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A practical and effective method for reducing differential reflectance spectroscopy noise

Differential reflectance spectroscopy (DRS) is a powerful tool to study processes during thin-film growth, especially that of transition metal dichalcogenides and organic thin films. To satisfy the requirements for in situ and real-time monitoring of film growth, including spectral resolution and sensitivity at the level of monolayers and even sub-monolayers, the most challenging technical task in DRS is to reduce noise to an extremely low level so that the best possible signal-to-noise ratio can be achieved. In this paper, we present a simplified and cost-effective DRS apparatus, with which we show that the measurement noise is mainly composed of thermal drift noise and explore the temperature-dependence of the DRS signal. Based on the results obtained, we propose an easily realized and effective scheme aiming to reduce the noise. Experimental results demonstrate that this scheme is effective in stabilizing reliable signals for a long period of several hours. Significant noise reduction is achieved, with the typical average noise of the DRS system being decreased to 0.5‰ over several hours. The improved DRS system is applied to study the growth of an organic semiconductor layer for an organic field-effect transistor device. The results indicate that the apparatus proposed in this paper has potential applications in fabrication of devices on the nanoscale and even the sub-nanoscale.