Ectopic Expression of Sugarcane ScAMT1.1 Has the Potential to Improve Ammonium Assimilation and Grain Yield in Transgenic Rice under Low Nitrogen Stress.

In China, nitrogen (N) fertilizer is excessively used in sugarcane planting areas, while the nitrogen use efficiency (NUE) of sugarcane is relatively low. Mining and identifying the key genes in response to low N stress in sugarcane can provide useful gene elements and a theoretical basis for developing sugarcane varieties with high NUE. In our study, RNA-Seq combined with qRT-PCR analysis revealed that the ScAMT1.1 gene responded positively to low N stress, resulting in the stronger low N tolerance and high NUE ability of sugarcane cultivar ROC22. Then, ScAMT1.1 was cloned from sugarcane. The full-length cDNA of the ScAMT1.1 gene is 1868 bp, containing a 1491 bp open reading frame (ORF), and encoding 496 amino acids. ScAMT1.1 belongs to the AMT superfamily and shares 91.57% homologies with AMT1.1 from Oryza sativa. Furthermore, it was stably overexpressed in rice (O. sativa). Under low N treatment, the plant height and the fresh weight of the ScAMT1.1-overexpressed transgenic rice were 36.48% and 51.55% higher than that of the wild-type, respectively. Both the activity of ammonium assimilation key enzymes GS and GDH, and the expression level of ammonium assimilation key genes, including GS1.1, GS1.2, GDH, Fd-GOGAT, and NADH-GOGAT2 in the transgenic plants, were significantly higher than that of the wild-type. The grain number and grain yield per plant in the transgenic rice were 6.44% and 9.52% higher than that of the wild-type in the pot experiments, respectively. Taken together, the sugarcane ScAMT1.1 gene has the potential to improve ammonium assimilation ability and the yield of transgenic rice under low N fertilizer conditions. This study provided an important functional gene for improving sugarcane varieties with high NUE.

Plasmonic Photocatalysis with Nonthermalized Hot Carriers.

Hot carriers generated by plasmonic damping have been suggested to promote photocatalysis, yet it remains unclear how the nonthermalized hot carriers dynamically activate and promote the energy transfer processes. Here, we present an Anderson-Newns model to describe the vibrational excitation and bond dissociation induced by plasmonic hot carriers. The nonthermal distribution of the hot carriers generated by plasmon damping is accounted for on equal footing with thermal carriers at a given temperature in the electron-molecule scattering. We found that the nonthermal electrons in the high energy region can, albeit in much smaller populations, provide an efficient and dominant channel for photodissociation especially in the low-temperature and quantum plasmon regime. Our model captures the wavelength dependence and reproduces the enhancement factors observed by experiments for oxygen dissociation on silver nanoparticles. It also paves a way to harvesting nonthermal plasmonic energy for photocatalysis in the quantum regime.

Characterization and Manipulation of Intervalley Scattering Induced by an Individual Monovacancy in Graphene.

Intervalley scattering involves microscopic processes that electrons are scattered by atomic-scale defects on the nanoscale. Although central to our understanding of electronic properties of materials, direct characterization and manipulation of range and strength of the intervalley scattering induced by an individual atomic defect have so far been elusive. Using scanning tunneling microscope, we visualize and control intervalley scattering from an individual monovacancy in graphene. By directly imaging the affected range of monovacancy-induced intervalley scattering, we demonstrate that it is inversely proportional to the energy; i.e., it is proportional to the wavelength of massless Dirac fermions. A giant electron-hole asymmetry of the intervalley scattering is observed because the monovacancy is charged. By further charging the monovacancy, the bended electronic potential around the monovacancy softens the scattering potential, which, consequently, suppresses the intervalley scattering of the monovacancy.

Effect of light polarization on plasmon-induced charge transfer.

