Silicon Nanocrystals: Photosensitizers for Oxygen Molecules

Molecular oxygen plays an important role in many of the chemical reactions involved in the synthesis of biological life. In this review, we explore the interaction between O₂ and silicon nanocrystals, which can be employed in the photosynthesis of singlet oxygen. We demonstrate that nanoscale Si has entirely new properties owing to morphological and quantum size effects, i.e., large accessible surface areas and excitons of variable energies and with well‐defined spin structures. These features result in new emerging functionality for nanoscale silicon: it is a very efficient spin‐flip activator of O₂, and therefore, a chemically and biologically active material. This whole effect is based on energy transfer from long‐lived electronic excitations confined in Si nanocrystals to surrounding O₂ via the exchange of single electrons of opposite spin, thus enabling the spin‐flip activation of O₂. Further, we discuss the implications of these findings for physics, chemistry, biology, and medicine.     

Cover Picture: Partially Oxidized Macroporous Silicon: A Three‐Dimensional Photonic Matrix for Microarray Applications (Adv. Mater. 23/2006)

Partial oxidation of macroporous silicon membranes with different pore wall thicknesses results in a regular compartmentalized structure of SiO₂ domains separated by opaque silicon, as shown on the cover. Dertinger and co‐workers report on p. 3135 that control of the experimental conditions ensures the flatness of the partially oxidized macroporous silicon. Fluorescence crossover is minimized within the photonic crystal, enabling its use as a microarray support for sensitive bioanalytic applications, such as DNA hybridization.     

Doping Silicon Wafers with Boron by Use of Silicon Paste

In this work we introduce recently developed silicon-paste-enabled p-type doping for silicon.Boron-doped silicon nanoparticles are synthesized by a plasma approach.They are then dispersed in solvents to form silicon paste. Silicon paste is screen-printed at the surface of silicon wafers.By annealing,boron atoms in silicon paste diffuse into silicon wafers.Chemical analysis is employed to obtain the concentrations of boron in silicon nanoparticles.The successful doping of silicon wafers with boron is evidenced by secondary ion mass spectroscopy(SIMS) and sheet resistance measurements.     

Silicon Nanocrystals: Size Matters

This paper reviews new approaches to size‐controlled silicon‐nanocrystal synthesis. These approaches allow narrowing of the size distribution of the nanocrystals compared with those obtained by conventional synthesis processes such as ion implantation into SiO₂ or phase separation of sub‐stoichiometric SiO_x layers. This size control is realized by different approaches to introducing a superlattice‐like structure into the synthesis process, by velocity selection of silicon aerosols, or by the use of electron lithography and subsequent oxidation processes. Nanocrystals between 2 and 20 nm in size with a full width at half maximum of the size distribution of 1 nm can be synthesized and area densities above 10¹² cm^–2 can be achieved. The role of surface passivation is elucidated by comparing Si/SiO₂ layers with superlattices of fully passivated silicon nanocrystals within a SiO₂ matrix. The demands on silicon nanocrystals for various applications such as non‐volatile memories or light‐emitting devices are discussed for different size‐controlled nanocrystal synthesis approaches.     

硅量子线的研究

利用常规硅工艺的反应离子刻蚀、各向异性化学腐蚀、热氧化和超低压ＣＶＤ生长技术，成功地硅单晶衬底上制作了硅／二氧化硅异质界面结构超精细硅量子线。本项研究结果对开展低维量子结构物理及硅量子器件的研究具有十分重要的意义。