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Abstract The emerging CdTe–BeTe semiconductor alloy that exhibits a dramatic mismatch in bond covalency and bond stiffness clarifying its vibrational-mechanical properties is used as a benchmark to test the limits of the percolation model (PM) worked out to explain the complex Raman spectra of the related but less contrasted Zn1−xBex-chalcogenides. The test is done by way of experiment ( $$x\le 0.11$$ x ≤ 0.11 ), combining Raman scattering with X-ray diffraction at high pressure, and ab initio calculations ( $$x$$ x ~ 0–0.5; $$x$$ x ~1). The (macroscopic) bulk modulus $${B}_{0}$$ B 0 drops below the CdTe value on minor Be incorporation, at variance with a linear $${B}_{0}$$ B 0 versus $$x$$ x increase predicted ab initio, thus hinting at large anharmonic effects in the real crystal. Yet, no anomaly occurs at the (microscopic) bond scale as the regular bimodal PM-type Raman signal predicted ab initio for Be–Te in minority ( $$x$$ x ~0, 0.5) is barely detected experimentally. At large Be content ( $$x$$ x ~1), the same bimodal signal relaxes all the way down to inversion, an unprecedented case. However, specific pressure dependencies of the regular ( $$x$$ x ~0, 0.5) and inverted ( $$x$$ x ~1) Be–Te Raman doublets are in line with the predictions of the PM. Hence, the PM applies as such to Cd1−xBexTe without further refinement, albeit in a “relaxed” form. This enhances the model’s validity as a generic descriptor of phonons in alloys.

Abstract Raman scattering and ab initio Raman/phonon calculations, supported by X-ray diffraction, are combined to study the vibrational properties of Zn1−xBexTe under pressure. The dependence of the Be–Te (distinct) and Zn–Te (compact) Raman doublets that distinguish between Be- and Zn-like environments is examined within the percolation model with special attention to x ~ (0,1). The Be-like environment hardens faster than the Zn-like one under pressure, resulting in the two sub-modes per doublet getting closer and mechanically coupled. When a bond is so dominant that it forms a matrix-like continuum, its two submodes freely couple on crossing at the resonance, with an effective transfer of oscillator strength. Post resonance the two submodes stabilize into an inverted doublet shifted in block under pressure. When a bond achieves lower content and merely self-connects via (finite/infinite) treelike chains, the coupling is undermined by overdamping of the in-chain stretching until a «phonon exceptional point» is reached at the resonance. Only the out-of-chain vibrations «survive» the resonance, the in-chain ones are «killed». This picture is not bond-related, and hence presumably generic to mixed crystals of the closing-type under pressure (dominant over the opening-type), indicating a key role of the mesostructure in the pressure dependence of phonons in mixed crystals.

The emerging CdTe-BeTe semiconductor alloy that exhibits a dramatic mismatch in bond covalency and bond stiffness clarifying its vibrational-mechanical properties is used as a benchmark to test the limits of the percolation model (PM) worked out to explain the complex Raman spectra of the related but less contrasted Zn 1-x Be x -chalcogenides. The test is done by way of experiment ([Formula: see text]), combining Raman scattering with X-ray diffraction at high pressure, and ab initio calculations ([Formula: see text] ~ 0-0.5; [Formula: see text]~1). The (macroscopic) bulk modulus [Formula: see text] drops below the CdTe value on minor Be incorporation, at variance with a linear [Formula: see text] versus [Formula: see text] increase predicted ab initio, thus hinting at large anharmonic effects in the real crystal. Yet, no anomaly occurs at the (microscopic) bond scale as the regular bimodal PM-type Raman signal predicted ab initio for Be-Te in minority ([Formula: see text]~0, 0.5) is barely detected experimentally. At large Be content ([Formula: see text]~1), the same bimodal signal relaxes all the way down to inversion, an unprecedented case. However, specific pressure dependencies of the regular ([Formula: see text]~0, 0.5) and inverted ([Formula: see text]~1) Be-Te Raman doublets are in line with the predictions of the PM. Hence, the PM applies as such to Cd 1-x Be x Te without further refinement, albeit in a "relaxed" form. This enhances the model's validity as a generic descriptor of phonons in alloys., (© 2023. Springer Nature Limited.)

