Kenichi Ishizuka

Effect of Molecule–Electrode Contacts on Single-Molecule Conductivity of π-Conjugated System Measured by Scanning Tunneling Microscopy under Ultrahigh Vacuum

A π-conjugated compound with two thioacetate end groups was synthesized using a recently developed method. A self-assembled monolayer (SAM) of corresponding dithiol was prepared by dipping a Au(111) surface for 1 min in a 2 mM dithiol toluene solution formed 30 min after the addition of a drop of 30% NH4OH in water to the dithioacetate toluene solution. We investigated electronic conduction through isolated single molecules of the π-conjugated compound by statistical analysis of molecular junctions repeatedly formed between a gold tip and the SAM on Au(111) using scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV). The single-molecular conductivity of the π-conjugated compound is described as Gm=Tcontact with tipTπ-systemTcontact with substrateG0 according to the Landauer equation. Here, Ts are transmission functions and G0 is the quantum conductance, i.e., 2e2/h. Because of observed high values of Gm for the π-conjugated compound, we could readily analyze the effect of molecule–electrode contacts on Tcontact with tipTcontact with substrate. Namely, we successfully observed the dependence of Tcontact with tipTcontact with substrate on binding sites of –S- on a Au(111) surface, i.e., the bridge (or the hollow) and the top sites.

Quadrupled Compact Disk-Read Only Memory Fabricated Using UV Light Source

Quadrupled compact disk-read only-memory (CD-ROM) mastering processes with a 363.8 nm UV light source have been developed. The UV light source exposure power for pit formation is less than that for the 457.9 nm conventional light source, because the photoresist exposure characteristic depends on light source wavelength. The fabricated disk exposed by EFM signals with doubled-linear-density CD format has a 0.8 µm track pitch and about 0.25 µm pit width. Under optimum fabrication exposure power for reduced crosstalk and better modulation amplitude, an excellent jitter value, 10 ns, is achieved for the quadrupled CD-ROM.

Magneto-optical Disk for Magnetic Field Modulation Recording Method with Multi-Pulsed Laser Irradiation

The authors report magnetic field modulation (MFM) recording characteristics for magneto-optical (MO) disks, whose magnetic sensitivity was improved through sputter-etching treatment of the SiN layer beneath the magnetic layer. The sputter-etching treatment increased weak-field recording noise, as well as reproduced signal amplitude. Jitter caused by such noise can be reduced by the introduction of a new MFM recording method with multi-pulsed laser irradiation. This paper discusses the mechanism for the improvement of such MFM recording characteristics on the sputter-etched MO disks.

Reliability Test on One-Side-Recordable Magnetooptical Disks by Block Error Rate Measurement

One-sided magnetooptical (MO) disks of compact-disc size have been evaluated with respect to their reliability by block error rate (BLER) measurement. We have carried out high-temperature and high-humidity tests on our disks. No marked changes in mechanical properties or carrier-to-noise ratio (CNR) after accelerated tests were observed. However, C1 and C2 error count increases were observed. The C2 error count increase indicated increase on large media defect numbers. An Arrhenius plot on the maximum BLER values at elevated temperatures revealed an activation energy of approximately 0.9 eV. Estimated lifetimes of our disks at 31°C are more than 10 years, which means one-sided MO disks have lifetimes as long as two-sided disks, such as the 130-mm MO disk.

High-density optical disk mastering using UV light source

For high density optical disk mastering processes, it is important to appropriately select the light source and optical layout as well as to optimize photoresist and exposure method. A g-line type photoresist is preferred for use in the mastering processes, compared with i-line type photoresist. By using the UV light source, the pit width is narrowed down to 0.25 micrometers , which is easily fabricated. Under preferred fabrication exposure power for cross talk and modulation amplitude, excellent jitter values, 8/8 ns, 10.8 ns and 16.9 ns were achieved for quadrupled, quintupled and 6-times density CD-ROMs.