Negative-capacitance and bulk photovoltaic phenomena in gallium nitride nanorods network

An enhanced self-powered near-ultraviolet photodetection phenomenon was observed in epitaxial gallium nitride (GaN) nanorods network grown on an intermediate layer of N:GaN on a nitridated HfO₂(N:HfO₂)/SiO₂/p-Si substrate. The fabricated Au/GaN/N:GaN/N:HfO₂/Ag heterostructure exhibited a giant change (OFF/ON ratio > 50 without applying any external electrical field) in its conductance when illuminated by a very weak (25 mW cm⁻²) near-UV monochromatic light with a low dark current (nearly 20 nA). The presented near-UV photodetector offers photoresponsivity of ∼2.4 mA W⁻¹ at an applied voltage of 1 V. We observed an optically generated internal open circuit voltage of ∼155 mV and short circuit current ∼430 nA, which can be attributed to the quantum confinement of free charge carriers in the nanorod matrix. Interestingly, it also shows a negative capacitance after near-UV illumination. It has great potential as a self-powered UV photodetector and in metamaterial applications.

An enhanced self-powered near-ultraviolet photodetection phenomenon was observed in epitaxial gallium nitride (GaN) nanorod networks grown on an intermediate layer of N:GaN on a nitridated HfO₂(N:HfO₂)/SiO₂/p-Si substrate.     

Highly stable ITO/Zn2TiO4/Pt resistive random access memory and its application in two-bit-per-cell

We discuss the fabrication procedure and device characteristics of ITO/Zn₂TiO₄/Pt resistive random-access memory (RRAM) at room temperature. Four different resistive states were obtained by applying different current compliances, all of which showed good retention characteristics with no obvious degradation and were individually distinguished after 10 000 s at a read voltage of 100 mV. The multilevel memory effect can be attributed to the combination of the radial growth of filaments and the formation of conductive filaments when applying different compliance current values during the set process. The set and reset voltages of the ITO/Zn₂TiO₄/Pt RRAM device were maintained within ±1 V. The device performed well at low operation voltages. The mechanisms of multilevel resistive switching characteristics were investigated to illustrate the multilevel carrier conduction phenomenon associated with Zn₂TiO₄-based RRAM devices. In this study, our group illustrated the application of zinc titanate (Zn₂TiO₄) in non-volatile memories for the first time.

We discuss the fabrication procedure and device characteristics of ITO/Zn₂TiO₄/Pt resistive random-access memory (RRAM) at room temperature.     

Reliability and sensitivity analysis of double inverted-T nano-cavity label-free Si:HfO2 ferroelectric junctionless TFET biosensors

In this work, we propose and simulate an ultrasensitive, label-free, and charge/dielectric modulated Si:HfO₂ ferroelectric junctionless tunnel field effect transistor (FE-JL-TFET) based biosensor. The proposed sensing device employs a dual inverted-T cavity and uses ferroelectric gate stacking of Si-doped HfO₂, a key enabler of negative capacitance (NC) behavior. The two cavities are carved in gate-source underlap regions by a sacrificial etching technique to sense biomolecules such as streptavidin (2.1), bacteriophage T7 (6.3) and gelatin (12). Two dimensional (2D) calibrated simulations have been performed and the impact of various device parameters, including cavity length and height, on various performance measuring parameters has been studied. It has been observed that the biosensor exhibits better sensitivities for both neutral and charged biomolecules. The maximum values of the I_ON/I_OFF sensitivity for the neutral, positively charged and negatively charged biomolecules are as high as 3.77 × 10⁹, 5.85 × 10⁹, and 1.72 × 10¹⁰, respectively. It has been observed that optimizing the cavity length and height can significantly improve the sensing capability of the proposed device. The comparative analysis of the proposed biosensor and other state of the art biosensors shows a significant improvement in the sensitivity (10¹ to 10⁶ times) in the proposed biosensor. The detrimental effect of interface trapped charges on the biosensor performance is also analyzed in detail.

We propose and simulate an ultrasensitive, label-free, and charge/dielectric modulated Si:HfO₂ ferroelectric junctionless tunnel field effect transistor (FE-JL-TFET) based biosensor.     

Improved resistive switching characteristics of a multi-stacked HfO2/Al2O3/HfO2 RRAM structure for neuromorphic and synaptic applications: experimental and computational study

Atomic Layer Deposition (ALD) was used for a tri-layer structure (HfO₂/Al₂O₃/HfO₂) at low temperature over an Indium Tin Oxide (ITO) transparent electrode. First, the microstructure of the fabricated TaN/HfO₂/Al₂O₃/HfO₂/ITO RRAM device was examined by the cross-sectional High-Resolution Transmission Electron Microscopy (HRTEM). Then, Energy Dispersive X-ray Spectroscopy (EDS) was performed to probe compositional mapping. The bipolar resistive switching mode of the device was confirmed through SET/RESET characteristic plots for 100 cycles as a function of applied biasing voltage. An endurance test was performed for 100 DC switching cycles @0.2 V wherein; data retention was found up to 10⁴ s. Moreover, for better insight into the charge conduction mechanism in tri-layer HfO₂/Al₂O₃/HfO₂, based on oxygen vacancies (V_OX), total density of states (TDOS), partial density of states (PDOS) and isosurface three-dimensional charge density analysis was performed using WEIN2k and VASP simulation packages under Perdew–Burke–Ernzerhof _Generalized Gradient approximation (PBE-GGA). The experimental and theoretical outcomes can help in finding proper stacking of the active resistive switching (RS) layer for resistive random-access memory (RRAM) applications.

Atomic Layer Deposition (ALD) was used for a tri-layer structure (HfO₂/Al₂O₃/HfO₂) at low temperature over an Indium Tin Oxide (ITO) transparent electrode.     

Resistive switching of the HfOx/HfO2 bilayer heterostructure and its transmission characteristics as a synapse

In this work, HfO_x/HfO₂ homo-bilayer structure based resistive random access memory devices were fabricated, and the resistive switching characteristics of the devices were investigated. The samples with an Ar/O₂ ratio of 12 : 2 exhibited improved switching performance including better uniformity, endurance and retention, which was selected to imitate the “learning” and “forgetting” function of biological synapses. The multilevel conductance of the HfO_x/HfO₂ homo-bilayer structure under the model of pulse voltage suggests its potential to emulate the nonlinear transmission characteristics of the synapse, and a model of multilevel conductance of the HfO_x/HfO₂ homo-bilayer structure was proposed. The device conductance continuously increases (decreases) in accordance with the number of positive (negative) voltage pulses during the potentiation (depression) process, which can emulate the change of synaptic weight in a biological synapse.

