IR spectral shifts and adsorption potentials of CO and N2 adsorbed on LiF and LiCl

Following our recent work on IR spectra of molecules adsorbed on C₆₀ embedded in LiF and LiCl films, adsorption potentials of CO and N₂ adsorbed on LiF (100) and LiCl (100) were calculated. For CO on LiF, a value of 2.0 kcal mol⁻¹ was obtained, close to that calculated for CO adsorbed on a single C₆₀ molecule. The calculated value for CO on LiCl is much higher, 6.8 kcal mol⁻¹. It is therefore concluded that in the case of CO adsorbed on mixed LiF/C₆₀ films, the adsorbed CO molecules are distributed almost evenly on the LiF and C₆₀ single molecules, whereas in the case of CO adsorbed on mixed LiCl/C₆₀ films the salt is greatly preferred as the adsorption site. Adsorption potential calculations for a similar system, N₂ on LiF and LiCl, gave values of 1.5 and 4.4 kcal mol⁻¹, respectively. In this case, a much too large value was found for the adsorption potential on the LiCl surface. IR spectra of CO on the two substrates showed two strong absorptions for each of them. With N₂ induced spectra were obtained. Spectral shifts have been calculated for the above systems and were all toward higher frequencies, in agreement with experimental findings.     

A DFT study on the formaldehyde (H2CO and (H2CO)2) monitoring using pristine B12N12 nanocluster

The interaction between formaldehyde monomer (H₂CO) as well as dimer ((H₂CO)₂) and pristine B₁₂N₁₂ nanocluster is investigated at B3LYP/6-311++G(d,p) level of theory. It is found that in contrary to the pristine boron nitride nanotube and nanosheet, formaldehyde adsorption induce considerable variation in the electronic properties of the B₁₂N₁₂ nanocluster. Also it is shown that the pristine B₁₂N₁₂ cluster could adsorb up to four monomer and three dimer of formaldehyde molecules in which the HOMO–LUMO gap decreased about 38–55%. Since the conductivity of the B₁₂N₁₂ nanocluster changes by the adsorption of formaldehyde molecules, the presence of this toxic gas could be detected. The Bader theory of atoms in molecules (AIM) is also applied to analyze the interaction of formaldehyde with nanocluster. It is suggested pristine B₁₂N₁₂ nanocluster could be a promising candidate for detecting formaldehyde molecule. The results indicate that B₁₂N₁₂ may be a promising chemical sensor for detection of formaldehyde molecule.     

Amantadine antiparkinsonian drug adsorption on the AlN and BN nanoclusters: A computational study

To find a sensor for Amantadine (AM) antiparkinsonian drug, we studied its interaction with Al₁₂N₁₂ and B₁₂N₁₂ nanoclusters by density functional theory calculations. The AM molecule attaches via its –NH₂ group to the Al or B atoms of Al₁₂N₁₂ or B₁₂N₁₂ with Gibbs free energy change about −31.5 or −26.1 kcal/mol. Increasing the AM concentration, the interaction becomes weaker due to steric effects. The AM adsorbs on the Al₁₂N₁₂ and B₁₂N₁₂ with two different mechanisms, including electrostatic and charge transfer, respectively. The AM significantly reduces the Al₁₂N₁₂ work function from 4.50 to 3.66 eV, increasing the electron field emission. Thus, the AlN cluster may be a work function type sensor. Upon the AM adsorption on the BN cage, the HOMO level is largely destabilized, reducing the E_g from 6.84 to 5.01 eV which largely increases the electrical conductivity. This indicates that the BN cluster may be a potential electronic sensor.     

Infrared study of triruthenium dodecacarbonyl interactions with gold

We present here a study of the interaction of triruthenium dodecacarbonyl Ru₃(CO)₁₂ with gold surfaces using time-evolved and temperature-programmed infrared reflection absorption spectroscopy (IRAS) and STM. Ru₃(CO)₁₂ exhibits drastically different adsorption/desorption behavior on high-index surfaces of gold in comparison to the smooth Au(111) surface. On the smooth Au(111) surface, the adsorption of Ru₃(CO)₁₂ at 200 K is observed to be molecular and reversible with the molecule's Ru₃-plane oriented essentially perpendicular to the surface in the first and second layer. In the multilayer (> 3 ML), the molecule is oriented parallel (or moderately inclined) to the surface. On high-index gold surfaces, prepared by partial annealing of rough gold films, the molecules dissociate. Vibrational spectra reveal dissociation of carbonyl to Ru and CO at elevated temperature (> 250 K) with the formation of CO covered Ru-islands and the subsequent desorption of CO from Ru-islands. Increasing amounts of CO observed with increasing surface roughness demonstrate that the rate of Ru₃(CO)₁₂ dissociation is related directly to the surface roughness of the gold surface. STM images reveal at low coverage the formation of 2-D islands of carbonyl fragments with lateral sizes of 1 to 1.5 nm and at higher coverage the formation of larger 3-D islands of 1 to 3 layers and lateral sizes above 10 nm.     

