Semiconductors nanoscale

Komarakis I, Lykakis IN, Vordos N, Armatas GS (2014) Efficient visible-light photocatalytic activity by band alignment in mesoporous ternary polyoxometalate-Ag2S-CdS semiconductors. Nanoscale 6 8694—8703... 

The formation of semiconductor nanoparticles and related stmctures exhibiting quantum confinement within LB films has been pmsued vigorously. In 1986, the use of the metal ions in LB films as reactants for the synthesis of nanoscale phases of materials was described [167]. Silver particles, 1-2 mn in size, were produced by the treatment of silver be-henate LB films with hydrazine vapor. The reaction of LB films of metal salts (Cd, Ag, Cu, Zn, Ni, and Pb ) of behenic acid with H2S was mentioned. The use of HCl, HBr, or HI was noted as a route to metal halide particles. In 1988, nanoparticles of CdS in the Q-state size range (below 5 mn) were prepared inside LB films of cadmium arachi-... 

The work described here is concerned with the development of electrochemical methodologies to grow compound semiconductors with nanoscale or atomic layer control. That thin-films of some compounds can be formed electrochemically is clear. The questions are how much control over deposit composition, structure and morphology can be obtained What compounds, and of what quality, can be formed ... 

The creation of nanoscale sandwiches of compound semiconductor heterostructures, with gradients of chemical composition that are precisely sculpted, could produce quantum wells with appropriate properties. One can eventually think of a combined device that incorporates logic, storage, and communication for computing—based on a combination of electronic, spintronic, photonic, and optical technologies. Precise production and integrated use of many different materials will be a hallmark of future advanced device technology. 

To what extent do the insights and information obtained from measuring terms in the NMR Hamiltonian for bulk semiconductors, as discussed above, apply to nanoscale studies ... 

Answer NMR characteristics observed in bulk semiconductors such as electron hyperfine effects in dilute magnetic semiconductors [322-324], Knight shifts [234], and chemical shift differences resulting from alloying [325-327] and possibly different polytypes [322, 328] have been observed at the nanoscale. 

Answer Chemical shift calculations for nanoscale semiconductors by DFT methods and comparison with experimental results have recently appeared [140], and while quite challenging hold much promise. 

Answer. There has been little effective interplay between experimental results obtained on single nanostructures grown as quantum-wells and studied by optical-pumping methods and those obtained on bulk nanoscale semiconductors by more conventional NMR approaches. However, this situation may change, since the former studies can provide information about the effects of, e.g., charge carriers or strain or compositional interfaces upon NMR parameters such as chemical and Knight shifts and EFGs in reasonably well-defined systems. 

From a very general outlook, one can argue that the NMR studies of quadrupolar nuclei present in nanoscale semiconductors should offer a more incisive look into the chemical and electronic structure than do studies of spin-1/2 nuclei. The rationale is that quadrupolar nuclei can report on the same chemical, hyperftne, or Knight shifts and dipolar or indirect couplings as observed for spin-1/2 nuclei, but also provide an additional dimension of information in terms of the NQCC and associated EFGs. Although not yet reported, DFT calculations of both chemical shifts and NQCC values for the same nuclei in nano-semiconductors should provide a more stringent comparison of theoretical and experimental results, particularly if the two parameters can be correlated experimentally, as seems feasible. 

The NMR of semiconductors in a nanoscale form (QD or NC, NW, etc.) presents special problems of sensitivity, resolution, and theoretical interpretation. In... 

One-dimensional (ID) nanostructures have also been the focus of extensive studies because of their unique physical properties and potential to revolutionize broad areas of nanotechnology. First, ID nanostructures represent the smallest dimension structure that can efficiently transport electrical carriers and, thus, are ideally suited for the ubiquitous task of moving and routing charges (information) in nanoscale electronics and optoelectronics. Second, ID nanostructures can also exhibit a critical device function and thus can be exploited as both the wiring and device elements in architectures for functional nanosystems.20 In this regard, two material classes, carbon nanotubes2131 and semiconductor nanowires,32"42 have shown particular promise. 

The fundamental physical properties of nanowire materials can be improved even more to surpass their bulk counterpart using precisely engineered NW heterostructures. It has been recently demonstrated that Si/Ge/Si core/shell nanowires exhibit electron mobility surpassing that of state-of-the-art technology.46 Group III-V nitride core/shell NWs of multiple layers of epitaxial structures with atomically sharp interfaces have also been demonstrated with well-controlled and tunable optical and electronic properties.47,48 Together, the studies demonstrate that semiconductor nanowires represent one of the best-defined nanoscale building block classes, with well-controlled chemical composition, physical size, and superior electronic/optical properties, and therefore, that they are ideally suited for assembly of more complex functional systems. 

Huang, Y., Lieber, C. M. 2004. Integrated nanoscale electronics and optoelectronics Exploring nanoscale science and technology through semiconductor nanowircs. Pure Appl. Chem. 76 2051-2068. 

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