ARPES spectra

Fig. 4. Upper panel Experimental ARPES spectra of the surface state of Cu(lll) as a function of the angle of emission near the normal. The photon energy was 11.8 eV and the second peak is a replica due to a doublet in the light source. From [43]. Lower panel High resolution ARPES spectra at normal emission of the (111) surface states of noble metals. The spectra have been measured at 30K using photons of 21.2eV. From [44],...

Table 2. Energy and linewidths of the L-gap surface states of noble metal (111) surfaces at the band minimum. The ARPES spectra have been recorded at 30 K [44], and the STS at 4.6 K [58]. All values are given in meV.

The ARPES spectra signal for the sulfur compound (TMTTF)2PF,5, displays a rigid shift of the leading edge near the Fermi energy to about 100 meV. This value is consistent with the charge gap of 900 K obtained from transport experiments DC or 800 cm from optical conductivity of (TMTTF)2PF6, Within a onedimensional frame of interpretation, this gap has been ascribed to a Mott-Hubbard localization gap [99],... 

Figure 20 ARPES spectra of (TMTSF)2PFj and (TMTSF)2C104 at T point (cf. Fig. 6). The inset identifies an energy shift compatible with a charge gap in (TMTTF)2PF5, after...

The fundamental features of the ARPES spectra reported by Shen et al. are reproduced with the experimental error which is about 0.1 eV in energy and 0.1 t in wavevector. 

Fig. 12. Momentum and temperature dependence of the energy gap estimated ftom leading edge shifts of ARPES spectra for BSCCO-2212. (a) i-dependence of the gap in the rc = 87K, 83 K, and lOK samples, measured at 14 K. The inset shows the Brillouin zone with a large Fermi surface (FS) closing the (3t,3t) point, with the occupied region shaded, (h) Temperature dependence of the maximum gap in a near-optimal 7), = 87 K sample (circles), and two underdoped samples with rc = 83K (squares) and 7). = lOK (triangles). From Ding et...

Extensive studies of the surface electronic structure for binary 3d-5d-metal carbides and nitrides has been performed using XES, ARPES and AES methods (see the list of references to this chapter). ARPES of the (100) surface of TiC, for example, have been obtained by Callenas et al (1983) using Hei and Nei excitation. Figure 8.1 shows ARPES spectra... 

The comparison by Lindberg and Johansson (1987b) between the ARPES spectra of the nonpolar NbC surface recorded at various emission angles, 9, relative to the (001) and (011) planes reveals the distinct differences caused by the anisotropy of electron distribution in the sample. 

Much less studied are the surface states of 5d-metal carbides and nitrides. ARPES spectra were recorded for the (100) surface of TaC by Gruzalski, Zehnor and Ownby (1985a,b) and Garbe and Kirschner (1989), for HfCjc by Gruzalski et al (1985b), for HfN by Perry and Schlapbach (1985) and Lindstrom et al (1989) and for WC by Stefan et al (1984, 1985) and Jain, Kanski and Nilsson (1987). 

The ARPES spectra for the HfNo.93 (100) surface (Lindstrom et al, 1989) allow the peculiarities of band dispersions along the symmetry... 

Fig. 39. CePtj, ARPES spectra at the indicated point in the Brillouin zone. Note that the 4f /2 amplitude shows amplitude variations exactly periodic with the Brillouin zone, suggestive of band states (from Andrews et al.

Fig. 43. CeBe,3(100) ARPES spectra taken at 40 eV photon energy to improve both the energy and momentum resolution. The 4f,/2 peak dispersed by about 65meV while a clear 20meV of dispersion is seen for the 4f5/2 peak, made possible by sampling a smaller portion of the Brillouin zone. The FWHM of the 4f5/2 is about 80meV, smaller than in the resonance data (from Arko et al., unpublished).

Fig. 44. Wide scan ARPES spectra for CeBe,3(100) and CeBe 3(110) to show the dispersion of the / peak as well (about lOOmeV). The time dependence of the qjectra is attributed to residual gas adsorption which suppresses some of the siuface-related features. The/ peak for CeBejsil 10) may be entirely surface-related (from Andrews et al. 1996).

Fig. 45. Wide scan ARPES spectra for several uranium heavy fermions taken at 110 eV photon energy and T = 20K. The crystallographic directions are known for USb2 and UPtj, but not for others. Note the persistent sharp features at Ef. Additional features are indicated with tic marks and are probably 6d-related, except for features near -0.5 eV (Arko et al., unpublished).

Fig. 49. ARPES spectra of USb2(001) for analyzer settings within 13° of the F-point (001). Feature B contains substantial 5f character based on photon energy dependence and shows 600 meV of dispersion, while feature A is almost of purely 5f character. Note the amphtude effect of feature A similar to that observed in Ce systems (Arko et al. 1997b).

Fig. 50. A near- p blowup of feature A in USb2 ARPES spectra of fig. 49 to emphasize dispersion of about 30meV. Normalizatian is arbitrary to enable viewing of dispersion (Aifco et al. 1997b).

Fig. 55. Near- p ARPES spectra for UPtj showing clear evidence of dispersion. The intense peaks may not derive fiom the same band as the weak peaks, as predicted by band calculations. Similar data are obtained at a measuring temeperature of 80 K, thus indicating a lack of a temperature effect.

Fig. 56. Wide scan ARPES spectra of UPt3(001) at Av=110eV and 7 =20K. The fresh cleave (t = 0) indicates a strong peak at -0.5 eV which is nearly of negligible intensity at t = 3h. This is strongly suggestive of a surface-related feature. An LDA calculated spectrum (Albers et al.) is superimposed for comparison and shows a valley in the -0.5 eV region, while the two features near both of 5f character, are rqxoduced by LDA.

Fig. 4.2 ARPES spectra for O-Cu(llO) surfaces (reprinted with permission from [16]). Additional (shaded) features around — 1.2 and —6 eV are the nonbonding and bonding states...

The electronic structure of the TMC(IOO) surface has been studied most extensively among the low-index TMC surfaces. It is well known that the use of angle-resolved photoemission spectroscopy (ARPES) can give direct information about the valence band structure around the surface (18,19), and extensive ARPES studies have been performed on the valence band structure of TMC(IOO) surfaces such as TiC(lOO) (20,21), ZrC(lOO) (22,23), VC(IOO) (24-27), NbC(lOO) (28-31), and TaC(lOO) (32,33). These studies have shown that most of the features in ARPE spectra can be understood as emissions from the bulk bands, and thus the electronic structures of TMC(IOO) are well regarded as the cross sections of the bulk electronic states. However, in some systems, surface induced electronic states have been identified as described in the following. 

As described before, a Tamm surface state is observed in ARPE spectra for the NbC(lOO) surface. However, the Tamm surface state has not always been observed on compound crystal surfaces because the degree of the modification of the electrostatic potential at the surface is dependent on several factors, such as the degree of charge transfer and surface relaxation. As for the transition metal nitride and carbide (100) surfaces, similar surface states have been found only for TiN(lOO) (36), ZrC(lOO) (36,37), and VC(IOO) (26) in addition to NbC(lOO) (28-31). 

In this part, ARPES studies of the electronic structure and reactivity of the three typical low-index surfaces of TMCs, (100), (110), and (111), are reviewed. For the neutral (100) and (110) surfaces, most of the features in the ARPE spectra can be understood as the emissions from... 

Figure 3.2.2.25 ARPES spectra from Cu(lll) collected at normal emission as a function of photon energy. The Shock-ley surface state S appears at a constant binding energy of 0.4 eV, and the peak intensity reaches a maximum at Hv = 69 eV. The...

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