In this work, HfO_x/HfO₂ homo-bilayer structure based resistive random access memory devices were fabricated, and the resistive switching characteristics of the devices were investigated.     

Fabrication of low-density carbon-bonded carbon fiber composites with an Hf-based coating for high temperature applications

A novel Hf-based anti-oxidation coating has been prepared on the surface of low-density carbon-bonded carbon fiber composites (CBCFs). The coating exhibits a gradient transition structure, with mainly HfB₂, Hf₂Si and SiC ceramics. Oxyacetylene torch testing has been utilized to evaluate the ablation resistance under the condition ranging from 1.6 MW m⁻² to 2.2 MW m⁻² for 300 s. The experimental results show that the as-prepared Hf-based coating can effectively protect CBCFs under high-temperature oxidation conditions. The surface maximum temperature can reach 1616–2037 °C, and the mass ablation rates vary from −3.5 × 10⁻⁵ g s⁻¹ cm⁻² to 1.5 × 10⁻⁵ g s⁻¹ cm⁻². The formation of a dense SiO₂ glass layer embedded with HfO₂ grains or particle accumulation in the HfO₂ layer is responsible for the good ablation resistance.

A novel low-density CBCF composite with an Hf-based coating was designed and prepared, which exhibited a good ablation resistance at the maximum temperature range of 1616–2037 °C for 300 s.     

Polymer–carbon dot hybrid structure for a self-rectifying memory device by energy level offset and doping

A strategy for self-rectifying memory diodes based on a polymer–carbon dot hybrid structure, with a configuration of rGO/PEDOT : PSS/carbon dots/MEH-PPV/Al, has been proposed. The fabricated device exhibits a rectification of 10³ in the rectification model and an ON/OFF current ratio of 121 in the memory model. The rectifying behavior was attributed to an energy level offset between the electrodes and the bilayer polymers and the memory effect was induced by carrier trapping of carbon dots within the polymers.

A strategy for self-rectifying memory diodes based on a polymer–carbon dot hybrid structure, with a configuration of rGO/PEDOT : PSS/carbon dots/MEH-PPV/Al, has been proposed.

