1D Semiconductor Nanostructures Research Articles

2D Semiconductor Nanostructures for Solar‐Driven Photocatalysis: Unveiling Challenges and Prospects in Air Purification, Sustainable Energy Harvesting, and Water Treatment

AbstractThe use of solar light to accelerate chemical processes (photocatalysis) has the potential to alleviate the pollution and energy crises. Thanks to their large surface area, unusual electronic structure, and abundance of low‐coordinate surface atoms, 2D semiconductors have shown enormous promise in photocatalytic applications. The synthesis, photoexcitation processes, design, and development of 2D semiconductor photocatalysts are thoroughly examined in this perspective, as well as their possible applications in air purification, solar energy conversion, organic synthesis, carbon capture and storage, and water treatment. This work highlights ongoing research efforts focused on improving the selectivity and efficiency of photocatalytic applications based on 2D semiconductors by means of hybrid systems, heterostructures, doping, and computational methodologies, together with open challenges. Finally, the integration of 2D semiconductor photocatalysts into indoor and outdoor environments is discussed, thereby facilitating the purification of air and water and generating clean energy, which assists in the pursuit of sustainable development objectives.

Peculiarities of exciton formation in 2D semiconductor nanostructures induced by quantum electromagnetic field under nonlinear self-phase modulation

Specific features of the excitation of a 2D semiconductor nanosystem by non-classical light in a solid state micro-resonator are found under the impact of the Kerr phase nonlinearity in the cavity. Different regimes of excitation are revealed in dependence on the efficiency of the nonlinearity. A negative impact of the nonlinear self-phase modulation on the excitation is found to be compensated by proper choice of the field frequency detuning. The possibility to controllably enhance a certain excitation channel by varying field frequency detuning is demonstrated and the value of the optimal detuning is found analytically. The effect of transfer of non-classical features from the field to the electronic subsystem is revealed. The formation of the photon-like non-classical excitonic states is demonstrated. The obtained results seem to be a basis for the creation of the light–matter interface and development of quantum information algorithms in solid state nanosystems.

Facile preparation of hexagonal WO3 nanopillars and its reduced graphene oxide nanocomposites for high-performance supercapacitor

One-dimensional (1D) nanostructures are extremely important due to better charge transport capabilities. The ability to anchor 1D semiconductor nanostructures on graphene may give advantages in electrochemical charge storage applications. In this study, the authors explored the synthesis, growth mechanism, and insertion-type pseudocapacitive properties of 1D hexagonal (h) phase-WO3 (h-WO3) nanopillars and h-WO3/rGO nanocomposite. The nanocomposite is composed of h-WO3 nanopillars uniformly grown on a reduced graphene oxide (rGO) matrix and the resulting h-WO3/rGO nanocomposite shows the hexagonal structure and, 3D networks gathered during a hydrothermal process. XRD confirms the phase purity and crystalline nature, SEM confirms the hexagonal bundled nanopillar morphology of h-WO3 and its graphene composites, and rGO offered crumpled two-dimensional sheet-like morphologies. HRTEM and SAED analysis confirmed the highly oriented growth of h-WO3 nanowire along the [001] zone axis. XPS analysis confirms the presence of tungsten in +6 and + 5 oxidation states, indicating the formation of the oxygen-deficient h-WO3-x structure. The electrochemical characterizations are performed using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and stability tests. From the CV measurements, the outperformed exceptional h-WO3 and h-WO3/rGO nanocomposites exhibit specific capacitance (Csp) of ∼545 Fg−1 and ∼926 Fg−1, respectively, at a 5 mVs−1 scan rate, and from GCD measurements Csp found to be ∼504 Fg−1 and ∼991 Fg−1, respectively at 0.1 Ag−1 current density. Supercapacitor capacitances with carbon and metal oxide electrodes are typically related to the accessible surface areas. However, this work indicates that proton insertion, a rare capacitive charge storage mechanism, may significantly increase the capacitance of metal oxides with a limited surface area but a particular structure. Nonetheless, using the proton insertion process, scientists have shown that the electrodes made from an assembly structure of h-WO3 nanopillars have enhanced charge storage performance. According to detailed investigations, the electrochemical behavior of h-WO3 is dominated by the proton insertion mechanism and is critical in achieving high capacitance by eliminating alternative mechanisms. This research work presents a novel method for attaining extraordinary charge storage contribution into the ordered tunnels in crystalline metal oxides due to efficient proton insertion, which is especially significant for the construction of high-performance electrochemical energy storage systems: batteries and supercapacitors.

