780 research outputs found
Large-area three-dimensional optical imaging and subdiffraction photolithography with polydimethylsiloxane (PDMS) nanotip array
No full textWith the challenge of obtaining high resolution three-dimensional images of
nanostructures over large areas as well as fabricating these nanostructures in a low-cost manner,
developing cost-effective strategies which enable high-resolution, large-area nanostructures
imaging as well as fabrication is a long standing goal in nanotechnology community. In this
thesis, a pristine or modified polydimethylsiloxane (PDMS) tip array consisting of thousands of
nanotips was utilized to address the above challenge.
The first part of the dissertation explored a new optical microscopy which enables the
measurement of topography and chemical properties of sample surfaces by taking advantage of
the interaction between a transparent and elastomeric tip array and underlying surfaces. Since the
reflected light intensity at the apexes of nanotips changed significantly when the soft probes
contact and separate with underlying sample surfaces, the exact contact and separation positions
in the vertical direction can be precisely determined and therefore used for measuring the feature
height. This imaging method has never been reported before. One remarkable advantage of
parallel scanning optical microscopy (PSOM) is the multiple tip nature. As hundreds of nanotips
scan at different places on the underlying surface simultaneously, the image covering the areas of
square millimeter scale could be obtained in just one run with sub-diffraction vertical resolution.
Currently, the feature height down to 35 nm can be measured by PSOM, which has broken the
diffraction limit in the vertical direction. Three-dimensional topographical image covering the
surface area of 0.15 mm? was acquired by using 91 tips parallel scanning. The adhesive force
between tips and chemically modified surfaces during the separation process can be detected.
Based on this, the hydrophilic and hydrophobic surfaces can be differentiated by this tip array.
This potentially enables the probes to map the spatial distribution of different functional groups on the surfaces. The application of low-cost PDMS tips as the scanning probes and utilization of
white light intensity change as the feedback impart the cost-effective and simple characteristics
toPSOM.
The second part of the thesis explored near-field photolithography approaches allowing
for nanoscale sub-diffraction nanostructure fabrication over large areas on surfaces in a low-cost
manner. In this work, pristine and metal-coated PDMS nanostructures were used as the
photomasks to produce wafer-scale sub-diffraction nanostructures via near-field
photolithography. The PDMS based photomasks gain the merits of low-cost, easy fabrication,
ease-of-use, repeatedly usage. Since the elastomeric PDMS nanostructures can contact with
underlying surfaces intimately, which enables the incident light to expose underlying photoresist
in the optical near-field, the diffraction limit has been circumvented and therefore sub-diffraction
nanostructures can be produced. The following three types of near-field photolithography
strategies were developed in this work.
Firstly, wafer-scale sub-IOO nm near-field photolithography strategy with metal-coated
elastomeric masks was developed. The incident light was strictly allowed to pass from the
nanoscopic apertures at the apexes of tips to expose underlying photoresist, producing sub-IOO
nm features over wafer-scale areas based on common mask aligner patterning platform.
Secondly, a centimeter-scale sub-IOO nm near-field photolithography strategy with
light leaking photomasks was developed. By using electron-beam evaporation to evaporate
metals towards the PDMS relief nanostructures of vertical side walls with controlled evaporation
direction, two-side or one-side nanoscopic apertures at the side walls were produced
straightforwardly. Through the apertures, the incident passed to expose underlying photoresist at nanoscale areas. This facile near-field photolithography strategy bypassed the complicated
procedures of creating nanoscopic apertures after metal-coating, while possessed the capability
of producing sub-lOf nm features with arbitrary shapes.
Thirdly, wafer-scale sub-LOu nm near-field photolithography by usmg V-shape
transparent and elastomeric nanotip array as photomasks was developed. Rather than utilize
opaque metal layer coating to fabricate the photomasks, herein, the V-shape total reflective
PDMS nanostructures were used as the light intensity modulator. Only the photoresist at the
nanoscale contact areas between the apexes of tips and surfaces was allowed to be exposed
completely, generating sub-l Of nm nanopattems over wafer-scale areas.
