X-ray diffraction(20120412)
X射线衍射分析
X射线的产生及性质
X射线的性质
X射线与可见光一样，具有电磁波性质。 X射线波长范围：1×10-3～10nm之间。 用于测定晶体结构的X射线，波长为0.05～0.25nm，
K Dhkl Cos
Dhkl：垂直于hkl晶面方向的晶粒尺寸（nm）。 ：（2X）射：线晶波粒长细（化n引m起）的。衍射峰的宽化（弧度）。 ：衍射角（度）。 K：常数，若取半高宽，K=0.94
一.注意事项
公式中的是由晶粒大小引起的衍射峰加宽。 实验测得的衍射峰半高宽 1，除了晶粒加 宽，还有仪器造成的加宽以及K1、K2衍 射迭加造成的加宽，需经过双线校正和仪 器因子校正才能得到晶粒加宽
氟化钾的标准卡片
三．卡片索引 为了从几万张卡片中快速找到所需卡片，必
须使用索引。索引有二种：
1.Hanawalt数字索引 每条的格式为：规格、8条最强线的d值和相对强 度、分子式、卡片号。 规格表示该卡片的可靠性符号，d值的下标代表 相对强度，八个d值中的前三个是2<90的三条最 强线的d值。 数字索引的编排顺序：先按八个d值中的第一个d 值的大小范围分组，在同一组中，按第二个d值 由大到小顺序往下排，第二个d值相同，按第三 个d值由大到小排列，依次类推。
晶体结构
晶体的定义
由原子或分子在三维空间周期排列而成 的固体物质
一．晶体结构的特征 晶体中原子或分子的排列具有三维空间的周
期性，隔一定的距离重复出现。
二．晶胞 按照晶体内部结构的周期性，划分出一个个
X-Ray环保测试仪软件建立标准检量线
※ X-ray軟體功能測量作業指導書
項次 一 項目內容 步驟 塊體分析(檢量 » 點選應用選單 線)的標准物質 (標准曲線)建立 作業內容 ，彈出如圖A的視窗：
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圖A
1
» 點選第4項“塊體分析(檢量線)＂，軟體自動進入檢量線操作畫面。 ＊ 在軟體標題欄可以看到如圖B： 2
» 用標點選中“1＂，如圖F畫面
6
圖F
第 2 頁，共 3 頁
文件名稱 建立標准檢量線檔說明 制作日期 2006/2/15 版本號 Ver1.0 制作人 胡國宋
※ X-ray軟體功能測量作業指導書
項次 項目內容 塊體分析(檢量 線)的標准物質 (標准曲線)建立 步驟 作業內容
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» 把塑料標准品(一個盒子裝四顆標准片)的第一顆(RM1)or(PE BLK)，放入樣 品台(打開影像視窗觀察放置位置)，合上蓋子(蓋好時會聽到合蓋聲：卡)。 7 » 按工具列開始按鈕 即可開始測量。
» 待測量完成後，點選圖F視窗的“2＂。 » 把塑料標准品(一個盒子裝四顆標准片)的第二顆(RM2)or(PE 100)，放入樣 8 品台(打開影像視窗觀察放置位置)，合上蓋子(蓋好時會聽到合蓋聲：卡)。 » 按工具列開始按鈕 即可開始測量。
» 待測量完成後，點選圖F視窗的“3＂。 » 把塑料標准品(一個盒子裝四顆標准片)的第三顆(RM3)or(PVC BLK)，放入樣 9 品台(打開影像視窗觀察放置位置)，合上蓋子(蓋好時會聽到合蓋聲：卡)。 » 按工具列開始按鈕 即可開始測量。
※ X-ray軟體功能測量作業Fra bibliotek導書項次 一 項目內容 塊體分析(檢量 線)的標准物質 (標准曲線)建立 步驟 作業內容
基因组学
Chapter 1. The Human Genome1. The Human GenomeLearning outcomesWhen you have read Chapter 1, you should be able to:•Describe the two experiments that led molecular biologists to conclude that genes are made of DNA, and state the limitations of each experiment•Give a detailed description of the structure of a polynucleotide and summarize the chemical differences between DNA and RNA•Discuss the evidence that Watson and Crick used to deduce the double helix structure of DNA and list the key features of this structure•Explain why the DNA double helix has structural flexibility•Describe in outline the content of the human nuclear genome•Draw the structure of an ‘average' human gene•Categorize the human gene catalog into different functional classes•Distinguish between conventional and processed pseudogenes and other types of evolutionary relic•Give specific examples of the repetitive DNA content of the human genome•Give an outline description of the structure and organization of the human mitochondrial genome•Discuss the importance of the Human Genome ProjectLife as we know it is specified by the genomes of the myriad organisms with which we share the planet. Every organism possesses a genome that contains the biological information needed to construct and maintain a living example of that organism. Most genomes, including the human genome and those of all other cellular life forms, are made of DNA (deoxyribonucleic acid) but a few viruses have RNA (ribonucleic acid) genomes. DNA and RNA are polymeric molecules made up of chains of monomeric subunits called nucleotides.The human genome, which is typical of the genomes of all multicellular animals, consists of two distinct parts (Figure 1.1):•The nuclear genome comprises approximately 3 200 000 000 nucleotides of DNA, divided into 24 linear molecules, the shortest 50 000 000 nucleotides in length and the longest 260 000 000 nucleotides, each contained in a different chromosome. These 24 chromosomes consist of 22 autosomes and the two sex chromosomes, X and Y.•The mitochondrial genome is a circular DNA molecule of 16 569 nucleotides, multiple copies of which are located in the energy-generating organelles called mitochondria. Each of the approximately 1013 cells in the adult human body has its own copy or copies of the genome, the only exceptions being those few cell types, such as red blood cells, that lack a nucleus in their fully differentiated state. The vast majority of cells are diploid and so have two copies of each autosome, plus two sex chromosomes, XX for females or XY for males - 46 chromosomes in all. These are called somatic cells, in contrast to sex cells or gametes, which are haploid and have just 23 chromosomes, comprising one of each autosome and one sex chromosome. Both types of cell have about 8000 copies of the mitochondrial genome, 10 or so in each mitochondrion.Figure 1.1. The nuclear and mitochondrial components of the human genome. For more details on the anatomy of the human genome, see Section 1.2.This book is about genomes. It explains what genomes are (Part 1), how they are studied (Part 2), how they function (Part 3), and how they replicate and evolve (Part 4). We begin our journey with our own genome, which is quite naturally the one that interests us the most. Later in this chapter we will examine how the human genome is constructed, some of this information dating from the old days when biologists studied genes rather than genomes, but much of it revealed only since the Human Genome Project was completed in the first year of the new millennium. First, however, we must understand the structure of DNA.1.1. DNADNA was discovered in 1869 by Johann Friedrich Miescher, a Swiss biochemist working in Tübingen, Germany. The first extracts that Miescher made from human white blood cells were crude mixtures of DNA and chromosomal proteins, but the following year he moved to Basel, Switzerland (where the research institute named after him is now located) and prepared a pure sample of nucleic acid from salmon sperm. Miescher's chemical tests showed that DNA is acidic and rich in phosphorus, and also suggested that the individual molecules are very large, although it was not until the 1930s when biophysical techniques were applied to DNA that the huge lengths of the polymeric chains were fully appreciated.Three years before Miescher discovered DNA, Gregor Mendel had published the results of his breeding experiments with pea plants, carried out in the monastery gardens at Brno, a centraleuropean city some 550 km from Tübingen in what is now the Czech Republic. Mendel's paper in the Proceedings of the Society of Natural Sciences in Brno describes his hypothesis that inheritance is controlled by unit factors, the entities that geneticists today call genes. It is very unlikely that Miescher and Mendel were aware of each other's work, and if either of them had happened to read about the other's discoveries then they certainly would not have made any connection between DNA and genes. To make such a connection - to infer that genes are made of DNA - would have been quite illogical in the late 19th century or indeed for many decades afterwards. The precise biological function of DNA was not known, and the supposition that it was a store of cellular phosphorus seemed entirely reasonable at the time. The chemical nature of genes was equally unknown, and indeed was an irrelevance for most geneticists, who in the years immediately after 1900, when Mendel's work was rediscovered, were able to make remarkable advances in understanding heredity without worrying about what genes were actually made of.It was not until the 1930s that scientists began to ask more searching questions about genes. In 1944, Erwin Schrödinger, more famous for the wave equation which still terrifies many biology students taking