Two-dimensional devices and integration towards the silicon lines.

Despite technical efforts and upgrades, advances in complementary metal-oxide-semiconductor circuits have become unsustainable in the face of inherent silicon limits. New materials are being sought to compensate for silicon deficiencies, and two-dimensional materials are considered promising candidates due to their atomically thin structures and exotic physical properties. However, a potentially applicable method for incorporating two-dimensional materials into silicon platforms remains to be illustrated. Here we try to bridge two-dimensional materials and silicon technology, from integrated devices to monolithic 'on-silicon' (silicon as the substrate) and 'with-silicon' (silicon as a functional component) circuits, and discuss the corresponding requirements for material synthesis, device design and circuitry integration. Finally, we summarize the role played by two-dimensional materials in the silicon-dominated semiconductor industry and suggest the way forward, as well as the technologies that are expected to become mainstream in the near future.

Hypoxia-Responsive T2-to-T1 Dynamically Switchable Extremely Small Iron Oxide Nanoparticles for Sensitive Tumor Imaging In Vivo.

To realize the accurate diagnosis of tumors by magnetic resonance imaging (MRI), switchable magnetic resonance contrast agents (CAs) between T1 and T2 contrast enhancement that are constructed based on extremely small iron oxide nanoparticles (ESIONPs) have been developed in recent years. We herein report, for the first time, a novel ESIONP-based nanocluster (named EAmP), which exhibited hypoxia responsiveness to the tumor microenvironment and offered a T2-to-T1-switchable contrast enhancement function, effectively distinguishing between the normal tissue and tumor tissue. In detail, active perfluorophenyl ester-modified ESIONPs with a diameter of approximately 3.6 nm were initially synthesized, and then 4,4'-azodianiline was used as a cross-linker to facilitate the formation of nanoclusters from ESIONPs through the reaction between the active ester and amine. Finally, poly(ethylene glycol) was further modified onto nanoclusters by utilizing the remaining active ester residues. The resulting EAmP demonstrated satisfactory colloidal stability and favorable biosafety and exhibited a desired T2-to-T1-switchable function, as evidenced by conversion from nanocluster to the dispersed state and a significant decrease in the r2/r1 ratio from 14.86 to 1.61 when exposed to a mimical hypoxic environment in the solution. Moreover, EAmP could decompose into dispersed ESIONPs at the tumor region, resulting in a switch from T2 to T1 contrast enhancement. This T2-to-T1-switchable contrast agent offers high sensitivity and signal-to-noise ratio to realize the accurate diagnosis of tumors. In conclusion, hypoxia-responsive EAmP is a potential MRI nanoprobe for improving the diagnostic accuracy of solid tumors.

Photoelectric characteristics of hydrogen-terminated polycrystalline diamond MESFETs.

In the field of diamond MESFETs, this work is what we believe to be the first to investigate the optoelectronic properties of hydrogen-terminated polycrystalline diamond MESFETs under visible and near-UV light irradiation. It is shown that the diamond MESFETs are well suited for weak light detection in the near-ultraviolet region around the wavelength of 368 nm, with a responsivity of 6.14 × 106 A/W and an external quantum efficiency of 2.1 × 107 when the incident light power at 368.7 nm is only 0.75 µW/cm2. For incident light at 275.1 nm, the device's sensitivity and EQE increase as the incident light power increases; at an incident light power of 175.32 µW/cm2 and a VGS of -1 V, the device's sensitivity is 2.9 × 105 A/W and the EQE is 1.3 × 106. For incident light in the wavelength range of 660 nm to 404 nm with an optical power of 70 µW/cm2, the device achieves an average responsivity of 1.21 × 105 A/W. This indicates that hydrogen-terminated polycrystalline diamond MESFETs are suitable for visible and near-UV light detection, especially for weak near-UV light detection. However, the transient response test of the device shows a long relaxation time of about 0.2 s, so it is not yet suitable for high-speed UV communication or detection.

