Following a nanotechnology lifecycle,1 materials selection and characterization of fabricated energy devices will form a critical fundamental basis of any alternative energy systems. The thriving fields of photovoltaics, fuel cells, batteries and photocatalysis all require novel approaches to characterize each and every material component and architecture embedded within the device.2 The characterization approaches can be microscopic, spectroscopic, surface and interface, chemical, optical, electronic, mechanical and thermal techniques.3 However, surface area measurements are critical for understanding chemisorption and physiosorption of molecules on the surface of energy-relevant nanomaterials. From the point of view of a hardcore materials scientist and metallurgist, any developed material must be first characterized because this critical step aids in knowing what is produced. In this regard, learning about developed materials is exactly like the job of an investigator or a detective, where we scientists/engineers/researchers play the role of a detective, and our material becomes analogous to an entity to be explored, understood and probed in-depth. In this whole process, mentioned characterization techniques are of great value.
As nanoscale materials for energy applications are synthesized, it is critical to understand their crystal structures, phases, chemical composition, topography and morphologies. These can be achieved by using high-resolution electron microscopy, scanning transmission electron microscopy (STEM) mode energy dispersive (EDS) composition line profiles and electron energy loss spectroscopy (EELS).4–,6 For example, shape and size of the nanomaterials is an important aspect to understand, which can be accomplished using high-resolution scanning electron microscopy, transmission electron microscopy (TEM) and atomic force microscopy, where not only the topography of the nanomaterials but also lattice scale images can be observed. In addition, these techniques can lead to understanding defects and their density within nanostructures as well as presence of impurities or dopants.3,7,8 Approaches such as X-ray diffraction and X-ray photoelectron spectroscopy can be merged with microscopy techniques to result in detailed quantitative estimations of chemical compositions and kinetics of defect or impurity diffusion.9,10 All such techniques can be of greater importance if a multicomponent nanomaterial system or nanoscale heterostructures are of interest.11 As in this scenario, interfaces will be very critical, and knowing the strains, lattice mismatch and material diffusion at interfaces is of great importance in energy nanomaterials.12,13 Techniques such as STEM-mode EDS line profiles can be effectively utilized to understand chemical composition profiles of heterostructured nanomaterials by using a high-resolution probe (spot size ∼1 nm).4 A greater precision in chemical composition profiles in 3D could be obtained by innovative instrumentation techniques such as local electrode atom probe and 3D tomography.14,15 If a dopant such as nitrogen or other a relevant light elements are present then one can understand it by using EELS method to detect such light elements.5
Interfaces in nanomaterials play a critical role in charge transport, separation and generation mechanisms, which in-turn influence the efficiency of a energy device.2–,4 16,17 In such a case, a fundamental approach could be to evaluate the band gap energy and absorption spectroscopy for the nanostructured material.4 Further correlation of these results with the microscopic evaluation of interfaces, surface photovoltage spectroscopy and contact potential difference can lead to complete derivation of the energy band diagram (or energy structure).18 Such useful characterization data could facilitate understanding conduction and valance band edge locations of the energy materials (e.g. semiconductor nanostructures), interface field generation and Fermi levels. All these are very important for understanding light-matter interactions and developing a suitable photoactive device that has efficient charge transfer and separation processes along with very low charge recombination probability. In regard to the latter, an interesting technique is time-resolved spectroscopic methods,15 where the photoactive nanomaterials are excited by a pulsed laser and then the dynamic charge carrier transfer or behavior is observed in very short time scales such as 10−16 s. This can lead to enhanced understanding about the light-induced chemical reactions, absorption of excitation energy, electronic structure, charge carrier mobilities and even detect the presence of charge species such as electrons, positive ions and photo-products. For example, hole transfer on irradiated semiconductor surface can be studied by using transient absorption spectroscopy.15,19
This last issue of volume 1 of Nanomaterials and Energy brings forward a diverse set of articles for our audience with a focus on novel characterization technique such as precision electron diffraction by Mohseni, Collins and Scharf. A review article by Singh and coworkers focuses on polymer-ceramic system for lithium ion batteries. The article by Sethi et al. evaluates Si thin-film photovoltaic technologies. Readers will also find a book review on fuel cells. With the first issue of volume 2 (2013) coming out shortly, I will encourage our readers to consider submitting to Nanomaterials and Energy, which is a rising star in this field and meticulously combines nanoscale materials, their characterization and properties and energy applications onto a single unique platform. Finally, I on behalf of my editorial board members and ICE publishing team would like to extend a special welcome to our Honorary Editorial Board Members:
Professor Jagdish (Jay) Narayan, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, USA
Dr. Stephen J. Pennycook, Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
Dr. Robert D. Shull, Magnetic Materials Group, National Institute of Standards and Technology, Gaithersburg, MD, USA
