Haisheng Zheng

Large sensitivity enhancement in semiconducting organic field effect transistor sensors through incorporation of ultra-fine platinum nanoparticles

We report remarkable improvement in sensitivity of pentacene-based field effect transistor devices towards trace nitro-aromatic explosive vapors through the incorporation of high density, sub-2 nm platinum nanoparticles (NPs) within these structures. Exploiting the unique electronic properties of these NPs, we have demonstrated a detection limit of 56.6 parts per billion of 2,4-dinitrotoluene (DNT) vapor while control samples without any embedded NPs showed no observable sensitivity to DNT vapor. We attribute this remarkable enhancement in sensitivity to the ability of these NPs to function as discrete nodes, participating in the charge transfer with adsorbed nitro-aromatic molecules.

Layer-by-layer charging in non-volatile memory devices using embedded sub-2 nm platinum nanoparticles

In this work, we demonstrate multi-level operation of a non-volatile memory metal oxide semiconductor capacitor by controlled layer-by-layer charging of platinum nanoparticle (PtNP) floating gate devices with defined gate voltage bias ranges. The device consists of two layers of ultra-fine, sub-2 nm PtNPs integrated between Al2O3 tunneling and separation layers. PtNP size and interparticle distance were varied to control the particle self-capacitance and associated Coulomb charging energy. Likewise, the tunneling layer thicknesses were also varied to control electron tunneling to the first and second PtNP layers. The final device configuration with optimal charging behavior and multi-level programming was attained with a 3 nm Al2O3 initial tunneling layer, initial PtNP layer with particle size 0.54 ± 0.12 nm and interparticle distance 4.65 ± 2.09 nm, 3 nm Al2O3 layer to separate the PtNP layers, and second particle layer with 1.11 ± 0.28 nm PtNP size and interparticle distance 2.75 ± 1.05 nm. In this devi...

Size-dependent work function and single electron memory behavior of pentacene non- volatile memory with embedded sub-nanometer platinum nanoparticles

We present a low operation voltage pentacene-based non-volatile memory transistor by embedding sub-2 nm size-tunable platinum nanoparticles (Pt NPs) between the tunneling and blocking dielectric layers. Controllable work function was observed in the embedded Pt NPs through the size-dependent threshold voltage shift. Non-volatile memory transistors containing embedded Pt NPs exhibited significant memory windows in their transfer characteristics, which was attributed to charging and discharging behaviors of electrons and holes by the Pt NPs. Additionally, the memory transistor showed controllable Pt NP size- and density-dependent memory window behavior. While devices with small (0.5 nm) Pt NPs demonstrated strong Coulomb blockade and quantum confinement with electron addition energy as large as 1.993 eV, those made with larger (1.8 nm) Pt NPs allowed for storage of a single charge per NP memory.

Barrier Modification of Metal-contact on Silicon by Sub-2 nm Platinum Nanoparticles and Thin Dielectrics.

We report metal/p-Si contact barrier modification through the introduction of either “isolated” or “nonisolated” tilted-target-sputtered sub-2 nm platinum nanoparticles (Pt NPs) in combination with either a 0.98 nm Atomic Layer Deposited Al2O3 or a 1.6 nm chemically grown SiO2 dielectric layer, or both. Here, we study the role of these Pt NP’s size dependent properties, i.e., the Pt NP-metal surface dipole, the Coulomb blockade and quantum confinement effect in determining the degree of Fermi level depinning observed at the studied metal/p-Si interfaces. By varying only the embedded Pt NP size and its areal density, the nature of the contact can also be modulated to be either Schottky or Ohmic upon utilizing the same gate metal. 0.74 nm Pt NPs with an areal density of 1.1 × 1013 cm−2 show ~382 times higher current densities compared to the control sample embedded with similarly sized Pt NPs with ~1.6 times lower areal densities. We further demonstrate that both Schottky (Ti/p-Si) and poor Ohmic (Au/p-Si) contact can be modulated into a good Ohmic contact with current density of 18.7 ± 0.6 A/cm2 and 10.4 ± 0.4 A/cm2, respectively, showing ~18 and ~30 times improvement. A perfect forward/reverse current ratio of 1.041 is achieved for these low doped p-Si samples.

In Situ Characterization of Photothermal Nanoenergetic Combustion on a Plasmonic Microchip

Plasmonic gratings facilitate a robust in situ diagnostic platform for photothermal combustion of nanoenergetic composite thin films using an optical microscope and a high-speed camera. Aluminum nanoparticles (Al NPs) embedded in a fluoropolymer oxidizer are cast onto a plasmonic grating microchip and ignited using a low-power laser. The plasmonic grating enhances both spatial resolution and sufficient photothermal coupling to combust small Al NP clusters, initiating localized flames as small as 600 nm in size. Two-color pyrometry obtained from a high-speed color camera indicates an average flame temperature of 3900 K. Scattering measurements using polarized light microscopy enabled precise identification of individual Al NPs over a large field of view, leading to 3D reconstruction of combustion events.

Surface-plasmon-enhanced Raman and photoluminescence of few-layers and bulk MoS 2 on silver grating

We report the observation of surface-plasmon-enhanced Raman and photoluminescence of few-layers and bulk MoS 2 on silver grating compared with SiO 2 substrate, suggesting an indirect to direct bandgap transition for MoS 2 .

Fluorescence-based temperature sensor for in-situ imaging local temperature of aluminum nanoparticles on plasmonic gratings

We developed a novel plasmonic grating platform as a fluorescence-based temperature sensor for in-situ imaging of localized temperature and dynamic mapping of temperature in nanoscale due to photothermal heating of aluminum nanoparticles. Al/polymer nanoenergetics films with temperature sensitive dyes (Rhodamine 6G) were prepared and calibrated to obtain temperature-dependent dye fluorescence intensity. A tunable laser heating setup was developed for microscope imaging. We monitored the in-situ laser heating on Al/polymer/R6G systems by microscope and then constructed the spatial thermal mapping over time. Based on the fluorescence microscopic imaging, we can monitor Al nanoparticles movement and morphology changes for Al/polymer/Rhodamine 6G systems induced by laser heating. Al nanoparticles play an important role in laser heating due to the plasmonic, interband and intraband absorption characteristics of Al nanoparticles. Plasmonic grating platforms can not only significantly enhance the photothermal heating of Al compared with glass platforms, but also act as superlensing for sub-diffraction limited imaging of nanoparticles.