Abstract Heterostructures of van der Waal (vdW) materials show novel optical properties when stac... more Abstract Heterostructures of van der Waal (vdW) materials show novel optical properties when stacked on top of each other. In this report, using the first principle calculations, we study the electronic band structures of heterostructures composed of two VdW semiconductors namely g-ZnO/ZnX (X = S, Se, and Te). Here the cation is common while the anion is different. Our calculations reveal the formation of a type II band alignment in these heterostructures. The optical band gap shows a linear dependence to the external electric field (E) applied normally to the interface. Bader charge analysis results indicate (1) the number of electrons lost (gained) by ZnX is equal to the number of electrons gained (lost) by g-ZnO (2) indicating that the linear relationship with the applied electric field, is closely related to charge transfer. We have also explored the effects of layer thickness. We observe that as the g-ZnO layer increases, the band gap reduces. Such tunability of g-ZnO/ZnX heterostructures can make them potential candidates for optoelectronic devices.
Size, shape, and density of self-assembled GaN nanorods grown on Si͑111͒ substrates by plasma-ass... more Size, shape, and density of self-assembled GaN nanorods grown on Si͑111͒ substrates by plasma-assisted molecular beam epitaxy were successfully controlled by inserting a GaN buffer layer. The structure of the GaN buffer layer plays a vital role in the nanorod growth. Only a broken buffer layer with a suitable opening size can grow nanorods. Evolution of the nanorod is traced to the initial growth stage. Crystal seed grown at the wall of the opening in the buffer layer initiates the beginning of the nanorod, and a self-catalytic vapor-liquid-solid process, triggered by the nanocapillary condensation effect, enhances the GaN nanorod growth. Furthermore, the nanorod density can be largely controlled by using the beam equivalent pressure of the N / Ga ratio. Other GaN nanostructures grown at different growth conditions are also discussed in details.
Periodic arrays of GaN nanostructures are fabricated by MBE growth on self-implanted (1 1 1) Si s... more Periodic arrays of GaN nanostructures are fabricated by MBE growth on self-implanted (1 1 1) Si substrates. Nanocapillary condensation is found to be an effective catalytic process fostering the formation of epitaxially aligned GaN nanorods in company with the thin film matrix. Changes of Si substrate surface morphology prior to deposition as a result of ion bombardments are responsible for the enhanced nanorod growth. This is attributed to the nanocapillary condensation of Ga droplets that serve as a medium to the vaporliquid-solid growth of nanorods out of its supporting matrix.
Gas cluster ion beams (GCIB) have been used to fabricate nano-ripple structures on Si substrates.... more Gas cluster ion beams (GCIB) have been used to fabricate nano-ripple structures on Si substrates. In this work, using (Ar)n^+ clusters at 30 kV acceleration, where n 3,000, we have observed nano-ripple formations on the silicon surface after GCIB bombardment. The wavelength, amplitude and the dimensions of the ripples were studied in an effort to characterize the morphology as a function of angle of incidence, crystallographic orientations of the substrate, and the ion dosages. The underlying physics of ripple formation will be discussed and fabrication of nanorods on rippled (111)-Si substrates using III-nitrides, such as GaN, InGaN, and InAlN, will be presented.
Using the effective medium approximation and the theory of photoemission from small particles, co... more Using the effective medium approximation and the theory of photoemission from small particles, consideration is given to the design-rules of infrared materials based upon the metal-semiconductor random heterostructures with Ag particles embedded in the semiconductor. It is found that semiconductor host matrices with higher dielectric constants show better optical absorption in the infrared and that optical properties are closely related to microstructural parameters such as volume fraction of metal particles, percentage of aggregation and particle size. Cu, Ag and Au particles all show similar characteristics. Materials with small silver particles embedded in Si are synthesized.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2006
We have used molecular beam epitaxy grown Sb markers within Si to detect vacancy fluxes created b... more We have used molecular beam epitaxy grown Sb markers within Si to detect vacancy fluxes created by high energy Si + ion implants at various energies. Our experiments show that for a constant ion fluence of 1 · 10 15 cm À2 , the number of free vacancies created by ion implantation, followed by annealing at 900°C, increases with implantation energy. This is in contrast to the instantaneous vacancy creation rate during ion bombardment at the surface, which decreases with increasing ion energy. The possible mechanisms are discussed based on the separation distance between excessive interstitials (at the projected range of ions) and vacancies (near the surface), and the interaction between free vacancies and vacancy clusters.
Page 1. Mol. Cryst. Liq. Cryst., 1984, Vol. 106, p. 411 0 1984 Gordon and Breach, Science Publish... more Page 1. Mol. Cryst. Liq. Cryst., 1984, Vol. 106, p. 411 0 1984 Gordon and Breach, Science Publishers, Inc Printed in the United States of America 0026-8941 /84/1064-04 1 1 /$18.50/0 SYNTHESIS AND CHARACTERIZATION OF POLYPHENOTHIAZENE IODINE COMPLEXES ...
