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Single-atom catalysts (SACs), featuring high atom utilization, have captured widespread interests in diverse applications. However, the single-atom sites in SACs are generally recognized as independent units and the interplay of adjacent sites is largely overlooked. Herein, by the direct pyrolysis of MOFs assembled with Fe and Ni-doped ZnO nanoparticles, a novel Fe1-Ni1-N-C catalyst, with neighboring Fe and Ni single-atom pairs decorated on nitrogen-doped carbon support, has been precisely constructed. Thanks to the synergism of neighboring Fe and Ni single-atom pairs, Fe1-Ni1-N-C presents significantly boosted performances for electrocatalytic reduction of CO2, far surpassing Fe1-N-C and Ni1-N-C with separate Fe or Ni single atoms. Additionally, the Fe1-Ni1-N-C also exhibits superior performance with excellent CO selectivity and durability in Zn-CO2 battery. Theoretical simulations reveal that, in Fe1-Ni1-N-C, single Fe atoms can be highly activated by adjacent single-atom Ni via non-bonding interaction, significantly facilitating the formation of COOH* intermediate and thereby accelerating the overall CO2 reduction. This work supplies a general strategy to construct single-atom catalysts containing multiple metal species and reveals the vital importance of the communitive effect between adjacent single atoms toward improved catalysis.

Converting CO2 emissions, powered by renewable electricity, to produce fuels and chemicals provides an elegant route towards a carbon-neutral energy cycle. Progress in the understanding and synthesis of Cu catalysts has spurred the explosive development of electrochemical CO2 reduction (CO2RR) technology to produce hydrocarbons and oxygenates; however, Cu, as the predominant catalyst, often exhibits limited selectivity and activity towards a specific product, leading to low productivity and substantial post-reaction purification. Here, we present a single-atom Pb-alloyed Cu catalyst (Pb1Cu) that can exclusively (~96% Faradaic efficiency) convert CO2 into formate with high activity in excess of 1 A cm–2. The Pb1Cu electrocatalyst converts CO2 into formate on the modulated Cu sites rather than on the isolated Pb. In situ spectroscopic evidence and theoretical calculations revealed that the activated Cu sites of the Pb1Cu catalyst regulate the first protonation step of the CO2RR and divert the CO2RR towards a HCOO* path rather than a COOH* path, thus thwarting the possibility of other products. We further showcase the continuous production of a pure formic acid solution at 100 mA cm–2 over 180 h using a solid electrolyte reactor and Pb1Cu. Alloying copper with isolated heteroatoms enables the C protonation of CO2 to HCOO* on activated copper sites, resulting in exclusive electrochemical CO2-to-HCOOH conversion with considerably high activity.

The water–gas shift (WGS) reaction is an industrially important source of pure hydrogen (H2) at the expense of carbon monoxide and water1,2. This reaction is of interest for fuel-cell applications, but requires WGS catalysts that are durable and highly active at low temperatures3. Here we demonstrate that the structure (Pt1–Ptn)/α-MoC, where isolated platinum atoms (Pt1) and subnanometre platinum clusters (Ptn) are stabilized on α-molybdenum carbide (α-MoC), catalyses the WGS reaction even at 313 kelvin, with a hydrogen-production pathway involving direct carbon monoxide dissociation identified. We find that it is critical to crowd the α-MoC surface with Pt1 and Ptn species, which prevents oxidation of the support that would cause catalyst deactivation, as seen with gold/α-MoC (ref. 4), and gives our system high stability and a high metal-normalized turnover number of 4,300,000 moles of hydrogen per mole of platinum. We anticipate that the strategy demonstrated here will be pivotal for the design of highly active and stable catalysts for effective activation of important molecules such as water and carbon monoxide for energy production. A stable, low-temperature water–gas shift catalyst is achieved by crowding platinum atoms and clusters on α-molybdenum carbide; the crowding protects the support from oxidation that would cause catalyst deactivation.

