Crystallization of amorphous silicon by self-propagation of nanoengineered thermites

Abstract

Crystallization of amorphous silicon ͑a-Si͒ thin film occurred by the self-propagation of copper oxide/aluminum thermite nanocomposites. Amorphous Si films were prepared on glass at a temperature of 250°C by plasma enhanced chemical vapor deposition. The platinum heater was patterned on the edge of the substrate and the CuO / Al nanoengineered thermite was spin coated on the substrate that connects the heater and the a-Si film. A voltage source was used to ignite the thermites followed by a piranha solution ͑4 Unlike most other techniques, laser induced crystallization does not require high temperatures ͑Ͼ180°C͒ and long processing times to produce good quality poly-Si films. The major disadvantage of laser crystallization is its low throughput due to small laser spot size, which is not suitable for large area such as solar cells. Thus, high temperature and long processing times for various crystallization methods, and small spot size of the laser are not suitable for producing poly-Si film on a large surface area of glass or flexible plastic substrates. Low cost plastic substrates such as polyethersulphone can be used for flexible electronics if the device is fabricated under 180°C. This study investigates the crystallization of a-Si layer achieved by the ignition of nanoengineered thermite materials such as CuO / Al. Explosives have been utilized previously to crystallize amorphous materials; 5,6 however, there is no information currently available on thin film crystallization using nanoengineered thermites. Our approach utilizes thermite reaction to induce crystallization of a-Si thin film; such energetic reactions are self-propagating exothermic reactions, which produce localized heating effects. We discovered that thermites, nanoengineered by the self-assembly approach, produced a self-propagating chemical reaction over a period of microseconds. 7,8 The exothermic reaction propagates at a rate of 1500-2000 m / s resulting in heat release. This heat can be used advantageously to crystallize a-Si. High quality poly-Si films can be prepared on large substrates utilizing this released heat. Nanoengineered thermites were prepared by sonicating a mixture of CuO nanorods ͑10 nm diameter and 70 nm long͒ and aluminum nanopowder ͑80 nm diameter͒. The details of the nanorod preparation and the characterization of the thermites are presented in Ref. 9. The thermites displayed the following chemical reaction:where ⌬H is the released heat. For CuO / Al exothermic reaction, the released heat is 604 kJ/ mol and the adiabatic reaction temperature is 3794 K. 10The a-Si samples were prepared by plasma enhanced chemical vapor deposition on glass substrates. The thickness of the a-Si layer was 300 nm. A thin layer of platinum ͑90 nm thick and 2.5 mm wide͒ was deposited on the edge of the substrates, which functioned as a heater for initiating the self-propagating reaction for the energetic materials. The substrates with a-Si and the platinum heater were spin coated with the thermites and dried at 105°C in an oven for 10 min. Th...

Physiochemical Characterization of Iodine (V) Oxide Part II: Morphology and Crystal Structure of Particulate Films

“…This control results in an inexpensive, fast, and reliable methodology, applied at the industrial level for film fabrication of dielectric, optical and microelectronic materials [28]. Remarkably, however, only a limited number of articles have been published that utilize spin coating to produce binary energetic material films [31][32][33]. While our interest is to produce and investigate such binary fuel-oxidizer energetic materials, this particular paper focuses solely on the effects of drop and spin casting of the oxidizer, given that the oxidizer seems to be most sensitively affected by the conditions of the casting process.…”

Modeling the Pressure Generation in Aluminum‐Based Thermites

“…Alumino-thermite is an oxidation-reduction reaction involving am etal (fuel) and am etallic oxide (or possibly an on-metallic oxide) that forms as table product after reaction.Thermite materials have been actively investigated for aw ide range of potential applications including railroad welding, materials processing to form refractory materials, additives in propellants, explosives and pyrotechnics [1][2][3], and more recently also for micro initiation [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20],e nvironmentally clean primers, and in situ welding [21].Among the numerous possible exothermic metal/oxide pairs listed in the literature [22],t he most investigated ones mix Al with MoO 3 ,C uO, Bi 2 O 3 ,F e 2 O 3 ,M nO 2 ,W O 3 ,a nd I 2 O 5 .F or the last two decades most of the research efforts aimed at reducing metal and oxide components size, improving their intimacy,t oi ncrease the reaction rate and decrease the ignition delay while improving safety.More recently,t hermite materials were also considered to produce gas species or pressure bursts, opening new potential fields of application such as pressure mediated molecular delivery [23,24],b iological agent inactivation [25][26][27],h ydrogen production [28,29],o rp ropulsion systems [7][8][9].Af ew teams demonstrated experimentally that Al/Bi 2 O 3 and, to al esser extent, Al/I 2 O 5 mixtures generate the highest pressure pulses [27,30,31] in comparison with other thermites. Martirosyan [31] considered tha...…”

Crystallization of amorphous silicon thin films using nanoenergetic intermolecular materials with buffer layers

“…In this case, the calculating average crystalline volume fraction is of no use because of the fluctuating crystallinity region by region in the film. To propagate thermal energy uniformly, the metal layer was introduced between NPH and a-Si as was done in a previous report [10]. On the other hand, to avoid the possibility of forming a silicide layer and metal diffusion through the Si film, a SiO 2 buffer layer was additionally introduced as a diffusion barrier.…”

“…Hossain et al [10] reported that a metal buffer layer can act as a heat transporter between NPH and a-Si layers and expedite the crystallization of a-Si. However, the use of metal film as a heat transporting layer may cause serious problemproblems such as forming a metal silicide between metal and silicon, which cannot be removed easily.…”

“…These nanocomposites can be used as a heating source for the crystallization of a-Si, so we'll name it nanoparticle heater (NPH) in this paper. The exothermic reaction from energetic materials propagates at a rate of 1500-2000 m/s, which implies that only microseconds scale is needed to crystallize a large area of a-Si [10].…”