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Nanostructures composed of rare earth oxides, specifically Ho2O3 and Nd2O3, exhibit a range of desirable characteristics. Notably, neodymium oxides are renowned for their distinctive electrical and optical properties. Consequently, the development of rare earth oxide nanostructures, encompassing the aforementioned compositions, has emerged as a prominent area of research. The introductory section provides an overview of recent advancements pertaining to diverse applications of these nanostructures. Due to the technological significance of this class of materials, various methods for synthesizing these rare earth oxides have been introduced. This review provides a comprehensive description and examination of the synthesis of Ho2O3 and Nd2O3 nanostructures through different techniques. Finally, a comparative analysis is conducted, considering aspects such as methodology, efficiency, morphology, and grain size of the resulting samples.

In this work, the possibility of fabricating composite magneto-optical ceramics by electrophoretic deposition (EPD) of nanopowders and high-temperature vacuum sintering of the compacts was investigated. Holmium oxide was chosen as a magneto-optical material for the study because of its transparency in the mid-IR range. Nanopowders of magneto-optical (Ho0.95La0.05)2O3 (HoLa) material were made by self-propagating high-temperature synthesis. Nanopowders of (Y0.9La0.1)2O3 (YLa) were made by laser synthesis for an inactive matrix. The process of formation of one- and two-layer compacts by EPD of the nanopowders from alcohol suspensions was studied in detail. Acetylacetone was shown to be a good dispersant to obtain alcohol suspensions of the nanopowders, characterized by high zeta potential values (+29–+80 mV), and to carry out a stable EPD process. One-layer compacts were made from the HoLa and YLa nanopowders with a density of 30–43%. It was found out that the introduction of polyvinyl butyral (PVB) into the suspension leads to a decrease in the mass and thickness of the green bodies deposited, but does not significantly affect their density. The possibility of making two-layer (YLa/HoLa) compacts with a thickness of up to 2.6 mm and a density of up to 46% was demonstrated. Sintering such compacts in a vacuum at a temperature of 1750 °C for 10 h leads to the formation of ceramics with a homogeneous boundary between the YLa/HoLa layers and a thickness of the interdiffused ion layer of about 30 μm. [ABSTRACT FROM AUTHOR]

To comprehend the effect of the e-beam deposited high-k holmium oxide (Ho 2 O 3) on the electrical possessions of Au/n-GaN/Ti/Al Schottky contact (SC), Au/Ho 2 O 3 /n-GaN/Ti/Al MIS-type contact was created with a Ho 2 O 3 interlayer. The microstructural and chemical possessions of Ho 2 O 3 film were assessed using XRD, XPS, TEM and EDX approaches. XRD, XPS, TEM and EDX studies indicate that the Ho 2 O 3 layer exists on the GaN. The electrical features of the SC and MIS contact were probed using I-V and C-V approaches. The MIS contact shows a notable rectifying manner with a lower reverse leakage current than the SC. The MIS contact exhibits superior Φ b (0.85 eV) than the SC (0.72 eV), indicating the Ho 2 O 3 interlayer greatly rehabilitated the Φ b of the SC. Using I-V, C-V, Cheung's and Norde processes, Φ b , n, and R S of the SC and MIS contacts were estimated, and the estimated Φ b were well matched with each other, which signifying the techniques used here steadiness and validity. The MIS contact exhibits a lower magnitude of N SS compared to the SC, portentous that the presence of the Ho 2 O 3 layer played a significant part in diminishing N SS. The log (I) versus log (V) of forward bias of the SC and MIS contact reveals the ohmic nature and space charge limited current (SCLC) at the lower bias and upper bias sections. The conclusions suggest that the Ho 2 O 3 material has potential for building MIS/MOS devices. • Chemical and structural properties of Ho 2 O 3 films are investigated by XPS, XRD and TEM. • Electrical properties of Au/n-GaN SC and Au/Ho 2 O 3 /n-GaN MIS contacts were investigated. • Higher barrier height is attained for the MIS contact than the SC. • Lower interface state density is obtained for MIS contact than the SC. • Forward current transport mechanism was investigated for the SC and MIS contacts. [ABSTRACT FROM AUTHOR]

