Group III-Nitride three-dimensional structures have gained substantial interest for application in optoelectronic, energy, and sensor devices with non-planar geometries [1-4]. The benefits of 3D structures, such as GaN-based nano-/micro-rods, compared to planar films include large surface area, high structural quality, non-polar-surface utilization, small footprint, mechanical flexibility, and enhanced light absorption/extraction efficiency. To advance the technology of non-planar III-Nitride semiconductors, it is necessary to optimize and scale up the fabrication of such structures with controlled geometries and desired electronic and optical properties. Here, we report the fabrication of wafer-scale periodic arrays of vertically aligned GaN core-shell micropillars using a combination of top-down etch and epitaxial overgrowth. The two-step process consists of inductively coupled plasma (ICP) etching of lithographically patterned GaN-on-Si substrate to produce an array of micropillars followed by selective growth of GaN shells over these pillars using Hydride Vapor Phase Epitaxy (HVPE). The most significant aspect of the study is the demonstration of the sidewall facet control in the shells, ranging from truncated hexagonal pyramids with the (1-101) semi-polar sidewalls to hexagonal prisms with the (1-100) non-polar sidewalls, by employing a post-ICP wet chemical etch and by tuning the HVPE growth temperature. Optimization of both ICP etching and epitaxial overgrowth reduced dislocation density in the GaN shells, thus enhancing the transport and optical characteristics of these device platforms. Photo- and cathodoluminescence showed a substantial reduction of parasitic yellow luminescence as well as strain-relaxation in the core-shell structures, supported by Raman scattering, electron-backscatter-diffraction (EBSD), and X-ray-diffraction measurements. Transmission electron microscopy revealed improved crystal quality with reduced dislocation density in the epitaxially grown shells. This work demonstrates the feasibility of selective epitaxy on micro/nano-engineered 3D templates for realizing high-quality GaN-on-Si devices such as LEDs and p-i-n photodetectors. References: Zhao, Y.; Fu, H.; Wang, G.T.; Nakamura, S. Toward ultimate efficiency: progress and prospects on planar and 3D nanostructured nonpolar and semipolar InGaN light-emitting diodes. Opt. Photonics 2018 , 10, 246-308. Chen, F.; Ji, X.; Lau, S.P. Recent progress in group III-nitride nanostructures: From materials to Applications. Materials Science & Engineering R 2020 , 142, No. 100578 Kazanowska, B.A.; Sapkota, K.R.; Lu, P.; Talin, A.A.; Bussmann, E.; Ohta, T.; Gunning, B.P.; Jones, K.S.; Wang, G.T. Fabrication and field emission properties of vertical, tapered GaN nanowires etched via phosphoric acid. Nanotechnology 2022 , 33, No. 035301 Pandey, A.; Min, J.; Reddeppa, M.; Malhotra, Y.; Xiao, Y.; Wu, Y.; Sun, K.; Mi, Z. An Ultrahigh Efficiency Excitonic Micro-LED. Nano Letters 2023 , 23, 1680-1687

Self-terminated Pt electrodeposition on Au occurs at large negative overpotentials where hydrogen adsorption Hads inhibits the coordination of PtCl42− and/or PtCl3(H2O)− to the electrode surface in chloride-supported electrolytes. Potential control can be used to toggle the Hads coverage to enable multicycle Pt deposition. Specifically, the applied potential is stepped between + 0.4 VSSCE and − 0.8 VSSCE, transiting the regime of overpotential activated Pt electrodeposition. The amount of metal deposited depends on capacitive charging delays associated with the double layer and competitive Cl−, H, and PtCl4-x(H2O)x−2+x adsorption. In addition, significant potential deviations arise from ohmic losses that are a function of the supporting electrolyte, cell geometry, and PtCl4-x(H2O)x−2+x concentration. Taken in combination, the delay in reaching the growth termination potential leads to additional metal deposition and roughening per pulse cycle. Experiments with a parallel plate cell enable the resistive component of the ohmic losses to be specified by the separation between the working and reference electrodes. During multicycle deposition, the Hupd pseudo-capacitance associated with Pt surface sites leads to further RC time constant delays and roughening. The transition to three-dimensional growth leads to low-density films as clearly evidenced after 50 deposition cycles. The difficulties with the pulsed potential scheme can be circumvented, or at least minimized, by using electrolyte exchange to introduce the PtCl4-x(H2O)x−2+x reactant at a fixed potential, i.e., − 0.8 VSSCE into the weakly acidic electrolyte. The resulting fractional Pt coverage per cycle is a monotonic function of K2PtCl4 concentration and ranged from 0.2 to almost a complete monolayer reflecting the competition between PtCl4-x(H2O)x−2+x reduction and adsorption of the blocking Hads layer.

