Semiconducting Nanostructures Research Articles

Sputtered Deposited Cu Functionalized MoS2 Nanoworm Thin Films for Nitrogen Dioxide (NO2) Gas Sensor

Semiconducting nanostructures thin films are used in state-of-arts applications due to their heightened physical properties. Semiconducting metal sulfides nanostructures are a growing asset in current semiconductor technology due to their extraordinary physical, chemical, and electronic properties and their outstanding applications in different sensing and optoelectronic devices. The gas sensing capability of semiconducting nanostructures is a recent research interest of many researchers. The MoS2 thin films were grown using reactive sputteringand the sensing performance of pure MoS2 and Cu-MoS2 thin films was studied towards nitrogen dioxide (NO2) gas concentrations (2-200 ppm) at the optimum working temperature of 100℃. The Cu-MoS2 sensor provides a high sensing response as compared to the pure MoS2 thin-film sensor towards 20 ppm of NO2 gas with a fast response and recovery time of 54 s and 82 s, respectively. It was observed that the proposed sensor chip displays an almost stable signal up to the 5th cycle. It is observed that the proposed sensor device exhibits the highest response (30%) to NO2 concerning weak response (10%) towards additional potentially interfering gases (NH3, CO, and H2) at 100°C. It reveals that the Cu-MoS2 thin-film sensor chip is highly selective to NO2 gas at 100 °C.

Estimating Nonradiative Excited-State Lifetimes in Photoactive Semiconducting Nanostructures.

The time evolution of the exciton generated by light adsorption in a photocatalyst is an important feature that can be approached from full nonadiabatic molecular dynamics simulations. Here, a crucial parameter is the nonradiative recombination rate between the hole and the electron that form the exciton. In the present work, we explore the performance of a Fermi's golden rule-based approach on predicting the recombination rate in a set of photoactive titania nanostructures, relying solely on the coupling of the ground and first excited state. In this scheme the analysis of the first excited state is carried out by invoking Kasha's rule thus avoiding computationally expensive nonadiabatic molecular dynamics simulations and resulting in an affordable estimate of the recombination rate. Our results show that, compared to previous ones from nonadiabatic molecular dynamics simulations, semiquantitative recombination rates can be predicted for the smaller titania nanostructures, and qualitative values are obtained from the larger ones. The present scheme is expected to be useful in the field of computational heterogeneous photocatalysis whenever a complex and computationally expensive full nonadiabatic molecular dynamics cannot be carried out.

Nitrogen ion induced CdS clusterization: Structural, morphological, and optoelectrical properties

Semiconducting nanostructures are unique system to study the nanoscale phenomenon for diverse applications in new generation electronic devices. Ion implantation is a promising approach for producing nanoscale crystals or clusters in the near-surface region for doping of semiconductors which repair the respective optical and electrical properties. In the present study, cadmium sulfide (CdS) thin films are grown on a glass substrate via an easy and economical chemical bath deposition method. Thereafter, CdS thin films are implanted with 80 keV nitrogen (N+) ions with different fluences. Implanted thin films are characterized with the support of various characterization techniques. X-ray diffraction (XRD) analysis indicates that the hexagonal phase of CdS nanoflakes remains consistent while scanning electron microscopy (SEM) imaging reveals the formation of defect clusterization after implantation. The defect clusterization in CdS thin films is explained on the basis of local heating after the transmission of implantation energy. Optical properties such as absorption and emission spectra of implanted CdS thin films also get affected on the account of the generation of donor and acceptor level owing to Cd and S vacancies. Furthermore, a considerable increase in the magnitude of the electric current is observed as compared to the pristine sample with the implantation dose.

