Cr 2p Research Articles

Spin-polarized electron spectroscopy as a combined chemical and magnetic probe

Photoelectron spectra of inner core states of magnetic material show polarization features determined by the magnetic properties of the valence electrons. This offers a new possibilty of using electron spectroscopy as a magnetic probe. The low intensity of these photoemission lines led us to use very-low-energy-electron-scattering from Fe as spinpolarimeter with an efficiency about 20 times higher than previously used spin detection techniques. First experiments on the Fe 3p and 3s core levels confirm exchange split lines. For thin Cr overlayers on Fe(001) we find the polarization of the Cr 3p level for Cr coverages up to two monolayers to be opposite to that of the Fe 3p core level. Effects of the film thickness on the spin-resolved core level spectra are discussed.

オーステナイト系焼結ステンレス鋼の機械的性質に及ぼすりん添加の影響

Influences of the addition of phosphorus and the sintering temperature on the mechanical properties of P/M Austenite type stainless steels were investigated. As a result, the best produced conditions obtaining high mechanical properties on P/M Austenite stainless steels were necessary to add 0.2-0.5wt% phosphorus and to sinter in the range of 1626K to 1673K. The tensile strength, elongation and impact values of these specimens obtained were over 550MPa, 40% and 250J/cm2 respectively. The mechanism of improvement of these mechanical properties was caused by a high sintered density of Austenite matrix obtained by the eutectic reaction between the matrix (δ-phase) and minor phosphide (Fe, Cr)3P.

Magnetic properties of Cr overlayers on Fe (invited)

The magnetic properties of Cr overlayers deposited on Fe(100) were investigated by spin-resolved photoemission. Valence band spectra show a reduction of the overall polarization after deposition of Cr. Data of the Cr 3p core level show for Cr coverages up to about 2 monolayers a polarization opposite to that of the Fe 3p core level. Both findings are evidence for an orientation of the Cr moments antiparallel to the Fe moments. The core level as well as the valence band results are consistent with an average moment of about 1 μB per Cr atom, which is significantly smaller than calculated for a monolayer of Cr on Fe.

Quantitative resolution of X‐ray photoelectron spectra of mixtures of chromium compounds by the Kalman filter after cubic spline background removal

AbstractThe potential of a new procedure for the quantitative analysis of ESCA spectra was exploited by determining the composition of powder mixtures of some chromium compounds. The quantitative separation of the overlapped Cr 2p peak doublets was accomplished by the Kalman filter algorithm. Background removal from the spectra was carried out by a new approach employing the cubic splines as smooth interpolators between the peak valleys. The results of the analyses compared well with those obtained by factor analysis (typical errors were ±4%). However, the Kalman filter operating recursively on the data points of the spectrum is preferable when the analysis is limited to only one mixture plus standards. Cubic spline interpolation was as effective as the Shirley method in yielding quantitative background subtraction.

Multielectron excitations in the K-edge x-ray-absorption near-edge spectra of V, Cr, and Mn 3d0 compounds with tetrahedral coordination.

Multielectron excitations involving metal deep 1s and shallow 3p core levels have been identified in the x-ray-absorption spectra in the range 50--60 eV above the K edge of transition-metal ions V, Cr, and Mn with tetrahedral coordination geometry. The many-body transitions have been found after subtraction of the dominant one-electron transitions to continuum states giving the x-ray-absorption near-edge structure. The presence of many-body excitations involving valence electrons has been found at \ensuremath{\sim}7 eV above threshold. The energy positions are in good agreement with calculated excitation energies for the many-body configurations, where the two excited electrons are in the unoccupied molecular ${\mathit{t}}_{2}^{\mathrm{*}}$ orbital. Experimental comparison of the intensities of corresponding many-body satellites between the Cr 2p x-ray photoelectron spectrum and Cr K-edge absorption spectrum is reported for ${\mathrm{K}}_{2}$${\mathrm{CrO}}_{4}$.

The effect of microcrystallites in the amorphous matrix on the corrosion behavior of melt-spun CrNiP alloys

The metallurgical structures of the melt-spun CrNiP alloys prepared by changing the ratio between eutectic Cr-13 at% P and Ni-19 at% P alloys were studied with TEM techniques. The presence of the microcrystalline phases in the amorphous matrix of Cr-27Ni-15P alloy was undetectable by X-ray diffraction, but was confirmed by TEM. Both phosphorus and chromium enhance the glass-forming ability of Cr-Ni-P alloys, but the microcrystalline bee Cr(Ni,P) and Cr(Ni) 3P phases appear in the amorphous matrix with increasing chromium and decreasing phosphorus. The corrosion behavior is significantly sensitive to the presence of the microcrystallites in the amorphous matrix, and depassivation takes place by the presence of microcrystallites which are undetectable by X-ray diffraction. It is necessary to form a single amorphous phase for maintaining the highly corrosion-resistant passive film in a severe environment such as 6 M HCl.

