V. Grasso

A new evaporation method for preparing hydrogenated amorphous silicon films

Abstract We describe a new evaporation method for preparing hydrogenated amorphous silicon films under different deposition conditions. The films obtained have characteristics comparable to those prepared by other conventional techniques. Infrared spectra and d.c.-electrical conductivity results are reported.

Soft x-ray absorption of FePS3 and NiPS3

Abstract With the partial yield technique we measured the absorption spectra of several core levels in FePS 3 and NiPS 3 . The M 2, 3 spectra of Fe and Ni are interpreted as localized transitions 3p 6 3d m− 3p 5 3d m+1 of the transition metal ion, split into a multiplet by final state multiconfiguration interaction. The P L 2, 3 , S L 2, 3 , and S L 1 spectra are similar to each other and are interpreted in terms of the projected density of states of the conduction bands derived from the states of the (P 2 S 6 ) 4− cluster.

Electronic conduction in the layered semiconductor MnPS3

Thermopower, conductivity and photoconductivity measurements as a function of temperature, from 130 to 320 degrees C, have been carried out on manganese thiophosphate, MnPS3. The transport mechanisms involved in distinct temperature ranges and under different illumination conditions have been identified. At 130 degrees C a dark conductivity value of 8.6*10-13 Omega -1 cm-1 has been measured, while photoconductivity values ranged from 8.8*10-13 to 6.1*10-8 Omega -1 cm-1. In particular, the dark conductivity process has been attributed to holes in the phosphorus 3pz valence band. The results have been interpreted on the basis of a model, already used for NiPS3, that assumes a weak, ionic, interaction between the transition-metal and the sulphur atoms. A possible energy distribution of both valence and conduction bands, together with Mn 3d levels, is also provided.

Optical absorption spectra of some transition metal thiophosphates

Abstract Near-infrared and visible absorption spectra at room temperature of MnPS 3 , CoPS 3 , CoPS 3 are reported. These materials show weak structures below their fundamental absorption thresholds, due to the 3d-3d transitions occurring on the transition metal ion. By comparison with other transition metal compounds, such excitations are interpreted on the basis of the ligand field theory. The appearance of well developed crystal field spectra is a further confirmation that these materials are considerably ionic.

Optical constants and interband transitions in the layer compound InSe

Abstract The relevant optical constants of InSe are obtained by applying the Kramers-Kronig relations to accurate near normal incidence reflectance data in the 1.5–5.5 eV energy range. In absence of band calculations, the observed structures are tentatively interpreted by analogy with GaSe ones.

Optical spectra of the layered Cd2P2S6 and Cd2P2Se6 compounds in the region from 1.6 to 5.5 eV

Room temperature absorption and reflectivity data are presented for Cd2P2S6 and Cd2P2Se6 crystals in the range of photon energies between 1.6 and 5.5 eV. For both compounds the characteristic feature of the optical absorption is that their absorption edge appears to correspond to an indirect allowed transition with an optical energy gap of 3.06 eV for Cd2P2S6 and 2.29 eV for Cd2P2Se6. An associated phonon energy of 74 meV for Cd2P2S6 and 50 meV for Cd2P2Se6 is also deduced. The Cd2P2X6 (with X=S or Se) reflectivity spectra are compared with the early reflectivity spectrum of Zn2P2S6. As observed in previous reflectivity spectra of the Hg2P2X6 compounds, near the fundamental absorption edges the Cd2P2X6 reflectivity spectra show a pronounced rise in reflectivity, a feature common to most layered compounds. For photon energies greater than their absorption edges, the reflectivity spectra of both materials look similar to one another and to that of Zn2P2S6. On the basis of these similarities we have adopted ...

Magneto-optical measurements on the C band in KBr: Tl+

Abstract The 1 A 1 g → 1 T 1 u transition of thallium center in KBr has been investigated using the technique of circular dichroism. The agreement between the experimental and theoretical spectra is excellent and seems to support the mechanism of the Jahn-Teller effect.

X-ray photoelectron spectroscopy and x-ray excited Auger spectroscopy studies of manganese thiophosphate intercalated with sodium ions

Polycrystalline powders of Na2xMn1−xPS3 have been synthesized from layered MnPS3 material by successive ion-exchange intercalation of potassium and sodium ions. Their x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger spectroscopy spectra have been measured at room temperature using Mg Kα (1253.6 eV) x-ray source. In particular, the Mn, P, and S 2p and Na 1s and 2p core-level regions and the Na Auger KL23L23 transition have been investigated. All the analyzed XPS core-level spectra display a single-peak structure, suggesting the absence of nonequivalent atoms of Na, Mn, P, and S. The manganese XPS spectrum shows, as observed in MnPS3 and in its cesium and potassium intercalation compounds, typical shake-up satellites, suggesting that the Mn–S bond is yet mainly ionic in nature. The comparison with the XPS spectra relative to MnPS3 and its potassium intercalation compound (K2xMn1−xPS3) does not emphasize any relevant difference in the binding energy positions of the investigated core levels, in...

An XPS analysis of the interaction of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin with exfoliated manganese thiophosphate

Composite thin films of (C72H66N8O12S4)yLi2xMn1−xPS3 have been obtained through a solution approach by interacting the tosylate salt of the cationic water soluble 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (H2T4) and MnPS3 exfoliated in the presence of lithium ions. The thin films have been investigated through x-ray diffraction (XRD), ultraviolet/visible (UV/vis) absorption and mainly x-ray photoemission spectroscopy (XPS). N 1s core-level XPS spectra emphasize the presence of three non-equivalent nitrogen atoms, similarly to the film of the pure H2T4 salt. This result, together with the interlayer spacing determined by the XRD pattern and the evidence from absorption measurements, indicates that the porphyrin is intercalated into MnPS3 layers in a non-protonated form and substantially flattened with respect to the free molecule. The striking likeness between the N 1s core levels in the XPS spectra of the composite material, of the H2T4 salt and of the neutral meso-tetrapyridylporphyrin (H2TPyP) suggests that H2T4 is present between the MnPS3 nanosheets together with its counter-ion (tosylate). This hypothesis is confirmed by the observation of a structure which can be attributed to the sulfur of the counterion in the S 2p core-level XPS spectra of the composite material. An analysis of the Mn 2p and 3p, S and P 2p core-level regions through XPS reveals a strong similarity between the starting MnPS3 and the composite material, suggesting that no charge transfer occurs from the guest (H2T4-tosylate) to the host species (MnPS3).

NIR-VIS reflectivity spectra of some transition metal thiophosphates

SummaryRoom temperature optical-reflectivity measurements on some transition metal thiophosphates were carried out in the near infrared and visible regions. The resulting spectra, interpreted on the basis of the «transition metal weakly interacting» model, agree well with earlier optical transmission measurements. Below the fundamental absorption edge, the observed features have been assigned to 3d–3d transitions occurring on the transition metal ion, while those observed at photon energies greater than the absorption threshold have been attributed to transitions from the valence bands to discrete 3d orbital levels or to the conduction bands. A more detailed information on the metal ion 3d levels energy distribution with respect to the valence band states belonging to the (P2S6)4- cluster and a more precise determination of the MPS3 absorption edge energy position have been obtained.