Low Sn Research Articles

Coexisting Early Cretaceous High-Mg Andesites and Adakitic Rocks in the North China Craton: the Role of Water in Intraplate Magmatism and Cratonic Destruction

High-Mg andesites (HMAs) and adakitic rocks are purported to occur exclusively in subduction zones in the modern Earth. In the North China Craton, early Cretaceous HMAs and adakitic dacites were erupted in a continental setting, apparently unrelated to subduction given their location distal (>1000 km) to the trench at that time. Here we report petrological, mineralogical and geochemical data for these rocks with the aim of constraining their petrogenesis and elucidating the role of water in intraplate magmatism and cratonic destruction. The HMAs can be subdivided into olivine (Ol-)HMAs and clinopyroxene (Cpx-)HMAs. The former have high MgO (>9·8 wt %) and Mg# (>71), with rare high-Fo (up to 91) olivine phenocrysts, corresponding to (near-)primary magmas that equilibrated with mantle peridotite. The latter have moderate MgO (7·8–8·8 wt %) and Mg# (mostly <70) and low-Fo (mostly < 83) olivine phenocrysts. The Cpx-HMAs are interpreted as magmas differentiated from the Ol-HMAs by olivine-dominated fractionation at lower-crust levels. P–T–XH2O estimations show that the primary HMAs are melts of shallow (1·1–1·2 GPa), hot (∼1250°C) and wet (H2O > 3 wt %) lithospheric mantle. The coexisting adakitic dacites are hydrous (H2O ≥ 5 wt %) magmas with high SiO2 (>63 wt %), Sr/Y ratios (≥39) and YbSN (source-normalized), low (Sm/Yb)SN, and negligible Eu anomalies. They also have unradiogenic whole-rock Nd [εNd(t) = –19 to –9] and zircon Hf [εHf(t) = –23 to –21] isotopic compositions consistent with derivation by melting of ancient lower crust at depths < 40 km. Melting may have been induced by heating and addition of H2O from underplated HMAs. Mixing between Cpx-HMAs and low-Mg adakitic dacites in magma chambers produced high-Mg adakitic rocks. The petrogenetic model presented here explains the occurrence of intraplate HMAs and adakitic magmas elsewhere in the North China Craton. The P–T–XH2O conditions inferred for HMA generation imply that the subcontinental lithospheric mantle beneath the craton was hot and hydrous in the early Cretaceous, which may have triggered the destruction of the cratonic root. The occurrence of young HMAs and adakitic rocks in an intraplate extensional environment also casts doubts on the common use of a similar igneous rock association as an indicator of subduction processes in Archean time.

Measurements of Laminar Flame Speeds of Gas-to-Liquid-Diesel Fuel Blends

This work investigates the laminar flame speed, SN, of gas-to-liquid (GTL) fuel and its 50–50% by volume blends with conventional diesel, in a cylindrical bomb capable of measuring SN at different initial temperatures and equivalence ratios at ambient pressure. SN was measured by analysing the pressure signals after combustion detected by a pressure transducer mounted on the bomb. Direct visualization has also been conducted to observe the ignition and flame propagation. It was found that pure GTL fuel has the highest SN near stoichiometric conditions, which is about 88.3 cm/s. However, at lean and rich mixtures, SN of GTL is slightly lower than that of the conventional diesel. The blended fuel has the lowest SN at lean and rich mixture conditions comparing with those of GTL and diesel fuels. Studying the effect of increasing the initial temperature on SN revealed that SN of the three tested fuels increases with the increase in the initial temperature almost linearly. However, the blended fuel has the lowest SN at the highest temperature, about 89.7 cm/s at 250 °C.

