Tuning the Inter-Nanoplatelet Distance and Coupling Strength by Thermally Induced Ligand Decomposition.

CdSe nanoplatelets (NPLs) are promising 2D semiconductors for optoelectronic applications, in which efficient charge transport properties are desirable. It is reported that thermal annealing constitutes an effective strategy to control the optical absorption and electrical properties of CdSe NPLs by tuning the inter-NPL distance. Combining optical absorption, transmission electron microscopy, and thermogravimetric analysis, it is revealed that the thermal decomposition of ligands (e.g., cadmium myristate) governs the inter-NPL distance and thus the inter-NPL electronic coupling strength. Employing ultrafast terahertz spectroscopy, it is shown that this enhanced electronic coupling increases both the free carrier generation efficiency and the short-range mobility in NPL solids. The results show a straightforward method of controlling the interfacial electronic coupling strength for developing functional optoelectronic devices through thermal treatments.

In Situ Measurement of Evolving Excited-State Dynamics During Deposition and Processing of Organic Films by Single-Shot Transient Absorption.

A significant advantage of organic semiconductors over many of their inorganic counterparts is solution processability. However, solution processing commonly yields heterogeneous films with properties that are highly sensitive to the conditions and parameters of casting and processing. Measuring the key properties of these materials in situ, during film production, can provide new insight into the mechanism of these processing steps and how they lead to the emergence of the final organic film properties. The excited-state dynamics is often of import in photovoltaic, electronic, and light-emitting devices. This review focuses on single-shot transient absorption, which measures a transient spectrum in a single shot, enabling the rapid measurement of unstable chemical systems such as organic films during their casting and processing. We review the principles of instrument design and provide examples of the utility of this spectroscopy for measuring organic films during their production.

Grain-size adjustment in Hf0.5Zr0.5O2ferroelectric film to improve the switching time in Hf0.5Zr0.5O2-based ferroelectric capacitor.

By adjusting the rising time in annealing ferroelectric HfO2-based films, the grain size of the film can be controlled. In this study, we found that increasing the rising time from 10 to 30 s at an annealing temperature of 700 °C in N2atmosphere resulted in improved ferroelectric switching speed. This is because the larger grain size reduces the internal resistance components, such as the grain bulk resistance and grain boundary resistance, of the HZO film. This in turn lowers the overall equivalent resistance. By minimizing the RC time constants, increasing the grain size plays a key role in improving the polarization switching speed of ferroelectric films.

Defect Healing in Graphene via Rapid Thermal Annealing with Polymeric "Nanobandage".

Overcoming throughput challenges in current graphene defect healing processes, such as conventional thermal annealing, is crucial for realizing post-silicon device fabrication. Herein, a new time- and energy-efficient method for defect healing in graphene is reported, utilizing polymer-assisted rapid thermal annealing (RTA). In this method, a nitrogen-rich, polymeric "nanobandage" is coated directly onto graphene and processed via RTA at 800 °C for 15 s. During this process, the polymer matrix is cleanly degraded, while nitrogen released from the nanobandage can diffuse into graphene, forming nitrogen-doped healed graphene. To study the influence of pre-existing defects on graphene healing, lattice defects are purposefully introduced via electron beam irradiation and investigated by Raman microscopy. X-ray photoelectron spectroscopy reveals successful healing of graphene, observing a maximum doping level of 3 atomic nitrogen % in nanobandage-treated samples from a baseline of 0-1 atomic % in non-nanobandage treated samples. Electrical transport measurements further indicate that the nanobandage treatment recovers the conductivity of scanning electron microscope-treated defective graphene at ≈85%. The reported polymer-assisted RTA defect healing method shows promise for healing other 2D materials with other dopants by simply changing the chemistry of the polymeric nanobandage.

Uniform Gold Nanostructure Formation via Weakly Adsorbed Gold Films and Thermal Annealing for Reliable Localized Surface Plasmon Resonance-Based Detection of DNase-I.

