EFFECTS OF SURFACE STATES, DEFECTS AND DOPANTS ON THE OPTICAL AND MAGNETIC PROPERTIES OF LOW-DIMENSIONAL MATERIALS

Nanomaterials have attracted the attention of researchers from various fields due to their unique features (that are otherwise absent in the bulk) such as quantum confinement, high surface to volume ratio, ability for surface modification etc. Since the discovery of fullerenes and carbon nanotubes, several synthesis techniques have been developed for nanomaterial growth. However, different control parameters in different synthesis techniques often result in nanostructures with varying defects that may alter their fundamental behavior. Such defects or disorder in the crystal lattice can lead to the disruption of lattice symmetry. The defect-induced symmetry lowering (or breaking) effects play a vital role in the determination of fundamental material characteristics. Thus, it is very important to characterize the defects in order to understand their effects on the nanomaterial properties. This thesis describes the effects of defects in low dimesional systems such as ZnO nanowires, graphene and carbon nanotubes are studied. Firstly, it describes the synthesis and characterization of ZnO nanostructures and discusses the effects of surface states, defects and dopants on their optical and magnetic properties. An unexpected presence of ferromagnetic (FM) ordering in nanostructured nonmagnetic metal oxides has been reported previously. Though this property was attributed to the presence of defects, systematic experimental and theoretical studies to pinpoint its origin and mechanism were lacking. While it is widely believed that oxygen vacancies are responsible for FM ordering, surprisingly annealing as-prepared samples at low temperature (high temperature) in flowing oxygen actually enhances (diminishes) the FM ordering. For these reasons, we have prepared, annealed in different environments, and measured the ensuing magnetization in micrometer and nanoscale ZnO with varying crystallinity. We further find from our magnetization measurements and ab-initio calculations that a range of magnetic properties in ZnO can result, depending on the sample preparation and annealing conditions. For example, within the same ZnO sample we have observed ferro- to para- and diamagnetic responses depending on the annealing conditions. We also explored the effects of surface states on the magnetic behavior of nanoscale ZnO through detailed calculations. In the case of grapheme, we have observed new combination modes in the range from 1650 to 2300 cm−1 in single-(SLG), bi-, few-layer and incommensurate bilayer graphene (IBLG) on silicon dioxide substrates. A peak at 1860 cm−1 (iTALO−) is observed due to a combination of the in-plane transverse acoustic (iTA) and the longitudinal optical (LO) phonons. The intensity of this peak decreases with increasing number of layers and this peak is absent for bulk graphite. The overtone of the out-of-plane transverse optical (oTO) phonon at 1750 cm−1, also called the M band, is suppressed for both SLG and IBLG. In addition, two previously unidentified modes at 2200 and 1880 cm−1 are observed in SLG. The 2220 cm−1 (1880 cm−1) mode is tentatively assigned to the combination mode of in-plane transverse optical (iTO) and TA phonons (oTO+LO phonons) around the K point in the graphene Brillouin zone. Finally, the peak frequency of the 1880 (2220) cm−1 mode is observed to increase (decrease) linearly with increasing graphene layers. Finally, we find that the high curvature in sub-nm SWCNTs leads to (i) an unusual S-like dispersion of the G-band frequency due to perturbations caused by the strong electron-phonon coupling, (ii) an activation of diameter-selective intermediate frequency modes that are as intense as the radial breathing modes (RBMs), and (iii) a clear observation of the IR modes

Intravenously delivered graphene nanosheets and multiwalled carbon nanotubes induce site-specific Th2 inflammatory responses via the IL-33/ST2 axis

Carbon-based nanomaterials (CBN), such as graphene nanosheets (GNS) and multiwalled carbon nanotubes (MWCNT), have been proposed for potential nanomedicine applications such as biomedical devices and carriers for drug delivery. However, our current understanding regarding the systemic toxicity of these CBN through intravenous (iv) injection is limited. In this study, we compare the immune response resulting from GNS and MWCNT exposure. We hypothesize that iv administration of GNS and MWCNT would result in divergent systemic inflammatory responses due to physicochemical differences between these two CBN. In the lungs of C57BL/6 mice, GNS actuate a Th2 immune response 1 day following iv administration, which consists of neutrophilic influx and a significant increase in interleukin (IL)-5, IL-13, IL-33, and its soluble receptor (sST2) in the bronchoalveolar lavage fluid. MWCNT elicited a significant increase in the messenger ribonucleic acid expression of cytokines in the spleen including IL-4 and IL-33, which are associated with an increase in splenic cell differentiation (CD)4+ and CD8+ T-cells in C57BL/6 mice following iv injection. The observed Th2 responses in both the lung and spleen are absent in ST2−/− mice administrated GNS or MWCNT, suggesting a critical role for IL-33. In conclusion, the use of GNS or MWCNT as nanocarriers for drug delivery may result in Th2 immune responses that are mediated through the IL-33/ST2 axis and therefore may promote adverse allergic reactions

