Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 91-95).

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硅對現今科技至關重要。而有機物吸附於硅表面可能大大擴展硅的用途。在本論文中，我採用密度泛函理論研究了六種分子於硅表面的反應。本論文大致可分為四部分。 / 第一部分包含四個分子（吡嗪、吡啶、嘧啶與1,3,5-三氮嗪）的吸附研究。它們都擁有類似於苯的結構而環中又包含氮原子。分子可以用氮原子與表面形成配位鍵並作為進一步反應的前體故其反應更為容易預測。而反應通常只消除π 鍵而不會使分子分解這使得分子可以在平衡狀態下與表面生成最為穩定的結構。此兩種特性使它們成為硅表面吸附的絶佳研究對象。不同的實驗都顯示出吡嗪於硅表面只會生成Cross-row bridge 結構加熱硅表面更會促進納米線的生成。過往的計算無法解釋實驗結果而我的計算表明范德華力對導出正確計算結果非常重要加入范德華力的修正可以同時解釋單一產物與納米線的生成。吡啶的吸附實驗結果相比之下較為複雜。低溫下的吸附與飽和只生成兩種產物可是室溫下的實驗卻顯示多種產物並存於表面。加入范德華力的計算結果指出覆蓋度和溫度與吸附密切相關並指出對低溫下形成的飽和表面加溫可能促使納米線的生成。而於室溫下吡啶可進入多條反應路徑致使多種產物於表面並存。基於范德華力對這兩個分子的顯著影響我又將此效應加諸於嘧啶與1,3,5-三氮嗪的吸附研究。結果表明於低覆蓋度與低溫下它們只生成Double-dative 產物。然而增加覆蓋度會使Double-dative 的能量高於其它產物導致多種產物並存。由於嘧啶與1,3,5-三氮嗪都可生成一種特別的tight-bridge 結構加溫會使它們輕易解離。對此四種分子的研究顯示出氮原子的數量與位置如何影響吸附過程。 / 第二部分包含對1,2-環己二酮的吸附研究。於室溫下此分子會以互變異構體形式存在。之前的實驗指出它會先變回二酮才進行後續反應這種硅表面輔助互變反應的現象是前所未見的卻無後續研究以驗証其說。我的計算結果指出雖然互變反應的能壘被硅表面大幅降低可是仍不足以與其他反應路徑相匹敵。其中三種新產物既與實驗譜相吻合而反應能壘和能量都低故比之前所提產物更為可取。 / 第三部分包含對氰基苯的吸附研究。之前的三個實驗給出完全不同的結論。探明其與覆蓋度和溫度的關係後我提出氰基苯於低溫下飽和只會生成一種產物。而在室溫下的吸附會先生成valley-bridge 結構增加覆蓋度將使多種產物並存。計算結果不但表明有序吸附的可能性同時又解釋為何不同實驗給出看似不相容的結論。 / Silicon is an important material and substrate in modern technologies. Adsorption of organic molecules on silicon surface has attracted much attention due to the possibility of functionalizing the surface. In this thesis, density functional theory has been applied to study the adsorption of several organic molecules on Si(100) surface. / Results on the adsorption of benzene-like N-heteroaromatic molecules on Si(100)surface, including pyrazine, pyridine, pyrimidine and s-triazine, are presented in Chapters 2-4. This class of molecules, containing nitrogen atoms, can datively attach to dimer and act as precursor for further reaction. Thus, their reactions on surface can be easily predicted. Their reaction with surface would sacrifice π bond rather than dissociation under very mild condition such that the most stable adsorption product can be obtained under thermal equilibrium. These two properties of N-heteroaromatic compounds makes them good models for the study of reaction on surface Experiments repeatedly showed that pyrazines formed cross-row bridge structures on Si(100) under various conditions, and thermal annealing led to the formation of ordered nano-lines. Previous calculations did not explain these observations. This thesis demonstrates that addition of van der Waals (vdW) correction is critical to explain the formation of both the cross-row bridge and the nano-lines. For pyridine, the situation is more complex. Only two products were observed in low temperature adsorption experiments. In contrast, room temperature experiments yielded a mixture of products. With vdW corrections added, results show that pyridine adsorption is dependent on both coverage and temperature. Adsorption and saturation started at low temperature and followed by annealing may produce nano-lines consisted of cross-row bridge structures. Adsorption at room temperature opens up all reaction channels such that nano-line formation becomes difficult, which explains the discrepancy among experimental studies. In light of these results, the pyrimidine and s-triazine adsorption on Si(100) are also explored. The results show that they form double-dative structures at low coverage and low temperature. Increasing coverage will destabilize it and lead to mixture of products. These structures decompose easily upon heating due to the formation of a particular tight-bridge structure. These results show that the position and number of heteroatom are important to explain the difference in reaction selectivity among N-heteroaromatic molecules. For all four molecules, cooperative effect and the addition of vdW correction, which are almost neglected in similar study, are shown to be important in surface adsorption process. / In Chapter 5, the adsorption of 1,2-cyclohexanedione (1,2-CHD) on surface is studied. Gas molecule of 1,2-CHD exists in the tautomeric form (2-hydroxylcyclohex-2-ene-1-one) at room temperature. Previous experimental studies claimed that surface assisted tautomerization back to 1,2-CHD took place before further reaction, although there was no follow-up