We integrated single wall carbon nanotubes (SWNT), several water-soluble pyrene derivatives, which either bear negatively (pyrene^-) or positively charged (pyrene⁺) charged ionic headgroups, and a series of water-soluble metalloporphyrins (MP⁸⁺/MP^8-) into functional nanohybrids through a combination of associative van-der-Waals and electrostatic interactions. The resulting SWNT / pyrene and SWNT / pyrene / MP were characterized by spectroscopic and microscopic means and were found to form stable nanohybrid structures in aqueous media. When the nanohybrid systems are photoexcited with visible light, a rapid intrahybrid charge separation causes the reduction of the electron accepting SWNT and, simultaneously, the oxidation of the electron donating MP. Beneficial are charge recombination dynamics that are located in the Marcus-inverted region.

Photocurrent improvement for the photoelectrochemical cell, based on a Cu₂O/Cu electrode in hydrophobic ionic liquid electrolyte, was demonstrated by modifying the Cu₂O surface using cyanide treatment, in this case the photocurrent amplitude drastically increased at least by a factor of 10 compared with the non-treatment. Passivation of the surface defect sites through the cyanide treatment process resulted in significantly raising the charge separation yield at the interface. From this experimentation the optimization of the cyanide treatment and the limitation of the photocurrent are considered.

A novel concept based on a general thermodynamic model of nucleation and growth monitoring by chemical and electrostatic control of the water-oxide interfacial tension and an aqueous thin film direct growth technique have been developed to fabricate very large 3-D arrays of crystalline transition and post transition metal oxides and oxyhydroxides onto various substrates at mild temperatures. The goal is the low-cost design of a new generation of functional purpose-built metal oxide particulate thin films consisting of nano-, meso- and micro-scale building-blocks of controlled size, morphology, and orientation. Such well-designed materials should lead to a better fundamental understanding of the electronic structure and physical/chemical properties of nanomaterials as well as to contribute to the development of novel and optimized nanodevices.

Single rhodamine B (RhB) molecule-Sb:SnO₂(ATO) nanoparticle junctions were studied using two-photon excitation single molecule fluorescence spectroscopy. For each molecule-nanoparticle junction, fluorescence decay of RhB was found to be single exponential, indicating a static heterogeneous distribution of junction properties. The measured fluorescence lifetime is shorter than RhB on inert substrates but longer than that expected on ATO based on ensemble averaged electron transfer rates. Possible origins for the shorten single molecule lifetimes and distribution are discussed.

Porous interfaces are being transformed within the framework of nanotechnology to develop highly efficient sensors, nanostructure modified microreactors, and active battery electrodes. We demonstrate the rapid and reversible sensing of HCl, NH₃, CO, SO₂, H₂S, and NO_x at or below the ppm level. Gold and tin-based nanostructured coatings are introduced to improve the detection of NH₃, CO, and NO_x as these coatings form the initial basis for introducing significant selectivity. These sensor suites are being extended to develop microreactors, with a goal to introduce quantum dot (QD) based photocatalysts within the porous interface structure. Highly efficient, visible light absorbing, anatase TiO_2-xN_x nanophotocatalysts have been formed in seconds at room temperature via the direct nitridation of anatase TiO₂ nanocolloids. A tunability throughout the visible is found to depend upon the degree of nanoparticle agglomeration and upon the ready ability to seed these nanoparticles with metal (metal ions) including Pt, Co, and Ni. This metal ion seeding also leads to unique efficient phase transformations, including that of anatase to rutile TiO₂, at room temperature. The visible light absorbing photocatalysts readily photodegrade methylene blue and gaseous ethylene. They can be transformed from liquids to gels and, in addition, can be placed on the surfaces of sensor and microreactor based configurations 1) to produce an improved photocatalytically induced solar based sensor response, and 2) with a goal to facilitate catalytically induced disinfection of airborne pathogens. In contrast to the nitridation process which is facile at the nanoscale, we find little or no direct nitridation of micrometer sized anatase or rutile TiO₂ powders at room temperature. Thus, we illustrate an example of how a traversal to the nanoscale can vastly improve the efficiency for producing important submicron particles.