Thickness effect of 2D PdSe2film on performance of PdSe2/Si heterostructure photodetectors.

Two-dimensional (2D) PdSe2film has the characteristics of adjustable bandgap, high carrier mobility, and high stability. Photodetector (PD) based on 2D PdSe2exhibits wide spectral self-driving features, demonstrating enormous potential in the field of optical detection. Here, we design and fabricate PdSe2/Si heterojunction PDs with various thicknesses of the PdSe2films from 10 to 35 nm. Due to the enhancement of light absorption capacity and built-in electric field of heterojunction, the photodetector with thicker PdSe2film can generate more photo-generated carriers and effectively separate them to form a large photocurrent, thus showing more excellent photodetection performance. The responsivity and specific detectivity of the PdSe2/Si PDs with 10 nm, 20 nm, and 35 nm PdSe2films are 2.12 A W-1and 6.72 × 109Jones, 6.17 A W-1and 1.95 × 1010Jones, and 8.02 A W-1and 2.54 × 1010Jones, respectively (808 nm illumination). The PD with 35 nm PdSe2film exhibits better performance than the other two PDs, with the rise/fall times of 15.8µs/138.9µs atf= 1 kHz and the cut-off frequency of 8.6 kHz. Furthermore, we demonstrate that the properties of PdSe2/Si PD array have excellent uniformity and stability at room temperature and shows potential for image sensing in the UV-vis-NIR wavelength range.

Large-Area Flexible Memory Arrays of Oriented Molecular Ferroelectric Single Crystals with Nearly Saturated Polarization.

Molecular ferroelectrics (MFs) have been proven to demonstrate excellent properties even comparable to those of inorganic counterparts usually with heavy metals. However, the validation of their device applications is still at the infant stage. The polycrystalline feature of conventionally obtained MF films, the patterning challenges for microelectronics and the brittleness of crystalline films significantly hinder their development for organic integrated circuits, as well as emerging flexible electronics. Here, a large-area flexible memory array is demonstrated of oriented molecular ferroelectric single crystals (MFSCs) with nearly saturated polarization. Highly-uniform MFSC arrays are  prepared on large-scale substrates including Si wafers and flexible substrates using an asymmetric-wetting and microgroove-assisted coating (AWMAC) strategy. Resultant flexible memory arrays exhibit excellent nonvolatile memory properties with a low-operating voltage of <5 V, i.e., nearly saturated ferroelectric polarization (6.5 µC cm-2 ), and long bending endurance (>103 ) under various bending radii. These results may open an avenue for scalable flexible MF electronics with high performance.

Egg white protein-based delivery system for bioactive substances: a review.

Some bioactive substances in food have problems such as poor solubility, unstable chemical properties and low bioavailability, which limits their application in functional food. Recently, many egg white protein-based delivery carriers have been developed to improve the chemical stability, biological activity and bioavailability of bioactive substances. This article reviewed the structure and properties of several major egg white proteins commonly used to construct bioactive substance delivery systems. Several common carrier types based on egg white proteins, including hydrogels, emulsions, micro/nanoparticles, aerogels and electrospinning were then introduced. The biological functions of common bioactive substances, the limitations, and the role of egg white protein-based delivery systems were also discussed. At present, whole egg white protein, ovalbumin and lysozyme are most widely used in delivery systems, while ovotransferrin, ovomucoid and ovomucin are less developed and applied. Egg white protein-based nanoparticles are currently the most commonly used delivery carriers. Egg white protein-based hydrogels, emulsions, and microparticles are also widely used. Future research on the application of various egg white proteins in developed new delivery systems will provide more choices for the delivery of various bioactive substances.

Extremely high-gain source-gated transistors.