Influence of one CO molecule on structural and electronic properties of monatomic Cu chain

By using first-principles calculations, we have systematically investigated the structural and electronic properties of an infinite linear monatomic Cu chain with an adsorbed CO molecule. We find that the bridge geometry is energeticabsally favored not only when the Cu–Cu bond below the molecule is unstretched, but also for a wide range of d_Cu–Cu up to about 4.20 Å, while the substitutional geometry is favored only in the hyperstretched situation d_Cu–Cu>4.80 Å. Charge density differences point out the electron transfer is from the Cu atoms to the adsorbed CO molecule. The binding mechanism of CO to Cu chain can be described by the Blyholder’s model, in terms of σ-donation of electron density from the nonbonding CO-5σ orbital into empty metal orbitals and π-backdonation from the occupied metal d orbitals to empty CO-2π^⁎ orbital. The donation/backdonation process leads to the formation of bonding/antibonding pairs, 5σ_b/5σ_a and 2π_b^⁎/2π_a^⁎, with the 5σ_a lying above E_f and the 2π_b^⁎ below E_f.     

Crystal chemistry and physical properties of the ternary compounds RE5B4C5 (RE=Ce,Pr, Nd)

The ternary rare-earth metal boride carbides RE₅B₄C₅ (RE=Ce, Pr, Nd) were prepared by arc melting the mixtures of the pure elements and subsequent annealing at 1270 K. Their crystal structures were determined from single crystal X-ray diffraction data. They crystallize in the Ce₅B₄C₅ type of structure (space group Pna2₁, Z=8). Two new compounds were found, Pr₅B₄C₅: a=24.592(2) Å, b=8.4563(5) Å, c=8.4918(5) Å, R₁=0.043 (wR₂=0.076) for 2871 reflections with I_o?2σ(I_o)); for Nd₅B₄C₅: a=24.301(1) Å, b=8.3126(5) Å, c=8.3545(4) Å, R₁=0.035 (wR₂=0.069) for 3707 reflections with I_o?2σ(I_o)). Its structural arrangement consists of a three-dimensional framework of rare-earth atoms resulting from the stacking of slightly corrugated two-dimensional square nets, leading to voids filled with B₄C₄, B₃C₃, BC₂ finite chains and isolated carbon atoms. Ce₅B₄C₅ is an antiferromagnet at 5 K followed by a metamagnetic transition in elevated external fields. Pr₅B₄C₅ and Nd₅B₄C₅ are ferromagnets below T_C=12 and 15 K, respectively.     

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 77 K to 300 K. An excitation band having a doublet structure at 240 nm and 262 nm was observed for the emission at 370 nm that corresponds to ¹A_1g→¹E_g and ¹A_1g→¹T_2g 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 370 nm emission in both the crystals slightly decreases with temperature; however a sudden increase in the intensity around 264 K was observed.     

DFT study on the chemical sensitivity of C3N nanotubes toward acetone

Potential application of single-walled C₃N nanotubes was investigated as chemical sensors for acetone molecules based on the density functional theory calculations. It was found that the pristine nanotube weakly adsorbs an acetone molecule with the adsorption energy of − 9.7 kcal/mol, and its electronic properties are not sensitive to this molecule. By replacing a C atom with a Si atom, the nanotube becomes a p-type semiconductor. The adsorption energy of the acetone molecule on the Si-doped nanotube becomes much more negative (E_ad=−67.4 kcal/mol). The adsorption process leads to a sizable increase in the resistance of the Si-doped tube, thereby, it can show the presence of acetone molecule, creating an electronic signal. Also, the sensitivity of these devices can be controlled by the doping level of Si atoms. By increasing the number of dopant atoms from 1 to 4, the sensitivity is gradually increased.     