Hollow inorganic nanofibers have great potential application in the field of photocatalysis due to their special three-dimensional structure. In our work, we have fabricated ZnO hollow nanofibers (ZnO-HNF) by simple single-spinneret electrospinning of polyacrylonitrile (PAN)/zinc acetate precursor solution, followed by stepwise annealing at 300–500 °C. The results show that long and continuous ZnO-HNF with shell consisting of uniform compacted ZnO nanoparticles are successfully fabricated, and the shell thickness is approximately 30 nm. The formation mechanism of ZnO-HNF is speculated to be consequence of the different rate of mass diffusion during the annealing process (Kirkendall effect). The prepared Zn-HNF exhibits good performance in photocatalysis. The photocatalytic removal efficiency of Rhodamine B (RhB) under ultraviolet light irradiation can reach 94.08% in 1 hour, and the removal efficiency of Cr(VI) is 94.49% in 2 hours. This work provides new ideas for the development of ZnO in the field of photocatalysis, and provides new possibilities for more types of subsequent photocatalytic materials.

We report the syntheses of highly dispersed CoNi bimetallic catalysts on the surface of α-MoC based on the strong metal support interaction (SMSI) effect. The interaction between the nearly atomically dispersed Co and Ni atoms was observed for the first time by the real-space chemical mapping at the atomic level. Combined with the ability of α-MoC to split water at low temperatures, the as-synthesized CoNi/α-MoC catalysts exhibited robust and synergistic performance for the hydrogen production from hydrolysis of ammonia borane. The metal-normalized activity of the bimetallic 1.5Co1.5Ni/α-MoC catalyst reached 321.1 molH2·mol-1CoNi·min-1 at 298 K, which surpasses all the noble metal-free catalysts ever reported and is four times higher than that of the commercial Pt/C catalyst.

Methanol-water reforming is a promising solution for H2 production/transportation in stationary and mobile hydrogen applications. Developing inexpensive catalysts with sufficiently high activity, selectivity, and stability remains challenging. In this paper, nickel-supported over face-centered cubic (fcc) phase α-MoC has been discovered to exhibit extraordinary hydrogen production activity in the aqueous-phase methanol reforming reaction. Under optimized condition, the hydrogen production rate of 2% Ni/α-MoC is about 6 times higher than that of conventional noble metal 2% Pt/Al2O3 catalyst. We demonstrate that Ni is atomically dispersed over α-MoC via carbon bridge bonds, forming a Ni1-Cx motif on the carbide surface. Such Ni1-Cx motifs can effectively stabilize the isolated Ni1 sites over the α-MoC substrate, rendering maximized active site density and high structural stability. In addition, the synergy between Ni1-Cx motif and α-MoC produces an active interfacial structure for water dissociation, methanol activation, and successive reforming processes with compatible activity.

Electrocatalytic CO2 reduction (CO2RR) to valuable fuels is a promising approach to mitigate energy and environmental problems, but controlling the reaction pathways and products remains challenging. Here a novel Cu2O nanoparticle film was synthesized by square-wave (SW) electrochemical redox cycling of high-purity Cu foils. The cathode afforded up to 98% Faradaic efficiency for electroreduction of CO2 to nearly pure formate under ≥45 atm CO2 in bicarbonate catholytes. When this cathode was paired with a newly developed NiFe hydroxide carbonate anode in KOH/borate anolyte, the resulting two-electrode high-pressure electrolysis cell achieved high energy conversion efficiencies of up to 55.8% stably for long-term formate production. While the high-pressure conditions drastically increased the solubility of CO2 to enhance CO2 reduction and suppress hydrogen evolution, the (111)-oriented Cu2O film was found to be important to afford nearly 100% CO2 reduction to formate. The results have implications for CO2 reduction to a single liquid product with high energy conversion efficiency.

The development of the aberration correction technique has enabled atomic resolution imaging in scanning transmission electron microscopy (STEM) under low accelerating voltages and pushed the detection limit of STEM-based imaging and spectroscopy analysis down to the single-atom level. The so-called “single-atom electron microscopy” brings new opportunities to study the structure–property relationship in energy-related nanomaterials at the atomic scale. In this review, we will firstly summarize some recent advances in low-voltage STEM imaging and spectroscopy with single-atom sensitivity, including emerging techniques such as STEM-DPC imaging and in situ STEM, by using two-dimensional (2D) materials as model systems. We will then discuss the application of these single-atom electron microscopy techniques to more complex energy materials via specific examples. These powerful and comprehensive capabilities of aberration-corrected STEM with single-atom sensitivity have proven to be invaluable for unveiling the origins of functionalities of energy-related nanomaterials and guiding the design of novel materials with desired performance.

