ScAlMgO4 (SAM) is a promising substrate material for group III-nitride semiconductors. SAM has a lower lattice mismatch with III-nitride materials compared to conventionally used sapphire (Al2O3) and silicon substrates. Bulk SAM substrate has the issues of high cost and lack of large area substrates. Utilizing solid-phase epitaxy to transform an amorphous SAM on a sapphire substrate into a crystalline form is a cost-efficient and scalable approach. Amorphous SAM layers were deposited on 0001-oriented Al2O3 by sputtering and crystallized by annealing at a temperature greater than 850 °C. Annealing under suboptimal annealing conditions results in a larger volume fraction of a competing spinel phase (MgAl2O4) exhibiting themselves as crystal facets on the subsequently grown InGaN layers during MOCVD growth. InGaN on SAM layers demonstrated both a higher intensity and emission redshift compared to the co-loaded InGaN on GaN on sapphire samples, providing a promising prospect for achieving efficient longer-wavelength emitters.

Energy dispersive X-ray spectroscopy (EDS) is a well-established technique analysing characteristic X-rays generated as a by-product from the electron beam interaction within a scanning electron microscope (SEM).The conventional approach to EDS combines large area silicon drift detectors (SDD) with high working distances, typically 10 -15 mm, to maximise the number of X-rays being detected.The working distance is derived from the microscope set up, specifically the geometry of the detector, and is required to perform accurate quantitative analysis [1].This results in a loss of surface sensitivity due to the large interaction, generated by high energy electrons penetrating deep into a material.

Journal Article Measuring the Thickness of 2D Materials Using EDS Get access Samuel Marks, Samuel Marks Oxford Instruments, High Wycombe, England, United Kingdom Search for other works by this author on: Oxford Academic Google Scholar Philippe Pinard, Philippe Pinard Oxford Instruments NanoAnalysis, High Wycombe, England, United Kingdom Search for other works by this author on: Oxford Academic Google Scholar Simon Burgess, Simon Burgess Oxford Instruments NanoAnalysis, High Wycombe, England, United Kingdom Search for other works by this author on: Oxford Academic Google Scholar Jo Bithell, Jo Bithell University of Warwick, Coventry, England, United Kingdom Search for other works by this author on: Oxford Academic Google Scholar Richard Beanland Richard Beanland University of Warwick, Coventry, England, United Kingdom Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 26, Issue S2, 1 August 2020, Pages 1212–1214, https://doi.org/10.1017/S1431927620017353 Published: 01 August 2020

These notes are for a lecture given at STAGE. They cover the basics of Serre’s theory of p-adic modular forms, as presented in [2]. In this concrete and elementary theory, Serre defines a p-adic modular form (on SL2(Z)) to be a q-expansion f ∈ Qp[[q]] which is the p-adic limit of q-expansions of classical modular forms. Theorems are proved about p-adic modular forms by studying the algebra M(Fp) of mod p modular forms, which is nothing more than the collection of q-expansions f ∈ Fp[[q]] that are mod p reductions of classical modular forms. Especially important is a result of Swinnerton-Dyer which shows that the kernel of this reduction map is generated by Ep−1 − 1, where Ep−1 is an Eisenstein series. Despite its elementarity, Serre’s theory proves fruitful. Here we present the two applications that most motivated Serre’s work: proving congruence properties of modular forms and constructing p-adic zeta functions. Both of these applications capture the general principal that the nonconstant Fourier coefficients of a p-adic modular form determine the constant term. Moreover, by studying how the nonconstant terms of Eisenstein series vary in a family, Serre easily deduces that the p-adic zeta function is continuous. Nowadays, the study of p-adic modular forms finds its foundations in Katz’s geometric appraoch (see [1]) instead of Serre’s theory. Accordingly, STAGE will study Katz’s theory in greater detail. Why, then, are we spending a lesson on Serre’s theory? I think there are three reasons. First, the concreteness of Serre’s theory helps to fix ideas. We will encounter many objects – such as the ordinary space, the ordinary projector, the p-adic weight space, and the space of p-adic or mod p modular forms themselves – which will reappear in Katz’s framework with much more abstract definitions. Serre’s theory provides concrete models of these objects, making them much easier to think about. Second, and relatedly, the simplicity of the theory makes clear what sort of problems we hope to solve with the study of p-adic modular forms, and what sorts of methods will be useful. And third, Serre’s theory gives us great results with minimal set-up; questions posed at the start of the lecture will be answered by the end, not after wading through three lectures of complicated algebraic geometry. We simply can’t resist the instant gratification. Throughout p denotes a prime. Although results are stated in general, we will restrict proofs to the case p ≥ 3 or p ≥ 5 when simpler. Following Serre, we will also consider modular forms on the full modular group SL2(Z) only. The space of weight k classical modular forms is denoted Mk.