Raman scattering and ab initio Raman/phonon calculations, supported by X-ray diffraction, are combined to study the vibrational properties of Zn 1-x Be x Te under pressure. The dependence of the Be-Te (distinct) and Zn-Te (compact) Raman doublets that distinguish between Be- and Zn-like environments is examined within the percolation model with special attention to x ~ (0,1). The Be-like environment hardens faster than the Zn-like one under pressure, resulting in the two sub-modes per doublet getting closer and mechanically coupled. When a bond is so dominant that it forms a matrix-like continuum, its two submodes freely couple on crossing at the resonance, with an effective transfer of oscillator strength. Post resonance the two submodes stabilize into an inverted doublet shifted in block under pressure. When a bond achieves lower content and merely self-connects via (finite/infinite) treelike chains, the coupling is undermined by overdamping of the in-chain stretching until a «phonon exceptional point» is reached at the resonance. Only the out-of-chain vibrations «survive» the resonance, the in-chain ones are «killed». This picture is not bond-related, and hence presumably generic to mixed crystals of the closing-type under pressure (dominant over the opening-type), indicating a key role of the mesostructure in the pressure dependence of phonons in mixed crystals., (© 2022. The Author(s).)

The generic 1-bond → 2-mode "percolation-type" Raman signal inherent to the short bond of common A 1-x B x C semiconductor mixed crystals with zincblende (cubic) structure is exploited as a sensitive "mesoscope" to explore how various ZnSe-based systems engage their pressure-induced structural transition (to rock-salt) at the sub-macroscopic scale-with a focus on Zn 1-x Cd x Se. The Raman doublet, that distinguishes between the AC- and BC-like environments of the short bond, is reactive to pressure: either it closes (Zn 1-x Be x Se, ZnSe 1-x S x ) or it opens (Zn 1-x Cd x Se), depending on the hardening rates of the two environments under pressure. A partition of II-VI and III-V mixed crystals is accordingly outlined. Of special interest is the "closure" case, in which the system resonantly stabilizes ante transition at its "exceptional point" corresponding to a virtual decoupling, by overdamping, of the two oscillators forming the Raman doublet. At this limit, the chain-connected bonds of the short species (taken as the minor one) freeze along the chain into a rigid backbone. This reveals a capacity behind alloying to reduce the thermal conductivity as well as the thermalization rate of photo-generated electrons.

Volume-phonon-polaritons (VPP's) propagating at a light-in-vacuum-like speed are identified in the wurtzite-type Zn 0.74 Mg 0.26 Se mixed crystal by near-forward Raman scattering. Their detection is selective to both the laser energy and the laser polarization, depending on whether the ordinary (n 0 ) or extraordinary (n e ) refractive index is addressed. Yet, no significant linear birefringence (n 0  [Formula: see text] n e ) is observed by ellipsometry. The current access to ultrafast VPP's is attributed to the quasi-resonant Raman probing of an anomalous dispersion of n 0 due to impurity levels created deep in the optical band gap by oriented structural defects. The resonance conditions are evidenced by a dramatic enhancement of the Raman signals due to the polar modes. Hence, this work reveals a capacity for the lattice defects' engineering to "accelerate" the VPP's of a mixed crystal up to light-in-vacuum-like speeds. This is attractive for ultrafast signal processing in the terahertz range. On the fundamental side we provide an insight into the VPP's created by alloying ultimately close to the center of the Brillouin zone.

