Wenbin Li

Experimental realization of two-dimensional boron sheets

A variety of two-dimensional materials have been reported in recent years, yet single-element systems such as graphene and black phosphorus have remained rare. Boron analogues have been predicted, as boron atoms possess a short covalent radius and the flexibility to adopt sp(2) hybridization, features that favour the formation of two-dimensional allotropes, and one example of such a borophene material has been reported recently. Here, we present a parallel experimental work showing that two-dimensional boron sheets can be grown epitaxially on a Ag(111) substrate. Two types of boron sheet, a β12 sheet and a χ3 sheet, both exhibiting a triangular lattice but with different arrangements of periodic holes, are observed by scanning tunnelling microscopy. Density functional theory simulations agree well with experiments, and indicate that both sheets are planar without obvious vertical undulations. The boron sheets are quite inert to oxidization and interact only weakly with their substrate. We envisage that such boron sheets may find applications in electronic devices in the future.

Stable expression of hepatitis B surface antigen gene in Dunaliella salina (Chlorophyta)

A stable transformation system for theexpression of foreign genes in theunicellular marine green alga Dunaliella salina was established. Amongfive antibiotics, 60 μg mL-1chloramphenicol completely inhibitedgrowth. Of five promoters tested, theubiquitin-

Highly efficient expression of rabbit neutrophil peptide-1 gene in Chlorella ellipsoidea cells

Ohgr; promoter yielded thehighest β-glucuronidase (GUS) activity.The hepatitis B surface antigen (HBsAg)gene was introduced into the cells by usingelectroporation. PCR and Southern blotanalysis amd it was shown that the gene wasintegrated into the genome. The stableexpression of HBsAg protein was confirmedby enzyme-linked immunosorbent assay(ELISA) and Western blot analysis. Theintroduced DNA and HBsAg expression weremaintained stable for at least 60generations in medium devoid ofchloramphenicol. This is an important steptoward the production of useful foreignproteins in the alga.

Rapid isolation and functional analysis of promoter sequences of the nitrate reductase gene from Chlorella ellipsoidea

Abstract. A highly efficient system was developed for the expression of foreign genes in Chlorella ellipsoidea cells. The effect of five promoters on the expression efficiency of β-glucuronidase (GUS) gene was evaluated by transient expression of the UidA gene. Among these promoters, Ubiquitin-Ω was found to be the most efficient and was selected to drive the expression of foreign genes in Chlorella cells. A gene encoding the mature rabbit neutrophil peptide-1 (NP-1) was introduced into the cells. Integration of the gene for NP-1 into the Chlorella genome was confirmed by PCR and Southern blot analysis. In vitro anti-microbial testes demonstrated the expression of biologically active NP-1 by the transgenic Chlorella cells.

Expression of rabbit defensin NP-1 gene in transgenic tobacco plants and its activity against bacterial wilt

The thermal asymmetric interlaced (TAIL) PCR technique was used to isolate the 5-flanking regions of the nitrate reductase (NR) gene of Chlorella ellipsoidea. Isolated 5-flanking regions were fused to the GUS gene, and tested for transient expression in the alga. The isolated 5-flanking regions were able to drive GUS reporter gene expression with a strong activity, showing that the isolated 5-flanking regions contained the promoter elements necessary for the transcription of the NR gene. The expression pattern of the GUS gene and the transcriptional pattern of the NR gene are similar, which demonstrates that NR-specific regulation is mainly under transcriptional control. The nucleotide sequence data reported have been deposited in the DDBJ/EMBL/GenBank databases under the accession number AY307383.

Synthesis of borophene nanoribbons on Ag(110) surface

A cDNA-derived 200 bp fragment encoding a rabbit defensin NP-1 mature peptide was ligated into the GUS-less pBH21 to yield pBIC-35NP1. Tobacco leaf discs were genetically transformed with anAgrobacterium tumefaclens strain harbouring pBIC-3SNP1. Northern blot analysis showed that the defensin NP-1 expression cassette was normally transcribed in transgenic plants. Resistance tests demonstrated that expression of native defensin NP-1 can confer partial resistance to the bacterial wilt pathogen,Ralstonia solanacearum.

Metastable phases of 2D boron sheets on Ag(1 1 1).

We present the successful synthesis of single-atom-thick borophene nanoribbons (BNRs) by self-assembly of boron on Ag(110) surface. The scanning tunneling microscopy (STM) studies reveal high quality BNRs: all the ribbons are along the [-110] direction of Ag(110), and can run across the steps on the surface. The width of ribbons is distributed in a narrow range around 10.3 nm. High resolution STM images revealed four ordered surface structures in BNRs. Combined with DFT calculations, we found that all the four structures of boron nanoribbons consist of the boron chains with different width, separated by hexagonal hole arrays. The successful synthesis of BNRs enriches the low dimensional allotrope of boron and may promote further applications of borophene

Delocalized Surface State in Epitaxial Si(111) Film with Spontaneous √3 × √3 Superstructure

Two reproducible new phases of 2D boron sheets have been found on Ag(1u20091u20091). One of them shares the identical atomic structure of the previously reported S1 phase (β 12 sheet) but has a different rotational relationship with the substrate, and thus exhibits very different features in scanning tunneling microscopy (STM) images. The other new phase has a hexagonal symmetry and is proposed to be the long-expected α-sheet. Both of these two boron sheets are confirmed to be metallic by scanning tunneling spectroscopy.

Strained monolayer germanene with 1 × 1 lattice on Sb(111)

The “multilayer silicene” films were grown on Ag(111), with increasing thickness above 30 monolayers (ML). Scanning tunneling microscopy (STM) observations suggest that the “multilayer silicene” is indeed a bulk-like Si(111) film with a (√3u2009×u2009√3)R30° honeycomb superstructure on surface. The possibility for formation of Si(111)(√3u2009×u2009√3)R30°-Ag reconstruction on the surface can be distinctively ruled out by peeling off the surface layer with the STM tip. On this surface, delocalized surface state as well as linear energy-momentum dispersion was observed from quasiparticle interference patterns. Our results indicate that a bulklike silicon film with diamondlike structure can also host delocalized surface state, which is even more attractive for potential applications, such as new generation of nanodevices based on Si.

Strain-induced band engineering in monolayer stanene on Sb(111)

Monolayer germanene, the germanium analog of graphene, has been successfully synthesized on Sb(111) surface via molecular beam epitaxy. Scanning tunneling microscopy revealed a dendrite structure at low Ge coverage and mosaic patterns at high coverage, both with local 1 × 1 lattice. First-principle calculations confirmed the 1 × 1 low-buckled structure of germanene. The dendrite and mosaic patterns stem from strain modulation induced by large lattice mismatch between germanene and Sb substrate. This work provide a new system to explore the physical properties and applications of germanene.