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Remote epitaxy via graphene has acquired much attention because of its potential for epi-layer mechanical exfoliation. The stability of graphene during the epitaxy process is a key point in realizing epi-layer exfoliation. In this work, GaN and AlN buffer layers were grown on a graphene-coated AlN/sapphire template and studied for the stability of graphene during the different stages of III-nitrides' remote epitaxy. The annealing experiments of graphene in different atmospheres illustrate that N2 carrier gas is the better choice to protect graphene. The graphene transition layer can remain stable during the low-temperature GaN or AlN buffer growth process, making the epi-layer exfoliable. However, when the temperature increased to a common value for GaN growth in MOCVD, recrystallization of the buffer layers happened and the graphene transition layer could be destroyed. As a result, the epi-layers cannot be exfoliated in this case. These results illustrate that the recrystallization process should be avoided or weakened to achieve exfoliation of the epi-layer. [ABSTRACT FROM AUTHOR]

The rapid development of artificial intelligence requires faster information processing capabilities. However, the traditional von Neumann architecture is limited by transmission speed. The combination of neuromorphic structure and photon calculation will break this limitation and effectively improve the calculation efficiency. Here, we demonstrate an optical synaptic device based on GaN/AlN periodic structure that exhibits strong persistent photoconductivity in ultraviolet (UV) detection, which is caused by the strong polarization of GaN/AlN heterojunction. In our devices, photogenerated carriers are trapped in potential wells and then recombine slowly. This physical process alters the initial distribution of the electric field, thus changing the resistance state of the device. Based on this characteristic, the device exhibits optically tunable synaptic behaviors, such as short/long-term memory, excitatory postsynaptic current, and spike-timing-dependent plasticity stimulated by pulsed light. At the same time, our devices exhibit high response and contrast at high bias voltage, making it sensitive to quite weak UV light. Then, it is demonstrated experimentally that the devices can be applied to image information preprocessing, greatly reducing the amount of input information and subsequent training costs in the task of handwritten number recognition. Overall, this work shows an unreported structure of an optical synaptic device with memory and learning behaviors, with great potential for applications in weak UV light detection and neural computing. [ABSTRACT FROM AUTHOR]

The terminal ligand influence on the electronic structure and the intrinsic redox properties of the [Fe4S4](super 2+) cubane core was probed using photoelectron spectroscopy. The results revealed the electrostatic nature of the interactions between the cubane core and its coordination environment.

Density functional and coupled cluster methods are combined with photodetachment spectroscopy to study the electronic structures and gas-phase redox potentials of the [Fe(SCH)(sub 3))(sub 4)](super 2-/-/0) and [Fe(SCH(sub 3))(sub 4)](super -) involve mainly the Fe 3d and S 3p orbitals, respectively. The thermodynamic method cycle can be used to estimate metal-ligand bonding energies and to determine intrinsic reduction potentials from photodetachment experiments when the reduced forms are not stable in the gas phase.

A photoelectron spectroscopic investigation of a series of monoiron-sulfur clusters FeS (sub n)(super -) (n=1-6) at various photon energies is reported. Preliminary density functional calculations were carried out and the obtained structures supported the proposed structural evolution of the FeS (sub n)(super -) clusters.

Research has been conducted on pi-electron tetrapnictogen dianions in Na (super)+ Pn (sub)4 (super)2- (Pn= Sb, As, P). Results demonstrate that from being aromatic these dianions become antiaromatic upon electron detachment and yield inorganic antiaromatic Na (super)+ Pn (sub)4 (super)- molecules.

The electronic structure as well as the chemical bonding of six anionic complexes is investigated using photo detachment photoelectron spectroscopy (PES). The results obtained are found to be in line with theoretical values, and the observed PES values are interpreted on the basis ] of theoretical values as well as previous spectroscopic studies.

The production of hydrated clusters of the sulfate dianion, SO(sub 4)(super 2-)(H2O)(sub n) (n = 4-40) and the investigation of their energetics and stabilities using photodetachment photoelectron spectroscopy is presented. A simple electrostatic model is used to evaluate the repulsive Coulomb barrier (RCB) and excellent agreement is observed with the experimentally derived RCB.