study. Computational results showed that although surface adsorption lowers the barrier for tautomerization, the barrier is still at least 5 times larger than other reaction channels. Three new structures are proposed, which are in better agreement with previous spectroscopic results. / In the final chapter, the adsorption of benzonitrile on Si(100) is studied. Three previous experimental studies presented conflicting results. With the coverage and temperature dependence effects clarified, my results suggest that adsorption at saturation and low temperature leads to a single product. Adsorption at room temperature first leads to a valley-bridge structure, while a mixture of adsorption structures is produced upon increasing coverage, which explained the conflicting experimental results. The last two chapters show the importance of computational modeling for interpretation and summarizing experimental results. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Ng, Kwok Hung. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references. / Abstracts also in Chinese. / Ng, Kwok Hung.

Styrene (C2H3-C6H5) is expected to have a more complex reaction process due to active reaction sites located in both vinyl group and phenyl group. Our exploration indicates that the adsorption products are coverage dependent. At low coverage, both vinyl group and phenyl group are possible to take part in the adsorption process. A new AsymT adsorption state covered two adjacent Si dimers is identified through two [4+2] cycloaddition. At high coverage, only vinyl group can interact with Si dimer to form cis and trans stereoisomers with different thermal energies and kinetic reaction barriers. STM images and vibrational frequencies are also explored to further support the experimental observations. / The adsorption of unsaturated organic molecules on reconstructed Si(100) surface is widely applied in the modification and functionalization of silicon surface to design new semiconductor materials. The present project is devoted to explore the adsorption mechanisms and the related properties of adsorption species for unsaturated organic molecules: acetylene (C2H 2), ethylene (C2H4), vinyl bromide (C2H 3Br) and styrene (C8H8) by quantum chemical calculation, based on density functional theory (DFT) method with pseudopotentials and plane wave basis set. / The investigation of vinyl bromide (C2H3Br) chemisorption on Si(100) resolves the conflicting conclusions between previous experimental and theoretical studies. The orientation of the vinyl bromide molecule relative to the titled silicon dimer is found to be an important factor for both the stability and reactivity of the precursor state. A new precursor pi-complex is identified, which is metastable and trapped by barriers around 0.1eV. Comparisons between theoretical and experimental vibrational frequencies support the conclusion that such a pi-complex is present on the surface at very low temperature. Careful analysis on the electronic structure also demonstrates that it is indeed a pi-complex rather than a diradical as previously suggested. Reaction mechanisms at higher vinyl bromide coverage are also modeled to explain the decrease in activation barrier observed in experiments. / The reaction processes for acetylene (C2H2) and ethylene (C2H4) chemisorption on the surface silicon dimer and the sub-layer silicon atoms are compared. Acetylene can undergo a new type of cycloaddition on sub-layer Si atoms (called sub-di-sigma) with no barrier, which is identified by ab initio Molecular Dynamics. The related properties including vibrational frequencies and STM images are calculated and found to be similar with those of the end-bridge adsorption structure. The identification of such a sub-di-sigma adsorption structure explains the discrepancy between STM experiments and theoretical calculations. In addition, the analysis of calculated vibrational frequencies, simulated STM images and the reaction barriers for di-sigma and end-bridge structures indicate that inter-dimer reaction for C2H4 is possible. / Zhang, Qiuji. / Adviser: Zhi Feng Liu. / Source: Dissertation Abstracts International, Volume: 70-09, Section: B, page: . / Thesis submitted in: October 2008. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 86-87). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

