Ag Single Crystals Research Articles

Successful melting and density measurements of Cu and Ag single crystals with an electrostatic levitation (ESL) system

By using grain-free single crystal specimens, the melting of Cu and Ag using electrostatic levitation (ESL) and obtaining their high-temperature densities were accomplished for the first time.

Evidence for graphite-like hexagonal AlN nanosheets epitaxially grown on single crystal Ag(111)

Ultrathin (sub-monolayer to 12 monolayers) AlN nanosheets are grown epitaxially by plasma assisted molecular beam epitaxy on Ag(111) single crystals. Electron diffraction and scanning tunneling microscopy provide evidence that AlN on Ag adopts a graphite-like hexagonal structure with a larger lattice constant compared to bulk-like wurtzite AlN. This claim is further supported by ultraviolet photoelectron spectroscopy indicating a reduced energy bandgap as expected for hexagonal AlN.

Molecular dynamics study of the temperature dependence and surface orientation dependence of the calculated vacancy formation energies of Al, Ni, Cu, Pd, Ag, and Pt

The bulk vacancy formation energies (Ev) were calculated for Al, Ni, Cu, Pd, Ag, and Pt single crystals with a molecular dynamics simulation that made use of the Sutton–Chen many-body potential. The vacancy formation energies for single crystals with the surface orientations of (111), (100) and (110) were calculated at temperatures ranging from 0K to 1000K or to below the melting temperatures of some of the elements. This study aims to investigate temperature and surface orientation dependence of the vacancy formation energy in bulk FCC crystals. Disordering occurred in (111) and (100) surface orientations at high temperatures, but well below the melting points of Al, Cu, Ag and Ni.

A dislocation dynamics analysis of the critical cross-slip annihilation distance and the cyclic saturation stress in fcc single crystals at different temperatures

Cross-slip is treated as a deterministic, mechanically activated process governed by the applied stress, by the interaction force between approaching screw dislocations of the opposite sign and by the line tension related to the persistent slip band channel width. The dislocations are modeled as moving polygons. In the evaluation of the critical cross-slip annihilation distance and the saturation stress in cycling, we accept two assumptions inspired by Brown [Brown L. Philos Mag A 2002;82:1691]: (i) the critical parameter associated with cross-slip is the spreading of the dislocation loop on the cross-slip plane, not the critical formation of a constriction in an extended screw dislocation core. (ii) The saturation stress in cycling is controlled by the stress required to separate two screw dislocations of opposite signs which are just on the point of mutual annihilation by cross-slip. The proposed model predicts the critical annihilation distance and the cyclic saturation stress in agreement with the available experimental data for Cu, Ni and Ag single crystals.

TL and OSL studies on lithium borate single crystals doped with Cu and Ag

Lithium borate (LBO) single crystals doped with Cu and Ag (0.25mol% each) (Li2B4O7:Cu,Ag) are grown by the Czochralski method. The thermoluminescence readout on Li2B4O7:Cu,Ag crystals showed three glow peaks at∼375, 441 and 516K for the heating rate of 1 K/s. The thermoluminescence sensitivity of the grown Li2B4O7:Cu,Ag single crystals is found to be 5 times TLD-100 and a linear dose response in the range 1mGy to 1kGy. The glow curve deconvolution reveals nearly first order kinetics for all the three peaks with trap depths 0.77, 1.25 and 1.34eV respectively and corresponding frequency factors 1.6×109, 1.3×1013 and 6.8×1011s−1. The continuous wave optically stimulated luminescence (CW-OSL) measurements were performed on the LBO:Cu,Ag single crystals using blue light stimulation. The traps responsible for the three thermoluminescence peaks in Li2B4O7:Cu,Ag are found to be OSL sensitive. The qualitative correlation between TL peaks and CW-OSL response is established. The photoluminescence studies show that in case of co-doping of Ag in LBO:Cu the emission at 370nm in Cu states dominates over the transitions in Ag states implying doping of Ag plays a role as sensitizer when co-doped with Cu and increases overall emission.

Photo-luminescence properties of Cu and Ag doped Li2B4O7 single crystals at low temperatures

UV excited photo luminescence from Li2B4O7:Cu and Li2B4O7:Cu, Ag single crystals has been investigated in the temperature range from 77K to 300K. An excitation band having a doublet structure at 240nm and 262nm was observed for the emission at 370nm that corresponds to 1A1g→1Eg and 1A1g→1T2g crystal field components of the 3d10→3d94s1 transition of Cu+. The relative intensity of these components and their temperature dependence provide a measure of the off-center displacement of the Cu+ ground state in the crystal lattice site. The co-doped Ag plays a role of a sensitizer when doped with Cu and increases the overall emission as the emission between Ag states lies in the excitation region of Cu states. The 370nm emission in both the crystals slightly decreases with temperature; however a sudden increase in the intensity around 264K was observed.