introductory courses in physical chemistry, published a book entitled What is Life?, which encapsulated a variety of issues that were being discussed not only by geneticists but also by physicists such as Niels Bohr and Max Delbrück. These scientists were the first molecular biologists and the first to suggest that ‘life' could be explained in molecular terms; our current knowledge of how the genome functions stems directly from their pioneering work. The starting point for the new molecular biology was to discover what genes are made of.1.1.1. Genes are made of DNAHow could the molecular nature of the genetic material be determined? Back in 1903, WS Sutton had realized that the inheritance patterns of genes paralleled the behavior of chromosomes during cell division. This observation led to the proposal that genes are located in chromosomes and by the 1930s it was universally accepted that the chromosome theory was correct. Examination of cells by cytochemistry, after staining with dyes that bind specifically to just one type of biochemical, had shown that chromosomes are made of DNA and protein, in roughly equal amounts. Some biologists looked on the combination between the two (‘nucleoprotein') as the genetic material, but others argued differently. From today's perspective it can be difficult to understand why these arguments favored the notion that genes were made, not of DNA, but of protein. The explanation is that, at the time, many biochemists thought that all DNA molecules were the same, which meant that DNA did not have the immense variability that was one of the postulated features of the genetic material. Billions of different genes must exist and for each one to have its own individual activity, the genetic material must be able to take many different forms. If every DNA molecule were identical then DNA could not satisfy this requirement and so genes must be made of protein. This assumption made perfect sense because proteins were known, correctly, to be highly variable polymeric molecules, each one made up of a different combination of 20 chemically distinct amino-acid monomers (Section 3.3.1).The errors that had been made in understanding DNA structure lingered on until the late 1930s. Gradually, however, it was accepted that DNA, like protein, has immense variability. Could DNA therefore be the genetic material? The results of two experiments performed during the middle decades of the 20th century forced biologists to take this possibility seriously.Bacterial genes are made of DNAThe first molecular biologists realized that the most conclusive way to identify the chemical composition of genes would be to purify some and subject them to chemical analysis. But nothing like this had ever been attempted and it was not clear how it could be done. Ironically, the experiment was performed almost unwittingly by a group of scientists who did not look upon themselves as molecular biologists and who were not motivated by a curiosity to know what genes are made of. Instead, their objective was to find a better treatment for one of the most deadly diseases of the early 20th century, pneumonia.Before the discovery of antibiotics, pneumonia was mainly controlled by treating patients in the early stages of the disease with an antiserum prepared by injecting dead cells of the causative bacterium (now called Streptococcus pneumoniae) into an animal. In order to prepare more effective antisera, studies were made of the immunological properties of the bacterium. It was shown that there is a range of different types of S. pneumoniae, each characterized by the mixture of sugars contained in the thick capsule that surrounds the cell and elicits the immunological response (Figure 1.2A). In 1923, Frederick Griffith, a British medical officer, discovered that as well as the virulent strains, there were some types of S. pneumoniae that did not have a capsule and did not cause pneumonia. This discovery was not a huge surprise because other species of pathogenic bacteria were known to have avirulent, unencapsulated forms. However, 5 years later Griffith obtained some results that were totally unexpected (Griffith, 1928). He performed a series of experiments in which he injected mice with various mixtures of bacteria (Figure 1.2B). He showed that, as anticipated, mice injected with virulent S. pneumoniae bacteria developed pneumonia and died, whereas those injected with an avirulent type remained healthy. What he did not anticipate, however, was what would happen when mice were injected with a mixture made up of live avirulent bacteria along with some virulent cells that had been killed by heat treatment. The only live bacteria were the harmless ones, so surely the mice would remain healthy? Not so: the mice died. Griffith carried out biopsies of these dead mice and discovered that their respiratory tracts contained virulent bacteria, which were always of the same immunological type as the strain that had been killed by heat treatment before injection. Somehow the living harmless bacteria had acquired the ability to make the capsule sugars of the dead bacteria. This process - the conversion of living harmless bacteria into virulent cells - was called transformation. Although not recognized as such by Griffith, the transforming principle - the component of the dead cells that conferred on the live cells the ability to make the capsular sugars - was genetic material.Figure 1.2. Griffith's experiments with virulent and avirulent Streptococcus pneumoniae bacteria. (A) Representation of a S. pneumoniae bacterium. A serotype is a bacterial type with distinctive immunological properties, conferred in this case by the combination of sugars present in the capsule. Avirulent types have no capsule. (B) The experiments which showed that a component of heat-killed bacteria can transform living avirulent bacteria into virulent cells. Griffith showed that the avirulent bacteria were always transformed into the same serotype as the dead cells. In other words, the living bacteria acquired the genes specifying synthesis of the capsule of the dead cells.Oswald Avery, together with his colleagues Colin MacLeod and Maclyn McCarty, of Columbia University, New York, set out to determine what the transforming principle was made of. The experiments took a long time to carry out and were not completed until 1944 (Avery et al., 1944). But the results were conclusive: the transforming principle was DNA. The transforming principle behaved in exactly the same way as DNA when subjected to various biophysical tests, it was inactivated by enzymes that degraded DNA, and it was not affected by enzymes that attacked protein or any other type of biochemical (Figure 1.3).Figure 1.3. The transforming principle is DNA. Avery and his colleagues showed that the transforming principle is unaffected by treatment with a protease or a ribonuclease, but is inactivated by treatment with a deoxyribonuclease.Avery's experiments were meticulous but, because of several complicating factors, they did not immediately lead to acceptance of DNA as the genetic material. It was not clear in the minds of all microbiologists that transformation really was a genetic phenomenon, and few geneticists really understood the system well enough to be able to evaluate Avery's work. There was also