A pillared layer network containing amide functional groups (Cu(pzdc)(pia); pzdc = pyrazine-2,3-dicarboxylate; pia = N-(4-pyridyl)isonicotinamide) was used to test a postsynthesis metalation rationale to insert lithium and create a porous surface with enhanced CO2 adsorption capacity. Synchrotron powder X-ray diffraction (XRD) was used to determine variations after lithiation in long-range and textural properties. CO2 adsorption measurements at room temperature showed a concave up isotherm shape with an increasing adsorption at high pressures, surpassing by 1 order of magnitude the values previously reported for the unmodified material. There was significant hysteresis upon desorption, which suggests structural variations consequent to different or stronger adsorption sites. Results from elemental, thermal gravimetric, and crystal refinement analyses indicate that the lithium content is ca. 3 Li atoms per asymmetric unit. Raman scattering showed N-Li and Li-O stretching bands, a shift of pia amide- and pyridyl-related bands, and other significant skeletal vibrations associated with nitrogen and oxygen lone pair variations. In situ XRD and CO2 adsorption observations at up to 50 bar at ambient temperature were consistent with the anticipated structural dynamic variation. The lattice changes observed at pressures below 10 bar following lithiation may be directly related to an enhancement in the CO2 adsorption amount.

Powders produced by air-melted gas atomization (AMGA) and vacuum induction gas atomization (VIGA) from Ti-V microalloyed 316L and Al-V microalloyed 17-4PH stainless steels along with their feedstock material and Hot Isostatically Pressed (HIP'd) products have been examined. Inclusion characteristics and development through process along with changes in grain size have been characterized. The main findings are that a thin oxide film forms on the powder surface, thicker for the 316L powder than the 17-4PH powder as indicated by XPS analysis of selected powder precursors, and large inclusions (predominantly oxides) are also observed on the 316L powder. This results in a high number of inclusions, including more complex two-phase inclusions, on the prior particle boundaries in the HIP'd material. Grain growth occurs during HIPping of the 316L powders with some evidence of inclusions locally pinning boundaries. In the vacuum-melted powder, smaller Ti-rich inclusions are present which give more grain boundary pinning than in the air-melted powder where Ti was lost from the material during melting. Consideration has also been made to determine the variation of Ti and V microalloying elements and residual Cu through processing. It was found that Ti was lost during air melting but partly retained after vacuum melting leading to the presence of fine and complex Ti-containing precipitates which provided grain boundary pinning during HIPping and heat treatment. V was retained in the melt by the use of both AMGA and VIGA processes, and therefore available for precipitation during HIPping. Residual Cu was retained during both air and vacuum melting and was associated with Mn S and Mn O S inclusions overwhelmingly outweighing that of Mn O inclusions in the two HIP'd 316L samples.

This study has shown the advantages and disadvantages of live continuous EDS mapping with respect to in situ heating experiments.It has also allowed us to study in detail the adverse effects of acquiring EDS data at high temperatures and its influence on spectral resolution.

The theory of monstrous moonshine asserts that the coefficients of Hauptmoduln, including the j-function, coincide precisely with the graded characters of the monster module, an infinite-dimensional graded representation of the monster group.On the other hand, Lehner and Atkin proved that the coefficients of the j-function satisfy congruences modulo p n for p ∈ {2, 3, 5, 7, 11}, which led to the theory of p-adic modular forms.We combine these two aspects of the j-function to give a general theory of congruences modulo powers of primes satisfied by the Hauptmoduln appearing in monstrous moonshine.We prove that many of these Hauptmoduln satisfy such congruences, and we exhibit a relationship between these congruences and the group structure of the monster.We also find a distinguished class of subgroups of the monster with graded characters satisfying such congruences.

Nanostructuring, e. g., reduction of dimensionality in materials, offers a viable route toward regulation of materials electronic and hence functional properties. Here, we present the extreme case of nanostructuring, exploiting the capillarity of single-walled carbon nanotubes (SWCNTs) for the synthesis of the smallest possible SnTe nanowires with cross sections as thin as a single atom column. We demonstrate that by choosing the appropriate diameter of a template SWCNT, we can manipulate the structure of the quasi-one-dimensional (1D) SnTe to design electronic behavior. From first principles, we predict the structural re-formations that SnTe undergoes in varying encapsulations and confront the prediction with TEM imagery. To further illustrate the control of physical properties by nanostructuring, we study the evolution of transport properties in a homologous series of models of synthesized and isolated SnTe nanowires varying only in morphology and atomic layer thickness. This extreme scaling is predicted to significantly enhance thermoelectric performance of SnTe, offering a prospect for further experimental studies and future applications.