In this work, the possibility of fabricating composite magneto-optical ceramics by electrophoretic deposition (EPD) of nanopowders and high-temperature vacuum sintering of the compacts was investigated. Holmium oxide was chosen as a magneto-optical material for the study because of its transparency in the mid-IR range. Nanopowders of magneto-optical (Ho0.95La0.05)2O3 (HoLa) material were made by self-propagating high-temperature synthesis. Nanopowders of (Y0.9La0.1)2O3 (YLa) were made by laser synthesis for an inactive matrix. The process of formation of one- and two-layer compacts by EPD of the nanopowders from alcohol suspensions was studied in detail. Acetylacetone was shown to be a good dispersant to obtain alcohol suspensions of the nanopowders, characterized by high zeta potential values (+29–+80 mV), and to carry out a stable EPD process. One-layer compacts were made from the HoLa and YLa nanopowders with a density of 30–43%. It was found out that the introduction of polyvinyl butyral (PVB) into the suspension leads to a decrease in the mass and thickness of the green bodies deposited, but does not significantly affect their density. The possibility of making two-layer (YLa/HoLa) compacts with a thickness of up to 2.6 mm and a density of up to 46% was demonstrated. Sintering such compacts in a vacuum at a temperature of 1750 °C for 10 h leads to the formation of ceramics with a homogeneous boundary between the YLa/HoLa layers and a thickness of the interdiffused ion layer of about 30 μm.

This study illustrates the fabrication of Ho2O3 film as gate dielectric using the physical vapour deposition method followed by thermal oxidation on a 4H‐SiC substrate. The impacts of oxidation duration on the structural and electrical characteristics of the resulting Ho2O3 layers were studied experimentally at various oxidation periods from 5 to 20 min at a constant temperature of 900°C. The structural characteristics of the Ho2O3 thin film were examined by x-ray diffraction (XRD) and a high-resolution transmission electron microscopy (HRTEM). The crystallinity of the Ho2O3 films was identified by XRD, while crystallite size and microstrain were approximated by a Williamson–Hall (W–H) plot. The electrical properties were investigated by leakage current density–electric breakdown field (J–E), Fowler–Nordheim (F–N) tunnelling, and barrier height. The electrical characterization results have shown an optimized dielectric behaviour of the Ho2O3/SiC obtained at 15 min duration, with the highest breakdown field (7.57 MV/cm) and lowest leakage current density (6.14 × 10−3 A/cm2) recorded. The results of the morphology and thickness of the film have shown that there is no interfacial layer recorded. These findings can be used to provide useful information on the potential of Ho2O3 film to be used as a gate dielectric on 4H-SiC in high-power microelectronics. [ABSTRACT FROM AUTHOR]

Binary transparent magneto-optical (Ho 1- x Dy x) 2 O 3 (x = 0.01–1) ceramics derived from layered rare-earth hydroxide (LRH) compounds were fabricated by vacuum sintering. They have in-line transmittances of ∼67‒77 % at the visible wavelength of 700 nm and ∼77‒84 % at the mid-infrared wavelength of 5 μm with similar maximal infrared cut-off at ∼9.5 μm. The impacts of Dy3+ doping on particle properties, sintering kinetics and Faraday magneto-optical effects were systematically investigated. The results show that (1) The LRH precursors exhibit the nanosheet morphology with the thickness of ∼6‒10 nm. Dy3+ incorporation not only induces an expansion for the hydroxide host layer but also a contracted interlayer distance; (2) Upon calcination at 1100 °C, the LRH nanosheets collapse into sphere-like oxide particles. The addition of Dy3+ leads to increasing lattice constants and decreasing theoretical densities for the (Ho,Dy) 2 O 3 solid solutions; (3) A smaller bandgap energy for Dy 2 O 3 (∼4.85 eV) was obtained relative to those of (Ho 0.9 Dy 0.1) 2 O 3 (∼5.24 eV) and Ho 2 O 3 (∼5.31 eV); (4) Dy3+ dopant promotes grain growth and the pure Dy 2 O 3 bulk has a rather smaller grain-boundary-diffusion controlled activation energy (∼457 kJ/mol) than the (Ho 0.9 Dy 0.1) 2 O 3 counterpart (∼626 kJ/mol); (5) The Verdet constants of magneto-optical (Ho 1- x Dy x) 2 O 3 ceramics generally linearly increase with the rise of Dy3+ concentration. [ABSTRACT FROM AUTHOR]