Structural properties of host laser single crystal Yb:YAG

High quality Yb xY 1 − x AG (0 ≤ × ≤ 1) single crystals were grown by using the Czochralski method. The structural properties of Yb xY 1 − x AG (0 ≤ x ≤ 1) single crystals were also investigated using the EXAFS method. Additionally, for the first time, EXAFS results were compared with XRD results. Moreover, without essential lattice structure transformation, Yb xY 1 − x AG crystals can be found due to the varying of doping concentration in XRD measurements. However, EXAFS measurements indicated that the local fine structural variation around the Yb 3+ ion depends on the Yb 3+ concentration.

Cyclic Deformation Behaviors of $$ [\bar{5}79] $$-Oriented Al Single Crystals

During the cyclic deformation of \( [\bar{5}79] \), Al single crystals with a high stacking fault energy produced slip bands that were characterized by wavy slip. Its cyclic stress response curve demonstrated that the specimen experienced hardening–softening–secondary hardening in sequence with repeated fluctuation stresses usually less than 10 MPa, which is far lower than those of Cu, Ni, and Ag single crystals. Finally, the whole surface of the Al single crystals was covered with intense intrusion and extrusion, and the cell structure is the most typical dislocation arrangement. These cells mainly comprise loose clusters of dislocations, which move more freely. In the center of the cell, the dislocation density is relatively low, and most dislocations concentrate in the cell wall. At room temperature, compared with cyclically deformed Cu, Ni, and Ag single crystals, the cyclic deformation behaviors of Al single crystals show significant differences, which are highlighted in this study.

Dislocation arrangements in cyclically deformed Au single crystal

Cyclic deformation was carried out on [ 2 ¯ 2 7 ] Au single crystal at plastic resolved strain amplitudes of 1.11 × 10 −3 and 2.22 × 10 −3 with a cyclic saturation stress of 23.4 MPa. Persistent slip bands (PSBs) were also found in the cyclically saturated specimens. In comparison with the fatigue-induced dislocation arrangements of other fcc metals, such as Cu, Ni and Ag, two basic criteria for determining whether the ladder-like PSBs form or not were proposed. Besides PSBs, the vein, wall and labyrinth structure also appeared in cyclically deformed [ 2 ¯ 2 7 ] Au single crystals. Experimental results show that cyclic deformation behaviors of Au single crystals are very similar to those of Cu, Ni and Ag single crystals, which will become the important and fundamental basis to determine the cyclic deformation mechanism of fcc single crystal.

Magnetic Phase Diagram in NdCu4Ag Single Crystal

The magnetic properties of cubic intermetallic compound NdCu 4 Ag single crystals were studied in detail through magnetization, susceptibility, specific heat and electrical resistivity measurements. An observed anomaly in C ( T ) with a sharp peak 26 J/(mol K) at 4.2 K, together with an antiferromagnetic behavior of χ( T ), indicated that an antiferromagnetic phase transition occurred at this temperature. Anisotropic properties in M ( H ), χ( T ), and C ( T ) at external fields were investigated in directions of [001], [110], and [111], respectively. Two metamagnetic transitions were observed below the Neel temperature T N when a magnetic field was applied in three directions. In all the three directions, T N decreased with an increase in magnetic field and new anomalies induced by a high H ext were observed in both χ( T ) and C ( T ), implying that two new magnetic phases coexisted with the antiferromagnetic phase. From the specific heat measurements, it is speculated that the crystalline electric field ...

Effect of orientation on cyclic stress–strain curves and dislocation patterns of Ag and Cu single crystals

Cu and Ag single crystals with different orientations show great similarities in their cyclic deformation behavior, including cyclic stress–strain (CSS) curves and dislocation patterns. Based on a large amount of experimental results, it is found that single-slip, conjugate double-slip and [0 1 1] multiple-slip oriented Cu and Ag single crystals exhibit obvious plateau behavior in their CSS curves and the corresponding dislocation patterns are composed of typical two-phase structure including persistent slip bands (PSBs) and veins. However, the critical and coplanar double-slip oriented Cu and Ag single crystals do not exhibit clear plateau region in their CSS curves and labyrinth and cell structures are typical due to the different dislocation reactions. The relationship between the CSS curves and the saturation dislocation patterns was discussed and summarized.