Despite being a fundamental electronic component for over 70 years, it is still possible to develop different transistor designs, including the addition of a diode-like Schottky source electrode to thin-film transistors. The discovery of a dependence of the source barrier height on the semiconductor thickness and derivation of an analytical theory allow us to propose a design rule to achieve extremely high voltage gain, one of the most important figures of merit for a transistor. Using an oxide semiconductor, an intrinsic gain of 29,000 was obtained, which is orders of magnitude higher than a conventional Si transistor. These same devices demonstrate almost total immunity to negative bias illumination temperature stress, the foremost bottleneck to using oxide semiconductors in major applications, such as display drivers. Furthermore, devices fabricated with channel lengths down to 360 nm display no obvious short-channel effects, another critical factor for high-density integrated circuits and display applications. Finally, although the channel material of conventional transistors must be a semiconductor, by demonstrating a high-performance transistor with a semimetal-like indium tin oxide channel, the range and versatility of materials have been significantly broadened.

High-performance broadband photoresponse of self-powered Mg2Si/Si photodetectors.

Infrared optoelectronic devices are capable of operating in harsh environments with outstanding confidentiality and reliability. Nevertheless, suffering from the large band gap value, most semiconductor materials are difficult to detect infrared light signals. Here, Mg2Si/Si heterojunction photodetectors (PDs), which possess the advantages of low-cost, easy process, environmental friendliness, and compatibility with silicon CMOS technology, have been reported with a broadband spectral response as tested from 532 to 1550 nm under zero-bias. When the incident light wavelength is 808 nm, the Mg2Si/Si photodetector (PD) has a responsivity of 1.04 A W-1and a specific detectivity of 1.51 × 1012Jones. Furthermore, we find that the Ag nanoparticles (Ag_NPs) assembled on the Mg2Si layer can greatly improve the performance of the Mg2Si/Si PD. The responsivity and specific detectivity of Mg2Si/Si device with Ag_NPs under 808 nm illumination are 2.55 A W-1and 2.60 × 1012Jones, respectively. These excellent photodetection performances can be attributed to the high-quality of our grown Mg2Si material and the strong built-in electric field effect in the heterojunction, which can be further enhanced by the local surface plasmon effect and local electromagnetic field induced by Ag_NPs. Our study would provide significant guidance for the development of new self-powered infrared PDs based on silicon materials.

Ambipolar transport in Ni-catalyzed InGaAs nanowire field-effect transistors for near-infrared photodetection.

Weak n-type characteristics or poor p-type characteristics are limiting the applications of binary semiconductors based on ambipolar field-effect transistors (FETs). In this work, a ternary alloy of In0.2Ga0.8As nanowires (NWs) is successfully prepared using a Ni catalyst during a typical solid-source chemical-vapor-deposition process to balance the weak n-type conduction behavior in ambipolar GaAs NWFETs and the poor p-type conduction behavior in ambipolar InAs NWFETs. The presence of ambipolar transport, contributed by a native oxide shell and the body defects of the prepared In0.2Ga0.8As NWs, is confirmed by the constructed back-gated NWFETs. As demonstrated by photoluminescence, the bandgap of the prepared In0.2Ga0.8As NWs is 1.28 eV, offering the promise of application in near-infrared (NIR) photodetection. Under 850 nm laser illumination, the fabricated ambipolar NWFETs show extremely low dark currents of 50 pA and 0.5 pA when positive and negative gate voltages are applied, respectively. All the results demonstrate that with careful design of the surface oxide layer and the body defects, NWs are suitable for use in next-generation optoelectronic devices.

Fluorescent carbon dots with excellent moisture retention capability for moisturizing lipstick.

Long-lasting moisture retention is a huge challenge to humectants, and effective methods or additives for promote these functions are limited, especially nano-additives. Carbon dots (CDs) have attracted increasing research interest due to its ultra-small size, excellent optical properties and low toxicity, etc. However, most of researches have been focused on the photoexcited CDs and its subsequent photophysical and chemical processes, such as photoluminescence, photodynamic, photothermal and photocatalytic behavior. The intrinsic chemo-physical properties of the pristine CDs are not fully explored. Here, we report an excellent moisture retention capability of a new carmine cochineal-derived CDs (Car-CDs) for the first time. The relationship between the structure of Car-CDs and its moisture retention capability is revealed. More interestingly, the effective applications of Car-CDs in moisturizing lipstick are demonstrated. This work expands the research and application of CDs into a broad, new area, potentially in skin care.

