NMR Studies of Hydrogen-Hydrate Clathrates and Large Band-Gap Amorphous Semiconductors and Development of Ultra-High Sensitivity NMR
氢水合物和大带隙非晶半导体的核磁共振研究及超高灵敏度核磁共振的发展
基本信息
- 批准号:0400512
- 负责人:
- 金额:$ 36万
- 依托单位:
- 依托单位国家:美国
- 项目类别:Continuing Grant
- 财政年份:2004
- 资助国家:美国
- 起止时间:2004-05-01 至 2008-04-30
- 项目状态:已结题
- 来源:
- 关键词:
项目摘要
NMR studies on hydrogen-hydrate clathrate structures and amorphous Ga(Al)N films are proposed to understand their structural details. The clathrate compound is important from hydrogen storage aspects and amorphous nitrides are useful electronic materials. Hydrogen and deuterium NMR will be used to study a newly discovered clathrate compound, which forms at only 2000 bars and has hydrogen (or deuterium) held in two different size cages of an water-ice framework. The 0.45:1 hydrogen:water ratio results in a 5 weight-% payload of hydrogen and so is relevant to hydrogen-storage technologies. The clathrate offers a clean environment in which to study small numbers of interacting H2 molecules: two in the small cages and four in the large cages. In particular, orientational freezing at low temperatures and ortho-para conversion are expected to be profoundly different than for bulk solid H2 and will be examined by NMR. At higher temperatures, the rate of H2-exchange between the small and large cages will be determined from NMR line-narrowing. Preliminary experiments will investigate hydrogen and deuterium dissolved in ordinary bulk water-ice (phase Ih). An eventual goal is to understand the 1:1 hydrogen:water cII clathrate which forms at higher pressures. The predicted electronic structure of the amorphous phase of wide-band-gap GaN and AlGaN alloys indicates a defect-free energy band gap and more delocalized band tails than that found in other III-V amorphous semiconductors. These features make amorphous Ga(Al)N potentially more useful as electronic materials. The proposed research will use nuclear magnetic resonance to study the local amorphous structure in GaN and AlGaN thin films grown by MBE. These experiments combined with other optoelectronic measurements will be used to determine the local atomic and electronic structure for comparison with theoretical predictions. The research will produce broader impacts, through the training of graduate students. They will learn magnetic resonance, laboratory high-pressure techniques, and semiconductor fabrication and characterization. This broad base of knowledge and experience will strengthen the scientific workforce.Hydrogen has been proposed as an ideal fuel for automobiles and trucks, burning with essentially zero pollution and yielding higher efficiency in fuel cells. But the on-board storage of hydrogen remains an unsolved problem. Each of the technologies being considered now, has one or more substantial drawbacks indicated in parentheses: high-pressure gas cylinders (safety), liquid hydrogen (impractical temperature of -253 C), and metal-hydrides (weight and expense). The proposed work investigates a newly discovered compound of ice and hydrogen, in which ice molecules form cages around 2 or 4 hydrogen molecules. While this compound itself is not appropriate for practical hydrogen storage, it may point towards more practical systems. The present research will use nuclear magnetic resonance to study the rotational motions of the caged hydrogen molecules and how they diffuse from cage to cage. High-density optical storage of data requires short-wavelength light (blue or ultraviolet), because the smallest focal spot is about a wavelength in diameter (diffraction limit). Currently, most semiconducting sources and detectors of blue light use thin-film crystals of nitride materials (e.g., gallium nitride). However, the manufacture of such crystalline films is expensive and limited to devices of a few inches (not suitable for large displays). Recent calculations have indicated that amorphous (non-crystalline) nitrides may provide suitable performance as blue emitters and detectors; the growth methods for amorphous materials are not size limited and are comparatively inexpensive. We will prepare amorphous nitride materials and characterize their structures with nuclear magnetic resonance methods as well as electrical and optical techniques. The research will provide training to graduate students, crossing the traditional discipline boundaries. Real-world problems (such as hydrogen storage and nitride semiconductors) require a combination of diverse skills and knowledge. In the proposed research, students will learn high-pressure techniques, nuclear magnetic resonance (the basis for all magnetic resonance imaging, MRI), semiconductor physics, and semiconductor growth.
