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Articles 1 - 20 of 20
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6:1 Aspect Ratio Silicon Pillar Based Thermal Neutron Detector Filled With 10B, R. J. Nikolic, A. M. Conway, C. E. Reinhart, R. T. Graff, T. F. Wang, N. Deo, Barry Chin Li Cheung
6:1 Aspect Ratio Silicon Pillar Based Thermal Neutron Detector Filled With 10B, R. J. Nikolic, A. M. Conway, C. E. Reinhart, R. T. Graff, T. F. Wang, N. Deo, Barry Chin Li Cheung
Barry Chin Li Cheung Publications
Current helium-3 tube based thermal neutron detectors have shortcomings in achieving simultaneously high efficiency and low voltage while maintaining adequate fieldability performance. By using a three-dimensional silicon p-i-n diode pillar array filled with boron-10 these constraints can be overcome. The fabricated pillar structured detector reported here is composed of 2 μm diameter silicon pillars with a 4 μm pitch and height of 12 μm. A thermal neutron detection efficiency of 7.3+/−0.6% and a neutron-to-gamma discrimination of 105 at 2 V reverse bias were measured for this detector. When scaled to larger aspect ratio, a high efficiency device is possible.
Fabrication Of Pillar-Structured Thermal Neutron Detectors, Rebecca J. Nikolić, Adam M. Conway, Catherine E. Reinhardt, Robert T. Graff, Tzu Fang Wang, Nirmalendu Deo, Chin Li Cheung
Fabrication Of Pillar-Structured Thermal Neutron Detectors, Rebecca J. Nikolić, Adam M. Conway, Catherine E. Reinhardt, Robert T. Graff, Tzu Fang Wang, Nirmalendu Deo, Chin Li Cheung
Barry Chin Li Cheung Publications
Pillar detector is an innovative solid state device structure that leverages advanced semiconductor fabrication technology to produce a device for thermal neutron detection. State-of-the-art thermal neutron detectors have shortcomings in achieving simultaneously high efficiency, low operating voltage while maintaining adequate fieldability performance. By using a 3-dimensional silicon PIN diode pillar array filled with isotopic boron 10, (10B) a high efficiency device is theoretically possible. The fabricated pillar structures reported in this work are composed of 2 μm diameter silicon pillars with a 4 μm pitch and pillar heights of 6 and 12 μm. The pillar detector with a …
Searching For Smart Durable Coatings To Promote Bone Marrow Stromal Cell Growth While Preventing Biofilm Formation, Fereydoon Namavar, John D. Jackson, J. Graham Sharp, Ethan E. Mann, Kenneth W. Bayles, Chin Li Cheung, Connie A. Feschuk, Shailaja Varma, Hani Haider, Kevin L. Garvin
Searching For Smart Durable Coatings To Promote Bone Marrow Stromal Cell Growth While Preventing Biofilm Formation, Fereydoon Namavar, John D. Jackson, J. Graham Sharp, Ethan E. Mann, Kenneth W. Bayles, Chin Li Cheung, Connie A. Feschuk, Shailaja Varma, Hani Haider, Kevin L. Garvin
Barry Chin Li Cheung Publications
There is a great need to develop methods to regulate cellular growth in order to enhance or prevent cell proliferation, as needed, to either improve health or prevent disease. In this work we evaluated the adhesion, survival and growth of bone marrow stromal cells on the surface of several new ion beam engineered nano-crystals of ceramic hard coatings such as zirconium, titanium, tantalum and cerium oxides. Cell adhesion and growth on the ceramic coatings were compared to adhesion and growth on a nano-crystalline silver coating which is known to possess antibacterial properties. The initial results of a study to determine …
Fabrication Of Nanopillars By Nanosphere Lithography, Chin Li Cheung, R. J. Nikolic, C. E. Reinhardt, T. F. Wang
Fabrication Of Nanopillars By Nanosphere Lithography, Chin Li Cheung, R. J. Nikolic, C. E. Reinhardt, T. F. Wang
Barry Chin Li Cheung Publications
A low cost nanosphere lithography method for patterning and generation of semiconductor nanostructures provides a potential alternative to the conventional top-down fabrication techniques. Forests of silicon pillars of sub-500 nm diameter and with an aspect ratio up to 10 were fabricated using a combination of the nanosphere lithography and deep reactive ion etching techniques. The nanosphere etch mask coated silicon substrates were etched using oxygen plasma and a timemultiplexed “Bosch” process to produce nanopillars of different length, diameter and separation. Scanning electron microscopy data indicate that the silicon etch rates with the nanoscale etch masks decrease linearly with increasing aspect …