Effects of salt and heat treatment on the physicochemical properties, microstructure, secondary structure, and simulated in vitro gastrointestinal digestion of duck egg white.

BACKGROUND: The texture and structure of the duck egg white (DEW) gel under salt and heat treatment are crucial to its digestibility. Specifically, the structural changes of food protein gels have been recognized for their potential to regulate in vitro digestion. In this study, the effects of gel characteristics and simulated in vitro gastrointestinal digestion of DEW under combined salt and heat treatment were investigated. RESULTS: With the increase in salting time and temperature, a porous opaque gel with large particles was formed, the moisture content of DEW showed a downward trend, and the same was true for hardness changes. The microstructure suggested that, with the penetration of NaCl, DEW proteins were denatured, and the protein molecules gradually unfolded and then aggregated after 7 days. The secondary structure revealed that, as the salting time and temperature increased, the proportion of intermolecular ß-sheets and α-helices decreased. In terms of in vitro digestion, the highest digestibility was obtained at 14 days of salting combined with 100 °C heat treatment, and the digestibility was the lowest when marinated for 7 days at 121 °C. Liquid chromatography and tandem mass spectrometry (LC-MS/MS) indicated that the number of different types of peptides and specific peptides was positively correlated with the salting time and temperature of the DEW at the end of gastric digestion. CONCLUSIONS: Heat treatment at 100 °C has a higher in vitro digestibility than at 121 °C. Gels with low hardness, large pores, and rough textures are easier to digest by pepsin and release more peptides. © 2021 Society of Chemical Industry.

UV-Vis-NIR Full-Range Responsive Carbon Dots with Large Multiphoton Absorption Cross Sections and Deep-Red Fluorescence at Nucleoli and In Vivo.

Carbon dots (CDs), with excellent optical property and cytocompatibility, are an ideal class of nanomaterials applied in the field of biomedicine. However, the weak response of CDs in the near-infrared (NIR) region impedes their practical applications. Here, UV-vis-NIR full-range responsive fluorine and nitrogen doped CDs (N-CDs-F) are designed and synthesized that own a favorable donor-π-acceptor (D-π-A) configuration and exhibit excellent two-photon (λex = 1060 nm), three-photon (λex = 1600 nm), and four-photon (λex = 2000 nm) excitation upconversion fluorescence. D-π-A-conjugated CDs prepared by solvothermal synthesis under the assistance of ammonia fluoride are reported and are endowed with larger multiphoton absorption (MPA) cross sections (3PA: 9.55 × 10-80 cm6 s2 photon-2 , 4PA: 6.32 × 10-80 cm8 s3 photon-3 ) than conventional organic compounds. Furthermore, the N-CDs-F show bright deep-red to NIR fluorescence both in vitro and in vivo, and can even stain the nucleoli of tumor cells. A plausible mechanism is proposed on the basis of the strong inter-dot and intra-dot hydrogen bonds through NH···F that can facilitate the expanding of conjugated sp2 domains, and thus not only result in lower highest occupied molecular orbital-lowest unoccupied molecular orbital energy level but also larger MPA cross sections than those of undoped CDs.

Cera alba-assisted ultraclean graphene transfer for high-performance PbI2 UV photodetectors.

