Tin disulfide displays a wide range of attractive physical and chemical properties and are potentially important for various device applications including nanoelectronics, optoelectronics, as well as energy conversion. Here, we report on the largescale synthesis of tin disulfide granular thin films on silicon dioxide substrates by soft chalcogenization method in which the pre-deposited tin thin films are transformed into tin disulfide thin films via exposure to sulfur vapor. The obtained tin disulfide films have been comprehensively characterized to study their fundamental properties in detail by using atomic force microscopy, scanning electron microcopy, Raman spectroscopy, photoluminescence spectroscopy and X-ray photoelectron spectroscopy.
Three dimensional pillared graphene nanostructures were grown on metal substrates through a one-step chemical vapor
deposition (CVD) by introducing a mixture precursor gases (H2, C2H4). We further explored sputtering evaporation system to uniformly deposited a layer of amorphous silicon on the as grown 3D carbon nanostructure. The surface morphologies of the carbon-silicon nanocomposites were investigated by scanning electron microscopy (SEM). Cyclic
voltammetry and charge-discharge are conducted to determine the performance of the 3D hybrid carbon-silicon
nanostructure for lithium ion battery anode.
We fabricated 1.4 nm nanogold and molecular dark quencher assembled quantum dot for estimating their performances in a target specific conformal changing molecular event. For the assembling, we immobilized each acceptor linked molecular beacons using interaction between biotin at molecular beacon and streptavidins on quantum dot. Through optical analysis of the purified hybrids of the acceptors and quantum dots, we could estimate numbers of the assembled acceptors per quantum dot and their efficiency of energy transfer depending on conformal changes of molecular beacons. We obtained maximum 95 % and 78% of energy transfer efficiency with 17 metallic nanocrystals and 41 black hole quencher 2, the molecular dark quencher per single quantum dote, respectively. Molecular beacons form linear helix from a hair-pin structure by hybridizing with complementary DNA. In the presence of target DNA, energy transfer efficiency of the organic quencher was 22 % while only 2 % decreased efficiency was obtained with the nanogold, indicating higher fluorescence recovery with the ordinary organic quencher. Considering the relatively low assembled number and the large size, a steric hindrance might be attributed to the low fluorescence recovery. Since the energy transfer efficiency obtained with the nanogold at a fixed distance is high enough, it would be still effective to apply nanogold a system, where nanogold is removed permanently from quantum dots.
We investigate the application of fluorescence quenching microscopy (FQM) for visual characterization of graphene quality, number of layers and uniformity over its landscape. The method relies on the fact that pristine, modified and multi-layer graphene regions quench fluorescence with different rates. Steady-state and time-resolved emission spectroscopy are used to comparatively characterize the photophysical behavior of pristine graphene relative to unquenched dye on bare substrate. The results demonstrate that with premeditated choice of Fluorescence dye, the interaction between fluorophores and graphene provides valuable tools for identifying the chemical structure and thickness of graphene. Fluorescence quenching metrology can be implemented as the basis for a microscopy based metrology for 2D materials.
Graphene’s unique mechanical, electrical, and thermal properties have made it a very attractive material desired for use in future technologies. Over the recent years, there have been many breakthroughs in research on graphene. Recently, the focus of the latest research has shifted towards scaling graphene production for commercial use by industry. The most promising method for scaling graphene growth for industry usage is chemical vapor deposition (CVD). CVD is a low cost, economic and scalable method for producing graphene. However, consistently producing high quality graphene quickly on a large scale has eluded researchers. Here we detail a method for reducing growth time required to produce high quality, large area graphene by adjusting the fluid mechanics of the CVD.
We investigated the data transmission performance of indium antimonide (InSb) nanowires (NWs) synthesized on InSb
(100) substrate using chemical vapor deposition (CVD) having diameters below 20 nm. The data transmission
measurement was accomplished over the NW field effect transistors (NWFETs) fabricated on Si/SiO2 substrates. Digital
data stream is randomly generated and then uploaded to a waveform generator which generates the stream and transmits
it repeatedly with the desired frequency. The signal was applied on the sources of the NWFETs and collected from the
drains of the same devices. Collected data was first filtered with a low pass filter (LPF), and then the output of the filter
was used to create the eye diagrams of the NWs. Bit error rate (BERs), attenuation , quality factor (Q-factor) and
maximum data transmission are extracted from eye diagrams. The results indicate that the data transmission performance
of NWs suffer from low mobility values on the order of 10-to-15 cm2V-1s-1 because of their small diameters, crystal defects and oxidation occurs during growth and cooling. 20 nm NWs can sustain data rates up to 10 mega bits per second (Mbps) and the data rate is directly proportional to the diameter of the NWs.