Plasmonic nanoclusters can strongly absorb light energy and generate hot carriers, which have great potentials in photovoltaic and photocatalytic applications. A vital step for those plasmonic applications is the charge transfer at the metal-semiconductor interface. The effect of the light polarization on the charge transfer has not been theoretically investigated so far. Here, we take the Ag-TiO2 system as a model system to study the polarization effect using time-dependent density functional theory simulations. We find that the charge transfer is sensitive to the light polarization, which has its origin in the polarization-dependent hot carrier distributions. For the linearly polarized light, it shows a sine-square dependence on the polar angle, indicating that the charge transfer response to the linear polarization can be decomposed into components perpendicular and parallel to the interface. We also find that there exists directional charge transfer with a circular light polarization. Our results demonstrate that the light polarization can significantly affect the charge transfer behavior and, thus, offer a new degree of freedom to manipulate the plasmonic applications.

Identification of Low-Nitrogen-Related miRNAs and Their Target Genes in Sugarcane and the Role of miR156 in Nitrogen Assimilation.

Chemical nitrogen (N) fertilizer is widely used in sugarcane production, especially in China and India. Understanding the molecular mechanisms and mining miRNAs and their target genes associated with nitrogen use efficiency (NUE) in sugarcane can aid in developing the N-efficient varieties, and thus is beneficial to reduce N fertilizer application. In this study, the root miRNA database of N-efficient sugarcane variety ROC22 under low N stress (0.3 mM NH4NO3) for 3 h was constructed, along with their transcriptome-rearranged data. KEGG analysis indicated that those candidate target genes, corresponding to differentially expressed miRNAs, were mainly enriched in N metabolism, amino acid metabolism, carbohydrate metabolism, photosynthesis, and hormone signal transduction pathways. It was found that under low N stress for 0-24 h, there was a negative correlation between miR168 and SPX, along with miR396 and acnA. Furthermore, the expression of miR156 in the roots of ROC22 was significantly up-regulated under low N treatment. Compared with the wild-type, the Arabidopsis plants overexpressing sugarcane miR156 exhibited significantly improved length and surface area of roots, while the expression of one NO3- transporter gene NRT1.1, three N assimilation key genes (NR1, NIR1, and GS), and the activity of two N assimilation key enzymes (NR and GS) were up-regulated under low N treatment. It can be reasonably deduced that sugarcane miR156 can enhance the nitrogen assimilation ability of the overexpressed Arabidopsis plants under low N application, and thus has a potential ability for improving sugarcane NUE. The present study should be helpful for understanding the molecular regulatory network in the N-efficient sugarcane genotype responding to low N stress and could provide the candidate miRNAs with a potential function in improving sugarcane NUE.

Integrated Plasmonics: Broadband Dirac Plasmons in Borophene.

The past decade has witnessed numerous discoveries of two-dimensional (2D) semimetals and insulators, whereas 2D metals were rarely identified. Borophene, a monolayer boron sheet, has recently emerged as a perfect 2D metal with unique electronic properties. Here we study collective excitations in borophene, which exhibit two major plasmon modes with low damping rates extending from the infrared to ultraviolet regime. The anisotropic 1D plasmon originates from electronic transitions of tilted Dirac cones in borophene, analogous to that in extreme doped graphene. These features enable borophene as an integrated platform of 1D, 2D, and Dirac plasmons, promising for directional polariton transport and broadband optical communication in next-generation optoelectronic devices.

Anomalous Dirac Plasmons in 1D Topological Electrides.

The plasmon opens up the possibility to efficiently couple light and matter at subwavelength scales. In general, the plasmon frequency, intensity, and damping are dependent on the carrier density. These dependencies, however, are disadvantageous for stable functionalities of plasmons and render fundamentally a weak intensity at low frequency, especially for the Dirac plasmon (DP) widely studied in graphene. Here we demonstrate a new type of DP, emerging from a Dirac nodal-surface state, which can simultaneously exhibit a density-independent frequency, intensity, and damping. Remarkably, we predict the realization of anomalous DP (ADP) in 1D topological electrides, such as Ba_{3}CrN_{3} and Sr_{3}CrN_{3}, by first-principles calculations. The ADPs in both systems have a density-independent frequency and high intensity, and their frequency can be tuned from terahertz to midinfrared by changing the excitation direction. Furthermore, the intrinsic weak electron-phonon coupling of anionic electrons in electrides affords an added advantage of low-phonon-assisted damping and hence a long lifetime of the ADPs. Our Letter paves the way to developing novel plasmonic and optoelectronic devices by combining topological physics with electride materials.

