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Special Seminar

Nanoscale Magnetic Recording

by: Dr. Dimitri Litvinov

Date: Friday September 05, 2003

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Magnetic recording is rapidly shifting into the realm of nanoscale technologies. At 1 Terabit/in2, the size of a recording bit is 50x13nm2 (assuming 4:1 bit aspect ratio.) To store such small magnetic features, the characteristic dimensions of all supporting recording system components have to be shrunk correspondingly. The read/write transducers are being scaled down into 40nm range. The characteristic size of the smallest magnetic feature in a recording medium is being refined to hit the 5nm mark. The flying height of the recording heads is targeted to be a few nanometers at the most. The servoing capabilities of the tracking system are being optimized for the capability to position a recording transducer on a 3.5” diameter media disk with a precision of 10nm in a fraction of a millisecond. This presentation will review the major critical issues related to the recording physics, device fabrication, and system integration at nanoscale. The prospects of extending magnetic recording technologies above Terabit/in2 range as well as alternative approaches to data storage and retrieval will be discussed. Among the open issues critical to the development of nanoscale probe recording is the ability to fabricate magnetic transducers with the dimensions in the nanometer range as well as the detailed understanding of the recording physics of such nanomagnetic devices. Magnetic probe heads with a cross-section of 60x60nm2 were successfully fabricated using focused ion-beam (FIB) processing. The ability of such probe heads to controllably conduct magnetic flux is critical to the performance of a recording system. The results of both experimental and theoretical study of micro/nano-magnetic behavior of fabricated nanoscale probe heads will be reported. The recording demonstration using 60nm wide magnetic nanowriters will be presented. The key advantages of FIB technology with respect to magnetic materials processing will be reviewed. The resolution limits and Ga+ ions interaction with magnetic materials will be discussed.

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Special Seminar

High Energy Atomic Beam Nanolithography

Dr. John C. Wolfe

by: Dr. John C. Wolfe

Date: Friday December 06, 2002

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Ion beam proximity (IBP) lithography is “stencil printing” where helium ions are the “paint” and the stencils are thin silicon membranes with etched open windows. Diffraction, penumbral blur, and ion scattering in the resist are all consistent with 1 nm printing. However, the scattering of the lithography ions by electrostatic charge in the mask and substrate limit the practical resolution to the 50-100 nm regime. This seminar describes the discovery of a remarkable source of energetic helium atoms that eliminates this last obstacle to sub-10 nm printing. Applications to nanomagnetics and nanoelectronics will be discussed.

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Special Seminar

Ferroelectric and Ferromagnetic Micro-Crystalline and Nanocrystalline Glass Ceramics

by: Dr. Yao Xi

Date: Friday September 28, 2001

Time: 11:00 am – 12:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Microcrystalline and nanocrystalline glass ceramics are those materials bearing the major characteristics of both glass and ceramic. In the development of high performance ceramic materials, structural, compositional and chemical purifications are the most important concerns of ceramic scientists and engineers. However, in many cases, even the purist single crystalline materials can no longer satisfy the very complicated and comprehensive requirements on the properties and processes of ceramic materials from modern technology. It is time for us to look for help from novel multiphase ceramic materials.

Sol-gel process is introduced to prepare ferroelectric and ferromagnetic microcrystalline and nanocrystalline glass powders. Various ferroelectric and ferromagnetic crystallites in the size of nanometers and micrometers can be in-situ precipitated from amorphous glass matrices. Then, conventional ceramic processing is used to sinter such microcrystalline glass powders into ceramics. The processing, structure, property and application of PT, BT and KTP based ferroelectric glass ceramics, spinel Ni-Zn ferrite and magnetoplumbite Ba ferrite ferromagnetic glass ceramics will be discussed in this presentation.

Special Seminar

Chemical Physics of Strongly Correlated Electron Systems

by: Prof. Frank Steglich

Date: Tuesday June 12, 2001

Time: 11:00 am – 12:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

In a number of lanthanide- and actinide-based intermetallic compounds unconventional metallic, superconducting and magnetic states have been observed. These originate in a strong local Coulomb repulsion between the 4f/5f electrons and a weak hybridization of these atomic and the conduction-electron wavefunctions.

I shall discuss (1) the antiferromagnetically ordered heavy-fermion superconductor UPd2Al3 for which recent tunneling and inelastic-neutron-scattering experiments strongly support a magnetic-exciton-mediated pairing mechanism [1], (2) several compounds of the RET2X2 family showing pronounced “non-Fermi-liquid” effects [2-4] which cannot be fully explained by the existing spinfluctuation theories, and (3) the charge-ordered state of Yb4As3 characterized by an extremely low charge-carrier concentration and antiferromagnetic effective S = 1/2 chains. In a transverse magnetic field, the latter give rise to the opening of a spin gap which has the same origin as the pronounced soliton excitations that show up in several physical properties [5, 6]. Finally, I address a recent collaboration between chemists and physicists in our institute devoted to finding new small-gap semiconductors.

References: 1. N. K. Sato et al., Nature 410, 340 (2001); 2. P. Gegenwart et al., Phys. Rev. Lett. 81, 1501 (1998); 3. P. Gegenwart et al., Phys. Rev. Lett. 82, 1293 (1999); 4. O. Trovarelli et al., Phys. Rev. Lett. 85, 626 (2000); 5. M. K?ppen et al., Phys. Rev. Lett. 82, 4548 (1999); 6. F. Steglich et al., Acta Phys. Pol. A 97, 91 (2000).

Special Seminar

Metal-Metal Bonded Supramolecular Chemistry Assembly, Symmetry, and Molecular Architecture on the Rational Design of Advanced Materials Based on Nanoscale-sized Molecules

by: Dr. Chun Lin

Date: Thursday May 17, 2001

Time: 11:00 am – 12:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

This work pioneered the concept of introducing metal-metal bonds into supramolecular chemistry. This cutting-edge project is focused on the design and self-assembly of nanomolecules mediated by pairs of bonded dimetal units. Coupling of such units in pairs can form one-, two-, and three-dimensional materials containing metal-metal bonds wherein cooperative interaction among the dimetal centers may give rise to tunable physical properties in the bulk material.

Metal-metal bonded cationic complexes of the type [M2(DAniF)4-n(MeCN)8-2n]m+, where M = Mo or Rh and DAniF is an N,N'-di-p-anisylformamidinate anion, have been used as precursors for subunit pieces and then linked by various equatorial and axial bridging groups such as polycarboxylate anions, polypyridyls and polynitriles. Characterization of the products by single-crystal X-ray diffraction, CV, DPV, NMR and other spectroscopic techniques have revealed the presence of discrete tetranuclear (chains or loops), hexanuclear (triangles), octanuclear (squares), dodecanuclear (cages) species, and one-, two-, three-dimensional molecular nanotubes. These compounds display a rich electrochemical behavior which is affected by the nature of the linkers.

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