Polymer-based resistive switching memory devices, as ideal candidates for future emerging memory devices, have attracted a great deal of attention due to their simple structure, tunable properties, high-density integration, low-power consumption, facile fabrication process, and low-cost potential.^1–4 Generally, a cross-bar architecture in memory arrays has been designed to achieve high-density data storage.^5–8 However, the sneaking current issue, which is caused by a cross-talk effect in the cross-bar array, results in a misreading of a cell in a high resistance state (HRS) when the neighboring cells are in a low resistance state (LRS).^9–13 To alleviate the sneaking current issue, great effort has therefore been devoted to the search for a memory device with a rectifying effect. For example, the architecture of one diode-one resistor (1D1R) or one transistor-one resistor (1T1R) can improve reading accessibility in an integrated memory array structure.^11,12,14,15 However, they still suffer from limitations of complex device structure, fabrication process, low yield and high energy consumption,¹⁶ which could be circumvented by creating a self-rectifying memory device with a simple sandwich architecture and solution process fabrication.Self-rectifying memory devices with metal/insulator/metal structure have risen as an important class of memory technology in high density data storage. Numerous transition metal oxide materials, e.g., Cr-doped SrTiO₃,¹⁶ Pr_0.7Ca_0.3MnO₃ (PCMO),¹⁷ ZrO₂,¹⁸ TiO₂,¹⁹ HfO_2−X,^20,21 and TaO_X,²² and Si-based materials, e.g., a-Si^23,24 and Si₃N₄,²⁵ can serve as the insulator layer and exhibit excellent self-rectifying memory features such as short switching time, large resistance ratio, and good retention ability. Unfortunately, most devices are fabricated by traditional film plating technology such as pulsed laser deposition, electron beam deposition, sputtering deposition and thermal evaporation, leading to very complicated process. Nowadays, polymer rectifying devices by energy level offset^26,27 and memory devices by doping method^28,29 have been widely fabricated, with the merit of solution process. Therefore, combining energy level offset and doping technique in solution processed polymer diodes are anticipated to achieve self-rectifying memory performance.In this letter, we reported a solution processed polymer–carbon dots hybrid structure for self-rectifying memory device by energy level offset and doping method, with a configuration of reduced graphene oxide (rGO)/poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS)/carbon dots/poly(2-methoxy-5(2′-ethyl)hexyloxy-phenylenevinylene) (MEH-PPV)/Al. Bilayer PEDOT : PSS and MEH-PPV are used as the rectifying active layers due to their energy level offset with electrodes. Carbon dots are doped as the memory active layer due to their carrier trapping behavior within polymers. rGO film as bottom electrode and Al as top electrode are fabricated by thermal annealing and thermal evaporation, respectively. The fabricated device in a 6 × 6 cross-bar array exhibits rectifying function with a rectifying ratio of 10³, and also possesses stable memory effect with a minimum ON/OFF current ratio of 121. Our strategy is promising for preparation of other polymer–nanoparticle hybrid structures for self-rectifying memory devices.The self-rectifying memory devices were fabricated basing on a facial solution-based process as shown in Fig. 1. The patterned rGO electrodes with a square resistance of 1 kΩ sq⁻¹ were fabricated from solution-processed GO films via an oxygen-plasma etching approach.^30,31 A 30 nm-thick PEDOT : PSS layer was spin-coated on rGO electrode surface, then treated with 20 W oxygen-plasma for 20 s, followed by thermal annealing in air at 120 °C for 20 min. The carbon dots aqueous with a concentration of 3 mg ml⁻¹ was spin-coated onto PEDOT : PSS layer at 3000 rpm and subsequently annealed at 100 °C for 20 min. Subsequently, a 30 nm-thick MEH-PPV layer was spin-coated and then annealed in a N₂ gas environment at 70 °C for 30 min. Finally, 6 Al lines of 500 μm in width were deposited perpendicularly to rGO lines, through a shadow mask via thermal evaporation. Electrical properties of the as-fabricated devices were investigated using a semiconductor parameter analyzer (Keithley 4200) in the ambient environment.Open in a separate windowFig. 1Schematic diagrams of the fabrication process for rGO/PEDOT : PSS/carbon dots/MEH-PPV/Al self-rectifying memory devices.To illuminate that the memory effect is caused by the carrier trapping effect of carbon dots, the rectifying device without carbon dots was fabricated and characterized (Fig. 2(a)). The current–voltage (I–V) characteristics of the rectifying diode device are shown in Fig. 2(b). Basing on optimal fabrication conditions, the rectifying diode device with the optimized structure exhibited a maximum rectification ratio (RR) of ∼10³ following RR = |I_forward/I_reverse (here – I(V−)/I(V+))|.³² This rectifying effect is attributed to the Schottky barrier between Al electrode and MEH-PPV layer when a negative bias is applied to the rGO electrode. As is shown in the energy band diagram (Fig. 2(c)), the work function of rGO and Al is 4.8 eV and 4.3 eV, respectively. The highest occupied molecular orbital (HOMO) of PEDOT : PSS and MEH-PPV occurs at 5.2 and 5.1 eV, respectively. In this case, during the positive voltage sweep, holes from the rGO electrode can be efficiently injected into the HOMO of PEDOT : PSS layer with a 0.4 eV barrier height. On the other hand, when applying a negative voltage, it''s difficult to realize the injection of holes from Al electrode to the LUMO of MEH-PPV layer due to a large barrier height up to 0.8 eV.Open in a separate windowFig. 2(a) Schematic structure, (b) typical I–V characteristics and (c) energy band diagram of the rectifying device. (d) Schematic structure, (e) typical I–V characteristics (the arrows represent the sweep directions) and (f) energy band diagram of the rectifying memory device.To obtain the self-rectifying memory effect, carbon dots are introduced as the memory active layer due to their carrier trapping behavior within polymers (Fig. 2(d)). Carbon dots were prepared by pyrolyzing citric acid as described elsewhere.³³ The UV-vis absorption and PL spectra of carbon dot are demonstrated in Fig. 3(a), from which an apparent UV-vis absorption band centered at 335 nm is observed and the maximum PL emission occurs at a wavelength of 445 nm, suggesting their semiconductor properties. High quality TEM image shows that carbon dots have a diameter of ∼4 nm (Fig. 3(b)), suggesting their strong ability to capture charges. Moreover, current–voltage (I–V) characteristics of the self-rectifying memory device are investigated and demonstrated in Fig. 2(e). When a negative bias was initially applied to the rGO bottom electrode, the device exhibited a high resistance state (HRS, namely OFF state). By applying a low positive voltage, the holes injected from rGO electrode were captured by carbon dots, the carbon dots served as trap centers due to the boundary and quantum confinement effect.³⁴ With the increase of sweep voltage, the injected carriers increase rapidly and the traps were nearly filled. When the power supply approaches the threshold voltage, the traps were filled completely, the device underwent a resistive switching from HRS to low resistance state (LRS, namely ON state). The device maintained a LRS with trap filling when the voltage swept from 4 to 0 V. The device exhibits rectifying effect at LRS due to the Schottky effect coming from the bilayer''s energy level offset with electrodes. When the power was turned off, the captured charges might be released from the trap centers due to the shallow traps of carbon dots and the device returned to HRS.Open in a separate windowFig. 3(a) UV-vis absorption and PL spectra of the carbon dots. (b) TEM image of the carbon dots.The performance of the self-rectifying memory devices was evaluated under ambient conditions. Fig. 4(a) shows the typical I–V characteristics of the self-rectifying memory device under positive voltage sweep. The device could not maintain in the ON state steadily and it relaxed to the OFF state as once the power was removed, suggesting its volatile property. Fig. 4(b) shows the statistical distribution of ON-/OFF-state current (measured at 3 V) of the operative memory cells. The distribution of OFF- and ON-state current values lays within two orders of magnitude, the maximum currents at ON state and OFF state are about 10⁻⁴ and 10⁻⁷ A, respectively, with a ON/OFF current ratio of 10² to 10³ : 1, reducing the misreading probability during the operation process. We also measured 40 randomly selected memory cells to evaluate the uniform distribution of switching threshold voltages, as shown in Fig. 2(c). The memory cells demonstrate an average value nearly 3 V of switching voltage. The retention time of the ON and OFF state with a continuous 3 V is measured in Fig. 4(d). The ON state can be maintained by applying a refreshing pulse of 4 V every 5 s, a slightly degradation was observed at the beginning and underwent stable with an ON/OFF current ratio of 30. The curves of first sweep in Fig. 4(e) and (f) indicated that both devices with the same structure basing on rGO electrode and ITO electrode can realize the self-rectifying memory effect, even though the former one exhibits higher endurance stability. After 100 consecutive voltage sweeps, the rectifying ratio of rGO/PEDOT : PSS/carbon dots/MEH-PPV/Al device still maintains 10² (Fig. 4(e)). Simultaneously, the ON/OFF ratio of the device at 3 V remained approximately 36. In contrast, the phenomenon of rectifier and memory gradually disappeared after six consecutive voltage sweeps for ITO based devices (Fig. 4(f)). This performance degradation was caused by the unstable property of the ITO/PEDOT : PSS interface in ambient environment. The acidic PEODT : PSS solution can etch ITO during the polymer spin-coating process, and hydrolysis of deposited PEDOT : PSS via moisture absorption can also etch ITO.³⁵ On the contrary, rGO electrodes are physically, chemically and electrically stable in ambient environment, guaranteeing a higher endurance stability of self-rectifying memory devices with rGO electrode.Open in a separate windowFig. 4(a) Typical I–V curves of the rGO/PEDOT : PSS/carbon dots/MEH-PPV/Al device. (b) Statistical distribution of the ON-/OFF-state currents measured at 3 V. (c) Statistics histograms of switching voltages of the rGO/PEDOT : PSS/carbon dots/MEH-PPV/Al devices from 40 memory cells. (d) Retention time for the rGO/PEDOT : PSS/carbon dots/MEH-PPV/Al device under a continuous positive bias stress. (e) Cycle endurance test of the rGO/PEDOT : PSS/carbon dots/MEH-PPV/Al device. (f) Cycle endurance test of the ITO/PEDOT : PSS/carbon dots/MEH-PPV/Al device. The arrows represent the sweep directions.In summary, a self-rectifying polymer memory device with the configuration of rGO/PEDOT : PSS/carbon dots/MEH-PPV/Al has been designed and fabricated through solution process. The memory effect of the as-fabricated device is attributed to the carrier trapping effect of carbon dots within polymers and the corresponding rectifying characteristic comes from the bilayer''s energy level offset with electrodes. The self-rectifying memory device exhibits a maximum rectification of 10³ in rectify model and a minimum ON/OFF current ratio of 121 in memory model. Moreover, the devices show high endurance stability of self-rectifying memory effect with rGO electrode compared to that with ITO electrode. Importantly, the solution process fabrication make this device extremely simple. Because of the self-rectifying memory feature, the simple devices have great potential application in cross-bar structure memory for high-density data storage.     