A study of potentiostatic and galvanostatic electrochemical etching of silicon in tetramethylammonium hydroxide (TMAH) has been carried out. In TMAH baths,, we find that biased (100) silicon etch rates increase 21% over OCP etch rates. For TMAH baths seasoned with silicon, biased silicon etch rates increase to 63% over those at OCP. Electrochemical etching eliminates the growth of hillocks on etching surfaces regardless of etchant pH, [TMAH] or silicon loading, resulting in highly smooth etching surfaces. Potentiostatic and galvanic etching yield similar etch rates and surface consistency. / Graduation date: 2003

The fundamental atomic and electronic behaviour of clean silicon surfaces has been studied within a simple tight-binding picture of bonding in solids. Of the various contributions to the surface binding energy, the lowering in the promotion energy (i.e. rehybridization) which accompanies localized Jahn-Teller distortions has been identified as a major electronic driving force underlying the stability of silicon surfaces. The structure of Si(113) has been experimentally determined by the technique of scanning tunnelling microscopy (STM). Despite its high index, the Si(113) surface is found to be highly stable. STM images of both empty and filled states provide strong evidence for a particular structural model with a 3x2 unit cell. The STM results are explained in terms of a general rehybridization principle, suggested by the earlier theoretical study, which accounts for the low surface energy as well as the observed spatial distribution of empty and filled states. In addition, the STM images reveal a high density of domain boundaries which introduce energy states that pin the Fermi level and explain earlier reports of a 3x1 reconstruction for this surface. Voltage-dependent STM image simulations for the Si(113)3x2 surface have been carried out using a simple tight-binding description of surface electronic structure. Quantitative agreement with experiment is obtained confirming the qualitative rehybridization arguments used previously. The local barrier for tunnelling electrons is shown to have an important effect on the interpretation of STM images. The high stability of clean Si(l 13) is shown by STM to be disrupted by adsorption of submonolayer amounts of atomic hydrogen which saturates dangling bonds. Mass transport of silicon occurs and structural models are proposed for the resultant mixed 2x2 and 2x3 surface.

包含少於1000 個原子的金屬納米顆粒會與此金屬的常規尺寸材料有很大差別。它們擁有一些特殊的物理和化學的性質，因而在過去的二十年中吸引了大量的研究工作。但是由於尺寸太小，對於這些納米結構的深入和全面的研究十分困難。掃描隧道顯微鏡方法是一種強大的研究此類問題的技術。它擁有的極強的空間分辨力和原子操縱的能力使得我們可以獲得一些納米顆粒的細緻信息。在這篇論文中，我將報道我的關於在半導體Si(111)-(7x7)的重構表面的貴金屬（銀/金）顆粒的研究。 / 我首先研究了在Si(111)-(7x7)上的金屬顆粒的製備方法。使用熱蒸發方法，我製備了在Si(111)-(7x7)上的金屬顆粒。在研究了這些金屬顆粒在半元胞中的的整體生長過程之後，我的研究集中在本論文的主要目標--獨立的銀納米顆粒上。通過仔細觀察記錄單個銀原子的擴散過程，我們確認了Ag3‐Ag13 顆粒中的原子數目。這些掃描隧道顯微鏡的圖像同時也指出了這些顆粒的動態性質，包括自發跳動、分解和與鄰近的單個Ag 原子的合成。為了獲得對這些Ag 顆粒的控制，我們找到了一種垂直操縱單個Ag 原子的方法。在樣品的表面，掃描隧道顯微鏡的針尖通過特定的程序被用來抓起和放下單個Ag 原子。它被用來組裝和拆裝Ag的顆粒。各種Ag 顆粒在半元胞中被組裝，同時我們發現單個半元胞中的最大的顆粒是Ag25。同時這項技術被用來組裝複雜的Ag 顆粒的圖形。 / 使用上面這些操縱的技術（熱蒸發方法和原子操縱方法），我們細緻的研究了顆粒的兩方面性質：第一，我們發現對於單個元胞中的Ag 顆粒都存在着顯著的電學的整流效應，同時我們比較了它們各自的特點。通過實驗測量和第一性原理計算，我們發現這種電學整流效應源自電子態密度的耦合效應。當這些顆粒在平面內連接起來從而增加橫向的尺寸時，這種顆粒的整流效應將會繼續存在；但當顆粒形成多層Ag 的結構即垂直方向尺寸增加時，這個整流效應將會消失。另外一個所研究的性質是所有的Ag顆粒都存在一種對周圍單個Ag原子的吸引作用，從而讓自身長大的過程。這一過程對於Ag 顆粒的生長起到了至關重要的作用。我們選擇了幾個有代表性的顆粒，通過原子操縱的方法測量了它們與一個鄰近的Ag 原子的融合過程。測量的結果說明一個顆粒的存在通常會降低一個鄰近Ag 原子向此顆粒擴散的勢壘高度，同時也會影響此單個原子在靠近此顆粒的吸附位上的吸附能。 / Metal nanoclusters with less than 1000 atoms differ very much from their bulk counterparts. They possess many unique chemical and physical properties and have attracted extensive studies during the past two decades. However, in-depth and comprehensive researches of these structures are difficult for their small size. Scanning tunneling microscopy (STM) is a versatile technique to study the nanostructures. Its extreme powerful spatial resolution as well as its atomic manipulation capability enabled us to obtain the detailed information of some nano-clusters. In this thesis, I report on my studies on the noble metal (mainly Ag) clusters on the reconstructed Si(111)-(7x7) surface. / I firstly studied the fflbrication methods of the metal clusters on the Si(111)-(7x7) surface. By thermal deposition, I fabricated Ag clusters on Si(111)-( 7x7). After studying the overall growth process of the Ag clusters in half unit cells, I focused on the main target of this thesis: individual Ag clusters. By carefully observing the diffusion process of the Ag atoms on the surface, we identified of the number of atoms inside Ag3-Ag13 clusters. The STM images also showed the dynamic behaviors of each cluster, including self-hopping, dissociation and association with nearby Ag atoms. For a better controllability, a vertical manipulation technique was developed to transfer single Ag atoms across difference locations on the Si(111)-(7x7) surface. The STM tip was used to pick up or drop off metal atoms from or to the sud"ace following specific procedures. The assembly and disassembly of Ag clusters were achieved by this method. Various Ag clusters were built and the largest occupation of a FRUC was found to be 25 Ag atoms. This technique was demonstrated to be able to manipulate Au atoms and to assemble Au clusters. / With the developed fabrication methods, by thermal deposition as well as by atomic manipulation, two properties of the clusters were studied carefully: first, a prominent electrical rectifying behavior was observed for all the Ag clusters. Their individual behaviors were compared with each other. A combination of experimental measurements and first principle calculations unveiled the mechanism of the electronic rectifying behaviors to be a wave function coupling effect. The rectifying behavior for the clusters was found to persist when clusters connected laterally, whereas to disappear when the vertical size of the cluster increased to form multiple Ag layers. The second property studied is that all the clusters are found to attract nearby single Ag atoms to grow larger. This behavior plays a critical role in the growth process of the Ag clusters. we chose several typical Ag clusters and measured the merging process with single neighboring Ag atoms by atomic manipulation. The results indicate that the presence of a Ag cluster will mostly reduce the diffusion barrier of a single Ag atom in the neighboring half unit cells to diffuse to the cluster and even affect / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Ming, Fangfei = 在Si(111)-(7x7)表面的金屬納米顆粒的製備和性質 / 明方飛. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 116-122). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Ming, Fangfei = Zai Si(111)-(7x7) biao mian de jin shu na mi ke li de zhi bei he xing zhi / Ming Fangfei. / Chapter 1 --- Introduction: metal nano-clusters on semiconductor surfaces --- p.2 / Chapter 1.1 --- Background and Motivation --- p.2 / Chapter 1.1.1 --- Nano-science and nano-technology --- p.2 / Chapter 1.1.2 --- Metal nano-clusters --- p.3 / Chapter 1.2 --- Scanning tunneling microscopy (STM) --- p.6 / Chapter 1.2.1 --- Introduction to STM --- p.6 / Chapter 1.2.2 --- Basic components of STM --- p.7 / Chapter 1.2.3 --- STM working modes --- p.9 / Chapter 1.2.4 --- STM experiments in this thesis --- p.11 / Chapter 1.3 --- Substrate: the Si(111)-(7 x 7) reconstruction surface --- p.12 / Chapter 1.3.1 --- Atomic Structure --- p.12 / Chapter 1.3.2 --- Preparation in ultra high vacuum --- p.14 / Chapter 1.4 --- Growth of Ag on Si(111)-(7 x 7) at room temperature --- p.14 / Chapter 1.4.1 --- Growth method --- p.15 / Chapter 1.4.2 --- Adsorption and diffusion of single Ag atoms --- p.17 / Chapter 1.4.3 --- Forming Ag clusters --- p.20 / Chapter 1.4.4 --- Forming Ag islands --- p.23 / Chapter 1.5 --- Conclusion --- p.25 / Chapter 2 --- Individual Ag clusters: size, dynamics and stability --- p.27 / Chapter 2.1 --- Introduction --- p.27 / Chapter 2.2 --- Experiment --- p.29 / Chapter 2.3 --- Results and discussion --- p.31 / Chapter 2.3.1 --- Growth kinetics --- p.31 / Chapter 2.3.2 --- STrvr images of typical Ag structures Intra-HUC diffusion --- p.33 / Chapter 2.3.3 --- Inter-HUC diffusion --- p.37 / Chapter 2.3.4 --- Inter-HUC diffusion & identification of the number of atoms inside each cluster --- p.38 / Chapter 2.3.5 --- Stability of Ag structures. --- p.45 / Chapter 2.4 --- Conclusion --- p.49 / Chapter 3 --- Assembling and disassembling Ag/ Au clusters by atomic manipulation --- p.51 / Chapter 3.1 --- Introduction --- p.51 / Chapter 3.2 --- Experiment --- p.54 / Chapter 3.3 --- Results and disscussion --- p.55 / Chapter 3.3.1 --- Basic procedures for manipulating a single Ag atom --- p.55 / Chapter 3.3.2 --- Assembly of Ag clusters --- p.58 / Chapter 3.3.3 --- Disassembly of Ag clusters --- p.66 / Chapter 3.3.4 --- Assembly of Ag cluster patterns --- p.70 / Chapter 3.3.5 --- Comparison with the manipulation of Au atoms --- p.71 / Chapter 3.3.6 --- STrvr tip for atomic manipulation --- p.74 / Chapter 3.4 --- Conclusion --- p.75 / Chapter 4 --- Study on the electronic properties of the Ag clusters --- p.76 / Chapter 4.1 --- Introduction --- p.76 / Chapter 4.2 --- Experiment --- p.78 / Chapter 4.2.1 --- Experimental parameters. --- p.78 / Chapter 4.2.2 --- Precise tip positioning --- p.79 / Chapter 4.2.3 --- First principle calculation parameters --- p.80 / Chapter 4.3 --- Results and Discussion --- p.81 / Chapter 4.3.1 --- Grow Ag clusters --- p.81 / Chapter 4.3.2 --- I-V of the clusters. --- p.82 / Chapter 4.3.3 --- Theoretical calculation --- p.88 / Chapter 4.3.4 --- Transition from cluster to bulk in I-V. --- p.91 / Chapter 4.4 --- Conclusion --- p.94 / Chapter 5 --- Dynamics of Ag atoms near an interacting Ag cluster --- p.95 / Chapter 5.1 --- Introduction --- p.95 / Chapter 5.2 --- Results and Discussion --- p.97 / Chapter 5.2.1 --- Different Ag clusters and their orientations --- p.97 / Chapter 5.2.2 --- Association time measurement --- p.99 / Chapter 5.2.3 --- Energy barrier and diffusion prefactor --- p.101 / Chapter 5.2.4 --- Influenced intra-HUC diffusion --- p.105 / Chapter 5.2.5 --- Energy diagram --- p.107 / Chapter 5.3 --- Conclusion --- p.109 / Chapter 6 --- Conclusion and Future Work --- p.111 / Chapter 6.1 --- Conclusion --- p.111 / Chapter 6.2 --- Future work --- p.113 / Bibliography --- p.116

Hydrogen desorption mechanisms on hydrogenated silicon surface such as H/Si(1 00)-1x1, H/Si(l00)-2xl and H/Si(100)-3x1 surfaces have been explored by theoretical calculations with slab models. Similar desorption mechanisms have been identified for three hydrogenated surfaces and the calculated barriers were in agreement with experimental values. More interestingly, a common bridge structure has been identified as an intermediate. Its unique electronic structure is analyzed in detail. The identification of such a structure provides an alternative account for previous experimental results on STM tip-induced desorption. / Metal atom clusters are nanoscale intermediates between metal atoms and the bulk metal. Al13- can be regarded as a cluster model for Al(111) due to its special electronic and geometric structures. The reaction between Al13- and O2 was explored by various DFT methods such as BLYP, PW91, PBE, B3LYP and BHHLYP and post-HF methods such as CCSD and QCISD(T). The calculation results demonstrated that the reaction was exothermic and thermodynamically quite favorable, and the reason for the stability of Al13- towards oxygen exposure was kinetic, due to the presence of a reaction barrier. True to the expectation of Al13- as a molecular model for the Al surface, the identification of this barrier resolved a long standing puzzle in the initial chemisorption of O2 on Al(111): a barrier was identified in experiment but not in any theoretical calculations on the ground state potential surface. / Reactions on solid surfaces play a crucial role in many technologically important areas such as corrosion, adhesion, synthesis of new materials and heterogeneous catalysis. Theoretical studies on chemical reactions at surfaces can provide much useful information to understand and control these chemical processes. The present project is devoted to explore chemical reactions occurred on the aluminum cluster of Al13- and on the Si(100) surface by first principle calculations, using Gaussian 03 and Vienna Ab Initio Simulation Package (VASP). / The Al13-+HX reactions, with HX being either HCl or HI, are explored by first principle calculations