Future Of Semiconductor Based Thermal Neutron Detectors, R. J. Nikolić, Chin Li Cheung, C. E. Reinhardt, T. F. Wang
Future Of Semiconductor Based Thermal Neutron Detectors, R. J. Nikolić, Chin Li Cheung, C. E. Reinhardt, T. F. Wang
Barry Chin Li Cheung Publications
Thermal neutron detectors have seen only incremental improvements over the last decades. In this paper we overview the current technology of choice for thermal neutron detection – 3He tubes, which suffer from, moderate to poor fieldability, and low absolute efficiency. The need for improved neutron detection is evident due to this technology gap and the fact that neutrons are a highly specific indicator of fissile material. Recognizing this need, we propose to exploit recent advances in microfabrication technology for building the next generation of semiconductor thermal neutron detectors for national security requirements, for applications requiring excellent fieldability of small …
Roadmap For High Efficiency Solid-State Neutron Detectors, R. J. Nikolic, Chin Li Cheung, C. E. Reinhardt, T. F. Wang
Roadmap For High Efficiency Solid-State Neutron Detectors, R. J. Nikolic, Chin Li Cheung, C. E. Reinhardt, T. F. Wang
Barry Chin Li Cheung Publications
Solid-state thermal neutron detectors are generally fabricated in a planar configuration by coating a layer of neutron-to-alpha converter material onto a semiconductor. The as-created alpha particles in the material are expected to impinge the semiconductor and create electron-hole pairs which provide the electrical signal. These devices are limited in efficiency to a range near (2-5%)/cm2 due to the conflicting thickness requirements of the converter layer. In this case, the layer is required to be thick enough to capture the incoming neutron flux while at the same time adequately thin to allow the alpha particles to reach the semiconductor. A …
Atomic Force Microscopy Investigation Of Virus Aggregation And Assembly At Chemical Templates Formed By Scanned Probe Nanolithography, Chin Li Cheung, S. -W. Chung, J. J. De Yoreo, A. Chatterji, T. Lin, J. E. Johnson
Atomic Force Microscopy Investigation Of Virus Aggregation And Assembly At Chemical Templates Formed By Scanned Probe Nanolithography, Chin Li Cheung, S. -W. Chung, J. J. De Yoreo, A. Chatterji, T. Lin, J. E. Johnson
Barry Chin Li Cheung Publications
Aggregation and assembly of macromolecules are important processes in a number of scientific fields including structural biology, medicine, and materials science. For example, growth of well-ordered two-dimensional (2-D) arrays and bulk crystals remains the rate-limiting step in macromolecular structure determination. Uncontrolled aggregation of proteins is the source of a number of devastating pathologies such as Creutzfeldt-Jakob syndrome. Moreover, the demonstrated ability of engineered viruses and proteins to act as templates for growth of inorganic nanostructures is driving a need for methods to deterministically pattern their assembly at surfaces in order to fabricate hierarchical materials and devices.
The Creation Of Organic And Biological Nanostructures At Surfaces Using Scanning Probe Nanolithography, B. L. Weeks, Chin Li Cheung, J. J. De Yoreo
The Creation Of Organic And Biological Nanostructures At Surfaces Using Scanning Probe Nanolithography, B. L. Weeks, Chin Li Cheung, J. J. De Yoreo
Barry Chin Li Cheung Publications
As the size of microelectronic devices continues to shrink and the desire to build in hierarchical structures of organic and biological materials grows, control of the chemistry and structure of materials at the molecular level will become increasingly important. Conventional lithographic techniques to pattern polymeric thin films are beginning to reach their resolution limit and several alternative "bottom-up" strategies have emerged that use the scanning probe microscope to manipulate matter at the atomic or molecular scale. Of these new scanning probe nanolithography (SPN) techniques, dip-pen nanolithography (DPN) [I] and scanning probe nanografting (SNG) [2] are particularly promising.
