Effect of metasurface and process parameters on adhesion during transfer printing using a nanoscratch test.

Transfer printing of metasurface has emerged as a promising technique for realising ultra-high-resolution displays beyond the limits of conventional patterning methods. Reliable transfer requires precise control of adhesion at the interfaces between the metasurface and transfer mold/transfer substrate. Here, we quantitatively investigate adhesion variations at interfaces without or with metasurface, as well as the effects of transfer printing parameters such as applied pressure and temperature. Four paired transfer molds and transfer substrates were fabricated for simulating actual process conditions, and adhesion forces were measured independently using nanoscratch tests. We find that, compared to the specimen without metasurface, adhesion to transfer mold with metasurface is slightly reduced due to the formation of dimples, while adhesion to the transfer substrate with metasurface is significantly decreased resulting from void formation. Application of 5 bar pressure enhances adhesion at both interfaces. In contrast, increasing the temperature to 90 °C decreases adhesion at the transfer mold due to thermally induced residual stresses whereas the transfer substrate adhesion remains nearly unchanged as APS1 activation and residual stress effects counterbalance. Based on the adhesion difference between paired transfer molds and transfer substrates, the optimal conditions of transfer printing are identified as 5 bar and 90 °C. These results elucidate the mechanisms governing adhesion in transfer printing of metasurface and provide guidelines for optimising transfer printing for next-generation ultra-high-resolution displays.