Futoshi Katsuki

Crystallization of amorphous germanium in an Al/a-Ge bilayer film deposited on a SiO2 substrate

The crystallization of amorphous Ge(a-Ge) in an Al (134 nm) and a-Ge (108 nm) thin-film bilayer deposited on a SiO2 substrate has been examined by a cross section transmission electron microscope technique. When crystallization of a-Ge begins at 125 °C, amorphous AlGe (a-AlGe) alloy is formed in the Ge layer. Then, the a-AlGe alloy layer also appeared at the surface of the bilayer. After complete crystallization, those amorphous layers disappeared and the bilayer film has been converted to a polycrystalline film. We discussed the crystallization of a-Ge and proposed the mechanism of the diffusion of Ge atoms from the inner a-Ge layer through the outer Al layer to the topmost surface that involves the formation of the metastable a-AlGe alloy in the Ge layer, followed by the crystallization of this alloy by the pseudo-eutectic reaction, leading to the decomposition into an equilibrium Al and Ge crystal mixture and a-Ge. Then, Ge atoms is released to the Al layer for the compensation of the Al diffusion down...

AFM Studies on the Difference in Wear Behavior Between Si and SiO2 in KOH Solution

Wear behavior between a Si tip and a SiO 2 film in KOH solution at various pH values has been examined by using an atomic force microscope We found that the Si tip removal amount strongly depended on the solution pH value and was at a maximum at pH 10.2-12.5 This result indicates that wear behavior of the Si tip is similar to that of actual chemical mechanical polishing of a Si wafer It was also found that the Si removal volume in moles was approximately equal to that of SiO 2 irrespective of the solution pH value This equality implies that a Si-O-Si bridge is formed between one Si atom and one SiO 2 molecule at the wear interface, followed by the oxidation of the Si tip, and finally the bond rupture by the tip movement and the silica species including the Si-O-Si bridge is dissolved in the KOH solution.

Single asperity tribochemical wear of silicon by atomic force microscopy

Measurements of single asperity wear on oxidized silicon surface in aqueous potassium hydroxide (KOH) using atomic force microscopy (AFM), where the single crystal silicon tip was used both to tribologically load and image the surface, is presented. AFM was also operating in the lateral (frictional) force mode to investigate the pH dependence of kinetic friction between the tip and the SiO 2 surface. It was shown that the Si tip wear amount strongly depended on the solution pH value and was at a maximum at around pH 10. It was also found that the Si removal volume in mol was approximately equal to that of SiO 2 irrespective of the solution pH value. This equality implies that the formation of the Si–O–Si bridge between one Si atom of the tip and one SiO 2 molecule of the specimen at the wear interface. The surface of the Si tip is then oxidized. Finally, the bond rupture by the tip movement will occur, the dimeric silica (OH) 3 Si–O–Si(OH) 3 , including the Si–O–Si bridge, is dissolved in the KOH solution. The frictional signal is also sensitive to the pH values of the solution and peaked at around pH 10. These results indicate that the removal behavior of the Si tip and SiO 2 surface would be affected by the frictional force between the Si and the SiO 2 , because of an increased liquid temperature and a compressive stress in Si and SiO 2 networks. Strong influence is observed by the pH of the ambient solution confirming the important role of the OH − in the wear mechanism. Pressure dependence of the microwear behavior under aqueous electrolyte solutions has also been investigated. A microscopic removal mechanism, which is determined by interplay of the diffusion of water in Si and SiO 2 , is presented.

The Atomic-Scale Removal Mechanism during Si Tip Scratching on Si and SiO2 Surfaces in Aqueous KOH with an Atomic Force Microscope

The atomic-scale removal mechanism during Si tip scratching on Si wafer or SiO2 film in aqueous KOH has been examined using an atomic force microscope. We have found that the Si tip removal volume in moles was in good agreement with that of the corresponding Si or SiO2 specimen. This equality implies that the process begins with formation of the Si–O–Si bridge between one Si atom of the tip and one Si atom or one SiO2 molecule of the specimen at the wear interface, followed by the local oxidation of the Si surface, and finally the bond rupture by the tip movement, the dimeric silica (OH)3Si–O–Si(OH)3, including the Si–O–Si bridge is dissolved in the KOH solution. Comparison of the wear behavior of Si and SiO2 shows that they are almost the same, indicating that a similar reaction would occur due to the local development of oxide nuclei on the Si surface.

Development of a thermoelectric power generation system using reciprocating flow combustion in a porous FeSi2 element

A thermoelectric power generation system using reciprocating flow combustion in a porous thermoelectric conversion element has been developed and examined in its performance. Mn- (n-type) and Co- (p-type) doped FeSi2 powders were molded into the cylindrical element via a spark plasma sintering process, in which Mn- and Co-doped parts were separated by a thin insulator sheet exclusive of a terminus. The porous element consisted of two semicylindrical p/n couples, arranged electrically in series but thermally in parallel. A thermopower of 1.0–1.2 mV/K at 295–624 K and an apparent internal resistivity of 1.6×10−1 Ω cm at 556–624 K have been obtained for the element. A power generation system was then made using a pair of the elements, which were arranged lengthwise in a cylindrical combustion chamber. A reciprocatory flow of dilute fuel gas was introduced into the element, and it was ignited between the element. A steep temperature gradient of about 200 K/cm was formed lengthwise in both elements. The energy...

Pattern evolution of crystalline Ge aggregates during annealing of an Al/Ge bilayer film deposited on a SiO2 substrate

When an Al/Ge bilayer film deposited on a SiO2 substrate is annealed at 373- 398 K, Ge atoms diffuse out from the inner amorphous Ge layer and spread over the free surface of the outer Al layer to form crystalline Ge aggregates exhibiting complex substructures. Scanning electron microscopy observations indicate that the activation energy for the pattern evolution of Ge aggregates on the free surface because of annealing is 1.56 eV which is about half the activation energy for crystallization of amorphous Ge.

Single Asperity Tribochemical Wear of Silicon by Atomic Force Microscopy

We report measurements of single asperity wear on oxidized silicon surface in aqueous KOH using atomic force microscopy (AFM), where the single crystal silicon tip was used both to tribologically load and image the surface. AFM was also operating in the lateral (frictional) force mode (LFM) to investigate the pH dependence of kinetic friction between the tip and the SiO 2 surface. We found that the Si tip wear amount strongly depended on the solution pH value and was at a maximum at around pH 10. It was also found that the Si removal volume in moles was approximately equal to that of SiO 2 irrespective of the solution pH value. This equality implies that the formation of the Si-O-Si bridge between one Si atom of the tip and one SiO 2 molecule of the specimen at the wear interface, followed by the oxidation of the Si surface, finally the bond rupture by the tip movement, the dimeric silica (OH) 3 Si-O-Si(OH) 3 , including the Si-O-Si bridge is dissolved in the KOH solution. It was also found the frictional force is highly sensitive to the pH values of the solution and peaked at around pH 10. These results indicate that the interfacial reaction would be affected by the frictional force between the Si tip and the SiO 2 surface, due to an increased liquid temperature and a compressive stress in Si and SiO 2 networks. Strong influence is observed by the pH of the ambient solution confirming the important role of the OH- in the wear mechanism. We present a microscopic removal mechanism which is determined by an interplay of the diffusion of water in Si and SiO 2 .