Study on the selective hydrogenation of isophorone

3,3,5-Trimethylcyclohexanone (TMCH) is an important pharmaceutical intermediate and organic solvent, which has important industrial significance. The selective hydrogenation of isophorone was studied over noble metal (Pd/C, Pt/C, Ir/C, Ru/C, Pd/SiO₂, Pt/SiO₂, Ir/SiO₂, Ru/SiO₂), and non-noble metal (RANEY® Ni, RANEY® Co, RANEY® Cu, RANEY® Fe, Ni/SiO₂, Co/SiO₂, Cu/SiO₂, Fe/SiO₂) catalysts and using solvent-free and solvent based synthesis. The results show that the solvent has an important effect on the selectivity of TMCH. The selective hydrogenation of isophorone to TMCH can be influenced by the tetrahydrofuran solvent. The conversion of isophorone is 100%, and the yield of 3,3,5-trimethylcyclohexanone is 98.1% under RANEY® Ni and THF. The method was applied to the selective hydrogenation of isopropylidene acetone, benzylidene acetone and 6-methyl-5-ene-2-heptanone. The structures of the hydrogenation product target (4-methylpentan-2-one, 4-benzylbutan-2-one and 6-methyl-heptane-2-one) were characterized using ¹H-NMR and ¹³C-NMR. The yields of 4-methylpentan-2-one, 4-benzylbutan-2-one and 6-methyl-heptane-2-one were 97.2%, 98.5% and 98.2%, respectively. The production cost can be reduced by using RANEY® metal instead of noble metal palladium. This method has good application prospects.

The selective hydrogenation of isophorone to TMCH can be influenced by the tetrahydrofuran solvent. The conversion of isophorone is 100%, and the yield of 3,3,5-trimethylcyclohexanone is 98.1% under RANEY® Ni and THF.     

Bistable electrical switching and nonvolatile memory effects by doping different amounts of GO in poly(9,9-dioctylfluorene-2,7-diyl)

Poly(9,9-dioctylfluorene-2,7-diyl) (PFO) was synthesized under a Suzuki coupling reaction, and its structure was proved by Fourier transform infrared (FT-IR) spectroscopy, and hydrogen and carbon nuclear magnetic resonance (¹H-NMR and ¹³C-NMR). A nonvolatile organic memristor, based on active layers of PFO and PFO:GO composite, was prepared by spin-coating and the influence of GO concentration on the electrical characteristics of the memristor was investigated. The results showed that the device had two kinds of conductance behavior: electric bistable nonvolatile flash memory behavior and conductor behavior. With an increase in GO concentration, the device has an increased ON/OFF current ratio, increasing from 2.1 × 10¹ to 1.9 × 10³, a lower threshold voltage (V_SET), decreasing from −1.1 V to −0.7 V, and better stability. The current remained stable for 3 hours in both the ON state and OFF state, and the ON and OFF state current of the device did not change substantially after 9000 read cycles.

The device shows different conductive behavior: electric bistable nonvolatile flash memory behavior and conductor behavior.     

Interfacial synthesis of a large-area coordination polymer membrane for rewritable nonvolatile memory devices

The facile synthesis of large-area coordination polymer membranes with controlled nanoscale thicknesses is critical towards their applications in information storage electronics. Here, we have reported a facile and substrate-independent interfacial synthesis method for preparing a large-area two-dimensional (2D) coordination polymer membrane at the air–liquid interface. The prepared high-quality 2D membrane could be transferred onto an indium tin oxide (ITO) substrate to construct a nonvolatile memory device, which showed reversible switching with a high ON/OFF current ratio of 10³, good stability and a long retention time. Our discovery of resistive switching with nonvolatile bistability based on the substrate-independent growth of the 2D coordination polymer membrane holds significant promise for the development of solution-processable nonvolatile memory devices with a miniaturized device size.

Stable nonvolatile memory devices with a high ON/OFF current ratio have been realized based on a large-area two-dimensional coordination polymer membrane.