Dual phenomenon of surface plasmon and laser optics induced EM enhancement for rapid DNA detection with semiconductor nanostructures (SiNWs/AgNPs)

Recently exploring bioanalytical instrumentation principles emphasized with combination of optics and EM fields in surface enhanced Raman spectroscopy (SERS). The principles favour the rapid detection of DNA with proper fabrication of SERS sensor. 1D semiconductor nanostructures (SiNWs) functionalization with plasmonic silver nanoparticles are fabricated by PLD process and exploited for SERS detection of DNA. The DNA nucleotide bands are indexed with reference to their Raman shift as Adenine (A), Guanine (G), Cytosine (C), Thymine (T) at Raman spectral regions of 1352 cm-1, 676 cm-1, 1625 cm-1, 1441 cm-1 respectively. The finest conditions for sensitive detection of DNA were investigated and their interaction mechanism are presented. The point-to-point reproducibility measurements imprinted higher degree of concordancy. The designed SERS sensor will be definitely helpful almost in all application fields with portable handheld Raman spectrophotometer in near future.

ZnO Nanoplatelets with Controlled Thickness: Atomic Insight into Facet‐Specific Bimodal Ligand Binding Using DNP NMR

AbstractColloidal nanoplatelets (NPLs) and nanosheets with controlled thickness have recently emerged as an exciting new class of quantum‐sized nanomaterials with substantially distinct optical properties compared to 0D quantum dots. Zn‐based NPLs are an attractive heavy‐metal‐free alternative to the so far most widespread cadmium chalcogenide colloidal 2D semiconductor nanostructures, but their synthesis remains challenging to achieve. The authors describe herein, to the best of their knowledge, the first synthesis of highly stable ZnO NPLs with the atomically precise thickness, which for the smallest NPLs is 3.2 nm (corresponding to 12 ZnO layers). Furthermore, by means of dynamic nuclear polarization‐enhanced solid‐state 15N NMR, the original role of the benzamidine ligands in stabilizing the surface of these nanomaterials is revealed, which can bind to both the polar and non‐polar ZnO facets, acting either as X‐ or L‐type ligands, respectively. This bimodal stabilization allows obtaining hexagonal NPLs for which the surface energy of the facets is modulated by the presence of the ligands. Thus, in‐depth study of the interactions at the organic–inorganic interfaces provides a deeper understanding of the ligand–surface interface and should facilitate the future chemistry of stable‐by‐design nano‐objects.

One-dimensional semiconductor nanostructures grown on two-dimensional nanomaterials for flexible device applications

This Perspective presents a review of current research activities on one-dimensional (1D) semiconductor nanostructures grown on two-dimensional (2D) nanomaterials for flexible electronic and optoelectronic device applications. For hybrid-dimensional nanostructures, 1D nanostructures exhibit excellent material characteristics, including high carrier mobility and radiative recombination rate as well as long-term stability, while 2D layers show good optical transparency, mechanical flexibility, and electrical characteristics. Accordingly, the versatile and fascinating properties of 1D nanostructures grown on 2D layers enable the fabrication of high-performance optoelectronic and electronic devices even in transferable, flexible, or stretchable forms. We initially present a variety of 1D/2D hybrid nanostructures and their preparation methods, followed by a discussion of techniques for fabricating aligned 1D nanostructure arrays on 2D layers and their heterostructures. Furthermore, we discuss a wide range of devices based on the 1D/2D hybrid nanostructures. These devices include light-emitting devices, photodetectors, transistors, and pressure sensors. Several important issues, including 1D/2D junction properties and device fabrication processes for device applications, are also addressed. We conclude with personal remarks on the issues and perspectives for research on 1D/2D hybrid nanostructures for more sophisticated device applications.

