Explosive Porous Silicon

Desorption/lonization on Silicon Mass Spectrometry (DIOS-MS) 

The advances of DIOS-MS since its earliest work promise the reliable measurement of low-molecular weight species in tandem with, and possibly without, MALDI-MS. Additionally, the well-established integration of devices upon silicon chips offer the ability to fashion samples capable of supporting multiple analyses in series or parallel, confining all characterizations of biological or chemical species to a lone substrate. It is clear that surface termination and bound functionalities are important not only for analysis but also for recycling the porous silicon chip for multiple uses. 

76 Recent Developments in the Chemistry and Chemical Applications of Porous Silicon 

Support from the Purdue Research Foundation is acknowledged. J. M. B. is a Research Fellow of the Alfred P. Sloan Foundation (2000-2002), a Cottrell Teacher-Scholar of Research Corporation (2000-2002), and a Camille and Henry Dreyfus Foundation Teacher-Scholar (2002-2004). 

5 Properties of Porous Silicon, ed. Canham, L. T., INSPEC, London 1997. 

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Clement D, Diener J, Kovalev D (2004) Explosive porous silicon - Irom laboratory accident to industrial application. In Proceedings of the 35th international conference of Institut Chemische Technologic (ICT), Energetic materials - stmcture and properties, Karlsruhe, 29 Jun-2 Jul 2004, pp 5.1-5.11... 

INFLUENCE OF THE POROUS SILICON STRUCTURE ON ITS COMBUSTION AND EXPLOSION... 

Porous silicon structures have been studied in order to provide combustion and explosion this material. The combustion process has been observed in the porous silicon layers formed by anodization if the specific area is more than 100 mVcm We have also found that the combustion intensity increases with porous silicon specific area and if the latter is larger than 200 mVcm the explosion process occurs. The time response of explosion development is in the microsecond range. 

Porous silicon is compatible with standard silicon K-MOS technology and different microsystems based on this nanostructured material have been successfully fabricated [1], Porous silicon impregnating with solid state oxidants demonstrats combustion and explosion processes [2-5]. These processes can be used for various microactuators [6], In present work we have studied the influence of the porous silicon structure on the combustion and explosion processes. 

Fig. 2 shows the flash diameter of combustion and explosion processes in porous silicon filled with solid state oxidants. It should be noted that the explosion process occurred only in the samples formed on p-type silicon wafers. Meantime the explosion and combustion processes were not observed in porous silicon formed on n-type silicon wafers without light exposition during... 

It is well known that the fundamental distinctions between combustion and explosion are the value of the time response and presence of a shock wave. Thus, the combustion time response is in millisecond and second ranges, while the time typical of explosion development is within the microsecond range. Fig. 3 shows the fragments of fast oxidation process in the porous silicon layer formed on p-type silicon wafer. The time response of flash development is in the microsecond range (Fig. 3a,b,c). That confirms the explosion nature of the investigating oxidation process. Also the sound accompaniment of this process was similar to the gunshot, testifying presence of the shockwave. The flash is appeared to be the fireball. 

Fast oxidation process in a way of combustion and, in some cases, of explosion in porous silicon films has been observed at pore wall thickness less than 10 nm. The increasing of porous specific area results in an enhancement of combustion and explosion intensity. The explosion process has been observed at the specific area more than 200 m /cm. Thus combustion and explosion processes in the porous silicon layers can be attributed to nanoscale phenomena. 

Recent work by Mikulec et al. [117] has exploited an unusual property of porous silicon and used this material as an explosive matrix for atomic emission spectroscopy. Freshly prepared, hydride-terminated substrates soaked in aqueous solutions of Gd(N03)3 were detonated with mechanical or electrical triggers in a flashy, exothermic reaction not unlike the combustion of black powder (Figure 16.17). The estimated high ( 2000 K) local temperature created by the explosion was employed to generate emission spectra for alkali metals and heavy metals deposited upon the substrates from solution or suspension. Detonation was completed for a range of porous specimens and did not depend upon either the crystalline identity of the precursor or the morphology of the etched material however, oxidized substrates exhibited a lesser propensity to explode. The intensity of the explosion was... 