A High Molecular Weight Donor for Electron Injection Interlayers on Metal Electrodes

The molecular donor 9,9'-ethane-1,2-diylidene-bis(N-methyl-9,10-dihydroacridine) (NMA) has been synthesized, and its electronic properties were characterized both in solution using cyclic voltammetry and optical absorption spectroscopy, and at interfaces to metals with photoelectron spectroscopy (PES). The optical energy gap of NMA in solution increases by 0.10 eV when the compound is doubly oxidized. On the basis of quantum-chemical calculations, this ipsochromic effect is rationalized by a change in geometry involving a severe torsion of the two acridinium moieties with respect to the central double bond, thus reducing conjugation upon oxidation. PES is reported for NMA deposited on Au(111), Ag(111), and Cu(111) single crystals. A decrease of the sample work function is observed that becomes larger with increasing molecular coverage and clearly exceeds values that would be expected for metal surface electron "push back" alone, confirming the electron donating nature of NMA. The growth mode of NMA on all three surfaces is almost layer-by-layer (Frank-van der Merwe). For tris(8-hydroxyquinoline)aluminum (Alq(3)) deposited on top of a NMA-modified Au(111) surface, the electron injection barrier (EIB) is reduced by 0.25 eV compared to that on pristine Au(111). Furthermore, the EIB reduction depends linearly on Phi of the donor-modified Au(111) surface, adjustable by NMA precoverage. This enables continuous tuning of the EIB in organic electronic devices, in order to optimize device efficiency and performance.

Cyclic deformation and fatigue damage behaviors of oriented Ag single crystal

The cyclic deformation and fatigue damage behaviors of oriented Ag single crystal were investigated in terms of cyclic stress–strain (CSS) curves, surface slip morphologies and dislocation configurations. A clear plateau region appears in the CSS curve of the Ag single crystal over a strain range of with average saturation shear stress amplitude of ∼26.6 MPa. Corresponding ladder-like persistent slip bands (PSBs) also appear in the Ag single crystal. Compared with other Cu and Ag single crystals with single or double-slip orientations, the saturation resolved shear stresses of the critical double-slip-oriented single crystals, no matter whether for Cu or Ag, are significantly higher than that of the single-slip-oriented ones. Combining the two-phase model with the hindering effect of sessile jogs on screw dislocation movement, a three-phase model is proposed to rationalize the increase of saturation stress. In addition, the surface slip morphologies of the Ag single crystal were characterized by the interactions between the primary and secondary SBs. According to the difference in their slippage, their interactions can be divided into three types, which could simultaneously appear in different local areas of the same crystal. The current experimental results extend the fundamental understanding of the intrinsic fatigue damage behaviors of fcc metal crystals.

Three Ag(I) and Cu(II) complexes of 4-pyridin-4-yl-(1,3) dithiol-2-one

Single crystals of Ag(I) and Cu(II) complexes with 4-pyridin-4-yl-(1,3) dithiol-2-one (PYDO), [Ag(PYDO)2]ClO4, [Ag(PYDO)2(NO3)], and [Cu(PYDO)2(NO3)2] have been prepared and characterized. PYDO displays excellent coordination to Cu(II) and Ag(I). The 1,3-dithiol five-member ring is an electron donor that enhances the coordination ability of the py group. HOMO-1 σ coordination and d–π electron back-donating from metal to ligand (LUMO) are suggested based on the calculation. Weak interactions and secondary bonds from the anion to cation play an important role in the molecular assembly.

A versatile apparatus for time-resolved photoemission spectroscopy via femtosecond pump-probe experiments

A laser-based system for time-resolved photoemission spectroscopy using up to 6.2 eV photons is presented. The versatility of the laser source permits several combinations of pump and probe photon energies with pulse durations of 50-100 fs. The ultrahigh vacuum system, equipped with evaporators, a low energy electron diffraction system and an Auger spectrometer, grants the possibility to grow and characterize thin films in situ. The electron energy analyzer is a time-of-flight spectrometer with a multianode detector allowing high count rates. The performance of the whole experimental setup is investigated on Cu(100), Cu(111), and Ag(111) single crystals.

Comparison of dislocation patterns in cyclically deformed fcc metals

Cyclic deformation behaviors of face-centered cubic (fcc) metals, especially Cu and Ag single crystals, were compared. It was found that the dislocation patterns of fatigued Cu and Ag single crystals display similar features with ladder-like persistent slip bands (PSBs). The current finding confirms that, after Cu and Ni, Ag is the third pure fcc metal to form the ladder-like PSB structure. Based on the two-phase model of the saturation shear stress, a new criterion for PSB formation has been established.