Toward the Intrinsic Superiority of Aligned One‐Dimensional TiO2 Nanostructures: the Role of Defect States in Electron Transport Process

AbstractElectrodes made up of aligned 1D semiconductor nanostructures have drawn much attention in photoelectrochemical applications, as they are expected to be ideal configuration for channeling electrons towards the substrate without lateral electron scattering. However, efforts were hardly made to optimize the defect states in such systems. Herein, we observed significant enhancement (∼20 fold) in photoelectrochemical performance of TiO2 nanorod arrays (NRAs) after a simple calcination procedure. Through a series of structural and electrochemical characterizations, we revealed an underlying role of defects states in electron transport: even in electrodes composed of 1D TiO2 nanorods, lateral electron scattering would be avoided, which was confirmed by measuring the trap‐free electron diffusion coefficient (D0), the electron transport process can be severely affected by defect states distributed in the band gap. The calcination procedure can bring structural optimization for TiO2 NRAs, therefore facilitates electron transport process. Intrinsically, this work provides a structural view for realizing the superior performance of aligned 1D semiconductor nanostructures.

Photoluminescent Detection of Human T-Lymphoblastic Cells by ZnO Nanorods.

The precise detection of cancer cells currently remains a global challenge. One-dimensional (1D) semiconductor nanostructures (e.g., ZnO nanorods) have attracted attention due to their potential use in cancer biosensors. In the current study, it was demonstrated that the possibility of a photoluminescent detection of human leukemic T-cells by using a zinc oxide nanorods (ZnO NRs) platform. Monoclonal antibodies (MABs) anti-CD5 against a cluster of differentiation (CD) proteins on the pathologic cell surface have been used as a bioselective layer on the ZnO surface. The optimal concentration of the protein anti-CD5 to form an effective bioselective layer on the ZnO NRs surface was selected. The novel biosensing platforms based on glass/ZnO NRs/anti-CD5 were tested towards the human T-lymphoblast cell line MOLT-4 derived from patients with acute lymphoblastic leukemia. The control tests towards MOLT-4 cells were performed by using the glass/ZnO NRs/anti-IgG2a system as a negative control. It was shown that the photoluminescence signal of the glass/ZnO NRs/anti-CD5 system increased after adsorption of T-lymphoblast MOLT-4 cells on the biosensor surface. The increase in the ZnO NRs photoluminescence intensity correlated with the number of CD5-positive MOLT-4 cells in the investigated population (controlled by using flow cytometry). Perspectives of the developed ZnO platforms as an efficient cancer cell biosensor were discussed.

Single-nanostructure bandgap engineering enabled by magnetic-pulling thermal evaporation growth.

Realizing the substantial potential of bottom-up 1D semiconductor nanostructures in developing functional nanodevices calls for dedicated single-nanostructure bandgap engineering by various growth approaches. Although thermal evaporation has been advised as a facile approach for most semiconductors to form 1D nanostructures from bottom-up, its capability of achieving single-nanostructure bandgap engineering was considered a challenge. In 2011, we succeeded in the direct growth of composition-graded CdS1−xSex (0 ≤ x ≤ 1) nanowires by upgrading the thermal-evaporation tube furnace with a home-made magnetic-pulling module. This report aims to provide a comprehensive review of the latest advances in the single-nanostructure bandgap engineering enabled by the magnetic-pulling thermal evaporation growth. The report begins with the description of different magnetic-pulling thermal evaporation strategies associated with diverse examples of composition-engineered 1D nanostructures. Following is an elaboration on their optoelectronic applications based on the resulting single-nanostructure bandgap engineering, including monolithic white-light sources, proof-of-concept asymmetric light propagation and wavelength splitters, monolithic multi-color and white-light lasers, broadband-response photodetectors, high-performance transistors, and recently the most exciting single-nanowire spectrometer. In the end, this report concludes with some personal perspectives on the directions toward which future research might be advanced.

A review on nanomaterial-based field effect transistor technology for biomarker detection.