B12N12纳米笼：潜在的二氧化氮检测传感器

利用密度泛函理论通过计算吸附能量、HOMO/LUMO能隙变化、电荷转移、结构扭曲等研究二氧化氮分子在B12N12纳米笼的吸附．此外,通过计算B₁₂N₁₂的电子结合能、Gibbs自由能、态密度和分子表面的静电势研究其稳定性和其它特性．B₁₂N₁₂纳米笼吸附二氧化氮显示三种构型．B₁₂N₁₂团簇的HOMO/LUMO能隙变化对二氧化氮分子的存在非常敏感,从自由团簇的6.84 eV降为NO₂/团簇稳定团簇的3.23 eV．团簇的导电性被极大地提高,表明B₁₂N₁₂纳米簇可能是潜在的二氧化氮气体分子检测传感器.     

Influence of a magnetic field on the electronic Raman response in high-Tc cuprates

The effect of a magnetic field parallel to the CuO₂ plane on the Raman spectra is investigated based on the Slave–Boson approach to the t − t′ − J model with a Zeeman field and the random-phase approximation. We find that the Raman spectra intensities in the superconducting (SC) state are suppressed for both the B_1g and the B_2g channels with a slight shift of the peaks position toward lower frequency in the B_1g channel and a negligible shift in the B_2g channel due to the Zeeman splitting. There is a field-induced peak and dip structure at low energy response in the B_2g channel at very low temperature. While rising temperature has a similar effect in reducing the Raman response peak in the superconducting (SC) state, it smears out the field-induced peak and dip structure in the B_2g channel. We compare these results with experiments and give explanations based on the field-induced changes of the density of the superconducting condensate, the momentum distribution of the quasiparticle energy and the scattering rate.     

High resolution emission spectroscopy of the E2Π–X2Σ+ transition of SrH and SrD

Emission spectra of SrH and SrD have been studied at high resolution using a Fourier transform spectrometer. The molecules have been produced in a high temperature furnace from the reaction of strontium metal vapor with H₂/D₂ in the presence of a slow flow of Ar gas. The spectra observed in the 18 000–19 500 cm^?1 region consist of the 0–0 and 1–1 bands of the E²Π–X²Σ⁺ transition of the two isotopologues. A rotational analysis of these bands has been obtained by combining the present measurements with previously available pure rotation and vibration–rotation measurements for the ground state, and improved spectroscopic constants have been obtained for the E²Π state. The present analysis provides spectroscopic constants for the E²Π state as ΔG(½) = 1166.1011(15) cm^?1, B_e = 3.805503(32) cm^?1, α_e = 0.098880(47) cm^?1, r_e = 2.1083727(89) Å for SrH, and ΔG(½) = 839.1283(23) cm^?1, B_e = 1.918564(15) cm^?1, α_e = 0.034719(23) cm^?1, r_e = 2.1121943(83) Å for SrD.     

CO adsorption on clean and oxidized Pt3Ti(111)

CO adsorption on clean and oxidized Pt₃Ti(111) surfaces has been investigated by means of Auger Electron Spectroscopy (AES), Thermal Desorption Spectroscopy (TDS), Low Energy Electron Diffraction (LEED) and High Resolution Electron Energy Loss Spectroscopy (HREELS). On clean Pt₃Ti(111) the LEED patterns after CO adsorption exhibit either a diffuse or a sharp c(4 × 2) structure (stable up to 300 K) depending on the adsorption temperature. Remarkably, the adsorption/desorption behavior of CO on clean Pt₃Ti(111) is similar to that on Pt(111) except that partial CO decomposition on Ti sites and partial CO oxidation have also been evidenced. Therefore, the clean surface cannot be terminated by a pure Pt plane. Partially oxidized Pt₃Ti(111) surfaces (< 135 L O₂ exposure at 1000 K) exhibit a CO adsorption/desorption behavior rather similar to that of the clean surface, showing again a c(4 × 2) structure (stable up to 250 K). Only the oxidation of CO is not detectable any more. These results indicate that some areas of the substrate remain non-oxidized upon low oxygen exposures. Heavily oxidized Pt₃Ti(111) surfaces (> 220 L O₂ exposure at 1000 K) allow no CO adsorption indicating that the titanium oxide film prepared under these conditions is completely closed.     