Comparative Analysis of two Sugarcane Ancestors Saccharum officinarum and S. spontaneum based on Complete Chloroplast Genome Sequences and Photosynthetic Ability in Cold Stress.

Polyploid Saccharum with complex genomes hindered the progress of sugarcane improvement, while their chloroplast genomes are much smaller and simpler. Chloroplast (cp), the vital organelle, is the site of plant photosynthesis, which also evolves other functions, such as tolerance to environmental stresses. In this study, the cp genome of two sugarcane ancestors Saccharum officinarum and S. spontaneum were sequenced, and genome comparative analysis between these two species was carried out, together with the photosynthetic ability. The length is 141,187 bp for S. officinarum and that is 7 bp longer than S. spontaneum, with the same GC content (38.44%) and annotated gene number (134), 13 with introns among them. There is a typical tetrad structure, including LSC, SSC, IRb and IRa. Of them, LSC and IRa/IRb are 18 bp longer and 6 bp shorter than those in S. spontaneum (83,047 bp and 22,795 bp), respectively, while the size of SSC is same (12,544 bp). Five genes exhibit contraction and expansion at the IR junctions, but only one gene ndhF with 29 bp expansion at the border of IRb/SSC. Nucleotide diversity (Pi) based on sliding window analysis showed that the single copy and noncoding regions were more divergent than IR- and coding regions, and the variant hotspots trnG-trnM, psbM-petN, trnR-rps14, ndhC-trnV and petA-psbJ in the LSC and trnL-ccsA in the SSC regions were detected, and petA-psbJ with the highest divergent value of 0.01500. Genetic distances of 65 protein genes vary from 0.00000 to 0.00288 between two species, and the selective pressure on them indicated that only petB was subjected to positive selection, while more genes including rpoC2, rps3, ccsA, ndhA, ndhA, psbI, atpH and psaC were subjected to purifying or very strong purifying selection. There are larger number of codons in S. spontaneum than that in S. officinarum, while both species have obvious codon preference and the codons with highest-(AUG) and lowest frequency (AUA) are same. Whilst, the most abundant amino acid is leucine in both S. officinarum and S. spontaneum, with number of 2175 (10.88% of total) and 2228 (10.90% of total) codons, respectively, and the lowest number is cysteine, with only 221 (1.105%) and 224 (1.096%), respectively. Protein collinearity analysis showed the high collinearity though several divergences were present in cp genomes, and identification of simple sequence repeats (SSRs) were included in this study. In addition, in order to compare cold tolerance and explore the expanding function of this environmental stress, the chlorophyll relative content (SPAD) and chlorophyll fluorescence Fv/Fm were measured. The significantly higher SPAD were observed in S. spontaneum than those in S. officinarum, no matter what the control conditions, exposure to low temperature or during recovery, and so was for Fv/Fm under exposure to low temperature, together with higher level of SPAD in S. spontaneum in each measurement. Aforementioned results suggest much stronger photosynthetic ability and cold tolerance in S. spontaneum. Our findings build a foundation to investigate the biological mechanism of two sugarcane ancestor chloroplasts and retrieve reliable molecular resources for phylogenetic and evolutionary studies, and will be conducive to genetic improvement of photosynthetic ability and cold resistance in modern sugarcane.

Foreign cry1Ac gene integration and endogenous borer stress-related genes synergistically improve insect resistance in sugarcane.

