distribution of subsurface defects is modeled as small inclusions in a continuous elastic medium. This approximate model is consistent with the measured growth of the deformation amplitude wz, for a range of possible parameter choices for small defect clusters located in a shallow layer below the surface. The surface deformation is partially removed by annealing above 870K.

Fluid pressure arrival-time tomography: Estimation and assessment in the presence of inequality constraints with an application to production at the Krechba field, Algeria

Deformation in the overburden proves useful in deducing spatial and temporal changes in the volume of a producing reservoir. Based on these changes, we have estimated diffusive traveltimes associated with the transient flow due to production, and then, as the solution of a linear inverse problem, the effective permeability of the reservoir. An advantage of the approach based on traveltimes, as opposed to one based on the amplitude of surface deformation, is that it is much less sensitive to the exact geomechanical properties of the reservoir and overburden. Inequalities constrain the inversion, under the assumption that the fluid production only results in pore volume decreases within the reservoir. The formulation has been applied to satellite-based estimates of deformation in the material overlying a thin gas production zone at the Krechba field in Algeria. The peak displacement after three years of gas production is found to be approximately [Formula: see text], overlying the eastern margin of the anticlinal structure defining the gas field. Using data from 15 irregularly spaced images of range change, we have calculated the diffusive traveltimes associated with the startup of a gas production well. The inequality constraints were incorporated into the estimates of model parameter resolution and covariance, improving the resolution by roughly 30% to 40%.

Temperature of spatially modulated surface of solid film heated by repetitive laser pulses

An analytical solution is obtained for the classical heat conduction problem for a solid film with a surface that is simply deformed and irradiated by repetitive laser pulses. Convective heat losses from the surface and the film–substrate interface are taken into account. The solution, evaluated for large times, shows that the surface deformation increases the average surface temperature. This increase is pronounced when the absorption length of the laser radiation is less than the film thickness (even in the case when the amplitude of surface deformation is much less than its wavelength). At any point on a deformed surface the temporal dependence of temperature is characterized by narrow spikes, which are repeated with the period of pulse repetition. The spatial dependence of surface temperature follows surface deformation.