Local Oxidation Nanolithography on Metallic Transition Metal Dichalcogenides Surfaces

The integration of atomically-thin layers of two dimensional (2D) materials in nanodevices demands for precise techniques at the nanoscale permitting their local modification, structuration or resettlement. Here, we present the use of Local Oxidation Nanolithography (LON) performed with an Atomic Force Microscope (AFM) for the patterning of nanometric motifs on different metallic Transition Metal Dichalcogenides (TMDCs). We show the results of a systematic study of the parameters that affect the LON process as well as the use of two different modes of lithographic operation: dynamic and static. The application of this kind of lithography in different types of TMDCs demonstrates the versatility of the LON for the creation of accurate and reproducible nanopatterns in exfoliated 2D-crystals and reveals the influence of the chemical composition and crystalline structure of the systems on the morphology of the resultant oxide motifs

Scanning Probe Microscopy and Oxidation of Silicon at Breakdown Voltages

The growing importance of Scanning Probe Microscopy (SPM) as a tool for nanofabrication is opening many avenues in lithography nano-science. One type of Scanning Probe Lithography involves electrochemistry at the tip/substrate interface. Atomic Force Microscopy (AFM) with conductive tips and substrates was used in our study to both pattern and image those patterns on silicon substrates. Our long-term objective is to design and fabricate micron-scale patterns of nanometer sized spots on silicon chips that can serve as attachment sites for DNA based nano-arrays. In order to fabricate such substrates a study of the underlying electrochemistry was required. A most promising approach to preparing patterned silicon chips was introduced by the work of Dagata et al., using AFM to locally oxidize silicon surfaces and create controllable nanometer scale features. This thesis reports the determination of the influence of voltage and holding time on oxide growth for three different surfaces, native oxide layers, hydrogenterminated silicon surfaces, and silicon surfaces functionalized with ultrathin organic films. Both line and dot patterns were generated at several selected voltages and exposure times. In order to evaluate current efficiency, current was measured during line production. Oxide growth correlates with voltage until it reaches a saturation potential. This saturation appears to be associated with the onset of alternative conduction processes

A flexible single-step 3D nanolithography approach via local anodic oxidation : theoretical and experimental studies