Deoxyribonuclease-I (DNase-I), a representative endonuclease, is an important biomarker for the diagnosis of infectious diseases and cancer progression. However, enzymatic activity decreases rapidly ex vivo, which highlights the need for precise on-site detection of DNase-I. Here, a localized surface plasmon resonance (LSPR) biosensor that enables the simple and rapid detection of DNase-I is reported. Moreover, a novel technique named electrochemical deposition and mild thermal annealing (EDMIT) is applied to overcome signal variations. By taking advantage of the low adhesion of gold clusters on indium tin oxide substrates, both the uniformity and sphericity of gold nanoparticles are increased under mild thermal annealing conditions via coalescence and Ostwald ripening. This ultimately results in an approximately 15-fold decrease in LSPR signal variations. The linear range of the fabricated sensor is 20-1000 ng mL-1 with a limit of detection (LOD) of 127.25 pg mL-1 , as demonstrated by spectral absorbance analyses. The fabricated LSPR sensor stably measured DNase-I concentrations from samples collected from both an inflammatory bowel disease (IBD) mouse model, as well as human patients with severe COVID-19 symptoms. Therefore, the proposed LSPR sensor fabricated via the EDMIT method can be used for early diagnosis of other infectious diseases.

Remarkable Enhancement of Hole Mobility of Novel DA-D'-AD Small Molecules by Thermal Annealing: Effect of the D'-Bridge Block.

Conjugated small molecules are advanced semiconductor materials with attractive physicochemical and optoelectronic properties enabling the development of next-generation electronic devices. The charge carrier mobility of small molecules strongly influences the efficiency of organic and hybrid electronics based on them. Herein, we report the synthesis of four novel small molecules and their investigation with regard to the impact of molecular structure and thermal treatment of films on charge carriers' mobility. The benzodithiophene-containing compounds (BDT) were shown to be more promising in terms of tuning the morphology upon thermal treatment. Impressive enhancement of hole mobilities by more than 50 times was found for annealed films based on a compound M4 comprising triisopropylsilyl-functionalized BDT core. The results provide a favorable experience and strategy for the rational design of state-of-the-art organic semiconductor materials (OSMs) and for improving their charge-transport characteristics.

High photoresponsivity MoS2phototransistor through enhanced hole trapping HfO2gate dielectric.

Phototransistor using 2D semiconductor as the channel material has shown promising potential for high sensitivity photo detection. The high photoresponsivity is often attributed to the photogating effect, where photo excited holes are trapped at the gate dielectric interface that provides additional gate electric field to enhance channel charge carrier density. Gate dielectric material and its deposition processing conditions can have great effect on the interface states. Here, we use HfO2gate dielectric with proper thermal annealing to demonstrate a high photoresponsivity MoS2phototransistor. When HfO2is annealed in H2atmosphere, the photoresponsivity is enhanced by an order of magnitude as compared with that of a phototransistor using HfO2without annealing or annealed in Ar atmosphere. The enhancement is attributed to the hole trapping states introduced at HfO2interface through H2annealing process, which greatly enhances photogating effect. The phototransistor exhibits a very large photoresponsivity of 1.1 × 107A W-1and photogain of 3.3 × 107under low light illumination intensity. This study provides a processing technique to fabricate highly sensitive phototransistor for low optical power detection.

Tunable Ga2O3solar-blind photosensing performance via thermal reorder engineering and energy-band modulation.

As an ultra-wide bandgap semiconductor, gallium oxide (Ga2O3) has been extensively applied in solar-blind photodetectors (PDs) owing to the absorbance cut-off wavelength of shorter than 280 nm, and the optimized technologies of detection performance is seriously essential for its further usages. Herein, a feasible thermal reorder engineering method was performed through annealing Ga2O3films in vacuum, O2and oxygen plasma atmospheres, realizing to tune solar-blind photosensing performance of Ga2O3PDs. Thermal treatment, in fact a crystal reorder process, significantly suppressed the noise in Ga2O3-based PDs and enhanced the photo-sensitivity, with the dark current decreasing from 154.63 pA to 269 fA and photo-to-dark current ratio magically raising from 288 to 2.85 × 104. This achievement is dependent of energy-band modulation in Ga2O3semiconductor, that is certified by first-principles calculation. Additionally, annealing in oxygen atmospheres notably reduces the concentration of oxygen vacancies in the surface of films, thereby improving the performance of the PDs; the oxygen vacancy is extremely concerned in oxide semiconductors in the view of physics of surface defects. In all, this work could display a promising guidance for modulating the performance of PDs based on wide bandgap oxide semiconductor, especially for hot Ga2O3issue.

The Process-Directed Self-Assembly of Block Copolymer Particles.