Three samples of self-assembled In0.44Ga0.56As quantum dots (QDs) grown on (001) GaAs by molecular beam epitaxy (MBE) were studied using atomic force microscopy (AFM) and high-resolution transmission electron microscopy (TEM) in order to characterize the height, faceting, and densities of the QDs. The cross-sectional TEM images show both pyramidal dots and dots with multiple side facets. Multiple faceting has been observed only in dots more than 8.5 nm in height and allows increased dot volume without a substantial increase in base area. Addition of a GaAs capping layer is found to increase the diameter of the QDs from roughly 40 nm to as much as 200 nm. The areal QD density is found to vary up to 50 % over the central 2 cm x 2 cm section of wafer and by as much as 23 % on a length scale of micrometers.

This rather long-standing project has resulted in a National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) for the analysis of crystallite size from a consideration of powder diffraction line profile broadening. It consists of two zinc oxide powders, one with a crystallite size distribution centered at approximately 15 nm, and a second centered at about 60 nm. These materials display the effects of stacking faults that broaden specific hkl reflections and a slight amount of microstrain broadening. Certification data were collected on the high-resolution powder diffractometer located at beamline 11-BM of the Advanced Photon Source, and on a NIST-built laboratory diffractometer equipped with a Johansson incident beam monochromator and position sensitive detector. Fourier transforms were extracted from the raw data using a modified, two-step profile fitting procedure that addressed the issue of accurate background determination. The mean column lengths, (L)area and (L)vol, were then computed from the Fourier transforms of the specimen contribution for each reflection. Data were also analyzed with fundamental parameters approach refinements using broadening models to yield (L)area and (L)vol values. These values were consistent with the model-independent Fourier transform results; however, small discrepancies were noted for the (L)area values from both machines and both crystallite size ranges. The fundamental parameters approach fits to the laboratory data yielded the certified lattice parameters.

Particle size is a key parameter that must be measured to ensure reproducible production of cellulose nanocrystals (CNCs) and to achieve reliable performance metrics for specific CNC applications. Nevertheless, size measurements for CNCs are challenging due to their broad size distribution, irregular rod-shaped particles, and propensity to aggregate and agglomerate. We report an interlaboratory comparison (ILC) that tests transmission electron microscopy (TEM) protocols for image acquisition and analysis. Samples of CNCs were prepared on TEM grids in a single laboratory, and detailed data acquisition and analysis protocols were provided to participants. CNCs were imaged and the size of individual particles was analyzed in 10 participating laboratories that represent a cross section of academic, industrial, and government laboratories with varying levels of experience with imaging CNCs. The data for each laboratory were fit to a skew normal distribution that accommodates the variability in central location and distribution width and asymmetries for the various datasets. Consensus values were obtained by modeling the variation between laboratories using a skew normal distribution. This approach gave consensus distributions with values for mean, standard deviation, and shape factor of 95.8, 38.2, and 6.3 nm for length and 7.7, 2.2, and 2.9 nm for width, respectively. Comparison of the degree of overlap between distributions for individual laboratories indicates that differences in imaging resolution contribute to the variation in measured widths. We conclude that the selection of individual CNCs for analysis and the variability in CNC agglomeration and staining are the main factors that lead to variations in measured length and width between laboratories.