In this work, a holmium oxide (Ho 2 O 3 /CNT) photocatalysts were successfully synthesized through a MOF assisted route for the first time. The effects of the morphology and purity on the photocatalytic behavior of the products, were investigated by determining various physicochemical properties. The Ho 2 O 3 /CNT nanocomposite was systematically analyzed by powder X-ray diffraction (P-XRD), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy studies. The Ho 2 O 3 derived from a MOF assisted synthetic route using Ho(NO 3) 3 ·5H 2 O and terephthalic acid with a 1:1 M ratio at a temperature of 750 °C for 3 h prove the most advantageous, 98% degradation of 20 mg/L aqueous tetracycline pollutant was observed within 60 min. The elevated photocatalytic activity was mainly attributable to the unique synthetic route, improved crystallinity, wide UV-light absorption rate and excellent adsorption capabilities of CNT, as well as enhanced oxygen deficiency. The photocatalytic results confirm that the Ho 2 O 3 /CNT nanocomposite is an efficient photocatalyst for the degradation of toxic tetracycline pollutant and is thus suitable for use in environmental remediation. [ABSTRACT FROM AUTHOR]

Transparent cubic‐phase solid solution (Ho1–xLax)2O3 (where x = 0, 0.03, 0.05, 0.07, and 0.1) ceramics are sintered in a vacuum at 1780 °C for 3 h from nanopowders made by self‐propagating high‐temperature synthesis. The lanthana is proved to significantly influence the microstructure of the ceramics. The average crystallite sizes of the (Ho1–xLax)2O3 ceramics decrease with an increase in the concentration of lanthana. After vacuum sintering and low‐temperature annealing in air, the ceramics have second‐phase grains at the crystallite boundaries and the triple points. The volume fraction of the second phase is found to be in direct proportion to the lanthana content in the ceramics. This second phase is believed to be (Ho1–xLax)2O3 solid solutions with a higher lanthanum content in comparison with the surrounding crystallites. Annealing of the ceramics at 1500 °C for 2 h leads to the elimination of the second phase. [ABSTRACT FROM AUTHOR]

Polycrystalline transparent magneto-optical Ho 2 O 3 ceramics were successfully fabricated by vacuum sintering using the self-reactive resultant HoOF as a sintering aid. They had an in-line transmittance of 72.0% at 1550 nm and the wavelength-dependent Verdet constants of −182 ± 8, −46 ± 3, and −22 ± 2 rad/Tm at 633, 1064 and 1550 nm (approximately 1.3 times those of terbium gallium garnet ceramics), respectively. The HoOF additive was generated by pyrolyzing Ho(OH) 2 F from the chemical reaction between the layered Ho 2 (OH) 5 NO 3 compound and NH 4 F in the liquid phase. The role of the HoOF additive and the sintering kinetics of the Ho 2 O 3 ceramic were systematically studied. The results show that: (1) the proper amount of F− additive helps to obtain an oxide powder with a narrow particle distribution and significantly improves the optical quality of the sintered body; (2) HoOF induces a transient second phase to effectively suppress the grain growth in the Ho 2 O 3 ceramics during sintering; (3) the diffusion mechanism is primarily controlled by grain-boundary diffusion around 1400 °C; (4) the activation energy of the grain-boundary-controlled diffusion was determined to be approximately 545 kJ/mol via the grain growth method. [ABSTRACT FROM AUTHOR]

