17 research outputs found
Effect of Silver Addition on the Ethanol-Sensing Properties of Indium Oxide Nanoparticle Layers: Optical Absorption Study
In2O3 and In2O3:Ag nanoparticle layers have been deposited using a two-step method consisting of chemical capping and dip coating techniques. The result of optical absorption analysis of In2O3:Ag samples shows the presence of Ag2O and Ag in air-annealed and vacuum-annealed samples, respectively. These results have been correlated with the gas sensing properties of these layers towards ethanol and support the proposed mechanism that increase in sensor response on Ag addition is due to the conversion of Ag2O to Ag in the presence of ethanol
Modulating thermoelectric properties in oxygen-passivated Sb2Te3 thin film through grain boundary engineering
The present study demonstrates the effectiveness of incorporating oxygen
atoms into the Sb2Te3 thin film, leading to an improved power factor and
reduction in thermal conductivity. Based on the experimental evidence, it can
be inferred that oxygen-related impurities preferentially wet the grain
boundary (GB) and introduce a double Schottky barrier at the GB interface,
promoting energy-dependent carrier scattering, ultimately leading to a rise in
the Seebeck coefficient. Additionally, the introduction of chemisorbed oxygen
creates a high mobility state within the valence band of Sb2Te3, as
corroborated by theoretical calculations, resulting in a significantly
increased electrical mobility. These factors collectively contribute to
improved thermoelectric performance. A set of Scanning probe (SPM) techniques
is used to experimentally confirm the alteration in charge transport resulting
from the oxygen-passivated grain boundary. Additionally, Scanning Thermal
Microscopy (SThM) is employed to observe the spatial variations of thermal
conductivity at the nanoscale regime. This study presents a comprehensive
microscopic investigation of the impact of oxygen on the phonon and charge
carrier transport characteristics of Sb2Te3 thermoelectric materials and
indicates that incorporating oxygen may represent a feasible approach to
improve the thermoelectric efficiency of these materials
Anisotropic thermal transport using xSThM studies in 2D-3D heterostructures and composites
Thermal conductivity is a crucial parameter defining the thermal transport as well as thermophysical properties of materials in thermoelectric, manufacturing and processing applications of materials where heat transport plays a major role. To address a current challenge of measuring these properties locally, in the areas of few tens or hundreds nanometres, we used a novel approach of cross-sectional scanning thermal microrcopy, or SThM, (xSThM). In this method, we first create a fine low angle wedge of the studied material via precision Ar ion cross-sectional polishing [1] and then measure a thermal conductance via SThM with each measurement point providing thermal conductance of the material with different thickness. Furthermore, an analytical model is then used to extract not only anisotropic values of thermal conductivity but also determines the effect of interfacial thermal resistance between the substrate and complex structured materials (heterostructure and composite structures). This technique thus facilitates a direct measurement of thermal conductance as a function of thickness in 2D-3D based heterostructures (Sb2Te3/MoS2) and composites structures (Sb2Te3/AgSbTe2). The thickness and number of layers of MoS2 was optimized to achieve extremely lower values of thermal conductivity (0.7 0.1 Wm-1K-1) along with higher values of power factor ((4.97 0.39) ×10-3 Wm-1K-2) leading to high values of ZT of 2.08 0.37 at room temperature. Similarly, the concentration of Ag in Sb2Te3/AgSbTe2 is optimized for highest values of ZT. A major enhancement in the value of TE performance was observed due to the effective majority carriers filtering and phonon scattering at the potential barrier present due to multiple interfaces. The current methodology provides an efficient tool for quantifying the thermal transport in thin films and 2D materials, and hence is useful in establishing the thermal transport in such complex structures. References: [1] Jean Spièce, Charalambos Evangeli, Alex J. Robson, Alexandros El Sachat, Linda Haenel, M. Isabel Alonso,○ Miquel Garriga,○ Benjamin J. Robinson, Michael Oehme, Jörg Schulz, Francesc Alzina, Clivia Sotomayor Torres, Oleg V. Kolosov, Nanoscale, 24, 10829 (2021)
Tuning thermoelectric properties of SbTe-AgSbTe nanocomposite thin film -- synergy of band engineering and heat transport modulation
The present study demonstrates a large enhancement in the Seebeck coefficient
and ultralow thermal conductivity (TE) in SbTe-AgSbTe nanocomposite
thin film. The addition of Ag leads to the in-situ formation of AgSbTe
secondary phase nanoaggregates in the SbTe matrix during the growth
resulting in a large Seebeck coefficient and reduction of the thermal
conductivity. A series of samples with different amounts of minor AgSbTe
phases are prepared to optimize the TE performance of SbTe thin films.
