https://iopscience.iop.org/article/10.1088/0022-3727/49/41/413002/pdf

Intrinsic and extrinsic doping of ZnO and ZnO alloys

The development of three-dimensional (3-D), characterisation techniques with high spatial and mass resolution is crucial for understanding and developing advanced materials for many engineering applications as well as for understanding natural materials. In recent decades, atom probe tomography (APT), which combines a point projection microscope and time-of-flight mass spectrometer, has evolved to be an excellent characterisation technique capable of providing 3-D nanoscale characterisation of materials with sub-nanometer scale spatial resolution, with equal sensitivity for all elements. This review discusses the current state, as of APT instrumentation, new developments in sample preparation methods, experimental procedures for different material classes, reconstruction of APT results, the current status of correlative microscopy, and application of APT for microstructural characterisation in established scientific areas like structural materials as well as new applications in semiconducting nano...

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Three-dimensional nanoscale characterisation of materials by atom probe tomography

This paper presents a flexible ultraviolet (UV) photodetector (PD) system based on zinc oxide (ZnO) nanowires (NWs) for wearable UV dosimetry. High-crystal quality ZnO NWs have been synthesized by chemical vapour transport technique on c-plane sapphire substrates, and thereafter, transferred and aligned at pre-defined locations on a flexible substrate using dielectrophoresis (DEP). The accurate control over DEP parameters permitted the fabrication of large-area (wafer scale) arrays of ZnO NWs-based UV PDs. Resulting PDs showed photocurrent-to-dark current ratios above 103%, fast response times (<1 s), high sensitivity to different UV light intensities, and good stability under several UV/dark irradiation cycles. In addition, above PDs presented a robust response under extreme bending conditions, which is critical for their application in high-performance wearable UV dosimeters.

/pdf/zno-nanowires-based-flexible-uv-photodetector-system-for-2nlikuep6o.pdf

ZnO Nanowires-Based Flexible UV Photodetector System for Wearable Dosimetry

We present a highly sensitive detection of skin cancer using a novel water-based terahertz (THz) metamaterial (MM) and a semiconductor film. We apply the application of terahertz pulsed imaging in reflection geometry for the study of skin tissue and related cancers. As a refractive index (RI) sensing application of the proposed device, with placing different sensing materials in the biosensor design, the effective RI will also change that in turn leads to measuring the sensitivity of the biosensor to detect the normal skin and basal cell carcinoma. The RI figure of merit (FOM) value of the proposed device is much higher than that of the sensor using a semiconductor film to detect biomarkers in the literature. Significantly, the sensitivity increases by about 117 $\mu {\mathrm{ m}}$ /RIU and the RI FOM increases by more than 20.53. This results from a combination of size-related factors, leading to field enhancement accompanying strong field localization. We observed the resonance-frequency shift of the THz MM following the RI changing of the detected skin. The dip reflectance resonance has a blue shift for normal skin. Finally, we suggest that this water-based MM can be used to the control of the gene expression. The advantage of our design depends on two factors. First, we used the MM structure that has micro-scale, and the smaller the size of the structure, the more sensitive to the changes in the RI. Second, we used water in our structure, which is very well-suited to the human body, highly bio-absorbable and inexpensive, and abundantly found in nature.

Water-Based Terahertz Metamaterial for Skin Cancer Detection Application

http://smeng.ucsd.edu/wp-content/uploads/Effects-of-laser-energy-and-wavelength-on-the-analysis-of-LiFePO4-using-laser-assisted-atom-probe-tomography.pdf

Effects of laser energy and wavelength on the analysis of LiFePO4 using laser assisted atom probe tomography

Wide-bandgap zinc oxide (ZnO) semiconductors and nanowires have become important materials for electronic and photonic device applications. In this work, we report the growth of well-aligned single-crystal ZnO nanowire arrays on sapphire substrates by chemical vapor deposition and the development of atom probe tomography, an emerging nanoscale characterization method capable of providing deeper insight into the three-dimensional distribution of atoms and impurities within its structure. Using a metal-catalyst-free approach, the influence of the growth parameters on the orientation and density of the nanowires were studied. The resulting ZnO nanowires were determined to be single crystalline, with diameter on the order of 50 nm to 150 nm and length that could be controlled between 0.5 μm to 20 μm. Their density was on the order of high 108 cm−2 to low 109 cm−2. In addition to routine characterizations using scanning and transmission electron microscopy, x-ray diffraction, photoluminescence, and Raman spectroscopy, we developed the atom probe tomography technique for ZnO nanowires, comparing the voltage pulse and laser pulse modes. In-depth analysis of the data was carried out to determine the accurate chemical composition of the nanowires and reveal the incorporation of nitrogen impurities. The current–voltage characteristics of individual nanowires were measured to determine their electrical properties.

