No abstract

Manufacturing at the atomic scale is the next generation of the industrial revolution. Atomic and close-to-atomic scale manufacturing (ACSM) helps to achieve this. Atomic force microscopy (AFM) is a promising method for this purpose since an instrument to machine at this small scale has not yet been developed. As the need for increasing the number of electronic components inside an integrated circuit chip is emerging in the present-day scenario, methods should be adopted to reduce the size of connections inside the chip. This can be achieved using molecules. However, connecting molecules with the electrodes and then to the external world is challenging. Foundations must be laid to make this possible for the future. Atomic layer removal, down to one atom, can be employed for this purpose. Presently, theoretical works are being performed extensively to study the interactions happening at the molecule–electrode junction, and how electronic transport is affected by the functionality and robustness of the system. These theoretical studies can be verified experimentally only if nano electrodes are fabricated. Silicon is widely used in the semiconductor industry to fabricate electronic components. Likewise, carbon-based materials such as highly oriented pyrolytic graphite, gold, and silicon carbide find applications in the electronic device manufacturing sector. Hence, ACSM of these materials should be developed intensively. This paper presents a review on the state-of-the-art research performed on material removal at the atomic scale by electrochemical and mechanical methods of the mentioned materials using AFM and provides a roadmap to achieve effective mass production of these devices.

Atomic scale manufacturing is a necessity of the future to develop atomic scale devices with high precision. A different perspective of the quantum realm, which includes the tunnelling effect, leakage current at the atomic-scale, Coulomb blockade and Kondo effect, is inevitable for the fabrication and hence, the mass production of these devices. For these atomic-scale device development, molecular level devices must be fabricated. Proper theoretical studies could be an aid towards the experimental realities. Electronic transport studies are the basis to realise and interpret the problems happening at this minute scale. Keeping these in mind, we present a periodic energy decomposition analysis (pEDA) of two potential candidates for moletronics: phthalocyanines and porphyrins, by placing them over gold substrate cleaved at the (111) plane to study the adsorption and interaction at the interface and then, to study their application as a channel between two electrodes, thereby, providing a link between pEDA and electronic transport studies. pEDA provides information regarding the bond strength and the contribution of electrostatic energy, Pauli’s energy, orbital energy and the orbital interactions. Combining this analysis with electronic transport studies can provide novel directions for atomic/close-to-atomic-scale manufacturing (ACSM). Literature survey shows that this is the first work which establishes a link between pEDA and electronic transport studies and a detailed pEDA study on the above stated molecules. The results show that among the molecules studied, porphyrins are more adsorbable over gold substrate and conducting across a molecular junction than phthalocyanines, even though both molecules show a similarity in adsorption and conduction when a terminal thiol linker is attached. A further observation establishes the importance of attractive terms, which includes interaction, orbital and electrostatic energies, in correlating the pEDA study with the transport properties. By progressing this research, further developments could be possible in atomic-scale manufacturing in the future.

Atomic force microscopy (AFM)-based electrochemical etching of a highly oriented pyrolytic graphite (HOPG) surface is studied toward the single-atomic-layer lithography of intricate patterns. Electrochemical etching is performed in the water meniscus formed between the AFM tip apex and HOPG surface due to a capillary effect under controlled high relative humidity (~ 75%) at otherwise ambient conditions. The conditions to etch nano-holes, nano-lines, and other intricate patterns are investigated. The electrochemical reactions of HOPG etching should not generate debris due to the conversion of graphite to gaseous CO and CO2 based on etching reactions. However, debris is observed on the etched HOPG surface, and incomplete gasification of carbon occurs during the etching process, resulting in the generation of solid intermediates. Moreover, the applied potential is of critical importance for precise etching, and the precision is also significantly influenced by the AFM tip wear. This study shows that the AFM-based electrochemical etching has the potential to remove the material in a single-atomic-layer precision. This result is likely because the etching process is based on anodic dissolution, resulting in the material removal atom by atom.

In this work we present a simulation study of current flow in inorganic molecular metal oxide clusters known as polyoxometalates (POMs). The simulations are carried out by using combination of the density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. To investigate the current flow in POMs, we investigate two possible ways to place the POM cluster between two gold (Au) electrodes -vertical and horizontal. Our results show that the position of the POM molecule and the contact between the molecule and the Au electrodes determines the current flow. Overall, the vertical configuration of the molecule between the two Au electrodes shows better current flow in comparison to the horizontal configuration. In this work we also establish a link between the underlying electronic structure and transmission spectra and conductance.