Visualize photoluminescence from silicon quantum dots!
Subject of the 2023 Nobel Prize in Chemistry, quantum dots are nanoparticles made from solid materials known as semiconductors that are finding uses in a wide range of applications, from medical diagnostic systems, to solar cells, to television sets. The most well-known semiconductor is silicon, the material at the heart of all modern microelectronics.
When a semiconductor is made into a nanoparticle, electrons in the material behave profoundly differently than they do in the "bulk" large-scale semiconductor. One manifestation of the confinement of an electron in a semiconductor nanoparticle is the visible photoluminescence seen with this sample--the color of luminescence is directly related to the confinement dimensions in the silicon nanoparticles.
This module was developed by Ellie Bauer, Keying Deng, Clémentine Gevers, Sophia Hsu, Eileen Huffer-Ege, Louise Lejeune, Siran Rao, Jocelyn Zhang, and Ashley Tamura, who were trainees or mentors in the 2022 and 2023 Summer School for Silicon Nanotechnology (SSSiN), one of the Research Immersion in Materials Science and Engineering (RIMSE) programs of the UC San Diego MRSEC.
What is it?
A 1-inch silicon wafer containing a nano-sponge array of silicon quantum dots. This kit contains a non-toxic sample of silicon quantum dots, which glow with a bright orange color when placed under a small ultraviolet, or "black" light. The kit explains the concept of photoluminescence, through common materials that display photoluminescence (such as a highlighter pen), and it illustrates the synthesis and properties of quantum dots and describes how they can be configured to display all the colors of the rainbow-an enabling feature for their current application in computer displays and televisions.
How to use it?
This kit also contains a small "blacklight" which emits ultraviolet light of wavelength 395 nm. This blacklight can be used to excite photoluminescence from a variety of materials. To see photoluminescence in action, simply shine the blacklight on one of the “glow in the dark” items in the kit, the mark on a sheet of paper made by a highlighter pen, or an alcohol extract of chlorophyl from a green leaf. See which items glow under the UV rays, and which do not, and how their perceived color changes under the blacklight.
How is it made?
(CONTENT UNDER DEVELOPMENT) The procedure used to prepare these materials involves carving nanometer-scale pores throughout the silicon wafer, using an electrochemical process. The silicon wafers are etched in an electrolyte that contains HF, water, and alcohol to develop macro-, meso-, and nano-pores, creating the porous nanostructure. The small silicon features that remain after all the holes are drilled out can be as small as only a few nanometers thick. At this size scale, the silicon is transformed into a quantum material--electrons become trapped in these tiny silicon features and their color under normal "white" light and the color of their photoluminescence are then controlled by the size of the silicon feature in which they reside. This phenomenon is known as quantum confinement of the electrons.