arXiv subjects

Xiaolin Li

Publications and source records attributed to Xiaolin Li.

70 records · Page 4Linked to original sources

arXiv2011

Secure Multiplex Coding Over Interference Channel with Confidential Messages

In this paper, inner and outer bounds on the capacity region of two-user interference channels with two confidential messages have been proposed. By adding secure multiplex coding to the error correction method in [15] which achieves the best achievable capacity region for interference channel up to now, we have shown that the improved secure capacity region compared with [2] now is the whole Han-Kobayashi region. In addition, this construction not only removes the rate loss incurred by adding dummy messages to achieve security, but also change the original weak security condition in [2] to strong security. Then the equivocation rate for a collection of secret messages has also been evaluated, when the length of the message is finite or the information rate is high, our result provides a good approximation for bounding the worst case equivocation rate. Our results can be readily extended to the Gaussian interference channel with little efforts.

cs.IT↗

arXiv2010

Multiplexed five-color molecular imaging of cancer cells and tumor tissues with carbon nanotube Raman tags in the near-infrared

Single-walled carbon nanotubes (SWNTs) with five different C13/C12 isotope compositions and well-separated Raman peaks have been synthesized and conjugated to five targeting ligands in order to impart molecular specificity. Multiplexed Raman imaging of live cells has been carried out by highly specific staining of cells with a five-color mixture of SWNTs. Ex vivo multiplexed Raman imaging of tumor samples uncovers a surprising up-regulation of epidermal growth factor receptor (EGFR) on LS174T colon cancer cells from cell culture to in vivo tumor growth. This is the first time five-color multiplexed molecular imaging has been performed in the near-infrared (NIR) region under a single laser excitation. Near zero interfering background of imaging is achieved due to the sharp Raman peaks unique to nanotubes over the low, smooth autofluorescence background of biological species.

cond-mat.mtrl-sci↗

arXiv2010

Edge Magneto-Fingerprints in Disordered Graphene Nanoribbons

We report on (magneto)-transport experiments in chemically derived narrow graphene nanoribbons under high magnetic fields (up to 60 Tesla). Evidences of field-dependent electronic confinement features are given, and allow estimating the possible ribbon edge symmetry. Besides, the measured large positive magnetoconductance indicates a strong suppression of backscattering induced by the magnetic field. Such scenario is supported by quantum simulations which consider different types of underlying disorders (smooth edge disorder and long range Coulomb scatters).

cond-mat.mes-hall↗

arXiv2009

Simultaneous Nitrogen-Doping and Reduction of Graphene Oxide

We develop a simple chemical method to obtain bulk quantities of N-doped, reduced graphene oxide (GO) sheets through thermal annealing of GO in ammonia. X-ray photoelectron spectroscopy (XPS) study of GO sheets annealed at various reaction temperatures reveals that N-doping occurs at a temperature as low as 300C, while the highest doping level of ~5% N is achieved at 500C. N-doping is accompanied by the reduction of GO with decreases in oxygen levels from ~28% in as-made GO down to ~2% in 1100C NH3 reacted GO. XPS analysis of the N binding configurations of doped GO finds pyridinic N in the doped samples, with increased quaternary N (N that replaced the carbon atoms in the graphene plane) in GO annealed at higher temperatures (>900C). Oxygen groups in GO were found responsible for reactions with NH3 and C-N bond formation. Pre-reduced GO with fewer oxygen groups by thermal annealing in H2 exhibits greatly reduced reactivity with NH3 and lower N-doping level. Electrical measurements of individual GO sheet devices demonstrate that GO annealed in NH3 exhibits higher conductivity than those annealed in H2, suggesting more effective reduction of GO by annealing in NH3 than in H2, consistent with XPS data. The N-doped reduced GO shows clearly n-type electron doping behavior with Dirac point (DP) at negative gate voltages in three terminal devices. Our method could lead to the synthesis of bulk amounts of N-doped, reduced GO sheets useful for various practical applications.

cond-mat.mtrl-sci↗

arXiv2009

Solvothermal Reduction of Chemically Exfoliated Graphene Sheets

Graphene has attracted much attention due to its interesting properties and potential applications. Chemical exfoliation methods have been developed to make graphene recently, aimed at large-scale assembly and applications such as composites and Li ion batteries. Although efficient, the chemical exfoliation methods involve oxidation of graphene and introduce defects in the as-made sheets. Hydrazine reduction at 100 has shown to partially restore the structure and conductance of graphite oxide. However, the reduced GO still shows strong defect peaks in Raman spectra with higher resistivity than pristine graphene by 2 to 3 orders of magnitude. It is important to produce much less defective graphene sheets than GO, and develop more effective graphene reduction. Recently, we reported a mild exfoliation-reintercalation-expansion method to form high-quality GS with higher conductivity and lower oxidation degree than GO.5 Here, we present a 180 solvothermal reduction method for our GS and GO. The solvothermal reduction is more effective than the earlier reduction methods in lowering the oxygen and defect levels in GS, increasing the graphene domains, and bringing the conductivity of GS close to pristine graphene. The reduced GS possess the highest degree of pristinity among chemically derived graphene.

