Maruf Hossain

Capacitance-voltage characterization of polyfluorene-based metal-insulator-semiconductor diodes

Metal-insulator-semiconductor structures with conjugated polymer ethyl-hexyl substituted polyfluorene (PF26) as the active semiconductor layer, Al2O3 as the insulating oxide layer, and p+-Si as the metal layer have been characterized by means of capacitance-voltage (C-V) and conductance-voltage methods. The negative shift of the flat-band voltage with increasing frequency arises from positive interface charges in the PF26∕Al2O3 layer. From C-V measurements the unintentional doping density is evaluated as ∼5.7×1017cm−3 at frequencies above 20kHz. The interface trap density is estimated as ∼7.7×1011eV−1cm−2 at the flat-band voltage.

Sub-2 nm Size-Tunable High-Density Pt Nanoparticle Embedded Nonvolatile Memory

The charge-storage characteristics of a metal-oxide-semiconductor (MOS) structure containing size-tunable sub-2 nm Pt nanoparticles (NPs) between Al2O3 tunneling and capping oxide layers were studied. Significantly different amounts of memory window were obtained with the different sizes of Pt NP embedded MOS structures and reached a maximum of 4.3 V using a 1.14 nm Pt NP, which has the strongest charging capability caused by optimum size and the largest particle density obtained in our deposition method. Satisfactory long-term nonvolatility was attained in a low electric field due to the Coulomb blockade and quantum confinement effects in ~ 1 nm Pt NP. These properties are very promising in view of device application.

Development of a Miniaturized Liquid Core Waveguide System With Nanoporous Dielectric Cladding—A Potential Biosensing Platform

We present a high-throughput optofluidic light waveguide system consisting of etched microchannels in silicon using water as the core and an ultra low refractive index nanoporous dielectric (ND) as the cladding organosilicate nanoparticulate films with refractive index of 1.16 have been used as the cladding layer. Although NDs offers many advantages over Teflon AF for use as the cladding layer, integration of these coatings to the waveguide design is not trivial. In this paper, we address the various integration issues of the NDs to the liquid core waveguide architecture followed by testing of these waveguides for their light guiding capability. Compared to uncoated channels, ND clad channels offer a high light guiding efficiency. In addition, the high surface areas associated with them could be potentially used to immobilize higher density of sensor probes implying a great potential for biosensor applications in an integrated system.

Electrochemical Properties of Carbon Nanoparticles Entrapped in Silica Matrix

Carbon-based electrode materials have been widely used for many years for electrochemical charge storage, energy generation, and catalysis. We have developed an electrode material with high specific capacitance by entrapping graphite nanoparticles into a sol-gel network. Films from the resulting colloidal suspensions were highly porous due to the removal of the entrapped organic solvents from sol-gel matrix giving rise to high Brunauer-Emmett-Teller (BET) specific surface areas (654 m(2)/g) and a high capacitance density ( approximately 37 F/g). An exponential increase of capacitance was observed with decreasing scan rates in cyclic voltammetry studies on these films suggesting the presence of pores ranging from micro (< 2 nm) to mesopores. BET surface analysis and scanning electron microscope images of these films also confirmed the presence of the micropores as well as mesopores. A steep drop in the double layer capacitance with polar electrolytes was observed when the films were rendered hydrophilic upon exposure to a mild oxygen plasma. We propose a model whereby the microporous hydrophobic sol-gel matrix perturbs the hydration of ions which moves ions closer to the graphite nanoparticles and consequently increase the capacitance of the film.

Crystallization of amorphous silicon by self-propagation of nanoengineered thermites

Crystallization of amorphous silicon (a-Si) thin film occurred by the self-propagation of copper oxide/aluminum thermite nanocomposites. Amorphous Si films were prepared on glass at a temperature of 250°C by plasma enhanced chemical vapor deposition. The platinum heater was patterned on the edge of the substrate and the CuO∕Al nanoengineered thermite was spin coated on the substrate that connects the heater and the a-Si film. A voltage source was used to ignite the thermites followed by a piranha solution (4:1 of H2SO4:H2O2) etch for the removal of residual products of thermite reaction. Raman spectroscopy was used to confirm the crystallization of a-Si.

On-Chip Initiation and Burn Rate Measurements of Thermite Energetic Reactions

Burn rates of various nano-energetic composites were measured by two techniques; on-chip method and conventional optical method. A comparison is presented to confirm the validity of on-chip method. On-chip initiators were prepared using platinum heater films and nanoenergetic composites. Thin film Pt heaters were fabricated with different dimensions and ignition delay was studied using a nano-energetic composite of CuO nano-rods and Al-nano-particles. The ignition delay as a function of electrical power is presented for the same energetic composite. Heater with smaller surface area is found to be more efficient, which may be due to the lower heat losses.

Development of a novel nanomaterial-based optical platform for a protease biosensor

We have been investigating a new nanomaterial-based optical platform for the immobilization of protease substrates for the development of a biosensor to detect medically relevant enzymes. Metallic nanoparticles have been deposited onto thin films and are being used for their optical properties. Two different peptide sequences have been designed as trypsin substrates that are designed to be immobilized onto the surface of the thin films. The peptides were synthesized with a fluorophore attached at the terminal end of the peptide to allow for fluorescence sensing. Fluorescent molecules in close proximity to metallic elements will have their fluorescence signal quenched due to surface plasmon resonance (SPR) effects. When the peptide is cleaved by trypsin, the fluorophore is separated, resulting in a detectable change in fluorescence intensity. These novel nanomaterial-based optical platforms have been fabricated using physical vapor deposition. Innovative techniques have been invented using these machines to acquire nanoparticles in the range of a few nanometers on these thin films. It is known that nanoparticles with dimensions less than their bandwidth display optical properties much different from their bulk counterparts. We have immobilized the peptide substrates to the surface of the metallized thin films so they are in close proximity with each other. Polydimethlysiloxane (PDMS) was molded to create small wells and placed on the thin films. Fluorescent microscopy was used to image the wells as various concentrations of the enzyme were introduced resulting in a recovery of green fluorescence from the fluorophore on the cleaved portion of the peptide. Different size nanoparticles and different immobilization processes are being used to optimize the design of the protease biosensor.