Yinyan Gong

University of Bristol | UB · School of Physics

Semiconductors have attracted great attention for surface‐enhanced Raman scattering (SERS) applications due to their rich variety, adjustable band structure, good chemical stability, and biocompatibility. However, their intrinsic weak SERS activity limited the further development of semiconductor substrates. Here, the α‐Fe 2 O 3 films with high { }...

Featuring its ultra-high sensitivity and molecule-specific detection ability, surface-enhanced Raman scattering (SERS) is suitable for rapid sensing of trace-level chemicals in biological, environmental, and agricultural samples. Although crystal facet junction...

The correlations between the experimental methods and catalytic activities are urgent to be defined for the design of highly efficient catalysts. In this work, a new oxygen evolution reaction electrocatalyst of high-entropy oxide (HEO) FeCoNiZrOx was designed and analyzed by experimental and theoretical methods. On account of the shortened coordina...

Crystal facet engineering is an effective strategy for precisely regulating the orientations and electrochemical properties of metal oxides. However, the contribution of each crystal facet to pseudocapacitance is still puzzling, which is a bottleneck that restricts the specific capacitance of metal oxides. Herein, α-MnO2 nanorods with different exp...

There are growing interests in the development of bifunctional semiconducting nanostructures for photocatalysis and real-time monitoring of degradation process on catalysts. Defect engineering is a low-cost approach to manipulating the properties of semiconductors. Herein, we prepared CuS nanoplates by a hydrothermal method at increasing amounts of...

Surface enhanced Raman spectroscopy (SERS) is a rapid and ultrasensitive analytical technique. For practical applications, it is highly desirable to explore metal/semiconductor hybrid substrates, which utilize the synergistic enhancement effects of plasmons and charge transfer (CT). Herein, we successfully fabricated Ag nanoparticles decorated ZnAl...

Semiconductors exhibit great potential as a surface enhanced Raman scattering (SERS) substrate due to their low cost, good stability and biocompatibility. However, the extensive application of semiconductors has been restricted by their intrinsically low SERS sensitivity. It is urgently required to design uniform metal oxide substrates with enhance...

Semiconductors have been extensively studied for SERS applications owing to the advantage of inexpensive, nontoxic and easy fabrication. However, the facile design of uniformity substrates with enhanced charge transfer and SERS activity are highly desirable. Herein, we reported the fabrication of Cu2O films with (100) and (111) facets exposed by ad...

The development of a physical factor to correlate the experimental methods and catalytic activity of catalysts is quite important for the design of highly-efficient catalysts. In this work, with the aid of our pre-designed correlation factor of d electron density, a new oxygen evolution reaction electrocatalyst of FeCoPO4 was designed on account of...

In recent, though lots of gas opto-sensing materials have been developed to detect toxic gases, the degradation of toxic gases quantitatively still cannot be separated from catalysts, a new type of opto-sensing material needs to be developed for realizing the dual-functions of quantitative detection and cyclic degradation. For this purpose, an armc...

The development of highly active and stable photocatalysts, an effective way to remediate environment pollution and alleviate energy shortages, remains a challenging issue. In this work, a CdIn2S4/In(OH)3 nanocomposite was deposited in-situ on NiCr-LDH nanosheets by a simple hydrothermal method, and the obtained CdIn2S4/In(OH)3/NiCr-LDH heterostruc...

Crystal facet engineering is an effective way to modulate the intrinsic physicochemical properties of metal oxide materials. It is crucial to improve the ratio and site density of active facet to enhance the pseudocapacitance of electrodes. In this work, we present a simple method by using ammonia as a structure-directing agent to increase the expo...

Graphitic carbon nitride (g-C3N4) is regarded as a favorable candidate of gas opto-sensing materials due to its active nitrogen atoms and unique photoelectric performances. To investigate the gas opto-sensing performances of layered g-C3N4 (L-g-C3N4) and armchair tubular g-C3N4 (T-g-C3N4), the toxic target gas molecules of CO and NO2 are confirmed...

Photovoltaic technology provides a promising approach for solar energy conversion. One significant factor limiting the efficiency is the poor light harvesting of solar energy, which is related to the mismatch between the energy distribution of photons and the absorption of semiconductor materials or dye. Light-conversion phosphors have been explore...

