Graphene, a single layer of graphite, has attracted considerable research attention recently due to its intriguing physical properties and potential applications in nanoelectronics [1][2][3][4][5]. Both experimental and theoretical studies have shown that, by carving a graphene sheet into one-dimensional nanoribbons, the electronic band gap of the graphene nanoribbon (GNR) opens up and is dependent on its width and crystallographic orientation [6][7][8][9][10][11][12][13][14][15][16]. These findings render graphene-based band-structure engineering conceivable [14][15][16][17][18][19][20][21]. Moreover, theoretical calculations have shown that half-metallicity may be realized in GNR either by applying an external in-plane electric field or by chemically functionalizing zigzag-edges of GNR with different groups such as H, COOH, OH, NO 2 , NH 3 , CH 3 , etc. [23][24][25][26]. Half-metallic GNR may find application in spintronics.Two-dimensional hexagonal boron nitride (h-BN) is structurally similar to graphene, and has been fabricated experimentally [27]. Unlike graphene, the h-BN has a large energy band gap due to strong ionicity of BN. Hence, it is expected that nanoribbons carved out of h-BN also have large band gaps. It has been shown that the band gap of boron nitride nanoribbons (BNNRs) whose zigzag edges are passivated by hydrogen decreases with increasing width, while that of BNNRs with armchair edges oscillate periodically with the width [28][29][30][31][32][33][34]. Moreover, recent calculations indicate that electronic properties of BNNRs can be modulated by applying external transversal electric field, and BNNRs may undergo metallic to semiconducting to half-metallic transition [29][30][31][32][33]. The half-metallicity is also found in BNNRs with only one edge passivated with hydrogen [34]. These findings suggest potential applications of BNNRs in nanoelectronic devices. In this work, we show, through density functional theory (DFT) calculations, that electronic properties of BNNRs can be modulated by chemical decoration at the ribbons' edges. Four chemical functional groups were considered, including -H, -NO 2 , -F, and -Cl. Our studies suggest that edge decoration is a viable way to tailor electronic properties of BNNRs.The first-principles calculations were based on the linear combination of atomic orbital DFT method implemented in DMol3 package* [35,36]. The generalized gradient approximation (GGA) in the Perdew-Burke-Ernzerhof (PBE) form as well as an all-electron double numerical basis set with polarized function (DNP) were chosen for the spin-unrestricted DFT calculation [37]. The real-space global cutoff radius was set to be 3.70 Å. To simulate chemically modified BNNRs, a tetragonal supercell was selected. BNNRs with either zigzag or armchair edges were considered for pristine models. The nearest distance between two neighboring BNNRs is greater than 30 Å. The k-points sampling was employed using the Monkhorst-Pack scheme with spacing of 0.04 Å −1 [38]. The structures were fully optimized with...

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Terahertz (THz) emission from ZnSe and ZnTe nano dots and nano gratings is experimentally studied compared with that from <111> orientation bulk ZnSe and <110> orientation bulk ZnTe. These nano dots and nano gratings are fabricated by the femtosecond laser ablation technique. Three main mechanisms coexist in the THz radiation from ZnSe and ZnTe surface nano structures as the same as from bulk sample: current surge effect (drift current), Photo Dember effect (diffusion current), and optical rectification. Moreover, it is found that nano structures not only contribute to an enhancement of THz emission, but also increase the threshold of polarity reversal of THz wave, and widen the spectrum of THz radiation. We also observe a two-fold symmetry in rotating pump polarization angle from ZnTe nano gratings, which is completely different from the three-fold symmetry observed from bulk ZnTe.

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