About the image: The metaphor of inferring the state of the forest through the study of a few selected trees has often been invoked to describe electron microscopy sciences.For this strategic planning, the organizers find this image of a trail through the varying flora and terrain appealing.

Heat transfer through thermal barrier coatings (TBCs) composed of alternating nanometer thick layers of aluminum oxide and 7% yttria stabilized zirconia (7YSZ) was studied by pulsed heating at temperatures in the range 1275K to 1375K. The thermal diffusivity of the TBCs, deposited on thin metal foils by electron beam evaporation and coated with an opaque, submicrometer metal capping layer, was studied by applying a sub-μs duration heating pulse from a Q-switched laser to the substrate and then monitoring the temperature rise on the opposing, metal-capped surface of the TBC. The recorded temperature transients were modeled using properties of the constituent materials in order to obtain an upper bound of the thermal resistance associated with the interfaces between layers. The results thus provide insight into the feasibility of using interfacial thermal resistance in this material system to improve TBC performance by decreasing thermal conductivity.

In this work, high-performance top-gated nanowire molecular flash memory has been fabricated with redox-active molecules. Different molecules with one and two redox centers have been tested. The flash memory has clean solid/molecule and dielectric interfaces, due to the pristine molecular self-assembly and the nanowire device self-alignment fabrication process. The memory cells exhibit discrete charged states at small gate voltages. Such multi-bit memory in one cell is favorable for high-density storage. These memory devices exhibit fast speed, low power, long memory retention, and exceptionally good endurance (>10(9) cycles). The excellent characteristics are derived from the intrinsic charge-storage properties of the protected redox-active molecules. Such multi-bit molecular flash memory is very attractive for high-endurance and high-density on-chip memory applications in future portable electronics.

In this work, multi-bit flash-like memory cell based on Si nanowire field-effect transistor and multiple Ta2O5 charge-trapping stacks have been fabricated and fully characterized. The memory cells exhibited staircase, discrete charged states at small gate voltages. Such discrete multi-bit on one memory cell is attractive for high memory density. These non-volatile memory devices exhibited fast programming/erasing speed, excellent retention, and endurance, indicating the advantages of integrating the multilayer of charge-storage stacks on the nanowire channel. Such high-performance flash-like non-volatile memory can be integrated into the microprocessor chip as the local memory which requires high density and good endurance. (C) 2014 AIP Publishing LLC.

Carbon nanotubes (CNT) are one of the most promising nanomaterials for use in medicine. The blood biocompatibility of CNT is a critical safety issue. In the bloodstream, proteins bind to CNT through non-covalent interactions to form a protein corona, thereby largely defining the biological properties of the CNT. Here, we characterize the interactions of carboxylated-multiwalled carbon nanotubes (CNTCOOH) with common human proteins and investigate the effect of the different protein coronas on the interaction of CNTCOOH with human blood platelets (PLT). Molecular modeling and different photophysical techniques were employed to characterize the binding of albumin (HSA), fibrinogen (FBG), γ-globulins (IgG) and histone H1 (H1) on CNTCOOH. We found that the identity of protein forming the corona greatly affects the outcome of CNTCOOH's interaction with blood PLT. Bare CNTCOOH-induced PLT aggregation and the release of platelet membrane microparticles (PMP). HSA corona attenuated the PLT aggregating activity of CNTCOOH, while FBG caused the agglomeration of CNTCOOH nanomaterial, thereby diminishing the effect of CNTCOOH on PLT. In contrast, the IgG corona caused PLT fragmentation, and the H1 corona induced a strong PLT aggregation, thus potentiating the release of PMP.

