Photoluminescent porous silicon properties

Photoluminescent porous silicon nanoparticles have many potential medical uses if their properties can be optimized. The techniques for both fabricating such particles and their surface chemistry manipulation are reviewed, including recent approaches whereby such nanoparticles are embedded in other biomaterial matrices. 

Octasilacubanes were used as a model in an attempt to understand the optical properties of porous silicon because both porous silicon and octasilacubane show a broad photoluminescence spectra and large Stokes shifts52. 16 for example, shows an absorption edge at ca 3.2 eV and a broad photoluminescence spectrum with a peak at 2.50 eV. 

Non-Debye dielectric relaxation was also observed in porous silicon (PS) [25,160,161], PS has attracted much attention recently, mainly due to its interesting optical and electro-optical properties that can be utilized for device applications [164,165], So far, most of the activity in this field has focused on the intense visible photoluminescence (PL) from nano-PS and the underlying physical mechanism that is responsible for the generation of light. In addition, transport and dielectric relaxation phenomena in PS have also attracted... 

Cubic Si-skeleton clusters were used to model the optical properties of porous silicon (40). In the octasilacubane 15, the absorption edge is observed at approxiamtely 3.2 eV, and a broad photoluminescence spectrum is also observed with a peak of 2.50 eV. Both porous silicon and octasilacubane show broad photoluminescence spectra and large Stokes shifts. 

Beyond the motivation to fabricate working systems from functionalized porous silicon, there is also more fundamental interest in the reactions of its surfaces. Because the vast surface of nanocrystalline silicon contains a large fraction of the total atoms, the composition and environment of the silicon interface are believed to affect greatly the physical, chemical, and electronic properties of the material. In particular, functionalization of porous silicon with certain organic groups is known to diminish photoluminescence [27] however, the mechanism of quenching has... 

Optical properties of dielectrics can be modified by incorporating nanosize clusters of foreign materials. Recently Si nanoclusters were shown to excite rare-earth element Er in the silica glass host [1,2]. The favorable effect of Si nanoclusters on the photoluminescence of Er in oxidized porous silicon (OPS) was also demonstrated [3], In silica hosts doped with Si nanoclusters it was shown that the excitation energy can be transferred from nanoclusters to Er ions located in a silicalike environment near the clusters. Nowadays, there is a principal interest to incorporate Er ions inside clusters due to influence on the excitation process. 

Clusters of small and intermediate size play an important role in the explanation of the chemical and physical properties of matter on the way from molecules to solids. The great interest in silicon clusters stems from the importance of silicon in solid-state physics and from the photoluminescence properties of porous silicon. In Chapter 20, A. F. Sax presents theoretical models to describe bare and hydrogenated small silicon clusters and discusses... 

The study of small and intermediate-sized clusters has become an important research field because of the role clusters play in the explanation of the chemical and physical properties of matter on the way from molecules to solids/ Depending on their size, clusters can show reactivity and optical properties very different from those of molecules or solids. The great interest in silicon clusters stems mainly from the importance of silicon in microelectronics, but is also due in part to the photoluminescence properties of silicon clusters, which show some resemblance to the bright photoluminescence of porous silicon. Silicon clusters are mainly produced in silicon-containing plasma as used in chemical vapor deposition processes. In these processes, gas-phase nucleation can lead to amorphous silicon films of poor quality and should be avoided.On the other hand, controlled production of silicon clusters seems very suitable for the fabrication of nanostructured materials with a fine control on their structure, morphological, and functional properties. ... 

Since the discovery of the intense red photoluminescence of porous silicon,much work has been devoted to this particular nanostructured material and, in the meantime, also to silicon nanoparticles. An important issue in current studies is the influence of the passivation on the photoluminescence properties. It has already been noted that, in the quantum... 

Since the discovery of the intense red photoluminescence of porous silicon [1,2], much work has been devoted to this particular nanostructured material [4, 5] and, in the meantime, also to silicon nanoparticles [6, 7]. An important issue of current studies is the influence of the surface passivation on the photoluminescence properties. It has already been said that, in the quantum confinement model, it is essential that the surface is well passivated to avoid any dangling bonds [8]. Being middle-gap defects, these dangling bonds will quench the PL. On the other hand, the surface itself may lead to surface states that can be the origin of another kind of photoluminescence [9,10]. 