Influence of Zn-Sn ratio on optical property and microstructure of Zn-Sn-O films deposited by magnetron sputtering

Zinc-tin oxide (ZTO) films can exhibit high visible light transparency, high electrical conductivity and glass-like dense structures; therefore, they are expected to be applied as transparent conductive oxide and barrier layers. In this study, the influence of the Zn-Sn ratio on the optical properties and microstructures of the ZTO films was investigated. The ZTO films were deposited on glass substrates by reactive magnetron sputtering without intentional substrate heating. The chemical state, crystal structure, density, surface morphology and optical properties were evaluated. The ZTO films deposited using lower Sn concentration targets of 0 to 7at.% had wurtzite structures of ZnO. In contrast, the ZTO films were amorphous when Sn concentrations of 15 to 100at.% were used. The ZTO films had higher densities at higher Sn concentrations. Additionally, the ZTO films exhibited smooth surfaces compared with the pure ZnO and SnO2 films. The refractive indices of the ZTO films increased with increasing Sn concentration of the Zn-Sn targets. These results show that the optical properties and microstructures of the ZTO films varied with the Zn-Sn ratio.

Electromodulation spectroscopy of direct optical transitions in Ge1−xSnx layers under hydrostatic pressure and built-in strain

Unstrained Ge1−xSnx layers of various Sn concentration (1.5%, 3%, 6% Sn) and Ge0.97Sn0.03 layers with built-in compressive (ε = −0.5%) and tensile (ε = 0.3%) strain are grown by molecular beam epitaxy and studied by electromodulation spectroscopy (i.e., contactless electroreflectance and photoreflectance (PR)). In order to obtain unstrained GeSn layers and layers with different built-in in-plane strains, virtual InGaAs substrates of different compositions are grown prior to the deposition of GeSn layers. For unstrained Ge1−xSnx layers, the pressure coefficient for the direct band gap transition is determined from PR measurements at various hydrostatic pressures to be 12.2 ± 0.2 meV/kbar, which is very close to the pressure coefficient for the direct band gap transition in Ge (12.9 meV/kbar). This suggests that the hydrostatic deformation potentials typical of Ge can be applied to describe the pressure-induced changes in the electronic band structure of Ge1−xSnx alloys with low Sn concentrations. The same conclusion is derived for the uniaxial deformation potential, which describes the splitting between heavy-hole (HH) and light-hole (LH) bands as well as the strain-related shift of the spin-orbit (SO) split-off band. It is observed that the HH, LH, and SO related transitions shift due to compressive and tensile strain according to the Bir-Pikus theory. The dispersions of HH, LH, and SO bands are calculated for compressive and tensile strained Ge0.97Sn0.03 with the 8-band kp Hamiltonian including strain effects, and the mixing of HH and LH bands is discussed. In addition, the dispersion of the electronic band structure is calculated for unstrained Ge1−xSnx layers (3% and 6% Sn) at high hydrostatic pressure with the 8-band kp Hamiltonian, and the pressure-induced changes in the electronic band structure are discussed.

On the tin impurity in the thermoelectric compound ZnSb: Charge-carrier generation and compensation

The technique for measuring the Hall coefficient and electrical conductivity in the thermal cycling mode is used to study the effect of the Sn impurity on the microstructure and properties of pressed ZnSb samples. Tin was introduced as an excess component (0.1 and 0.2 at %) and as a substitutional impurity for Zn and Sb atoms in a concentration of (2–2.5) at % The temperature dependences of the parameters of lightly doped samples are fundamentally like similar curves for ZnSb with 0.1 at % of Cu. The highest Hall concentration, 1.4 × 1019 cm–3 at 300 K, is obtained upon the introduction of 0.1 at % of Sn; the dimensionless thermoelectric figure of merit attains its maximum value of 0.85 at 660 K. The experimental data are discussed under the assumption of two doping mechanisms, which are effective in different temperature ranges, with zinc vacancies playing the decisive role of acceptor centers. In two ZnSb samples with SnSb and ZnSn additives, the charge-carrier compensation effect is observed; this effect depends on temperature and markedly changes with doping type. As in p-type AIV–BVI materials with a low Sn content, hole compensation can be attributed to atomic recharging Sn2+ → Sn4+. Types of compensating complexes are considered.