Single-atom catalysts (SACs), featuring high atom utilization, have captured widespread interests in diverse applications. However, the single-atom sites in SACs are generally recognized as independent units and the interplay of adjacent sites is largely overlooked. Herein, by the direct pyrolysis of MOFs assembled with Fe and Ni-doped ZnO nanoparticles, a novel Fe

Electrochemical reduction of CO

Converting CO

Atomically dispersed metal catalysts maximize atom efficiency and display unique catalytic properties compared with regular metal nanoparticles. However, achieving high reactivity while preserving high stability at appreciable loadings remains challenging. Here we solve the challenge by synergizing metal–support interactions and spatial confinement, which enables the fabrication of highly loaded atomic nickel (3.1 wt%) along with dense atomic copper grippers (8.1 wt%) on a graphitic carbon nitride support. For the semi-hydrogenation of acetylene in excess ethylene, the fabricated catalyst shows extraordinary catalytic performance in terms of activity, selectivity and stability—far superior to supported atomic nickel alone in the absence of a synergizing effect. Comprehensive characterization and theoretical calculations reveal that the active nickel site confined in two stable hydroxylated copper grippers dynamically changes by breaking the interfacial nickel–support bonds on reactant adsorption and making these bonds on product desorption. Such a dynamic effect confers high catalytic performance, providing an avenue to rationally design efficient, stable and highly loaded, yet atomically dispersed, catalysts. Synergizing metal–support interactions and spatial confinement through atomic copper grippers boost the dynamics of highly loaded atomic nickel for high activity, high thermal/chemical stability and unprecedented coke inhibition in hydrogenation reactions.

Electrocatalytic CO

The water-gas shift (WGS) reaction is an industrially important source of pure hydrogen (H

InP- and GaAs-based metamorphic In 0.83 Ga 0.17 As photodetectors were grown and investigated. Compared to InP-based photodetector, the dark current of GaAs-based photodetector at room temperature increased 2–3 times but still comparable, whereas at 77 K the dark current increased 2–3 orders. The deep-level transient spectroscopy results reveal that a deep level trap state exists in the GaAs-based photodetector structure. The higher dark current in GaAs-based photodetector at low temperature was mainly ascribed to a deep level trap induced tunneling current. The deep trap centers can also induce non-radiative recombination with smaller thermal active energy in the GaAs-based photodetector structure.

The effects of well shapes and waveguide materials on InP-based InAs quantum well lasers have been investigated. The laser structures were grown on metamorphic In 0.65 Al 0.35 As buffers. A novel trapezoidal quantum well composed of In y Ga 1−y As grading and InAs layer was used to improve the quality of quantum well. Quaternary In 0.65 Al 0.2 Ga 0.15 As waveguide was applied instead of ternary In 0.65 Ga 0.35 As to enhance the carrier injection. The material qualities have been characterized by X-ray diffraction, transmission electron microscopy and photoluminescence measurements, while the device properties of the lasers with various structures were investigated at different temperatures. Results show that the laser performances have been improved by the use of trapezoidal quantum wells and InAlGaAs waveguides.

Supported metal nanocrystals have exhibited remarkable catalytic performance in hydrogen generation reactions, which is influenced and even determined by their supports. Accordingly, it is of fundamental importance to determine the direct relationship between catalytic performance and metal-support interactions. Herein, we provide a quantitative profile for exploring metal-support interactions by considering the highest occupied state in single-atom catalysts. The catalyst studied consisted of isolated Rh atoms dispersed on the surface of VO2 nanorods. It was observed that the activation energy of ammonia-borane hydrolysis changed when the substrate underwent a phase transition. Mechanistic studies indicate that the catalytic performance depended directly on the highest occupied state of the single Rh atoms, which was determined by the band structure of the substrates. Other metal catalysts, even with non-noble metals, that exhibited significant catalytic activity towards NH3 BH3 hydrolysis were rationally designed by adjusting their highest occupied states.