TiO2(110)-(1 × 1) supported Cu particles: An FT-RAIRS investigation

The morphology of TiO₂(110)-(1 × 1) supported Cu particles has been investigated by Fourier Transform Reflection Absorption Infrared Spectroscopy (FT-RAIRS), employing adsorbed CO as a probe molecule sensitive to local surface structure. For Cu coverage (deposited at 300 K) less than 2.85 MLE nucleated Cu particles in the range 2 nm–4 nm are formed, as indicated by a final state shift in the core level Cu(2p_3/2) binding energy and by the existence of only transmission bands in the FT-RAIRS spectra for adsorbed CO. ν_S(CO) indicates that these small particles expose sites similar to those of the stepped Cu surfaces Cu(211), Cu(311), and Cu(755). At Cu coverages in the range of 6 MLE and above, corresponding to particle sizes above 4.6 nm, ν_S(CO) indicates the predominance of (110), (100) and (111) adsorption sites. Annealing the Cu layers to 650 K results in the slight growth of the particle sizes, and transformation of the CO adsorption sites corresponding to the close packed facets. The transformation of the local dielectric from that of titania to that dominated by the Cu particle is shown to take place between 3.7 and 4.2 nm, and this change is also to a smaller extent sensitive to the dispersion of the particles.     

Luminescent properties of red-emitting LiSr4B3O(9−3x/2)Nx:Eu2+ phosphor for white-LEDs

An Eu²⁺-activated oxynitride LiSr_(4?y)B₃O_(9?3x/2)N_x:yEu²⁺ red-emitting phosphor was synthesized by solid-state reactions. The synthesized phosphor crystallized in a cubic system with space group Ia–3d. The LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphors exhibited a broad red emission band with a peak at 610 nm and a full width at half maximum of 106 nm under 410 nm excitation, which is ascribed to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The optimal doped nitrogen concentration was observed to be x=0.75. The average decay times of two different emission centers were estimated to be 568 and 489 ns in the LiSr_3.99B₃O_8.25N_0.5:0.01Eu²⁺ phosphors, respectively. Concentration quenching of Eu²⁺ ions occurred at y=0.07, and the critical distance was determined as 17.86 Å. The non-radiative transitions via dipole–dipole interactions resulted in the concentration quenching of Eu²⁺-site emission centers in the LiSr₄B₃O₉ host. These results indicate LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphor is promising for application in white near-UV LEDs.     

DFT-GGA study of NO adsorption on the LaO (001) surface of LaFeO3

In order to demonstrate the adsorption of the nitrogen monoxide molecule (NO) on the LaO (001) surface of LaFeO₃, we perform simulations based on density functional theory. The generalized gradient approximation (GGA) for the exchange-correlation energy functional indicates that the electronic state of the LaFeO₃ bulk is an anti-ferromagnetic insulator with a local magnetic moment of 4.1 μ_B at each Fe atom. Using the ultrasoft pseudo-potential method with spin-polarized GGA, fully optimized internal parameters as well as charge and spin density are determined for the NO-adsorbed structure prepared in a slab model. The calculated adsorption energy of NO is around ? 1.4 eV on the LaO (001) surface of LaFeO₃. This value decreases down to ? 4.46 eV at an oxygen vacancy site, where the nitrogen atom of NO is embedded in the 1st LaO layer forming a bond with Fe in the 2nd FeO layer.     

Vibrational spectroscopy of oxygen on the (100) and (111) surfaces of lanthanum hexaboride

Reflection absorption infrared spectroscopy (RAIRS) and high resolution electron energy loss spectroscopy (HREELS) have been used to study the adsorption of oxygen on the (100) and (111) surfaces of lanthanum hexaboride. Exposure of the surface at temperatures of 95 K and above to O₂ produces atomic oxygen on the surface and yields vibrational peaks in good agreement with those observed in previous HREELS studies. On the La-terminated (100) surface, RAIRS peaks correspond to vibrations of the boron lattice that gain intensity due to a decrease in screening of surface dipoles that accompanies oxygen adsorption. A sharp peak at ～ 734 cm^?1 in the HREEL spectrum shows isotopic splitting with RAIRS into two components at 717 and 740 cm^?1 with full widths at half maxima of only 12 cm^?1. The sharpness of this mode is consistent with its interpretation as a surface phonon that is well separated from both the bulk phonons and other surface phonons of LaB₆. On the boron-terminated LaB₆(111) surface, broad and weak features are assigned to both vibrations of the boron lattice and of boron oxide. On the (100) surface, oxygen blocks the adsorption sites for CO, and adsorbed CO prevents the dissociative adsorption of O₂.     