and two importance dynamic factors are identified. Firstly, there was a barrier to the dissociative adsorption of FIX on the surface of an Al13- cluster, which involved charge transfer from Al13-. Secondly, the H atom could be bonded to the cluster in multiple ways, similar to the top, bridge and hollow adsorption sites on Al(111) surface. With a large amount of energy (>40 kcal/mol) deposited during the formation of Al13 -HX-, the H atom could easily migrate among these sites, similar to the diffusion of H on metal surfaces. The two dynamic factors were therefore important considerations in the formation and dissociation of Al 13-HX- And moreover, these dynamic factors make Al13- a fascinating model to probe the dynamic aspect of surface reactions, which should be an important consideration in the reactivity of other metal clusters. / Yuan, Qinghong. / "October 2009." / Source: Dissertation Abstracts International, Volume: 72-01, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

An STM head based on the design of Besocke was designed and constructed to have superior vibrational and thermal stability in order to produce very high resolution images. The vibrational properties and thermal properties of the head design are quantitatively analyzed and compared to the actual performance achieved. With this new STM head, we were able to implement spectroscopic dI/dV imaging techniques (conductance imaging) to observe electronic features on surfaces. Using this conductance imaging, benzene and chlorobenzene on the Si(111)7x7 surface were studied. We also present the first solid evidence that confirms that the rest atom is involved in the bonding of benzene to this surface. We show that conductance imaging does indeed show variations in the electronic structure of the surface with adsorbates, illustrating that this technique has strong potential for assigning binding sites. / xiv, 155 leaves ; 29 cm.

Hydrogen terminated silicon surfaces have been utilized to develop sensors for semiconductor and environmental applications. The interaction of these surfaces with different environments has also been studied in detail. The sensor assembly relevant to the semiconductor industry utilizes a silicon-based sensor to detect trace levels of metallic contaminants in hydrofluoric acid. The sensor performance with respect to two non-contaminating reference electrode systems was evaluated. In the first case, conductive diamond was used as a reference electrode. In the second case, a dual silicon electrode system was used with one of the silicon-based electrodes protected with an anion permeable membrane behaving as the quasi reference electrode. Though both systems could function well as a suitable reference system, the dual silicon electrode design showed greater compatibility for the on-line detection of metallic impurities in HF etching baths. The silicon-based sensor assembly was able to detect parts- per-trillion to parts-per-billion levels of metal ion impurities in HF. The sensor assembly developed for the environmental application makes use of a novel method for the detection of Ni2+using attenuated total reflection (ATR) technique. The nickel infrared sensor was prepared on a silicon ATR crystal uniformly coated by a 1.5 micron Nafion film embedded with dimethylglyoxime (DMG) probe molecules. The detection of Ni2+ was based on the appearance of a unique infrared absorption peak at 1572 cm-1 that corresponds to the C=N stretching mode in the nickel dimethylglyoximate, Ni(DMG)2, complex. The suitable operational pH range for the nickel infrared sensor is between 6-8. The detection limit of the nickel infrared sensor is 1 ppm in the sample solution of pH=8. ATR - FTIR spectroscopy was used to study the changes that the hydride mode underwent when subjected to different environments. The presence of trace amounts of Cu2+ in HF solutions was found to roughen the silicon surface as observed ATR-IR spectroscopy. The initial stages of oxidation in UPW and Cu2+ / UPW was studied. Trace amounts of Cu2+ were found to drastically increase the rate of oxidation, while the rate of oxidation was found to be retarded on removing dissolved oxygen that was present in UPW.