Rh-based heterogeneous catalysts generally have limited selectivity relative to their homogeneous counterparts in hydroformylation reactions despite of the convenience of catalyst separation in heterogeneous catalysis. Here, we develop CoO-supported Rh single-atom catalysts (Rh/CoO) with remarkable activity and selectivity towards propene hydroformylation. By increasing Rh mass loading, isolated Rh atoms switch to aggregated clusters of different atomicity. During the hydroformylation, Rh/CoO achieves the optimal selectivity of 94.4% for butyraldehyde and the highest turnover frequency number of 2,065 h−1 among the obtained atomic-scale Rh-based catalysts. Mechanistic studies reveal that a structural reconstruction of Rh single atoms in Rh/CoO occurs during the catalytic process, facilitating the adsorption and activation of reactants. In kinetic view, linear products are determined as the dominating products by analysing reaction paths deriving from the two most stable co-adsorbed configurations. As a bridge of homogeneous and heterogeneous catalysis, single-atom catalysts can be potentially applied in other industrial reactions., Despite the advantages of using heterogeneous catalysts, most successful rhodium hydrogenations are carried out with homogeneous catalysts. Here the authors report a supported single atom rhodium catalyst providing high activities and selectivities for propene hydroformylation.

Nanofiber mats produced by electrospinning, with the advantages of specific surface area, porosity and chemical tenability, are an ideal support material for deposition of metal[Formula: see text]organic framework (MOF) crystals. In this study, four types of MOFs (MIL-53(Al), ZIF-8, UiO-66-NH2 and NH2-MIL-125(Ti)) were deposited on polydopamine (PDA)-modified electrospun polyvinyl alcohol (PVA)/SiO2 organic[Formula: see text]inorganic hybrid nanofiber mats by bulky synthesis. Because of the formation of Si–O–C–O–Si bridges between PVA chains and silica network, electrospun PVA/SiO2 organic[Formula: see text]inorganic hybrid nanofiber mats are quite stable in water or organic solvents and at high temperature are suitable as supports for MOFs deposition. The PDA layer, which exhibits a powerful adhesive ability to attach foreign objects, can effectively improve growth of MOFs on the surface of PVA/SiO2 nanofiber mats. The obtained MOF composites combining the unique properties of electrospun nanofibers mats and MOFs particles become flexible and tailorable, greatly expanding the application range of MOFs materials. The synthesized MOF composites were used to adsorb chloramphenicol (CAP) in water. It was found that the four MOF composites could remove CAP from water effectively and MIL-53(Al) composite had the highest adsorption capacity due to the higher specific surface area.

The effects of well widths and well numbers of InGaAs triangular quantum well lasers in 2.30–2.44 μm range using antimony-free material system on InP substrates are investigated. The triangular quantum well was equivalently formed by using gas source molecular beam epitaxy grown InAs/In0.53Ga0.47As digital alloy and the pseudomorphic growth was confirmed by the X-ray diffraction measurements. Lasing at 2.30 μm above 330 K under continuous wave operation has been achieved for the laser with four 13 nm quantum wells. By increasing the well width to 19 nm, the continuous wave wavelength has been extended to 2.44 μm at 290 K, whereas the epitaxial quality and laser performances are deteriorated. For those lasers with well width up to 19 nm, the moderate reduction of the quantum well numbers can restrict the strain accumulation and improve the laser performances. Continuous wave lasing at 2.38 μm above 300 K has been achieved.

The impact of buffer schemes on the strain relaxation and structural characteristics of In 0.83 Ga 0.17 As photodetector structures with relatively high lattice mismatch (5.9%) grown on GaAs substrate by gas source molecular beam epitaxy has been investigated. Reduction of surface roughness, full widths at half maximum of X-ray diffraction signals and threading dislocations, as well as an enhancement of photoluminescence intensity were observed for the In 0.83 Ga 0.17 As photodetector structure with fixed-composition In 0.83 Al 0.17 As buffer compared to those with continuously graded In x Al 1− x As buffer. The role of fixed-composition In 0.83 Al 0.17 As buffer layer is investigated, and it is believed that a couple monolayers of In 0.83 Al 0.17 As at the initial growth stage can provide high density of nucleation site by the formation of quantum dots at the interface and thus to reduce the strain energy caused by the large lattice mismatch between In 0.83 Al 0.17 As and GaAs.

InP-based high indium content In 0.83 Ga 0.17 As photodetector structures with lattice mismatch up to 2.1% have been grown by gas source molecular beam epitaxy system. The photodetectors using continuously graded and step-graded In x Al 1−x As buffer structures were grown and demonstrated. The effects of the buffer scheme were investigated by the measurements of atomic force microscopy, high-resolution X-ray diffraction, photoluminescence and device performance. Results show that the full relaxation of the photodetector structure has been achieved by using continuously graded InAlAs buffer. Superior optical properties and lower dark currents can be reached for the photodetector structure with continuously graded buffer layer.