some doubt about the veracity of the experiments. In particular, there were worries about the specificity of the deoxyribonuclease enzyme that he used to inactivate the transforming principle. This result, a central part of the evidence for the transforming principle being DNA, would be invalid if, as seemed possible, the enzyme contained trace amounts of a contaminating protease and hence was also able to degrade protein. These uncertainties meantthat a second experiment was needed to provide moreinformation on the chemical nature of the geneticmaterial.Virus genes are made of DNAFigure 1.4. Bacteriophages are viruses that infect bacteria. (A) The structure of a head-and-tail bacteriophage such as T2. The DNA genome of the phage is contained in the head part of the protein capsid. (B) The infection cycle. After injection into an Escherichia coli bacterium, the T2phage genome directs synthesis of new phages. For T2, the infection cycle takes about 20 minutes at 37 °C and ends with lysis of the cell and release of 250–300 new phages. This is the lytic infection cycle. Some phages, such as λ, can also follow a lysogenic infection cycle, in which the phage genome becomes inserted into the bacterial chromosome and remains there, in quiescent form, for several generations of the bacterium (Section 4.2.1).The second experiment was carried out by two bona fide molecular biologists, Alfred Hershey and Martha Chase, at Cold Spring Harbor, New York, in 1952 (Hershey and Chase, 1952). Like the work on the transforming principle, the Hershey-Chase experiment was not done specifically to determine the chemical nature of the gene. Hershey and Chase were two of several biologists who were studying the infection cycle of bacteriophages (or ‘phages') - viruses that infect bacteria. Phages are relatively simple structures made of just DNA and protein, with the DNA contained inside the phage, surrounded by a protein capsid (Figure 1.4A). To replicate, a phage must enter a bacterial cell and subvert the bacterial enzymes into expressing the information contained in the phage genes, so that the bacterium synthesizes new phages. Once replication is complete, the new phages leave the bacterium, possibly causing its death as they do so, and move on to infect new cells (Figure 1.4B). The objective of Hershey and Chase's experiment was to determine if the entire phage particle entered the bacterium at the start of the infection cycle, or if part of the phage stayed outside. If only one component of the phage - the DNA or the protein - entered the cell then that component must be the genetic material.Figure 1.5. The Hershey-Chaseexperiment. The bacteriophages werelabeled with 32P and 35S. A few minutesafter infection, the culture was agitated todetach the empty phage capsids from thecell surface. The culture was thencentrifuged and the radioactive content ofthe bacterial pellet determined. This pelletcontained most of 32P-labeled componentof the phages (the DNA) but only 20% ofthe 35S-labeled material (the phageprotein). In a second experiment, Hersheyand Chase showed that new phagesproduced at the end of an interruptedinfection cycle contained less than 1% ofthe protein from the parent phages.Their experimental strategy was based onthe use of radioactive labels, which hadrecently been introduced into biology.DNA contains phosphorus, which is absent from protein, so DNA can be labeled specifically with the radioactive phosphorus isotope, 32P. Protein, on the other hand, contains sulfur, which is absent from DNA, and so protein can be labeled with 35S. Hershey and Chase were not the first to useradiolabeling to try to determine which part of the phage entered the cell, but previous experiments by James Watson, Ole Maaløe and others had been inconclusive because of the difficulty in distinguishing between phage material that was actually inside a bacterium and a component that did not enter the cell but remained attached to the outer cell surface. To get round this difficulty, Hershey and Chase made an important modification to the previous experiments. They infected Escherichia coli bacteria with radiolabeled T2 phages but, rather than allowing the infection process to go to completion, they left the culture for just a few minutes and then agitated it in a blender. The idea was that the blending would detach the phage material from the surface of the bacteria, enabling this component to be separated from the material inside the cells by centrifuging at a speed that collected the relatively heavy bacteria as a pellet at the bottom of the tube but left the detached material in suspension (Figure 1.5). After centrifugation, Hershey and Chase examined the bacterial pellet and found that it contained 70% of the 32P-labeled component of the phages (the DNA) but only 20% of the 35S-labeled material (the phage protein). In a parallel experiment, the bacteria were left for 20 minutes, long enough for the infection cycle to reach completion. With T2 phage, the cycle ends with the bacteria bursting open and releasing new phages into the supernatant. These new phages contained almost half the DNA from the original phages, but less than 1% of the protein.Hershey and Chase's results suggested that DNA was the major component of the infecting phages that entered the bacterial cell and, similarly, was the major, or perhaps only, component to be passed on to the progeny phages. These observations lent support to the view that DNA is the genetic material, but were they conclusive? Not according to Hershey and Chase (1952) who wrote ‘Our experiments show clearly that a physical separation of phage T2 into genetic and non-genetic parts is possible . . . . The chemical identification of the genetic part must wait, however, until some questions . . . have been answered.' Even if the experiment had provided compelling evidence that the genetic material of phages was DNA, it would have been erroneous to extrapolate from these unusual life forms (which some biologists contend are not really ‘living') to cellular organisms. Indeed, we know that some phage genomes are made of RNA. The Hershey-Chase experiment is important, not because of what it tells us, but because it alerted biologists to the fact that DNA might be the genetic material and was therefore worth studying. It was this that influenced Watson and Crick to study DNA and, as we will see below, it was their discovery of the double helix structure, which solved the puzzling question of how genes can replicate, that really convinced the scientific world that genes are made of DNA.1.1.2. The structure of DNAThe names of James Watson and Francis Crick are so closely linked with DNA that it is easy to forget that, when they began their collaboration in Cambridge, England in October 1951, the detailed structure of the DNA polymer was already known. Their contribution was not to determine the structure of DNA per se, but to show that in living cells two DNA chains are intertwined to form the double helix. We will consider the two facets of DNA structure separately. Nucleotides and polynucleotidesDNA is a linear, unbranched polymer in which the monomeric subunits are four chemically distinct nucleotides that can be linked together in any order in chains hundreds, thousands or even millions of units in length. Each nucleotide in a DNA polymer is made up of three components (Figure 1.6):Figure 1.6. The structure of a nucleotide. (A) The general structure of a deoxyribonucleotide, the type of nucleotide found in DNA. (B) The four bases that occur in deoxyribonucleotides.1. 