Structural and magnetic properties of Mn50Fe50−xSnx (x=10, 15 and 20) alloys

In this work we report measurements and comparisons of the structural, magnetic and transport properties of a series of Mn50Fe50−xSnx alloys (x=10, 15 and 20). We found that while the lower Sn composition sample stabilized in β-Mn-type crystallographic phase, the higher Sn composition alloys contained both β-Mn-type as well as Mn3Sn-type hexagonal DO19 phases. Through d.c. and a.c. magnetic property measurements we have established the existence of a ferromagnetic transition near room temperature followed by a spin reorientation at lower temperature in the Mn3Sn-type crystallographic phase of the alloys. Our resistivity study also revealed an interesting behavior with negative temperature coefficient (TCR) in these alloys.

Time-dependent deformation of Sn micropillars

In this study, time-dependent plastic deformation of micropillars fabricated from low melting point metal Sn (~505K) was investigated at room temperature. Size-dependent strength was first evaluated and creep tests were then performed on the micropillars having diameters of 1 and 5μm. Sn pillars showed significant creep deformation, and creep rate was independent of pillar size. Creep stress exponent was determined to be ~1, and negligible effect of e-beam irradiation on creep rate confirmed that the lattice diffusion must be the predominant creep mechanism. Creep deformation of Sn micropillars, therefore, differs from the dislocation-climb based creep in bulk Sn.

Effect of Diffusion Annealing and Design of Internal Tin Wires on the Structure and Morphology of Superconducting Nb3Sn Layers

The structure and morphology of superconducting Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn layers in multifilamentary internal tin (IT) wires have been studied by transmission electron microscopy and scanning electron microscopy. The composites under study differed in the initial Sn concentration, the presence of strengthening Cu-Nb inserts, and the number of Nb filaments and their diameter in the final wire. In all the analyzed wires, columnar Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn grains were always present. The Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn grains are coarser and their size distribution is wider in the filaments of IT strands compared with the bronze-processed wires, the J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> in the former being as high as 2276 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Much lower J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values (850 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) were observed in a wire with a smaller diameter and a higher number of Nb filaments, which is not only due to the lower Sn concentration in the matrix but also to larger sizes and size scattering of equiaxed Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn grains, as well as to wider zones of columnar grains.

Titration and quantification of open and closed Lewis acid sites in Sn-Beta zeolites that catalyze glucose isomerization

Methods to quantify framework Lewis acidic Sn4+ sites in zeolite Beta (Sn-Beta) with four Lewis base titrants (pyridine, deuterated acetonitrile, n-propylamine, ammonia) were developed using infrared (IR) spectroscopy or temperature programmed desorption (TPD). Integrated molar extinction coefficients (E, cmμmol−1) were measured for IR bands of pyridine adsorbed to Lewis acidic Sn sites (E(1450cm−1)=1.42±0.30) and of CD3CN adsorbed to open (E(2316cm−1)=1.04±0.22) and closed (E(2308cm−1)=2.04±0.43) Sn sites, and differ from analogous E values for Lewis acidic Al sites by up to 3.6×. TPD of Sn-Beta samples after saturation with NH3 or n-propylamine (NPA) and purging to remove physisorbed species also enabled quantification of Lewis acid sites, which is seldom performed despite analogous methods that use such titrants to quantify Brønsted sites in solid acids. These four Lewis bases titrated Lewis acidic Sn sites with equimolar stoichiometry and counted similar numbers of Sn sites on low-defect Sn-Beta samples synthesized in fluoride media (Sn-Beta-F) with high Sn content (Si/Sn <150). NPA binding on residual silanol defect sites, however, caused overestimation of Sn sites by TPD on Sn-Beta-F samples with low Sn content (Si/Sn >175) or high defect Sn-Beta samples prepared via post-synthetic insertion of Sn atoms into framework vacancy defects of dealuminated Beta zeolites (Sn-Beta-OH). Molar ratios of open-to-closed Sn sites varied widely (0.29–1.64) among the eight Sn-Beta samples studied here. Open Sn sites have been proposed as the dominant active sites for aqueous-phase glucose–fructose isomerization via intramolecular 1,2-hydride shift, consistent with successive poisoning of Sn-Beta samples with pyridine prior to measurement of initial glucose isomerization rates that suppressed reactivity at pyridine uptakes similar to the number of open Sn sites counted ex-situ by CD3CN. Measured first-order glucose isomerization rate constants in water (per open Sn, 373K), which reflect free energy differences between isomerization transition states and two coordinated water molecules at Sn sites, were ∼50× higher on hydrophobic Sn-Beta-F than on hydrophilic Sn-Beta-OH zeolites. The characterization methods reported herein enable normalization of initial glucose isomerization turnover rates on Sn-Beta zeolites by their number of open Sn sites, as required prior to interpreting the catalytic consequences of structural heterogeneities introduced by differences in sample preparation or treatment history.