Certification data were collected on a NIST built diffractometer equipped with a Johansson incident beam monochromator. Two complete data sets were collected, one using a scintillation detector, and a second using silicon strip position sensitive detector. SRM 660b was used to characterize the instrument profile function and to verify that a fundamental parameters approach, FPA, model for the machine was accurate. Data were analyzed using several codes: Topas [1] is being used to obtain the certified lattice parameters, PM2K [2] and a Python based, Fourier-space code that was developed in-house are being used to determine microstructural data. The profiles from SRM 660b were fit to FPA model using Topas, and then Fourier transforms of the re-synthesized peaks were computed to deconvolve the instrument function from the SRM 1979 peak shapes. Although in general, deconvolution can be numerically unstable, it can be carried out accurately under two conditions: first, the Fourier transform of the IPF does not approach zero within the Fourier transform domain of the ZnO, and, second, statistical weights are properly carried onto the deconvolved data when it is analyzed. Since the SRM 1979 peaks are much wider than the SRM 660b peaks, which is equivalent to saying the resolution of the instrument is high enough that critical information is not being lost, the first criterion is met. The second one is a matter of correct coding. The Fourier-space code allows direct computation of particle size and size distribution from the first-principles models as developed by Bertaut [3]. These microstructural data determined from Fourier-space approach are to be reported in the SRM certificate as certified information. These ZnO powders may be less than ideal as the effects stacking faults, as reported by J.I. Langford, et al. [4] are observed. However this is a second-order effect and many lines are not influenced by these defects. The effects of these defects were modeled in TOPAS and PM2K using the hexagonal stacking fault model as detailed by Warren [5].

Carbon nanotubes (CNTs) exhibit a number of unique properties that make them attractive for various nanomedicine applications including their intravascular use. Therefore, the vascular toxicity of CNTs is a critical safety concern and methods of CNTs toxicity modulation are of great interest. Here, we report that carboxylated multiwalled carbon nanotubes (MWCNTs) induce a decrease in viability of cultured human umbilical vein endothelial cells (HUVECs) associated with the profound accumulation of autophagosomes. This autophagosome accumulation was mTOR kinase independent and was caused by blockade of the autophagic flux rather than by activation of autophagy. Stimulation of the autophagic flux with 1 nmol/L bafilomycin A1 attenuated the cytotoxicity of carboxylated MWCNTs in HUVECs and was associated with the extracellular release of the nanomaterial in autophagic microvesicles. Thus, pharmacological stimulation of the autophagic flux may represent a new method of cytoprotection against toxic effects of nanomaterials.From the Clinical Editor: This study investigates the mechanisms of toxicity of multiwalled carbon nanutubes on human endothelial cells, concluding that pharmacological stimulation of autophagic flux may represent a new method of cytoprotection against the toxic effects of these nanomaterials. Published by Elsevier Inc.

Metal-Oxide-Semiconductor (MOS) capacitors with Bi2Te3 thin film sandwiched and embedded inside the oxide layer have been fabricated and studied. The capacitors exhibit ferroelectric-like hysteresis which is a result of the robust, reversible polarization of the Bi2Te3 thin film while the gate voltage sweeps. The temperature-dependent capacitance measurement indicates that the activation energy is about 0.33 eV for separating the electron and hole pairs in the bulk of Bi2Te3, and driving them to either the top or bottom surface of the thin film. Because of the fast polarization speed, potentially excellent endurance, and the complementary metal–oxide–semiconductor compatibility, the Bi2Te3 embedded MOS structures are very interesting for memory application.

We show experimentally that single-crystal nanowires of the topological insulator Bi 2 Se 3 can be used as the conduction channel in high-performance field effect transistor, a basic circuit building block. The current-voltage characteristics are superior to many of those reported for semiconductor nanowire transistors. The metallic electron transport at the surface with good mobility can be effectively separated from the bulk conduction and adjusted by field effect at a small gate voltage. These properties open up a many potential applications in nanoelectronics and spintronics.

