Minseong Yun

Polyfluorene as a model system for space-charge-limited conduction

Ethyl-hexyl substituted polyfluorene (PF) with its high level of molecular disorder can be described very well by one-carrier space-charge-limited conduction for a discrete set of trap levels with energy � 0.5 eV above the valence band edge. Sweeping the bias above the trap-filling limit in the as-is polymer generates a new set of exponential traps, which is clearly seen in the density of states calculations. The trapped charges in the new set of traps have very long lifetimes and can be detrapped by photoexcitation. Thermal cycling the PF film to a crystalline phase prevents creation of additional traps at higher voltages.

Charge storage characteristics of ultra-small Pt nanoparticle embedded GaAs based non-volatile memory

Charge storage characteristics of ultra-small Pt nanoparticle embedded devices were characterized by capacitance-voltage measurements. A unique tilt target sputtering configuration was employed to produce highly homogenous nanoparticle arrays. Pt nanoparticle devices with sizes ranging from ∼0.7 to 1.34 nm and particle densities of ∼3.3–5.9 × 1012 cm−2 were embedded between atomic layer deposited and e-beam evaporated tunneling and blocking Al2O3 layers. These GaAs-based non-volatile memory devices demonstrate maximum memory windows equivalent to 6.5 V. Retention characteristics show that over 80% charged electrons were retained after 105 s, which is promising for device applications.

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.

Room temperature observation of size dependent single electron tunneling in a sub-2?nm size tunable Pt nanoparticle embedded metal?oxide?semiconductor structure

In this paper we report size dependent single electron tunneling behavior at room temperature in a metal-oxide-semiconductor structure with uniformly sized Pt nanoparticles embedded in an Al(2)O(3) dielectric. The sub-2 nm size Pt nanoparticles sandwiched between the Al(2)O(3) layers are deposited by a unique tilted target sputter deposition technique which produces metal nanoparticles as small as 0.5 nm with narrow size distributions at room temperature. The charging behavior of these nanoparticles shows clear single electron tunneling peaks due to the Coulomb blockade effect. Moreover, the average single electron addition energy and height of the single electron tunneling current strongly depend on the size of the Pt nanoparticle. These controllable single electron tunneling behaviors suggest a new route for fabrication of single electron devices.

Entropy driven spontaneous formation of highly porous films from polymer–nanoparticle composites

Nanoporous materials have become indispensable in many fields ranging from photonics, catalysis and semiconductor processing to biosensor infrastructure. Rapid and energy efficient process fabrication of these materials is, however, nontrivial. In this communication, we describe a simple method for the rapid fabrication of these materials from colloidal dispersions of Polymethyl Silsesquioxane nanoparticles. Nanoparticle-polymer composites above the decomposition temperature of the polymer are examined and the entropic gain experienced by the nanoparticles in this rubric is harnessed to fabricate novel highly porous films composed of nanoparticles. Optically smooth, hydrophobic films with low refractive indices (as low as 1.048) and high surface areas (as high as 1325 m(2) g(-1)) have been achieved with this approach. In this communication we address the behavior of such systems that are both temperature and substrate surface energy dependent. The method is applicable, in principle, to a variety of nanoparticle-polymer systems to fabricate custom nanoporous materials.

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.