Targeted control of growth dynamics of tin nanolayers

(Nanowerk News) Nanometer-scale coatings with functional materials play an important role in many sensory, electronic and photonic applications. An international research team – coordinated by Leibniz IPHT in Jena, Germany – has for the first time been able to observe the novel growth effect of tin coating on the surface of silicon’s nanometer structure. With the knowledge gained, the chemical composition of deposited thin films can be precisely controlled and monitored in the future, opening up new applications in the fields of biophotonics, energy generation or mobility.

The results are published in a journal Small (“Spectromicroscopy Study of Silicon Nanowire Arrays Covered by a Tin Oxide Layer” And “Nano-Structured Silicon Matrix for Materials Engineering”). Dynamics of molecular precursors in nanochannels during the MOCVD process (left in fig.) and typical SEM cross-section view of a silicon nanostructured matrix after plating (right in fig.). (Image: Leibniz IPHT)

Tin-containing coatings are required for a wide variety of electronic parts and components in the electrical industry as well as in sensor or photovoltaic technology. Researchers from the Leibniz Institute of Photonic Technology (Leibniz IPHT) investigated the process of developing nanoscale tin coatings together with scientists from Germany, Russia and the UK and summarized their results in the renowned journal Small.

The starting material for the observed tin-containing film growth process is an ultra-thin silicon-based structure in the form of nanowires with a diameter of less than 100 nanometers. In the experimental study, the researchers were able to demonstrate for the first time the effect of the specific distribution of tin along these silicon nanostructures: Tin-containing layers of varying degrees of oxidation form along the semiconductor nanowires through the metal-organics. chemical vapor deposition at a deposition temperature of 600 degrees Celsius.

„By understanding how tin plating grows and what factors influence this growth process, we create conditions to specifically control the plating process. This allows the surface to be refined very precisely and provided with the desired functional properties at a predetermined position,” explained Dr. Vladimir Sivakov, head of the Silicon Nano Structures Group at Leibniz IPHT, who investigated and discovered the growth mechanism with his team.

Ultra thin tin coating application

Nanometer-thin coating with tin enables certain optical and electrical properties and allows, among other things, to further enhance the research and development of optical and biophotonic methods. Tin coatings can be used as UV-SERS active surfaces in surface-enhanced Raman scattering spectroscopy (SERS), which can be applied to determine the molecular fingerprints of biological samples using SERS-active metal nanostructures. Additionally, there are gas sensor application areas where lead reacts to gas as a very sensitive coating. Application scenarios in high-performance lithium-ion batteries for electromobility and heat energy storage are also conceivable, where lead-coated anodes ensure high electronic conductivity.

Mechanism and dynamics of growth of tin-bearing films

The researchers investigated the growth dynamics of the tin-based coating observed on the nanostructured surface using microscopic and spectroscopic methods. In contrast to planar and unstructured silicon surfaces, where deposition occurs homogeneously, the surface of semiconductor nanowires is covered with lead-containing crystals of various sizes and shapes along their entire length.

The results are presented in a journal Small demonstrated the formation of distinct tin oxide phases along the nanostructured silicon surface, which can be identified with tin dioxide (SnO2) at the top, tin monoxide (SnO) in the middle and with metallic tin (Sn) at the bottom.

The amount and distribution of the formed Sn metal along with its SnO and SnO2 oxides can be described and effectively controlled by the length, diameter, porosity, and spacing of silicon-based semiconductor nanostructures. In addition to these geometric parameters, the researchers were able to reveal the formation of by-products containing hydrocarbons as reducing agents for the reduction of tin oxide as another factor affecting the distribution of the tin layer formed along the semiconductor nanostructures. The thermal conductivity of the silicon structure and thus the temperature distribution along the nanowires during high-temperature vapor deposition may also affect the formation of distinct tin oxide phases.