• Fabrication of Pt nanowires with a diffraction-unlimited feature size by high-threshold lithography

      Li, Li; Wang, Zuobin; Li, Wenjun; Peng, Kuiqing; Zhang, Ziang; Yu, Miao; Song, Zhengxun; Weng, Zhankun; Wang, Dapeng; Zhao, Le; et al. (American Institute of Physics Inc., 2015-09-29)
      Although the nanoscale world can already be observed at a diffraction-unlimited resolution using far-field optical microscopy, to make the step from microscopy to lithography still requires a suitable photoresist material system. In this letter, we consider the threshold to be a region with a width characterized by the extreme feature size obtained using a Gaussian beam spot. By narrowing such a region through improvement of the threshold sensitization to intensity in a high-threshold material system, the minimal feature size becomes smaller. By using platinum as the negative photoresist, we demonstrate that high-threshold lithography can be used to fabricate nanowire arrays with a scalable resolution along the axial direction of the linewidth from the micro- to the nanoscale using a nanosecond-pulsed laser source with a wavelength λ0 = 1064 nm. The minimal feature size is only several nanometers (sub λ0/100). Compared with conventional polymer resist lithography, the advantages of high-threshold lithography are sharper pinpoints of laser intensity triggering the threshold response and also higher robustness allowing for large area exposure by a less-expensive nanosecond-pulsed laser.
    • In situ lift-off of InAs quantum dots by pulsed laser irradiation

      Deng, Changwei; Shi, Zhenwu; Yang, Linyun; Zhang, Wei; Chen, Chen; Miao, Lili; Yang, Xinning; Wang, Chinhua; Chen, Linsen; Peng, Changsi; et al. (AIP Publishing, 2018-08-24)
      InAs/GaAs quantum dots (QDs) grown by molecular beam epitaxy were subjected to in situ irradiation using a mono-beam pulsed laser. The evolution of the QD morphology was investigated as a function of irradiation intensity at temperatures of 525 °C and 480 °C. The temperature was found to exert a considerable influence on the reaction of the QDs to the irradiation. At the higher temperature (525 °C), both the height and width of the InAs QDs gradually decreased with increasing irradiation intensity, which was ascribed to the dominant effect of the laser desorption of indium. In contrast, at the lower temperature (480 °C), the height of the InAs islands decreased with increasing irradiation intensity while the width exhibited unexpected broadening, which was attributed to a combination of laser desorption and laser diffusion of indium. Remarkably, at the higher temperature, laser irradiation above a certain threshold intensity resulted in the lift off of the InAs QDs to afford a clear, smooth, and perfect GaAs surface. Through subsequent growth of QDs on this surface, it was found that the QDs exhibited the same nucleation properties and optical quality as the common Stranski–Krastanov mode on an as-prepared GaAs surface. Therefore, we have developed a technology for the damage-resistant fabrication of QDs using in situ pulsed laser irradiation (LIR), which is expected to find potential applications in the manufacture of patterned QDs upon upgrading the mono-beam irradiation to multi-beam interference irradiation in the future.
    • In-situ laser nano-patterning for ordered InAs/GaAs(001) quantum dot growth

      Zhang, Wei; Shi, Zhenwu; Huo, Dayun; Guo, Xiaoxiang; Zhang, Feng; Chen, Linsen; Wang, Qinhua; Zhang, Baoshen; Peng, Changsi; Soochow University; et al. (AIP Publishing, 2018-04-12)
      A study of in-situ laser interference nano-patterning on InGaAs wetting layers was carried out during InAs/GaAs (001) quantum dot molecular beam epitaxy growth. Periodic nano-islands with heights of a few atomic layers were obtained via four-beam laser interference irradiation on the InGaAs wetting layer at an InAs coverage of 0.9 monolayer. The quantum dots nucleated preferentially at edges of nano-islands upon subsequent deposition of InAs on the patterned surface. When the nano-islands are sufficiently small, the patterned substrate could be spontaneously re-flattened and an ordered quantum dot array could be produced on the smooth surface. This letter discusses the mechanisms of nano-patterning and ordered quantum dot nucleation in detail. This study provides a potential technique leading to site-controlled, high-quality quantum dot fabrication.