Fig. 16.17. Photograph of the bright flash from explosion of porous silicon treated with GdlNOsjj. Detonation was provided from a transformer (upper right). (M. J. Sailor is thanked for permission to reprint this figure.)...

Based on the optical thickness of films on porous silicon, this new generation of sensors relies on changes in the film to detect chemicals. In tests for volatile organic compounds, polycyclic aromatic hydrocarbons, explosives, and other chemicals, these sensors have been sensitive to ppb ranges (Sailor, 1997). 

Luminescent inorganic polymer sensors had received little attention as explosive sensors. The observation of electron transfer quenching of luminescence in porous silicon nanostructures [27] suggested that polysilicon organometallic species might be especially promising for sensor applications. Several luminescent polysilicon based structures are known. 

The performed experiments demonstrated that explosion and combustion processes can be carried out in porous silicon formed by anodizing of p-type silicon wafers. Fig. 1 presents the TEM images of as-formed porous. The pore walls are 4-6 nm for p-type silicon wafers and 10-20 nm for n-type silicon wafers. 

Figure 2. Ball lightning produced by thermal ignition of 100 pm thick 1 cm in diameter porous silicon filled with KNO3 a) as formed, b) 0.1 s after formation, c) 0.3 s after formation, d) 1 s after formation. Other photos illustrating combustion and explosion of porous silicon can be seen in [14],...

S.K.Lazarouk, A.V.Dolbik, V.E.Borisenko, Photogallery of lightning ball formed by porous silicon explosion and combustion processes, www.nano-center.org (2005). 

Table 2 The porous silicon properties of selected explosive devices...

The energy yield of porous silicon explosive devices was measured using a calorimetric bomb test, resulting in a value of 7.3 kJ/g with calcium perchlorate as oxidizer (Clement et al. 2005). Differential scanning calorimetry techniques were also used to measure the energy output for sodium perchlorate at almost 9 kJ/g (Plummer et al. 2008). The extent of the NaC104 reaction was observed with bomb calorimetry in N2 and O2 atmospheres. Without the supplementary O2 environment, the heat of reaction was measured to be 9.9 1.8 kJ/g, but with supplementary O2, the reaction yielded 27.3 3.2 kJ/g and approached the theoretical value of 33.0 kJ/g for complete Si oxidation (Becker et al. 2010). 

The temperature of the flame and the amount of gas generated during the nano-explosion were also experimentally investigated (Mason et al. 2009). The nominal maximum flame temperature for most porous silicon oxidizer systems is about 3,000 K, with the oxidant sulfur an exception where the flame temperature is only 1,600 K. The maximum gas production of the porous silicon explosives ranged from 650 cm /g of reactant for sulfur to 4,800 cm /g of reactant for NaC104. 

In recent studies on the combustion performance of silicon-based nanoenergetic composites (Thiruvengadathan et al. 2012) and the explosive composite of porous silicon and sodium perchlorate (Becker et al. 2010), the need to passivate the silicon surface with hydrogen was clearly demonstrated. 

Since the 2002 discovery of nano-explosive devices using solid-state oxidants in porous silicon at room temperature, the technology has reached the stage where several applications are considered. Issues of interest are the cost-effectiveness of fabrication, future integration with CMOS technology, the long-term stability, and the sensitivity to electrostatic discharge. 

Koch EC, Clement D (2007) Special materials in pyrotechnics VI. Silicon - an old fuel with new perspectives. Propell Explos Pyrotech 32(3) 205-212 Kovalev D, Timoshenko VY, Kiinzner N, Gross E, Koch F (2001) Strong explosive interaction of hydrogenated porous silicon with oxygen at cryogenic temperatures. Phys Rev Lett 87 68301(1-4)... 

McCord P, Yau S-L, Bard AJ (1992) Chemiluminescence of anodized and etched sihcon evidence for a luminescent siloxene-like layer on porous silicon. Science 257 68-69 Mikulec FV, Kirtland JD, Sailor MJ (2002) Explosive nanocrystalline porous silicon and its use in atomic emission spectroscopy. Adv Mater 14 38-41 Parimi VS, Tadigadapa SA, Yetter RA (2012) Control of nanoenergetics through organized micro-stmctures. J Micromech Microeng 22 055011(1-6)... 

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