The DPN methodology …
Direct Haplotyping Of Kilobase-Size Dna Using Carbon Nanotube Probes, Adam T. Woolley, Chantal Guillemette, Chin Li Cheung, David E. Housman, Charles M. Lieber
Direct Haplotyping Of Kilobase-Size Dna Using Carbon Nanotube Probes, Adam T. Woolley, Chantal Guillemette, Chin Li Cheung, David E. Housman, Charles M. Lieber
Barry Chin Li Cheung Publications
We have implemented a method for multiplexed detection of polymorphic sites and direct determination of haplotypes in 10-kilobasesize DNA fragments using single-walled carbon nanotube (SWNT) atomic force microscopy (AFM) probes. Labeled oligonucleotides are hybridized specifically to complementary target sequences in template DNA, and the positions of the tagged sequences are detected by direct SWNT tip imaging. We demonstrated this concept by detecting streptavidin and IRD800 labels at two different sequences in M13mp18. Our approach also permits haplotype determination from simple visual inspection of AFM images of individual DNA molecules, which we have done on UGT1A7, a gene under study as …
Direct Imaging Of Human Swi/Snf-Remodeled Mono- And Polynucleosomes By Atomic Force Microscopy Employing Carbon Nanotube Tips, Gavin R. Schnitzler, Chin Li Cheung, Jason H. Hafner, Andrew J. Saurin, Robert E. Kingston, Charles M. Lieber
Direct Imaging Of Human Swi/Snf-Remodeled Mono- And Polynucleosomes By Atomic Force Microscopy Employing Carbon Nanotube Tips, Gavin R. Schnitzler, Chin Li Cheung, Jason H. Hafner, Andrew J. Saurin, Robert E. Kingston, Charles M. Lieber
Barry Chin Li Cheung Publications
Chromatin-remodeling complexes alter chromatin structure to facilitate, or in some cases repress, gene expression. Recent studies have suggested two potential pathways by which such regulation might occur. In the first, the remodeling complex repositions nucleosomes along DNA to open or occlude regulatory sites. In the second, the remodeling complex creates an altered dimeric form of the nucleosome that has altered accessibility to transcription factors. The extent of translational repositioning, the structure of the remodeled dimer, and the presence of dimers on remodeled polynucleosomes have been difficult to gauge by biochemical assays. To address these questions, ultrahigh-resolution carbon nanotube tip atomic …
Structural And Functional Imaging With Carbon Nanotube Afm Probes, J. H. Hafner, Chin Li Cheung, A. T. Woolley, C. M. Lieber
Structural And Functional Imaging With Carbon Nanotube Afm Probes, J. H. Hafner, Chin Li Cheung, A. T. Woolley, C. M. Lieber
Barry Chin Li Cheung Publications
Atomic force microscopy (AFM) has great potential as a tool for structural biology, a field in which there is increasing demand to characterize larger and more complex biomolecular systems. However, the poorly characterized silicon and silicon nitride probe tips currently employed in AFM limit its biological applications. Carbon nanotubes represent ideal AFM tip materials due to their small diameter, high aspect ratio, large Young’s modulus, mechanical robustness, well-defined structure, and unique chemical properties. Nanotube probes were first fabricated by manual assembly, but more recent methods based on chemical vapor deposition provide higher resolution probes and are geared towards mass production, …
Energy Gaps In “Metallic” Single-Walled Carbon Nanotubes, Min Ouyang, Jin-Lin Huang, Chin Li Cheung, Charles Lieber
Energy Gaps In “Metallic” Single-Walled Carbon Nanotubes, Min Ouyang, Jin-Lin Huang, Chin Li Cheung, Charles Lieber