Ultrathin‐Walled 3D Inorganic Nanostructured Networks Templated from Cross‐Linked Cellulose Nanocrystal Aerogels

AbstractA key challenge in the development of materials for applications in the fields of opto‐ and nanoelectronics, catalysis, separation, and energy conversion is the ability to fabricate 3D inorganic semiconductive nanostructures in a precisely‐controlled and cost‐effective manner. This work describes the fabrication of 3D nanostructured TiO2 monoliths by coating ultraporous cross‐linked cellulose nanocrystal (CNC) aerogel templates with TiO2 layers of controlled thickness via atomic layer deposition (ALD). Following calcination, the resulting hollow inorganic ultraporous 3D networks form the thinnest self‐supporting semiconductive structure (7 nm) fabricated directly on a conductive substrate. The CNC‐templated ALD–TiO2 electrodes are applied toward photoelectrochemical water splitting. The results show that a TiO2 coating as thin as 15 nm produces a maximum water splitting efficiency, resulting in materials savings and reduced fabrication time.

Bone Morphogenetic Protein-2 Conjugated to Quantum Dot®s is Biologically Functional.

Quantum Dot®s (QDot®s) are novel, semi-conductive nanostructures that emit a certain fluorescence when excited by specific wavelengths. QDot®s are more photostable, brighter, and photobleach less than other fluorescent dyes. These characteristics give them the potential to be used in many biological applications. The shells of QDot®s are coated with functional groups, such as carboxylate and organic groups, allowing them to couple to peptides/proteins and be used for real-time imaging and high-resolution microscopy. Here, we utilize Quantum Dot®s and Bone Morphogenetic Protein-2 (BMP-2) to create a BMP-2-QDot®s conjugate. BMP-2 is a growth factor that drives many processes such as cardiogenesis, neural growth, and osteogenesis. Despite its numerous roles, the trafficking and uptake of BMP-2 into cells is not well-established, especially during progression of diseases. The results presented here demonstrate for the first time a fluorescent BMP-2 analog that binds to the BMP-receptors (BMPRs), remains biologically active, and is stable for long time periods. Previous attempts to develop a biological BMP-2 analog with Fluorescein isothiocyanate (FITC) or nanodiamonds lacked data on the analog’s stability. Furthermore, these analogs did not address whether they can signal within the cell by binding to the BMPRs or were mediated by non-stable conjugates.

Direct Measurements of the Picosecond Kinetics of Heating of a Spin Subsystem in Semimagnetic Semiconducting Nanostructures

The kinetics of variation of the magnetization of Zn0.99Mn0.01Se/Be0.93Mn0.07Te type-II semimagnetic semiconducting superlattices in external magnetic fields has been studied using the optical technique with high time resolution. Picosecond times of transfer of the energy and spin of photoexcited carriers to a magnetic subsystem of manganese ions have been directly measured for the first time.

Stability evaluation of ZnO nanosheet based source-gated transistors

Semiconducting nanostructures are one of the potential candidates to accomplish low-temperature and solution-based device assembly processes for the fabrication of transistors that offer practical solutions toward realizing low-cost flexible electronics. Meanwhile, it has been shown that by introducing a contact barrier, in a specific transistor configuration, stable device operation can be achieved at much reduced power consumption. In this work, we investigate both one-dimensional ZnO nanowires (NWs) and two-dimensional nanosheets (NSs) for high performance and stable nano-transistors on conventional Si/SiO2 substrates. We have fabricated two variant of transistors based on nanoscale single-crystalline oxide materials: field-effect transistors (FETs) and source-gated transistors (SGTs). Stability tests are performed on both devices with respect to gate bias stress at three different regimes of transistor operation, namely off-state, on-state and sub-threshold state. While in the off-state, FETs shows comparatively better stability than SGTs devices, in both sub-threshold and on-state regimes of transistors, SGTs clearly exhibits better robustness against bias stress variability. The present investigation experimentally demonstrates the potential advantages of SGTs over FETs as driver transistor for AMOLEDs display circuits which require very high stability in OLED driving current.

Revealing the Relationship between Energy Level and Gas Sensing Performance in Heteroatom-Doped Semiconducting Nanostructures.

