Publisher's Note: Morphology of copper nanoparticles in a nitrogen atmosphere: A first-principles investigation [Phys. Rev. B<b>77</b>, 125423 (2008)]

Soon, Aloysius; Wong, Lindee; Delley, B.; Stampfl, Catherine

doi:10.1103/physrevb.77.159901

Cited by 15 publications

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“…Taking into account the N-Cu binding length of 183 pm, which is comparable to atomic distances within pentacene, we argue as follows: N exhibits a local σ character and therefore the matrix element concerning the CO's π orbital is zero, resulting in a very confined depression over N. Between N and Cu the CO tip probes a local π orbital enabling a tunneling current. Cu also has local σ character, but its wave function only extends half as far compared to N. Furthermore, Cu is located 21 pm lower than N [20,21]. From this we conclude that our microscope setup is not able to laterally resolve a depression over Cu as well, resulting in elongated protrusions centered over Cu.…”

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confidence: 69%

“…They used Chen's derivative rule [27] to explain that due to the CO's π orbital the tunneling matrix element turns to zero over regions where the pentacene's orbital resembles one with σ and δ symmetries, whereas it does not where the orbital locally has π symmetry. We propose a similar tunneling contrast formation for copper nitride, motivated by the DFT calculations of Soon et al [21]. For the eigenstate closest to our bias voltage of 10 mV, N and Cu atoms show a local σ character, in which the N wave function has twice the spatial extension of Cu.…”

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“…Compared to alkali halides, the Cu 2 N's cð2 × 2Þ unit cell structure has a lower symmetry; thus, its atomic positions are easier to designate. STM experiments led to two criteria to locate N atoms within the islands [18]: first, N adsorbs on the hollow sites of Cu(100) [19][20][21] and should therefore appear fourfold symmetric; second, island boundaries and sharp edges are determined by N atoms [15]. With this, N-, Cu-, and hollow sites can be identified in the Cu 2 N unit cell [ Fig.…”

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confidence: 99%

“…From experimental [18] as well as theoretical work [17,20,21], the structural parameters and net charges of the Cu 2 N's unit-cell atoms are known. The distance between N and Cu is 183 pm, the N atoms are vertically displaced by 21 pm with respect to the Cu surface layer, and the charged subsurface Cu layer has a distance of 197 pm to the Cu surface layer, as indicated in Figs.…”

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CO Tip Functionalization Inverts Atomic Force Microscopy Contrast via Short-Range Electrostatic Forces

et al. 2014

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We investigate insulating Cu 2 N islands grown on Cu(100) by means of combined scanning tunneling microscopy and atomic force microscopy with two vastly different tips: a bare metal tip and a CO-terminated tip. We use scanning tunneling microscopy data as proposed by Choi, Ruggiero, and Gupta to unambiguously identify atomic positions. Atomic force microscopy images taken with the two different tips show an inverted contrast over Cu 2 N. The observed force contrast can be explained with an electrostatic model, where the two tips have dipole moments of opposite directions. This highlights the importance of short-range electrostatic forces in the formation of atomic contrast on polar surfaces in noncontact atomic force microscopy. DOI: 10.1103/PhysRevLett.112.166102 PACS numbers: 68.37.Ps, 61.46.−w, 68.37.Ef The combination of scanning tunneling microscopy (STM) with noncontact atomic force microscopy (NC-AFM) in a single probe enables a wide range of atomic-scale studies on surfaces. Whereas contrast mechanisms in STM for different tip-sample systems are widely understood, the interpretation of NC-AFM data remains challenging. In NC-AFM the sum over all tip-sample interactions is measured, and the source of atomic resolution is often hard to identify. On semiconductors [1]-as well as on metals [2]-imaged with reactive tips (e.g., Si) atomic contrast is dominated by the formation of covalent bonds that often reach magnitudes of nanonewtons. For nonreactive CO-functionalized tips, Pauli repulsion was attributed to the observed intramolecular resolution [3,4]. Lantz et al. [5] showed that the dangling bonds of Si(111)-(7 × 7) can induce a dipole moment in (nonreactive) oxidized Si tips resulting in a short-range electrostatic interaction, which contributes to atomic resolution. Electrostatic interaction and an induced tip dipole moment was also used to explain atomic contrast on ionic crystals [6]. A similar model describes the interaction with charged adatoms on thin insulating layers [7,8]. Moreover, it was found that clean metallic tips carry an intrinsic dipole moment [9,10], which is caused by the Smoluchowski effect [11]. All of these examples underline the importance of atomic-scale electrostatic interactions in NC-AFM.Electrostatic forces become even more meaningful as polar thin insulating layers (e.g., NaCl, MgO, Cu 2 N) are used to decouple adsorbates in STM and AFM experiments [3,7,[12][13][14][15][16]. In this study we explore the influence of electrostatic forces in NC-AFM on Cu 2 N islands on Cu(100). N and Cu atoms on Cu 2 N form a periodic charge arrangement, as calculated by density functional theory (DFT) [17] [Figs. 1(c)-1(e)]. Compared to alkali halides, the Cu 2 N's cð2 × 2Þ unit cell structure has a lower symmetry; thus, its atomic positions are easier to designate. STM experiments led to two criteria to locate N atoms within the islands [18]: first, N adsorbs on the hollow sites of Cu(100) [19][20][21] and should therefore appear fourfold symmetric; second, island boundaries and sharp edg...