Electrodeposition of Sn from supercritical difluoromethane has been performed into anodic alumina templates with pores down to 3 nm in diameter and into mesoporous silica templates with pores of diameter 1.5 nm. Optimized deposits have been characterized using X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy (bright field, high-angle annular dark field, and energy-dispersive X-ray elemental mapping). Crystalline 13 nm diameter Sn nanowires have been electrodeposited in symmetric pore anodic alumina. Direct transmission electron microscopy evidence of sub 7 nm Sn nanowires in asymmetric anodic alumina has been obtained. These same measurements present indirect evidence for electrodeposition through 3 nm constrictions in the same templates. A detailed transmission electron microscopy study of mesoporous silica films after Sn deposition is presented. These indicate that it is possible to deposit Sn through the 1.5 nm pores in the mesoporous films, but that the nanowires formed are not stable. Suggestions of why this is the case and how such extreme nanowires could be stabilized are presented.

Extreme nanowires (ENs) represent the ultimate class of crystals: They are the smallest possible periodic materials. With atom-wide motifs repeated in one dimension (1D), they offer a privileged perspective into the physics and chemistry of low-dimensional systems. Single-walled carbon nanotubes (SWCNTs) provide ideal environments for the creation of such materials. Here we present a comprehensive study of Te ENs encapsulated inside ultranarrow SWCNTs with diameters between 0.7 nm and 1.1 nm. We combine state-of-the-art imaging techniques and 1D-adapted ab initio structure prediction to treat both confinement and periodicity effects. The studied Te ENs adopt a variety of structures, exhibiting a true 1D realization of a Peierls structural distortion and transition from metallic to insulating behavior as a function of encapsulating diameter. We analyze the mechanical stability of the encapsulated ENs and show that nanoconfinement is not only a useful means to produce ENs but also may actually be necessary, in some cases, to prevent them from disintegrating. The ability to control functional properties of these ENs with confinement has numerous applications in future device technologies, and we anticipate that our study will set the basic paradigm to be adopted in the characterization and understanding of such systems.

Background: Thermoelectric materials (TEMs) are of interest for both cooling (Peltier effect) and voltage generation applications (Seebeck effect). Thermoelectric generators (TEGs) convert heat energy into electrical voltage via the Seebeck effect. In a typical TEG the thermoelectric elements, usually alternating p-type and n-type semiconductors, are arranged electrically in series and thermally in parallel. The power that can be generated depends on many factors: geometrical design of the module, thermal coupling to the heat exchangers, thermal and electrical conductivity of the materials supporting and separating the TEM elements and fundamentally the thermal and electrical conductivity of the TEM itself. The latter is summed up by the materials dimensionless “figure of merit”: zT = S2σT/κ. Where: S = Seebeck coefficient (thermoelectric sensitivity often given in μV/K); σ = electrical conductivity and κ = thermal conductivity (usually in W/mK). The current consensus is that, to be truly competitive for power generation, TEMs should have zT of 2-3[1]; although there are plenty of cases where this is less important. For instance where waste heat can be used on a large scale for power generation; here the conversion efficiency and the cost of the TEM is far more important. For certain niche applications requiring low to moderate power and low maintenance (e.g. for remote, standalone power supplies) cost is less important and there are a range of exotic materials with zT on the order of 1. One such material that has been widely studied is bismuth Telluride (Bi2Te3) which has a figure of merit typically between 0.7 and 0.8. This can be doped (often with antimony to produce p-type or selenium to produce n-type) to give zT >1.4[2, 3]. Modifying the carrier concentration to improve electrical conductivity (σ) is one way of improving zT but as can be seen from the equation above the figure of merit is also inversely proportional to the thermal conductivity (κ). Unfortunately σ and κ tend to vary likewise and good electrical conductivity usually goes hand in hand with good thermal conductivity. One strategy for reducing the thermal conductivity of a TEM, with minimal impact on the electrical conductivity, is nanostructuring[4, 5]. In in bidimensional or monodimensional structures (i.e. very thin films or nanowires) as the critical dimension is reduced it approaches the same scale as the mean free path of the phonons and their propagation is limited by surface scattering. Thus by tuning the size of the TE elements along with surface roughness and grain boundaries it should be possible to optimise both the thermal and electrical conductivities and produce superior TEGs. In this work: Previously we have demonstrated that, through judicious choice of electrolyte and design of precursor complex, supercritical solvents such as CO2 and difluoromethane (R32) may be used to electroplate a range of metal and semiconductor elements[6]. Furthermore supercritical fluid electrodeposition (SCFED) has distinct advantages over electroplating from conventional solvents: the broad potential window offered by R32 and CO2 allowing for electrodeposition of elements such as germanium; an ability to operate at high temperatures (since the reaction cells are all sealed); tunability of solvent properties (such as density and viscosity) and the absence of surface tension and very high rates of diffusion. The latter is a particular advantage when trying to electrodeposit into high aspect ratio nanopores and we have shown that filling of pores of 2-3 nm is viable by SCFED[7]. Here we demonstrate electrodeposition from binary solutions in supercritical R32 to produce bismuth telluride and antimony telluride films and nanowires of 13-55 nm diameter. We also demonstrate deposition of bismuth-tellurium and antimony-tellurium heterojunction nanowires. It is thought that Bi2Te3nanowires with a diameter <30 nm would offer a significant improvement in thermoelectric figure of merit[8, 9]. This work is conducted as part of the ADEPT project funded by EPSRC (EP/N035437/1). References: [1] W. He et. al., Appl. Energy, 143 (2015) 1-25. [2] X.A. Yan et. al., Nano Letters, 10 (2010) 3373-3378. [3] O. Yamashita et. Al., Journal of Applied Physics, 93 (2003) 368-374. [4] L.D. Hicks et. al., Phys. Rev. B, 47 (1993) 12727-12731. [5] L.D. Hicks et. al., Phys. Rev. B, 47 (1993) 16631-16634. [6] P.N. Bartlett et. al., PCCP, 16 (2014) 9202-9219. [7] J. Ke et.al., PNAS, 106 (2009) 14768-14772. [8] A. Mavrokefalos et. al., J. Appl. Phys., 105 (2009). [9] O. Picht et. al., J. Phys. Chem. C, 116 (2012) 5367-5375. Figure 1