The cation substitutional doping of metal oxide semiconductors plays pivotal rolesin improving the gas sensing performances, but the doping effect on surface sensing reaction is still not well understood. In this study, indium oxides doped with various heteroatoms are investigated to obtain in-depth understanding of how doping (or the resulting change in the electronic structure) alters the surface-absorbed oxygen chemistry and subsequent sensing process. The experimental results reveal that energy level of In2O3 can be modulated by introduction of these dopants, some of which (e.g., Al, Ga, and Zr) lead to the elevation of Fermi level, whereas others (e.g., Ti, V, Cr, Mo, W, and Sn) bring about relative drop in Fermi level. However, only the former can improve the response to formaldehyde, indicating a strong link between Fermi level and sensing properties. Mechanistic study suggests that the elevation of Fermi level increases energy level difference between oxide semiconductor and oxygen molecules and facilitates the surface absorption of oxygen species, resulting in superior formaldehyde sensing activity. Especially, Al-doped In2O3 exhibits remarkably enhanced sensing performances toward formaldehyde at low working temperature (150 °C) with high response, good selectivity, ultralow limit of detection (60 ppb), and short response time (2-23 s). Our findings not only promote the understanding of sensing reaction process and its correlation with the semiconductor electronic structure but also offer a general guideline for large-scale screening of promising oxide semiconductor-based sensing materials for gas detection.

Insulator Nanostructure Desorption Ionization Mass Spectrometry.

Surface-assisted laser desorption ionization (SALDI) is an approach for gas-phase ion generation for mass spectrometry using laser excitation on typically conductive or semiconductive nanostructures. Here, we introduce insulator nanostructure desorption ionization mass spectrometry (INDI-MS), a nanostructured polymer substrate for SALDI-MS analysis of small molecules and peptides. INDI-MS surfaces are produced through the self-assembly of a perfluoroalkyl silsesquioxane nanostructures in a single chemical vapor deposition silanization-step. We find that surfaces formed from the perfluorooctyltrichlorosilane monomer assemble semielliptical features with a 10 nm height, diameters between 10 and 50 nm, and have attomole-femtomole sensitivities for selected analytes. Surfaces prepared with silanes that either lack the trichloro or perfluoro groups, lack sensitivity. Further, we demonstrate that hydrophobic INDI regions can be micropatterned onto hydrophilic surfaces to perform on-chip self-desalting in an array format.

Visible Light Metasurfaces Based on Single-Crystal Silicon

Semiconducting nanostructures are promising as components in high-performance metasurfaces. We show that single-crystal silicon can be used to realize efficient metasurface devices across the entire visible spectrum, ranging from 480 to 700 nm. Alternative forms of silicon, such as polycrystalline and amorphous silicon, suffer from higher absorption losses and do not yield efficient metasurfaces across this wavelength range. To demonstrate, we theoretically and experimentally characterize the resonant scattering peaks of individual single-crystal silicon nanoridges. In addition, we design high-efficiency metagratings and lenses based on nanoridge arrays, operating at visible wavelengths, using a stochastic optimization approach. We find that at wavelengths where single-crystal silicon is effectively lossless, devices based on high aspect ratio nanostructures are optimal. These devices possess efficiencies similar to those made of titanium oxide, which is an established material for high-efficiency visible...

Fixed Aspect Ratio Rod-to-Rod Conversion and Localized Surface Plasmon Resonance in Semiconducting I-V-VI Nanorods.

Fixed-aspect-ratio rod-to-rod conversion of binary V-VI Sb2 Se3 to ternary I-V-VI Cu3 SbSe3 semiconducting nano structures is reported. Capturing the inter mediate products, the insight mechanisms of the ion-diffusion process for the structural transformation are established. The final ternary structure shows localized surface plasmonresonance-induced absorption in the near-infrared regions.

Crystallographic Characterization of II-VI Semiconducting Nanostructures via Optical Second Harmonic Generation.