Nanomaterials have gained considerable importance in various fields such as chemistry, physics, materials science, biology, and bio-engineering due to the great demand in designing nanomaterial with controlled size, shape and physico-chemical properties. The conventional methods for the preparing metal chalcogenide suffer from several limitations, such as high processing temperature, relatively high cost, non-stoichiometric compositions and poor crystallinity. Metal chalcogenide particles with fine size and spherical morphology and non-aggregation have important applications for the on going technological advancement. It is important to develop a process that can produce particles having controlled characteristics such as morphology, composition and size. In recent years, sonochemistry offers an advantageous alternate in design of nanomaterial with desired properties. This review is mainly focused on the preparation of nanosized metal chalcognide using sonochemistry and their practical applications.

Narrow and symmetric emission spectrum, continuous excitation spectrum, high quantum yields and resistance to photobleaching are outstanding advantages semiconductor nanoparticles exhibit ideally compared to conventional fluorescent dyes. However, it is still a challenge to replace existing organic fluorophores and develop a tool for imaging and site-specific drug delivery. In this presentation, we demonstrate the chemistry and spectroscopy of homogeneously alloyed nanocrystals and nanocrystal-doped protein microspheres, emitting the IR and near-infra red as tools for bio-imaging, and drug delivery, respectively. In addition, nanoparticles are studied as energy donors to photosensitizer phthalocyanine dyes, which have proven potential for photodynamic therapy.

Building blocks with a nanoscale dimension (typically <100nm) have different properties compared with their bulk counterparts. For instance, the absorption and photoluminescence of semiconductor quantum dots show a strong size dependence [1, 2]. Charge injection onto a single quantum dot has to overcome a strong Coulomb charging energy. The magnetic moment of the surface atoms are strongly enhanced due to unquenched orbital moments in transition metal clusters [3]. Fundamentally, all these new phenomena can be attributed to two major effects on the nanometer scale, namely the quantum confinement of charge and spin [4] and the low coordination of surface atoms [5]. Development in colloidal chemistry during the past two decades has produced a variety of high quality nanoscale building blocks with many unique properties [6-10]. Although it is possible to study and utilize the physical properties of nanoparticles on a single particle level, it remains to be a technically challenging task. On the other hand, experiments on macroscopic 2D and 3D nanocrystal superlattices are more accessible. Self-assembly of nanocrystal building blocks not only provides a way to connect the nanoscale dimension to the macroscopic length scale, but it also creates a revolutionary new class of materials. New collective behavior is expected to emerge because of the strong coupling between building blocks [11, 12].

The saturable absorbing properties of PbSe core nanocrystals (NCs), and their corresponding PbSe/PbS core-shell and PbSe/PbSeS core-alloyed shell NCs, were examined at an energy of 1.54 micron. These NCs act as an efficient passive Q-switch in near infra-red pulsed lasers. Saturation fluence values in the order of a few hundreds mJ/cm² were obtained, leading to a laser power output of 2.0-3.5 mJ with a pulse duration of 40-53 nsec. We demonstrated a substantial increase of the emission quantum yield and a slight decrease of the saturation fluence values, when using PbSe/PbS and PbSe/PbSe_xS_1-x core-shells structures, in comparison with the corresponding PbSe core NCs. A quasi-three level energy manifold was used for the simulation of saturation fluence curves and of the absorption cross sections. All samples were prepared in a novel colloidal synthetic method.

The mechanism of resonance energy transfer between quantum dots is investigated theoretically. In order to incorporate explicit account of the selection rules for absorption of circularly polarized light, a quantum electrodynamical treatment of the electronic coupling is derived. The electronic coupling is mediated by the exchange of a virtual photon, which in the far zone limit acquires real character and is circularly polarized. The conditions by which quantum information, in terms of exciton spin orientation (total angular momentum quantum number), can be exchanged or switched through resonance energy transfer are discussed. Intrinsic exciton spin flip processes are shown experimentally to compete with typical energy transfer rates. Exciton spin flip times correspondingly range from <100 fs to 1.2 ps are reported.