At last, a facile method was developed to synthesize large-area single sub-la nm
nanoparticle array in-situ by polymer pen lithography (PPL). Herein, small molecules such as
ethylene glycol (EG) or glycerol were utilized to facilitate the delivery of nanoparticle precursors
to the substrates in polymer pen lithography. Subsequently, large-area ordered single
nanoparticle arrays including sub-la nm Ag nanoparticle, 30 nm Au nanoparticle and 80 nm
Fe203 nanoparticle have been synthesized in-situ with controllable size and pitches.Doctor of Philosophy (MSE
The Relationships between the Shih-huo-chih in the Sung-chao kuo-shih and the Shih-huo-chih in the Sung-shi
No full textDuring the Sung dynasty many versions of the national history were compiled. All these national histories included a chapter called Shih-huo-chih 食貨志. These versions of the Shih-huo-chih are not extant now in their original form, but fragments of them have been included in such books as the Sung-shih Shih-huo-chih 宋史食貨志, the Hsü Tzŭ-chih-t’ung-chien ch’ang-pien 續資治通鑑長編, the Wên-hsien t’ung-k’ao 文獻通考, the Yü-hai 玉海, the Huang-chao pien-nien kang-mu pei-yao 皇朝編年綱目備耍, and the Shang-t’ang ch’ün-shu k’ao-so 山堂群書考索. The original form of the Shih-huo-chih, therefore, can be traced to some extent. Among the above works, the preface to the Shih-huo-chih in the Sung-shih states that, though the chapter was based on the Shih-huo-chih in the Sung-chao kuo-shih 宋朝國史, the quotation was limited only to the facts worth quoting because otherwise the chapter would become too voluminous. Comparing, however, the chapter of the Sung-chao kuo-shih with the similar chapters of the above works, the Sung-shih Shih-huo-chih seems to have borrowed in its entirety this chapter in the Sung-chao kuo-shih. In other words, although the Sung-shih Shih-huo-chih is mostly based on the Shih-huo-chih in the Sung-chao kuo-shih, such chapters as the fang-t’ien 方田 were newly added, and the description of the Sung-chao kuo-shih is sometimes corrected or illustrated by new facts. Moreover, for the period after Li-tsung 理宗 at the end of the Southern Sung (1225~1279), the Sung-shih Shih-huo-chih has a unique description because the corresponding part of the Sung-chao kuo-shih is lacking.The author then compares the text of the Sung-shih Shih-huo-chih with that of the above books for the purpose of restoring the original form of the Shih-huo-chih in the Sung-chao kuo-shih. The Hsü Tzŭ-chih t’ung-chien ch’ang-pien not only quotes the Sung-chao kuo-shih most extensively but also exhaustively corrects its errors of the latter. The Wên-hsien t’ung-k’ao also greatly depends upon the Sung-chao kuo-shih without indicating the source, while the Yü-hai, indicating the source, borrows some passages. The Shan-t’ang ch’ün-shu k’ao-so quotes the sections covering the reigns of Chê-tsung 哲宗 and Hui-tsung 徽宗in the Sung-chao kuo-shih which are not clearly recorded in the other books. The Huang-chao pien-nien kang-mu pei-yao quotes, mostly in its notes, the description from the Sung-chao kuo-shih without indicating the source.Thus the Shih-huo-chih in the Sung-chao kuo-shih remains in the form of various versions quoted in other works and from these the author endeavors to restore part of the text of the Shih-huo-chih in the Sung-chao kuo-shih.journal articl
Synthesis and self-assembly of metal-organic frameworks
No full textMetal-organic frameworks (MOFs), also known as porous coordination
polymer(PCPs), are organic-inorganic compounds which are self-assembled from
metal ions/clusters with organic ligands attaining permanent pores, ultrahigh
surface area and infinite structure tailorability. These unique properties have
rendered MOFs as great candidates in gas adsorption and separation, catalysis,
sensing, drug delivery, etc. Structural control over both the molecular level and
particle level is believed to be an efficient way for both creating new properties
and enhancing the current performance of MOFs. To further developing the
properties of MOFs, MOFs particles were modified through various techniques to
achieve the goal above. Techniques, including self-assembly, were applied to
make structure based new or enhanced properties of MOFs.Doctor of Philosophy (MSE
Incorporation of nanoparticles in metal-organic frameworks materials for selective catalysis
No full textPermanently microporous metal-organic frameworks (MOFs), as a new member of heterogeneous catalyst, have shown great promise for catalysis due to their flexible as well as designable structure and outstanding properties. Further, the potential catalysis application of MOFs can be extended by incorporation varieties of nanoparticles (NPs). The traditional heterogeneous catalysts always show the lower selectivity in catalysis due to the limitation of self structure. How to design the NPs/MOFs as a novel heterogeneous catalyst to overcome the limitation of selective catalysis is still a challenge. In this research, the NPs/MOFs as heterogeneous catalyst for selective catalysis was investigated with assistant of the encapsulation of NPs in MOFs as well as the design of NPs/MOFs structure. The first part of the dissertation explored a facile encapsulation strategy to incorparate NPs into MOFs family. Nobel-metal NPs on porous carriers have been attracting an increasing research interest as the important heterogeneous catalyst. However, the fusion and aggregation of noble-metal NPs is a common observed during catalysis reaction by using existing carrier, such as carbon, zeolites and silica, due to high surface energies of free noble-metal NPs. To the best of our knowledge, the development of a suitable method to overcome the problem of NPs aggregation and ideally, introducing new properties to the catalyst at the same time remains a challenge. Herein, the noble metal NPs was encapsulated in carboxylic acid ligands based MOFs, which is the most enormous branch of MOFs family. MOFs matrix has demonstrated convincing advantages as catalytic carriers, which not only avoid the NPs aggregation but also impart new properties