Transparent magneto‐optical Ho2O3 ceramics were successfully prepared with an in‐line transmittance of ~73% at the wavelength of 1000 nm (~90% of the theoretical transmittance of Ho2O3 single crystal) and an average grain size of ~28 μm. The ceramics were fabricated using sulfate‐exchanged nitrate‐type layered rare‐earth hydroxide as the precipitation precursor at a relatively low sintering temperature of 1700°C. The layered compound exhibited nanosheet morphology and fully collapsed into a round oxide powder with an average particle size of ~48 nm by pyrolysis. Calcination temperature for Ho2O3 powder significantly affected the optical quality of the sintered body and the optimum calcination temperature was found to be 1050°C. The transparent magneto‐optical Ho2O3 ceramics displayed wavelength‐dependent Verdet constants of −180, −46, and −20 rad/Tm at 632, 1064, and 1550 nm, respectively. Thus, the Ho2O3 ceramics show good potential for applications in high‐power laser systems. [ABSTRACT FROM AUTHOR]

In this work, highly photocatalytically active Ho 2 O 3 -SiO 2 nanocomposites have been designed and applied for decomposition of methylene blue pollutant. Ho 2 O 3 -SiO 2 nanocomposites have been produced by new, quick and facile sonochemical process with the aid of tetramethylethylenediamine as a novel basic agent for the first time. The effect of the kind of basic agent, ultrasonic time and dosage of Ho source on the grain size, photocatalytic behavior and shape of the Ho 2 O 3 -SiO 2 nanocomposites have been evaluated for optimization the production condition. FESEM, EDX, FT-IR, DRS, XRD and TEM have been applied to characterize the as-produced Ho 2 O 3 -SiO 2 nanocomposites. Use of the as-produced Ho 2 O 3 -SiO 2 nanocomposites as photocatalyst via destruction of methylene blue pollutant under UV illumination has been compared. It was observed that SiO 2 has notable impact on catalytic activity of holmium oxide photocatalyst for destruction. Introducing of SiO 2 to holmium oxide can enhance destruction efficiency of holmium oxide to methylene blue pollutant under ultraviolet light. [ABSTRACT FROM AUTHOR]

In recent years, paramagnetic nanoparticles (NPs) have been widely used for magnetic resonance imaging (MRI). This paper reports the fabrication and toxicity evaluation of polyethylene glycol (PEG)-functionalized holmium oxide (Ho2O3) NPs for potential T2-weighted MRI applications. Various characterization techniques were used to examine the morphology, structure and chemical properties of the prepared PEG-Ho2O3 NPs. MRI relaxivity measurements revealed that PEG-Ho2O3 NPs could generate a strong negative contrast in T2-weighted MRI. The pilot cytotoxicity experiments showed that the prepared PEG-Ho2O3 NPs are biocompatible at concentrations less than 16 μg/mL. Overall, the prepared PEG-Ho2O3 NPs have potential applications for T2-weighted MRI imaging. [ABSTRACT FROM AUTHOR]

Holmium oxide nanostructures were prepared through a facile precipitation way applying triethylenetetramine as a novel precipitant and Ho(NO 3 ) 3 ·6H 2 O as a holmium precursor. The effect of different capping agents on the size, shape and photocatalytic behavior of holmium oxide was studied. It was found that the type of capping agent has an effective role in shape, size and photocatalytic behavior control. The as-produced holmium oxide has been analyzed with applying EDX, FESEM, DR-UV–vis, TEM, XRD and FT-IR. The photocatalytic performances of as-obtained holmium oxide samples have been compared in the degradation of methyl violet pollutant under UV illumination. [ABSTRACT FROM AUTHOR]

