Islanding, growth mode and ordering in Si heteroepitaxy on Ge(001) substrates structured by thermal annealing

Si/Ge heteroepitaxial dots under tensile strain are grown on nanostructured Ge substrates produced by high-temperature flash heating exploiting the spontaneous faceting of the Ge(001) surface close to the onset of surface melting. A very diverse growth mode is obtained depending on the specific atomic structure and step density of nearby surface domains with different vicinal crystallographic orientations. On highly-miscut areas of the Ge(001) substrate, the critical thickness for islanding is lowered to about 5 ML, in contrast to the 11 ML reported for the flat Ge(001) surface, while on unreconstructed (1x1) domains the growth is Volmer-Weber driven. An explanation is proposed considering the diverse relative contributions of step and surface energies on misoriented substrates. In addition, we show that the bottom-up pattern of the substrate naturally formed by thermal annealing determines a spatial correlation for the dot sites

Low field magnetotransport in strained Si/SiGe cavities

Low field magnetotransport revealing signatures of ballistic transport effects in strained Si/SiGe cavities is investigated. We fabricated strained Si/SiGe cavities by confining a high mobility Si/SiGe 2DEG in a bended nanowire geometry defined by electron-beam lithography and reactive ion etching. The main features observed in the low temperature magnetoresistance curves are the presence of a zero-field magnetoresistance peak and of an oscillatory structure at low fields. By adopting a simple geometrical model we explain the oscillatory structure in terms of electron magnetic focusing. A detailed examination of the zero-field peak lineshape clearly shows deviations from the predictions of ballistic weak localization theory.Comment: Submitted to Physical Review B, 25 pages, 7 figure

Conductance quantization in etched Si/SiGe quantum point contacts

We fabricated strongly confined Schottky-gated quantum point contacts by etching Si/SiGe heterostructures and observed intriguing conductance quantization in units of approximately 1e2/h. Non-linear conductance measurements were performed depleting the quantum point contacts at fixed mode-energy separation. We report evidences of the formation of a half 1e2/h plateau, supporting the speculation that adiabatic transmission occurs through 1D modes with complete removal of valley and spin degeneracies.Comment: to appear in Physical Review

Appendiceal mucinous neoplasms: An uncertain nosological entity. Report of a case

Introduction: Appendiceal mucocele is a relatively rare condition characterized by progressive dilation of the appendix caused by intraluminal accumulation of mucoid substance. Its incidence is 0.07 - 0,63% of all appendectomies performed. Case report: We report the case of a 70-year-old man who came to our observation with gravative pain in right lower abdominal region. A computed tomography abdominal scan revealed a cystic/tubular structure like an appendicular mass with wall enhancement but without calcifications suggestive of a mucocele. Into peritoneal cavity we found profuse mucinous material with a 1,5 cm size parietal nodule. We also identified a free perforation of the cecum with consensual spillage of gelatinous material mimicking a pseudomyxoma peritonei. We decided to perform a right hemicolectomy with excision of peritoneal lesion. Discussion: The controversy in the pathologic terminology can give rise to a clinical dilemma in terms of the management and follow-up plans. For mucosal hyperplasia and cystadenoma simple appendectomy is curative. Only in case of large base of implantation it may be necessary the resection of the ileum and caecum or right hemicolectomy. In case of mucinous cystoadenocarcinoma authors perform a right hemicolectomy. Conclusion: Appendiceal mucinous neoplasms are different pathological entities. The correct surgical management depends on size and location of lesion. A preoperative diagnosis is obviously needed in order to perform the correct treatment. CT abdominal scan is the better diagnostic tool, but different authors show their inability to reach a preoperative diagnosis in the larger majority of cases