to the catalysts composites. Interestingly, the obtained NPs/MOFs composites as hetergeous catalysts exhibited excellent shape-selectivity in olefin hydrogenation, CO oxidation and reduction of 4-nitrophenol. Furthermore, the present results bring hope to the development of heterogeneous catalysts with high activity by using MOFs as a new host for different NPs. The second part of the thesis explored a facile encapsulation and etching strategy of NPs to craft mesopores in MOFs. Especially, the mesopore structure and space distribution could be designed by control of size, shape of NPs and encapsulation condition. It is well known that porous MOFs can be of a powerful tool for many important applications such as gas storage, catalysis, and separation because of the tunable shape and size selectivity of their pore apertures. Large pore aperture will make MOFs lose the unique selectivity; nevertheless, their small pore aperture inherently limits the diffusion of chemical species within MOFs, giving rise to low efficiency in real applications. To date, the development of a suitable method to enhance the molecular diffusion within MOFs while preserving their selectivity remains a challenge. To solve this issue, here, we reported a facile encapsulation and etching strategy of NPs to craft mesopores with controlled size, shape and space distribution in MOFs. Interestingly, we simultaneously incorporated two kinds of NPs in MOFs, where one kind of NPs were served as the catalytic active sites and another kind of NPs were used as the sacrificial template that was subsequently removed by simple etching, leaving mesopores inside the MOFs. In addition, the hierarchical meso-MOFs were be achieved by flexible design of NPs encapsulation as well as simple etching of NPs. It is worth noticing that the obtained MOFs maintained a well-defined crystal structure, showing good selectivity as well as enhanced conversion in liquid phase hydrogenation reaction. Due to the reason that the methods of incorporating NPs of different kinds, shapes and sizes in MOFs have been well developed, the encapsulation strategy is thus general and universal, and can seek a broad range of applications in the field of sensor, storage, medicine and catalysis. The third part of the thesis describes a simple heterogeneous catalyst, NPs/MOFs, which exhibited the unprecedented site-selectivity for oxidation of diol and hydrogenation of alkadiene by simple physical space limitation of MOFs pore. The selective reaction of one functional group of a molecule with several similar functional groups has been the hot topic and always challenge in the field of heterogeneous catalysis. Historically, homogeneous catalyst has provided the only precedents by specific chemical interactions. Although heterogeneous catalysts that meet some of these challenges became known, a simple solution has remained persistent issue. Selective oxidation of diol and selective hydrogenation of alkadiene provide archetypical examples for this challenge. Here, we describe a simple heterogeneous catalyst, NPs/MOFs, which exhibited the unprecedented site-selectivity for oxidation of diol and hydrogenation of alkadiene by simple physical space limitation of MOFs pore, thereby protecting the secondary functional group. Interestingly, in the case of the selective hydrogenation of unsaturated epoxide, NPs/MOFs not only utilized the Pt NPs completely encapsulated in MOFs matrixes but also limited the stretch and movement of PVP by MOFs matrixes to offer the enough steric effect, thereby perfectly performing 100% of selectivity on C=C hydrogenation and protecting the epoxy group. The results suggested exploiting the NPs/MOFs as a heterogeneous catalyst make the position-selectivity catalysis become easy, further open a new door for heterogeneous catalyst in the field of site-selective catalysis, previously, exclusively belonging to homogenous catalyst. The last part of thesis explores a facile encapsulation strategy to prepare NPs/MOFs hybrid thin films which show the optical, magnetic, and catalytic properties originating from the NPs as well as the size-selectivity deriving from microporous structure of the MOFs thin films. Fabrication of MOFs thin films is the starting point of extending MOFs to practical applications of nano-devices. Recently, the controllable integration of functional NPs with MOFs thin film, has been garnering growing research interests for the reason that hybrid MOFs thin films often exhibit optimized as well as novel properties compare to their intrinsic MOFs and thus, could open promising opportunities for developing novel functional nanomaterials such as sensing devices, electronic, and catalytic. To the best of our knowledge, it remains to be a challenge to develop a general, controlled fabrication technique of hybrid MOFs thin films that could efficiently utilize the pore space of MOFs crystals and the functionalities of the incorporated NPs. To solve this issue, herein, we report a simple method to incorporate several types of NPs in zeolitic imidazolate framework thin films by direct growth and spin coating. The as prepared dense, continuous and tunable NPs/MOFs hybrid thin films exhibited both novel properties and molecules sieve behaviors. The results presented here successfully overcome the difficulties of NPs incorporation into thin films by existing methods and would provide valuable insights for the preparation of MOFs-based nano-devices in the future.Doctor of Philosophy (MSE
Synthesis of noble metal-based nanocomposites for enhanced catalytic performance
No full textNoble metals have been applied as heterogeneous catalysts for a long time. In recent decades, it was found that noble metal nanostructures exhibit superior catalytic performance than their bulk counterpart owing to the high surface-to-volume ratio. However, it is challenging for single-component nanomaterials to achieve multiple goals such as catalytic activity, selectivity and stability. Noble metal nanocomposites thus have drawn growing attention spontaneously.