Near-forward Raman scattering combined with ab initio phonon and bond length calculations is used to study the 'phonon-polariton' transverse optical modes (with mixed electrical-mechanical character) of the II-VI ZnSe1-x S x mixed crystal under pressure. The goal of the study is to determine the pressure dependence of the poorly-resolved percolation-type Zn-S Raman doublet of the three oscillator [1  ×  (Zn-Se), 2  ×  (Zn-S)] ZnSe0.68S0.32 mixed crystal, which exhibits a phase transition at approximately the same pressure as its two end compounds (~14 GPa, zincblende  →  rocksalt), as determined by high-pressure x-ray diffraction. We find that the intensity of the lower Zn-S sub-mode of ZnSe0.68S0.32, due to Zn-S bonds vibrating in their own (S-like) environment, decreases under pressure (Raman scattering), whereas its frequency progressively converges onto that of the upper Zn-S sub-mode, due to Zn-S vibrations in the foreign (Se-like) environment (ab initio calculations). Ultimately, only the latter sub-mode survives. A similar 'phonon freezing' was earlier evidenced with the well-resolved percolation-type Be-Se doublet of Zn1-x Be x Se (Pradhan et al 2010 Phys. Rev. B 81 115207), that exhibits a large contrast in the pressure-induced structural transitions of its end compounds. We deduce that the above collapse/convergence process is intrinsic to the percolation doublet of a short bond under pressure, at least in a ZnSe-based mixed crystal, and not due to any pressure-induced structural transition.

Background: Pulmonary metastasectomy of renal cell carcinomas (RCC) remains controversial. Thoracic lymph node involvement (LNI) is a known prognostic factor. The aim of our analysis is to evaluate whether patients with LNI, and particularly N2 patients, should be excluded from surgical treatment., Methods: We retrospectively reviewed data from 122 patients who underwent operations at two French thoracic surgery departments between 1993 and 2011 for RCC lung metastases., Results: The population consisted of 38 women and 84 men; the average age at time of metastasectomy was 63.3 years (min: 43, max: 82). LNI was identified as a prognostic factor using univariate and multivariate analysis (median survival: 107 months vs. 37 months, P = 0.003; HR = 0.384 (0.179; 0.825), P = 0.01, respectively). Although differences in survival between metastases at the hilar and mediastinal locations were not significant (median survival: 74 months vs. 32 months, respectively, P = 0.75), length of survival time was associated with disease-free interval less than 12 months (median survival: 23 months vs. 94 months, P < 0.0001; HR = 3.081 (1.193; 7.957), P = 0.02)., Conclusion: Although LNI has an adverse effect on survival; long-term survival can be achieved in pN+ patients. Consequently, these patients should not be excluded from surgery. Systematic lymphadenectomy should be performed to obtain more accurate staging and to determine appropriate adjuvant treatment., (© 2014 Wiley Periodicals, Inc.)

Objectives: Resection of pulmonary metastases originating from colorectal cancer is increasingly considered. While several adverse risk factors for long-term outcome are known, the selection of patients who may benefit from surgery remains unclear. In particular, few studies have addressed the impact of lymph node involvement, and signification of the hilar or mediastinal level of extent., Methods: We retrospectively reviewed the data of 320 patients operated in two thoracic departments between 1992 and 2011. Appropriate statistical tests were used to compare groups at risk., Results: There were 105 women and 215 men with a mean age of 63.3 years (range: 27-86) at the time of metastasectomy. Lymph node involvement appeared as a significant prognostic factor in both the univariate and multivariate analyses [median survival: 94 months N0 vs 42 months N+, P < 0.0001; OR = 0.573 (0.329-1), P = 0.05]. Survival was similar for hilar and mediastinal locations (median survival: 47 months vs 37 months, respectively, P = 0.14). Associated hepatic metastases had a negative impact on survival in both univariate and multivariate analyses [median survival: 74 months vs 47 months, P < 0.01; OR = 0.387 (0.218-0.686), P = 0.001]. Multiple lung metastases significantly decreased survival in univariate analysis only (median survival: 81 months vs 55 months, P < 0.01). Disease-free survival and preoperative carcinoembryonic antigen had no impact on survival., Conclusions: While lymph node involvement was associated with decreased survival, the impact of mediastinal location on survival did not differ from that of hilar location. Consequently, these patients should not be excluded from surgical treatment.