Large polymer residues introduced by the graphene transfer process is still a major obstacle limiting the integration of chemical vapor deposition (CVD)-grown graphene into next-generation electronic and photoelectronic devices. Here we use cera alba, a natural and environmental-friendly material that derives from honeycomb, as the supporting layer for ultraclean graphene transfer. The transferred graphene has a low surface roughness with a surface height fluctuation within 5 nm and an only 80.08% average sheet resistance of the polymethyl methacrylate (PMMA)-transferred graphene. Further, the ultraclean graphene is used as electrodes for the PbI2-based UV photodetector and enables a 135% improvement on responsivity. The cera alba assisted transfer method reported here could achieve clean and damage-free graphene transfer, promoting the application of CVD-grown two-dimensional (2D) materials in large-area thin-film electronic and optoelectronic devices.

Growth of Ultraflat PbI2 Nanoflakes by Solvent Evaporation Suppression for High-Performance UV Photodetectors.

2D lead iodide (PbI2 ) is attracting great interest due to its great potential in the application of UV photodetectors. In this work, a facile solution-based method is developed to synthesize ultraflat PbI2 nanoflakes for high-performance UV photodetectors. By maintaining at proximate room temperature and adding an evaporation suppression solvent for slow-rate crystal growth, high-quality PbI2 nanoflakes with an ultraflat surface are obtained. The UV photodetectors based on 2D PbI2 nanoflakes exhibit a high photoresponsivity of 0.51 A W-1 , a high detectivity of 4.0 × 1010 Jones, a high external quantum efficiency (EQE) of 168.9%, and a rapid response speed including a rise time of 14.1 ms and a decay time of 31.0 ms. The balanced and excellent photodetector performance of these devices paves the road for practical UV photodetection based on 2D PbI2 nanoflakes.

Copper-Doped Carbon Dots for Optical Bioimaging and Photodynamic Therapy.

Carbon dots (CDs), as an effective bioimaging agent, have aroused widespread interest. With the increasing number of CDs used in photodynamic therapy (PDT), developing efficient CDs with multiple functions such as imaging and phototherapy has become a new challenge. Herein, a new type of copper-doped CDs (Cu-CDs) with a high fluorescence quantum yield of 24.4% was synthesized from a copper complex of poly(acrylic acid) through coordination between the carboxyl group and copper ions. Owing to their good solubility, bright fluorescence, and low cytotoxicity, the Cu-CDs can be used for fluorescence imaging in both the HeLa (human cervical cancer) cell line and SH-SY5Y (human neuroblastoma cells) multicellular spheroids (3D MCs). More importantly, the Cu-CDs show a high quantum yield of singlet oxygen (1O2; 36%), good photoinduced cytotoxicity, and effective inhibition of 3D MC growth. Therefore, the Cu-CDs can be used as a promising imaging-guided PDT agent. This study provides a new carbon-based nanomaterial for multifunctional photodiagnostic and therapeutic agents for biological applications.

High-performance printable 2.4 GHz graphene-based antenna using water-transferring technology.

Liquid-phase exfoliated graphene sheets are promising candidates for printing electronics. Here, a high-performance printed 2.4 GHz graphene-based antenna is reported. Graphene conductive ink prepared by using liquid-phase exfoliation process is printed onto a water-transferable paper by using blade printing technique, which is then patterned as dipole antenna and transferred onto a target substrate. The fabricated dipole antenna (43 × 3 mm), exhibiting typical radiation patterns of an ideal dipole antenna, achieves -10 dB bandwidth of 8.9% and a maximum gain of 0.7 dBi. The printed graphene-antennas satisfy the application requirements of the Internet of Things and suggest its feasibility of replacing conventional metallic antennas in those applications.

A review of theoretical study of graphene chemical vapor deposition synthesis on metals: nucleation, growth, and the role of hydrogen and oxygen.

