Microfluidic Synthesis of Semiconductor Materials: Toward Accelerated Materials Development in Flow

Abstract

Semiconductors are intriguing due to their unique electrical properties, particularly the behavior of their electrons in the presence of different stimuli (e.g., electric field, magnetic field, light irradiation), which differ greatly from conducting (i.e., metals) and insulating materials. In insulators and semiconductors, the available electronic states are discontinuous, with the existence of a gap between the lower energy states, commonly referred to as the valence band (VB), and the higher energy states, known as the conduction band (CB). The distinguishing factor between these materials is the size of the energy difference between the highest energy state in the VB and the lowest energy state in the CB, called the band gap. In insulators, the band gap is very large, making it difficult, if not impossible, to cause an electron to move from the VB to the CB. By comparison, semiconductors possess narrow to moderate band gaps, implying that it is possible to introduce enough energy to an electron to cause it to move from the VB to the CB, enabling electron transfer, the use of high energy electrons, or the emission of energy (i.e., photons) when the electron returns from the CB to the VB. The wide range of industrial application-specific requirements demands versatility in the target characteristics of semiconductor materials (e.g., size, morphology, composition, band gap, emission wavelength), which are vastly different from those commonly used in thin-film transistors. Typically, the semiconductor materials synthesized for use in the above applications are particulate materials produced across a range of sizes spanning five orders of magnitude (from just a few nm to hundreds of µm), and can be divided into two overarching categories, nano-and microsized particulate materials. Nanosized semiconductor materials, due in large part to their miniscule dimensions, present a variety of intriguing characteristics not observed in microsized semiconductor particles. First and foremost, if the dimensions of the semiconductor material decrease below a certain threshold known as the Bohr radius, the absorption and emission energies become highly dependent on the particle size, a phenomenon known as quantum confinement. [28-30] Moreover, nanosized structures have significantly larger surface-to-volume ratios which increases the surface contribution to the total free energy of the semiconductor materials, making them highly soluble [29] and therefore much easier to process and handle. Thus far, nanosized semiconductor particles have been effectively utilized in sensors, [7] LEDs, [9] Controlled synthesis of semiconductor nano/microparticles has attracted sub stantial attention for use in numerous applications from photovoltaics to photo catalysis and bioimaging due to the breadth of available physicochemical and optoelectronic properties. Microfluidic material synthesis strategies have recently been demonstrated as an effective technique for rapid development, controlled synthesis, and continuous manufacturing of solutionpr...

Effect of Nanoparticle Synthetic Conditions on Ligand Coating Integrity and Subsequent Nano-Biointeractions

“…Unlike previously established microfluidic metallic nanoparticle synthesis, our method does not involve complex protocols, specialized equipment, or harsh reaction conditions. 43 Notably, the staggered herringbone micromixer employed in our study has previously been used for generating organic nanomaterial formulations (e.g., lipid and polymeric nanoparticles). 44 Therefore, our work not only demonstrates the versatility and broad applicability of this chip type but also expands the microfluidic synthetic strategies for synthesizing inorganic nanomaterials, especially nontoxic (i.e., free of lead and cadmium) semiconductor nanoparticles.…”

“…To the best of our knowledge, we are the first to report the synthesis of ultrasmall semiconductor nanoparticles based on Ag 2 S using a simple microfluidic device. Unlike previously established microfluidic metallic nanoparticle synthesis, our method does not involve complex protocols, specialized equipment, or harsh reaction conditions . Notably, the staggered herringbone micromixer employed in our study has previously been used for generating organic nanomaterial formulations (e.g., lipid and polymeric nanoparticles) .…”

Autonomous Nanocrystal Doping by Self‐Driving Fluidic Micro‐Processors

“…Despite the ease of operation of the most commonly used NC synthesis technique, i.e., batch reactors (flaskbased synthesis), their irreproducible/uncontrollable heat and mass transfer rates, large chemical consumption and waste generation per synthesis condition, and lack of online characterization tools complicate their utilization in closed-loop exploration of LHP NC synthesis and processing parameter space. [45,46] Fluidic micro-processors, defined as microscale processing units which may operate different chemical/physical processes on fluids (e.g., mixing, reaction, extraction, separation) in a flow chemistry platform, with their reproducible and tunable mass and heat transfer rates, as well as ease of integration with online NC characterization probes are considered an ideal experimentation technique for autonomous synthetic route discovery and accelerated reaction space exploration of colloidal NCs. [46][47][48][49][50] Our research group has recently developed the Artificial Chemist technology, that is, a robo-fluidic experimentation platform for autonomous single-and multistage synthesis and multiobjective optimization of colloidal NCs.…”

Flow Synthesis of Single and Mixed Metal Oxides

“…Metal oxides, due in large part to their broad range of physicochemical and optoelectronic properties, remain among the most widely studied and utilized functional materials in the world today. Commonly found in fields including catalysis, [1,2] imaging, [3,4] sensing, [5] adsorption, [6] photovoltaics, [7,8] energy storage, [9,10] and many others, [11] different oxides exhibit a wide variety of characteristics (e. g., tunable band gap, charge carrier conduction, metal-support interactions) which make them intriguing candidates for these categories of applications.…”