We present a novel method to characterize the internal quantum efficiency and internal optical loss of semiconductor lasers. Its basic concept is studying the dependence of the external quantum efficiency on the mirror reflectivity. This method is very different from the conventional one, which focuses on the external quantum efficiency as a function of cavity length. Our method has great advantages, such as the capability of measuring the internal quantum efficiency and optical loss of a single laser diode, which is intrinsically impossible by the conventional method.

InAlGaAs photodiodes with 50% cut-off wavelength of 1.41 μm at room temperature have been grown by using gas source MBE with convenient and reliable procedure, and the performances have been characterized in detail. The InAlGaAs absorption layer shows a mismatch of −8×10 −5 to the InP substrate with a full width at half maximum of around 20 arcs. Dark current of 247 pA at reverse bias of 10 mV and zero bias resistance of 41 M Ω has been measured for the devices at room temperature with 200 μm mesa diameter. The dark current of this InAlGaAs photodetector is about 20 times lower than the In 0.53 Ga 0.47 As photodetector with similar structure processed at the same time.

A variety of metamorphic InGaAs photodetector structures have been grown on InP substrates by gas source molecular beam epitaxy. Their characteristics have been measured by atomic force microscopy, X-ray diffraction and photoluminescence to investigate the effects of growth temperature, grading profile and digital alloy intermediate layers in the buffer. The growth temperature is optimized to linearly decrease during the growth of In x Al 1− x As graded buffer, and kept at a relatively high temperature to grow the InGaAs absorption layer. The linearly grading profile of the composition in the buffer is superior to the convex grading profile, which indicates that the grading rate in the beginning could not be too high. The insertion of digital alloy intermediate layers in the In x Al 1− x As buffer improves the structural and surface qualities of the photodetector structures, whereas it introduces some negative effects on the optical quality.

Effects of the injector doping densities on lasing properties of mid-infrared InAlAs–InGaAs–InP quantum cascade lasers at 4.3 μm have been studied. Lasers with different average injector doping between 1.29E17 cm −3 and 2.07E17 cm −3 have been grown by gas source molecular beam epitaxy (GSMBE), and their lasing characteristics were investigated. Lasers with low doped injectors (1.68E17 cm −3 ) exhibited lower threshold current density, longer emission wavelength and lower characteristic temperature T 0 . The lower injector doping density decreases waveguide loss. On the other hand, the high doping of the injector increases heat transfer through phonon in QCL active region, and thus results in high characteristic temperature T 0 .

The effects of bismuth on the performances of InP-based detectors and multiple triangular quantum wells in 2–3 µm band have been investigated. The cut-off wavelength of the InGaAsBi detector is tailored to 2.1 µm by the bismuth incorporation in the absorption layer, but the detector still shows an encouraging dark current due to decreased lattice mismatch to InP substrate. The material quality of the InAs/InGaAs triangular quantum wells has been significantly improved by introducing bismuth as a surfactant during growth. The moderate bismuth reduces the surface roughness, improves the heterostructure interfaces and enhances the photoluminescence intensity obviously, whereas deterioration occurs in the case of excessive bismuth flux. Bismuth shows a promising potential to improve InP-based detector and laser structures both by incorporating into the alloys and acting as a surfactant.

Integrated, compact, and economical pulse driving and TE control modules for pulsed quantum cascade lasers (QCL) have been developed. Based on those modules, an effective tunable diode laser spectroscopy (TDLS) setup has been constructed for the evaluation of pulsed QCL and demonstration of TDLS concepts. Connecting our mid-infrared QCL module to the driving module using cable of 10 Ω characteristic impedance results in down chirp light pulses suitable for intrapulse scheme of TDLS; a usable down chirp of about 0.78 cm−1 is achieved for current pulse with 240-ns pulse width. Connecting the QCL module to the driving module using stripline of characteristic impedance

Wavelength-extended In y Ga 1− y As photodiodes with cut-off wavelengths of 2.0, 2.4 and 2.7 μm at room temperature were grown using gas source molecular beam epitaxy with linearly graded In x Al 1− x As ( x =0.52 to y ) buffer layers and In y Al 1− y As cap layers. A convenient and reliable correlating ramping procedure was developed for the growth. Detector performances were compared with our standard homojunction detectors containing linearly graded In x Ga 1− x As buffer layers. The heterojunction detectors showed better performance than the homojunction detectors. Also, the use of wider bandgap buffer and cap made the heterojunction detectors more suitable for both front and back illumination. For the photodiodes with 500 μm mesa diameter at room temperature, the typical dark current ( V R =10 mV) and R 0 A were 74 nA and 104 Ω cm 2 at 290 K for the cut-off wavelength of 2.4 μm. Optimization of the buffer structure was necessary for further extension of the response wavelength.

