Metal-catalyzed growth of semiconductor nanostructures without solubility and diffusivity constraints

Perspectives on metal induced crystallization of a-Si and a-Ge thin films

In recent times, the metal induced crystallization (MIC) process in amorphous semiconductors (a-Si and a-Ge) has been extensively investigated by many researchers due to potential applications of crystalline semiconductors in high-density data storage devices, flat panel displays, and high performance solar cells. In this context, we have presented a review on different schemes of MIC in metal/a-Si and metal/a-Ge bilayer films (with stacking change) on various substrates under different annealing conditions. The parameters, which limit crystallization of a-Si and a-Ge have been analyzed and discussed extensively keeping in mind their applications in solar cells and flat panel displays. The MIC of a-Si and a-Ge films under ion beam irradiation has also been discussed in detail. At the end, some suggestions to overcome the limitations of the MIC process in producing better crystalline semiconductors have been proposed. We believe that this review article will inspire readers to perform a thorough investigation on various aspects of MIC for further development of high efficiency solar cells and high quality flat panel displays.

Highly sensitive non-enzymatic hydrogen peroxide monitoring platform based on nanoporous gold via a modified solid-phase reaction method

In this work, nanoporous gold (NPG) fabricated using a modified solid-phase reaction method was developed as an electrocatalyst for the nonenzymatic detection of hydrogen peroxide (H₂O₂). The NPG morphology and structure were characterized by scanning electron microscopy and high-resolution transmission electron microscopy. The fabricated NPG exhibited a nanoporous framework with numerous structural defects. The NPG-based amperometric H₂O₂ sensor had a good selectivity, reproducibility, and low detection limit (0.3 μM) under near physiological conditions (pH = 7.4). The sensitivities of this sensor over concentration ranges of 0.002–5 mM and 5–37.5 mM were 159 and 64 μA mM⁻¹ cm⁻², respectively. These results indicate that the developed NPG is a promising material for the electrochemical sensing of H₂O₂.

Ge/Au/Ge triple-layered precursor was proposed to prepare nanoporous gold (NPG) with much smaller grain sizes and nanopores as an electrochemical sensor for highly sensitive and selective detection of hydrogen peroxide.

An assessment on crystallization phenomena of Si in Al/a-Si thin films via thermal annealing and ion irradiation

In the present study, crystallization of amorphous-Si (a-Si) in Al/a-Si bilayer thin films under thermal annealing and ion irradiation has been investigated for future solar energy materials applications. In particular, the effect of thickness ratio (e.g. in Al : a-Si, the ratio of the Al and a-Si layer thickness) and temperature during irradiation on crystallization of the Si films has been explored for the first time. Two sets of samples with thickness ratio 1 : 1 (set-A: 50 nm Al/50 nm a-Si) and thickness ratio 1 : 3 (set-B: 50 nm Al/150 nm a-Si) have been prepared on thermally oxidized Si-substrates. In one experiment, thermal annealing of the as-prepared sample (of both the sets) has been done at different temperatures of 100 °C, 200 °C, 300 °C, 400 °C, and 500 °C. Significant crystallization was found to initiate at 200 °C with the help of thermal annealing, which increased further by increasing the temperature. In another experiment, ion irradiation on both sets of samples has been carried out at 100 °C and 200 °C using 100 MeV Ni7+ ions with fluences of 1 × 1012 ions per cm2, 5 × 1012 ions per cm2, 1 × 1013 ions per cm2, and 5 × 1013 ions per cm2. Significant crystallization of Si was observed at a remarkably low temperature of 100 °C under ion irradiation. The samples irradiated at 100 °C show better crystallization than the samples irradiated at 200 °C. The maximum crystallization of a-Si has been observed at a fluence of 1 × 1012 ions per cm2, which was found to decrease with increasing ion fluence at both temperatures (i.e. 100 °C & 200 °C). The crystallization of a-Si is found to be better for set-B samples as compared to set-A samples at all the fluences and irradiation temperatures. The present work is aimed at developing the understanding of the crystallization process, which may have significant advantages for designing crystalline layers at lower temperature using appropriate masks for irradiation at the desired location. The detailed mechanisms behind all the above observations are discussed in this paper.

Impact of the carbon membrane inserted below Ni in the layer exchange of multilayer graphene

High-quality multilayer graphene on glass is achieved at a low temperature (400 °C).

Beyond dealloying: development of nanoporous gold via metal-induced crystallization and its electrochemical properties

Nanoporous metals (NPMs) possess a number of intriguing properties that result in NPMs being an important family of nanomaterials for many advanced applications. However, the methods of preparing NPMs are relatively complicated and have many limitations, which have hindered the commercial application of NPMs thus far. By introducing metal-induced crystallization, a solid-phase reaction method for preparing NPMs was developed in this study, which is highly efficient and environmentally friendly. The microstructure of the prepared nanoporous gold (NPG) was characterized on an atomic scale by scanning electron microscopy and high-resolution transmission electron microscopy. The results confirmed that the solid-phase reaction method is an effective alternative means of preparing highly pure NPG. The results of electrochemical tests demonstrated that thus-prepared NPG possesses higher electrocatalytic activity than other types of gold electrodes toward oxygen reduction in alkaline media. The combination of a simple preparation process and higher activity suggests that the developed method may promote the future use of NPG in new energy applications, such as fuel cells and metal-air batteries.

Eutectic nano-droplet template injection into bulk silicon to construct porous frameworks with concomitant conformal coating as anodes for Li-ion batteries

Building porosity in monolithic materials is highly desired to design 3D electrodes, however ex-situ introduction or in-situ generation of nano-scale sacrificial template is still a great challenge. Here Al-Si eutectic droplet templates are uniformly injected into bulk Si through Al-induced solid-solid convection to construct a highly porous Si framework. This process is concomitant with process-inherent conformal coating of ion-conductive oxide. Such an all-in-one method has generated a (continuously processed) high-capacity Si anode integrating longevity and stable electrolyte-anode diaphragm for Li-ion batteries (e.g. a reversible capacity as large as ~1800 mAh/g or ~350 μAh/cm²-μm with a CE of ~99% at 0.1 C after long-term 400 cycles).

Metal-induced crystallization of highly corrugated silicon thick films as potential anodes for Li-ion batteries

Silicon has turned into one of the most promising anodes for high energy rechargeable Li-ion batteries. However, a huge volume expansion during alloying with Li always induces serious pulverization/delamination for microsized electrodes as well as undesired accumulation of solid electrolyte interphase (SEI). Many efforts have focused on various nanoengineering and binding strategies to construct integrated, robust ionic/electronic wiring networks but with a trade-off between active/inactive material ratio and performance retention. Here, we first apply a metal-induced crystallization (AIC) principle for immiscible metal/semiconductor systems (Si/Al bilayers in this work) to prepare microthick Si films consisting of a high density of isolated nanocolumns. This method furthermore brings about low temperature crystallization of initial amorphous Si and conformal coating of ion-conductive oxide to enhance the Li transport kinetics of bulk and interface. Both highly satisfactory capacity retention (1650 mAh/g after 500 cycles) and rate performance (∼1000 mAh/g at 8C) are achieved for such thick Si film anodes. This methodology can be used to prepare thick film samples with well-defined nanostructures but free of extra binder and conductive additives. It enables much higher area specific capacity than for inactive-component contained slurry samples and thin film samples. This postdeposition pore-creating can be extended to more alloying or conversion electrodes of thick films for high capacity Li/Na ion batteries.