The exponential growth of communication for information and the miniaturization of electronic devices have caused an urgent demand for the design and preparation of new memory materials and devices.^1–4 Organic/polymer memory devices have attracted considerable attention as promising alternatives to the conventional inorganic semiconductor-based memory devices.⁵ They have distinguished themselves as potential candidates for flexible and high-density data storage due to their low cost, structural tenability, mechanical strength, flexibility, and ease of processing.^6–16 Nonetheless, the intrinsically weak intermolecular interactions between organic molecules result in low thermal stability and poor long-term environmental stability, which hinder their potential applications.^17–19As an important class of organic materials, coordination polymers demonstrate attractive switching properties and exhibit promising applications in the data storage field.^20–22 Compared with polymers that have pure organic skeletons, coordination polymers comprising metal and organic ligands offer a potential alternative due to their facile preparation and high thermal stability, combining the advantages of both polymers and metal complexes. Particularly, by the flexible design of metal and organic constituents as well as by modifying the functional groups in the coordination complexes, the properties of memory devices based on the resultant coordination polymers can be fine-tuned.¹⁵ For instance, ternary resistive random access memory devices have been fabricated from one-dimensional conjugated coordination polymer chains coordinated with Co ions,²³ which exhibit excellent thermal and long-term stability benefiting from their strong intermolecular interactions. Moreover, the successful growth of high-quality metal–organic framework (MOF) membranes on flexible gold-coated polyethylene terephthalate (PET) substrates has been achieved by liquid phase epitaxy for practical wearable information storage applications; moreover, a uniform and reproducible resistive switching effect has been observed.²⁴Besides molecular design, the formation of the thin films of active materials is crucial for the memory performance and coordination polymers downsized to nanoscale membranes with controllable electrical conductivity are promising for high-density data storage with a miniaturized device size. To date, vacuum-deposited, spin-coated or inkjet-printed films of the as-synthesized memory materials have been reported for memory applications.²⁵ Unfortunately, severe problems such as easy cracking, unsatisfactory uniformity and thickness uncontrollability usually accompany the above-mentioned elaborate membrane deposition approaches, seriously limiting the memory performance. To address these issues, the growth and preparation of high-quality memory material membranes through facile chemical synthesis has been an urgent demand. Currently, liquid phase epitaxy or a layer-by-layer (LbL) approach is commonly used to grow high-quality coordination polymer membranes on organically functionalized surfaces for memory devices.²⁶ Memory devices based on LbL approach-processed coordination polymer membranes have been reported to show excellent switching performance with a high ON/OFF current ratio and multilevel storage. Though the LbL approach offers unique opportunities, the substrate-dependent characteristics of the LbL thin-film preparation scheme seriously limit the applications of coordination polymers in memory devices. Despite the above-mentioned advances, coordination polymer membranes with an appropriate molecular design concomitant with a good film preparation approach are still urgently needed to obtain high-performance memory devices.In this work, we have presented a facile and substrate-independent interfacial synthesis method for the preparation of a continuous and large-area coordination polymer membrane with nanoscale thickness at the air–liquid interface. The high-quality two-dimensional (2D) membrane can be transferred onto an indium tin oxide (ITO) substrate as the active layer to construct a nonvolatile memory device. The sandwiched device shows excellent rewritable nonvolatile memory performance with a low operational voltage, a large ON/OFF ratio, good stability and a long retention time.Through a mild coordination reaction between a cobalt salt and the ligand 1,2,4,5-benzenetetramine tetrahydrochloride, a large-scale d–π conjugated coordination polymer membrane at the air–liquid interface can be prepared (Fig. 1). The resulting brown membrane demonstrates great substrate independence and can be transferred on to any substrate by dipping the support in the reaction solution and then lifting the membrane, making it practically applicable in diverse fields. The scanning electron microscopy (SEM) characterizations of the as-prepared membrane transferred onto the SiO₂/Si substrate indicated a large-scale and continuous distribution of the membrane with a uniform thickness of ∼300 nm.Open in a separate windowFig. 1(a) Illustration of the polymer membrane formation process at the interface. (b) Schematic of the polymer membrane at the air–liquid interface. (c) SEM images of the as-prepared membrane with a thickness of 300 nm.The structure of the as-prepared brown membrane was characterized by powder X-ray diffraction (PXRD) utilizing two individual scattering geometries, namely, out-of-plane scattering geometry and in-plane geometry. The PXRD profile obtained using grazing-incidence XRD is presented in Fig. 2a. Different diffraction patterns were observed under these two XRD scattering geometries, suggesting an orientation-dependent characteristic of the prepared membrane (Fig. 2b).²⁷ X-ray photoelectron spectroscopy (XPS) of the as-prepared membrane was conducted (Fig. 2c and S1^†). The strong peak at 399.1 eV suggests a strong coordination between Co(ii) and the ligand. The quantification of the elements present in the coordination polymer membrane based on XPS analysis demonstrated a 3.53 : 1 atomic ratio of N : Co (Table S1^†), which was close to the theoretical stoichiometric ratio (4 : 1) for the membrane structure, as shown in the inset of Fig. 2d; this further confirmed the strong coordination between one Co cation and two benzenetetramine groups of the organic ligand.²⁸ In addition, the characteristic N–H stretching mode of –NH₂ disappeared in the IR spectra after the reaction,²⁹ whereas the phenyl-related vibration remained, further indicating that the coordination reaction occurred (Fig. 2d). On the basis of facile preparation, substrate independence, highly oriented structure and d–π conjugation construction facilitating carrier transportation, the synthesized 2D coordination polymer membranes are expected to possess potential applications in electronic devices.Open in a separate windowFig. 2(a) The orientation of the films for (i) out-of-plane XRD scan and (ii) in-plane XRD scan. (b) PXRD profiles of out-of-plane XRD and in-plane XRD of the polymer membrane. (c) N 1s core level spectra of the membrane. (d) FT-IR spectra of the membrane and the ligand; the inset is the structure of the polymer membrane.With the use of the synthesized coordination polymer membrane as the active material layer, a typical memory device with the Al/polymer membrane/ITO sandwich structure was fabricated by directly transferring the as-prepared membrane with a thickness of 300 nm from the air–liquid interface onto the ITO substrate, followed by the thermal evaporation of the top Al electrodes (inset of Fig. 3a). The as-fabricated device exhibited progressively increasing injection currents as the initial voltage was swept from 0 to −5 V (ITO as the reference level, Sweep 1), and a sharp increase from 10⁻⁵ A to 10⁻² A was observed at a switching threshold voltage of −1 V (Fig. 3c), indicating the device transition from a high-resistance state (OFF state) to a low-resistance state (ON state). This electrical transition from OFF to ON states represents the “writing” process of the memory device. Significantly, the abrupt increase in the current level with a high current ratio of 10³ contributed to a minimal misreading error for the memory device and a small switching threshold voltage of −1 V was desirable for low-power memory applications. The device maintained the ON state with high stability in the subsequent voltage sweep (Sweep 2). When the voltage was swept from 0 to 5 V (Sweep 3), an abrupt decrease in the current was observed at the threshold voltage of about 3 V and the transition from the ON state to OFF state was equivalent to the “erasing” process. Furthermore, the device maintained the OFF state with high stability in the subsequent voltage sweep (Sweep 4). The current–voltage curve sweeps revealed an integrated write-read-erase-read switching process of this memory cell, suggesting a typical nonvolatile bistable FLASH-type memory device.Open in a separate windowFig. 3(a) I–V curves of the Al/polymer membrane/ITO memory device. Inset: schematic of the device structure. (b) Retention ability test of the device at a reading voltage of −0.5 V in the HRS and LRS states. (c) The ON/OFF ratio of the device under different applied voltages. (d) Currents of the device in the ON and OFF states. (e) Statistic histograms of SET/RESET voltages. (f) The cell area dependence of resistances in HRS and LRS.Moreover, the long-term stability of the coordination polymer memory device was evaluated from the retention time tests in both the ON and OFF states (Fig. 3b). Under a constant voltage stress of 0.5 V, the OFF state current remained stable but with some slight variations. When a bias of −0.5 V was applied, the device exhibited a stable current of about 0.04 A (ON state) for up to 10 000 s and no significant decrease was observed. A high ON/OFF current ratio of 10³ was maintained and the precise control of both ON and OFF states promised a quite low misreading rate of the memory device. To evaluate the reliability of memory devices, their cycling endurance was investigated. Fig. 3d shows that the OFF state currents remain between 4 × 10⁻⁷ and 3 × 10⁻⁶ A and the ON state currents range from 3 × 10⁻³ to 6 × 10⁻³ A. According to the statistical current distribution (measured at −0.5 V), no significant difference was observed in the ON/OFF state currents, indicating the good stability of the device. Compared with the endurance of previously reported devices,^30,31 the endurance of our memory device is relatively short, which can be attributed to the fact that the top aluminum electrode is easily oxidized in an ambient environment without effective device packaging. It is expected that the device stability can be further improved if effective packaging is carried out or measurements are obtained in a vacuum system.The uniformity in the distribution of switching voltages was evaluated by measuring 100 randomly selected device cells. Fig. 3e shows that the V_SET values of most device cells are distributed in the range from 0 to −2 V and more than 50% devices exhibit a switching threshold voltage from 0 to −1 V. The average values of V_SET and V_RESET were −0.89 V and 3.09 V (the standard deviations were 0.26 (V_SET) and 0.41(V_RESET)), respectively, which coincided well with the measured results of the as-fabricated FLASH memory device. Notably, the difference between V_SET and V_RESET was large enough to ensure a low misreading rate and promise reliability when a readout was made.Moreover, the dependence of the device resistance on the cell area was systematically studied based on a series of controlling tests to explore the underlying switching mechanism in the as-fabricated memory cell (Fig. 3f). When the applied voltage was in the range from 1 to −0.5 V, the memory cell was in a high resistance state (HRS) and the resistance (RHRS) was inversely proportional to the cell area due to the homogeneous current flowing through the memory cell.³² In contrast, for the low-resistance state (LRS) from 0 to 0.5 V, RLRS was independent of the cell area, suggesting that the LRS was dominated by the localized conducting path.To investigate the resistance mechanism of the 2D coordination polymer membrane-based memory device, log I–log V plots were studied to analyze the carrier transport mechanism of the OFF and ON states (Fig. 4a and b). The fitting results reveal that the I–V curve of the flash memory device in the OFF state consists of two distinct linear regions, corresponding to the ohmic conduction mechanism and trap-limited space charge limited conduction (TL-SCLC) mechanism,^33–39 whereas the device in the ON state only obeys the ohmic conduction mechanism. The corresponding resistive switching phenomenon was further studied by exploring the transportation mechanism of charge carriers via physical models (Fig. 4c–f). When a bias voltage was applied to the Al electrode and the scanning voltage was low, the density of the injected charge carriers was lower than that of the free carriers generated by thermal excitation in the film, which contributed to most of the charge transportation. The corresponding I–V curve shows linear behavior governed by ohmic conduction, resulting in a high resistance state (Fig. 4c). With the increase in the applied bias voltage, space charges appeared and some traps in the dielectric layer were occupied by the injected free carriers, leading to SCLC with limited trap filling dominating the carrier transport process, and the charge transport mechanism was dominated by TL-SCLC (Fig. 4d). With increasing carriers injected, the carrier transport changed from a trap-limited stage to a trap-free stage. When all the traps were filled, the injected carriers could move freely in the dielectric layer, which corresponded to trap-free SCLC conduction, indicating that the device underwent a transition from HRS to LRS. When the device changed to a low resistance state, the charge transfer still followed the ohmic conduction mechanism (Fig. 4f). The RESET process where the device changed from LRS to HRS (Fig. 4b) showed an I ∝ V relationship in the low resistance state, indicating that ohmic conduction dominated the charge transport process. As the device transfer to HRS, the trap center releases charges from a fully filled state to an unfilled state which shows a I ∝ V² relationship. Then the state is continuously dominated by ohmic conduction. The device exhibited typical non-volatile flash characteristics, affording new ways to achieve 2D coordination polymer membrane-based memory devices via interfacial nanostructure engineering.Open in a separate windowFig. 4(a) Fitted I–V curves of the memory device at the SET process. (b) Fitted I–V curves of the memory device at the RESET process. (c–f) Transportation mechanisms of charge carriers from low conductive state to intermediate conductive state and further to high conductive state.     