Oxygen deficiency and Sn doping of amorphous Ga2O3

The potential of effectively n-type doping Ga2O3 considering its large band gap has made it an attractive target for integration into transistors and solar cells. As a result amorphous GaOx is now attracting interest as an electron transport layer in solar cells despite little information on its opto-electrical properties. Here we present the opto-electronic properties, including optical band gap, electron affinity, and charge carrier density, for amorphous GaOx thin films deposited by pulsed laser deposition. These properties are strongly dependent on the deposition temperature during the deposition process. The deposition temperature has no significant influence on the general structural properties but produces significant changes in the oxygen stoichiometry of the films. The density of the oxygen vacancies is found to be related to the optical band gap of the GaOx layer. It is proposed that the oxygen deficiency leads to defect band below the conduction band minimum that increases the electron affinity. These properties facilitate the use of amorphous GaOx as an electron transport layer in Cu(In,Ga)Se2 and in Cu2O solar cells. Further it is shown that at low deposition temperatures, extrinsic doping with Sn is effective at low Sn concentrations.

Evaluation of portable Raman spectroscopy and handheld X-ray fluorescence analysis (hXRF) for the direct analysis of glyptics

In archaeometry, the advantages of a combined use of Raman spectroscopy and X-ray fluorescence spectroscopy are extensively discussed for applications such as the analysis of paintings, manuscripts, pottery, etc. Here, we demonstrate for the first time the advantage of using both techniques for analysing glyptics. These engraved gemstones or glass materials were originally used as stamps, to identify the owner, for instance on letters, but also on wine vessels. For this research, a set of 64 glyptics (42 Roman glass specimens and 22 modern ones), belonging to the collection of the museum ‘Quinta das Cruzes’ in Funchal (Madeira, Portugal), was analysed with portable Raman spectroscopy and handheld X-ray fluorescence (hXRF). These techniques were also used to confirm the gemological identification of these precious objects and can give extra information about the glass composition. Raman spectroscopy identifies the molecular composition as well as on the crystalline phases present. On the other hand, hXRF results show that the antique Roman glass samples are characterised with low Pb and Sn levels and that the modern specimens can be discriminated in two groups: lead-based and non-lead-based ones.

Characterization and activity of novel tin incorporated ordered cubic mesoporous silicate, Sn-KIT-6

Tin incorporated ordered mesoporous silicate having Ia3d cubic structure, Sn-KIT-6, was prepared using nonionic Pluronic P123 triblock copolymer as a structure directing agent and n-butanol as co-solvent. Characterization techniques including SAXS, HR-TEM, N2 sorption verified the structural ordering and morphology of Sn-KIT-6 samples. At low Sn loading (<3wt% Sn), mainly framework substituted isolated Sn4+ species were obtained. As the loading increased, SnOx particles are found either uniformly distributed or agglomerated on the surface of Sn-KIT-6. The BET surface, pore volume and pore diameter of Sn-KIT-6 samples are respectively observed in the range of 1153–1045m2/g, 1.59–0.93cm3/g and 9.1–9.3nm. Sn-KIT-6 samples revealed excellent catalytic activity in the synthesis of nopol via the Prins condensation of β-pinene and paraformaldehyde.