Barry Chin Li Cheung Publications
Metallic single-walled carbon nanotubes have been proposed to be good one-dimensional conductors. However, the finite curvature of the graphene sheet that forms the nanotubes and the broken symmetry due to the local environment may modify their electronic properties. We used low-temperature atomically resolved scanning tunneling microscopy to investigate zigzag and armchair nanotubes, both thought to be metallic. “Metallic” zigzag nanotubes were found to have energy gaps with magnitudes that depend inversely on the square of the tube radius, whereas isolated armchair tubes do not have energy gaps. Additionally, armchair nanotubes packed in bundles have pseudogaps, which exhibit an inverse dependence …
Atomically Resolved Single-Walled Carbon Nanotube Intramolecular Junctions, Min Ouyang, Jin-Lin Huang, Chin Li Cheung, Charles M. Lieber
Atomically Resolved Single-Walled Carbon Nanotube Intramolecular Junctions, Min Ouyang, Jin-Lin Huang, Chin Li Cheung, Charles M. Lieber
Barry Chin Li Cheung Publications
Intramolecular junctions in single-walled carbon nanotubes are potentially ideal structures for building robust, molecular-scale electronics but have only been studied theoretically at the atomic level. Scanning tunneling microscopy was used to determine the atomic structure and electronic properties of such junctions in single-walled nanotube samples. Metal-semiconductor junctions are found to exhibit an electronically sharp interface without localized junction states, whereas a more diffuse interface and low-energy states are found in metal-metal junctions. Tight-binding calculations for models based on observed atomic structures show good agreement with spectroscopy and provide insight into the topological defects forming intramolecular junctions. These studies have important …
Magnetic Clusters On Single-Walled Carbon Nanotubes: The Kondo Effect In A One-Dimensional Host, Teri W. Odom, Jin-Lin Huang, Chin Li Cheung, Charles M. Lieber
Magnetic Clusters On Single-Walled Carbon Nanotubes: The Kondo Effect In A One-Dimensional Host, Teri W. Odom, Jin-Lin Huang, Chin Li Cheung, Charles M. Lieber
Barry Chin Li Cheung Publications
Single-walled carbon nanotubes are ideal systems for investigating fundamental properties and applications of one-dimensional electronic systems. The interaction of magnetic impurities with electrons confined in one dimension has been studied by spatially resolving the local electronic density of states of small cobalt clusters on metallic single-walled nanotubes with a low-temperature scanning tunneling microscope. Spectroscopic measurements performed on and near these clusters exhibit a narrow peak near the Fermi level that has been identified as a Kondo resonance. Using the scanning tunneling microscope to fabricate ultra-small magnetic nanostructures consisting of small cobalt clusters on short nanotube pieces, spectroscopic studies of this …
Structural Biology With Carbon Nanotube Afm Probes, Adam T. Woolley, Chin Li Cheung, Jason H. Hafner, Charles M. Lieber
Structural Biology With Carbon Nanotube Afm Probes, Adam T. Woolley, Chin Li Cheung, Jason H. Hafner, Charles M. Lieber
Barry Chin Li Cheung Publications
Carbon nanotubes represent ideal probes for high-resolution structural and chemical imaging of biomolecules with atomic force microscopy. Recent advances in fabrication of carbon nanotube probes with sub-nanometer radii promise to yield unique insights into the structure, dynamics and function of biological macromolecules and complexes.
