Porous silicon uniformity

Another problem in application of the basic theories is associated with surface geometry. Most theories are developed to describe the relationships among the area-averaged quantities such as charge density, current density, and potentials assuming a uniform electrode surface. In fact, the silicon surface may not be uniform at the micrometer, nanometer, or atomic scales. There can be great variations in the distribution of reactions from extremely uniform, for example, in electropolishing, to extremely nonuniform, for example, in the formation of porous silicon. 

We provide a literature survey of a number of classical techniques used to quantify the chemical composition of porous silicon, highlighting their general merits and potential limitations with the material. Much of the early literature was focused on photoluminescent material, but increasingly there are studies on nanocomposites where chemical composition analysis is required to assess the degree and uniformity of impregnation or surface attachment. 

For porous silicon multilayer structures (see chapter Porous Silicon Multilayers and Superlattices of this handbook), improved interface uniformity has been achieved by incorporating a short period of zero bias between individual layers, thereby allowing the hydrogen to diffuse from... 

For uniform thick films, slow etching using V02 or with low H2 production is preferred. Critical point drying is a must (see chapter Drying Techniques Applied to Porous Silicon ). V2O5 dissolves in concentrated HF(aq) but not water. To make diluted solutions, always dissolve first in concentrated HF then add water. 

Direet TXRF mapping of Cu on the front side showed that the embedded PSi reduced the amount of Cu reaching the top surface by 10 times, compared to the periphery areas without PSi (see Fig. 2 right). A control wafer without porous silicon showed no such pattern with uniform and high Cu surface concentrations, confirming barrier properties of porous silicon. Similar TXRF maps were obtained for Ni and Fe. 

Electrochemical etching of silicon can generate porous silicon where porosity is modulated with depth. The overall fabrication technique, experimental tips for improving uniformity, typical porosity profiles, and methods of patterning and stabilization are reviewed. Due to its ease of fabrication, such multilayers have been extensively fabricated and applied in different fields, such as photonics, phononics, sensing etc. 

Lomov AA, Bushuev VA, Karavanski VA (2000) Study of surface and interface roughnesses in porous silicon by high-resolution X-ray methods. Crystallogr Rep 45 842-847 Lopez-Villegas JM, Navarro M, Papadimitriou D, Bassas J, Samitier J (1996) Structure and non-uniform strain analysis on p-type porous silicon by X-ray reflectometry and X-ray diffraction. Thin Solid Films 276 238-240... 

Yao et al. [10] studied an electroosmotic pump made from porous silicon membranes having straight circular pores. Tortuosity is unity and ifr was measured directly from SEM images of the cross-section. Zeta potential is calculated by using the formula for the ratio 2max/Jmax and the measured data of Qmax and /max- Comparison between theory and experiment is good for the plots Qmax versus V and Jmax versus V. There was considerable deviation for the prediction of Apmax and Yao et al. attributed this discrepancy to the problem in the zeta potential measurement and non-uniform distribution of the pore size. At a lower flow... 

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