C6-P-09Image enhancement of electron microscope images with Gabor wavelets-based filtering

In general, an electron microscopic image is processed with some enhancement tools, such as integration types, various kinds of filtering and so on, because of the low sn ratio and low image contrast. Since, it is essentially desirable to suppress the electron dose, such an image enhancement method is significant. The Fourier filtering especially for enhancement of a crystal lattice image is well known as one among those methods. In this type of filtering (conventional case), diffraction spots and streaks appearing in a pattern of Fourier transform are extracted and the other spectra are filtered. However, because Fourier transform of an image reflects all localized lattice information, artificial lattice images are mixed in the filtered image. Fourier filtering cannot enhance local lattice images only. On the other hand, Gabor wavelets-based filtering is an alternative method to resolve the problem. It is well-known that the response characteristics of the cortical neurons are best modeled with a family of self-similar 2D Gabor wavelets [ 1 ]. We think that 2D Gabor wavelets are suitable to analyse the frequency characteristics of local lattice images. It seems that there are few applications of the Gabor wavelets filtering to electron microscopic images. Then, we have applied the Gabor wavelets filtering to some high-resolution transmission electron microscope images of locally crystalized specimens. As a result, local lattice image enhancements were achieved avoiding the artificial generation of the Fourier spectral lattice images.

Growth mechanism of intermetallic compound and mechanical properties of nickel (Ni) nanoparticle doped low melting temperature tin–bismuth (Sn–Bi) solder

This paper investigates the effects of Ni nanoparticles on the formation of intermetallic compound (IMC) layers and mechanical properties of low melting temperature Sn–58Bi (wt%) based solders on copper (Cu) substrate. At the initial reaction for the plain Sn–Bi solder/Cu substrate system, an island-shaped Cu6Sn5 IMC layer was found to adhere at the substrate surface. A very thin Cu3Sn IMC layer was also observed between the Cu6Sn5 IMC layer and Cu substrate as the reaction time increased. However, in the composite solders doped with Ni nanoparticles, a scallop-shaped ternary (Cu, Ni)–Sn IMC layer appeared at the interface without Cu3Sn IMC layer. In the solder ball region, the Bi phase with bright contrast was homogeneously distributed in the β-Sn matrix. After adding the Ni nanoparticles, an additional very fine Sn–Ni IMC particle was found to have been distributed in the β-Sn matrix. The IMC layer thicknesses were increased with the reaction time and temperature. However, the IMC growth behavior of composite solder was slower than that of the plain solder system. Furthermore, the mechanical properties of the composite solder exhibited higher values than that of the plain Sn–Bi solder due to the strengthening effect of fine Sn–Ni IMC particles.

Wafer-level Cu–Sn micro-joints with high mechanical strength and low Sn overflow

In this paper, we report wafer-level bonding using solid-liquid inter-diffusion (SLID) processes for fabricating micro-joints Cu–Sn at low temperature (270 °C). The evolution of multilayer Cu/Sn to micro-joint alloys has been characterized by optical microscopy and mechanical die-shear testing. The Cu–Sn joints with line width from 80 to 200 μm prove to be reliable packaging materials for bonding vacuum micro-cavities with controllable Sn overflow, as well as high mechanical strength (>70 MPa). A thermodynamic model has been performed to further understand the formation of Cu–Sn intermetallic alloys. There are two important findings for this work: 1) Using a two-step temperature profile may significantly reduce the amount of Sn overflow; 2) for packaging, a bond frame width greater than 80 μm will result in high yield.