BACKGROUND: Sugarcane (Saccharum spp. hybrids) is considered the most globally important sugar-producing crop and raw material for biofuel. Insect attack is a major issue in sugarcane cultivation, resulting in yield losses and sucrose content reductions. Stem borer (Diatraea saccharalis F.) causes serious yield losses in sugarcane worldwide. However, insect-resistant germplasms for sugarcane are not available in any collections all over the world, and the molecular mechanism of insect resistance has not been elucidated. In this study, cry1Ac transgenic sugarcane lines were obtained and the biological characteristics and transgene dosage effect were investigated and a global exploration of gene expression by transcriptome analysis was performed. RESULTS: The transgene copies of foreign cry1Ac were variable and random. The correlation between the cry1Ac protein and cry1Ac gene copies differed between the transgenic lines from FN15 and ROC22. The medium copy lines from FN15 showed a significant linear relationship, while ROC22 showed no definite dosage effect. The transgenic lines with medium copies of cry1Ac showed an elite phenotype. Transcriptome analysis by RNA sequencing indicated that up/down regulated differentially expressed genes were abundant among the cry1Ac sugarcane lines and the receptor variety. Foreign cry1Ac gene and endogenous borer stress-related genes may have a synergistic effect. Three lines, namely, A1, A5, and A6, were selected for their excellent stem borer resistance and phenotypic traits and are expected to be used directly as cultivars or crossing parents for sugarcane borer resistance breeding. CONCLUSIONS: Cry1Ac gene integration dramatically improved sugarcane insect resistance. The elite transgenic offspring contained medium transgene copies. Foreign cry1Ac gene integration and endogenous borer stress-related genes may have a synergistic effect on sugarcane insect resistance improvement.

Particle Bombardment of the cry2A Gene Cassette Induces Stem Borer Resistance in Sugarcane.

Sugarcane borer is the most common and harmful pest in Chinese sugarcane fields, and can cause damage to the whole plant during the entire growing season. To improve borer resistance in sugarcane, we constructed a plant expression vector pGcry2A0229 with the bar gene as the marker and the cry2A gene as the target, and introduced it into embryogenic calli of most widely cultivated sugarcane cultivar ROC22 by particle bombardment. After screening with phosphinothricin in vitro and Basta spray, 21 resistance-regenerated plants were obtained, and 10 positive transgenic lines harboring the cry2A gene were further confirmed by conventional PCR detection. Real-time quantitative PCR (RT-qPCR) analysis showed that the copy number of the cry2A gene varied among different transgenic lines but did not exceed four copies. Quantitative ELISA analysis showed that there was no linear relationship with copy number but negatively correlated with the percentage of borer-infested plants. The analysis of industrial and agronomic traits showed that the theoretical sugar yields of transgenic lines TR-4 and TR-10 were slightly lower than that of the control in both plant cane and ratoon cane; nevertheless, TR-4 and TR-10 lines exhibited markedly lower in frequency of borer-infested plants in plant cane and in the ratoon cane compared to the control. Our results indicate that the introduction of the cry2A gene via bombardment produces transgenic lines with obviously increased stem borer resistance and comparable sugar yield, providing a practical value in direct commercial cultivation and crossbreeding for ROC22 has been used as the most popular elite genitor in various breeding programs in China.

Plant jasmonate ZIM domain genes: shedding light on structure and expression patterns of JAZ gene family in sugarcane.