[Display omitted] • PPy and PPHO composites prepared by chemical polymerization. • composites characterized by FESEM, XRD, FTIR, TEM, and RAMAN techniques. • Humidity sensing behavior of the composites studied in RH range from 11 to 97%. • PPHO-3 composite shown maximum sensing response of 93% with a response and recovery times of 30 s and 40 s. Having a competent and efficient humidity sensing material is important for vivid applications. In the present work, holmium oxide, a well-known rare-earth oxide, has been composited with Polypyrrole (PPy) to form polypyrrole/holmium oxide (PPHO) composites. The composites were prepared by chemical polymerization reactions in 10 (PPHO-1), 30 (PPHO-2), and 50 wt% (PPHO-3) of holmium oxide in PPy matrix. These composites were characterized by Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectra, and Transmission electron microscopy (TEM) to study the structural and morphological changes in the PPy and PPHO composites. Humidity sensing behavior of the composites was investigated in the relative humidity range (RH) of 11 to 97%. Among all the composites, PPHO-3 has shown a maximum sensing response of 93% with response and recovery times of 30 s and 40 s respectively, furthermore, the composite has exhibited an appreciable limit of detection (LOD) of 4.98 % RH, good linearity (0.9981), real sensitivity (27.72 MΏ-cm / %RH) and stability. Based on Grotthus' reaction, the sensing mechanism has been discussed. [ABSTRACT FROM AUTHOR]

Novel highly-efficient low-temperature SCR catalysts were developed through modifying Fe-Mn/TiO 2 catalyst with holmium (Ho). It was found that Ho/Ti = 0.1 was the optimal molar ratio for the amount of Ho addition. With this ratio, 85% NO x conversion was obtained at 60 °C and the catalytic performance enhanced to 90% at 120 °C. The optimal catalyst presented a broad operating temperature window in the range of 60–200 °C and exhibited superior sulfur-poisoning resistance, while the further increase of the doped Ho did not have a positive effect on the catalytic performance and structural properties. [ABSTRACT FROM AUTHOR]

In the present work the optical properties of Polyvinylidene Fluoride (PVDF) have been studied as a function of the content of holmium oxide (Ho), 2-amino terephthalate (AMT) and Ho-AMT compounds as modifiers. The characterization of the samples performed by the Fourier Transform Infrared Spectroscopy (FT-IR), Optical Absorption (UV-Vis) and Optical Fluorescence Spectroscopy. The FT-IR studies have shown that the relative percentage of β phase does not change as a function of the concentration. The fluorescence measurements have shown that the AMT and Ho-AMT compound addition increase the bandwidth at half maxima of PVDF samples. Finally, these results reveal that the PVDF samples studied in this work have potential for some interesting optical applications. [ABSTRACT FROM AUTHOR]

Pure holmium oxide ceramic nanostructures were prepared via a new simple approach. Nanostructures were synthesized by heat treatment in air at 600 °C for 5 h, utilizing [Ho L(NO 3 ) 2 ]NO 3 (L=bis-(2-hydroxy-1-naphthaldehyde)-butanediamine Schiff base ligand), as precursor, which was prepared via a solvent-free solid–solid reaction from different molar ratios of holmium nitrate and Schiff base ligand. The as-prepared nanostructures were characterized by field emission scanning electron microscopy (FESEM), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDX), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. It was found that the calcination temperature and molar ratio of holmium nitrate and Schiff base ligand have significant and key effect on the morphology and particle size of the holmium oxide. To investigate the catalytic properties of as-obtained holmium oxide nanostructures, the photocatalytic degradation of rhodamine B as cationic dye under ultraviolet light irradiation was performed. [ABSTRACT FROM AUTHOR]

