Bottom Step Research Articles

Vlsi Metallization by Coherent Magnetron Sputtering

Magnetron sputtering has been used extensively to deposit interconnect layer, diffusion barrier layer, adhesion layer and anti-reflection layer in semiconductor production. As the dimension of VLSI devices get smaller, it is becoming increasingly difficult to deposit these metal layers into high aspect ratio contacts and vias using conventional sputtering method. Coherent sputtering, where a perforated plate (collimator) is placed between the sputtering target and wafer, improves bottom coverage and step coverage. In the recent years, coherent sputtering has been used to deposit titanium, titanium nitride and aluminum films. However, the existence of collimator changes the deposition processes and properties of the deposited films. In this article, we will discuss some of the properties of coherent deposition.

The relationship between catalyst morphology and performance in the oxidative coupling of methane

A detailed study of the oxidative coupling of methane over magnesium oxide and lithium-doped MgO catalysts is presented. The morphology of a number of different catalysts has been examined by detailed transmission electron microscopy and the results have been correlated with catalyst performance, in particular selectivity to C 2 hydrocarbons. Three samples of magnesium oxide have been prepared by different methods. Magnesium oxides prepared from the hydroxide, (ex OH), and from burning magnesium ribbon in air show similar morphology, exposing largely {100} planes; they also show very similar catalytic selectivity and specific activity. The ribbon residue material, however, has a cube length which is greater than that of the ex OH material by a factor of 5–10. Steps and corner sites are therefore present in much greater density on the ex OH sample than on the ribbon residue, and, since catalyst performance is unchanged, it is clear that these sites play no significant part in the catalysis over these materials. The active site is therefore located on the planar {100} surfaces. The most selective magnesium oxide catalyst was prepared by thermal decomposition of magnesium hydroxycarbonate and exposed a greater proportion of higher index mean crystal planes, e.g., {l11}, than the less selective forms of magnesium oxide. It is suggested that an additional selective site is present in this form of magnesium oxide, with density related to morphology but not directly to surface area, perhaps a “bottom step” site. The morphology/performance relationship has also been examined for lithium-doped magnesium oxide catalysts. In agreement with previous studies, addition of lithium causes a loss of surface area and of the morphology characteristic of the precursor magnesium oxide; the grain size also increases, grain boundary dislocations become evident, and dislocations are also observed in the bulk of the grains. These are immobile and of the type 1 2 〉110〈 , pinned by the presence of lithium ions. The emergence of a dislocation at the surface of the crystallite provides a locus for [Li +O −] centres, thought to be the active site in methyl radical generation in methane coupling. Similar dislocations are observed in Au/MgO catalysts, which are much less selective to C 2 hydrocarbons than is pure MgO.

Rags

Rags by Wanda Haynes Fries In the heat of the afternoon, Mamaw took away the cane-bottomed chairs that propped the doors to the rag store open, and they sat together on the wide front porch, hoping for a breeze from the river. In the shade at the far end, Grampa moved the green and white steel glider back and forth, rocking himself to sleep. The metal skreaked, but softly, like crickets from far off. Mamaw wore a printed cotton dress the color of the azaleas that grew by the broken bottom porch step, and Alice Ann sat on the top step next to Mamaw, the girl's face dark and flat as a spatter of mud. Alice Ann's mother had died two years ago when she was seven, 49 and since then she had carried herself more like an old woman than a child, her head drooping forward, her shoulders rounded and hunched. She was so skinny that down the middle of her thin white tee shirt, her backbone stood up like a saw blade. Her dark hair grew m a widow's peak on her wide pale forehead. She had the kind of eyes that looked as though she'd seen it all and was not impressed. She was staying with Mamaw and Grampa while her daddy was up north somewhere looking for a job. Mamaw squinted into the sunlight. "What?" asked Alice Ann, because Mamaw had her headtilted as though she was listening for something. "Sounds like a baby crying. Far off." Alice Ann leaned forward a little, to see if she could hear it. Mamaw often heard things before anybody else did-the hiss of a snake in the blackberry briars, the rumble of thunder from a storm a day away. Sometimes Grampa went behind the store and made noises just to fool her, trying to make her think the clothes in the store were full of crickets or that there was a whippoorwill calling in the middle ofthe day. But being smarter than Grampa, shehardly everfellfor it. When she did, he rode her about it for a week or two. At supper, when he stopped between bites, he'd make the sound again, laughing so hard sometimes that he choked on his food and had to call for her to bring him a glass of water. She always brought it, and Alice Ann would bend to feed a bite of her chicken to the cat rubbing her leg under the table, ashamed to see Mamaw, who had more sense in her little finger than Grampa had in his whole body, wait on him as though he were a hefpless little boy. Alice Ann, who had gone straight from the third grade to the fifth, was smarter than either one of them. She would die before she'd let anybody treat her that way. Mamaw picked up Sammy, her grandbaby , who lay on the porch next to her and Alice Ann. She lifted his hands, and he laughed, spit bubbling down his chin. His head was covered with sparse white hair that was fine and wispy like chicken feathers. He had eyes as dark and round as blueberries. He had started trying to sit up early, but his big head weighed him down. His mother took him to a doctor, but he told her not to worry. All babies started out this way and therestofSammy would grow in time to match the size of his head. But even now, when the baby was learning to walk, he had to roll over first from the flat of his back and use his arms for leverage. Mamaw rolled up the baby's undershirt andbent to blow on his belly. "I got you," she said, and Sammy kicked his feet and laughed. The wind caught the tail of her red dress, and she pulled it tight to cover the tops ofthe thick support stockings she wore rolled to the base of her knees. She leaned against the gray post behind her, narrowing hereyes as she studied the heat that hung between the store and the river. "It's Sammyyouheard,"AliceAnn said. She had listened for five whole minutes...

Concerning the Impressiveness of the Parthenon

Archaeologists interested in the Parthenon have often noted that the west fagade was built at a higher level than that of the east fagade. Penrose especially discusses the difference in levels.' He states that the reason for the difference was an economic one, because the foundations of the Older Parthenon, upon which the Parthenon of Pericles' time rested, were also higher at the west than at the east, and that, therefore, the old foundations, to receive the stylobate of the Parthenon, needed to be shaved down a minimum, at a considerable saving in labor. Penrose's economic point is well taken, but there is another advantage which he does not mention, and which, on account of its aesthetic importance, the writer would like to explain. But, before doing so, he wishes to make a few relevant remarks about the Older Parthenon. The foundations of the Older Parthenon rest upon the rock of the Acropolis so that there was no economic need as in the case of the Parthenon to raise the west fagade of the temple. The west fagade was elevated intentionally, the reason being for an advantage which was common to both temples. If we sight along the upper courses of the south foundations of the Older Parthenon, we will see that the top two courses are cut to a beautiful upward curve,2 which also appears, of course, in the bottom step of that temple. As the Parthenon has both the raising of the west fagade and the upward curve of the stylobate, Ictinus, when he incorporated these two features in the Parthenon, was but doing what had been intended for the Older Parthenon. The difference in level of the east and west fa?ades of the Parthenon was, as suggested above, intentional. Let us demonstrate this. It is hard to