Tuning of the electronic properties of semiconductors can be achieved by surface modification with organic molecules. In this work, we study, by periodic density functional theory, the change in work function that occurs upon the modification of nominally hydrogen-terminated Si(100)-2 × 1 by chemisorption of substituted styrene molecules. Our results show that monolayers derived from 4-X-styrene molecules, with X being electron donating groups or hydrogen, decrease the work function of the system. Conversely, monolayers derived from 4-X-styrene molecules, with X being electron withdrawing groups, increase the work function of the system. For the molecules used in the modeling, the calculations indicate that the work function can be substantially modified from −1.4 eV (XN(CH3)2) to +1.9 (XNO2) eV relative to H−Si(100)-2 × 1. Because the direction and magnitude of charge transferred upon chemisorption is the same for all molecules, the work function changes are not the result of band bending. The work function modification comes exclusively from the inherent dipoles of the molecules chemisorbed on the surface. The computed dipoles for the monolayers range from −1.3 (XN(CH3)2) to +1.4 (XNO2) Debye. We conclude that substantial local control over some of the electronic properties of silicon can be achieved by the chemisorption of dipole-containing molecules.

The total variation (TV) regularization method can be used to obtain solutions were edges and discontinuities are preserved. In this article, the TV method is applied to invert acoustic perturbations using the single-scattering Born modeling operator. The TV regularization imposes sparsity on the gradient of the model parameters. The latter leads to images of model parameters with preserved discontinuities and edges. Synthetic data examples are used to test the proposed seismic imaging algorithm.

Incorporating diversity into structures constructed from the organic modification of silicon surfaces requires the use of molecules that contain multiple substituents of different types. In this work we examine the possible dissociation pathways of diethylhydroxylamine (DEHA, (C(2)H(5))(2)NOH) on the surface of clean silicon(100)-2x1 using cluster and planewave computational methods and high resolution electron energy loss spectroscopy. Our computational results show that DEHA initially forms a strongly-bound complex with the surface via a dative N-Si bond. A low-barrier O-H bond scission then occurs yielding a surface silicon dimer capped by the (C(2)H(5))(2)NO and H fragments. Calculated and measured vibrational spectra support the computed reaction mechanism.

The computational cost of full-waveform inversion (FWI) is a major obstacle to estimating the velocity model for large-scale problems. One way to reduce the overall cost of waveform inversion is by adopting a simultaneous-source strategy. In other words, multiple sources are simultaneously fired to simulate supershot gathers and thereby reduce the number of seismic modeling simulations that are performed during the inversion. However, the use of simultaneous sources introduces crosstalk artifacts that arise from the interference among the sources that constitute a supershot. We analyzed the influence of different simultaneous multifrequency selection strategies on crosstalk artifacts. Our analysis focused on a frequency-domain FWI algorithm that is implemented with simultaneous sources that are randomly encoded with random time shifts. In the multiscale conventional FWI strategies, a finite set of discrete frequencies was selected and the inversion was carried out sequentially from low- to high-frequency data components. First, the long wavelength components of model parameters were recovered from the low-frequency data, and then more details and features were extracted as the inversion proceeded to the higher frequency data. We examined six frequency selection strategies and tested the performance of the algorithm with encoded data sets. Numerical tests showed that high-fidelity results could be attained by inverting partially overlapped groups of temporal frequencies. Our FWI algorithm is based on a matrix-free Gauss-Newton method. To mitigate crosstalk artifacts during the numerical inversion, a new encoding was generated at every iteration. We also found that high-resolution images can be obtained by resampling new source positions and new encoding functions at every iteration of the FWI algorithm.