The low charge transfer efficiency of isolated semiconductors is an urgent challenge in the photocatalytic degradation of hazardous contaminants. In this work, CaIn2S4/MXene Ti3C2Tx Schottky heterojunctions are synthesized via a simple hydrothermal method and applied for tetracycline hydrochloride degradation and Cr(VI) reduction. Results show that...

Cation vacancies can bring numerous surprising characters due to its multifarious electron and orbit distribution. In this work, δ–MnO2 with alkali–ion (K, Na, Li) associated manganese (Mn) vacancies is fabricated by a simple hydrothermal reaction, and the correlation between their electronic structure and pseudocapacitance are systematically inves...

Metal-free catalyst with favorable advantages of nonpolluting, cost-effective and stable catalytic performances may be used in various redox reactions. In this paper, we design a series of C6H4NO2/g-C3N4 composites by combining a polar nitrobenzene molecule with g-C3N4 monolayer using density functional theory calculations. The electrocatalytic per...

The large work function difference between two semiconductors will effectively adjust the interfacial electronic distribution and catalytic performances of heterojunction. In this work, a novel t-ZrO2/g-C3N4 composite photocatalyst was prepared by integrating t-ZrO2 nanoparticle with graphitic carbon nitride (g-C3N4) film considering the large work...

Considering the flexible chemical composition, tunable electronic properties and unique two-dimensional structure of layered double hydroxides (LDHs), we constructed NiFe-LDH/Cu2O heterostructure photocatalysts. The photocatalytic performance of NiFe-LDH/Cu2O heterostructure photocatalysts was evaluated by methyl blue (MB) degradation and CO2 reduc...

Photocatalysis activated by visible light remains highly challenging. Here, we report novel MoSe2/ZnO/ZnSe (ZM) hybrids fabricated via a simple hydrothermal method for photocatalytic reduction of Cr(VI) under visible light irradiation. ZM hybrids show improved photocatalytic reduction ability under visible light irradiation compared to pure ZnO owi...

Metal-organic frameworks (MOFs), self-assembled by metal ions and organic ligands via coordination bonds, have been broadly reported as an ideal template or precursor to design and prepare porous nanostructured materials for battery application due to their high specific surface areas, porous structures and large pore volumes as well as diverse and...

Defect engineering is an effective way to modulate the intrinsic physicochemical properties of materials. In this work, δ‐MnO2 with oxygen vacancies is fabricated by a simple oxidation or reduction process, and the relationship between the electronic structure and pseudocapacitance is systematically studied through experimental analysis and theoret...

The development of hybrid supercapacitors is limited due to the low specific capacity of traditional carbon-negative materials. Herein, we synthesized two different Fe-based negative electrodes (FeOOH and Fe2O3), and the relationships between structures and capacitive properties of electrodes are systematically studied. Results demonstrate that the...

Exploiting efficient visible light active photocatalyst is a great challenge with potential applications such as environmental pollution and solar energy conversion. Herein, a series of CaIn 2 S 4 /WS 2 hybrids was fabricated via a simple hydrothermal method. WS 2 as cocatalyst increases the visible light absorption and separation efficient of char...

Fabrication of high–performance electrodes from waste biomass has attracted increasing attention among the energy storage and conversion field. In this work, we have synthesized nitrogen–doped activated carbon by a simultaneous pyrolysis/activation method from waste bones. It is found that the specific surface area and pore structure of as–synthesi...

Full solar spectrum active heterogenous photocatalysis for environmental applications remains highly challenging. Here we report the novel Cu 2 In 2 ZnS 5 /Gd 2 O 2 S:Tb (CG) hybrid photocatalysts via a facile solvothermal method for efficient Cr(VI) and CO 2 reduction. The narrow band gap energies of the CG hybrid photocatalysts synthesized via a...

Exploring full solar spectrum from ultraviolet (UV) to visible even the near infrared (NIR) wavelength responsive photocatalysts is one of greatly significant issues. Here we show the composite ZnS/RGO (reduced graphene oxide) prepared via a microwave-assisted method for efficient Cr(VI) reduction over the full solar spectrum for the first time. Th...

