Zili Ma

Atomic‐scale modification on Si(111)7×7 surfaces

In this paper the scanning tunneling microscope (STM) has been used to fabricate atomic‐scale structures by removing atoms from the Si(111)7×7 surfaces at room temperature. Grooves a few nanometers in width are created. When the modification direction is along one of the base vector directions of the Si(111)7×7 surface (i.e., [110], [101], and [011]), the grooves have atomically straight edges and lateral features as small as a 7×7 unit cell wide. The study of the modification process reflects that the atomic‐scale structures are formed by extracting silicon atoms one by one from the sample surfaces. The dependence of critical current for creating a regular structure on Si(111)7×7 surface versus the bias voltage has been measured. Finally, based on the experimental data, the modification mechanism is designed.

Diamond tips and nanometer-scale mechanical polishing

Abstract The major application of the scanning tunneling microscope (STM) is as a local surface topography and structure probe. The scanning tip usually is made of metal such as tungsten (W), platinum-iridium (Pt-Ir), gold (Au), etc., by electrochemical etching or mechanical cutting. STM has also recently demonstrated its potential application as a powerful tool for nanometer-scale surface modification. We made a kind of diamond STM tips by the MPCVD technique. The tips are quite stable, and hard enough to polish the metal film surface to produce relatively flat areas. Both SEM and STM were employed to check and analyze the tips and the results of polishing.

Diamond‐coated tips and their applications

Scanning tunneling microscope (STM) has recently demonstrated its potential application as a powerful tool for nanometer‐scale surface modification. We have successfully fabricated new types of diamond‐coated STM tips by using microwave plasma chemical vapor deposition (MPCVD). The reactant is a gaseous mixture of methane and hydrogen, sometimes adding oxygen. While natural diamond is a good insulator, the electrical conductivity of diamond‐coated tips made by MPCVD technique is always high enough for STM experiments. These tips are quite stable, hard enough to make machining on metal or other solid surfaces in nanometer scale. We have applied the diamond‐coated STM tip to so‐called controlled machining on the metallic surfaces, such as gold, silver, and platinum films, and even polycrystal platinum, single crystal nickel, and palladium. Further investigations, including the results caused by different tips, applications for nanometer‐scale processing and engineering, etc., have been discussed. This techn...

Observation of small metal clusters on graphite surface with scanning tunneling microscopy

Abstract The motivation for studying the dynamic behavior and morphology of small metal clusters on solid single crystal surface is the desire to understand the physical mechanisms evolving in the initial stages of thin-film growth. In the experiments we have used a scanning tunneling microscope to study the static morphology of small Pt and Ni clusters supported on clean graphite surfaces, as well as the dynamic behaviors of small Pt clusters in an ultrahigh vacuum chamber. The metal deposition was fulfilled by controllable evaporation from ultra-pure superfine metal wires at room temperature in UHV. The STM images of small Pt and Ni clusters on graphite substrates with atomic resolution, as well as a series of STM images reveal some transformation processes of small metal clusters on the solid crystal surfaces, which provide us a better understanding on the procedure of atomic diffusion of metal clusters. All the STM images have been performed at room temperature.

Nanometer-scale regular grooves and ridges created with scanning tunnelling microscope

Abstract The scanning tunnelling microscope (STM) has been employed to fabricate grooves by extracting Si atoms out of the Si(111)-7×7 surface and deposit the Si atoms back onto the Si(111)-7×7 surface at room temperature. The deposited Si atoms can form a straight ridge under controlled conditions. The width of the ridge can be controlled better than 2 nm. Ridges can only be formed after the tip extracts enough atoms out of the Si(111)-7×7 surface. If the tip is clean, no atoms will be deposited from the tip under the depositing conditions. This suggests that the deposited atoms are silicon atoms extracted out of the Si(111)-7×7 surface. The deposition mechanism is discussed.

Hardness demonstration of diamond tips by nanometer‐scale controlled scratching on metallic surfaces

A new kind of diamond tip for the scanning tunneling microscope has been fabricated by a microwave plasma chemical vapor deposition method. The extreme hardness of the tips is demonstrated by doing nanometer‐scale controlled direct scratching on various metallic surfaces using these tips. The results indicate the potential of such diamond tips for nanometer‐scale mechanical polishing.

Behavior of small metal clusters on solid crystal surfaces

Abstract Association of single atoms into clusters and aggregation of small atomic clusters into a surface layer have been and are continued to be extensively studied as a tractable model system for the study of atomic processes and monolayer growth. In our experiments, the scanning tunneling microscope (STM) has been used to study some of the behavior of small Pt and Ni clusters on solid crystal surfaces. The samples have been prepared by controllable evaporation on HOPG from Wollaston wires at room temperature in UHV. Here we present a series of STM images of transformation processes of small atomic clusters, which provide us a better understanding on how substrate surfaces dominate this process. The transformation phenomena actually give rise to a complicated mechanism. STM images have been performed at room temperature.

Investigation of periodic structures of polyethylene crystal lamellas with STM

Abstract We have prepared polyethylene thin films with the ionized cluster beam (ICB) deposition technique. There are perfect polyethylene crystal lamellas in the thin films. We have observed the polyethylene lamellar surface topography with scanning tunneling microscopy (STM), and found the fold chain structures on the (001) surface of polyethylene crystal lamellas first. We have analyzed polyethylene thin films with transmission electron microscopy (TEM) and found the (001) plane parallel to the surface of the substrate. There are strict periodic structures in the (110) plane, but no good periodic structures in the [110] direction.

Structural analysis of domain boundaries on Si(111)7×7 surfaces by scanning tunneling microscope

The scanning tunneling microscope has been used to study domain boundaries on Si(111)7×7 surfaces. Several kinds of regular defect structures along the domain boundaries on Si(111)7×7 surfaces have been observed with atom resolution. By combining with the dimer‐adatom‐stacking fault model, their detailed atom structural models are given. It is found that there are three important factors that determine the boundary structure. The most important factor is the strong interaction between dimer and adatom. The next one, in some cases, is the difference between the faulted half and the unfaulted half. Additionally, the metastable (2n+1)×(2n+1) triangle subunit structure such as the 5×5 triangle subunit may play an important role in determining the defect structure along the domain boundary in some cases.

INVESTIGATION OF C-PHYCOCYANIN FROM BLUE-GREEN-ALGA SPIRULINA-PLATENSIS WITH SCANNING TUNNELING MICROSCOPE

C‐phycocyanin (C‐PC) was isolated from blue‐green alga spirulina platensis. A scanning tunneling microscope (STM) has been used to investigate its three‐dimensional structure. The samples were dialyzed before the STM experiment, and then deposited on highly oriented pyrolytic graphite (HOPG). The measurement was carried out in ambient condition at room temperature. STM images showed that C‐phycocyanin was uniformly distributed on solid‐state substrate HOPG. The shape of C‐phycocyanin is disklike with a channel in the center. It is concluded that STM has great potential to observe the structure of biliproteins and phycobilisomes.