This study aims to fabricate noble metal-based nanocomposites possessing enhanced catalytic performance. Experimental methods used include wet chemical reduction, solvothermal synthesis, and post synthetic modification. The as-synthesized materials were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and many other techniques. Ultraviolet-visible Spectroscopy (UV-Vis) and gas chromatography (GC) were used to monitor the catalytic reactions.
First of all, a facile and robust method was provided to prepare ultrathin bimetallic core-shell nanosheets (NSs), where the ultrathin 2D metallic NSs are incompletely covered by another atomically layered metal. Submonolayered Ru decorated-ultrathin Pd NSs was synthesized using this seed-mediated growth method for the first time, which is referred to as Pd@Ru NSs. The underpotential deposition process is responsible for the formation of Pd@Ru NSs. Impressively, the as-synthesized noble bimetallic Pd@Ru NSs exhibit superior catalytic performance toward the reduction of 4-nitrophenol and the semihydrogenation of 1-octyne as compared to the pure ultrathin Pd NSs and Ru NSs.
The second work elaborated the synthesis of 2D noble metal/porphyrinic metal-organic framework (MOF) composite via a seed-mediated growth method. Owing to the synergistic effect between the photothermal effect of Pd and the light-harvesting ability of the porphyrinic MOF Cu-TCPP, the composite exhibits superior catalytic performance than pure Pd NSs in the photo-oxidation of benzyl alcohol under high light irradiation intensity. Furthermore, the catalytic activity of the composite can be altered upon different light irradiation intensities.
In the last work, it was demonstrated that the pore size of NPs/MOF composite can be modified with alkyl chains of different lengths. The obtained products showed enhanced size-selective catalytic performance in the hydrogenation of olefins (triphenylethylene, trans-stilbene, cyclooctene), which revealed the flexibility of MOFs as supporting materials for heterogeneous catalysis.
Based on these accomplished works, a conclusion can be drawn that noble metal based nanocomposites provide better options for some chemical reactions in the following aspects. Firstly, coupling noble metal with another component may induce a synergistic effect, which can promote the catalytic activity. Secondly, combing noble metal with some functional materials, such as MOFs, can introduce some additional properties, which may be beneficial to the catalytic activity as well as selectivity. Last but not least, supporting materials can promote the dispersion and stability of noble metal nanostructures.Doctor of Philosophy (MSE
Increase the catalytic activity of metal-organic frameworks by synthesis modulator approach
No full textPermanently microporous metal-organic frameworks (MOFs), a group of crystalline organic-inorganic hybrid compounds formed by organic linker and metal ions or clusters coordination, have great potential for catalysis applications due to the diverse structure and properties. The applications can be improved further by incorporation various functional components (for instance, platinum (Pt) metal nanoparticles). After study and investigation done in this area on a specific case for the zirconium terephthalate UiO-66 (Zr), it is found that modulation can be used as an approach to increase the catalytic activity of UiO-66(Zr) significantly. With partial substitution of terephthalates by trifluoroacetate, using trifluoroacetic acid (TFA) and acetic acid together during the synthesis can result in a highly ordered crystalline structure. Aiming for obtaining a more open framework with more open sites, thermal treatment of the material is employed. Besides dehydroxylation of the inorganic Zr cluster, it also leads to post-synthetic removal of the trifluoroacetate groups. Here, the challenge was overcome by the incorporation of Pt nanoparticles and TFA which is aiming to create more active sites inside the MOFs without aggregation of Pt nanoparticles on the surfaces of framework. With the demonstration of the catalytic activity of UiO-66(Zr) for a series of reactions can be improved by adding TFA, it is observed that trifluoroacetate groups would replace part of the terephthalate linkers in the MOF structure synthesized, resulting in a more open structured with extra Lewis acid sites material. In addition, incorporation of Pt nanoparticles can further enhance the catalytic activity of the material as proven by the higher conversion during the experiment. Consequently, the material is a great canditate for several Lewis acid catalyzed reactions as highly active catalyst.Bachelor of Engineering (Materials Engineering