Gold nanoparticles with unique optical properties offer useful applications in biotechnology. In this article two applications that we have developed are summarized, in one they are used in cancer cell diagnostics and in the other they are found to have catalytic property for the NADH oxidation reaction which is important in ATP formations. By conjugation with anti-EGFR antibodies which specifically target EGFR that are usually overexpressed on most cancer cells, gold nanoparticles are used as a molecular contrast agent for cancer cell diagnostics using their both strong surface plasmon absorption and efficient Mie scattering properties. Au nanoparticles are also good catalysts for many reactions due to their high surface to volume ratio. Au nanoparticles are found to be the catalyst for the NADH oxidation reaction. This was studied by monitoring the effect of the nanoparticles on NADH fluorescence intensity and lifetime as well as the change of the surface plasmon absorption band during the reaction.

We present the investigation of optically-induced rotation of single DCM (4-(dicyano methylene)-2-methyl-6-(p-dimethyl aminostyril)-4H-pyran) molecules in a low-T_g polymer matrix. The rotation process is based on the photo-isomerization of the molecule occurring upon a resonant linearly polarized optical excitation. This pumping process creates a photo-selection angular cone, resulting in a motion of the molecular dipole perpendicularly to the linear excitation, stabilized by the polymer re-organization. Ensemble measurements are seen to be biased by the difficulty to discriminate between the re-orientation process and angular selective photo-bleaching. Such photo-bleaching effect can however be observed independently in single molecules data. The thermal rotational motion of single molecules in the polymer were first investigated, showing heterogeneous behaviors with orientational fluctuations of a about ten seconds time scale, due to the local viscosity and elasticity of the polymer environment. Under a linearly polarized pump at several hundreds of W/cm² intensity, a photo-induced orientation motion towards the perpendicular direction to the pump was observed for 50% of the molecules, within a typical time of a few tens of seconds. The remaining molecules showed orientational fluctuations dominating over the pump effect.

The ability to control the particle size and morphology of nanoparticles is of crucial importance nowadays both from a fundamental and industrial point of view considering the tremendous amount of high-tech applications. Controlling the crystallographic structure and the arrangement of atoms along the surface of nanostructured material will determine most of its physical properties. In general, electronic structure ultimately determines the properties of matter. Soft X-ray spectroscopy has some basic features that are important to consider. X-ray is originating from an electronic transition between a localized core state and a valence state. As a core state is involved, elemental selectivity is obtained because the core levels of different elements are well separated in energy, meaning that the involvement of the inner level makes this probe localized to one specific atomic site around which the electronic structure is reflected as a partial density-of-states contribution. The participation of valence electrons gives the method chemical state sensitivity and further, the dipole nature of the transitions gives particular symmetry information. The new generation synchrotron radiation sources producing intensive tunable monochromatized soft X-ray beams have opened up new possibilities for soft X-ray spectroscopy. The introduction of selectively excited soft X-ray emission has opened a new field of study by disclosing many new possibilities of soft X-ray resonant inelastic scattering. In this paper, some recent findings regarding soft X-ray absorption and emission studies of various nanostructured systems are presented.

The effects of protonation on the structure of the carbon single-walled nanotube (SWNT) polymer composites were studied by solid-state nuclear magnetic resonance (NMR) techniques and Raman spectroscopy. In addition, solid-state ¹³C NMR was used to elucidate the aggregation state of the SWNTs in the polymer films relative to pristine SWNTs.