Nanolaminate (nanomultilayer) thin films of TiO2 and Ho2O3 were grown on Si(001) substrates by atomic layer deposition at 300 °C from alkoxide and β-diketonate based metal precursors and ozone. Individual layer thicknesses were 2 nm for TiO2 and 4.5 nm for Ho2O3. As-deposited films were smooth and X-ray amorphous. After annealing at 800 °C and higher temperatures the nanolaminate structure was destroyed by solid-state reaction to form Ho2Ti2O7. The films demonstrated diamagnetic or paramagnetic behaviour in the as-deposited state. After annealing, the films possessed net magnetic moment, allowing one to record saturation magnetization and weak coercivity. =abstract= [ABSTRACT FROM AUTHOR]

Highlights: [•] Nanocrystalline C-Ho2O3 was prepared from Ho acetate at 600 and 700°C. [•] Nanocrystalline C-Ho2O3 was prepared from urea-containing complex of Ho at 700°C. [•] The bcc lattice parameter of C-Ho2O3 increases as the crystallite size decreases. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the structural properties and electrical characteristics of thin Ho2O3 gate dielectrics deposited on silicon substrates by means of reactive sputtering. The structural and morphological features of these films after postdeposition annealing were studied by X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy. It is found that Ho2O3 dielectrics annealed at 700°C exhibit a thinner capacitance equivalent thickness and excellent electrical properties, including the interface trap density and the hysteresis in the capacitance–voltage curves. Under constant current stress, the Weibull slope of the charge-to-breakdown of the 700°C-annealed films is about 1.7. These results are attributed to the formation of well-crystallized Ho2O3 structure and the reduction of the interfacial SiO2 layer. [Copyright &y& Elsevier]

Abstract: The microstructure and electrical properties of Ho2O3 doped Bi2O3-based ZnO varistor ceramics were investigated. The bulk density varies between 5.41 and 5.47gcm−3 with the maximum value of 5.47gcm−3 for 0.50mol% Ho2O3 content. The average grain size for all the samples was calculated from the scanning electron micrographs and were found between 5.1 and 7.1μm. The microstructure of the prepared samples shows a decrease in grain size of ZnO phase with Ho2O3 doping. The energy dispersive X-ray analysis and X-ray diffraction analysis of the samples show the presence of ZnO, Bi-rich, spinel Zn7Sb2O12 and Ho2O3-based phases. The nonlinear coefficient, α, obtained from electric field–current density plots has a maximum value of 78 for the ceramics with 0.50mol% Ho2O3 content. The leakage current, I L , has a minimum value of 1.30μA for the 0.50mol% Ho2O3 doped ZnO varistor ceramics. The breakdown field, E b , was found to increase with Ho2O3 content. [Copyright &y& Elsevier]

Holmium oxide glass has been used as a wavelength standard for over four decades. These standards have shown insignificant spectral variation from batch to batch and from one manufacturer to another. The National Institute of Standards and Technology (NIST) has certified and recertified holmium oxide glass samples for over four decades. Over this period of time there has been no recorded instance of a spectral shift of the certified bands for any of the samples measured. Moreover, these samples are known to be robust and relatively insensitive to a normal range of temperature and humidity. Based on the extensive experience that NIST has with this material and its long-term stability, NIST will no longer recommend the recertification of these standards. Furthermore, traceability may be established either through the supplier or by the end user without the need for NIST involvement. [ABSTRACT FROM AUTHOR]

FT-IR spectroscopy of adsorbed probe molecules of pyridine and CO2, has been used to characterize adsorption sites (acidic and basic sites) on holmium oxide. Ho2O3, was obtained by calcination of holmium nitrate penta hydrate [Ho(NO3)3·5H2O] at 970 K for 1 h in static air. The adsorption and surface reaction of 2-propanol on the test oxide were also examined using IR spectroscopy. The results of adsorbed pyridine and CO2 revealed that the surface of Ho2O3 exposes Lewis acid sites (cus Ho3+) and highly reactive basic sits (O2- and/or OH-). The results also revealed that 2-propanol is irreversibly adsorbed at 300 K giving rise to different surface species. The results revealed that Ho2O3 is a dual functioning catalyst ≥520 K, and that 2-propanol decomposes thereon via dehydration into propene and dehydrogenation into acetone. At ≥570 K, the acetone was used up in a secondary surface reaction, giving rise to gas phase isobutene, methane and carbon dioxide. [Copyright &y& Elsevier]