Single strand DNA (ss-DNA) fragments act as negative potential gating agents that increase the hole density in graphene.
Patterning of biomolecules on graphene could provide new avenues to modulate the electrical properties. Current-voltage
characterization of this hybrid ss-DNA / graphene system indicates a shift of the Dirac point and "intrinsic" conductance
after ss-DNA is deposited. The effect of the ss-DNA is to increase the hole density in the graphene. The increased hole
density is calculated to be 2 × 1012 cm-2. This increase is consistent with the Raman frequency shifts in the G peak and
2D band positions and the corresponding changes in the G-peak full-width half maximum. Ab initio calculations using
density functional theory rule out significant charge transfer or modification of the graphene bandstructure in the
presence of the ss-DNA fragments.
InSb nanowire field effect transistors (NWFET) were fabricated using electrochemically synthesized nanowires. To
accurately extract transistor parameters, we introduced a model which takes into account the often ignored ungated
nanowire segments. A significant improvement in extracted device parameters was observed which demonstrated that
conventional models tend to underestimate the gate effect and therefore lead to lower carrier mobilities. Based on the
model, we obtained a NWFET ON current of 11.8uA, an ION/IOFF ratio of 63.5 and hole mobility of 292.84 cm2V-1s-1.
Employing DNA molecules provide opportunities for electronics and photonics applications, serving to enhance the
device properties as active part of the device or being a linker agent to aid in the self assembly of nanostructures. In this
work, the effects of two different sets of biological materials, stand alone DNA sequences and Pt-DNA nanowires on the
device properties of bulk heterojunction solar cell devices are being investigated. During the metallization of DNA, a Pt
ion activation process over the DNA backbone is followed by a reduction process, where positively charged Pt
nanoparticles are assembled on the DNA sequences to form the Pt-DNA complexes via sequential ionic reduction. Pt
nanowires 20 nm in diameter are obtained by optimization of the salt reduction parameters of this. Several solar cell
devices consisting of Al/P3HT:PCBM/PEDOT:PSS/ITO layers, are fabricated where DNA sequences or the Pt-DNA
nanostructures are placed in between the P3HT:PCBM and the PEDOT:PSS layers. Both DNA sequences and Pt-DNA
nanostructures are spray coated onto the PEDOT:PSS layer before spin-coating the PEDOT:PSS polymer mixture. The
effects of the DNA and Pt-DNA nanostructures are observed from the I-V characteristics under the standard AM1.5G 1
Sun Test Condition. We observe that both DNA sequences and Pt-DNA nanostructures improve the power conversion
efficiency (PCE) by %12 and %25 respectively. We believe that this increase in PCE is provided by the enhancement of
hole collection and a reduction of the recombination loses. In addition, improvement in the short circuit current (Isc) is
observed for the DNA containing network. Similar improvements in both Isc and the open circuit voltage (Voc) are
observed for the Pt-DNA containing network. We hypothesize that while the high resistance of the DNA network limits
charge collection, comparably low resistance Pt-DNA network improves this feature.
We have developed conjugates with quantum-dots (QDs) for the purpose of analysis of nanosystems that are organic or inorganic in nature such as DNA and carbon nanotubes. First, by employing Florescence Resonant Energy Transfer (FRET) principles, a hybrid molecular beacon conjugates are synthesized. For water- solubilization of QDs, we modified the surface of CdSe-ZnS core-shell QD by using mercaptoacetic acid ligand. This modification does not affect the size of QDs from that of unmodified QDs. After linking molecular beacons to the carboxyl groups of the modified QDs using 1-Ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride, hybrid molecular beacons are prepared as a DNA probe. After hybridization with specific target DNA and non-specific target DNA, the hybrid conjugates show high specificity to the target DNA with 5-fold increase in the intensity of fluorescence. By developing atomic model of the conjugates, we calculated with 8 numbers of molecular beacons on a single quantum dots, we could increase the efficiency of FRET up to 90%. In other hands, for application of quantum dots to the carbon nanotubes, FRET is a barrier. Thus, after employing 1 % sodium-dodecyl-sulfonate (SDS), single-walled carbon nanotubes are decorated with QDs at their outer surface. This enables fluorescent microscopy imaging of single-walled carbon nanotubes which is a more common technique than electron microscopy. In summary, QDs can be used for analysis or detection of both organic and inorganic based nanosystems.