Excitation of metal nanoparticles with sub-picosecond laser pulses causes a rapid increase in the lattice temperature, which can impulsively excite the phonon modes of the particle that correlate with the expansion co-ordinates. The vibrational periods depend on the size, shape and elastic constants of the particles. Thus, time-resolved spectroscopy can be used to examine the material properties of nanometer sized objects. This article will provide a brief overview of our recent work in this area of research, specifically, how the vibrational modes observed in the experiments are assigned and what information can be obtained from the measurements. Our work has mainly been concerned with noble metal particles (gold and silver) in aqueous solution. The different shapes that have been examined include spheres, rods and triangles, all with different sizes.

Polarized femtosecond transient absorption spectroscopy and time-resolved polarized emission spectroscopy have been employed to study the spectroscopy and dynamics of charge carriers in GaSe nanoparticles and nanoparticle aggregates. Transient absorptions in the visible and near infrared spectral regions are assigned in terms of a simple effective mass, particle-in-a-cylinder model. A particle size independent, z-polarized hole intraband transition maximizing at 600-650 nm is resolved from a particle size dependent x,y-polarized electron transition involving transfer of electrons from the conduction band to surface states. For the small (2.7 nm) and mid-sized (5.1 nm) particles, the electron charge transfer transition decays relatively rapidly (≈15 ps timescale) due to a direct to indirect (Γ to M) electron momentum relaxation. The hole intraband transition decays relatively slowly (400 - 900 ps) due to hole trapping. The same decay components are also present in the emission kinetics. Particle aggregation significantly shifts the lowest energy allowed transition in the small particles, thereby changing the nature (Γ versus M) of the initially excited state and altering the observed transient absorption spectra. For the large (11.8 nm) particles, the relative energetics of the electron Γ and M states are reversed and the fast decay of the electron transition is not observed.

In this submission, we report on the results of spectroscopic studies of charge carrier dynamics in colloidal In_1-xGa_xP quantum dots (QDs) with low levels of Ga doping (x~1%). These QDs exhibit large global Stokes shift of fluorescence (up to 300 meV) along with high emission yield (up to 30% in solution and 25% in films under blue excitation at 300 K) after post-synthesis photo-chemical treatment. In order to reveal the nature of large fluorescence Stokes shift and study the band-edge carriers dynamics, we performed time-resolved measurements of emission and photo-induced absorption changes in QDs with different sizes and surface passivation. The work was focused on the studies of differences between QDs subjected to photochemical surface passivation and bare nanoparticles. Time-resolved absorption spectroscopy indicates that holes' trapping strongly depends on passivation of surface trap states and can even suppress Auger multiparticle recombination in poorly passivated nanoparticles. Transient fluorescence measurements in well-passivated nanoparticles demonstrate that at short delays (<2 ns), emission Stokes shift is almost twice smaller than in steady-state measurements and matches the emission band in unpassivated QDs. At longer delays, time-resolved emission matches the spectra obtained with continuous wave (CW) excitation. We propose that initially photoluminescence occurs from quantum-confined state and subsequent hole relaxation onto surface/interface sites gives rise to emission with large global Stokes shift. In poorly passivated QDs, holes escape quickly to deep-trap states that leads to formation of low-efficiency broad emission band red-shifted with respect to the excitonic PL band.

Recent studies of the relaxation of photoexcited electrons in PbSe quantum dots find that the relaxation of electrons from the 1P state to the 1S state occurs on the picosecond time scale, even when the states are more than 10 phonon energies apart. This ultrafast relaxation cannot be explained by mechanisms invoked to explain the absence of a phonon bottleneck in other quantum-dot materials. Linear spectroscopy reveals splitting of the lowest-energy states of PbSe quantum dots, but the splitting is inadequate to account for the ultrafast 1P-to-1S relaxation. We tentatively attribute the splitting to coupling of the equivalent L-valleys from which the quantum-dot states are derived. Fluorescence-line-narrowing experiments exhibit little narrowing, and substantial anti-Stokes fluorescence even at temperatures as low as 15 K. Finally, we observe microsecond-time-scale radiative recombination and resonant energy transfer between quantum dots. The time scale of these processes is consistent with dielectric screening of the electric field in the nanocrystals, which in turn highlights the need for better understanding of the dielectric function of a nanocrystal.

