Controlling the properties of silver nanoparticles deposited on surfaces using supercritical carbon dioxide for surface-enhanced Raman spectroscopy

Silver nanoparticles (AgNPs) have been deposited on silicon and glass surfaces via a supercritical carbon dioxide (sc-CO₂) synthesis route for application in surface-enhanced Raman spectroscopy (SERS). Arrhenius plots revealed that nucleation and growth processes in this system depend on both temperature and surface chemistry. Results also demonstrated that temperature and surface chemistry could be varied to control nanoparticle properties, such as the mean nanoparticle size, density, and surface coverage, providing two useful variables for manipulating the properties of AgNPs deposited on surfaces in this system. These data also provide scientific insight into the underlying mechanisms governing heterogeneous AgNP deposition on a substrate in a sc-CO₂ system in addition to engineering insight into the variables that can be used to manipulate AgNP characteristics. The mean particle size could be tuned over the range 20–200 nm, the interparticle distance could be tuned over the range 70 nm–1 μm, and the surface coverage could be tuned over the range 0.035–0.58. Products were analyzed by scanning electron microscopy with image analysis, transmission electron microscopy, X-ray diffraction, and SERS. The silver nanoparticle-coated substrates were successfully applied in SERS, detecting the model analyte Rhodamine 6G at a concentration of 1 μM, a three orders of magnitude improvement over SERS surfaces previously fabricated in sc-CO₂ systems. Such surfaces can find use in trace concentration analyte detection in biomedical, chemical, and environmental applications.     

From Schrödinger’s equation to the quantum search algorithm

The quantum search algorithm is a technique for searching N possibilities in only O(√N) steps. Although the algorithm itself is widely known, not so well known is the series of steps that first led to it, these are quite different from any of the generally known forms of the algorithm. This paper describes these steps, which start by discretizing Schrödinger’s equation. This paper also provides a self contained introduction to quantum computing algorithms from a new perspective.