The field of nanotechnology has experienced rapid growth in recent years, fuelled by the increasing need for high-performance next-generation nano/quantum devices/products possessing 3D nanostructures with sub-10 nm feature sizes. As a result, there is a high demand for a new flexible nanofabrication technique capable of generating various 3D nanostructures with high precision and efficiency. Local anodic oxidation (LAO) nanolithography is a promising nanofabrication technique for the in-lab prototyping of nanoproducts due to its high precision, low environmental requirement, and ease of use. However, challenges remain with current LAO nanofabrication techniques to meet the processing demands of next-generation nanoproducts. These challenges include limited throughput, high defect rates, and inflexibility in generating various nanostructures. Consequently, the existing 3D LAO nanofabrication methods suffer from high costs and inefficiencies. Addressing these challenges is crucial for advancing the capabilities of LAO nanolithography and unlocking its full potential in nanofabrication. In this thesis, a novel flexible single-step nanofabrication approach was developed to generate diverse 3D nanostructures with sub-10 nm feature sizes through pulse-modulated LAO nanolithography. Compared with other tool and condition control methods, pulse modulation is easier to achieve with precise tunability, enabling flexible, high-precision, and cost-effective 3D nanofabrication. A clear and in-depth understanding of the manufacturing mechanisms at the atomic and molecular scales is crucial in determining the influencing factors during the manufacturing process. This thesis thus first used the reactive force field (ReaxFF) molecular dynamics simulation method to investigate the reaction mechanisms of the LAO process. A comprehensive analysis of bonding, molecular, and charge indicates that the bias-induced oxidation led mainly to the creation of Si–O–Si bonds in the oxide film and the consumption of H2O. In contrast, the oxidised surface’s chemical composition remained unchanged during the bias-induced oxidation process. In addition, parametric studies further revealed the dependence of electric field strength and humidity on the bias-induced oxidation process and their respective influencing mechanisms. A good agreement was achieved through qualitative comparison between simulation and experimental results. Secondly, this thesis proposed a new pulse-modulated LAO nanolithography approach to realise flexible and efficient fabrication of various 3D nanostructures. The process was designed on the principle that the amplitude or width of the pulse can control the lateral and vertical growth of each nanodot while the tuning of pulse periods can determine the position of each nanodot based on certain tip scan speeds and trajectories. Feasibility tests were conducted on an atomic force microscope (AFM) to demonstrate the capability of this approach in fabricating various nanostructures with the minimum linewidth at sub-10 nm and height variations at sub-nm. Finally, nanofabrication experiments were conducted to investigate the capabilities of pulse-modulated LAO nanolithography in achieving flexible, accurate, and efficient fabrication of 3D nanostructures. Based on the systematic parametric study on the effects of pulse period, amplitude, and width through the LAO experiment, a process model was developed to provide a clear and detailed interpretation of the nanofabrication process. This model links the geometry of 3D nanostructures with arrays of pulse periods, amplitudes, and widths, allowing for active control of the LAO process. The fabrication of several 3D nanostructures was experimentally validated by comparing the fabricated and predicted results, demonstrating good agreement. The fabricated three-dimensional curved surface could achieve the average form accuracy and precision at sub-nm levels. Higher efficiency was achieved by using a high scan rate, enabling the creation of a nanoscale lens structure consisting of four thousand nanodots within 50 seconds. The efficiency and accuracy of the proposed flexible single-step nanofabrication approach were, therefore, fully demonstrated.The field of nanotechnology has experienced rapid growth in recent years, fuelled by the increasing need for high-performance next-generation nano/quantum devices/products possessing 3D nanostructures with sub-10 nm feature sizes. As a result, there is a high demand for a new flexible nanofabrication technique capable of generating various 3D nanostructures with high precision and efficiency. Local anodic oxidation (LAO) nanolithography is a promising nanofabrication technique for the in-lab prototyping of nanoproducts due to its high precision, low environmental requirement, and ease of use. However, challenges remain with current LAO nanofabrication techniques to meet the processing demands of next-generation nanoproducts. These challenges include limited throughput, high defect rates, and inflexibility in generating various nanostructures. Consequently, the existing 3D LAO nanofabrication methods suffer from high costs and inefficiencies. Addressing these challenges is crucial for advancing the capabilities of LAO nanolithography and unlocking its full potential in nanofabrication. In this thesis, a novel flexible single-step nanofabrication approach was developed to generate diverse 3D nanostructures with sub-10 nm feature sizes through pulse-modulated LAO nanolithography. Compared with other tool and condition control methods, pulse modulation is easier to achieve with precise tunability, enabling flexible, high-precision, and cost-effective 3D nanofabrication. A clear and in-depth understanding of the manufacturing mechanisms at the atomic and molecular scales is crucial in determining the influencing factors during the manufacturing process. This thesis thus first used the reactive force field (ReaxFF) molecular dynamics simulation method to investigate the reaction mechanisms of the LAO process. A comprehensive analysis of bonding, molecular, and charge indicates that the bias-induced oxidation led mainly to the creation of Si–O–Si bonds in the oxide film and the consumption of H2O. In contrast, the oxidised surface’s chemical composition remained unchanged during the bias-induced oxidation process. In addition, parametric studies further revealed the dependence of electric field strength and humidity on the bias-induced oxidation process and their respective influencing mechanisms. A good agreement was achieved through qualitative comparison between simulation and experimental results. Secondly, this thesis proposed a new pulse-modulated LAO nanolithography approach to realise flexible and efficient fabrication of various 3D nanostructures. The process was designed on the principle that the amplitude or width of the pulse can control the lateral and vertical growth of each nanodot while the tuning of pulse periods can determine the position of each nanodot based on certain tip scan speeds and trajectories. Feasibility tests were conducted on an atomic force microscope (AFM) to demonstrate the capability of this approach in fabricating various nanostructures with the minimum linewidth at sub-10 nm and height variations at sub-nm. Finally, nanofabrication experiments were conducted to investigate the capabilities of pulse-modulated LAO nanolithography in achieving flexible, accurate, and efficient fabrication of 3D nanostructures. Based on the systematic parametric study on the effects of pulse period, amplitude, and width through the LAO experiment, a process model was developed to provide a clear and detailed interpretation of the nanofabrication process. This model links the geometry of 3D nanostructures with arrays of pulse periods, amplitudes, and widths, allowing for active control of the LAO process. The fabrication of several 3D nanostructures was experimentally validated by comparing the fabricated and predicted results, demonstrating good agreement. The fabricated three-dimensional curved surface could achieve the average form accuracy and precision at sub-nm levels. Higher efficiency was achieved by using a high scan rate, enabling the creation of a nanoscale lens structure consisting of four thousand nanodots within 50 seconds. The efficiency and accuracy of the proposed flexible single-step nanofabrication approach were, therefore, fully demonstrated