High-throughput growth of HfO2 films using temperature-gradient laser chemical vapor deposition

The use of hafnia (HfO₂) has facilitated recent advances in high-density microchips. However, the low deposition rate, poor controllability, and lack of systematic research on the growth mechanism limit the fabrication efficiency and further development of HfO₂ films. In this study, the high-throughput growth of HfO₂ films was realized via laser chemical vapor deposition using a laser spot with a large gradient temperature distribution (100 K mm⁻¹), in order to improve the experimental efficiency and controllability of the entire process. HfO₂ films fabricated by a single growth process could be divided into four regions with different morphologies, and discerned for deposition temperatures increasing from 1300 K to 1600 K. The maximum deposition rate reached 362 μm h⁻¹, which was 10² to 10⁴ times higher than that obtained using existing deposition methods. The dielectric constants of high-throughput HfO₂ films were in the range of 16–22, which satisfied the demand of replacing the traditional SiO₂ layer for a new generation of microchips.

In this study, HfO₂ films were grown using a highly efficient HT-LCVD process with a large gradient (100 K mm⁻¹) temperature field, achieving four novel microstructures which appeared simultaneously on a high-throughput sample.     

Impact of Zr top electrode on tantalum oxide-based electrochemical metallization resistive switching memory: towards synaptic functionalities

Electrochemical metallization memory (ECM) devices have been made by sub-stoichiometric deposition of a tantalum oxide switching film (Ta₂O_5−x) using sputtering. We investigated the influence of zirconium as the active top electrode material in the lithographically fabricated ECM devices. A simple capacitor like (Pt/Zr/Ta₂O_5−x/Pt) structure represented the resistive switching memory. A cyclic voltammetry measurement demonstrated the electrochemical process of the memory device. The I–V characteristics of ECMs show stable bipolar resistive switching properties with reliable endurance and retention. The resistive switching mechanism results from the formation and rupture of a conductive filament characteristic of ECM. Our results suggest that Zr can be considered a potential active electrode in the ECMs for the next generation of nonvolatile nanoelectronics. We successfully showed that the ECM device can work under AC pulses to emulate the essential characteristics of an artificial synapse by further improvements.

Zr is a potential active electrode in the electrochemical metallization cells (ECMs) for the next generation of nonvolatile nanoelectronics. The ECM device works under AC pulses to emulate the essential characteristics of an artificial synapse.     

Ag decorated silica nanostructures for surface plasmon enhanced photocatalysis

In this article, we present a novel synthesis of mesoporous SiO₂/Ag nanostructures for dye (methylene blue) adsorption and surface plasmon mediated photocatalysis. Mesoporous SiO₂ nanoparticles with a pore size of 3.2 nm were synthesized using cetyltrimethylammonium bromide as a structure directing agent and functionalized with (3-aminopropyl)trimethoxysilane to introduce amine groups. The adsorption behavior of non-porous SiO₂ nanoparticles was compared with that of the mesoporous silica nanoparticles. The large surface area and higher porosity of mesoporous SiO₂ facilitated better adsorption of the dye as compared to the non-porous silica. Ag decorated SiO₂ nanoparticles were synthesized by attaching silver (Ag) nanoparticles of different morphologies, i.e. spherical and triangular, on amine functionalized silica. The photocatalytic activity of the mesoporous SiO₂/Ag was compared with that of non-porous SiO₂/Ag nanoparticles and pristine Ag nanoparticles. Mesoporous SiO₂ nanoparticles (k_d = 31.3 × 10⁻³ g mg⁻¹ min⁻¹) showed remarkable improvement in the rate of degradation of methylene blue as compared to non-porous SiO₂ (k_d = 25.1 × 10⁻³ g mg⁻¹ min⁻¹) and pristine Ag nanoparticles (k_d = 19.3 × 10⁻³ g mg⁻¹ min⁻¹). Blue Ag nanoparticles, owing to their better charge carrier generation and enhanced surface plasmon resonance, exhibited superior photocatalysis performance as compared to yellow Ag nanoparticles in all nanostructures.