2′-deoxyribose, which is a pentose, a type of sugar composed of five carbon atoms. These five carbons are numbered 1′ (spoken as ‘one-prime'), 2′, etc. The name ‘2′-deoxyribose' indicates that this particular sugar is a derivative of ribose, one in which the hydroxyl (-OH) group attached to the 2′-carbon of ribose has been replaced by a hydrogen (-H) group.2. A nitrogenous base, one of cytosine, thymine (single-ring pyrimidines), adenine or guanine (double-ring purines). The base is attached to the 1′-carbon of the sugar by a β-N-glycosidic bond attached to nitrogen number 1 of the pyrimidine or number 9 of the purine.Figure 1.7. A short DNA polynucleotide showing the structure of the phosphodiester bond. Note that the two ends of the polynucleotide are chemically distinct.Figure 1.8. The polymerization reaction that results in synthesis of a DNA polynucleotide. Synthesis occurs in the 5′→3′ direction, with the new nucleotide being added to the 3′-carbon at the end of the existing polynucleotide. The β- and γ-phosphates of the nucleotide are removed as apyrophosphate molecule.3. A phosphate group, comprising one, two or three linked phosphate units attached to the 5′-carbon of the sugar. The phosphates are designated α, β and γ, with the α-phosphate being the one directly attached to the sugar.A molecule made up of just the sugar and base is called a nucleoside; addition of the phosphates converts this to a nucleotide. Although cells contain nucleotides with one, two or three phosphate groups, only the nucleoside triphosphates act as substrates for DNA synthesis. The full chemical names of the four nucleotides that polymerize to make DNA are:•2′-deoxyadenosine 5′-triphosphate•2′-deoxycytidine 5′-triphosphate•2′-deoxyguanosine 5′-triphosphate•2′-deoxythymidine 5′-triphosphateThe abbreviations of these four nucleotides are dATP, dCTP, dGTP and dTTP, respectively, or, when referring to a DNA sequence, A, C, G and T, respectively.In a polynucleotide, individual nucleotides are linked together by phosphodiester bonds between their 5′- and 3′-carbons (Figure 1.7). From the structure of this linkage we can see that the polymerization reaction (Figure 1.8) involves removal of the two outer phosphates (the β- and γ-phosphates) from one nucleotide and replacement of the hydroxyl group attached to the 3′-carbon of the second nucleotide. Note that the two ends of the polynucleotide are chemically distinct, one having an unreacted triphosphate group attached to the 5′-carbon (the 5′ or 5′-P terminus) and the other having an unreacted hydroxyl attached to the 3′-carbon (the 3′ or 3′-OH terminus). This means that the polynucleotide has a chemical direction, expressed as either 5′→3′(down in Figure 1.8) or 3′→5′ (up in Figure 1.8). An important consequence of the polarity of the phosphodiester bond is that the chemical reaction needed to extend a DNA polymer in the 5′→3′ direction is different to that needed to make a 3′→5′ extension. All natural DNA polymerase enzymes are only able to carry out 5′→3′ synthesis, which adds significant complications to the process by which double-stranded DNA is replicated (Section 13.2). The same limitation applies to RNA polymerases, the enzymes which make RNA copies of DNA molecules (Section 3.2.2).RNAFigure 1.9. The chemical differences betweenDNA and RNA. (A) RNA contains ribonucleotides,in which the sugar is ribose rather than2′-deoxyribose. The difference is that a hydroxylgroup rather than hydrogen atom is attached to the2′-carbon. (B) RNA contains the pyrimidine calleduracil instead of thymine.Although our attention is firmly on DNA, thestructure of RNA is so similar to that of DNA that itmakes sense to introduce it here. RNA is also apolynucleotide but with two differences compared with DNA (Figure 1.9). First, the sugar in an RNA nucleotide is ribose and, second, RNA contains uracil instead of thymine. The four nucleotide substrates for synthesis of RNA are therefore:•adenosine 5′-triphosphate•cytidine 5′-triphosphate•guanosine 5′-triphosphate•uridine 5′-triphosphatewhich are abbreviated to ATP, CTP, GTP and UTP, or A, C, G and U, respectively.As with DNA, RNA polynucleotides contain 3′–5′ phosphodiester bonds, but these phosphodiester bonds are less stable than those in a DNA polynucleotide because of the indirect effect of the hydroxyl group at the 2′-position of the sugar. This may be one reason why the biological functions of RNA do not require the polynucleotide to be more than a few thousand nucleotides in length, at most. There are no RNA counterparts of the million-unit sized DNA molecules found in human chromosomes.1.1.3. The double helixIn the years before 1950, various lines of evidence had shown that cellular DNA molecules are comprised of two or more polynucleotides assembled together in some way. The possibility that unraveling the nature of this assembly might provide insights into how genes work prompted Watson and Crick, among others, to try to solve the structure. According to Watson in his book The Double Helix (see Further Reading), their work was a desperate race against the famous American biochemist, Linus Pauling (Section 3.3.1), who initially proposed an incorrect triple helix model, giving Watson and Crick the time they needed to complete the double helix structure (Watson and Crick, 1953). It is now difficult to separate fact from fiction, especially regarding the part played by Rosalind Franklin, whose X-ray diffraction studies provided the bulk of the experimental data in support of the double helix and who was herself very close to solving the structure. The one thing that is clear is that the double helix, discovered by Watson and Crick on Saturday 7 March 1953, was the single most important breakthrough in biology during the 20th century.The evidence that led to the double helixWatson and Crick used four types of information to deduce the double helix structure: •Biophysical data of various kinds. The water content of DNA fibers was particularly important because it enabled the density of the DNA in a fiber to be estimated. The number of strands in the helix and the spacing between the nucleotides had to be compatible with the fiber density. Pauling's triple helix model was based on an incorrect density measurement which suggested that the DNA molecule was more closely packed than it actually is.•X-ray diffraction patterns(Section 9.1.3), most of which were produced by Rosalind Franklin of Kings College, London, and which revealed the helical nature of the structure and indicated some of the key dimensions within the helix.•The base ratios, which had been discovered by Erwin Chargaff of Columbia University, New York. Chargaff carried out a lengthy series of chromatographic studies of DNA samples from various sources and showed that, although the values are different in different organisms, the amount of adenine is always the same as the amount of thymine,。
第二章 晶态和非晶态材料的特性
二、晶体点群和晶体的物理性质 1、晶体学点群的分类 2、晶体的点群和晶体的物理性质
储氢材料
2.4 液晶材料
目前作为一种新型的显示材料，与集成电路 一起在图像显示技术上开创了新的方法，在 电光学、热化学、分子光谱等许多领域中有 广泛的用途。
液晶属于晶体?非晶体?