A novel technique is presented which integrates the capacity of a laser tweezer to optically trap and manipulate objects in three-dimensions with the resolution-enhanced imaging capabilities of a solid immersion lens (SIL). Up to now, solid immersion lens imaging systems have relied upon cantilever-mounted SILs that are difficult to integrate into microfluidic systems and require an extra alignment step with external optics. As an alternative to the current
state-of-art, we introduce a device that consists of a free-floating SIL and a laser optical tweezer. In our design, the optical tweezer, created by focusing a laser beam through high numerical aperture microscope objective, acts in a two-fold manner: both as a trapping beam for the positioning and alignment of the SIL and as an near-field scanning beam to image the sample through the SIL. Combining the alignment, positioning, and imaging functions into a single device allows for the direct integration of a high resolution imaging system into microfluidic and biological environments.
An adaptive alignment technique is presented that provides precise control and active positioning of sub-millimeter-sized spherical lenses in two-dimensions through the application of electrophoretic forces in a microfluidic well. The device is comprised of a lithographically patterned microfluidic well and electrodes that can be addressed to position or align the spherical microlens to the corresponding beam source. The motion of the microlens is controlled using CMOS compatible voltages (3V - 1 (mu) A) that are applied to opposite electrodes in the microfluidic well, creating an electrical field in the solution. By applying voltages to opposite electrode pairs, we have demonstrated the movement of spherical microlenses with sizes ranging from 0.87 micrometers to 40 micrometers in directions parallel to the electrode surface. Under a bias of 3 volts, the microspheres had an experimentally measured electrophoretic velocities ranging from 13 to 16 micrometers /s. Optical alignment of the spherical or ball microlens can be accomplished using feedback from a photodetector to position the lens for maximum efficiency. Using this device, it is possible to actively align microlenses to optical fibers, VCSELs, LEDs, photodetectors, etc.
Current biochip technologies typically rely on electrostatic or mechanical forces for the transport and sorting of biological samples such as single cells. In this paper we have investigated how optical pressure forces can be effectively used for the manipulation of cells and switching in a microfluidic system. By projecting the optical beams externally non-contact between the control devices and the sample chip is possible thus allowing the sample chips to be disposable which reduces the chance of cross-contamination. In one implementation we have shown that vertical cavity surface emitting laser (VCSEL) array devices used as parallel optical tweezer arrays can increase the parallelism of sample manipulation on a chip. We have demonstrated the use of a high-order Laguerre-Gaussian mode VCSEL for optical tweezing of polystyrene microspheres and live cells. We have also shown that optical pressure forces from higher- power sources can be used for the switching of particles within microfluidic channels. Both the attractive gradient force and the scattering force of a focused optical beam have been used to direct small particles flowing through junctions molded in PDMS. We believe that by integrating optical array devices for simultaneous detection and manipulation, highly parallel and low-cost analysis and sorting devices may be achieved.
Electrophoresis is a classical electrochemical transport process, which is based on the migration of charged particles in a suspension by the influence of an electric field. One of the important applications of this technique is the study of DNA/RNA hybridization on bio-electronic chips. However, electrophoretic pick and place techniques are currently limited to the serial `pick' and `place' of individual devices or materials. There is a need for the rapid and parallel pick-and-place of individual devices to particular locations on a host substrate. In this paper, we present a novel electrochemical system for non-lithographic, field assisted, fluidic pick and place assembly of devices on a silicon substrate by means of electrical and optical addressing. The methodology presented here can be applied to massively parallel assembly of large semiconductor arrays (> 1000 X 1000) with fast (approximately a few seconds) and accurate positioning for a wide range of device sizes (0.8 - 100 micrometers ).