Effect of orientations on cyclic deformation behavior of Ag and Cu single crystals: Cyclic stress–strain curve and slip morphology

This work investigates the differences in the cyclic stress–strain (CSS) curves and surface slip morphologies of the fatigued Ag and Cu single crystals with different orientations. It is found that the average saturation resolved shear stress τ s of Ag single crystal is ∼6 MPa less than that of Cu single crystal with the same orientation. In addition, for the same kind of crystal, whether Cu or Ag, it seems that the saturation shear stress of coplanar double-slip-oriented single crystal is slightly higher than that of single-slip-oriented single crystal. In addition, the surface deformation morphologies (deformation bands and slip bands) are strongly dependent on the crystallographic orientations. As the crystallographic orientations of the crystals deviate from the best observation orientation [ 1 2 ¯ 1 ] zone, on the one hand, the resolved shear stress τ s rises and some braid slip bands (SB) appear on the crystal surface, and, on the other hand, the interacting angle between the primary slip bands and the deformation band II (DBII) changes from perpendicular to a gradually smaller angle. Based on the experimental results, the relationships between crystallographic orientation, CSS curves and slip morphologies (including DBII and SB) in the fatigued Ag and Cu single crystals are discussed.

Adsorption of transition metal atoms on the NiO(100) surface and on NiO/Ag(100) thin films

We have studied the adsorption of Au, Pd, and Pt atoms on the NiO(100) surface and on NiO/Ag(100) thin films using plane wave DFT+U calculations. The scope of this work is to compare the adsorption properties of NiO, a reducible transition metal oxide, with those of MgO, a simple binary oxide with the same crystal structure and similar lattice parameter. At the same time, we are interested in the adsorption characteristics of NiO ultra-thin films (three atomic layers) deposited on Ag(100) single crystals. Also in this case the scope is to compare NiO/Ag(100) with the corresponding MgO/Ag(100) films which show unusual properties for the case of Au adsorption. The results show that the transition metal atoms bind in a similar way on NiO(100) and NiO/Ag(100) films, with Pt, Pd, and Au forming bonds of decreasing strength in this order. No charging effects occur for Au adsorbed on NiO/Ag(100) films, at variance with MgO/Ag(100). The reasons are analyzed in terms of work function of the metal/oxide interface. Possible ways to modify this property by growing alternate layers of MgO and NiO are discussed.

Comparative Study of Thymine Adsorption on Cu- and Ag-Adlayers on Au(111) Electrodes

The electronic attributes of an electrochemically deposited copper monolayer on Au(111) were compared to its bulk equivalent by XPS experiments. Due to the modified interaction between the Cu-Cu as well as Cu-Au atoms at the surface a core level shift to lower binding energies occurs, which exceeds the values found for surface core level shifts of Cu atoms on Cu(100) surfaces. It could be shown that the thymine orientation on a copper layer depends on the externally applied potential in analogy to the adsorption behaviour on Au(111) and Ag(111) single crystals. The transition between a chemisorbed and a physisorbed phase occurs around the potential of zero charge. Independently of the adsorption state of thymine the electron density around the surface copper atoms is reduced by the interaction between thymine molecules and the copper surface. At electrochemically deposited silver monolayers, bilayers as well as at bulk silver on Au(111) different orientations and adsorption states of thymine could be evaluated. A comparison between XPS and electrochemical data reveal an alteration of the thymine–Ag interaction within the chemisorbed thymine layer deposited on 1 ML Ag/Au(111). It is notable that the transformation between the chemisorbed and physisorbed thymine phase does not seem to be dependent on the thickness of the silver adlayers, while the potential of zero charge differs by about 200 mV. In contrast, the onset of the hydrogen evolution shifts to lower potentials with increasing thickness of the Ag layers.

Effect of irradiation on photoluminescence and optical absorption spectra of Li 2B 4O 7:Mn and Li 2B 4O 7:Ag single crystals

Effects induced by high-dose irradiation on manganese- and silver-doped Li 2B 4O 7 (lithium tetraborate, LTB) single crystals were monitored by photoluminescence and optical absorption spectroscopy. High-dose (1.0×10 3 and 1.2×10 4 Gy) irradiation of the samples was performed using high-energy, short-time (4 MeV, 2.6 μs) electron pulses of a linear electron accelerator. Changes in the oxidation states of dopants were revealed. Recharging of manganese Mn 2+→Mn 3+ and Ag +→Ag 0 were observed. Ionization process Mn 2+→Mn 3++e − and creation of Ag 0-nanoparticles are supposed.