We measure the concentration of single-walled nanotubes (SWNTs) present in aqueous suspensions by a technique that involves surfactant removal followed by high-temperature oxidation and mass spectroscopy of the resulting products. We also analyze the shift in SWNT emission energy evident from photoluminescence excitation spectroscopy as the surfactant molecule is changed. Next we study spectroscopic changes as surfactant is gently removed by dialysis.

The current study highlights the possibility of fine-tuning the chemistry and structure of periodic mesoporous organosilica (PMO) upon incorporation of large heterocyclic bridging group, tris[3-(trimethoxysilyl)propyl]isocyanurate (ICS), into its framework. This PMO was prepared by direct co-condensation of ICS and tetraethylorthosilicate (TEOS)in the presence of block copolymer used as structure directing agent. It was shown that up to a relatively high percentage of ICS a hexagonally ordered mesostructure with P6mm symmetry is formed. The co-condensation of ICS, TEOS and (3-mercaptopropyl)trimethoxysilane (SH) in the presence of poly(ethylene)-poly(propylene)-poly(ethylene) block copolymer afforded novel PMO with isocyanurate groups in the framework and mercaptopropyl groups on the surface of mesopores. It was surprising to find that the structure symmetry of this bifunctional PMO was not hexagonal but cubic. This structural change was induced by addition of another organosilane to the synthesis gel that afforded PMO with I4₁32 symmetry. Nitrogen adsorption, thermogravimetry, and small angle X-ray scattering were employed to monitor structural and interfacial changes of the PMO studied.

Much can be learned about charge and magnetization dynamics at surfaces and in nanometer thickness films through terahertz emission spectroscopy (TES). In some respects, TES is the difference-frequency analog of second harmonic generation (SHG). As such, interface-specific properties contribute to the generation of a THz pulse upon ultrafast optical excitation. In addition, there can be bulk contributions as well, as is also true in SHG. The dependence of THz pulse emission on surface orientation has been used to study carrier dynamics, both real and virtual, in GaAs(111). We find that the dependence on the angle of linearly polarized excitation is well described by known theory. Magnetization dynamics in polycrystalline nickel films ranging in thickness from 5 nm to 60 nm have also been characterized with TES. Distinct bulk and surface contributions each play a role, and their origins are discussed.

Electrical and thermal conductivities of metal nanoparticles and their aggregates are important for many device applications involving nanomaterials. In this work, the electrical conductivity of gold nanoparticle aggregates has been measured and found to be a useful probe of the surface chemistry of the nanoparticles. It has been observed that the conductivity of the gold nanoparticle aggregates in solution increases with light illumination or thermal heating and recovers completely to the initial value upon removal of the light or heat. The amount of change in conductivity depends on the amount of heat or light. The conductivity change is tentatively attributed to ion dissociation from the nanoparticle surface due to heating or light illumination. Meanwhile, the thermal conductivity of dried silver nanoparticles (30-60 nm) has been measured and found to be around 2 W/m×K. This is consistent with previous prediction of significantly reduced thermal conductivity of Ag nanoparticles/aggregates. In addition, external DC electrical field enhanced surface-enhanced Raman scattering (SERS) was also observed with the excitation laser light focused in between the electrodes instead of on the electrodes. Various potential were applied and an enhancement factor of 5 has been achieved. Possible explanations for this enhancement are provided.