Holmium oxide films were prepared by an electron beam deposition method in vacuum. Films exhibited b.c.c. type structure of holmium sesquioxide as determined from electron diffraction studies. Optical properties of Ho2O3 films deposited onto quartz substrates were examined for the wavelength range of 0.2–2.5 μm. Films are characterized by a high transparency between 0.3 and 2.5 μm. The complex refractive index, n*=n−jk, and the complex dielectric function, &epsiv;*=&epsiv;′−j&epsiv;′′, for optical frequencies were evaluated. The dispersion characteristics for n(λ), k(λ), &epsiv;′(ω) and &epsiv;′′(ω) were presented. At λ=0.55 μm the refractive index was n=1.80. Ho2O3 films exhibited low absorption in the whole visible spectral range (k<0.002). The high frequency relative permittivity of Ho2O3 was also determined: &epsiv;′∞=3.24. [Copyright &y& Elsevier]

• Thermal oxidation of sputtered rare-earth Ho on 4H-SiC wide bandgap semiconductor. • Mixture of holmium trioxide and native silicon dioxide formed on 4H-SiC. • Optimization of oxidation temperature of rare-earth Ho in oxygen atmosphere. • An improved electrical breakdown field. The continuous down-sizing of metal oxide semiconductor field effect transistors have been confronted with various challenges in the last few decades, ranging from aggressive reduction of channel to miniaturization of dielectric gate thickness. In a bid to proffer solution to these challenges, a high-κ dielectric and metal gate technology was proposed to substitute the conventional silicon dioxide gate layers. Therefore, this study focused on the formation of Ho 2 O 3 thin film on a SiC substrate by sputtering and thermal oxidation. The effects of thermal oxidation on the structural, chemical, and electrical properties of the resulting Ho 2 O 3 layers were evaluated experimentally at various temperatures from 800 – 1100 °C. The crystallinity of the Ho 2 O 3 films were detected by x-ray diffraction, W-H plot, crystallites size, micro-strain, high resolution transmission electron microscopy. The result of electrical characterization shows that thermally oxidized samples at 900 °C have the optimum electrical properties, which could be attributed to the thinnest oxide and absence of interfacial layer that was recorded at that temperature. [ABSTRACT FROM AUTHOR]

• PANI and PANI/Ho 2 O 3 nanocomposites have been synthesized using in-situ chemical polymerization technique. • Humidity, and pressure sensing properties were investigated. • Hysteresis, response recovery, sensitivity, stability of the fabricated device has been studied. • Phase, microstructural, electrical and optical properties of PANI and PANI/Ho 2 O 3 nanocomposites thin film were studied. [Display omitted] Polyaniline (PANI) and polyaniline/holmium oxide (PANI/Ho 2 O 3) nanocomposite based humidity and pressure sensors were investigated in this study. PANI and PANI/Ho 2 O 3 composites were prepared by in-situ chemical oxidative polymerization of aniline monomer in acidic medium using ammonium peroxide sulfate. Structural, morphological and optical properties of the synthesized nanoparticles were investigated by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and photoluminescence spectroscopy techniques, respectively. Room temperature, frequency dependent A.C conductivity of the fabricated sensors were studied, which was found to decrease with the doping of Ho 2 O 3. Furthermore, thin films of PANI and PANI/Ho 2 O 3 composites were deposited on interdigitated electrodes (IDE) using spin coating technique and the humidity sensing characteristics were investigated and compared by exposing the sensors to relative humidity range of 20–90% at room temperature. Results indicated that the nanocomposite based sensor demonstrated an ultra-high sensitivity, good stability and quick response and recovery as compare to sensor based on pure PANI. Additionally, the response of sensors were also investigated and compared by applying different levels of pressure on the surfaces of sensors. By virtue of the microstructures and sensitive layers, the sensor based on composite exhibited an ultrahigh sensitivity at low pressure range as well as fast response time. The obtained results determined that PANI modified with Ho 2 O 3 might be a promising nanocomposite for developing high performance humidity and pressure sensors. [ABSTRACT FROM AUTHOR]