Carbon Nanotube-Based Nonvolatile Random Access Memory For Molecular Computing, Thomas Rueckes, Kyoungha Kim, Ernesto Joselevich, Greg Y. Tseng, Chin Li Cheung, Charles M. Lieber
Carbon Nanotube-Based Nonvolatile Random Access Memory For Molecular Computing, Thomas Rueckes, Kyoungha Kim, Ernesto Joselevich, Greg Y. Tseng, Chin Li Cheung, Charles M. Lieber
Barry Chin Li Cheung Publications
A concept for molecular electronics exploiting carbon nanotubes as both molecular device elements and molecular wires for reading and writing information was developed. Each device element is based on a suspended, crossed nanotube geometry that leads to bistable, electrostatically switchable ON/OFF states. The device elements are naturally addressable in large arrays by the carbon nanotube molecular wires making up the devices. These reversible, bistable device elements could be used to construct nonvolatile random access memory and logic function tables at an integration level approaching 1012 elements per square centimeter and an element operation frequency in excess of 100 gigahertz. The …
Growth And Fabrication With Single-Walled Carbon Nanotube Probe Microscopy Tips, Chin Li Cheung, Jason H. Hafner, Teri W. Odom, Kyoungha Kim, Charles M. Lieber
Growth And Fabrication With Single-Walled Carbon Nanotube Probe Microscopy Tips, Chin Li Cheung, Jason H. Hafner, Teri W. Odom, Kyoungha Kim, Charles M. Lieber
Barry Chin Li Cheung Publications
Single-walled carbon nanotube (SWNT) probe microscopy tips were grown by a surface growth chemical vapor deposition method. Tips consisting of individual SWNTs (1.5–4 nm in diameter) and SWNT bundles (4–12 nm in diameter) have been prepared by design through variations in the catalyst and growth conditions. In addition to high-resolution imaging, these tips have been used to fabricate SWNT nanostructures by spatially controlled deposition of specific length segments of the nanotube tips.
Carbon Nanotube Atomic Force Microscopy Tips: Direct Growth By Chemical Vapor Deposition And Application To High-Resolution Imaging, Chin Li Cheung, Jason H. Hafner, Charles M. Lieber
Carbon Nanotube Atomic Force Microscopy Tips: Direct Growth By Chemical Vapor Deposition And Application To High-Resolution Imaging, Chin Li Cheung, Jason H. Hafner, Charles M. Lieber
Barry Chin Li Cheung Publications
Carbon nanotubes are potentially ideal atomic force microscopy probes because they can have diameters as small as one nanometer, have robust mechanical properties, and can be specifically functionalized with chemical and biological probes at the tip ends. This communication describes methods for the direct growth of carbon nanotube tips by chemical vapor deposition (CVD) using ethylene and iron catalysts deposited on commercial silicon-cantilever-tip assemblies. Scanning electron microscopy and transmission electron microscopy measurements demonstrate that multiwalled nanotube and single-walled nanotube tips can be grown by predictable variations in the CVD growth conditions. Force-displacement measurements made on the tips show that they …
Growth Of Nanotubes For Probe Microscopy Tips, Jason H. Hafner, Chin Li Cheung, Charles M. Lieber
Growth Of Nanotubes For Probe Microscopy Tips, Jason H. Hafner, Chin Li Cheung, Charles M. Lieber
Barry Chin Li Cheung Publications
Carbon nanotubes, which have intrinsically small diameters and high aspect ratios and which buckle reversibly, make potentially ideal structures for use as tips in scanning probe microscopies, such as atomic force microscopy (AFM)1, 2, 3, 4. However, the present method of mechanically attaching nanotube bundles for tip fabrication is time consuming and selects against the smallest nanotubes, limiting the quality of tips. We have developed a technique for growing individual carbon nanotube probe tips directly, with control over the orientation, by chemical vapor deposition (CVD) from the ends of silicon tips. Tips grown in this way may become …
Covalently Functionalized Nanotubes As Nanometer-Sized Probes In Chemistry And Biology, Stanislaus S. Wong, Ernesto Joselevich, Adam T. Woolley, Chin Li Cheung, Charles M. Lieber
Covalently Functionalized Nanotubes As Nanometer-Sized Probes In Chemistry And Biology, Stanislaus S. Wong, Ernesto Joselevich, Adam T. Woolley, Chin Li Cheung, Charles M. Lieber
Barry Chin Li Cheung Publications
Carbon nanotubes combine a range of properties that make them well suited for use as probe tips in applications such as atomic force microscopy (AFM)1, 2, 3. Their high aspect ratio, for example, opens up the possibility of probing the deep crevices4 that occur in microelectronic circuits, and the small effective radius of nanotube tips significantly improves the lateral resolution beyond what can be achieved using commercial silicon tips5. Another characteristic feature of nanotubes is their ability to buckle elastically4, 6, which makes them very robust while limiting the maximum force that is …