In this article, we present a novel synthesis of mesoporous SiO₂/Ag nanostructures for dye (methylene blue) adsorption and surface plasmon mediated photocatalysis.     

ALD Al2O3 gate dielectric on the reduction of interface trap density and the enhanced photo-electric performance of IGO TFT

The amorphous indium gallium oxide thin film transistor was fabricated using a cosputtering method. Two samples with different gate dielectric layers were used as follows: sample A with a SiO₂ dielectric layer; and sample B with an Al₂O₃ dielectric layer. The influence of the gate dielectrics on the electric and photo performance has been investigated. Atomic layer deposition deposited the dense film with low interface trapping density and effectively increased drain current. Therefore, sample B exhibited optimal parameters, with an I_on/I_off ratio of 7.39 × 10⁷, the subthreshold swing of 0.096 V dec⁻¹, and μ_FE of 5.36 cm² V⁻¹ s⁻¹. For ultraviolet (UV) detection, the UV-to-visible rejection ratio of the device was 3 × 10⁵, and the photoresponsivity was 0.38 A W⁻¹ at the V_GS of −5 V.

The amorphous indium gallium oxide thin film transistor was fabricated using a cosputtering method.     

Intense-pulsed-UV-converted perhydropolysilazane gate dielectrics for organic field-effect transistors and logic gates

We fabricated a high-quality perhydropolysilazane (PHPS)-derived SiO₂ film by intense pulsed UV irradiation and applied it as a gate dielectric layer in high-performance organic field-effect transistors (OFETs) and complementary inverters. The conversion process of PHPS to SiO₂ was optimized by varying the number of intense pulses and applied voltage. The chemical structure and gate dielectric properties of the PHPS-derived SiO₂ films were systematically investigated via Fourier transform infrared spectroscopy and leakage current measurements, respectively. The resulting PHPS-derived SiO₂ gate dielectric layer showed a dielectric constant of 3.8 at 1 MHz and a leakage current density of 9.7 × 10⁻¹² A cm⁻² at 4.0 MV cm⁻¹. The PHPS-derived SiO₂ film was utilized as a gate dielectric for fabricating benchmark p- and n-channel OFETs based on pentacene and N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C₈), respectively. The resulting OFETs exhibited good electrical properties, such as carrier mobilities of 0.16 (±0.01) cm² V⁻¹ s⁻¹ (for the pentacene OFET) and 0.02 (±0.01) cm² V⁻¹ s⁻¹ (for the PTCDI-C₈ OFET) and an on–off current ratio larger than 10⁵. The fabrication of the PHPS-derived SiO₂ gate dielectric layer by a simple solution process and intense pulsed UV irradiation at room temperature serves as a novel approach for the realization of large-area flexible electronics in the flexible device industry of the future.

We fabricated a high-quality perhydropolysilazane (PHPS)-derived SiO₂ film by intense pulsed UV irradiation and applied it as a gate dielectric layer in high-performance organic field-effect transistors (OFETs) and complementary inverters.     

Homogeneous and highly dispersed Ni–Ru on a silica support as an effective CO methanation catalyst

The highly dispersed SiO₂-supported nickel-based catalysts for CO methanation were prepared by an ethylene glycol (EG) modified wet-impregnation method. The results indicate that the highly dispersed 20Ni/SiO₂ (EG) catalyst realized good stability and higher catalytic activity than the catalyst obtained from a non-pretreated silica support (20Ni/SiO₂) in CO methanation, due to the smaller nickel particles and strong nickel–silica interaction. By the addition of a small amount of noble metal promoter (Ru, Pt, Pd), the catalytic activity for CO methanation was further improved dramatically and follows the order Ru > Pt > Pd. The added noble metal promoter enhanced the reduction of the nickel oxide by spill-over-hydrogen during reduction treatment, and provided more active species for the methanation reaction, resulting in 7 times higher CO conversion than the non-pretreated 20Ni/SiO₂ catalyst. The 20Ni–0.5Ru/SiO₂ (EG) catalyst presents superb catalytic performance in CO methanation with high activity (CO conv. 80.2%) as well as high methane selectivity (90.3%) at 275 °C without any deactivation during 50 h reaction. The obtained catalysts were characterized by XRD, TG/DTA, TEM, XPS, TPR, H₂ chemisorption, and in situ DRIFTS.

The highly dispersed SiO₂-supported nickel-based catalysts for CO methanation were prepared by an ethylene glycol (EG) modified wet-impregnation method.     

Facile preparation of 3D porous agar-based heteroatom-doped carbon aerogels for high-energy density supercapacitors

The fabrication of heteroatom-doped porous carbon materials with high electrical conductivity and large specific surface area via an environmentally friendly route is critical and challenging. Herein, nitrogen and oxygen co-doped agar porous carbon (APC) was developed for supercapacitors via a one-step carbonization method with agar as the raw material and ammonia as the activator and nitrogen source. APC outperformed pectin porous carbon, tamarind porous carbon, and the previously reported carbon-based supercapacitors with a high capacitance retention of 72% even from 0.5 A g⁻¹ to 20 A g⁻¹ and excellent cycling stability in 6 M KOH solution (retained after 10 000 cycles) with a rate of over 98.5%. Furthermore, the APC electrode-based symmetric device exhibited an impressive energy density of 20.4 W h kg⁻¹ and an ultra-high power density of 449 W kg⁻¹ in 1 M Na₂SO₄ electrolyte together with excellent cycling stability (103.2% primary capacitance retentivity after 10 000 cycles). This study offers a novel method for the synthesis of nitrogen heteroatom-doped hierarchical porous carbon materials for performance-enhanced energy storage devices.

N and O co-doped agar porous carbon (APC) as electrode materials exhibit excellent performance. A respectable energy density of 20.4 W h kg⁻¹ and an ultra-high power density of 449 W kg⁻¹, as well as excellent cycle stability in 1 M Na₂SO₄ electrolyte.     

At room temperature in water: efficient hydrogenation of furfural to furfuryl alcohol with a Pt/SiC–C catalyst

Selective hydrogenation of furfural (FAL) to furfuryl alcohol (FOL) is challenging because of many side reactions. The highly selective hydrogenation of FAL to FOL can be achieved over a Pt catalyst supported on nanoporous SiC–C composites even at room temperature in water. A Pt/SiC–C-200-H₂ catalyst, which had a Pt loading of 3 wt% and was reduced in flowing hydrogen at 500 °C after calcination in air at 200 °C for 2 h, furnished complete FAL conversion and over 99% selectivity to FOL at 25 °C under 1 MPa of hydrogen in water. The kinetic behaviour of the selective hydrogenation of FAL to FOL with the 3 wt% Pt/SiC–C-200-H₂ catalyst was also investigated and the turnover frequency (TOF) reached 1148 h⁻¹. Moreover, the Pt/SiC–C catalyst is more active than other Pt catalysts supported on ordered mesoporous carbon CMK-3, activated carbon, periodic mesoporous silica SBA-15 or Al₂O₃. Detailed characterization using XRD, N₂-sorption, SEM, TEM and XPS techniques reveals that the striking performance of the Pt/SiC–C catalyst can be attributed to the optimal metal-support interaction and the interfacial effect.