Graphene has attracted intense research interest due to its extraordinary properties and great application potential. Various methods have been proposed for the synthesis of graphene, among which chemical vapor deposition has drawn a great deal of attention for synthesizing large-area and high-quality graphene. Theoretical understanding of the synthesis mechanism is crucial for optimizing the experimental design for desired graphene production. In this review, we discuss the three fundamental steps of graphene synthesis in details, i.e. (1) decomposition of carbon feedstocks and formation of various active carbon species, (2) nucleation, and (3) attachment and extension. We provide a complete scenario of graphene synthesis on metal surfaces at atomistic level by means of density functional theory, molecular dynamics (MD), Monte Carlo (MC) and their combination and interface with other simulation methods such as quantum mechanical molecular dynamics, density functional tight binding molecular dynamics, and combination of MD and MC. We also address the latest investigation of the influences of the hydrogen and oxygen on the synthesis and the quality of the synthesized graphene.

"W-shaped" injection current dependence of electroluminescence linewidth in green InGaN/GaN-based LED grown on silicon substrate.

Injection current, and temperature, dependences of the electroluminescence (EL) spectrum from green InGaN/GaN multiple quantum well (MQW)-based light-emitting diodes (LED) grown on a Si substrate, are investigated over a wide range of injection currents (0.5 µA-350 mA) and temperatures (6-350 K). The results show that an increasing temperature can result in the change of injection current-dependent behavior of the EL spectrum in initial current range. That is, with increasing the injection current in the low current range, the emission process of the MQWs is dominated by filling effect of low-energetic localized states at the low temperature range of around 6 K, and by Coulomb screening of the quantum confinement Stark effect followed by a filling effect of the higher levels of the low-energetic localized states at the intermediate temperature range of around 160 K. However, when the temperature is further raised to the higher temperature range of around 350 K, the emission process of the MQWs in the low current range is dominated by carrier-scattering effect followed by non-radiative recombination process. The aforementioned current-dependent behaviors of the EL spectrum are mainly attributed to the strong localized effect of the green LED, as confirmed by the anomalous temperature dependence of the EL spectrum measured at the low injection current of 5 µA. In addition, the injection current dependence of external quantum efficiency at different temperatures shows that, with increasing temperature from 6 to 350 K, in addition to the enhanced non-radiative recombination, electron overflow becomes more significant, especially in the higher temperature range above 300 K.

Increased permeability of oxygen atoms through graphene with ripples.

Graphene is an ideal membrane for selective separation because of its unique properties and single-layer structure. Considerable efforts have been made to alter the permeability of graphene. In this study, we investigate the pathways for an oxygen atom to pass through graphene sheets. We also identify the effect of the ripple's curvature in graphene sheets on the energy barrier of permeation through density functional theory calculations. Results show that oxygen atoms can easily pass through the concave side of graphene ripples with a large curvature. The analysis of transition states reveals that the space where an oxygen atom passes through keeps an almost identical structure with similar bond lengths regardless of the curvature. We find that the Cu(111) substrate may draw out the C-C bond lengths of graphene at the Cu(111) surface because of the strong interaction between the graphene edge and copper atoms. Consequently, the energy barrier of the permeation of oxygen atoms through graphene is reduced. These results suggest that the rippling of graphene significantly affects its permeation.

Silver nanowire-graphene hybrid transparent conductive electrodes for highly efficient inverted organic solar cells.

Silver nanowires (AgNWs) and graphene are both promising candidates as a transparent conductive electrode (TCE) to replace expensive and fragile indium tin oxide (ITO) TCE. A synergistically optimized performance is expected when the advantages of AgNWs and graphene are combined. In this paper, the AgNW-graphene hybrid electrode is constructed by depositing a graphene layer on top of the network of AgNWs. Compared with the pristine AgNWs electrode, the AgNW-graphene TCE exhibits reduced sheet resistance, lower surface roughness, excellent long-term stability, and corrosion resistance in corrosive liquids. The graphene layer covering the AgNWs provides additional conduction pathways for electron transport and collection by the electrode. Benefiting from these advantages of the hybrid electrodes, we achieve a power conversion efficiency of 8.12% of inverted organic solar cells using PTB7:PC71BM as the active layer, which is compared to that of the solar cells based on standard ITO TCE but about 10% higher than that based on AgNWs TCE.