根据固体物质的组成原子(分 子、离子)在空间排列是否长 程有序，可将固体物质分为 晶态和非晶态。
液晶——像晶体的液体
第四态
后来,德国物理学家Otto ·Leimann把处于“中间
地带”的浑浊液体叫做液晶，简称为
“LC”(liquid crystal)。在这以后用它制成的液
晶显示器件被称为LCD。液晶好比是既不象马,
又不象驴的骡子,所以有人称它为“有机界的骡
子”.
结晶状的固体
各向同性的液体
中间相
塑性晶体液态晶体源自圆球状长条状、圆盘状
非晶体的各种性质均具有均匀性, 但与晶体的均匀性的 起源并不相同, 前者是等同晶胞在空间按同一方式重复 排列的结果, 而后者则是质点的杂乱无章排列所致. 所 以二者有实质不同的均匀性。
(1) （2）各向异性
晶体的导热、导电、光的透射、折射、偏振、 压电性、硬度等性质常因晶体取向不同而异， 叫做各向异性。
（1）热致液晶
压致性液晶 流致性液晶
热致性液晶是依靠温度的变化，在某一温度范围形
成液晶态物质。
作为显示技术应用的液晶都是热致液晶。
第三章 X-射线衍射资料
连续X射线谱的总强度（能量）
I连续 I ()d KiZV 2 min
I
管流i3 >i2> i1
i3 i2 i1
不同阳极
I
W Ag Mo
λ
λ
影响因素
❖ 管电压和靶材一定，提 高管电流，各波长X射线 强度都提高，但λmin和 λmax不变
➢常用的X射线波长：0.5～2.5Å ➢波长太长： 样品和空气对X射线吸收太大 ➢波长太短：衍射线过分集中线传播，在穿过电场和磁场时不发生偏转； ❖ 有很强的穿透能力，能使底片感光，使荧光物质发光，使
气体电离； ❖ X光可为重元素所吸收，故可用于医学造影； ❖ X射线对动物有机体（其中包括对人体）能产生巨大的生理
I
续
X 射 线
定波长的谱线所组成。
特征X射线只取决于阳 极材料，与X射线管的工作 状态无关。
λmin
特征X射线 λ
连续X射线光谱
•连续光谱又称为“白色”X射 线，包含了从短波极限λmin 开始的全部波长，是各种波长 辐射的混合体。强度在λmax 处有一最大值。
•λmin它是由光子一次碰撞就 耗尽能量所产生的X射线。它 只与管电压有关，不受其它因 素的影响。
波动性：在晶体作衍射光栅 观察到的X射线的衍射现象
粒子性：与物质相互作用时 交换能量。如光电效应；二 次电子等。
❖ 硬X射线：波长较短，能量较高 晶体衍射（0.5~2.5Å ） 无损探伤 （0.05~1Å ）
❖ 软X射线：波长较长，能量较低 医学透视
在物质的微观结构中，原子和分子的距离（1 ～ 10Å左右）正好 落在X射线的波长范围内（10－2到102Å ），所以物质（特别是晶 体）对X射线的散射和衍射能够传递极为丰富的微观结构信息。
Thickness effect on electrical properties of PZT thick films embedded with ZnO nanowhiskers
Thickness effect on electrical properties of Pb(Zr 0.52Ti 0.48)O 3thick films embedded with ZnO nanowhiskers prepared by a hybrid sol –gel routeQ.L.Zhao a ,1,M.S.Cao a ,⁎,1,J.Yuan b ,1,R.Lu a ,D.W.Wang a ,D.Q.Zhang ca School of Materials Science and Engineering,Beijing Institute of Technology,Beijing 100081,Chinab The College of Information Engineering,Central University for Nationalities,Beijing 100081,China cCollege of Chemical Engineering,Qiqihar University,Qiqihar 161006,Chinaa b s t r a c ta r t i c l e i n f o Article history:Received 9October 2009Accepted 14December 2009Available online 23December 2009Keywords:FerroelectricsSol –gel preparation Thick filmsElectrical propertiesSilicon-based lead zirconate titanate thick films embedded with zinc oxide nanowhiskers (ZnO w –PZT)were prepared by a hybrid sol –gel route.ZnO w –PZT films with thickness from 1.5μm to 4μm are perovskite structure and have smooth surface without any cracks.As the thickness increases,the remanent polarization and dielectric constant increase,but the coercive field and tetragonality pared with PZT films,the ZnO w –PZT film has the close tetragonality and electrical properties which are different from those of bulk PZT-based ceramic doped with ZnO powder.The thickness dependences of the ferroelectric and dielectric properties are attributed to the relaxation of internal stress.©2009Elsevier B.V.All rights reserved.1.IntroductionLead zirconate titanate (Pb(Zr 1−x Ti x )O 3)thick films (N 1μm)are functional materials with superior ferroelectric,dielectric and piezoelectric properties and have potential applications in micro-electromechanical systems (MEMS).Sol –gel method is usually used to prepare PZT thick films because of its low sintering temperature,precisely controlling the homogeneity of the com-position,ease of use and low cost to fabricate large area films.Since the pores and cracks appear during annealing,organic polymer solvents [1–3]and non-ferroelectric/ferroelectric powder [4–6]have been added into the PZT sol to improve the electrical and mechanical properties.Recently,zinc oxide (ZnO)was added into piezoelectric ceramics and polymers as an additive to improve the fabrication process,electrical and mechanical properties [7–11].However,there are few studies on the ZnO nanowhiskers (ZnO w )addition in PZT thick films.Furthermore,ZnO nanowire has been proven to be a piezoelectric material [12],so it is expected to provide contributions to the piezoelectric property of PZT thick films.In this work,PZT thick films embedded with ZnO w (ZnO w –PZT)are prepared by a hybrid sol –gelroute,and the effects of thickness on electrical properties are investigated.2.ExperimentalIn brief,0.4mol/L PZT sol was prepared by lead acetate,zirconium nitrate,tetrabutyl titanate and polyvinylpyrrolidone (PVP,4.0×104in average molecular weight)with molar ratios 1.1:0.52:0.48:1.ZnO w were synthesized by combustion oxidation of pure zinc powders without any catalysts or additives [13].Then ZnO w slurry was prepared by dispersing ZnO w in ethanol with a concentration of 0.05mol/L.A PbTiO 3(PT)layer (∼100nm)was first deposited as a seed layer on a Pt/Cr/SiO 2/Si substrate by the sol –gel method.The PZT sol was spin-coated on the substrate with a spinning rate of 1600rpm for 1min and then the wet film was dried at 450°C for 30min.The ZnO w slurry was spin-coated on the PZT film with a spinning rate of 3000rpm for 1min,and dried at 100°C for 3min to evaporate the ethanol.Subsequently,the spin-coating procedure of PZT film was repeated until the desired thickness was achieved.The multilayer film was annealed at 700°C for 5min in air.In order to remove redundant ZnO w ,the thick film was dipped in dilute acetic acid solution for 30s.Finally,another PT layer (∼100nm)was deposited on the top of films to fill the pores and smooth the surface.X-ray diffraction (XRD)analyses were carried out with