The kinetic paths of structural evolution and formation of block copolymer (BCP) particles are explored using dynamic self-consistent field theory (DSCFT). It is shown that the process-directed self-assembly of BCP immersed in a poor solvent leads to the formation of striped ellipsoids, onion-like particles and double-spiral lamellar particles. The theory predicts a reversible path of shape transition between onion-like particles and striped ellipsoidal ones by regulating the temperature (related to the Flory-Huggins parameter between the two components of BCP, χAB ) and the selectivity of solvent toward one of the two BCP components. Furthermore, a kinetic path of shape transition from onion-like particles to double-spiral lamellar particles, and then back to onion-like particles is demonstrated. By investigating the inner-structural evolution of a BCP particle, it is identified that changing the intermediate bi-continuous structure into a layered one is crucial for the formation of striped ellipsoidal particles. Another interesting finding is that the formation of onion-like particles is characterized by a two-stage microphase separation. The first is induced by the solvent preference, and the second is controlled by the thermodynamics. The findings lead to an effective way of tailoring nanostructure of BCP particles for various industrial applications.

Ultranarrow plasmon resonances from annealed nanoparticle lattices.

This paper reports how the spectral linewidths of plasmon resonances can be narrowed down to a few nanometers by optimizing the morphology, surface roughness, and crystallinity of metal nanoparticles (NPs) in two-dimensional (2D) lattices. We developed thermal annealing procedures to achieve ultranarrow surface lattice resonances (SLRs) with full-width at half-maxima linewidths as narrow as 4 nm from arrays of Au, Ag, Al, and Cu NPs. Besides annealing, we developed a chemical vapor deposition process to use Cu NPs as catalytic substrates for graphene growth. Graphene-encapsulated Cu NPs showed the narrowest SLR linewidths (2 nm) and were stable for months. These ultranarrow SLR nanocavity modes supported even narrower lasing emission spectra and high nonlinearity in the input-output light-light curves.

Room-Temperature Nitric Oxide Gas Sensors Based on NiO/SnO2 Heterostructures.

Nitric oxide (NO) is a very well-known indoor pollutant, and high concentrations of it in the atmosphere lead to acid rain. Thus, there is great demand for NO sensors that have the ability to work at room temperature. In this work, NiO/SnO2 heterostructures have been prepared via the polyol process and were tested against different concentrations of NO gas at room temperature. The structural and morphological characteristics of the heterostructures were examined using X-ray diffraction and scanning electron microscopy, respectively, while the ratio of NiO to SnO2 was determined through the use of energy-dispersive spectrometry. The effects of both pH and thermal annealing on the morphological, structural and gas-sensing properties of the heterostructure were investigated. It was found that the morphology of the heterostructures consisted of rod-like particles with different sizes, depending on the temperature of thermal annealing. Moreover, NiO/SnO2 heterostructures synthesized with pH = 8 and annealed at 900 °C showed a response of 1.8% towards 2.5 ppm NO at room temperature. The effects of humidity as well as of stability on the gas sensing performance were also investigated.

Effects of etching process and annealing temperature on the ferroelectric properties of atomic layer deposited Al-doped HfO2thin film.

An investigation was conducted with regard to the effect of etching process on the ferroelectric (FE) characteristics of different device structures with Al-doped HfO2thin films; further, the effect of the rapid thermal annealing temperature on the FE properties was elucidated using metal-ferroelectric-metal (MFM) capacitors using TiN electrodes with varying thickness and 4 at.% Al-doped HfO2FE layer. The capacitors were annealed at different temperatures after lithography and etching process; this was aimed at incorporating the FE-orthorhombic phase. The samples annealed after patterning were able to obtain improved FE characteristics due to the amount of tensile stress. The MFM devices that were initially patterned were also studied as a reference. We found that even though it required higher temperature and shorter time to introduce the FE phase, it exhibited more stable as well as promising FE properties and electrical performances with a relatively large remnant polarization (2Pr âˆ¼ 60µC cm-2), a coercive electric field of approximately 2 MV cm-1and high switching current density with less leakage. Our results indicate how the FE properties of the HfO2-based thin films can be engineered through suitable process sequence and post-annealing conditions, thereby verifying the applicable flexibility of FE-HfO2for semiconductor device integration.

Vacuum-Assisted Thermal Annealing of CsPbI3 for Highly Stable and Efficient Inorganic Perovskite Solar Cells.