Incorporated nanoparticles in MOFs thin film for catalysis
No full textThin film MOF catalyst is not widely research on only until recent years. In this project, the focus of research will be to incorporate thin film MOF with a mixture of nanoparticles, Pt/Au and Pt/Cu2O to find out the best combination to achieve a novel catalyst. Au and Cu2O both act as sacrificial templates, they are embedded and etched off to create pores and increase the porosity of ZIF-8. However, Cu2O constantly aggregate and dispersed unevenly when embedded and the etching solution corrode both the Cu2O and ZIF-8. Therefore only Au and Pt nanoparticles are selected to be embedded on ZIF-8 for hydrogenation of hexene. Only samples with 5 cycles of nanoparticles displayed catalytic reaction mainly due to the small amount of Pt embedded and the low diffusion rate. Between Pt/ZIF-8 and porous Pt/ZIF-8, porous Pt/ZIF-8 displayed higher catalytic activity due to higher porosity.Bachelor of Engineering (Materials Engineering
Incorporation of nanoparticles in metal-organic frameworks materials for catalysis
No full textMetal organic framework incorporated with various nanoparticles composites were investigated for the oxidation of benzyl alcohol to benzyl aldehyde. Promising catalysis conversion and selectivity were obtained in this project, 45% and 100% respectively. Those high catalysis conversion and selectivity were obtained by having good synthesis methods for the nanoparticles and thereafter, good encapsulation method to incorporate the nanoparticles into the metal organic framework. Metal organic framework used in this project was zeolitic imidazolate framework 8, it provided selectivity via the small pore aperture of 3.4Å and allow nanoparticles to reside on its high pore surface area of over 1,500m2/g. As for nanoparticles, cerium oxide and palladium were used. Both nanoparticles were synthesized into desired shape and size, nanocube with about 5nm edge length for cerium oxide and nanosphere with about 3nm diameter for palladium. Surfactant grafting of polyvinylpyrroidone for the nanoparticles was successful and proven to be an essential step to ensure good encapsulation. Apart from surfactant grafting, prolong sonication of 8hours and the use of right concentration of nanoparticles for encapsulation were shown to be equally important for good encapsulation. Overall, with the comprehensive approach towards the making of the metal organic framework incorporated with various nanoparticles composites, this project has comparable and promising catalysis conversion and selectivity.Bachelor of Engineering (Materials Engineering
Sclerotherapy in Lymphatic Malformations with Intralesional Hemorrhage: A Retrospective Comparison with Non-Hemorrhagic Lymphatic Malformations [Corrigendum]
No full textWang W, Liu B, Long J, Bi J, Huo R. Clin Cosmet Investig Dermatol. 2022;15:2275–2284.
The authors have advised there is an error in the author list on page 2275. The author name “Junsong Long” should read “Junsang Long”.
The authors apologize for this error
Development of massively parallel nanolithography
No full textAs technology is becoming more and more advanced every day, lithography techniques are also moving towards nanoscale production of components needed in integrated electronic circuits, micro electrochemical systems (MEMS) and in medical and biology field etc. An ideal lithography method is essential to obtain high resolution patterns over to meet the rising needs of technology.
In this project, the task was to develop massively parallel nanolithography patterns. The report will demonstrate how the newly designed V-shaped PDMS trench array using beam pen lithography would fulfill the requirements of obtaining large surface area patterns with high resolution to cater for cell biology needs. Using this technique would overcome problems of low throughput and low resolution that other lithography techniques encounter.
To achieve large area patterns with high resolution, various experimental conditions were optimized to ensure that the patterns that the student wanted was ideal for use in the research for biology cell spreading and stem differentiation. This can be done through changing the shape and pitch of the PDMS mask to create patterns with different pitches.
From the experimental findings, it is evident that beam pen lithography can change between near and far field distances to allow both sub diffraction limit (100nm) and larger surface area to be produced.Bachelor of Engineering (Materials Engineering
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