We demonstrate the utility of optical second harmonic generation (SHG) polarimetry to perform structural characterization of noncentrosymmetric, single-crystalline II-VI semiconducting nanowires, nanobelts, and nanoflakes. By analyzing anisotropic SHG polarimetric patterns, we distinguish between wurtzite and zincblende II-VI semiconducting crystal structures and determine their growth orientation. The crystallography of these nanostructures was then confirmed via transmission electron microscopy measurements performed on the same system. In addition, we show that some intrinsic material properties such as nonlinear coefficients and geometry-dependent optical in-coupling coefficients can also be determined from the SHG experiments in WZ nanobelts. The ability to perform SHG-based structural characterization and crystallographic study of II-VI semiconducting single-crystalline nanomaterials will be useful to correlate structure-property relationships of nanodevices on which transmission electron microscopy measurements cannot be typically performed.

Near-Unity Quantum Yield in Semiconducting Nanostructures: Structural Understanding Leading to Energy Efficient Applications

Core/shell nanocrystal quantum dots (NQDs) have shown great potential as efficient electroluminescent materials in devices like down-conversion phosphors and light-emitting diodes (LEDs). The efficiency of these devices is nonlinearly enhanced by the use of high quantum yield (QY) materials. Though relatively high QY materials with inherent advantages for use in device applications are achieved by thick-shell CdSe/CdS NQDs, their QY is not anywhere near unity due to lack of correlation of the microstructure with their photophysical properties. Here, in this Letter, we show that the control of interfacial defects is crucial to achieve a near-unity QY using microstructure studies of CdSe/CdS NQDs. Simple unoptimized LEDs obtained from these NQDs as the active layer demonstrate performances in excess of 7000 Cd/m2 with a power conversion efficiency of ∼1.5 lm/W that is comparable to those of the best NQD-based LEDs (1–3%) despite the absence of an electron-injecting buffer layer.

Mechanical and Thermal Properties of Metallic and Semiconductive Nanostructures

Using a top-down approach, we report a theoretical investigation of the melting temperature at the nanoscale, Tm, for different shapes of “free-standing” nanostructures. To easily calculate the nanoscale melting temperature for a wide range of metals and semiconductors, a convenient shape parameter called αshape is defined. Considering this parameter, we argue why smaller size effects are observed in high bulk melting temperature materials. Using Tm, a phase transition stress model is proposed to evaluate the intrinsic strain and stress during the first steps of solidification. Then, the size effect on the Thornton & Hoffman's criterion at the nanoscale is discussed and the intrinsic residual stress determination in nanostructures is found to be essential for sizes below 100 nm. Furthermore, the inverse Hall-Petch effect, for sizes below ∼15 nm, can be understood by this model. Finally, the residual strain in hexagonal zinc oxide nanowires is calculated as a function of the wire dimensions.

Phonon Spectra and Thermodynamic Properties Of Crystalline Nanowires

AbstractPhonon spectra and allowed phonon states, as well as thermodynamic characteristics of nanowires of simple cubic crystalline structure, are analyzed using the method of two-time dependent Green's functions, adjusted to bounded crystalline structures. Poles of Green's functions, defining phonon spectra, can be found by solving of the secular equation. For different boundary parameters, this problem is presented graphically. The presence of boundaries as well as the change of boundary parameters leads to appearance of new properties of low dimensional structures (thin film and nanowire). The most important feature is that beside allowed energy zones (which are continuous as in the bulk structure), zones of forbidden states appear. Different values of boundary parameters lead to appearance of lower and upper energy gaps, or dispersion branches spreading out of bulk energy zone. The correlation with spectra of phonons in corresponding unbounded structures is maintained in the work. Determination of phonon spectra and allowed phonon energies has great importance for kinetic and thermodynamic properties of semiconductive nanostructures and devices. The temperature behavior of nanowire thermal capacitance is compared to that of bulk structures. It is shown that at extremely low temperature nanowire thermal capacitance is considerably lower than the thermal capacitance of bulk sample. It was discussed what are the consequences of this fact to the thermal, conducting and superconducting properties of materials.