Abstract Heterostructures of van der Waal (vdW) materials show novel optical properties when stac... more Abstract Heterostructures of van der Waal (vdW) materials show novel optical properties when stacked on top of each other. In this report, using the first principle calculations, we study the electronic band structures of heterostructures composed of two VdW semiconductors namely g-ZnO/ZnX (X = S, Se, and Te). Here the cation is common while the anion is different. Our calculations reveal the formation of a type II band alignment in these heterostructures. The optical band gap shows a linear dependence to the external electric field (E) applied normally to the interface. Bader charge analysis results indicate (1) the number of electrons lost (gained) by ZnX is equal to the number of electrons gained (lost) by g-ZnO (2) indicating that the linear relationship with the applied electric field, is closely related to charge transfer. We have also explored the effects of layer thickness. We observe that as the g-ZnO layer increases, the band gap reduces. Such tunability of g-ZnO/ZnX heterostructures can make them potential candidates for optoelectronic devices.
Size, shape, and density of self-assembled GaN nanorods grown on Si͑111͒ substrates by plasma-ass... more Size, shape, and density of self-assembled GaN nanorods grown on Si͑111͒ substrates by plasma-assisted molecular beam epitaxy were successfully controlled by inserting a GaN buffer layer. The structure of the GaN buffer layer plays a vital role in the nanorod growth. Only a broken buffer layer with a suitable opening size can grow nanorods. Evolution of the nanorod is traced to the initial growth stage. Crystal seed grown at the wall of the opening in the buffer layer initiates the beginning of the nanorod, and a self-catalytic vapor-liquid-solid process, triggered by the nanocapillary condensation effect, enhances the GaN nanorod growth. Furthermore, the nanorod density can be largely controlled by using the beam equivalent pressure of the N / Ga ratio. Other GaN nanostructures grown at different growth conditions are also discussed in details.
Periodic arrays of GaN nanostructures are fabricated by MBE growth on self-implanted (1 1 1) Si s... more Periodic arrays of GaN nanostructures are fabricated by MBE growth on self-implanted (1 1 1) Si substrates. Nanocapillary condensation is found to be an effective catalytic process fostering the formation of epitaxially aligned GaN nanorods in company with the thin film matrix. Changes of Si substrate surface morphology prior to deposition as a result of ion bombardments are responsible for the enhanced nanorod growth. This is attributed to the nanocapillary condensation of Ga droplets that serve as a medium to the vaporliquid-solid growth of nanorods out of its supporting matrix.
Gas cluster ion beams (GCIB) have been used to fabricate nano-ripple structures on Si substrates.... more Gas cluster ion beams (GCIB) have been used to fabricate nano-ripple structures on Si substrates. In this work, using (Ar)n^+ clusters at 30 kV acceleration, where n 3,000, we have observed nano-ripple formations on the silicon surface after GCIB bombardment. The wavelength, amplitude and the dimensions of the ripples were studied in an effort to characterize the morphology as a function of angle of incidence, crystallographic orientations of the substrate, and the ion dosages. The underlying physics of ripple formation will be discussed and fabrication of nanorods on rippled (111)-Si substrates using III-nitrides, such as GaN, InGaN, and InAlN, will be presented.
Using the effective medium approximation and the theory of photoemission from small particles, co... more Using the effective medium approximation and the theory of photoemission from small particles, consideration is given to the design-rules of infrared materials based upon the metal-semiconductor random heterostructures with Ag particles embedded in the semiconductor. It is found that semiconductor host matrices with higher dielectric constants show better optical absorption in the infrared and that optical properties are closely related to microstructural parameters such as volume fraction of metal particles, percentage of aggregation and particle size. Cu, Ag and Au particles all show similar characteristics. Materials with small silver particles embedded in Si are synthesized.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2006
We have used molecular beam epitaxy grown Sb markers within Si to detect vacancy fluxes created b... more We have used molecular beam epitaxy grown Sb markers within Si to detect vacancy fluxes created by high energy Si + ion implants at various energies. Our experiments show that for a constant ion fluence of 1 · 10 15 cm À2 , the number of free vacancies created by ion implantation, followed by annealing at 900°C, increases with implantation energy. This is in contrast to the instantaneous vacancy creation rate during ion bombardment at the surface, which decreases with increasing ion energy. The possible mechanisms are discussed based on the separation distance between excessive interstitials (at the projected range of ions) and vacancies (near the surface), and the interaction between free vacancies and vacancy clusters.
Page 1. Mol. Cryst. Liq. Cryst., 1984, Vol. 106, p. 411 0 1984 Gordon and Breach, Science Publish... more Page 1. Mol. Cryst. Liq. Cryst., 1984, Vol. 106, p. 411 0 1984 Gordon and Breach, Science Publishers, Inc Printed in the United States of America 0026-8941 /84/1064-04 1 1 /$18.50/0 SYNTHESIS AND CHARACTERIZATION OF POLYPHENOTHIAZENE IODINE COMPLEXES ...
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