Field effect transistor (FET) based sensors have attractive features such as small size, ease of mass production, high versatility and comparably low costs. Over the last decade, many FET type biosensors based on various nanomaterials (e.g. silicon nanowires, graphene, and transition metal dichalcogenides) have been developed to detect various classes of biomolecular targets due to their integration into portable and rapid test systems, both for use in the clinical lab and in point-of-care testing. This review (with 197 refs.)starts with an introduction into the specific features of FET biosensor technology. This is followed by a description of the essentials of methods for immobilization of recognition elements. The next section discusses the progress that has been made in FET based biosensors using semiconducting nanostructures composed of silicon, graphene, metal oxides, and transition metal dichalcogenides. A further section is devoted to microfluidic systems combined with FET biosensors. We then emphasize the biosensing applications of these diagnostic devices for analysis of clinically relevant biomarkers, specifically to sensing of neurotransmitters, metabolites, nucleic acids, proteins, cancer and cardiac biomarkers. Two tables are presented which summarize advances in applications of 1D and 2D nanomaterial-based FETs for biomarker sensing. A concluding section summarizes the current status, addresses current challenges, and gives perspective trends for the field. Graphical abstract Field effect transistor devices based on the use of1D and 2D semiconductor nanostructures (so called nano-FETs) are making use of materials including silicon nanowires, graphene, zinc oxide, indium oxide, titanium oxide, and molybdenum disulfidethat are further modified with recognition elements for biosensing application.

Directed Assembly of Au-Tipped 1D Inorganic Nanostructures via Nanolithographic Docking.

Controlled assembly of nanostructures is a key challenge in nanotechnology. In this work, we introduce an approach for the controlled assembly of 1D nanodumbbells-Au-tipped semiconductor nanorods-into arbitrary 2D higher architectures, by their chemical docking to nanopatterned functionalities. We realized the docking functionalities via nanoimprinted metallic nanodots functionalized with an organic monolayer, whose terminal thiol groups chemically bind the nanodumbbell tips. We demonstrated that the functional nanopattern encodes the nanodumbbell assembly and can be designed to deterministically position nanodumbbells in two possible modes. In the single-docking mode, the nanodot arrays are designed with a spacing that exceeds the nanodumbbell length, restricting each nanodumbbell to dock with one edge and physically connect with its free edge to one of the neighboring nanodumbbells. Alternatively, in the double-docking mode, the nanodots are spaced to exactly fit the nanodumbbell length, allowing nanodumbbell docking with both edges. We found that the docking kinetics can be described by a random attachment model, and verified that for the used docking chemistry, nanodumbbells that are docked to the same dot do not interact with each other. Our work demonstrates the possibility for massively parallel positioning of sub-100 nm 1D semiconductor nanostructures, and can potentially enable their future integration into functional nanodevices and nanosystems.

The aggregation of Mn2+, its d-d transition in CdS:Mn(II) nanobelts and bound magnetic polaron formation at room temperature

Tuning the photoluminescence (PL) and magnetic properties of 1D semiconductor nanostructures is extremely important in processing light, improving the speed and storage capacity for optoelectronic and spintronic applications. Here, we have reported the 1D Cd1−xMnxS (x = 0–0.102) nanobelts (NBs) and investigated their optical and magnetic properties. These NBs were synthesized by chemical vapor deposition method. The successful incorporation of Mn ions into an individual CdS NB has been confirmed through several characterization tools: SEM-EDX analysis, significant higher angle and phonon mode shifts were observed in the XRD and Raman spectra. Room-temperature PL showed two emission peaks at the near band edge. The first peak is related to exciton magnetic polaron (EMP) and the second one appeared on the low-energy side of the band edge emission and showed very large red-shift (∼33 nm) compared to EMP, which is attributed to bound magnetic polaron (BMP). BMP emission was detected for the first time in CdS low-dimensional nanostructures. Our study showed that Mn ions tuned CdS emission more than 400 nm (from 512 to 929 nm) covering the whole visible spectral region up to the near infrared region for the first time, and significantly boosted the room-temperature ferromagnetism, which shows promise for optoelectronic and spintronic applications.

Physical Mechanism Behind Enhanced Photoelectrochemical and Photocatalytic Properties of Superhydrophilic Assemblies of 3D-TiO2 Microspheres with Arrays of Oriented, Single-Crystalline TiO2 Nanowires as Building Blocks Deposited on Fluorine-Doped Tin Oxide.