Based on the experimental and theoretical evidence, it is concluded that a
small concentration of Ag promotes the band flattening and induces a sharp
resonate-like state deep inside the valence band of SbTe, concurrently
modifying the density of states (DOS) of the composite sample. In addition, the
electrical potential barrier introduced by the band offset between the host TE
matrix and the secondary phases promotes strong energy-dependent carrier
scattering in the composite sample, which is also responsible for enhanced TE
performance. A contemporary approach based on scanning thermal microscopy is
performed to experimentally obtain thermal conductivity values of both the
in-plane and cross-plane directions, showing a reduced in-plane thermal
conductivity value by ~ 58% upon incorporating the AgSbTe phase in the
SbTe matrix. Benefitting from the synergistic manipulation of
electrical and thermal transport, a large ZT value of 2.2 is achieved at 375 K.
The present study indicates the importance of a combined effect of band
structure modification and energy-dependent charge carrier scattering along
with reduced thermal conductivity for enhancing TE properties
A Special Issue - International Conference on Nano Science and Technology, 16-18 March 2006 (ICONSAT 2006), New Delhi, India
Dependence of Plasmonic Properties of Silver Island Films on Nanoparticle Size and Substrate Coverage
Localized surface plasmon resonance displayed by metal nanoparticles has been studied in silver island films prepared by the simple technique of vacuum evaporation, which is one of the options that is easily adaptable for large area and low cost applications. Silver island films with varying island sizes and areal coverages are prepared by depositing silver films with varying thicknesses followed by annealing. The optical properties of the samples have been explained in terms of dependence of scattering and absorption on the metal island size, interparticle interaction and matrix effects, and the wavelength range over which the plasmonic effects are present
Growth of Large-Area 2D MoS2 Arrays at Pre-Defined Locations Using Stencil Mask Lithography
Structural and photoluminescence properties of tin oxide and tin oxide: C core–shell and alloy nanoparticles synthesised using gas phase technique
In the present study, we report a controlled growth of tin oxide and tin oxide: carbon nanoparticles by an integrated method comprising of the gas phase agglomeration, electrical mobility based size selection, and in–flight sintering steps. The effect of in-flight sintering temperature and variation in growth environment (N2, H2 and O2) during nanoparticle formation, morphology and composition has been investigated by carrying out High Resolution Transmission Electron microscopy and X-Ray diffraction studies. The results highlight the novelty of the present technique to grow alloy and core-shell nanoparticles in which the stoichiometery (x) of SnOx and the mode of incorporation of carbon into the tin oxide lattice (alloy or core-shell structure), along with well-defined size can be controlled independently. Detailed Photoluminescence (PL) studies of well sintered monocrystalline SnO, SnOx and SnO2 nanoparticles along with SnOx:C and SnO2:C alloy and C@SnO core-shell nanoparticle has been carried out. The shift in the position and nature of PL peaks due to band edge, Sn interstitials and oxygen vacancy defect level energy states has been understood as a function of stoichiometery and nanoparticle structure (alloy and core-shell). These results suggest the possibility of tailoring the position of these levels by controlling the size, composition and alloying which is potentially important for gas sensing, photoconductivity and photo-electrochemical applications
Effect of Silver Addition on the Ethanol-Sensing Properties of Indium Oxide Nanoparticle Layers: Optical Absorption Study
In 2 O 3 and In 2 O 3 :Ag nanoparticle layers have been deposited using a two-step method consisting of chemical capping and dip coating techniques. The result of optical absorption analysis of In 2 O 3 :Ag samples shows the presence of Ag 2 O and Ag in air-annealed and vacuum-annealed samples, respectively. These results have been correlated with the gas sensing properties of these layers towards ethanol and support the proposed mechanism that increase in sensor response on Ag addition is due to the conversion of Ag 2 O to Ag in the presence of ethanol
Engineering Interfacial Effects in Electron and Phonon Transport of Sb 2 Te 3 /MoS 2 Multilayer for Thermoelectric ZT Above 2.0
Abstract: Efficient thermoelectric (TE) conversion of waste heat to usable energy is a holy grail promising to address major societal issues related to energy crisis and global heat management. For these to be economical, synthesis of a solid‐state material with a high figure‐of‐merit (ZT) values is the key, with characterization methods quantifying TE and heat transport properties being indispensable for guiding the development of such materials. In the present study, a large enhancement of the TE power factor in Sb2Te3/MoS2 multilayer structures is reported. A new approach is used to simultaneously experimentally determine the values of in‐plane (kxy) and out‐of‐pane (kz) thermal conductivities for multilayer samples with characteristic layer thickness of few nanometres, essential for the quantification of the ZT, the key parameter for the TE material. Combining simultaneous enhancement in the value of in‐plane power factor (to (4.9 ± 0.4) × mWm−1 K−2) and reduction of the in‐plane value of the thermal conductivity (to 0.7 ± 0.1 Wm−1 K−1) for Sb2Te3/MoS2 multilayer sample led to high values of ZT of 2.08 ± 0.37 at room temperature. The present study, therefore, sets the foundation for a new methodology of exploiting the properties of 2D/3D interfaces for the development of novel fully viable thermoelectric materials