Préparation et caractérisation d'un cyclohexaphosphate de chrome Cr 2P 6O 18 · 21 H 2O

Crystals of a chrome (III)-cyclohexaphosphate, Cr 2P 6O 18 · 21 H 2O, have been grown from CrCl 3 and Li 6P 6O 18 · 6 H 2O. Synthesis and structural characterization by X-ray diffraction, IR absorption, DTA and GTA are given. Cr 2P 6O 18 · 21 H 2O crystallizes with a cubic unit cell, P 4 3 n with parameters a = 19.039 (2), Å, V = 6901.3, Å 3, Z = 8 and D x = 1.84 g/cm 3. This compound is piezoelectric and has no known structural analog.

The ligand field spectrum of the hexafluorochromate (III) anion: An a b i n i t i o study including correlation effects

The ground and ligand field excited states of CrF3−6 have been studied, using different Gaussian basis sets of atomic natural orbitals. Each state was first optimized separately in a complete active space self-consistent field (CASSCF) calculation, including three active electrons in the 2t2g and 4eg shells. Further correlation was then added by using either a singles and doubles configuration interaction approach (SDCI) or by the average coupled pair functional method (ACPF) with the CASSCF configuration space as the reference space. Thereby the number of correlated electrons was raised up to 15. It is shown that the quartet–quartet transitions, corresponding to a 2t2g→4eg excitation, are described already very accurately at the CASSCF level. Further improvement of the 4A2g→4T2g transition was obtained by extending the CI treatment so as to include the F 2p electrons from the 1t2g,3eg, and finally also from the 6a1g shell. For the intraconfigurational t32g quartet–doublet transitions on the other hand, the best results were obtained by an 11 electron CI treatment, including the Cr(III) 3s and 3p electrons.

Application of factor analysis to the AES and XPS study of the oxidation of chromium

AbstractAuger electron spectroscopy (AES), x‐ray photoelectron spectroscopy (XPS) and factor analysis of the MVV Auger spectra and the Cr 2p XPS spectra were applied to study quantitatively the initial stages of the oxidation of polycrystalline chromium. Application of factor analysis allows the identification of up to three real factors. According to the previous works on chromium oxidation, the factors responsible for variations in data were identified as being due to pure metal, chromium oxide (Cr2O3) and chemisorbed oxygen, respectively. The very first stages of the oxidation, <1 L exposures, were found to be characterized by only two factors. Since two standard spectra are known (i.e. metal and chromium oxide spectra), the quantification of all three real factors mentioned above is possible by the application of target testing procedures.

Electronic properties of the Cr [sbnd]Si(111) interfaces

In comparison with the other 3d metal-Si(111), interfaces, the CrSi(111) interface has distinct electronic properties because of its special electronic structure of the free atom, 3d54s1. Interface formation at room temperature and elevated temperatures between Cr and Si(111)-7 × 7 has been studied using photoemission spectroscopy (XPS and UPS) and other techniques. Samples were fabricated by sequential deposition of Cr metal onto clean Si(111)-7 × 7 surfaces under uhv. At the initial stage (θ = 0.8 Å), the Cr 3p core line shifts 0.2 eV to a lower binding energy compared with that of pure Cr metal. With increasing coverage, the Cr 3p core line shifts decrease and subsequently approach that of pure Cr metal. Meanwhile, the Cr 2p3/2 core line shape of CrSi2 is widened and with greater asymmetry compared with that of pure metal Cr. These peculiar electronic properties compared with that of other 3d metal silicides have been discussed, taking into account the special electronic structure of Cr.

Formation and stability of radiation-induced phases in neutron-irradiated austenitic and ferritic steels

Ni 3Si (γ'), G, and in many cases M 2P or M 3P type phosphides are phases induced by irradiation in austenitic stainless steels. Radiation-induced segregation (RIS) of alloying elements (i.e., strong enrichment of Ni and Si, and often a relative depletion of Cr and/or Mo) appears to be the major factor affecting their formation and subsequent stability in such steels. These phases are also sensitive to variations of alloy composition, thermomechanical pretreatment, irradiation temperature, and He/dpa ratio. In some austenitic stainless steels, RIS and precipitation can lead to transformation of the matrix into ferrite during irradiation. In martenstic/ferritic 9Cr and 12Cr steels, irradiation can induce formation of M 6C(η), χ, α', and in some cases G, Cr 2X, σ, Cr 3P or MP phases. These phases are sensitive to irradiation temperature, and also vary somewhat with alloy composition, but not as much as in the austenitic steels. The RIS phenomenon in the ferritic steels appears to involve minor elements like Si, Ni, P and possibly V, judging from the compositions of the radiation-induced phases. As most of these phases are also Cr-rich, Cr supersaturation or segregation during irradiation may also play a role.