BACKGROUND: Sugarcane smut caused by Sporisorium scitamineum is one of the most severe fungal diseases in the sugarcane industry. Using a molecular biological technique to mine sugarcane resistance genes can provide gene resources for further genetic engineering of sugarcane disease-resistant breeding. Jasmonate ZIM (zinc-finger inflorescence meristem) domain (JAZ) proteins, which involved in the responses to plant pathogens and abiotic stresses, are important signaling molecules of the jasmonic acid (JA) pathway. RESULTS: Seven differentially expressed sugarcane JAZ genes, ScJAZ1-ScJAZ7, were mined from the transcriptome of sugarcane after inoculation with S. scitamineum. Bioinformatic analyses revealed that these seven ScJAZ genes encoded basic proteins that contain the TIFY and CCT_2 domains. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis demonstrated that the ScJAZ1-ScJAZ7 genes were tissue specific and differentially expressed under adverse stress. During S. scitamineum infection, the transcripts of ScJAZ4 and ScJAZ5 were both upregulated in the susceptible genotype ROC22 and the resistant genotype Yacheng05-179; ScJAZ1, ScJAZ2, ScJAZ3, and ScJAZ7 were downregulated in Yacheng05-179 and upregulated in ROC22; and the expression of ScJAZ6 did not change in ROC22, but was upregulated in Yacheng05-179. The transcripts of the seven ScJAZ genes were increased by the stimuli of salicylic acid and abscisic acid, particularly methyl jasmonate. The expression of the genes ScJAZ1-ScJAZ7 was immediately upregulated by the stressors hydrogen peroxide, sodium chloride, and copper chloride, whereas slightly induced after treatment with calcium chloride and polyethylene glycol. In addition, the expression of ScJAZ6, as well as seven tobacco immunity-associated marker genes were upregulated, and antimicrobial activity against Pseudomonas solanacearum and Fusarium solani var. coeruleum was observed during the transient overexpression of ScJAZ6 in Nicotiana benthamiana, suggesting that the ScJAZ6 gene is associated with plant immunity. CONCLUSIONS: The different expression profiles of the ScJAZ1-ScJAZ7 genes during S. scitamineum infection, the positive response of ScJAZ1-ScJAZ7 to hormones and abiotic treatments, and the function analysis of the ScJAZ6 gene revealed their involvement in the defense against biotic and abiotic stresses. The findings of the present study facilitate further research on the ScJAZ gene family especially their regulatory mechanism in sugarcane.

A sugarcane pathogenesis-related protein, ScPR10, plays a positive role in defense responses under Sporisorium scitamineum, SrMV, SA, and MeJA stresses.

KEY MESSAGE: A pathogenesis-related gene, ScPR10 , was isolated from sugarcane and its bio-function was characterized, demonstrating that ScPR10 was involved in plant defense responses to Sporisorium scitamineum , SrMV, SA, and MeJA stresses. Plant fungal and viral diseases are the major concerns in sugarcane industry. Many anti-fungal and antivirus components, including pathogenesis-related (PR) proteins, have been identified. The pathogenesis-related protein 10 (PR10) is the dominant group in PR families, involved in the plant defense mechanism. In this study, ScPR10 (GenBank Acc. No. KT887884), a 701-bp-length PR10 gene with a 483 bp-length open reading frame, was isolated from sugarcane. Its transient expression in the leaves of Nicotiana benthamiana indicated that the function role of ScPR10 is likely in the nucleus, and it increased the level of H2O2 accumulation in leaf cells. Moreover, ScPR10 could also enhance the resistance of N. benthamiana leaves to infection by Pseudomonas solanacearum and Fusarium solani var. coeruleum. Quantitative real-time PCR analysis revealed that ScPR10 was not constitutively expressed in sugarcane tissues due to its high expression in the buds and scant presence in root tips. In addition, the transcript of ScPR10 could be induced by a pathogenic fungus (Sporisorium scitamineum) and a virus (Sorghum mosaic virus, SrMV) in the resistant sugarcane cultivars, while it was down-regulated in the susceptible ones. After exposure to salicylic acid (SA) and methyl jasmonate (MeJA), ScPR10 peaked at 6 and 12 h, respectively. These results suggest that ScPR10 can play a positive role in sugarcane defense responses to S. scitamineum, SrMV, SA, and MeJA stresses.

Plasmon Enhanced Internal Photoemission in Antenna-Spacer-Mirror Based Au/TiO2 Nanostructures.