cond-mat.mtrl-sci↗

arXiv2009

Chemical Self Assembly of Graphene Sheets

Chemically derived graphene sheets were found to self-assemble onto patterned gold structures via electrostatic interactions between noncovalent functional groups on GS and gold. This afforded regular arrays of single graphene sheets on large substrates, characterized by scanning electron and Auger microscopy imaging and Raman spectroscopy. Self assembly was used for the first time to produce on-substrate and fully-suspended graphene electrical devices. Molecular coatings on the GS were removed by high current electrical annealing, which recovered the high electrical conductance and Dirac point of the GS. Molecular sensors for highly sensitive gas detections are demonstrated with self-assembled GS devices.

cond-mat.mtrl-sci↗

arXiv2008

Bose-Einstein condensation on an atom chip

We report an experiment of creating Bose-Einstein condensate (BEC) on an atom chip. The chip based Z-wire current and a homogeneous bias magnetic field create a tight magnetic trap, which allows for a fast production of BEC. After an 4.17s forced radio frequency evaporative cooling, a condensate with about 3000 atoms appears. And the transition temperature is about 300nK. This compact system is quite robust, allowing for versatile extensions and further studying of BEC.

physics.atom-ph↗

arXiv2008

Protein Microarrays with Carbon Nanotubes as Multi-Color Raman Labels

Detection of biomolecules is important in proteomics and clinical diagnosis and treatment of diseases. Here, we apply functionalized, macromolecular, single walled carbon nanotubes SWNTs as multi-color Raman labels to protein arrays for highly sensitive, multiplexed protein detection. Raman detection utilizes the sharp peaks of SWNTs with minimal background interference, affording a high signal to noise ratio needed for ultra-sensitive detection. Surface-enhanced Raman scattering SERS combined with the strong resonance Raman intensity of SWNTs, affords detection sensitivity down to 1 fM, a three order of magnitude improvement over most of reported fluorescence-based protein detections. We show that human autoantibodies to Proteinase 3 aPR3, a biomarker for the autoimmune disease Wegeners granulomatosis, is detected by Raman in human serum up to a 107 dilution. Moreover, SWNT Raman tags are stable against photobleaching and quenching, and by conjugating different antibodies to pure 12C and 13C SWNT isotopes, we demonstrate two-color SWNT Raman-based protein detection in a multiplexed fashion.

cond-mat.mtrl-sci↗

arXiv2008

Multiplexed Multi-Color Raman Imaging of Live Cells with Isotopically Modified Single Walled Carbon Nanotubes

We show that single walled carbon nanotubes with different isotope compositions exhibit distinct Raman Gband peaks and can be used for multiplexed multi-color Raman imaging of biological systems. Cancer cells with specific receptors are selectively labeled with 3 differently colored SWNTs conjugated with various targeting ligands including Herceptin, anti-Her2, Erbitux, anti-Her1, and RGD peptide, allowing for multi-color Raman imaging of cells in a multiplexed manner. SWNT Raman signals are highly robust against photo-bleaching, allowing long term imaging and tracking. With narrow peak features, SWNT Raman signals are easily differentiated from the auto-fluorescence background. The SWNT Raman excitation and scattering photons are in the near-infrared region, which is the most transparent optical window for biological systems in vitro and in vivo. Thus, SWNTs are novel Raman tags promising for multiplexed biological detection and imaging.

cond-mat.mtrl-sci↗

arXiv2008

Highly Conducting Graphene Sheets and Langmuir-Blodgett Films

Graphene is an intriguing material with properties that are distinct from those of other graphitic systems. The first samples of pristine graphene were obtained by peeling off and epitaxial growth. Recently, the chemical reduction of graphite oxide was used to produce covalently functionalized single-layer graphene oxide. However, chemical approaches for the large-scale production of highly conducting graphene sheets remain elusive. Here, we report that the exfoliation-reintercalation-expansion of graphite can produce high-quality single-layer graphene sheets stably suspended in organic solvents. The graphene sheets exhibit high electrical conductance at room and cryogenic temperatures. Large amounts of graphene sheets in organic solvents are made into large transparent conducting films by Langmuir-Blodgett assembly in a layer-by-layer manner. The chemically derived high quality graphene sheets could lead to future scalable graphene devices.

cond-mat.mtrl-sci↗

arXiv2008

Room Temperature All Semiconducting sub-10nm Graphene Nanoribbon Field-Effect Transistors

Sub-10nm wide graphene nanoribbon field-effect transistors (GNRFETs) are studied systematically. All sub-10nm GNRs afforded semiconducting FETs without exception, with Ion/Ioff ratio up to 10^6 and on-state current density as high as ~2000uA/um. We estimated carrier mobility ~200cm2/Vs and scattering mean free path ~10nm in sub-10nm GNRs. Scattering mechanisms by edges, acoustic phonon and defects are discussed. The sub-10nm GNRFETs are comparable to small diameter (d<=~1.2nm) carbon nanotube FETs with Pd contacts in on-state current density and Ion/Ioff ratio, but have the advantage of producing all-semiconducting devices.