Binary Nb-Sn thin film samples were fabricated and characterized in terms of their composition, morphology, and superconducting properties. Nb-Sn was magnetron-sputtered onto heated R-plane sapphire substrates at 700°C, 800°C, and 900°C, using a custom-built heater assembly. Samples were cut into strips, where each strip has a unique composition. For a subset of the samples, Nb-Sn was selectively etched away at an etching rate of 6 ± 1 nm/s using an aqueous solution of 3 vol.% hydrofluoric and 19 vol.% nitric acid. The sample composition was investigated with a scanning electron microscope with an X-ray energy dispersive spectroscopy detector. Surface and cross-section morphologies were investigated using scanning electron microscopy and scanning transmission electron microscopy, revealing a dense columnar poly-crystalline grain structure. X-ray diffraction measurements indicate a highly textured film that is (100) oriented out-of-plane and random in-plane. The critical temperature Tc (ranging from 9.8 to 17.9 K), critical magnetic field μ0Hc2 (ranging from 12.5 to 31.3 T), residual resistivity ratio (RRR), and normal state resistivity ρ0 were measured and found to be broadly consistent with literature data on bulk Nb3Sn.

A NIST SRM certified to address the issue of crystallite size measurement through a line profile analysis has been under development for several years. In order to prepare the feedstock for the SRM, nano-crystalline zinc oxide was produced from thermal decomposition of zinc oxalate. The thermal processing parameters were chosen to yield particles in two size ranges, one with a distribution centered at approximately 15 nm and another centered at 60 nm. Certification data were collected on a NIST-built diffractometer equipped with a Johansson incident beam monochromator and scintillation detector. Data were analyzed using whole powder pattern modeling to determine microstructural data. The analysis shows domains to be in the form of discs of a fairly small aspect ratio. While both materials exhibit the effects of stacking faults through broadening of specific hkl reflections, their presence in the 60 nm is more difficult to discern. Images of the crystallites obtained with transmission electron microscopy are consistent with the results from the X-ray diffraction analyses.

9:50 AM IV.B-3 Student Paper High Performance Bi2Se3 Nanowire Field-Effect Transistors H. Zhu, C. A. Richter, E. Zhao, J. E. Bonevich, H.-J. Jang, H.i Yuan, H. Li, A. Arab, O. Kirillov,W. A. Kimes, J. E. Maslar, and Q. Li, Semiconductor and Dimensional Metrology Division, National Institute of Standards and Technology, Gaithersburg, Maryland, USA, Department of Electrical and Computer Engineering, School of Physics, Astronomy, and Computational Sciences, George Mason University, Fairfax, Virginia, USA , Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland, USA, and Chemical and Biochemical Reference Data Division, National Institute of Standards and Technology, Gaithersburg, Maryland, USA

This paper reports an interlaboratory comparison that evaluated a protocol for measuring and analysing the particle size distribution of discrete, metallic, spheroidal nanoparticles using transmission electron microscopy (TEM). The study was focused on automated image capture and automated particle analysis. NIST RM8012 gold nanoparticles (30 nm nominal diameter) were measured for area-equivalent diameter distributions by eight laboratories. Statistical analysis was used to (1) assess the data quality without using size distribution reference models, (2) determine reference model parameters for different size distribution reference models and non-linear regression fitting methods and (3) assess the measurement uncertainty of a size distribution parameter by using its coefficient of variation. The interlaboratory area-equivalent diameter mean, 27.6 nm ± 2.4 nm (computed based on a normal distribution), was quite similar to the area-equivalent diameter, 27.6 nm, assigned to NIST RM8012. The lognormal reference model was the preferred choice for these particle size distributions as, for all laboratories, its parameters had lower relative standard errors (RSEs) than the other size distribution reference models tested (normal, Weibull and Rosin-Rammler-Bennett). The RSEs for the fitted standard deviations were two orders of magnitude higher than those for the fitted means, suggesting that most of the parameter estimate errors were associated with estimating the breadth of the distributions. The coefficients of variation for the interlaboratory statistics also confirmed the lognormal reference model as the preferred choice. From quasi-linear plots, the typical range for good fits between the model and cumulative number-based distributions was 1.9 fitted standard deviations less than the mean to 2.3 fitted standard deviations above the mean. Automated image capture, automated particle analysis and statistical evaluation of the data and fitting coefficients provide a framework for assessing nanoparticle size distributions using TEM for image acquisition.