Exploring visible light active semiconductor photocatalysts is one of greatly significant issues. We show herewith the Bi2MoO6/SnO2 hybrid photocatalysts meet the requirement for degradation of organic contaminant. The Bi2MoO6/SnO2 displays better visible light catalytic activity than that of Bi2MoO6. SnO2 as co-catalyst can provide more active sit...

Due to their high persistence and ecotoxicity, developing a green and efficient approach to remove antibiotic residuals from aquatic environments becomes a challenging task. Efficient, visible light-active and reusable semiconductor photocatalyst is a promising solution to address this issue. In this work, Z-scheme CdTe/TiO2 heterostructure photoca...

Reduced graphene oxide (RGO) and NiS sheets cocatalysts modified CdS hybrid photocatalysts were successfully synthesized via a facile solvothermal method for photocatalytic water splitting. RGO and NiS as cocatalysts can remarkably improve the photocatalytic hydrogen evolution and photoelectronchemical activity. High hydrogen evolution rate with 14...

In this study, we investigate the synergetic effect of Ni(OH)2-decorated ZnxCd1-xS on photocatalytic performance. To explore the effect of ternary alloying and cocatalyst deposition on the structural, electronic, optical, and photocatalytic properties, a series of Ni(OH)2-ZnxCd1-xS nanocomposite photocatalysts with different x were synthesized and...

It is still a great challenge to develop efficient semiconductive photocatalysts responding to visible light radiation. We show an efficient ZnIn2S4/UiO-66 hybrid photocatalysts with flowerlike 3D microspheres synthesized via a facile solvothermal method. A 20 wt.% UiO-66 emersion raises the Cr(VI) reduction rate up to 99% and higher after 60 min v...

This presentation features recent progress in understanding the phase diagram of water and ice from the perspective of hydrogen bond (O:HeO) cooperative relaxation with focus on how the segmental length and the containing angle of the O:HeO bond change with mechanical compression and thermal excitation. By interplaying theoretical predictions, nume...

HI and NaI solvation transforms different fractions of the H-O stretching phonons from the mode of ordinary water centred at ~3200 to the mode of hydration shell at ~3500 cm-1. Observations suggest that an addition of the HH anti-hydrogen-bond to the Zundel notion, [H(H2O)2]+, would be necessary as the H-O bond due H3O+ has a 4.0 eV energy, and th...

Low-temperature Raman spectroscopy revealed that sugar solvation depresses the critical temperature for homogeneous ice nucleation (TN) whose depression extent follows the order of: trehalose > glucose > fructose at the same concentration and the extent of TN depression for a specific sugar is proportional to its concentration. We attribute the TN...

Solvation of acid, base, and salt is ubiquitously important to all subject areas in chemistry, health care and life science. However, fine resolution of the solvation dynamics, solute-solvent molecular interactions, and solute capability of transforming the hydrogen bond (O:H–O, or HB) and surface stress remain great challenge. Incorporating the no...

To make full use of the solar energy, it remains a great challenge for semiconductor photocatalysts to harvest the full solar light spectrum from ultraviolet (UV) to visible even the near infrared (NIR) wavelength. Here we show firstly the CuS/RGO (reduced graphene oxide) hybrid photocatalyst synthesized via a microwave assisted method with full so...

A series of graphitic carbon nitride photocatalysts were prepared by thermally polymerizing the mixtures of melamine and alkali halides (MCl, M = Na, K, Rb, Cs) in air. XRD, FTIR, Raman, SEM and TEM were used to investigate the effect of alkali halides on the structure and morphology of g-C3N4. It is found that such prepared samples exhibit reduced...

An incorporation of the hydrogen bond (O:H–O or HB) cooperativity notion, contact angle detection, and the differential phonon spectrometrics (DPS) has enabled us to gain refined information on the HCl, KCl and KOH solvation resolved solute-solvent molecular interactions and the solution surface stresses. Results show that ionic polarization stiffe...

The solute-solvent interaction of salts has a striking impact on various biological and industrial processes but its mechanism remains yet mysterious despite intensive studies since 1888 when Franz Hofmeister established the salt series. A combination of confocal Raman spectroscopy and contact angle measurements has enabled us to resolve the hydrog...