a Cu K αradiation (X'pert pro MPD,PANalytical).Electron micrographs were obtained by a scanning electron microscope (SEM,Hitachi S-3500N)and an energy dispersive spectrometer (EDS,Oxford Inca).TheMaterials Letters 64(2010)632–635⁎Corresponding author.Tel.:+8601068914062.E-mail addresses:caomaosheng@ (M.S.Cao),yuanjie4000@ (J.Yuan).1These authors contributed equally to thiswork.0167-577X/$–see front matter ©2009Elsevier B.V.All rights reserved.doi:10.1016/j.matlet.2009.12.028Contents lists available at ScienceDirectMaterials Lettersj o u r na l ho m e p a g e :w w w.e l s ev i e r.c o m /l o c a t e /m a t l e tferroelectric and dielectric properties were measured by a ferro-electric test system (Precision Premier II,Radiant Technologies,Inc.)and precision impedance analyzer (Agilent 4294A).3.Results and discussionFig.1shows the XRD of ZnO w ,PZT and ZnO w –PZT thick films with different thicknesses.It is seen that ZnO w is well indexed and exhibits a hexagonal wurtzite structure.All the PZT-based thick films show perovskite structures with the dominant peaks corresponding to (110)and (100).The cell parameters are calculated from XRD results by least-square method.It is indicated that all the films are tetragonal phase,the cell parameter c is smaller,and a is larger than that of bulk PZT (a =4.032,c =4.147[14]),pressive stresses exist in the c direction.With the increasing thickness of the ZnO w –PZT film,c decreases and a increases,which make the tetragonality (c /a )pared with PZT film,ZnO w –PZT film gives the similar cell lattice parameters and tetragonality.In the previous report [7],it has been found that the addition of ZnO increases the tetragonality of PZT-based ceramics due to Zn 2+ion substitution of B-site ions because of its smaller ion radiuses.The discrepancy between the film and ceramic results should be attributed to the different fabrication processes.In this work,the film annealing temperature is 700°C,which is much smaller than that of ceramic (≥900°C),and there is nearly no Zn 2+ion substitution of B-site ions.Therefore,the addition of ZnO w has weak in fluence of the tetragonality of PZT films.The decreases of tetragonality should be caused by theinternal stress relaxation,which would reduce the effects of lattice mismatch between the films and substrates.Fig.2(a)shows the SEM micrograph of ZnO w and it is seen that ZnO w is tetraneedlelike structure,of which one needle length is ∼10μm.Fig.2(b)shows a ZnO w (in dash circle)embedded in 1μm-thick PZT film without any surface treatment.Three bottom needles are buried in the PZT film tightly and no crack appears at the boundary.Fig.2(c)and (d)shows the mapping of Zn and Pb elements,respectively.Due to the larger ZnO w dimension than the film thickness,the uncovered ZnO w would in fluence the surface rough-ness.Thus,dilute acetic acid solution is used to remove redundant ZnO w .Fig.2(e)and (f)shows the surface morphology and cross section of a 2-μm-thick ZnO w –PZT film completed by all processes.It is revealed that the film is of granular structure and crack free.The grain sizes are in the range of sub-micrometers.Fig.3(a)shows the ferroelectric hysteresis loops of the 2-μm-thick PZT and ZnO w –PZT films with an applied maximum voltage of 90V at a frequency of 10Hz.The remanent polarizations P r are 27.4and 24.3μC/cm 2,and both coercive fields E c are 176.5kV/cm.The smaller P r of the ZnO w –PZT film is attributed to the substitution of ZnO w for PZT,where the ferroelectric is replaced by a non-ferroelectric.However,ZnO w seems to have no effect on E c .Fig.3(b)shows the steady-state leakage current –voltage characteristics of the two films.The value of ZnO w –PZT film is larger than that of the PZT film under the same applied voltage.It is consistent with the fact that ZnO is a semiconductor and has less insulation than that of PZT.Therefore,ZnO w in PZT film would lead to more leakage current flowing through them.Fig.3(c)and (d)show that P r increases and E c decreases as the film thickness increases,which are caused by the film relaxation and structure activity increase,i.e.they are helpful for the movement of Ti 4+,Zr 4+,O 2−ions and the reverse of spontaneous polarization [15].The dielectric constants εr and dielectric loss tan δof the 2-μm-thick PZT film and ZnO w –PZT films are measured in a frequency range of 5–1000kHz,as shown in Fig.4.Here εr decreases slightly with increasing frequency;however,tan δhas less dependence on frequency except that of the 3-μm-thick ZnO w –PZT film.In the sol –gel fabrication process,some ZnO w aggregation in PZT thick films could not be avoided and would lead to more leakage current flowing through ZnO w and generate larger conduction loss.The enhancement of εr at low frequency could be attributed to the interfacial polarization,which has small contribution at high frequency [16].The increase of εr with the increasing film thickness is attributed to the effect of interfacial layers attenuated [17].Compared with PZT films,εr and tan δof ZnO w –PZT films are smaller in the measurement frequency range.According to the effective-medium theory,the addition of ZnO w ,an inclusive