INTRODUCTIONGeneration of hot electrons in metallic or semiconducting materials and hot electron-induced chemistry on their surfaces have been actively investigated for decades. For instance, optically excited hot electrons with excess energy above the Fermi level of metals demonstrated its capability to transfer part of the electron energy to the adsorbate molecules and excite their internal modes initiating various surface chemistries. 1À6 In semiconductors, hot electrons excited above the conduction band edge have been shown to be beneficial in catalysis and photovoltaic applications via fast interfacial charge transfer that can effectively compete with intraband relaxation. 7À9 Recently, a number of groups reported efficient interfacial charge transfer of optically excited hot electrons in semiconductor nanocrystals, 10À12 demonstrating the potential of harvesting hot electrons in nanocrystals that are widely employed in catalysis and photovoltaic applications. Hot electrons with larger excess energy will generally experience a lower energy barrier for interfacial charge transfer, and their wave functions can reach further away from the nanocrystals, making them potentially useful for photocatalytic and photovoltaic applications.Hot electrons in semiconductor nanocrystals can be excited via optical excitation in a number of different ways. The simplest way is the above-band-gap excitation with sufficient excess energy that can excite the electrons high in the conduction band. Hot electrons with higher excess energy generally require excitation with the higher-energy photons in the UV region, which is increasingly less convenient to work with. The lowerenergy photons can also excite hot electrons with large excess energy via multiphoton excitation. 13À15 However, multiphoton excitation is usually much less efficient than single photon excitation and requires high excitation intensity.

Trapping of charge carriers is the major process competing with radiative recombination or transfer of charge carriers important in the application of semiconductor nanocrystals in photonics and photocatalysis. In typical semiconductor quantum dots, trapping of charge carriers usually leads to quenching of exciton luminescence. In this study, we present evidence indicating that thiol ligands on the surface that quench exciton luminescence can have an opposite effect on sensitized dopant luminescence in doped semiconductor nanocrystals by facilitating the recovery of the trapped exciton for sensitization. Despite the increase in hole trapping by the added octanethiol to the surface of Mn-doped CdS/ZnS nanocrystals, the sensitized Mn luminescence increased by the added octanethiol and the enhancement became stronger with increasing Mn doping concentration. While the role of octanethiol as the hole trap and the enhancement of Mn luminescence may seem contradictory, the thiol-induced enhancement of Mn luminescence is possible, since thiols play dual role as the hole trap and as the facilitator of the energy transfer from the trapped exciton to Mn, in contrast to the pre-existing hole traps that inhibit the energy transfer.

We report a ratiometric temperature imaging method based on Mn luminescence from Mn-doped CdS/ZnS nanocrystals (NCs) with controlled doping location, which is designed to exhibit strong temperature dependence of the spectral lineshape while being insensitive to the surrounding chemical environment. Ratiometric thermometry on Mn luminescence spectrum was performed by using Mn-doped CdS/ZnS core/shell NCs that have a large local lattice strain on Mn site, which results in the enhanced temperature dependence of the bandwidth and peak position. Mn luminescence spectral lineshape is highly robust with respect to the change in the polarity, phase and pH of the surrounding medium and aggregation of the NCs, showing great potential in temperature imaging under chemically heterogeneous environment. The temperature sensitivity (ΔIR/IR = 0.5%/K at 293 K, IR = intensity ratio at two different wavelengths) is highly linear in a wide range of temperatures from cryogenic to above-ambient temperatures. We demonstrate the surface temperature imaging of a cyro-cooling device showing the temperature variation of >200 K by imaging the luminescence of the NC film formed by simple spin coating, taking advantage of the environment-insensitive luminescence.

Colloidal 2-D layered transition metal dichalcogenide (TMDC) nanodiscs synthesized with uniform diameter and thickness can readily form the vertically stacked assemblies of particles in solution due to strong interparticle cohesive energy. The interparticle electronic coupling that modifies their optical and electronic properties poses a significant challenge in exploring their unique properties influenced by the anisotropic quantum confinement in different directions taking advantage of the controlled diameter and thickness. Here, we show that the assemblies of 2-D layered TiS2 nanodiscs are efficiently separated into individual nanodiscs via photoexcitation of the charge carriers by pulsed laser light, enabling the characterization of the properties of noninteracting TiS2 nanodiscs. Photoinduced separation of the nanodiscs is considered to occur via transient weakening of the interparticle cohesive force by the dense photoexcited charge carriers, which facilitates the solvation of each nanodisc by the solvent molecules.

We report on a low-temperature fabrication of organic-inorganic nanohybrid nonvolatile memory transistors using molecular layer deposition combined with atomic layer deposition. A 3 nm ZnO:Cu charge trap layer is sandwiched between 6 nm tunneling and 20 nm blocking self-assembled organic layers. First, we identify a large memory window of 14.1 V operated at AE15 V using metal-oxidesemiconductor capacitors. Second, we apply the capacitor structure to the nonvolatile memory transistors which operate in the low voltage range of À1 to 3 V. The writing/erasing (+8 V/À12 V) current ratio of $10 3 of the memory transistors is maintained during the static and dynamic retention measurements. The reported organic-inorganic devices offer new opportunities to develop low-voltagedriven flexible memory electronics fabricated at low temperatures. Recently, we have developed a molecular layer deposition (MLD) method for high quality self-assembled organic layers (SAOLs). 24 The MLD method is a self-controlled layer-by-layer growth process under vacuum conditions, and can be combined with the atomic layer deposition (ALD) method. MLD combined with ALD (MLD-ALD) has been applied to fabricate precisely controlled organic-inorganic nanohybrid superlattices at relatively low temperatures. [24][25][26] Here we report on the low-temperature fabrication of organicinorganic nanohybrid floating-gate nonvolatile memory transistors (NMTs) using the MLD-ALD method with ZnO:Cu as a charge trap layer, AlOx-SAOLs as blocking and tunneling layers, and zinc oxide cross-linked polydiacetylene (ZnOPDA) as a semiconducting layer. Note that the organic-inorganic