Although the alcohol–water mixtures are ubiquitously important to beverage and pharmacy industries, it remains yet puzzling how the alcohols interact with water molecules and how the alcohol molecules functionalize the hydrogen bond network of liquid water and body fluid. We show spectrometrically that alcohol hydration softens both the H–O bond an...

Doping is an effective method to alter the electronic behavior of materials by forming new chemical bonds and bringing bond relaxation. With this aid of first principle calculations, the crystal configuration and electronic properties of monolayer MoS2 have been modulated by the nonmetal (NM) dopants (H, B, C, N, O, F, Si, P, Cl, As, Se, Br, Te and...

Nickel-based materials are promising positive electrode for hybrid supercapacitor due to their high theoretical specific capacity. The main obstacle preventing their practical applications is the low conductivity which limits rate capability of supercapacitors. Considering the good rate capability of CoWO4 and the high specific capacity of NiWO4, w...

We show phonon spectrometrically that the unprecedented H2Ö: ↔ :Ö:H– compression resolves the performance of the base solution networks with “:” being the electron lone pair of oxygen. At hydration, LiOH, NaOH, KOH molecules dissolve each into a :Ö:H– hydroxide and cations of Li⁺, Na⁺, and K⁺, respectively. The cations serve as charge centers to po...

Water skin is the toughest of ever known with a mechanism that remains unclear. We show phonon spectrometrically that molecular undercoordination induced hydrogen bond (O:HO) relaxation and nonbonding electron polarization furnished the skin with the supersolid nature – less dense, elastic, thermally more stable than the bulk. Heating from 5 to 95...

In situ Raman spectroscopy revealed that transiting H2O/NaX (∼64) solutions into an ice VI phase and then into an ice VII phase at a temperature of 298 K requires excessive pressures with respect to pure water. The increase of the critical pressures varies with the solute type in the Hofmeister series order: X = I > Br > Cl > F ∼ 0. The results sug...

The crystal phase structure, surface morphology, chemical states and optical properties of Mn, N mono-doped and co-doped TiO2 nanoparticles were investigated by X-ray powder diffractometry, Raman spectra, scanning electron microscopy, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. Meanwhile, geometry structures, forma...

The segregation of dopant inevitably affects the thermodynamic stability and electronic properties of transition metal (TM) doped TiO2 which were studied using first principles calculations. Here we show that the thermodynamic stability of doped systems is related with the doped position which is different for the considered TM dopants. The second...

This presentation features recent progress in understanding the phase diagram of water and ice from the perspective of hydrogen bond (O:H-O) cooperative relaxation with focus on how the segmental length and the containing angle of the O:H-O bond change with mechanical compression and thermal excitation. By interplaying theoretical predictions, nume...

The dependence of (EΓ6–EΓ8) on the lattice constants has been studied for four half- Heusler compounds. First principle simulation was carried out to calculate the electronic structure and the obtained results were compared among different compounds. It is found that the change of (EΓ6–EΓ8) with strain exhibits opposite trend for III-VIII-V half- H...

The effects of vertical compressive stress on Sb2Te3 nano-films have been investi-gated by the first principles calculation, including stability, electronic structure, crystal structure, and bond order. It is found that the band gap of nano-film is sensitive to the stress in Sb2Te3 nano-film and the critical thickness increases under compressive st...

Density functional theory (DFT) calculations with local spin density discrimination have been performed to examine the effect of atomic under-coordination on the catalytic and magnetic properties of cuboctahedral (CO) and marks decahedral (MD) structured Pt and Rh nanoclusters. Consistency between theoretical calculations and experimental observati...

The effects of external stress on Bi2Te3 nano-films have been investigated by first-principles calculation, including stability, electronic structure, crystal structure, and bond order. It is found that the critical thickness of nano-film is sensitive to the stress in Bi2Te3 nano-film while the band gap is near constant. The critical thickness decr...

Consistency between density functional theory (DFT) calculations and experimental observations confirmed our predictions on the behaviour of local bonds, and the electron binding energy of cuboctahedral and Marks decahedral structures of Ag and Cu nanoclusters. The shorter and stronger bonds between under-coordinated atoms cause local densification...

