Scanning probe lithography method can fabricate and modify a number of materials using the typical SPM equipment by applying the mechanical force or electric or thermal effects. Owing to the excellent electrical, thermal and electrical performance of carbon-based materials such as carbon nanotubes, graphene and highly oriented pyrolytic graphite as well as their huge potential in flexible and energy storage nanoelectronic gadgets, researchers are currently focusing on scanning tunneling microscope electric discharge lithography of the carbon-based materials.
Scanning tunneling microscope electric lithography exhibits good potential in the fabrication of carbon-based materials as well as devices. However, the problem of the scanning tunneling lithography probe tool wear in the course of the electric discharge lithography is still unresolved. This would significantly affect the machining efficiency and consistency.
Therefore, Ye Yang and Jun Lin at Shanghai Normal University investigated the primary issues with the scanning tunneling microscope electrode tool wear, along with the mechanisms as well as affecting parameters under both the positive and negative polarity schemes. The tool sharpening phenomena and evidences were observed under the selected machining parameters. They were able to not only reveal the underlying mechanism for scanning tunneling microscope tool wear as well as sharpening processes, but also nanoscale structures with high consistency. Their work is now published in Journal of Materials Processing Technology.
The authors used freshly cleaved highly oriented pyrolytic graphite with an atomic level surface as a conductive sample whose machining attributes could be implemented to other carbon-based materials.
The experiment encompassed two orthogonal procedures for the scanning tunneling microscope imaging and the electric discharge lithography. The authors applied working parameters, which included the bias voltage, and the tunneling current. The scanning tunneling microscope imaging was performed under bias voltage of about 0.1V and a tunneling current of 0.1nA with the constant current feedback. The researchers conducted the electric discharge lithography without applying the current feedback control. This meant that the positions of the scanning tunneling microscope probe as well as the specimens were fixed in the course of the machining processes.
Under positive polarity discharge lithography, the authors observed that the scanning tunneling microscope probe tool wear blunted the probe tip, and enlarged the machining gap in the course of successive machining. The width of the circular groove first increased and then decreased and the depth of the structure kept reducing in the effect of the continuous scanning tunneling microscope probe tool wear. The nanoscale electric discharge was strengthened by the sharp tip effect. For this reason, when applying the ultra-sharp probe, material removal was intensified on electrodes.
Under negative polarity electric discharge lithography, they observed that the probe sharpening was accompanied with ring-like deposition of the removed material at the edge of the probe. The probability of the probe sharpening was observed to go up to 60% under the voltage from -6 to -8V. The probe sharpening could be utilized to perform in-situ modification of the probe.
The outcomes of the study are important to the controlled nanoscale modification of the carbon-based materials, and could be helpful in the improvement of the machining reliability and lifetime of the tool.
Ye Yang, Jun Lin. Study of the electrode tool wear and the probe tip sharpening phenomena during the nanoscale STM electric discharge lithography of the bulk HOPG surface. Journal of Materials Processing Technology, volume 234 (2016), pages 150–157.Go To Journal of Materials Processing Technology