Abstract: High-pressure X-ray diffraction and Raman studies on holmium sesquioxide (Ho2O3) have been carried out up to a pressure of ∼17GPa in a diamond-anvil cell at room temperature. Holmium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase transition at around 9.5GPa. The high-pressure phase has been identified to be low symmetry monoclinic type. The two phases coexist to up to about 16GPa, above which the parent phase disappears. The high-pressure laser-Raman studies have revealed that the prominent Raman band ∼370cm−1 disappears around the similar transition pressure. The bulk modulus of the parent phase is reported. [Copyright &y& Elsevier]

Holmium oxide (Ho 2 O 3) nanocrystals were prepared through an uncomplicated precipitation technique applying Chemical Bath Deposition. The effect by the reaction temperature (∼20 °C and ∼90 °C samples) on the morphological, structural and some optical properties were investigated. Ho 2 O 3 powder samples have been analyzed by applying SEM, FTIR, XRD and absorbance techniques. The crystalline morphology shows differences in grain boundaries as well as porosity and granular packaging. These crystalline materials have an acceptable stoichiometric balance. FTIR spectra show OH- and ions bands of different intensities, that are commonly incorporated in the surface and volume of these crystals. According to the XRD diffractograms, the crystalline cubic phase in both materials is identified. The grain size for each sample is located at range ∼4.06–21.35 nm and ∼21.15–35.35 nm respectively. The absorbance spectra investigated at UV–vis shows eleven absorption bands of different intensities located at ∼278, ∼287, ∼333, ∼345, ∼360, ∼415, ∼448, ∼472, ∼485, ∼535 and ∼645 cm−1 identified as Ho+3 electronic transitions occurring in the UV- Vis-region. The bandgap energies for each sample were Eg ∼4.95 eV, and Eg ∼4.85 eV respectively. The effect of the reaction temperature is manifested with the decrease in the grain size and carries with it the shifting of the E g towards greater energy, which usually manifests itself in materials that have nanocrystals. [ABSTRACT FROM AUTHOR]

The work describes the methods and procedures used to determine the wavelengths of minimum transmittance of holmium oxide in perchloric acid solution. Measurements of spectral transmittance of the solutions were made by means of a high precision spectrophotometer over the wavelength range 200 nm to 680 nm. The wavelength scale accuracy of this instrument was verified by extensive measurements of mercury and deuterium emission lines. The measurements of spectral transmittance of the holmium oxide solutions were made as a function of temperature, purity, concentration, and spectral bandwidth. Analysis of the uncertainties associated with these parameters and the uncertainties associated with the calibration of the instrument wavelength scale and the data analysis have resulted in an estimated uncertainty of ±0.1 nm for the determination of the wavelengths of minimum transmittance of the holmium oxide solution.

This work describes the techniques used to prepare and analyze a reflectance wavelength standard composed of three rare-earth oxides. A mixture of dysprosium oxide (Dy 2 O 3 ), erbium oxide (Er 2 O 3 ), and holmium oxide (Ho 2 O 3 ) provides a pressed powder specimen exhibiting a near infrared reflectance spectrum characterized by many discrete absorption minima in the wavelength range 700 to 2000 nm. The object of this activity was to develop a wavelength standard for improving the accuracy of reflectance measurements in the near infrared. The reflectance minima of the rare-earth oxide mixture was analyzed for the effects of varying spectral resolution and temperature. The uncertainties associated with the various parameters affecting the measurements and the determination of the location of the reflectance minima have been analyzed. The overall uncertainty in the location of these reflectance minima is believed not to exceed ± 1 nm.