Ultrasensitive Immunosensing Platform Based on Analyte Induced Disruption of Luminescence Quenching (AIDLuQ)

In this study, we design an extremely fast and sensitive immunosensing platform using graphene as the sensing platform. A solution containing a mixture of graphene nanoplatelets and gold nanoparticles was coated on to a copier paper using a spray gun to form a uniform coating. Fluorescent quantum dots (QDs) functionalized with antibodies (Ab) were drop casted on to this platform, whose fluorescence was quenched by the graphene on the graphene/gold paper. With the addition of the antigen to this graphene/gold-QD-Ab complex, a disruption of quenching was observed, and the fluorescence intensity increased with increasing concentration of the antigen. A detection limit of as low as 10 fM was obtained for the detection of human Immunoglobulin G (IgG)

Polymer-nanocarbon composites, methods of making composites, and energy storage devices including the composite

Embodiments of the present disclosure, in one aspect, relate to composites including a carbon nanomaterial having a redox-active material, such as a polymer containing redox groups, disposed on the carbon nanomaterial, methods of making the composite, methods of storing energy, and the like

Polymer-nanocarbon composites, methods of making composites, and energy storage devices including the composite

Embodiments of the present disclosure, in one aspect, relate to composites including a carbon nanomaterial having a redox-active material, such as a polymer containing redox groups, disposed on the carbon nanomaterial, methods of making the composite, methods of storing energy, and the like

Spectroscopic Insights into the Nano-Bio Interface

Engineered nanomaterials (ENMs) strongly interact with biomolecules due to their unique physicochemical properties. From the standpoint of nanotoxicity, it is imperative to achieve a comprehensive understanding of various nano-bio interactions to ultimately design benign ENMs that do not elicit adverse physiological responses. Spectroscopic tools are ideal for elucidating the underlying biophysical mechanisms of nano-bio interactions. In this chapter, we review spectroscopy techniques, such as Raman, infrared, circular dichroism (CD), and hyperspectral imaging, to illuminate the nano-bio interface. Particularly, we discuss the role of spectroscopic tools in gaining a fundamental understanding of the formation and influence of protein corona on ENM physiological responses

A wireless triboelectric nanogenerator

We demonstrate a new paradigm for the wireless harvesting of mechanical energy via a 3D-printed triboelectric nanogenerator (TENG) which comprises a graphene polylactic acid (gPLA) nanocomposite and Teflon. The synergistic combination of eco-friendly PLA with graphene in our TENG exhibited an output voltage > 2 kV with an instantaneous peak power of 70 mW, which in turn generated a strong electric field to enable the wireless transmission of harvested energy over a distance of 3 m. Specifically, we demonstrate wireless and secure actuatation of smart-home applications such as smart tint windows, temperature sensors, liquid crystal displays, and security alarms either with a single or a specific user-defined passcode of mechanical pulses (e.g., Fibonacci sequence). Notably, such high electric output of a gPLA-based TENG enabled unprecedented wireless transmission of harvested mechanical energy into a capacitor, thus obviating the need for additional electronics or energy sources. The scalable additive manufacturing approach for gPLA-based TENGs, along with their high electrical output can revolutionize the present method of harnessing the mechanical energy available in our environment

A micro-Raman study of exfoliated few-layered \u3ci\u3en\u3c/i\u3e-type Bi\u3csub\u3e2\u3c/sub\u3e Te\u3csub\u3e2.7\u3c/sub\u3e Se\u3csub\u3e0.3\u3c/sub\u3e

Previously we showed that the thermoelectric (TE) performance of bulk n-type Bi2Te2.7Se0.3 can be enhanced by subjecting it to a combined process of chemical or mechanical exfoliation (C/ME) followed by a rapid densification and restacking of the exfoliated layers via the spark-plasma-sintering technique (SPS). Here, we present a systematic micro-Raman study of two-dimensional flakes of n-type Bi2Te2.7Se0.3 produced by the C/ME process, as a function of the flake thickness. We found Raman evidence for flakes with: (i) integer number of quintuples which exhibited a strong electron-phonon coupling, and (ii) non-integer number of quintuples, or sub-quintuples which exhibited the forbidden IR active mode due to symmetry lowering. Detailed atomic force microscopy was used to confirm the number of quintuples in all flakes examined in this study. The restacking and densification of these flakes by SPS promoted the formation of charged grain boundaries, which led to the enhanced TE properties via the energy filtering process