Development and characterization of Sn–1.3Ag–0.7Cu solder bearing Zn for electronic packaging

The effect of small amounts of Zn on microstructure, thermal behavior and mechanical properties of low silver-content Sn–1.3Ag–0.7Cu (SAC137) solder was investigated. Microstructural investigations of SAC137 solder revealed that both the intermetallic compounds of rod-like Cu6Sn5 and needle-like Ag3Sn particles are dispersed in β-Sn matrix, which are gradually diminished with increasing Zn content in plain solder. Moreover, addition of 0.75 wt% Zn promotes the nucleation of β-Sn grains and leads to formation of new (Cu,Ag)5Zn8 IMC particles. Although the strength and Young’s modulus of plain solder are increased with increasing Zn content, the elongation was firstly increased with 0.75 wt% Zn addition and then decreased after adding 1.5 % Zn. The higher mechanical strength was contributed by the fine β-Sn grains and precipitations strengthen effects of new (Cu,Ag)5Zn8 IMC particles. The presence of Zn in SAC137–0.75 wt% Zn solder seems to result in a complete reduction of brittle pro-eutectic Ag3Sn phase to maintain the ductility at the highest level. The new (Cu,Ag)5Zn8 IMC developed in Zn added specimens was found to enviably affect the thermal properties according to DSC analyses.

High hole mobility tin-doped polycrystalline germanium layers formed on insulating substrates by low-temperature solid-phase crystallization

We investigated the effects of incorporation of 0%–2% tin (Sn) into amorphous germanium (Ge) on its crystallization behavior and electrical properties. Incorporation of only 0.2% Sn caused the polycrystallization temperature of Ge to lower from 450 to 430 °C, while a polycrystalline Ge1−xSnx layer with high crystallinity compared to that of polycrystalline Ge was formed by incorporation of 2% Sn. A polycrystalline Ge1−xSnx layer with a low Sn content of 2% annealed at 450 °C exhibited a Hall hole mobility as high as 130 cm2/V s at room temperature even though it possessed a small grain size of 20–30 nm. The Hall hole mobility of a poly-Ge1−xSnx layer with an Sn content of 2% was four times higher than that of a polycrystalline Ge layer and comparable to that of single-crystalline silicon.

The effect of iron and bismuth addition on the microstructural, mechanical, and thermal properties of Sn–1Ag–0.5Cu solder alloy

This work investigates the effect of Fe and Bi addition, 0.05wt.% Fe and 1wt.% or 2wt.% Bi, on the microstructural, mechanical, and thermal properties of the low silver Sn–1Ag–0.5Cu (SAC105) solder alloy. Adding Bi and Fe to SAC105 increased ultimate tensile strength (UTS) and yield strength and decreased the total elongation which is related to solid-solution and precipitation strengthening effects by Bi in the Sn-rich phase. While 0.05wt.% Fe made few FeSn2 in the solder bulk which does not have considerable effect on mechanical properties. Scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) showed that Bi strengthen solder by scattering in the bulk of SAC105-Fe solder alloy, thereby increased β-Sn and degenerated Cu6Sn5 and Ag3Sn into a chain-like arrangement. Surface fracture of SAC–Fe–Bi solder alloys showed brittle fracture because Bi prevented β-Sn to deform and therefore Bi decreased its ductility. Finally, Bi significantly reduces the melting point and undercooling.

