T. Kinno

Depth resolution improvement in secondary ion mass spectrometry analysis using metal cluster complex ion bombardment

Secondary ion mass spectrometry analyses were carried out using a metal cluster complex ion of Ir4(CO)7+ as a primary ion beam. Depth resolution was evaluated as a function of primary ion species, energy, and incident angle. The depth resolution obtained using cluster ion bombardment was considerably better than that obtained by oxygen ion bombardment under the same experimental condition due to reduction of atomic mixing in the depth. The authors obtained a depth resolution of ∼1nm under 5keV, 45° condition. Depth resolution was degraded by ion-bombardment-induced surface roughness at 5keV with higher incident angles.

Magnetic properties of LaNiO3 films and Josephson characteristics of Y1Ba2Cu3O7−y/LaNiO3/Au/Ag/Pb junctions

A conductive perovskite oxide, LaNiO3, has been examined for the application to the normal layer for superconductor‐normal metal‐superconductor junctions for the first time. LaNiO3 films showed resistivity as low as 1.5×10−4 Ω cm. Pauli paramagnetism dominated in the film. The susceptibility measured was 0.9×10−6 emu/Oe g. Boundaries between the Y1Ba2Cu3O7−y and LaNiO3 layers were found to be abrupt in a Y1Ba2Cu3O7−y/LaNiO3 multilayer by transmission electron microscopy (TEM) observation. The coherence length in LaNiO3 was estimated to be 30–70 A from characteristics of the Y1Ba2Cu3O7−y/LaNiO3/Au/Ag/Pb junctions. The value was comparable to the dirty limit coherence length of (ℏD/2πkBT)1/2 of the conventional theory (D; the diffusion constant in LaNiO3).

Preparation and characterization of electrochemically etched Re tips for STM

Abstract We have investigated rhenium (Re) tips for scanning tunneling microscopy (STM). The tips were made by electrochemical etching from polycrystalline Re wires with two methods. The better method was the method using a ring reference electrode floating on a H2SO4 solution and a controller. Sharp tips with a single apex were obtained reproducibly; their diameter was inspected with transmission electron microscopy to be around 300 A. The tip apex was examined by field ion microscopy. Most of the Re tips were observed to have a [11 2 0]-oriented apex, where a single atom was expected to be stable. Atomic resolution STM images of Si(111)7×7 surface were obtained both at room temperature and at 600°C, demonstrating that a [11 2 0]-oriented Re tip is one of the most stable tips for STM.

High depth resolution SIMS analysis using metal cluster complex ion bombardment

SIMS depth profiles were measured using metal cluster complex ions of Ir4(CO)7+ as a primary ion beam in order to obtain high depth resolution. Depth resolution was evaluated as a function of primary ion species, energy and incident angle using a multiple boron delta-doped silicon sample. The depth resolution obtained using cluster ion bombardment was considerably better than that obtained by oxygen ion bombardment under the same bombardment condition due to reduction of atomic mixing in the depth. The best depth resolution was 0.9 nm under the bombardment condition of 5 keV, 45° with oxygen flooding, which approaches the value measured with state of the art SIMS analyses. However, depth resolution was not improved by decreasing the cluster ion energy (less than 5 keV), even though the roughness of the sputtered surface was suppressed. The limit of depth resolution improvement may be caused by a carbon cover-layer that prevents the formation of surface oxide that buffers atomic mixing. To overcome this issue, it will be necessary to eliminate carbon from the cluster ion.

Rhenium Tips for Stable Scanning Tunneling Microscopy

A rhenium (Re) tip has been investigated for scanning tunneling microscopy (STM). Most of the Re tips etched electrochemically from poly-crystalline wires were found to have a [110]-oriented apex by field ion microscopy. A single atom of the tip apex surface has been expected to be stable, because of its high coordination number. The 7×7 reconstructions of silicon (111) surfaces were observed at atomic level by STM using the Re tip. These results suggest that a Re tip with a single apex atom can be one of the most stable tips for STM.

Quantitativeness in laser-assisted atom probe analysis of boron and carbon codoped in silicon

Boron and carbon codoped in polysilicon thin films and carbon implanted in silicon substrates have been examined by laser-assisted atom probe tomography (La-APT). Clusters of dopants were observed in annealed samples. Compared with the results obtained by secondary ion mass spectrometry (SIMS), significant miscounts of both boron and carbon were found in La-APT results. On the basis of measurements using two different La-APT systems, it was suggested that the insufficiency of the multihit capability of the detection systems is an important origin of the miscounts.

Observation of Gold Thin Film on Cesium Graphite Intercalation Compound by Scanning Tunneling Microscopy

Thin film on stage-1 cesium graphite intercalation compound (Cs-GIC) which is known to be of very low work function has been studied using scanning tunneling microscopy (STM). After a small amount of Au was evaporated onto a Cs-GIC cleaved under ultrahigh-vacuum conditions, its surface was observed. At first, many islands with a diameter of several nanometers were found. These islands, however, gradually disappeared from the scanned region during observation. Our results suggest that the interaction of Au islands with Cs-GIC is weak, in spite of the large difference in work function between them.

Rhenium Tips for Scanning Tunneling Microscopy in Air.

The performance of rhenium (Re) tips has been investigated for scanning tunneling microscopy in air. Both tips machined mechanically and tips etched electrochemically from poly-crystalline wires were examined and the tip apexes were observed with a transmission electron microscope. Stable atomic images of graphite surfaces were almost always obtained using the Re tips sharpened mechanically, whose apexes were jagged and had thin oxide layers. Atomic images were not obtained, however, with the electrochemically etched Re tips, whose contamination layers were field-evaporated and the apexes of which were controlled so that a single atom was on the apex of the (110) surface, although atomic images were always observed stably in UHV with these tips.

Properties of LaNiO3 Films and YBCO/LaNiO3/Au/Ag/Pb Junctions

A conductive perovskite oxide, LaNiO3 has been examined to apply it to a normal layer for SNS junctions for the first time. LaNiO3 films showed the lowest resistivity of 1.5 x 10−4 Ω cm. Pauli paramagnetism dominated in the films prepared at lower substrate temperatures. On the other hand, the films prepared at high substrate temperatures showed a large amount of Curie paramagnetism together with Pauli paramagnetism. The measured susceptibility was 0.9 x 10−6 emu/Oe g. The boundary between the YBCO and LaNiO3 layers was investigated to be abrupt in LaNiO3/YBCO bilayers. The coherence length in LaNiO3 was obtained to be 3–7 nm from the characteristics of the YBC0/LaNi03/Au/Ag/Pb junctions. The value was comparable to the coherence length of (hD/2πkBT)1/2.