Emission of photoexcited hot electrons from plasmonic metal nanostructures to semiconductors is key to a number of proposed nanophotonics technologies for solar harvesting, water splitting, photocatalysis, and a variety of optical sensing and photodetector applications. Favorable materials and catalytic properties make systems based on gold and TiO2 particularly interesting, but the internal photoemission efficiency for visible light is low because of the wide bandgap of the semiconductor. We investigated the incident photon-to-electron conversion efficiency of thin TiO2 films decorated with Au nanodisk antennas in an electrochemical circuit and found that incorporation of a Au mirror beneath the semiconductor amplified the photoresponse for light with wavelength λ = 500-950 nm by a factor 2-10 compared to identical structures lacking the mirror component. Classical electrodynamics simulations showed that the enhancement effect is caused by a favorable interplay between localized surface plasmon excitations and cavity modes that together amplify the light absorption in the Au/TiO2 interface. The experimentally determined internal quantum efficiency for hot electron transfer decreases monotonically with wavelength, similar to the probability for interband excitations with energy higher than the Schottky barrier obtained from a density functional theory band structure simulation of a thin Au/TiO2 slab.

Nonlinear response of metal nanoparticles: Double plasmon excitation and electron transfer.

We investigate the dynamical response of a metal nanoparticle and the electron transfer to a molecule near its surface using time-dependent density functional theory. In addition to the linear response of the Mie resonance, double plasmon excitations and a low-frequency charge transfer band emerge and become prominent at high laser intensities. Both modes are nonlinear processes, which are derived from the re-excitation and decay of the primary plasmon mode, respectively. Our results shed light on the localised characters of the plasmon-molecule coupling and hot electron distributions. These findings have general implications to photoinduced phenomena in nanosystems.

Schottky barrier effect on plasmon-induced charge transfer.

Plasmon-induced charge transfer causes electron-hole spatial separation at the metal-semiconductor interface, which plays a key role in photocatalytic and photovoltaic applications. The Schottky barrier formed at the metal-semiconductor interface can modify the hot carrier dynamics. Taking the Ag-TiO2 system as an example, we have investigated plasmon-induced charge transfer at the Schottky junction using quantum mechanical simulations. We find that the Schottky barrier induced by n-type doping enhances the electron transfer and that induced by p-type doping enhances the hole transfer, which is attributed to the shift of the Fermi energy and the band bending of the Schottky junction at the interface. The Schottky barrier also modifies the layer distribution of hot carriers. In particular, for the system with a large band bending, there exists electron-hole spatial separation inside the TiO2 substrate. Our results reveal the mechanism and dynamics of charge transfer at the Schottky junction, and pave the way for manipulating plasmon-assisted photocatalytic and photovoltaic applications.

Characterization of silicon transporter gene family in Saccharum and functional analysis of the ShLsi6 gene in biotic stress.

Silicon, one of the most prevalent elements in the soil, is beneficial for plant growth and defense against different stresses. The silicon transporter gene (Lsi) plays an important role in the uptake and transport of silicon in higher plants. In this study, a total of 32 Lsi genes, including 20 SsLsi in sugarcane wild species Saccharum spontaneum, 5 ShLsi in Saccharum hybrid cultivar R570 and 7 SbLsi in sugarcane related species Sorghum bicolor, were identified and classified into three groups. Bioinformatics analysis showed that instability, hydrophobicity, localization of cell membranes and vacuoles were the main features of the Lsi proteins. Whole genome and segmental duplication contributed to the main expansion of Lsi gene family. Collinearity analysis of the Lsi genes showed that S. spontanum and R570 had a collinear relationship with monocotyledonous plants S. bicolor and Oryza sativa, but not with dicotyledonous plants Arabidopsis thaliana and Vitis vinifera. The replicated Lsi genes were mainly subjected to strong selection pressure for purification. The diverse cis-regulatory elements in the promoter of SsLsi, ShLsi and SbLsi genes suggested that they were widely involved in the response of plants to various stresses and the regulation of the growth and development. Transcriptome data and real time quantitative PCR analysis showed that the Lsi genes exhibited different expression profiles in sugarcane tissues and under Sporisorium scitamineum, drought and cold stresses. In addition, the cDNA and genomic DNA sequences of ShLsi6 that was homologous to SsLsi1b gene was cloned from Saccharum hybrid cultivar ROC22. Transient expression analysis showed that, compared with the control, Nicotiana benthamiana leaves which overexpressed the ShLsi6 gene showed a high sensitivity after inoculation with tobacco pathogens Ralstonia solanacearum and Fusarium solani var. coeruleum. This study provides important information for further functional analysis of Lsi genes and resistant breeding in sugarcane.