Porous silicon is a desirable surface material for sensors because of its photoluminescence properties. With excitation, the porous silicon surface can luminesce at a variety of easily detected wavelengths. Through various methods, such as quenching, the surface can show some evidence of interaction with a target molecule. However, plain porous silicon lacks the specificity needed to detect target molecules, and is subject to non-specific interferences. 

The as-prepared PS layers were firstly investigated with these complementary methods in order to achieve a complete image of the large internal area chemical map where about 20 % of the silicon atoms are located, looking forward to accomplish a general model for porosification process and also a mechanism for the most renowned property of this material, photoluminescence (see chapter Photoluminescence of Porous Silicon ). Table 2 provides example of the compositional studies of freshly prepared and passivated/oxidized PS. 

Besides the well-known effect of photoluminescence, the impinging of photons and other kinds of particles such as electrons, ions, and muons on porous silicon produces important effects. Some of these effects can modify the structure and properties of the material, distorting the interpretation of data based on the use of irradiation. Some of the irradiation effects are useful in different applications such as photodynamic therapy or display applications. This work is a review of the effects of irradiation on porous silicon. 

Bouaicha M, Khardani M, Bessais B (2006) Correlation of electrical conductivity and photoluminescence in nanoporous silicon. Mater Sci Eng C 26 486 Bouaicha M, Khardani M, Bessais B (2008) Evaluation of the electrical conductivity of nano-porous silicon from photoluminescence and particle size distribution. Mater Sci Eng B 147 235 Canham LT (ed) (1997) Properties of Porous Silicon. lEE INSPEC, The Institution of Electrical Engineers, London... 

Posada Y, Fonseca LF, Vallejo P, San Miguel L, Resto O, Balberg I (2006) Enhaneement of the photoluminescence properties of porous silicon by sflica gel coating. J Appl Phys 99 114313 Qiao YH, Wang D, Buriak JM (2007) Block copolymer templated etehing on silieon. Nano Lett 7 464... 

Table 7 provides a brief snnunary of the investigated properties of porous nanowires synthesized by MACE. For the applications listed, the most relevant handbook chapters are Porous Silicon and Solar Cells, Porous Silicon and Lithium Ion Batteries, Photoluminescence of Porous Silicon, and Thermoelectrics and Porous Silicon . 

The mechanical properties of mesoporous silicon have so far received nothing hke the intense scrutiny that its structural, luminescent, thermal, and optical properties have (see, e.g., the handbook chapters Microscopy of Porous Silicon, Photoluminescence of Porous Silicon, Thermal... 

Bsiesy A, Vial JC, Gaspard F et al (1991) Photoluminescence of high porosity and of electrochem-ically oxidized porous silicon layers. Surf Sci 254 195-200 Canham L (ed) (1997) Properties of porous silicon. INSPEC - The Institution of Electrical... 

Petrova-Koch V, Muschik T, Kux A et al (1992) Rapid-thermal-oxidized porous Si-the superior photoluminescent Si. Appl Phys Lett 61 943-945 Porter LA, Choi HC, Ribbe AE et al (2002) Controlled electroless deposition of noble metal nanoparticle films on germanium surfaces. Nano Lett 2 1067-1071 Rabinal MK, Mulimani BG (2007) Transport properties of molecularly stabilized porous silicon schottky junctions. New J Phys 9 440-448... 

Steiner P, Kozlowski F, Wielunski M et al (1994) Enhanced blue-light emission from an indium-treated porous sihcon device. Jpn J Appl Phys 33 6075-6077 Stievenard D, Deresmes D (1995) Are electrical properties of an aluminium-porous silicon junction governed by dangling bonds Appl Phys Lett 67 1570-1572 Sze SM (1985) Semiconductor devices physics and technology. Wiley, New York Tsai C, Li KH, Sarathi J et al (1991) Thermal treatment studies of the photoluminescence intensity of porous silicon. Appl Phys Lett 59 2814-2816... 

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