Inorganic cesium lead iodide perovskite CsPbI3 is attracting great attention as a light absorber for single or multi-junction photovoltaics due to its outstanding thermal stability and proper band gap. However, the device performance of CsPbI3 -based perovskite solar cells (PSCs) is limited by the unsatisfactory crystal quality and thus severe non-radiative recombination. Here, vacuum-assisted thermal annealing (VATA) is demonstrated as an effective approach for controlling the morphology and crystallinity of the CsPbI3 perovskite films formed from the precursors of PbI2 , CsI, and dimethylammonium iodide (DMAI). By this method, a large-area and high-quality CsPbI3 film is obtained, exhibiting a much reduced trap-state density with prolonged charge lifetime. Consequently, the solar cell efficiency is raised from 17.26 to 20.06 %, along with enhanced stability. The VATA would be an effective approach for fabricating high-performance thin-film CsPbI3 perovskite optoelectronics.

Morphology evolution and enhanced broadband photoresponse behavior of two-dimensional Bi2Te3nanosheets.

Bismuth telluride (Bi2Te3), as an emerging two-dimensional (2D) material, has attracted extensive attention from scientific researchers due to its excellent optoelectronic, thermoelectric properties and topological structure. However, the application research of Bi2Te3mainly focuses on thermoelectric devices, while the research on optoelectronic devices is scarce. In this work, the morphology evolution and growth mechanism of 2D Bi2Te3nanosheets with a thickness of 12 ± 3 nm were systematically studied by solvothermal method. Then, the Bi2Te3nanosheets were annealed at 350 °C for 1 h and applied to self-powered photoelectrochemical-type broadband photodetectors. Compared with the as-synthesized Bi2Te3photodetector, the photocurrent of the photodetector based on the annealed Bi2Te3is significantly enhanced, especially enhanced by 18.3 times under near-infrared light illumination. Furthermore, the performance of annealed Bi2Te3photodetector was systematically studied. The research results show that the photodetector not only has a broadband response from ultraviolet to near-infrared (365-850 nm) under zero bias voltage, but also obtains the highest responsivity of 6.6 mA W-1under green light with an incident power of 10 mW cm-2. The corresponding rise time and decay time are 17 ms and 20 ms, respectively. These findings indicate that annealed Bi2Te3nanosheets have great potential to be used as self-powered high-speed broadband photodetectors with high responsivity.

Effects of thermal annealing on the distribution of boron and phosphorus in p-i-n structured silicon nanocrystals embedded in silicon dioxide.

Thermal annealing temperature and time dictate the microstructure of semiconductor materials such as silicon nanocrystals (Si NCs). Herein, atom probe tomography (APT) and density functional theory (DFT) calculations are used to understand the thermal annealing temperature effects on Si NCs grown in a SiO2matrix and the distribution behaviour of boron (B) and phosphorus (P) dopant atoms. The APT results demonstrate that raising the annealing temperature promotes growth and increased P concentration of the Si NCs. The data also shows that the thermal annealing does not promote the incorporation of B atoms into Si NCs. Instead, B atoms tend to locate at the interface between the Si NCs and SiO2matrix. The DFT calculations support the APT data and reveal that oxygen vacancies regulate Si NC growth and dopant distribution. This study provides the detailed microstructure of p-type, intrinsic, and n-type Si NCs with changing annealing temperature and highlights how B and P dopants preferentially locate with respect to the Si NCs embedded in the SiO2matrix with the aid of oxygen vacancies. These findings will be useful towards future optoelectronic applications.

Superionic Halogen-Rich Li-Argyrodites Using In Situ Nanocrystal Nucleation and Rapid Crystal Growth.

Although several crystalline materials have been developed as Li-ion conductors for use as solid electrolytes in all-solid-state batteries (ASSBs), producing materials with high Li-ion conductivities is time-consuming and cost-intensive. Herein, we introduce a superionic halogen-rich Li-argyrodite (HRLA) and demonstrate its innovative synthesis using ultimate-energy mechanical alloying (UMA) and rapid thermal annealing (RTA). UMA with a 49 G-force milling energy provides a one-pot process that includes mixing, glassification, and crystallization, to produce as-milled HRLA powder that is ∼70% crystallized; subsequent RTA using an infrared lamp increases this crystallinity to ∼82% within 25 min. Surprisingly, this HRLA exhibits the highest Li-ion conductivity among Li-argyrodites (10.2 mS cm-1 at 25 °C, cold-pressed powder compact) reported so far. Furthermore, we confirm that this superionic HRLA works well as a promising solid electrolyte without a decreased intrinsic electrochemical window in various electrode configurations and delivers impressive cell performance (114.2 mAh g-1 at 0.5 C).