On the stability of the CO adsorption-induced and self-organized CuPt surface alloy

The stability of the recently discovered CO-induced and self-organized CuPt surface alloy was explored at near ambient pressures of O₂ (200 mbar) at room temperature, in a CO + H₂ mix (P_tot = 220 mbar, 4% CO) from room temperature to 573 K, as well as in a CO + H₂O mix (P_tot = 17 mbar, 50% CO) from room temperature to 673 K. No indications of substantial changes in surface structure were observed under the latter conditions compared to CO alone whereas the O₂ oxidation resulted in CO removal and the build-up of an ultrathin CuO_x-film. However, the oxidized CO/CuPt surface alloy could be regenerated by reducing the CuO_x in 100 mbar CO for 10 min at room temperature. The results show, amongst others, the stability of the CuPt surface alloy in various environments containing CO and how a novel coinage/Pt-group bimetallic surface alloy catalyst induced by CO adsorption can be reactivated before use in applications such as electrochemistry at ambient temperatures.     

Correlation between phosphorus concentration and opto-electrical properties of doped a-Si:H films

Phosphorus doped hydrogenated amorphous silicon (a-Si:H) films were prepared by decomposition of silane using RF plasma glow discharge. Both DC dark conductivity measurements, and spectrophotometric optical measurements through the range 200–3000 nm were recorded for the prepared films. The DC conductivity activation energy E_a decreased from 0.8 eV for the undoped sample to 0.34 eV for the highest used doping value. The optical energy gap E_g decreased ranging from 1.66 eV to 1.60 eV. The refractive index n, the density of charge carriers N/m* and the plasma frequency ω_p showed an opposite behavior, i.e. an increase in value with doping. Fitting the dispersion values to Sellmeier equation led to the determination of the material natural frequency of oscillating particles. A correlation between the changes in these parameters with the doping has been attempted.     

Exploring the role of samarium in the modification of rhodium catalysts through surface science approach

In this paper we review the preparation and reaction properties of ordered SmRh surface alloys and SmO_x/Rh(1 0 0) model catalyst which have been systematically investigated by low energy electron diffraction (LEED), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS) and temperature desorption spectroscopy (TDS). The growth of Sm on Rh(1 0 0) at room temperature follows the Stranski-Krastanov mode. Thermal treatment of the Sm films on Rh(1 0 0) leads to the formation of ordered SmRh surface alloys. An “inverse” SmO_x/Rh(1 0 0) model catalyst is produced under controlled oxidation of the SmRh surface alloy. CO adsorption on the SmRh alloy and SmO_x/Rh(1 0 0) surfaces gives rise to five TDS characteristic features originating from different adsorption sites. Both the site blocking of SmO_x and the electron transfer between SmO_x and Rh substrate significantly affect the CO adsorption. Acetate decomposition on both Rh(1 0 0) and the SmO_x/Rh(1 0 0) surfaces are found to undergo two competitive pathways that yields either (i) CO(a) and O(a) or (ii) CO₂(g) and H₂(g) at high temperature. The reactive desorption of acetic acid on SmO_x/Rh(1 0 0) is dramatically different from that on Rh(1 0 0). A rapid decomposition of acetic acid to produce CO(g) and CO₂(g) can be observed only on SmO_x/Rh(1 0 0), where CO(g) becomes the predominant product at 225 K, indicating a strong promotional effect of SmO_x in the selective decomposition of acetate. Finally, we briefly describe the future outlook of research on rare earth oxide/metal model catalysts.     

Magnetic behaviour of nanocrystalline Ni–Cu ferrite and the effect of irradiation by 100 MeV Ni ions

The effects of 100 MeV Ni ion irradiation on magnetic properties of nanoparticles of Ni_0.8Cu_0.2Fe₂O₄ with average particle sizes of 40 Å and 60 Å, synthesized by chemical co-precipitation method have been studied. The spinel cubic structures were confirmed by XRD. The average particle size estimated by XRD and by Langevin function fitting are in good agreement for both the pristine and irradiated samples. The blocking temperature increases with particle size and does not change after irradiation. On irradiation by 100 MeV Ni ions, significant changes in the hysteresis loop features are observed, which may be attributed to formation of cluster of defects in the nanocrystalline samples due to swift heavy ion (SHI) irradiation. It is also found that SHI irradiation produces more dominant changes in the hysteresis loop of smaller particle size of 40 Å as compared to that of 60 Å.