Measurement of Recombination Lifetimes in Gesn Alloys

Silicon photonics requires the development of Si-based lasers, modulators, waveguides, and detectors operating in the infrared beyond the band gap of silicon. A number of approaches to solving this problem have been pursued, including epitaxial growth of lower band gap materials on Si. The SiGe alloy system was explored for many years, but limitations in quality due the large lattice mismatch between Si and SiGe with high amounts of Ge, as well as the band gap (0.66 eV at its lowest for pure Ge) and its indirect nature, have prevented its widespread use. Integration of III-V materials such as InGaAs has also been tried extensively, but the problems of phase segregation and film quality have not been overcome. The GeSn alloy system has been gaining attention in the photonics world due to its unique optical properties, and the growth of these alloys on Si platforms has jumpstarted efforts to employ this technology for the fabrication of CMOS-compatible infrared optoelectronics. These crystalline alloy films are grown directly on Si or Ge-buffered Si, have band gaps below that of Si or Ge, and are grown to thicknesses of up to 1 µm. Additionally, the band gap of GeSn should be direct for concentrations greater than about 10% Sn. Much work has been done on the development of GeSn materials, and theoretical designs for lasers based on these alloys have been appearing in the literature frequently. However, the realization of complex optoelectronic devices like laser diodes requires materials with long recombination lifetimes to achieve population inversion. Thus, the study of recombination lifetimes in GeSn alloys is of paramount importance to the actualization of GeSn lasers. Unfortunately, the standard method of time-resolved photoluminescence (TRPL) is not well-suited to the study of GeSn alloys. For low Sn contents (<10% Sn), the band gap is indirect, so the intensity of optical emission is not high. Such a measurement would require single photon counting, but single photon detectors are not available at the emission wavelengths for the materials of interest. Conductivity-based methods should be more suitable, but the standard techniques of microwave photoconductive decay (µ-PCD) and RF-coupled photoconductive decay (RFPCD) suffer from low sensitivity in thin films or low temporal resolution. In this work, we employ a new conductivity-based method for measurement of recombination lifetimes in thin film GeSn alloys. The method of transmission-modulated photoconductive decay (TMPCD) uses the transverse transmission of microwaves through a thin film, allowing for a very large interaction volume between the free carriers and the microwaves, thereby increasing the sensitivity for thin film materials. We will discuss this new method and show preliminary results on GeSn films with up to 7% Sn.

Growth and complex characterization of nanoporous oxide layers on metallic tin during one-step anodic oxidation in oxalic acid at room temperature

Nanoporous tin oxide layers were synthesized by anodic oxidation of low purity Sn foil (98.8%) in oxalic acid electrolytes at various operating conditions including anodizing potential (3–10V), concentration of the electrolyte (0.1, 0.3 and 0.5M), and duration of the process (300s, 600s and 1800s). A detailed quantitative inspection of the effect of anodizing conditions on the structural features of anodic oxide layers was performed. A special emphasis was put on the correlation of the sample morphology with the current vs. time curves, especially in terms of differences between the surface morphology and the inner oxide structure. When the potential of 3V was applied during anodization, micron-sized particles of SnC2O4 were obtained on the surface of metallic tin, independently of the electrolyte concentration. On the contrary, the anodic oxidation of Sn foil at potentials between 4 and 8V resulted in the formation of nanoporous tin oxides with two distinguishable layers: a less regular outer layer with smaller nanopores formed at the beginning of anodization, and an inner layer with well-defined and larger nanochannels. A dense, compact barrier layer was also observed at the bottom side of oxide. The morphology of an outer layer was found to be strongly dependent on anodizing conditions. For instance, a significant increase in the average pore diameter in the outer layer with increasing potential and concentration of the electrolyte, being a result of more effective field-assisted etching of anodic oxide and more vigorous oxygen evolution under the severe anodizing conditions, was observed. Contrary to this, no significant effect of anodizing conditions on the structure of the inner oxide layer was found. A strong linear relationship between the average steady-state current density and anodizing potential was observed for the potentials in the range of 5–8V, what suggests that the reaction is limited by the mass transfer in the electrolyte. Finally, when potentials of 9 and 10V were applied, an initial formation of the dense, passive outer layer, its further breakdown, and formation of the well-defined, nanoporous inner oxide layer was observed.