Flexible Polymer-Organic Solar Cells Based on P3HT:PCBM Bulk Heterojunction Active Layer Constructed under Environmental Conditions.

In this study, some crucial parameters were determined of flexible polymer-organic solar cells prepared from an active layer blend of poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) mixed in 1:1 mass ratio and deposited from chlorobenzene solution by spin-coating on poly(ethylene terephthalate) (PET)/ITO substrates. Additionally, the positive effect of an electron transport layer (ETL) prepared from zinc oxide nanoparticles (ZnO np) on flexible photovoltaic elements' performance and stability was investigated. Test devices with above normal architecture and silver back electrodes deposed by magnetron sputtering were constructed under environmental conditions. They were characterized by current-voltage (I-V) measurements, quantum efficiency, impedance spectroscopy, surface morphology, and time-degradation experiments. The control over morphology of active layer thin film was achieved by post-deposition thermal treatment at temperatures of 110-120 °C, which led to optimization of device morphology and electrical parameters. The impedance spectroscopy results of flexible photovoltaic elements were fitted using two R||CPE circuits in series. Polymer-organic solar cells prepared on plastic substrates showed comparable current-voltage characteristics and structural properties but need further device stability improvement according to traditionally constructed cells on glass substrates.

Morphology Control of Doped Spiro-MeOTAD Films for Air Stable Perovskite Solar Cells.

Doped 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD), which acts as a hole-transporting layer (HTL), endows perovskite solar cells (PSCs) with excellent performance. However, the intrinsically hygroscopic nature of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dopants also aggravates the moisture instability of PSCs. In this work, the origins of the moisture instability of spiro-MeOTAD HTLs are explored and strategies to enhance moisture resistance are proposed. After 780 h of aging in air, 52% of the initial power conversion efficiency (PCE) can be sustained by prolonging the mixing time of the precursor solution of spiro-MeOTAD to reduce accumulated LiTFSI. In contrast, only 7% of the initial PCE remains if the precursor solution is mixed briefly. By thermally annealing an HTL to evaporate residual tBP in spiro-MeOTAD, pinholes are completely eliminated and 65% of the initial PCE remains after the same aging time. In this study, the significance of the initial morphology of spiro-MeOTAD HTLs on device stability is analyzed and strategies based on physical morphology for controlling PSC moisture instability induced by HTL dopants are developed.

Sensing of Oxygen Partial Pressure in Air with ZnO Nanoparticles.

The demand for sensors in response to oxygen partial pressure in air is increasingly high in recent years and small-size sensors on a micrometer scale and even a nanometer scale are particularly desirable. In this paper, the sensing of oxygen partial pressure in air was realized by a solution-processed ZnO nanoparticle (NP). Thin-film ZnO NP was prepared by spin-coating and a highly sensitive sensor was then fabricated. The oxygen sensing performance was characterized in air and compared with that in nitrogen, which showed an increase in electrical conductance by more than 100 times as a result of decreasing oxygen partial pressure from 103 mBar to 10-5 mBar. Moreover, higher sensitivity was achieved by increasing the annealing temperature and the effect of thermal annealing was also investigated. Furthermore, ZnO NP lines with 7 µm in width were successfully patterned with low cost by a mould-guided drying technique from ZnO NP dispersion, which makes ZnO NP extremely promising for miniaturized and integrated sensing applications.

Insights into the Structure and Energy of DNA Nanoassemblies.

Since the pioneering work of Ned Seeman in the early 1980s, the use of the DNA molecule as a construction material experienced a rapid growth and led to the establishment of a new field of science, nowadays called structural DNA nanotechnology. Here, the self-recognition properties of DNA are employed to build micrometer-large molecular objects with nanometer-sized features, thus bridging the nano- to the microscopic world in a programmable fashion. Distinct design strategies and experimental procedures have been developed over the years, enabling the realization of extremely sophisticated structures with a level of control that approaches that of natural macromolecular assemblies. Nevertheless, our understanding of the building process, i.e., what defines the route that goes from the initial mixture of DNA strands to the final intertwined superstructure, is, in some cases, still limited. In this review, we describe the main structural and energetic features of DNA nanoconstructs, from the simple Holliday junction to more complicated DNA architectures, and present the theoretical frameworks that have been formulated until now to explain their self-assembly. Deeper insights into the underlying principles of DNA self-assembly may certainly help us to overcome current experimental challenges and foster the development of original strategies inspired to dissipative and evolutive assembly processes occurring in nature.