Extreme nanowires (ENs) represent the ultimate class of crystalline materials: They are the smallest possible periodic materials. With atom-wide motifs repeated in 1D, they offer a unique perspective into the Physics and Chemistry of low-dimensional systems. Single-walled carbon nanotubes (SWCNTs) provide ideal environments for the creation of such materials. Here we report the observation of Te ENs grown inside ultra-narrow SWCNTs with diameters between 0.7nm and 1.1nm. Through state-of-the-art imaging techniques and high-precision, high-throughput ab initio calculations, we unambiguously determine the competing structures of encapsulated Te as a function of the encapsulating diameters. From 1-atom-wide Peierls-distorted linear chains -- the ultimate ENs, Te morphs into zigzag chains and then gives rise to helical structures that are the 1D analogues of bulk Te. The pitch of the encapsulated Te coils varies non-monotonically with the diameter of the encapsulating SWCNTs.

We report results for the electrochemistry of the germanium(II) tri-halide anions, [GeCl3](-), [GeBr3](-) and [GeI3](-), in supercritical difluoromethane containing 60 mM [(NBu4)-Bu-n][BF4] at 19.1 MPa and 358 K. The voltammetry shows mass-transport-limited currents for reduction to germanium at gold on the first scan. There is no evidence of a germanium stripping peak and, on subsequent scans, the electrode slowly passivates with the deposition of approximately 0.4 mu m of material. The redox potentials for the reduction of the three tri-halides are in the order [GeCl3](-) < [GeBr3](-) <[GeI3](-), with the iodide being the most easily reduced complex. Electrodeposition of germanium onto TiN electrodes from supercritical difluoromethane at 19.1 MPa and 358 K, using either 16 mM [EMIM][GeI3] with 60 mM [EMIM][BF4] or 16 mM [(NBu4)-Bu-n][GeI3] with 60 mm [(NBu4)-Bu-n] [BF4], gave deposition rates of 2-3 mu m h(-1). Raman spectroscopy and transmission electron microscopy showed that the resulting germanium films were protocrystalline, containing nanocrystals of germanium embedded in an amorphous germanium matrix.

The Inside Cover Picture shows that the electrodeposition of Ge in supercritical CH2F2 at 85 ºC from germanium (II) triiodide, the most readily reduced of the three trihalides studied, produces films containing nanocrystals of Ge embedded in an amorphous Ge film. More details can be found in the Full Paper by C. Cummings et al. on page 726 in Issue 5, 2016 (DOI: 10.1002/celc.201500539).