Crystal structure of the tetrapolyphosphate Cr 2P 4O 13

The structure of the tetrapolyphosphate Cr 2P 4O 13 was determined from single-crystal X-ray diffraction data. It crystallizes in the monoclinic space group P2 1 c with a = 8.097(2), b = 8.787(3), c = 13.098(4)Å, β = 105.54(2)°, V = 897.8(5) Å 3, Z = 4, and R = 0.0297, R w = 0.0287 for 1802 unique reflections. Hexagonal tunnels along the a-axis are formed by the edges of two CrO 6 octahedra and four PO 4 tetrahedra. The framework consists of pairs of edge-sharing CrO 6 octahedra forming Cr 2O 10 units and unusual tetrapolyphosphate anions P 4O 6− 13. The phosphate anion forms a “U” shape and is built up by four corner-sharing PO 4 tetrahedra. The present state of tetrapolyphosphate chemistry is briefly reviewed.

The coprecipitation of Cr 3P and Cr in Cu

During TEM studies on Cu-Cr alloys previously considered to be simple binaries it was found that a minor secondary precipitate phase was also present. Through electron diffraction, EDS, microprobe analyses and high-resolution imaging the additional phase was identified as bct Cr 3P and related to the presence of trace amounts of P in the alloys. It was concluded, however, that the phosphide particles precipitate on the primary Cr laths only after they are well developed. Thus earlier quantitative analyses of Cr precipitate morphologies in Cu remain valid.

Marked differences in the 3p photoabsorption between the Cr and Mn+ isoelectronic pair: Reasons for the unique structure observed in Cr.

Chromium is the only member of the transition-group elements with a well developed Rydberg structure appearing in its 3p-absorption spectrum. New high-resolution measurements of Mn, ${\mathrm{Mn}}^{+}$, and Cr have revealed weak Rydberg structure in ${\mathrm{Mn}}^{+}$ and an analysis of the data shows that the anomalous Cr 3p absorption spectra is due to a unique relationship between its energy levels, and not to the previously supposed fact that Cr has an unpaired 4s electron.

Coordination of Cp 2Cr 2(CO) 4(μ-η 2P 2) to metal carbonyl fragments and crystal structure of Cp 2Cr 2(CO) 4 − (μ-η 2-P 2)[Cr(CO) 5] 2

Cp 2Cr 2(CO 4(μ-η 2-P 2) (I) reacts with 2 mole equivalents of M(CO) 5THF to give Cp 2Cr 2(CO) 4(μ-η 2-P 2)[M(CO) 5] 2 (M = Cr, II; Mo, III; W, IV) in 65–70% yields. The reaction with 1 mole equivalent of Cr(CO) 5THF gave the mono-metallated complex Cp 2Cr 2(CO) 4(μ-η 2-P 2[Cr(CO) 5] (V) in 60% yield along with II in 18% yield. In the presence of stoichiometric amount of PPh 3 as a Cr(CO) 5 scavenger, II was converted into V and I. X-ray analysis showed that II has C 2 molecular symmetry; the CrCr′ and PP′ bond distances in the tetrahedral Cr 2P 2 core are 3.003(1) and 2.063(1) Å, respectively.

Surface properties of Cr2O3

Thin (<5 nm) air-oxidized Cr layers are deposited on the alumina output windows of radio-frequency klystron tubes to prevent electron multipactor by reducing the secondary electron emission yield of the alumina surface. The top several nanometers of these layers appear to be Cr2O3. To compare the measured surface properties of these layers with those of clean stoichiometric Cr2O3, quasibulk Cr2O3 layers were produced by wet-H2-firing magnetron-deposited Cr films on Cu substrates and characterized by x-ray photoelectron-, Auger electron-, and electron energy loss spectra and secondary electron emission yield measurements. Other properties measured were x-ray diffraction structure, sheet resistance, and optical reflectivity. In particular, the peak of the secondary electron yield was found to be ∼1.7, which is considerably higher than the <1 yield value reported earlier in the literature. The Cr2O3 Cr 2p x-ray photoelectron core level spectrum was curve-fit using Doniach–Sunjic line shapes and statistical fitting methods. It is shown that each 2p level is composed of three multiplet-split peaks 1.1 eV apart. In addition, the three 2p1/2 peaks are folded with a 2p3/2 3d satellite.