A Pt/SiC–C catalyst was proved to be active, selective and reusable for furfural hydrogenation to furfuryl alcohol at room temperature in neat water.     

Hydrodeoxygenation of 2,5-dimethyltetrahydrofuran over bifunctional Pt–Cs2.5H0.5PW12O40 catalyst in the gas phase: enhancing effect of gold

2,5-Dimethyltetrahydrofuran (DMTHF) is deoxygenated to n-hexane with >99% selectivity at mild conditions (90 °C, 1 bar H₂ pressure, fixed-bed reactor) in the presence of the bifunctional metal-acid catalyst Pt–CsPW comprising Pt and Cs_2.5H_0.5PW₁₂O₄₀ (CsPW), an acidic Cs salt of Keggin-type heteropoly acid H₃PW₁₂O₄₀. Addition of gold to the Pt–CsPW catalyst increases the turnover rate at Pt sites more than twofold, whereas the Au alone without Pt is not active. The enhancement of catalyst activity is attributed to PtAu alloying, which is supported by STEM-EDX and XRD analysis.

Addition of gold to the Pt–CsPW catalyst has an enhancing effect on the HDO of DMTHF, with a twofold increase of turnover rate at Pt sites.

Biomass-derived furanic compounds are of interest as a renewable feedstock, which can be processed into a range of value-added chemicals and green fuels via catalytic hydroconversion.^1–8 Hydrodeoxygenation (HDO) of furanic compounds using bifunctional metal–acid catalysis has been demonstrated to be an effective strategy to produce green fuels under mild conditions^3,4,6,8–12 and references therein. The HDO over bifunctional metal-acid catalysts is much more efficient compared to the reaction over monofunctional metal catalysts.^11,12 Previously, we have reported HDO of a wide range of oxygenates in the gas phase to produce alkanes in the presence of bifunctional catalysts comprising Pt, Ru, Ni and Cu as metal components and Keggin-type heteropoly acids, with their activity decreasing in the order Pt > Ru > Ni > Cu.^13,14 Pt–CsPW comprising Pt and strongly acidic heteropoly salt Cs_2.5H_0.5PW₁₂O₄₀ (CsPW) has been reported to be a highly efficient catalyst for the HDO of 2,5-dimethylfuran (DMF) and 2,5-dimethyltetrahydrofuran (DMTHF) to produce n-hexane with 100% yield at 90–120 °C and ambient pressure.^11,12 The HDO of DMTHF over Pt–CsPW occurs through a sequence of hydrogenolysis, dehydration and hydrogenation steps catalysed by Pt and proton sites of the bifunctional catalyst (Scheme 1). These include the ring opening of DMTHF to form 2-hexanol on Pt sites followed by its dehydration on proton sites of CsPW to hexene, which is finally hydrogenated to n-hexane on Pt sites.¹² It is the facile dehydration of the secondary alcohol intermediate that drives the HDO process forward.^11,12 The rate-limiting step is either the ring hydrogenolysis or 2-hexanol dehydration depending on the ratio of accessible surface metal and acid sites Pt/H⁺.¹² Other platinum group metals such as Pd, Ru and Rh, that have high selectivity to ring hydrogenation rather than ring hydrogenolysis,^2,7 have low activities in HDO of DMF and DMTHF.¹¹Open in a separate windowScheme 1Reaction pathway for hydrodeoxygenation of DMTHF over Pt–CsPW.Bimetallic PtAu and PdAu catalysts have been reported to have an enhanced performance in comparison to monometallic Pt and Pd catalysts,^15–31 for example, in hydrogenation,^16,21,29 hydrodesulphurisation,^27,28 oxidation,^22,24 isomerisation^15,19,30,31 and other reactions.^{17,18,20,25,26} The enhancement of catalyst performance by addition of gold can be attributed to geometric (ensemble) and electronic (ligand) effects of the constituent elements in PtAu and PdAu bimetallic species.^25,26Here we looked at the effect of Au on the performance of Pt–CsPW catalysts in the HDO of DMTHF in the gas phase (see the ESI for experimental details^†). The CsPW heteropoly salt is a well-known solid acid catalyst; it possesses strong proton sites, large surface area and high thermal stability (∼500 °C decomposition temperature).^9,32–34 Supported bimetallic catalysts PtAu/SiO₂ and PtAu/CsPW were prepared by co-impregnation of H₂PtCl₆ and HAuCl₃ onto SiO₂ and CsPW followed by reduction with H₂ at 250 °C (ESI^†). This method gives supported bimetallic PtAu nanoparticles of a random composition together with various Pt and Au nanoparticles.^15,16,31 Information about the catalysts studied is given in

Functionalization of polyacrylamide for nanotrapping positively charged biomolecules

Engineering new materials which are capable of trapping biomolecules in nanoscale quantities, is crucial in order to achieve earlier diagnostics in different diseases. This article demonstrates that using free radical copolymerization, polyacrylamide can be successfully functionalized with specific synthons for nanotrapping positively charged molecules, such as numerous proteins, through electrostatic interactions due to their negative charge. Specifically, two functional random copolymers, acrylamide/acrylic acid (1) and acrylamide/acrylic acid/N-(pyridin-4-yl-methyl)acrylamide (2), whose negative net charges differ in their water solutions, were synthetized and their ability to trap positively charged proteins was studied using myoglobin as a proof-of-concept example. In aqueous solutions, copolymer 1, whose net charge for a 100 chain fragment (Q_{pH 6}/M) is −1.323 × 10⁻³, interacted with myoglobin forming a stable monodisperse nanosuspension. In contrast, copolymer 2, whose value of Q_{pH 6}/M equals −0.361 × 10⁻³, was not able to form stable particles with myoglobin. Nevertheless, thin films of both copolymers were grown using a dewetting process, which exhibited nanoscale cavities capable of trapping different amounts of myoglobin, as demonstrated by bimodal AFM imaging. The simple procedures used to build protein traps make this engineering approach promising for the development of new materials for biomedical applications where trapping biomolecules is required.

Engineering new materials which are capable of trapping biomolecules in nanoscale quantities, is crucial in order to achieve earlier diagnostics in different diseases.