A group of AlInGaAs/InGaAs/InAs strain compensated triangular quantum well samples have been grown by using gas source molecular beam epitaxy (GSMBE), and their properties are investigated by X-ray diffraction and photoluminescence (PL) measurements. Through the adjustment of the growth temperature and barrier width, the quality of the quantum wells has been improved distinctly. The maximal PL peak wavelength of 2.38 μm at 300 K has been reached. The X-ray diffraction measurements show good structural properties and the full-width at half-maximum (FWHM) of PL spectrum is 17 meV at 12 K and 33 meV at 300 K. For the sample with larger well width, the transition involving the second sub-energy levels occurs.

We have investigated the growth of InAs/GaSb type-II superlattices by gas-source molecular-beam epitaxy, where Sb cracker cell and AH 3 high-temperature injector are used to provide Sb and As flux, respectively. Sharp InAs/GaSb interfaces can be obtained at optimized growth conditions, revealed by high-resolution transmission electron microscopy. Moreover, it was found that the intrinsic net tensile strain of the InAs/GaSb superlattices can be partially compensated by intentional insertion of a sub-monolayer InSb layer at the interfaces of InAs and GaSb. Finally, based on InAs/GaSb superlattices grown by gas-source molecular-beam epitaxy (GSMBE), we have fabricated a photodiode with cut-off wavelength of 4.9 μm.

A set of room temperature low threshold current densities of a mid-infrared InP-based quantum cascade lasers (QCLs) have been demonstrated. Threshold current densities as low as 1.7 kA/cm2 for multi-mode Fabry-Perot QCLs at an emission wavelength of 7.6 μm and 0.9 kA/cm2 for single-mode distributed feedback QCLs at an emission wavelength of 7.7 μm have been achieved at 300 K. The results obtained are through the precision control of doping incorporation and concentration, the active region of the structure for suppressing the current leakage, and the low resistance material choice in the wave guide cladding and plasmon for improving heat dissipation.

The ternary wide bandgap AlInP alloys have been grown on GaAs substrates by using gas source molecular beam epitaxy, and the relationship between various growth parameters and the composition, lattice mismatch, surface morphology as well as doping concentration of the AlInP epi-layers have been investigated in detail. The AlInP epi-layer with lattice mismatch of +4.3 × 10−4 and full-width at half-maximum of X-ray diffraction peaks of 21.6″ and 14.9″ for epi-layer and substrate respectively have been obtained. The maximum reachable p and n type carrier concentration for Be or Si doping were found to be around 1 × 1018 and 5 × 1018 cm−3 respectively around lattice match composition.

We have demonstrated the first Gas source molecular beam epitaxy (GSMBE) grown distributed feedback quantum cascade laser (DFB QC-laser) laser with low threshold current density operation at 7.6 μm. High quality DFB QC-laser heterostructures were grown by an one step GSMBE growth procedure. The first-order grating was defined by a holographic technology. A tunable single mode DFB QC-laser operation in pulsed mode with a low threshold current density of 574 A/cm 2 and a peak optical power of 50 mW at 70 K and 7.6 μm have been obtained. The side mode suppression ratio and the maximum single mode wavelength tuning range by changing their heat sink temperature are 23 dB and 20 nm, respectively.

The heat management of the AlGaAsSb/InGaAsSb ridge waveguide MQW laser at 2 μm wavelength range has been investigated by using the finite-element method (FEM). Results show that the thermal behavior of antimonide lasers is quite different from InP or GaAs-based lasers mainly due to the low thermal conductivities of antimonides, which are coincident with the observed results. By using junction down-mounting or using thick gold plating layer as heat spreader on the top contact for substrate down-mounting, the thermal characteristics of the antimonide lasers can be dramatically improved.