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CO Tip Functionalization Inverts Atomic Force Microscopy Contrast via Short-Range Electrostatic Forces

et al. 2014

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“…31 Recently, the Wulff construction has been employed to predict the shape of a nanoparticle when interactions between a nanoparticle and its environment are included. [32][33][34][35][36][37][38][39] In the present study, we performed DFT calculations to investigate the dissociative adsorption of dimethyl disulfide (CH 3 S-SCH 3 ) on Au(hkl) surfaces with h, k, l ≤ 3, and on the kinked Au(421) surface at low-coverage. Furthermore, adsorption energies were employed to calculate interfacial tension between CH 3 S and Au(hkl) surfaces.…”

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Thiolate adsorption on Au(${\bm {hkl}}$hkl) and equilibrium shape of large thiolate-covered gold nanoparticles

Barmparis

Honkala²,

Remediakis³

2013

The Journal of Chemical Physics

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The adsorption of thiolates on Au surfaces employing density-functional-theory calculations has been studied. The dissociative chemisorption of dimethyl disulfide (CH3S−SCH3) on 14 different Au(hkl) is used as a model system. We discuss trends on adsorption energies, bond lengths, and bond angles as the surface structure changes, considering every possible Au(hkl) with h, k, l ⩽ 3 plus the kinked Au(421). Methanethiolate (CH3S-) prefers adsorption on bridge sites on all surfaces considered; hollow and on top sites are highly unfavourable. The interface tensions for Au(hkl)-thiolate interfaces is determined at low coverage. Using the interface tensions in a Wulff construction method, we construct atomistic models for the equilibrium shape of large thiolate-covered gold nanoparticles. Gold atoms in a nanoparticle change their equilibrium positions upon adsorption of thiolates towards shapes of higher sphericity and higher concentration of step-edge atoms.

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The influence of oxygen and nitrogen contamination on the densification behavior of cryomilled copper powders during spark plasma sintering

et al. 2010

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It has been found difficult to fully densify some mechanically milled pure metal powders by spark plasma sintering (SPS). In this study, the densification behavior of cryomilled, nanostructured (NS) Cu powders during SPS was related to changes to the chemistry of the powders. The results showed that the presence of very small amounts of O and N in the powders, which were introduced during cryomilling and handling, significantly influenced the densification response. Moreover, reduction/removal of O/N via thermal annealing of the powders before SPS led to complete densification of the powders during subsequent SPS. The mechanisms responsible for this behavior were ascertained: O and N existed in the cryomilled powders in the form of thermally unstable compounds, and the subsequent thermal decomposition of these compounds during SPS generated the gaseous species, leading to porosity formation and incomplete densification; annealing of the powders before SPS removed the gases which resulted from thermal decomposition, thereby facilitating complete consolidation during subsequent SPS.

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Publisher's Note: Morphology of copper nanoparticles in a nitrogen atmosphere: A first-principles investigation [Phys. Rev. B77, 125423 (2008)]

Cited by 15 publications

References 0 publications

CO Tip Functionalization Inverts Atomic Force Microscopy Contrast via Short-Range Electrostatic Forces

CO Tip Functionalization Inverts Atomic Force Microscopy Contrast via Short-Range Electrostatic Forces

Thiolate adsorption on Au(${\bm {hkl}}$hkl) and equilibrium shape of large thiolate-covered gold nanoparticles

The influence of oxygen and nitrogen contamination on the densification behavior of cryomilled copper powders during spark plasma sintering

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