phase with lower εr ,will reduce εr of PZT films [18].In previous reports,it has been found that the stress in sol –gel derived PZT and PT films decreased with the increased film thickness [15,19].In the present study,the stress relaxation in ZnO w –PZT films reduces the tetragonality and makes non-180°domain wall motions easily,which would result in the increase of P r and decrease of E c [20].Meanwhile,as the film thickness increases,the effect of interfacial layers between PZT and substrate becomes weak and raise the εr of ZnO w –PZT films.4.ConclusionSilicon-based ZnO w –PZT thick films have been prepared via a hybrid sol –gel route using ZnO w suspension and PZT sol.As the film thickness increases,film tetragonality decreases and the film is pared with PZT film,it is suggested that the addition of ZnO w has less effect on the tetragonality of PZT films.ZnO w –PZT films show good ferroelectric and dielectric properties and probably are candidates in MEMSapplications.Fig.1.XRD of (a)ZnO w ,(b)2-μm-thick PZT and ZnO w –PZT films with thicknesses of (c)1.5μm,(d)2μm,(e)3μm,and (f)4μm.The lower figure shows the dependences of cell parameter and tetragonality on film thickness.633Q.L.Zhao et al./Materials Letters 64(2010)632–635634Q.L.Zhao et al./Materials Letters64(2010)632–635Fig.2.SEM micrographs of(a)ZnO w,(b)a ZnO w(in dash circle)embedded in PZTfilm,(c)mapping of Zn element,(d)mapping of Pb element,(e)surface morphology and(f)cross lm.section of the2-μm-thick ZnO w–PZTfiAcknowledgementThis study was supported by the National High-Tech Research and Development Program (863program)of China under Grant No.2007AA03Z103,the National Natural Science Foundation of China under Grant Nos.50742007,50972014and 50872159,the Key Laboratory Foundation of Sonar Technology of China under Grant No.9140C24KF0901.References[1]Kozuka H,Kajimura M,Hirano T,Katayama K.J Sol –Gel Tech 2000;19:205–9.[2]Hu SH,Meng XJ,Wang GS,Sun JL,Li DX.J Cryst Grow 2004;264:307–11.[3]Lin P,Ren W,Wu XQ,Shi P,Yan X,Yao X.J Appl Phys 2007;102:084109.[4]Tanaka K,Kubota T,Sakabe Y.Sens Actuators A 2002;96:179–83.[5]Zhu BP,Wu DW,Zhou QF,Shi J,Shung KK.Appl Phys Lett 2008;93:012905.[6]Duan ZX,Yuan J,Zhao QL,Liu HM,Lin HB,Zhang WT,et al.Chin Phys Lett 2008;25:1472–5.[7]Li H,Yang ZP,Wei LL,Chang YF.Mater Res Bull 2009;44:638–43.[8]Wang GS,Deng Y,Xiang Y,Guo L.Adv Funct Mater 2008;18:2584–92.[9]Dang ZM,Xie D,Yu YF,Xu HP,Hou YD.Mater Chem Phys 2008;109:1–4.[10]Lin HB,Cao MS,Zhao QL,Shi XL,Wang DW,Wang FC.Script Mater 2008;59:780–3.[11]Cao MS,Zhou W,Shi XL,Chen YJ.Appl Phys Lett 2007;91:021912.[12]Wang ZL,Song JH.Science 2006;312:242–6.[13]Shi XL,Cao MS,Zhao YN,Song WL,Rong JL.Sci China Ser E-Tech Sci 2008;51:1433–8.[14]Zhang T,Wasa K,Zhang SY,Chen ZJ,Zhou FM,Zhang ZN,et al.Appl Phys Lett 2009;94:122909.[15]Nagarajan V,Jenkins IG,Alpay SP,Li H,Aggarwal S,Riba LS,et al.J Appl Phys 1999;86:595-02.[16]Long YZ,Li MM,Sui WM,Kong QS,Zhang L.Chin Phys B 2009;18:1221–6.[17]Wang GS,Remiens D,Dogheche E,Herdier R.J Am Ceram Soc 2006;89:3417–20.[18]Cheng YH,Chen XL,Wu K,Wu SN,Chen Y,Meng YM.J Appl Phys 2008;103:034111.[19]Sengupta SS,Park SM,Payne DA,Allen LH.J Appl Phys 1998;83:2291–6.[20]Xu F,Mckinstry T,Ren W,Xu BM,Xie ZL,Hemker KJ.J Appl Phys 2001;89:1336–48.Fig.4.Frequency dependences of dielectric constant (εr )and dielectric loss (tan δ)of ZnO w –PZT and 2-μm-thick PZT films.635Q.L.Zhao et al./Materials Letters 64(2010)632–635。
晶体结构查询、绘图及面网间距计算
可知： (100)、(010)、(001)、(-100)、(0-10)、(00-1) 等相等； (110)、(101)、(011)、(-110)、(1-10)、 (-101)、(10-1)、(0-11)、(01-1)等相等。
在x射线粉晶衍射中，只能测定出独立的 面网间距，因此对于面网间距相等的面 网，在描述其面网符号时，选用其中的 一个面网符号表示。选符号的规则： a) 尽量采用正指数 b) 数字尽量靠前
（010）
（020）
（030）
（040）
（001）
（002）
（003）
（004）
[001]投影
（110）
（220）
（330）
（210）
（140）
2) 面网间距：描述一组等间距的面网中 相邻面网的垂直距离。记为 dhkl。 在直角坐标并且轴长相等的情况下：
d010=b
d020=b/2
d030=b/3
3.8184 3.1177 2.7000 2.4150 2.2045 1.9092 1.8000 1.7076 1.6282 1.5588
d123 d400 d104 d114 d133 d204 d124 d233 d224 d304
1.4432 1.3500 1.3097 1.2728 1.2388 1.2075 1.1784 1.1513 1.1023 1.0800
c) 斜方(正交)晶系
a≠b≠c
α=β=γ=90
d）单斜晶系 a≠b≠c ；β≠90 e) 三斜晶系 a≠b≠c α≠β≠γ≠90o
f) 三方及六方晶系按六方 指标化） a = b≠c α=β=90o,γ=120o
4) 面网间距含义： (1) 不同面网符号的面网间距有可能彼此相等。 如立方晶系，根据公式
X-ray diffraction(20120412)
1912年5月4日，索末菲将上述材料密封上报给巴伐 利亚科学院，以确定friedrich，Knipping,Laue在发 现X射线衍射方面的优先权； 索末菲出资购买立方ZnS晶体和测角头，得到清晰 的ZnS衍射图。 1912年6月8日，三人合写的论文在巴伐利亚科学院 宣读，并在院刊发表。
1937年，普朗克在柏林演讲中提到：那是1912年6月4日， 就在这里，我清楚记得当劳埃简单介绍了他的理论后，给 我们看了他的第一批照片，听众并未完全信服，似乎仍有 所期待，但是当看到ZnS的典型劳埃图后，每个听众都认 识到一件伟大的事发生了。”
Hale Waihona Puke Continuous X-ray spectrum
Production: The continuous spectrum results from the rapid deceleration of the electrons hitting the target. Not every electron decelerates in the same way. i=16mA, 1017 electrons/second Short-wavelength limit （短波极限） Those electrons which are stopped in one impact produce photons of maximum energy. eV=hγ=hc/λswl Total intensity of continuous X-ray Icontinuous spectrum= AiZVm
式中hkl称为衍射指标，不加括号表示这3个整数不必互质。dhkl为衍射面间距，它等 于d(hkl)/n。 Laue方程和Bragg方程是等效的。
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获 1914 年 诺贝尔物 理学奖
劳埃（ue）提出了用晶体作为天然立体光栅用 于X射线衍射的想法， 1912年劳埃和索莫菲的助手
W.Friedrich 、 伦琴的学生P.Knipping用CuSO4.5H2O
by the crystal? And, if so, under what conditions?