Research into the double charged anion ZrF(sub 6)(super 2-) is presented. The adiabatic detachment energy was found to be very high.

Research is presented describing the study of dicaboxylate dianion stability using acetylene and succinate.

PtX4(super2-) square planar 5 d transition metal complexes were studied in the gas phase using ion-trap spectrometry and electrospray ionization.

It has been possible to make a photoelectron spectroscopy study of SO4- and HSO4-. Substantial changes in geometry between the anion and neutral structures were identified.

It has been possible to make a photoelectron spectroscopy study of a quadruply charged gaseous anion, copper phthalocyanine (CuPc) tetrasulfonate tetraanion, and its monoprotonated and -sodiumated triply charged anions at four photon energies. This is the first observation of negative electron binding in a multiply charged anion.

The use of ab initio calculations combined with vibrationally resolved photoelectron spectroscopy to study the chemical bonding and structure in AlC2- and AlCSi- is reported. AlCSi- is found to have an almost linear structure and AlC2- a C2v structure.

A study was conducted to analyze alkali metal sulfate ion pairs and their double charged dimers in the gas phase. The anions were prepared using an electrospray method. Their photoelectron spectra were determined at three photon energies. The electron binding energies of the dimer dianions were lower than those of the monomers due to the strong electron-electron repulsion in the dianions.

A photoelectron spectroscopic (PES) study was performed on scandium (Sc) and yttrium (Y) oxide species, ScO(sub n)(super -) (n=1-4) and YO(sub n)(super -) (n=1-5), respectively, to further understand the electronic structure and chemical bonding between Sc, Y and oxygen. The PES technique determined the size-selected electronic structure and spectra of gas-phase oxides. It was revealed that ScO and YO had the same electron affinities with similar excitation energies for their excited forms.

Gas-phase mutliply charged anions and their intramolecular Coulomb repulsion and solvation stabilization were investigated by photoelectron spectroscopy combined with an electrospray ionization method. An initial study on a series of linear dicarboxylate dianions (DC2-), -O2C(CH2)nCO2- (n = 3-6), solvated by one and two waters. Results showed that the dianion with n = 2 can be stabilized by one water, and in general the first water stabilizes the electron binding energy of DC2 by approximately 0.3 eV.

Experiments revealed new prominent clusters in the anion mass spectra of titanium carbide clusters, TixC (super -) (sub y) where x/y = 3/8, 4/8, 6/13, 7/13, 9/15 and 13/22 which can not be localized in the positive ion mass spectra. The common components of the clusters were C2 dimers, cubic framework and layered structures. Moreover, two growth regions were identified in the clusters. A combined photoelectron spectroscopy and density functional theoretical studies were performed to understand the structure and bonding of the clusters.

The C-glycopeptide and the natural high-mannose N-glycopeptide can be synthesized through a strategy with two main steps. The first is a chemical synthesis of a GlcNAc containing glycopeptide or neoglycopeptide, and the second is an enzymatic transfer of a Mann-GlcNAc moiety to the terminal GlcNAc residue in the peptide. This approach also allows the biological activity of these glycopeptides towards a range of glycoamidases to be assessed. It can be established that the C-glycopeptide is the first, broad spectrum inhibitor for glycoamidases.

Anion photoelectron spectroscopy was used to study the electronic structure of metallocarbohedrenes Msub8Csub12 (M = Ti, V, Cr, Zr, Nb). The electron affinities of the metallocarbohedrenes were metal dependent and increased from Tisub8Csub12 to Crsub8Csub12. The Zrsub8Csub12 and Nbsub8Csub12 electronic structures were similar to Tisub8Csub12 and Vsub8Csub12. Molecular orbital schemes derived from a tetracapped tetrahedral Msub8Csub12 cluster can be used to qualitatively interpret all the spectra.

The molecular structures of iron oxides of the two series FeOy- (y = 1-4) and Fe2Oy- (y = 1-5) comply with their sequential oxidation behavior. Vibrationally resolved photoelectron spectroscopy gives better resolution for the higher oxides such as FeO3(super -), FeO4(super -), Fe2O4(super -), and Fe2O5(super -). The oxidation state of the monoiron series saturates at FeO3 and an O-O bond occurs in the next higher oxide FeO4.