Epitaxial growth of icosahedral B12As2 on c-plane 4 H-SiC substrates has been analyzed. On on-axis c-plane 4 H-SiC substrates, Synchrotron white beam x-ray topography (SWBXT) revealed the presence of a homogenous solid solution of twin and matrix B12As2 epilayer domains. High resolution transmission electron microscopy (HRTEM) and scanning transmis...

It is shown that the high p-type conductivity in GaN:Mg, grown by metal-organic chemical vapor deposition followed by post-growth annealing, is due to non-equilibrium acceptor concentrations. A series of samples cut from a single GaN:Mg wafer, which initially had undergone rapid thermal annealing (RTA) after growth, has been investigated. The sampl...

An excellent material for thermal neutron detectors is α-rhombohedral boron, due to the large neutron capture cross section of 10B, high hole mobility and ability to self-heal from radiation damage, to date, little work has been done on the crystal growth of α-rhombohedral boron. In this investigation, we attempt to grow α-rhombohedral boron by the...

Boron carbide crystals ranging in size from 50 microns to several millimeters have been grown from a copper-boron carbide flux at temperatures from 1500°C to 1750°C. The crystal size increased with growth temperature although copper evaporation limited growth at the higher temperatures. Synchrotron X-ray Laue patterns were indexed according to (001...

Elimination of degenerate epitaxy in the growth of icosahedral boron arsenide (B12As2, abbreviated as IBA) was achieved on m-plane 15R-SiC substrates and 4H-SiC substrates intentionally misoriented by 7 degrees from (0001) towards [1-100]. Synchrotron white beam x-ray topography (SWBXT) revealed that only single orientation IBA was present in the e...

The defect structure in B[subscript]12As[subscript]2 epitaxial layers grown at two different temperatures on (0001) 6H-SiC by chemical vapor deposition (CVD) was studied using synchrotron white beam x-ray topography (SWBXT) and high resolution transmission electron microscopy (HRTEM). The observed differences in microstructures were correlated with...

The sublimation–recombination crystal growth of bulk yttrium nitride crystals is reported. The YN source material was prepared by reacting yttrium metal with nitrogen at 1200 °C and 800 Torr total pressure. Crystals were produced by subliming this YN from the source zone, and recondensing it from the vapor as crystals at a lower temperature (by 50...

Multilayered Zn-Se-Te structures grown by migration enhanced epitaxy are studied by temperature- and excitation-dependent photoluminescence (PL) as well as magneto-PL. The PL consists of two bands: a blue band, overlaid with band edge sharp lines, dominant at low temperatures and high excitation, and a green band, which appears at elevated temperat...

Epitaxial growth of icosahedral boron arsenide (B[subscript]12As[subscript]2, abbreviated here as IBA) on 4HSiC substrates intentionally misoriented from (0001) towards [1-100] is shown to eliminate rotational twinning. Comparisons of IBA on on-axis and off-axis c-plane 4H-SiC by synchrotron white beam x-ray topography (SWBXT) and high resolution t...

The electron and hole states and confining potential for cylindrical core-shell structure with type-II band alignment are obtained from a numerical solution of the self-consistent Schrödinger-Poisson system of equa-tions. The photoluminescence PL kinetics is theoretically analyzed, with the nanostructure size dispersion taken into account. The resu...

We report growth by molecular beam epitaxy of a ZnxCd(1−x)Se/Znx′Cdy′Mg(1−x′−y′)Se quantum cascade (QC) structure that was designed for electroluminescence (EL) at ∼4.5 μm. The QC active region is comprised of a two-well asymmetric coupled quantum well (ACQW) structure, which was thoroughly investigated to establish the growth conditions for the QC...

The authors report the growth of a II-VI Zn _x Cd _1-x Se / Zn _x^′ Cd _y^′ Mg _{1-x^′-y^′} Se asymmetric coupled quantum well (asymmetric-CQW) structure that was used to investigate the active region of an intersubband electroluminescence structure designed for...

The properties of multiple type-II ZnTe∕ZnSe quantum dots (QDs), which are coexistent with isoelectronic centers formed by Te, grown by migration-enhanced epitaxy, are studied. The samples with a single deposition cycle of Zn-Te-Zn sandwiched between ZnSe barriers are investigated via temperature- and excitation-dependent photoluminescence (PL) as...