cond-mat.mes-hall↗

arXiv2008

Optical Properties of Ultrashort Semiconducting Single-Walled Carbon Nanotube Capsules Down to Sub-10 nm

Single-walled carbon nanotubes (SWNTs) are typically long (>100 nm) and have been well established as novel quasi one-dimensional systems with interesting electrical, mechanical, and optical properties. Here, quasi zero-dimensional SWNTs with finite lengths down to the molecular scale (7.5 nm in average) were obtained by length separation using a density gradient ultracentrifugation method. Different sedimentation rates of nanotubes with different lengths in a density gradient were taken advantage of to sort SWNTs according to length. Optical experiments on the SWNT fractions revealed that the UV-vis-NIR absorption and photoluminescence peaks of the ultrashort SWNTs blue-shift up to 30 meV compared to long nanotubes, owing to quantum confinement effects along the length of ultrashort SWNTs. These nanotube capsules essentially correspond to SWNT quantum dots.

cond-mat.mtrl-sci↗

arXiv2007

Selective Synthesis Combined with Chemical Separation of Single-Walled Carbon Nanotubes for Chirality Selection

Single-walled carbon nanotubes (SWNTs) are potential materials for future nanoelectronics. Since the electronic and optical properties of SWNTs strongly depend on tube diameter and chirality, obtaining SWNTs with narrow (n,m) chirality distribution by selective growth or chemical separation has been an active area of research. Here, we demonstrate that a new, bimetallic FeRu catalyst affords SWNT growth with narrow diameter and chirality distribution in methane CVD. At 600C, methane CVD on FeRu catalyst produced predominantly (6,5) SWNTs according to Uv-vis-NIR absorption and photoluminescence excitation/emission (PLE) spectroscopic characterization. At 850C, the dominant semiconducting species produced are (8,4), (7,6) and (7,5) SWNTs, with much narrower distributions in diameter and chirality than materials grown by other catalysts. Further, we show that narrow-diameter/chirality growth combined with chemical separation by ion exchange chromatography (IEC) greatly facilitate achieving single-(m,n) SWNT samples, as demonstrated by obtaining highly enriched (8,4) SWNTs with near elimination of metallic SWNTs existing in the as-grown material.

cond-mat.mtrl-sci↗

arXiv2007

A Radio-Frequency Atom Chip for Guiding Neutral Atoms

We propose two kinds of wire configurations fabricated on an atom chip surface for creating two-dimensional (2D) adiabatic rf guide with an inhomogeneous rf magnetic field and a homogenous dc magnetic field. The guiding state can be selected by changing the detuning between the frequency of rf magnetic field and the resonance frequency of two Zeeman sublevels. We also discuss the optimization of loading efficiency and the trap depth and how to decide proper construction when designing an rf atom chip.

physics.atom-ph↗

arXiv2007

Langmuir blodgett assembly of densely aligned single walled carbon nanotubes from bulk materials

Single walled carbon nanotubes exhibit advanced electrical and surface properties useful for high performance nanoelectronics. Important to future manufacturing of nanotube circuits is large scale assembly of SWNTs into aligned forms. Despite progress in assembly and oriented synthesis, pristine SWNTs in aligned and close-packed form remain elusive and needed for high current, speed and density devices through collective operations of parallel SWNTs. Here, we develop a Langmuir Blodgett method achieving monolayers of aligned SWNTs with dense packing, central to which is a non covalent polymer functionalization by PmPV imparting high solubility and stability of SWNTs in an organic solvent DCE. Pressure cycling or annealing during LB film compression reduces hysteresis and facilitates high degree alignment and packing of SWNTs characterized by microscopy and polarized Raman spectroscopy. The monolayer SWNTs are readily patterned for device integration by microfabrication, enabling the highest currents 3mA through the narrowest regions packed with aligned SWNTs thus far.

cond-mat.mtrl-sci↗

arXiv2006

Hydrogenation and Hydro-Carbonation and Etching of Single-Walled Carbon Nanotubes

We present a systematic experimental investigation of the reactions between hydrogen plasma and single-walled carbon nanotubes (SWNTs) at various temperatures. Microscopy, infrared (IR) and Raman spectroscopy and electrical transport measurements are carried out to investigate the properties of SWNTs after hydrogenation. Structural deformations, drastically reduced electrical conductance and increased semiconducting nature of SWNTs upon sidewall hydrogenation are observed. These changes are reversible upon thermal annealing at 500C via dehydrogenation. Harsh plasma or high temperature reactions lead to etching of nanotube likely via hydro-carbonation. Smaller SWNTs are markedly less stable against hydro-carbonation than larger tubes. The results are fundamental and may have implications to basic and practical applications including hydrogen storage, sensing, band-gap engineering for novel electronics and new methods of manipulation, functionalization and etching of nanotubes.

cond-mat.mtrl-sci↗