Today, LSI process has been one of the most defined techniques to fabricate nanoscale structures. In this field, the top down method, such as lithography is a mainstream approach. However, it is reaching physical and technological limitations as for further size scaling. So the bottom up method has been attracting a lot of attention recently. In order to realize well defined bottom up process, it is quite important to establish a suitable self-assembly technique with a proper substrate as a template. In the present study, the SiO2 fences were fabricated on Si(111) surface by anodic oxidation using an atomic force microscope (AFM) probe. Then the Si surface was etched in ultra low dissolved oxygen water (LOW). We have investigated into the effect of the SiO2 fences on the atomic step shape and the step flow speed as one of way to control the step shape and its position.
Recently, in the field of genome sequencing, next generation DNA sequencers are becoming available, and even the genome sequence analysis of a higher animal and/or a plant can be finished within a short period. However, the next generation DNA sequencers can only read relatively short sequence, which causes difficulty in the assemble step (i.e. reconstruction of original genomic sequence) and makes it labor and time consuming process and results in the long time requiring for gene isolation and breeding. When a target organism does not have enough genomic information, the assemble becomes much harder or not possible. This difficulty is arisen from the absence of positional index of the obtained nucleotide sequences by a whole genome shot-gun method. Therefore, we started the development of a new, scanning probe microscope based genome analysis method that can acquire the nucleotide sequences with positional indexes on the genome.
We investigated the zero field splitting (ZFS) of a single iron (II) phthalocyanine (FePc) molecule on clean Cu(110) and Cu(110) (2×1)-O surfaces mainly by using inelastic electron tunneling spectroscopy (IETS) with STM. On the Cu(110) (2×1)-O surface, the excitations between the spin states were observed. Adsorption of FePc on the (2×1)-O surface reduces the symmetry of the ligand field for the Fe atom, resulting in the switching of the easy-magnetization direction from the easy-plane to easy-axis. On the clean Cu(110) surface, there is no signal relevant to the excitation. The spin state converts from triplet to singlet due to the stronger coupling with the surface as is confirmed by photoelectron spectroscopy. These findings demonstrate the importance of coupling at molecule-substrate interface for manipulating the magnetic properties of adsorbates.
We have reported a one-step method that can enable the growth and parallel patterning of DNA nanofibers on a substrate. This method is based on the processes of solvent vapor-induced buildup and controlled drying front movement and forms parallelly aligned DNA nanofibers exceeding several hundred micrometers in length and 40 nm in diameter on a PDMS sheet. DNA nanofibers initially present on the PDMS sheet were transferred onto another surface using transfer-printing (TP). It was also possible to realize crossed two-dimensional patterns of DNA nanofibers by repeating TP. Polarized fluorescent microscope observations revealed that intercalated dyes are highly ordered in molecular alignment and that DNA strands in the fiber are aligned parallel to the growing direction of fibers.
Although self-assembled monolayers of oligo(ethylene glycol)-terminated alkanethiols (OEG-SAM) is widely known as a model system of bioinert surfaces, the underlying mechanism has not been clear. In this work, the interactions between the OEG-SAMs in water were explored with an atomic force microscope (AFM). We found that repulsion operates between the OEG-SAMs even at high ion concentrations and that the decay length of the repulsion is too large to be interpreted with the conventional DLVO theory. Disappearance of the repulsion in mixture of ethanol and water strongly indicates that the repulsion is attributed to the force induced by a water layer in vicinity of the OEG-SAM. In this review, we discuss the interfacial behavior of water molecules near the OEG-SAM with combining our findings and recent reports from other research groups.
The authors studied the structure and dynamics of individual water dimer and trimer on Cu(110) by using a scanning tunneling microscope (STM) and density functional theory (DFT). The dimer consists of hydrogen-bond donor and acceptor molecules, and dynamically rearranges the hydrogen bond resulting in the interchange of their roles. The large isotope effect (∼60) was founded in the interchange rate between (H2O)2 and (D2O)2, suggesting that the process involves quantum tunneling. The interchange motion was enhanced upon the excitation of an intermolecular mode that correlates with the reaction coordinate. In contrast, the water trimer was imaged as a static triangular shape. The calculation revealed that it forms a hydrogen-bond chain along the atomic row.
Some specified tips of AFM cantilever show three kinds of vertical atom interchange manipulation phenomena at room temperature. Those are successive Si deposition tip, successive Sn deposition tip, and alternate Si and Sn deposition tip. Former two types of tips correspond to atom pen modes because of successive Si or Sn deposition, while the last type of tip corresponds to atom switch mode because of alternate Si and Sn depositions. Using successive Si deposition tip, we demonstrate rapid construction of embedded atom letters “Si” consisted of relatively small Si adatoms substituted in the surface formed by a little large Sn adatoms at room temperature. Besides, we clarify the reproducibility of other two types of tips by investigating successive noncontact AFM topographic images and frequency shift curves before and after successive vertical atom interchange manipulation.