Disentangling elastic and inelastic scattering pathways in the intersubband electron dynamics of n -type Ge/SiGe quantum fountains

n-type Ge/SiGe quantum wells have been suggested as a promising platform for the realization of a Si-compatible THz laser. Focusing on this material system, we have developed a numerical model to describe the intersubband carrier dynamics which restores the equilibrium after pulsed optical excitation in asymmetric coupled Ge/SiGe quantum wells. We take into account inelastic and elastic scattering processes and investigate different quantum-well geometries, doping densities, and excitation regimes. In this configuration space, we disentangle the effect on the overall dynamics of each scattering channel and provide intersubband relaxation times, finding larger values with respect to III-V based materials, thanks to the weaker electron-phonon coupling with respect to III-V compounds. Finally, the model is used to study and optimize the population inversion between the first- and second-excited subband levels and to assess its dependence on the lattice temperature, providing a sound theoretical framework to guide forthcoming experiments

Endometrial cancer: Robotic versus Laparoscopic treatment. Preliminary report

Laparoscopic approach is today the standard treatment for benign and malignant gynecological pathologies. To traditional laparoscopic surgery in the last 10 years we can add the possibility to use a robotic platform. The adoption of this system allows undoubted advantages as the three-dimensional vision, the absence of the physiological tremor with enhanced ergonomics and possibility of using articulable tools. In this study we analyzed the results of 18 patients with endometrial cancer (Stage I) treated with robotic approach. The results were compared with a selected sample of 26 patients, with the same characteristics, treated with traditional laparoscopic approach in the same period by the same surgical team. The mean total operative time was significantly longer for robotic than laparoscopic group (125.6 min vs 102.3 min). However, if to this operative time we remove the time of preparation (docking time) we obtain the following results: 102.5 min for robotic group and 95.7 min for the laparoscopic control group. Intra-operative blood loss are significantly lower in the robotic group than in laparoscopic group. The robotic treatment of gynecological cancer is a safe and feasible technique. The oncological results are also equivalent to those of traditional laparoscopic surgery with advantages in terms of precision and reduction of intraoperative bleeding. Additional clinical studies on larger samples and heterogeneous patients are necessary in order to clarify the real advantages of robotic treatment

Asymmetric-coupled Ge/SiGe quantum wells for second harmonic generation at 7.1 THz in integrated waveguides: a theoretical study

We present a theoretical investigation of guided second harmonic generation at THz frequencies in SiGe waveguides embedding n-type Ge/SiGe asymmetric coupled quantum wells to engineer a giant second order nonlinear susceptibility. A characteristic of the chosen material system is the existence of large off-diagonal elements in the χ2 tensor, coupling optical modes with different polarization. To account for this effect, we generalize the coupled-mode theory, proposing a theoretical model suitable for concurrently resolving every second harmonic generation interaction among guide-sustained modes, regardless of which χ2 tensor elements it originates from. Furthermore, we exploit the presence of off-diagonal χ2 elements and the peculiarity of the SiGe material system to develop a simple and novel approach to achieve perfect phase matching without requiring any fabrication process. For a realistic design of the quantum heterostructure we estimate second order nonlinear susceptibility peak values of ∼7 and ∼1.4 × 105 pm/V for diagonal and off diagonal χ2 elements, respectively. Embedding such heterostructure in Ge-rich SiGe waveguides of thicknesses of the order of 10–15 μm leads to second harmonic generation efficiencies comprised between 0.2 and 2 %, depending on the choice of device parameters. As a case study, we focus on the technologically relevant frequency of 7.1 THz, yet the results we report may be extended to the whole 5–20 THz range

Early stage of CVD graphene synthesis on Ge(001) substrate

In this work we shed light on the early stage of the chemical vapor deposition of graphene on Ge(001) surfaces. By a combined use of microRaman and x-ray photoelectron spectroscopies, and scanning tunneling microscopy and spectroscopy, we were able to individuate a carbon precursor phase to graphene nucleation which coexists with small graphene domains. This precursor phase is made of C aggregates with different size, shape and local ordering which are not fully sp2 hybridized. In some atomic size regions these aggregates show a linear arrangement of atoms as well as the first signature of the hexagonal structure of graphene. The carbon precursor phase evolves in graphene domains through an ordering process, associated to a re-arrangement of the Ge surface morphology. This surface structuring represents the embryo stage of the hills-and-valleys faceting featured by the Ge(001) surface for longer deposition times, when the graphene domains coalesce to form a single layer graphene film