Comparative study of the formation of Cr/Ge and Ge/Cr thin-film interfaces.

The interface morphologies of Cr/Ge and Ge/Cr thin film junctions have been studied using synchrotron radiation photoemission. Ge 3d and Cr 3p core level results for Ge deposition onto Cr indicate that Ge chemisorbs without disrupting the substrate. With increasing coverage, an amorphous Ge film forms (a-Ge) and buries the abrupt Ge/Cr interface. Examination of the reverse Cr/Ge thin-film interface prepared under identical conditions shows extensive substrate disruption, metal-semiconductor interdiffusion, and a reacted interfacial region. Comparison of this Cr/Ge thin-film interface to Cr/Ge(111) shows analogous Ge outdiffusion and compound formation, demonstrating that disorder in the a-Ge substrate is not the only cause of the enhanced interdiffusion observed for Cr/Ge compared to Ge/Cr. The dissimilar reactivity of Ge/Cr and Cr/Ge is attributed to differing substrate disruption energetics and clustering at the earliest stages of interface formation.

Deposition and hallow crystal growth of CrP and Cr 3P by CVD process

CrP and Cr 3P were obtained from a gas mixture of CrCl 3, PCl 3, H 2 and Ar in the temperature range of 700–1200°C and with a gas flow ratio PCl 3/CrCl 3 of 4 to 10. A single phase of CrP was obtained below 800°C irrespective of the gas flow ratio PCl 3/CrCl 3, while Cr 3P was obtained above 1100°C and with a ratio of PCl 3/CrCl 3>8. Hollow crystals with interesting morphologies of CrP and Cr 3P were obtained. The microhardness of CrP and Cr 3P were 1160–1370 and 1420 kg/mm 2, respectively. At a temperature above 600°C, CrP and Cr 3P were oxidized to form CrPO 4 and a mixture of CrPO 4 and Cr 2O 3, respectively.

The reactive Cr/InP and Mn/InP interfaces

Soft x-ray photoemission spectroscopy studies were performed in ultrahigh vacuum on cleaved n-InP(110) with sequential room-temperature Cr and Mn depositions of up to 30 Å. The In 4d, P 2p, and Cr 3p or Mn 3p core levels were monitored as a function of coverage. Both systems exhibited strong metallic In-phase separation and surface segregation, formation of a metallic phosphide, and no evidence of island formation. Fermi level-pinning positions of 0.6 and 0.3 V below the CBM were estimated for the Cr and Mn systems, respectively, by deconvoluting the substrate from the interfacial components of the In core lines. These results are discussed in the context of different models of Schottky barrier formation.

Bis(dimethylphosphino)methane (dmpm) complexes of iron, molybdenum and chromium: X-ray crystal structures of FeCr(CO) 6(μ-dmpm) 2 and Fe 2(CO) 4(μ-CO)(μ-dmpm) 2

The photolysis of Fe(η 1-dmpm)(dmpm) 2 [dmpm = bis(dimethylphosphino) methane) with Cr(CO) 6 and Fe(CO) 5 under UV irradiation produces FeCr(CO) 6(μ-dmpm) 2, Fe 2(CO) 6(μ-CO)(μ-dmpm) and Fe 2(CO) 4(μ-CO)(μ-dmpm) 2 respectively. The interaction of Mo(CO) 3(MeCN) 3 and (C 7H 8)Cr(CO) 3 with dmpm produces Mo 2(CO) 6(μ-dmpm) 3 and cis-Cr(CO) 2(dmpm) 2 respectively. The X-ray crystal structure of FeCr(CO) 6(μ-dmpm) 2 shows the molecule to contain a trigonal bipyramidal Fe(CO) 3P 2 unit plus a square pyramidal Cr(CO) 3P 2 unit held closely together by the methylene bridges of the dmpm ligands with steric compression between the CO groups causing distortions from ideal geometry in each case. The Cr … Fe distance is 3.111(6) Å and there seems to be little structural evidence of any form of interaction between the 16 e Cr(O) centre and the Fe-containing unit. The structure of Fe 2(CO) 4(μ-CO)(μ-dmpm) 2 contains a symmetrical μ 2-carbonyl and a single bond between the two symmetry related (m) iron atoms. The Fe … Fe distance is 2.719(4) Å.