Showing papers by "Mahesh G. Samant published in 2001"

Epitaxial growth and properties of ferromagnetic co-doped TiO2 anatase

Abstract: We have used oxygen-plasma-assisted molecular-beam epitaxy (OPA-MBE) to grow CoxTi1−xO2 anatase on SrTiO3(001) for x=∼0.01–0.10, and have measured the structural, compositional, and magnetic properties of the resulting films. Whether epitaxial or polycrystalline, these CoxTi1−xO2 films are ferromagnetic semiconductors at and above room temperature. However, the magnetic and structural properties depend critically on the Co distribution, which varies widely with growth conditions. Co is substitutional in the anatase lattice and in the +2 formal oxidation state in ferromagnetic CoxTi1−xO2. The magnetic properties of OPA-MBE grown material are significantly better than those of analogous pulsed laser deposition-grown material.

Atomic-beam alignment of inorganic materials for liquid-crystal displays

Abstract: The technique used to align liquid crystals—rubbing the surface of a substrate on which a liquid crystal is subsequently deposited1,2,3—has been perfected by the multibillion-dollar liquid-crystal display industry. However, it is widely recognized that a non-contact alignment technique would be highly desirable for future generations of large, high-resolution liquid-crystal displays. A number of alternative alignment techniques have been reported4,5,6,7, but none of these have so far been implemented in large-scale manufacturing. Here, we report a non-contact alignment process, which uses low-energy ion beams impinging at a glancing angle on amorphous inorganic films, such as diamond-like carbon. Using this approach, we have produced both laptop and desktop displays in pilot-line manufacturing, and found that displays of higher quality and reliability could be made at a lower cost than the rubbing technique. The mechanism of alignment is explained by adopting a random network model of atomic arrangement in the inorganic films. Order is induced by exposure to an ion beam because unfavourably oriented rings of atoms are selectively destroyed. The planes of the remaining rings are predominantly parallel to the direction of the ion beam.

Liquid crystal alignment on carbonaceous surfaces with orientational order.

Abstract: We used near-edge x-ray absorption fine structure (NEXAFS) spectroscopy to link the orientational bond order at three carbonaceous surfaces-rubbed polyimide, ion beam-irradiated polyimide, and ion beam-irradiated diamondlike carbon films-with the direction of liquid crystal (LC) alignment on these surfaces. We show that, in general, LC alignment can be created on any carbonaceous substrate by inducing orientational order at its surface. Our results form the scientific basis for LC alignment layers consisting of amorphous carbon films in which orientational order near the surface is induced by a directional low-energy ion beam.

Magnetic random access memory with thermally stable magnetic tunnel junction cells

Abstract: A magnetic tunnel junction (MTJ) memory cell and a magnetic random access memory (MRAM) incorporating the cells has upper and lower cell electrodes that are formed of bilayers that provide electrical connection between the cells and the copper word and bit lines of the MRAM. The bilayers are formed of a first layer of tantalum nitride or tungsten nitride and a second layer of tantalum or tungsten. In one embodiment TaN is formed directly on the copper and low-resistivity alpha-Ta is formed directly on the TaN. If the cells use an antiferromagnetic layer to fix the moment of the pinned ferromagnetic layer, then Pt—Mn is the preferred material formed over the alpha-Ta. The bilayer can function as a lateral electrode to connect a horizontally spaced-apart cell and a copper stud in the MRAM.

34.4: Liquid Crystal Alignment Degradation Induced by Photo‐irradiation

Abstract: Degradation of liquid crystal alignment has been studied by monitoring the change in pre-tilt angle as a function of UV dosage, as well as by surface analysis methods, such as NEXAFS and surface energy measurement. The mechanism of the alignment degradation was understood for the first time at the surface chemistry level. The degradation happened in two steps. First there is oxygen absorption, followed by liquid crystal attachment. In addition, we have shown that filtering out short wavelengths is effective in prolonging the lifetime of liquid crystal displays. This work is important for improving display lifetime and quality.

56.1: Novel LC Alignment Method using Diamond Like Carbon Film and Ion Beam Alignment

Abstract: A novel LC alignment method has been developed. In this, the conventional polyimide film and cloth rubbing have been replaced by a diamond-like-carbon film and an ion beam respectively. The novel method has been used in pilot-line manufacturing to produce super high quality panels: 15″ TN mode and 22″ IPS mode. These panels will be demonstrated, and the advantage of new method will be discussed.

From NEXAFS spectroscopy to new flat panel displays: A story of basic science with technological impact

Abstract: Today's laptop computers utilize flat panel displays where the light transmission from the back to the front of the display is modulated by orientation changes of liquid crystal (LC) molecules [ 1,2]. The nematic LC consists of rod-like molecules that prefer to align with their long axes parallel to each other. One of the key steps in the manufacture of the displays is the reliable alignment of the LC molecules in the display. Today this is achieved by mechanical rubbing of two polymer surfaces and then sandwiching the LC between two such surfaces with orthogonal rubbing directions. Fig. 1 illustrates the relevant parts of a display. The light transmission from the back to the front of the display is controlled pixel by pixel by the local arrangement of the LC molecules. The rubbing process aligns the LC molecules in the rubbing direction, nearly parallel to the surface, so that they form a 900 helix from one surface to the other. By application of a small voltage to a pixel, the LC molecules align along the electric field lines within the

The Story behind IBM's New Flat Panel Displays: Technical Impact of Synchrotron Radiation Research

Abstract: Today's laptop computers utilize flat panel displays where the light transmission from the back to the front of the display is modulated by orientation changes in liquid crystal (LC) molecules. Details are discussed in Ref. 2 below. One of the key steps in the manufacture of the displays is the alignment of the LC molecules in the display. Today this is done by mechanical rubbing of two polymer surfaces and then sandwiching the LC between two such surfaces with orthogonal rubbing directions. Over the past years a great challenge of this $20 billion/year industry has been to devise an alternative method of liquid crystal alignment. The rubbing process is plagued with contamination issues and the polymer film is deposited by a wet process that is incompatible with high-tech manufacturing techniques. Also, the rubbing process does not lend itself to the manufacture of multidomain alignment layers that are necessary to increase the limited viewing angle in present displays. The development of a new alignment technology, however, has been impeded by the fact that the origin of LC alignment has remained a mystery since its discovery in 1907.