Biomedical subjects

Saw-Wai Hla

Publications and source records attributed to Saw-Wai Hla.

7 recordsLinked to original sources

PubMed2006

Realization of a four-step molecular switch in scanning tunneling microscope manipulation of single chlorophyll-a molecules.

Single chlorophyll-a molecules, a vital resource for the sustenance of life on Earth, have been investigated by using scanning tunneling microscope manipulation and spectroscopy on a gold substrate at 4.6 K. Chlorophyll-a binds on Au(111) via its porphyrin unit while the phytyl-chain is elevated from the surface by the support of four CH(3) groups. By injecting tunneling electrons from the scanning tunneling microscope tip, we are able to bend the phytyl-chain, which enables the switching of four molecular conformations in a controlled manner. Statistical analyses and structural calculations reveal that all reversible switching mechanisms are initiated by a single tunneling-electron energy-transfer process, which induces bond rotation within the phytyl-chain.

Chlorophyll↗

PubMed2006

Nanoassembly of a fractal polymer: a molecular "Sierpinski hexagonal gasket".

Mathematics and art converge in the fractal forms that also abound in nature. We used molecular self-assembly to create a synthetic, nanometer-scale, Sierpinski hexagonal gasket. This nondendritic, perfectly self-similar fractal macromolecule is composed of bis-terpyridine building blocks that are bound together by coordination to 36 Ru and 6 Fe ions to form a nearly planar array of increasingly larger hexagons around a hollow center.

Journal Article↗

PubMed2006

Manipulating Kondo temperature via single molecule switching.

Two conformations of isolated single TBrPP-Co molecules on a Cu(111) surface are switched by applying +2.2 V voltage pulses from a scanning tunneling microscope tip at 4.6 K. The TBrPP-Co has a spin-active cobalt atom caged at its center, and the interaction between the spin of this cobalt atom and free electrons from the Cu(111) substrate can cause a Kondo resonance. Tunneling spectroscopy data reveal that switching from the saddle to a planar molecular conformation enhances spin-electron coupling, which increases the associated Kondo temperature from 130 to 170 K. This result demonstrates that the Kondo temperature can be manipulated just by changing molecular conformation without altering chemical composition of the molecule.

Cobalt↗

PubMed2005

Probing the conformation of physisorbed molecules at the atomic scale using STM manipulation.

We use scanning tunneling microscope (STM) manipulation and density functional theory calculation to investigate the structural properties of individual sexiphenyl molecules physisorbed on a Ag(111) surface at 6 K. The molecule-surface atomic registry is precisely determined by using atomic markers and a sexiphenyl functionalized tip. The calculations confirm the alternating twist of the sexiphenyl pi-rings on Ag(111). The pi-ring torsional angle, 11.4 degrees, is directly determined from the geometry of STM manipulation. This innovative experiment opens up a novel application of STM manipulation to probe the properties of "physisorbed" species on surfaces at the atomic level.

Journal Article↗

PubMed2004

Controlled low-temperature molecular manipulation of sexiphenyl molecules on Ag111 using scanning tunneling microscopy.

A novel scanning tunneling microscope manipulation scheme for a controlled molecular transport of weakly adsorbed molecules is demonstrated. Single sexiphenyl molecules adsorbed on a Ag(111) surface at 6 K are shot towards single silver atoms by excitation with the tip. To achieve atomically straight shooting paths, an electron resonator consisting of linear standing-wave fronts is constructed. The sexiphenyl manipulation signals reveal a pi ring flipping as the molecule moves from the hcp to fcc site. Ab initio calculations show an incorporation of the Ag atom below the center of a pi ring.

Journal Article↗

PubMed2004

The scanning tunnelling microscope as an operative tool: doing physics and chemistry with single atoms and molecules.

The scanning tunnelling microscope, initially invented to image surfaces down to the atomic scale, has been further developed in the last few years to an operative tool, with which atoms and molecules can be manipulated at will at low substrate temperatures in different manners to create and investigate artificial structures, whose properties can be investigated employing spectroscopic dI/dV measurements. The tunnelling current can be used to selectively break chemical bonds, but also to induce chemical association. These possibilities give rise to startling new opportunities for physical and chemical experiments on the single atom and single molecule level. Here we provide a short overview on recent results obtained with these techniques.

Microchemistry↗

PubMed2002

STM control of chemical reaction: single-molecule synthesis.

The fascinating advances in single atom/molecule manipulation with a scanning tunneling microscope (STM) tip allow scientists to fabricate atomic-scale structures or to probe chemical and physical properties of matters at an atomic level. Owing to these advances, it has become possible for the basic chemical reaction steps, such as dissociation, diffusion, adsorption, readsorption, and bond-formation processes, to be performed by using the STM tip. Complete sequences of chemical reactions are able to induce at a single-molecule level. New molecules can be constructed from the basic molecular building blocks on a one-molecule-at-a-time basis by using a variety of STM manipulation schemes in a systematic step-by-step manner. These achievements open up entirely new opportunities in nanochemistry and nanochemical technology. In this review, various STM manipulation techniques useful in the single-molecule reaction process are reviewed, and their impact on the future of nanoscience and technology are discussed.

Copper↗