•
•
Bragg’s law: 2dhkl·sinθ=nλ
θ: Bragg angle • 2θ： diffraction angle • n: the order of diffraction n=1, sinθ1=λ/2d 一级衍射线 n=2, sinθ2=λ/d 二级衍射线 n, sinθn=nλ/2d≤1 n ≤2d/λ 当X射线波长和衍射面选定后，λ和d的值都定了，可 能有的衍射级数n也确定了，所以一组晶面只能在有限几 个方向“反射”X射线。 λ/2d ≤1 d≥λ/2 λ一定时，晶面间距≥λ/2的晶面，才能产生衍射； d一定时， λ ≤2d ， 但不能太小，一般取λ ～d
群贤毕至 慕尼黑大学 （ 1910 年 ）
1910年，索末菲实验室：埃瓦尔德博士论文题目：各向同性 的谐振子在各向异性介质中的光学性质，两年后答辩，之间 独立完成。 埃瓦尔德做晶体光学的理论分析工作时，请教Groth选用哪 一种各向异性的晶体，CuSO4。计算出来两个正交方向的双 折射率比实验结果大3-4倍，而在另一方向则小六倍。 1911年，埃瓦尔德去请教劳埃，劳埃感兴趣的是”非常短的 波进入晶体后会有什么事情发生？“ 埃瓦尔德将其论文中的公式给劳埃，此公式给出各个谐振子 发出的波的叠加，也适合非常短的波的情况。 1912年6月，埃瓦尔德得知劳埃的X衍射实验后，发现他给 劳埃的公式只要用倒格子作为各自的平移周期，再做一个与 入射X射线波长有关的球，就可以解释衍射的几何关系。 （1913年发表）
1913 － 1914 年 ， 英 国 科 学 家 W.H.Bragg 和 W.L.Bragg确定了X射线晶体结构分析方法并 首次测定了NaCl的晶体结构。获1915年诺贝
尔物理学奖。
此后，小布拉格的工作： 晶体结构分析以及X射线 波长的测定 如：NaCl的结构 金刚石的结构 1938年出任实验室主任，支持生物大分子的X射线 晶体结构的测定，肌红蛋白，血红蛋白的晶体结构， DNA晶体结构等 老布拉格承认X射线在晶体中的衍射后就设计制造 了一台X射线分光计，即X射线衍射仪的前身，为X 射线光谱研究以及有机分子结构研究，生物大分子 结构研究奠定基础。
E=hc/λ ħ: Planck’s constant 6.63*10-34J· S C : 3.00*108m/s
Production of X-rays
X-ray tube a source of electrons( cathode) a high accelerating voltage a metal target( anode)
小布拉格在1962年说：这是由一些无关联的 知识凑在一起产生新鲜事物的有意义的事， Thomson教我们X射线波动理论，Wilson以 他独到的方式讲”白光“的连续谱，Pope和 Barlow的晶体结构理论，使我得到有关晶体 规则性的概念。我清楚记得在学院后面的康 河岸边的那个地点，我忽然想起劳埃斑点就 是X射线从晶体中一些原子面反射的结果。
Laue方程以直线点阵为出发点，是联系点阵单位的3个基本矢量a,b,c以及X射线的 入射和衍射的单位矢量s0和s的方程。 Bragg方程以平面点阵为出发点，对一族晶面间距为d(hkl)的平面点阵的衍射方向为： 2d(hkl)· sinθn=nλ 式中n为整数，λ为波长， θ为衍射角。上式可改写为： 2dhkl· sinθ=λ
2dhkl·sinθ=nλ
2(dhkl/n)sinθ=λ 2(dnh,nk,nl)sinθ=λ 2(dHKL)sinθ=λ （HKL） diffraction index 衍射指数 Bragg’s law: simplify 2d·sinθ=λ
衍射方向：衍射线偏离入射线的角度。 晶体的衍射方向和晶胞的大小和形状有关，有两个基本的方程： Laue方程和Bragg方程。
Characteristic X-ray spectrum
The critical K excitation voltage （K系激发电压） The wavelength of Kα characteristic X-ray (Moseley’s law) Intensity IKline=Bi(V-Vk)n
Continuous X-ray spectrum
Production: The continuous spectrum results from the rapid deceleration of the electrons hitting the target. Not every electron decelerates in the same way. i=16mA, 1017 electrons/second Short-wavelength limit （短波极限） Those electrons which are stopped in one impact produce photons of maximum energy. eV=hγ=hc/λswl Total intensity of continuous X-ray Icontinuous spectrum= AiZVm
1912年5月4日，索末菲将上述材料密封上报给巴伐 利亚科学院，以确定friedrich，Knipping,Laue在发 现X射线衍射方面的优先权； 索末菲出资购买立方ZnS晶体和测角头，得到清晰 的ZnS衍射图。 1912年6月8日，三人合写的论文在巴伐利亚科学院 宣读，并在院刊发表。
1937年，普朗克在柏林演讲中提到：那是1912年6月4日， 就在这里，我清楚记得当劳埃简单介绍了他的理论后，给 我们看了他的第一批照片，听众并未完全信服，似乎仍有 所期待，但是当看到ZnS的典型劳埃图后，每个听众都认 识到一件伟大的事发生了。”
B proportionality constant; n: a constant,n~1.5
It is impossible to excite one K line without exciting all the others.
X-Ray Diffraction Ⅰ: Geometry
Whether the incident beam of x-rays will be diffracted
建立多功能晶体结构数据库
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粉末衍射数据解析晶体结构
Properties of X-Rays
Electromagnetic radiation Wavelength: 0.01-1000Å (0.5~2.5Å used for crystal diffraction)
Dual wave-particle character
光源产生：真空度为10-4Pa的X射线管内，由高速电子 冲击阳极金属靶产生的。P103 Fig. 3.25
X-ray spectrum
The continuous spectrum: made up of rays of many wavelengths The characteristic spectrum: narrow line of characteristic wavelengths P104 Fig. 3.26
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代表性的无机有机晶体结构测定 测定蛋白质的结构 衍射法和计算机技术结合，实现
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式中hkl称为衍射指标，不加括号表示这3个整数不必互质。dhkl为衍射面间距，它等 于d(hkl)/n。 Laue方程和Bragg方程是等效的。
Three scattering modes
By atoms arranged randomly in space, as in a monatomic gas, the scattering occurs in all directions and is weak. Intensities add. By atoms arranged periodically in space, as in perfect crystal, a) in a very few directions, those satisfying Bragg’s law, the scattering is strong and called diffraction. Amplitudes add. I ~A2 b) in most directions, those not satisfying Bragg’s law, there is no scattering because the scattered rays cancel one another.
晶体观察到了X射线衍射图。
这是世界上第一张X射线衍射图，同时诞生了两
门新兴学科：晶体X光结构分析和X光光谱学。
三人签名写了一份材料并与底片一起封存起来，内 容：从1912年4月21日起，签字人 （Friedrich,Knipping,Laue)曾从事X射线穿透晶体 实验，指导思想是晶体的晶格会产生干涉，因为晶 格常量大约是猜测的X射线波长的10倍。存档的53 号及54号底片为证。 照射物质：硫酸铜 曝光时间：30min;软X射线管电流：2mA 底片与晶体间的距离：53号30mm，54号60mm 光阑3（直径1.5mm）的距离：50mm 光源到晶体的距离=350mm 实验装置图