In comparison to the one-dimensional (1D) semiconductor nanostructures, the hierarchical, three-dimensional (3D) microstructures, composed of the arrays of 1D nanostructures as building blocks, show quite unique physicochemical properties due to efficient photon capture and enhanced surface to volume ratio, which aid in advancing the performance of various optoelectronic devices. In this contribution, we report the fabrication of surfactant-free, radially assembled, 3D titania (rutile-phase) microsphere arrays (3D-TMSAs) composed of bundles of single-crystalline titania nanowires (NWs) directly on fluorine-doped conducting oxide (FTO) substrates with tunable architecture. The effects of growth parameters on the morphology of the 3D-TMSAs have been studied thoroughly. The 3D-TMSAs grown on the FTO-substrate showed superior photon-harvesting owing to the increase in light-scattering. The photocatalytic and photon to electron conversion efficiency of dye-sensitized solar cells (DSSC), where the optimized 3D-TMSAs were used as an anode, showed around 44% increase in the photoconversion efficiency compared to that of Degussa P-25 as a result of the synergistic effect of higher surface area and enhanced photon scattering probability. The TMSA film showed superhydrophilicity without any prior UV irradiation. In addition, the presence of bundles of almost parallel NWs led to the formation of arrays of microcapacitors, which showed stable dielectric performance. The fabrication of single-crystalline, oriented, self-assembled TMSAs with bundles of titania nanowires as their building blocks deposited on transparent conducting oxide (TCO) substrates has vast potential in the area of photoelectrochemical research.

Controlled preparation and visible light photocatalytic activities of corn cob-like Au–ZnO nanorods

A facile method to prepare well-shaped nanohybrids of Au–ZnO nanorods (NRs) has been demonstrated, which is through polyvinylpyrrolidone-assisted in situ nucleation and growth of ZnONRs in the colloidal solution of Au nanoparticles (NPs). The obtained Au–ZnONRs shows uniform corn cob-like morphology with AuNPs evenly deposited on the surface of hexagonal ZnONRs and can be dispersed in aqueous solution to achieve photodegradation of organics. Moreover, the loading amount of AuNPs can be tuned to optimize the photocatalytic performance. The nanohybrid of Au–ZnONRs with optimized AuNP loading exhibits superior photocatalytic activity than ZnONRs alone, demonstrating ~90% Rhodamine B degradation within 18 h under the visible light of 420–780 nm, a wavelength range that does not overlap with ZnO absorption. The observed performance improvement is likely due to the coupling effect between ZnONRs and AuNPs, which functionalizes ZnONRs with visible light utilization and enhances charge separation. The strategy presented here not only provides a new approach for the controlled modification of 1D semiconductor nanostructures, but also holds good potential for applications such as degradation of organic pollutants.

Template-directed fabrication of vertically aligned Cu2ZnSnS4 nanorod arrays for photoelectrochemical applications via a non-toxic solution process

Cu2ZnSnS4 (CZTS), which is non-toxic and abundantly available, is a promising material for fabricating inexpensive large-scale photoelectrochemical (PEC) devices. With the current rapid developments in nanotechnology, one-dimensional (1D) semiconductor nanostructures have been widely investigated because of their short transport distance for photogenerated carriers, large specific surface areas, and efficient optical absorption, all of which are advantageous features. However, PEC devices based on vertical arrays of 1D CZTS nanostructures have not yet been realized. In this study, we report the fabrication of vertically aligned CZTS nanorod arrays using an anodic aluminum oxide template-assisted solution process. The nanorods exhibit a relatively pure phase with a CZTS kesterite structure and cathodic photocurrent response. The surfaces of the CZTS nanorod arrays were decorated with either ZnS or CdS via chemical bath deposition to increase the photocurrent with a positive flat band potential. By analyzing the photocurrent and flat band potential, we gained an insight into the effect of band alignment between the p-type CZTS and the n-type material.

Direct Observation of Photoexcited Hole Localization in CdSe Nanorods

Quantum-confined 1D semiconductor nanostructures are being investigated for hydrogen generation photocatalysts. In the photoreaction, after fast electron transfer, holes that remain in the nanostructure play an important role in the total quantum yield of hydrogen production. Unfortunately, knowledge of hole dynamics is limited due to lack of convenient spectroscopic signatures. Here, we directly probe hole localization dynamics within CdSe nanorods (NRs) by combining transient absorption (TA) and time-resolved terahertz (TRTS) spectroscopy. We show that when methylene blue is used as an electron acceptor, the resulting electron transfer occurs with a time constant of 3.5 ± 0.1 ps and leaves behind a delocalized hole. However, the hole quickly localizes in the Coulomb potential well generated by the reduced electron acceptor near the NR surface with time constant of 11.7 ± 0.2 ps. Our theoretical investigation suggests that the hole becomes confined to a ∼±0.8 nm region near the reduced electron acceptor ...

