The depth profiles of intentional or intrinsic constituents of a sample provide valuable information for the characterization of materials. For example, the subtle differences in spatial distribution and composition of many chemical species in the near surface region and across interfacial boundaries can significantly alter the electronic and optical properties of materials. A number of analytical techniques for depth profiling have been developed during the last two decades. neutron Depth Profiling (NDP) is one of the leading analytical techniques. The NDP is a nondestructive near surface technique that utilizes thermal/cold neutron beam to measure the concentration of specific light elements versus their depth in materials. The depth is obtained from the energy loss of protons, alphas or recoil atoms in substrate materials. Since the charged particle energy determination using surface barrier detector is used for NDP, the depth resolution is highly dependent on the detectors an d detection instruments. The depth resolutions of a few tens of nm are achieved with available NDP facilities in the world. However, the performance of NDP needs to be improved in order to obtain a few A depth resolutions.

Battery material research has been one of the major areas of study in the last ~30 years due to the huge impact of battery technology in our daily lives. Both the discovery of new materials and their electrochemical optimization requires an in-depth and fundamental understanding of the composition and structure at different length scales. Local, long-range structure, polymorphism, microstructure, composite formulation and nanoscale engineering all contribute to a materials innate ability to deliver the best performance as an electrode in a battery. Importantly, the evolution of all these components during battery function determine essentially all the pertinent battery characteristics such as lifetime and energy storage density. For these reasons, it is critical to determine materials structure at various length scales, in order to be able to predict or understand their properties and propose changes to improve their electrochemical behavior. In this sense, conventional characterization techniques of the material itself are very useful in the first stages of research but, in many cases, the use of in-situ or in operando characterization techniques provides a unique way of understanding materials performance or evolution during battery operation. The challenge becomes greater in terms of experimental design because these techniques involve devising and fabricating specific electrochemical cells that fulfill the requirements of the technique but deliver electrochemical performance akin to a real-life device.

Abstract: Neutron Depth Profiling (NDP) is a nondestructive analytical technique used to characterize the concentration of certain light isotopes in a material as a function of depth. The technique is based on the principle of measuring the residual energy of charged particles in neutron induced reactions. Historically, NDP has been performed using a single detector, resulting in low intrinsic detection efficiency, and limiting the technique largely to high flux research reactors. This work describes a new NDP instrument design with higher detection efficiency, achieved by summing the spectrum obtained from multiple detectors. A digital data acquisition system was chosen over the typical analog system for this instrument, as it allowed for an economical implementation of multiple detectors and a streamlined process for spectrum summing. This design is capable of acquiring a statistically significant charged particle spectrum at facilities limited in neutron flux and operation time. The spectrum obtained from a sample of Borophosphosilicate (BPSG) with this multidetector instrument was compared to the analysis performed on the same sample at the National Institute of Standards and Technology (NIST), using a benchmarked, single detector NDP instrument. Results of the analysis indicate the resolution of the multidetector instrument suffers slightly due to gamma contamination in the beam, but is capable of achieving nearly half the count rate of the NIST instrument. A model of the instrument investigating BPSG was constructed using the GEANT4 toolkit, and used to compare against the experimental results. A section of 6Li enriched scintillation screen was also analyzed using the multidetector instrument. This analysis gave insight into the concentration profile of this particular neutron converter, something that had previously been unknown.