A novel solution method to control the diameter of ZnO nanorods is reported. Small diameter (2-3 nm) nanorods were synthesized from trihexylamine, and large diameter (50–80 nm) nanorods were synthesized by increasing the alkyl chain length to tridodecylamine. The defect (green) emission of the photoluminescence (PL) spectra of the nanorods var...

We investigated the optical properties of colloidal-synthesized ZnO spherical nanoparticles prepared from 1-octadecene (OD), a mixture of trioctylamine (TOA) and OD (1:10), and a mixture of trioctylphosphine oxide (TOPO) and OD (1:12). It is found that the green photoluminescence (PL) of samples from the mixture of TOA/OD and TOPO/OD is largely sup...

Two ZnxCd1-xSe/Znx′Cdy′Mg1-x′-y′Se multiple quantum well structures were grown by molecular beam epitaxy. The quantum well layer thickness of the multiple quantum well region was varied in order to tune the intersubband transition energy. The high crystalline quality of the material was demonstrated by high resolution x-ray diffraction. Contactless...

Wide band gap semiconductors are important for many device applications, particularly for lasers and light emitting diodes. In this thesis, we studied (1) the enhancement, by thermal annealing, of p-type doping in Mg-doped GaN grown by metal-organic chemical vapor deposition (MOCVD), (2) the formation of type-II ZnTe quantum dots (QDs) in Zn-Se-Te...

The present Chapter deals with the wide-band-gap (defined here as greater than 2 eV) Zn chalcogenides, i.e. ZnSe, ZnS, and ZnO (mainly in bulk form). However, since recent literature on ZnS is minimal, the main coverage is of ZnSe and ZnO. In addition Zn1−x Bex Se (x ≤0.5) is included, since Be is expected to reduce degradation (from light irradiat...

Zn-Se-Te systems have been of great interest for both lighting applications and their unique optical properties. It is known that the PL of the dilute alloys [1] or quantum wells [2] is usually due to IBEs. ZnTe/ZnSe QDs have been grwon with full monolayer coverage of ZnTe on ZnSe using Volmer-Weber growth [3]. We have shown [4] the existence of ty...

GaN films are grown on [001] GaAs substrates by plasma-assisted molecular beam epitaxy using a three-step process that consists of a substrate nitridation, deposition of a low-temperature buffer layer, and a high-temperature overgrowth. X-ray diffraction and transmission electron microscopy indicate that this method promotes prismatic growth of c-o...

A long-standing problem for ZnSe (and related alloys) has been to obtain good p-type doping. Recent work has given about an order-of-magnitude improvement in such doping by use of Te as a “codopant” to facilitate the introduction of an acceptor dopant (N), since it is known that p-ZnTe can be obtained quite readily; the Te was introduced in submono...

We here report results of high resolution x-ray diffraction, x-ray reflectivity (XRR), as well as optical absorption and reflection measurements on ZnSe samples grown by molecular beam epitaxy, with insertion of planar (delta-) regions of both N as an acceptor dopant and Te as a ``co-dopant'' to facilitate a p-type doping. We note that to enhance t...

Nanocrystals of the wide band gap semiconductor zinc oxide of controllable morphologies were synthesized by a simple thermal decomposition method. The predominating factor in determining the morphology (spheres, triangular prisms, and rods) was the solvent, selected on the basis of coordinating power. The nanoparticles were structurally analyzed, a...

It has been difficult to obtain good p-type ZnSe. A delta-doping technique, with N as an acceptor and Te as a ``codopant'' (ZnTe is easily doped p-type), was employed to obtain a net acceptor concentration ˜ 6x10^18cm-3 using small amounts of Te. To understand the doping mechanism, we performed HRXRD with synchrotron radiation (NSLS) complemented b...

It has been shown that good bipolar doping in wide bandgap semiconductors often requires non-equilibrium dopant incorporation^1. We present experimental results proving that good p-type doping in MOCVD-grown and annealed GaN:Mg is due to Mg_Ga in excess of its equilibrium solubility limit in the absence of (donor) H. For this, five samples were cut...