Quantum mechanical study of the coupling of plasmon excitations to atomic-scale electron transport.

The coupling of optical excitation and electron transport through a sodium atom in a plasmonic dimer junction is investigated using time-dependent density functional theory. The optical absorption and dynamic conductance is determined as a function of gap size. Surface plasmons are found to couple to atomic-scale transport through several different channels including dipolar, multipolar, and charge transfer plasmon modes. These findings provide insight into subnanoscale couplings of plasmons and atoms, a subject of general interest in plasmonics and molecular electronics.

Semiclassical approach to plasmon-electron coupling and Landau damping of surface plasmons.

A semiclassical model is developed to describe plasmon-electron coupling and electronic damping of surface plasmons. It is compared with the ab initio linear response calculations for metallic thin films in the jellium approximation and for a realistic crystalline Mg(0001) surface. The semiclassical model is able to reproduce the quantum oscillations of plasmon linewidth, which was obtained in the previous ab initio calculations. In addition, state-resolved analysis reveals the origin of these oscillations, which result from superposition of the short-period oscillations of individual electron-hole pair transitions. The semiclassical model is further applied to a crystalline Mg(0001) surface, where linewidth dispersion of the surface plasmon is calculated and shows good agreement with earlier ab initio calculation and experiment. Our results suggest that this semiclassical approach is quite promising for the quantitative description of plasmon-electron coupling and associated processes such as surface-enhanced Raman scattering, light emission, and fluorescence.

Laterally tunable plasmon resonance in confined biatomic-layer ag nanodisks.

We report on the fabrication and investigation of the plasmon excitations in laterally confined quasi-two-dimensional (2D) Ag nanodisks on a Si(111) substrate. Different from the Mie resonance in Ag clusters and the propagating plasmon waves in 2D systems, these ultrathin nanodisks exhibit a low-energy plasmon resonance whose frequency is continuously tunable by the disk diameter. Quantum-mechanical simulations revealed the origin and the effects of screening and charge transfer on the plasmon excitation. The character and size-dependence are promising for engineering plasmonic and optical properties in supported 2D systems.

Tunable electron and hole injection channels at plasmonic Al-TiO2 interfaces.

Metallic nanostructures can strongly absorb light through their plasmon excitations, whose nonradiative decay generates hot electron-hole pairs. When the metallic nanostructure is interfaced with a semiconductor, the spatial separation of hot carriers plays the central and decisive roles in photovoltaic and photocatalytic applications. In recent years, free-electron metals like Al have attracted tremendous attentions due to the much higher plasmon frequencies that could extend to the ultraviolet regime. Here, the plasmon excitations and charge separations at the Al-TiO2 interfaces have been investigated using quantum-mechanical calculations, where the atomic structures and electronic dynamics are all treated from first-principles. It is found that the high-frequency plasmon of Al produces abundant and broad-band hot-carrier distributions, where the electron-hole symmetry is broken by the presence of the semiconductor band gap. Such an asymmetric hot-carrier distribution provides two competing channels, which can be controlled either by tuning the laser frequency, or by harnessing the plasmon frequency through the geometry and shape of the metallic nanostructure. Our study suggests that the Al plasmon offers a versatile and tunable pathway for the charge transfer and separation, and has general implications in plasmon-assisted photovoltaics and photocatalysis.