In this paper, we report results on the material quality of InGaAs/AlInAs lattice-matched to InP and the performance of a Fabry–Perot QC lasers grown by gas-source molecular beam epitaxy using a one-growth step procedure. The surface defect density of epi-layer with 10/cm 2 over a 2′′ diameter wafer are achieved. The Fabry–Perot QC lasers uncoated exhibit operation in quasi-continuous-wave at room temperature with a low threshold current density of 1.75 KA/cm 2 and 7.95 μm. The emitting wavelength is in good agreement with the predicted emission wavelength by design.

The thermal characteristics of antimonide ridge waveguide MQW lasers have been investigated numerically and experimentally, and compared with phosphide lasers in detail. Using the finite-element method, the heat accumulation and dissipation process of the lasers under CW and pulse driving conditions have been simulated, and quantitative thermal time constants were introduced to describe the cooling efficiency of the lasers. The non-uniform temperature distribution inside the active core of the laser and its effects on lasing spectra have been discussed, and confirmed by the measurement of the broadening of the lasing spectrum towards the blue side. A way to improve the thermal property of antimonide lasers have also been proposed and discussed.

Enhancement-mode (E-mode) operation In 0.49 Ga 0.51 P/In 0.2 Ga 0.8 As/GaAs PHEMTs were designed for high performance and were successfully grown by gas source molecular beam epitaxy (GSMBE). An optimized GSMBE growth process based on the memory effect studied has been applied to precisely control the InGaP/InGaAs and InGaP/GaAs interface quality and composition. The lattice mismatch of 10 −4 and composition uniformity of better than ±0.2% for 3″ diameter InGaP/GaAs layers were obtained. E-mode operation InGaP/InGaAs PHEMTs and related low-noise amplifier (LNA) circuits were obtained. The E-mode PHEMT had a threshold voltage near 0 V and the LNA can operate under a single-voltage supply of 1.5–3.0 V and at 2.5 GHz with a gain of over 20 dB and a noise figure ( N f ) of 3.43 dB.

Alkali and neutralized (NH 4 ) 2 S passivation treatment effects on the performance of MBE-grown InGaAsSb/GaSb PIN detectors have been studied. Results show the dark current density under −0.5 V bias decreased from 1.01 mA/cm 2 to 490 μA/cm 2 for alkali (NH 4 ) 2 S solution treatment and 87 μA/cm 2 for neutralized (NH 4 ) 2 S solution treatments, respectively. A modified neutralized (NH 4 ) 2 S passivation method for GaSb-based antimonide devices has been proposed. The XPS spectra indicated that (NH 4 ) 2 S passivation can suppress oxidization and form Ga–S and In–S bonds on the InGaAsSb surface.

A mid-infrared laser characterization system, including a gpib programmable I–P and I–V set-up based on direct waveform measurement with extraordinary wide pulse duration and duty cycle tuning range, in conjunction with a Fourier transform infrared spectroscopy system adapted with double modulation technique, has been developed. Based on this characterization system, the characteristics of gas source MBE grown InAlAs/InGaAs/InP quantum cascade lasers (QCL), especially their thermal property, have been evaluated. The results show that in the combination of I–P, I–V and spectral measurements at various driving pulse parameters, the thermal resistance, lasing conditions as well as spectral characteristics of the mid-infrared QCL could be deduced. This characterization system is also a useful tool for the evaluation of other types of diode lasers in the mid-infrared band.

The properties of graphene can be chemically altered by changing its local binding configurations. In the present work, we investigate fundamentals of chemisorption of atomic hydrogen on graphene and its influence on mechanical properties of as-hydrogenated graphene by means of molecular dynamics simulations. Our simulation results indicate that there are diversiform hydrogen-graphene configurations formed in the chemisorption process. Especially, energetically favorable hydrogen pairs result in less even no atomic distortion of graphene than sp3 hybridization. The hydrogenation-induced deterioration of mechanical properties of graphene shows a strong dependence on its chirality. The evolution of bond structures in uniaxial tension along armchair direction is more sensitive to local failure of graphene than zigzag direction, leading to a more pronounced decrease in both fracture stress and fracture strain. It is indicated that the chemisorption of hydrogen on graphene can be strongly affected by operating temperature primarily due to the temperature dependent graphene morphology. These findings advance our understanding of chemical vapor deposition of graphene synthesis and hydrogenation of graphene.

Correction for ‘Fabrication of free-standing membranes with tunable pore structures based on the combination of electrospinning and self-assembly of block copolymers’ by Meimei Zhou et al., RSC Adv., 2017, 7, 49568–49575.