Au Nanoparticles on Atomic-Thin Films

5 May 2015 NUS physicists have discovered that micro-landscaping of gold nanoparticles on a thin molybdenum disulphide (MoS2) film can be achieved.

The method works by first using a scanning focused laser beam to pre-modify the MoS2 film to achieve activated micropattern on the film. When the activated film is subsequently immersed in gold chloride solution for only 10 seconds, gold nanoparticles are found on the modified micropattern! This is akin to the process of garden landscaping with decorative stone except that this is achieved at the microscale by decorating gold nanoparticles on MoS2 film. The size and number density of these nanoparticles are controlled by the power of the laser beam, reaction time or the thickness of the film.

A team led by Prof SOW Chorng Haur and Dr LU Junpeng from the Department of Physics in NUS has discovered that micro-landscaping of gold nanoparticles on a thin MoS2 film can be achieved by simply dipping a laser activated MoS2 film into gold chloride solution. Interestingly, these decorated MoS2 micropatterns turn out to be great detector for aromatic molecules with high sensitivity by producing strong signal in Surface Enhanced Raman Spectroscopy.This high detection ability is due to the co-effects of the efficient adsorption of these molecules onto MoS2 and the strong coupling of the Au nanoparticles to the Raman signal.To the best of our knowledge, this is the first implementation of two-dimensional transition metal dichalcogenides as effective Raman active surfaces. This represents a positive step forward towards decorated two-dimensional hybrid materials with controlled functionalities.

Monolayer or few-layer transitional metal dichalcogenides have attracted great attention as emerging two-dimensional materials due to wide recognition of their potentials in many applications. However, the functions shown by an individual material are not able to meet the increasing requirements of applications. To realize of versatile material system, the team use noble metal nanoparticles to decorate the two-dimensional films. In doing so, the obtained nano/micro hybrid structure provides an avenue for controlling its electronic, catalytic, optoelectronic and magnetic functionalities.

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This figure depicts the Au nanoparticles can be landscaped to micropatterns (snowflake). The decoration would enhance the Raman signal of aromatic molecules. [Image credit: Lu Junpeng]

 

References

1. Lu JP, Lu JH, Liu HW, Liu B, Gong L, Tok ES, Loh KP, Sow CH. “Microlandscaping of Au Nanoparticles on Few-Layer MoS2 Films for Chemical Sensing.” Small. 11 (2015) 1792.

2. Lu JP, Lu JH, Liu HW, Liu B, Chan KX, Lin J, Chen W, Loh KP, Sow CH. “Improved Photoelectrical Properties of MoS2 Films after Laser Micromachining.” ACS Nano. 8 (2014) 6334.