Atom Probe Tomography of Zinc Oxide Nanowires

Zinc oxide (ZnO) nanowire (NW) arrays were grown by chemical vapor deposition using the carbothermal reduction of ZnO powder at different pressures from 0.13 to 1.0 atm on basal plane sapphire substrates. The ZnO NWs were oriented in their [0001] direction. Lower growth pressures led to generally longer and smaller diameter wires. A model relating the length and diameter of the NWs was used to interpret the growth mechanism of these ZnO NWs as a function of pressure as the combination of adatom diffusion along the NW sidewalls and direct impingement growth on the NW tip. Al-doped ZnO NWs were synthesized by introducing Al power into the source material, resulting in an Al mole fraction up to 1.8 at. % in the NWs and a concurrent reduction in NW resistivity. Raman spectroscopy revealed slight lattice distortion to the ZnO crystal lattice, while room temperature photoluminescence showed an increase in the near band edge emission concurrently with a reduction in the green emission. The near band edge emission was also blue shifted in a manner consistent with the Burstein–Moss effect in degenerated semiconductor materials.

Growth, doping, and characterization of ZnO nanowire arrays

The authors report a correlated study of the atom probe tomography (APT) of lattice matched AlInN/GaN and strained AlGaN/GaN high electron mobility transistor structures, before and after exposure to 60Co irradiation. The AlInN/GaN exhibited a decrease in carrier density while the AlGaN/GaN was found to be more radiation tolerant. Analysis of the APT data revealed that the buried interface near the channel exhibited a much larger increase in isosurface roughness at the AlInN/GaN than at the AlGaN/GaN interfaces. This is believed to contribute to the scattering of carriers out of the channel, and the resulting deterioration of the charge transport characteristics. A proxigram analysis showed that the observed increased roughness at the AlInN/GaN heterointerface was not concurrent with a significant change in its diffuseness.

Atom probe tomography of AlInN/GaN HEMT structures

In this work, we report the growth and nanoscale characterization of single crystal zinc oxide nanowires synthesized by thermal chemical vapor deposition. Scanning electron microscopy, high-resolution transmission electron microscopy, x-ray diffraction, photoluminescence and Raman spectroscopy confirmed the high quality nature of the materials. To analyze their electrical properties, terahertz time domain spectroscopy was used. Atom probe tomography experiments and analysis were successfully developed and carried out, for the first time, on individual ZnO nanowires. This analysis revealed the incorporation of small concentration levels of atomic nitrogen homogeneously in nanowires grown when nitrogen gas was present during synthesis. Atom probe tomography can yield valuable information on the distribution of dopants and other impurities in wide bandgap semiconductor nanostructures and thus help understand better the material characteristics at the nanoscale.

Nanoscale characteristics of single crystal zinc oxide nanowires

With the increasing worldwide need for energy, fossil fuels will not be able to keep up with demand in the coming decades Solar energy is one of the best solutions to this problem with the advantages of being clean and sustainable Among the various designs of solar cells, dye-sensitized solar cells provide relatively high efficiency with large scale for a low cost [1] Conventional dye-sensitized solar cells operate with light harvesting organic dye molecules adsorbed at the interface between TiO 2 nanoparticles and a hole-conducting liquid electrolyte [2] However, new combinations of materials potentially present an opportunity to further improve the performance and lower the cost of solar cells One such promising approach is to use quantum dots (QDs) instead of the organic materials as the main photosensitive constituent Several types of semiconductor QDs, including CdSe [3], CdS [4] and InP [5], have been investigated to realize quantum dot sensitized solar cells by taking advantage of the tunable absorption spectrum of the QDs through changes in their size Complementarily to this approach, it is desirable to use a semiconductor material with a high structural uniformity and surface area as the framework on which to attach these QDs and achieve efficient electron transport, such as well-aligned ZnO nanowires [6]

Nabil Dawahre

Papers

Atom Probe Tomography of Zinc Oxide Nanowires

Growth, doping, and characterization of ZnO nanowire arrays

Atom probe tomography of AlInN/GaN HEMT structures

Nanoscale characteristics of single crystal zinc oxide nanowires

InP/ZnS core-shell quantum dots sensitized ZnO nanowires for photovoltaic devices