One-dimensional hybrid nanostructures for heterogeneous photocatalysis and photoelectrocatalysis.

Semiconductor-based photocatalysis and photoelectrocatalysis have received considerable attention as alternative approaches for solar energy harvesting and storage. The photocatalytic or photoelectrocatalytic performance of a semiconductor is closely related to the design of the semiconductor at the nanoscale. Among various nanostructures, one-dimensional (1D) nanostructured photocatalysts and photoelectrodes have attracted increasing interest owing to their unique optical, structural, and electronic advantages. In this article, a comprehensive review of the current research efforts towards the development of 1D semiconductor nanomaterials for heterogeneous photocatalysis and photoelectrocatalysis is provided and, in particular, a discussion of how to overcome the challenges for achieving full potential of 1D nanostructures is presented. It is anticipated that this review will afford enriched information on the rational exploration of the structural and electronic properties of 1D semiconductor nanostructures for achieving more efficient 1D nanostructure-based photocatalysts and photoelectrodes for high-efficiency solar energy conversion.

Resonant indirect exchange in 1D semiconductor nanostructures

We consider resonant indirect exchange interaction between magnetic centers in 1D nanostructures. The magnetic centers are assumed to be coupled to the 1D conducting channel by the quantum tunneling which can be of resonant character. The indirect exchange between the centers is mediated by the free carriers of the channel. The two cases of quadratic and linear energy dispersion of the 1D free carriers are considered. The former case is attributed to conventional semiconductor (InGaAs based to be concrete) nanowires or nanowhiskers, while the latter case is associated with carbon nanotubes with magnetic adatoms. We demonstrate that whenever the energy of a bound state at the magnetic center lies within the continuum energy spectra of the delocalized carriers in the channel the indirect exchange is strongly enhanced due to effective tunnel hybridization of the bound states with the continuum.

Low Exciton-Phonon Coupling, High Charge Carrier Mobilities, and Multiexciton Properties in Two-Dimensional Lead, Silver, Cadmium, and Copper Chalcogenide Nanostructures.

The development of two-dimensional (2D) nanomaterials has revealed novel physical properties, like high carrier mobilities and the tunable coupling of charge carriers with phonons, which can enable wide-ranging applications in optoelectronic and thermoelectric devices. While mechanical exfoliation of graphene and some transition metal dichalcogenides (e.g., MoS2, WSe2) has enabled their fabrication as 2D semiconductors and integration into devices, lack of similar syntheses for other 2D semiconductor materials has hindered further progress. Here, we report measurements of fundamental charge carrier interactions and optoelectronic properties of 2D nanomaterials made from two-monolayers-thick PbX, CdX, Cu2X, and Ag2X (X = S, Se) using colloidal syntheses. Extremely low coupling of charge carriers with phonons (2-6-fold lower than bulk and other low-dimensional semiconductors), high carrier mobilities (0.2-1.2 cm(2) V(-1) s(-1), without dielectric screening), observation of infrared surface plasmons in ultrathin 2D semiconductor nanostructures, strong quantum-confinement, and other multiexcitonic properties (different phonon coupling and photon-to-charge collection efficiencies for band-edge and higher-energy excitons) can pave the way for efficient solution-processed devices made from these 2D nanostructured semiconductors.

Melting temperature of metal polycrystalline nanowires electrochemically deposited into the pores of anodic aluminum oxide.

The arrays of metallic nanowires are considered as promising precursors for 1D semiconductor nanostructures after appropriate treatment at temperatures close to the melting point. Therefore the melting behaviour of the metallic structures in oxide templates is a key parameter for the subsequent conversion process. The present paper focuses on understanding of the effect of mechanical stress generated during heating on the melting point of the metal nanowires deposited into the pores of anodic alumina. Extremely high local compressive stress appears due to the difference in the thermal coefficients of the oxide template and nanowires inside the pores. The effect of the composite structural parameter that may be related to the concentration of nanowires on the melting temperature has been investigated. A numerical model predicting the melting point has been developed for composites with indium, tin, and zinc nanowires. The simulation results obtained using the suggested model were compared with the experimental data.