Highly sensitive response of semiconducting single-walled carbon nanotubes (SWNTs) to molecular adsorption may lead to a unique direction in exploiting their exceptional electrical properties. For example, simultaneous doping and nearly ideal gate efficiencies are achieved with polymer electrolytes as gating medium for nanotube transistors. However, highly sensitive responses can also lead to difficulties in interpretation of many observations as exemplified by the controversy surrounding whether oxygen adsorption causes doping or changes in the nature of SWNT-metal contacts. Effects of molecular adsorption, both covalent and non-covalent, on the electronic properties of SWNTs are discussed. How electronically selective covalent chemistry changes Raman scattering and electrical conductivity of individual metallic and semiconducting as well as random networks of SWNTs are first discussed. Non-covalent adsorption of polymers is then explored where electrochemical gating can be applied to allow both chemical and electrostatic control of charge carriers.

The surface structure of C₂H₄ on Si(001) has been investigated by coaxial impact collision ion scattering spectroscopy (CAICISS). To determine the adsorption structure of the C₂H₄ molecules definitely, the computer simulation with the two-dimensional trajectory count method has been applied to the recently proposed most possible two single molecular adsorption configurations (di-σ on-top and di-σ end-bridge). The CAICISS spectra and simulation results show that the di-σ on-top structure is better fitted with the experimental results rather than the di-σ end-bridge.

Intense Cathodoluminescence (CL) emission is obtained for Electron Modified Porous Silicon films when excited with electron beams of kinetic energies below 2KeV, supporting the applicability of such material as light emitter in field emission display devices. Porous Silicon films were irradiated with an electron beam producing a collapsed nanostructure of reduced porosity. The CL intensity from the excited pixels made of such material reduced in less than 10% during a continuous burning of 10 hours. The CL spectra of the films correlate with its photoluminescence showing that the origin of the CL is the quantum confinement effect in the silicon nanoparticles. In situ SIMS analyses before and after prolonged e-beam excitation, as well as of the electron-eroded material from the sample, showed minor compositional changes of the film and reduced sputtering of the silicon nanoparticles due to the electron irradiation. In situ bombardment of the porous material with Hydrogen beams induced changes on the surface passivation of the nanoparticles through which we were able to maximize the CL of the films.

Self assembled synthetic opals composed of spheres with 200-1500nm diameters were infiltrated with poly[2-methoxy-5-(20-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and Poly [(m-phenylenevinylene)-co- (2,5-dioctoxy-p-phenylenevinylene)] (PmPV) which are luminescent polymers. The luminescence spectra of the polymers was blue shifted when infiltrated deep into the nano-scopic opal pores relative to the luminescence spectra from thick films of the bulk polymers. Inverse composite plastic and luminescent polymer opals were constructed resulting in a significant blue shift in the peek luminescence of MEH-PPV from 568nm for the bulk polymer to 520nm in the inverse opal structure. We found that the majority of the blue shifting observed could be explained by the formation of isolated polymer strands within the opals. Silica spheres were coated with MEH-PPV, dispersed in H₂O and coated with polyelectrolytes which recharged and sterically stabilized the colloidal surfaces. Luminescence spectra from individual and self-assembled silica spheres coated with MEH-PPV were also blue shifted.

Having been hibernated for almost 50 years, research in thermoelectric materials is beginning to regain activity because of the recent advances in nanoscience and nanotechnology. Thermoelectric is an old topic, which was discovered as early as 1821 by Thomas Johann Seebeck. During the following 120 years, great advances in both the theories and experiments were achieved. Since the 1950s, studies in thermoelectric have developed very little, because of the painful difficulties in elevating the efficiency of these kinds of materials. The efficiency of thermoelectric materials is determined by a dimensionless parameter--figure of merit (ZT), given by ZT = S2σT/κ where T is the temperature, S is the thermoelectric power (or Seebeck coefficient), σ is the electrical conductivity, and κ is the thermal conductivity. The best commercially available thermoelectric materials nowadays have a ZT around 1.0, which can be only used in some special cases. To be competitive to the kitchen refrigerators or air-conditioners, a ZT ⩾ 3 at room temperature is required. Recently, some exciting results indicated that higher ZT values can be realized by nanoengineering of these materials. Both theoretical calculations and experimental modulations have shown the promising potentials in the elevation of the efficiency of thermoelectric materials.