氢水合物笼形结构和非晶Ga(Al)N薄膜的核磁共振研究提出了了解他们的结构细节。 笼形化合物在储氢方面是重要的,非晶氮化物是有用的电子材料。氢和氘核磁共振将用于研究一种新发现的笼形化合物,这种化合物在2000巴的压力下形成,氢(或氘)被保持在水冰框架的两个不同大小的笼子里。 0.45:1的氢:水比率导致5重量%的氢有效载荷,因此与储氢技术相关。 笼形物提供了一个干净的环境,在其中研究少量的相互作用的H2分子:两个在小笼和四个在大笼。 特别是,在低温下的取向冻结和邻-对位转化预计将大大不同于散装固体H2,并将通过NMR检查。 在较高的温度下,小笼和大笼之间的H2-交换速率将由NMR谱线变窄来确定。 初步实验将研究氢和氘溶解在普通散装水冰(阶段Ih)。 最终的目标是了解在较高压力下形成的1:1氢:水cII包合物。 预测的宽带隙GaN和AlGaN合金的非晶相的电子结构表明无缺陷的能带隙和更多的离域带尾比在其他III-V族非晶半导体中发现的。这些特征使得非晶Ga(Al)N作为电子材料潜在地更有用。 本研究将利用核磁共振技术来研究分子束外延生长的氮化镓及氮化铝氮化镓薄膜的局部非晶结构。 这些实验与其他光电测量相结合,将用于确定局部原子和电子结构,以与理论预测进行比较。通过对研究生的培训,这项研究将产生更广泛的影响。 他们将学习磁共振,实验室高压技术,半导体制造和表征。 氢被认为是汽车和卡车的理想燃料,燃烧时基本上没有污染,燃料电池的效率也更高。 但是,氢的车载存储仍然是一个未解决的问题。 现在考虑的每一种技术都有一个或多个实质性的缺点,如括号中所示:高压气瓶(安全),液氢(不切实际的-253 ℃温度)和金属腐蚀(重量和费用)。 这项拟议中的工作研究了一种新发现的冰和氢的化合物,其中冰分子在2或4个氢分子周围形成笼子。 虽然这种化合物本身不适合实际的储氢,但它可能指向更实用的系统。 目前的研究将使用核磁共振来研究笼中氢分子的旋转运动以及它们如何从笼到笼扩散。 数据的高密度光学存储需要短波长的光(蓝色或紫外线),因为最小的焦点直径约为波长(衍射极限)。 目前,蓝光的大多数半导体源和检测器使用氮化物材料的薄膜晶体(例如,氮化镓)。 然而,这种结晶膜的制造是昂贵的并且限于几英寸的装置(不适合于大型显示器)。 最近的计算表明,无定形(非结晶)氮化物可以提供合适的性能作为蓝色发射器和检测器;无定形材料的生长方法没有尺寸限制,并且相对便宜。 我们将制备非晶氮化物材料,并用核磁共振方法以及电学和光学技术表征其结构。这项研究将为研究生提供培训,跨越传统的学科界限。 现实世界的问题(如氢存储和氮化物半导体)需要各种技能和知识的结合。 在拟议的研究中,学生将学习高压技术,核磁共振(所有磁共振成像的基础,MRI),半导体物理和半导体生长。
项目成果
期刊论文数量(0)
专著数量(0)
科研奖励数量(0)
会议论文数量(0)
专利数量(0)
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Mark Conradi其他文献
Mark Conradi的其他文献
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{{ truncateString('Mark Conradi', 18)}}的其他基金
Magnetic Resonance of Metal Hydrides and Transfer of Laser-Generated Polarization
金属氢化物的磁共振和激光产生的偏振的转移
- 批准号:
9987888 - 财政年份:2000
- 资助金额:
$ 36万 - 项目类别:
Continuing Grant
Magnetic Resonance: Metal Hydrides and Innovative Techniques
磁共振:金属氢化物和创新技术
- 批准号:
9705080 - 财政年份:1997
- 资助金额:
$ 36万 - 项目类别:
Continuing Grant
Magnetic Resonance of Solids at Extreme or Unusual Conditions
极端或异常条件下固体的磁共振
- 批准号:
9024502 - 财政年份:1991
- 资助金额:
$ 36万 - 项目类别:
Continuing Grant
Orientational Glasses and High Pressure Phases Studied by NMR
通过核磁共振研究取向玻璃和高压相
- 批准号:
8702847 - 财政年份:1987
- 资助金额:
$ 36万 - 项目类别:
Continuing Grant
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