HF Source Research Articles

Structural control in atomic layer deposited hafnium oxide thin films through vertical cavity surface-emitting laser (VCSEL)-Based ultra-rapid heating

HfO2 thin films were formed by plasma-enhanced atomic layer deposition (PEALD) using TDMAHf precursor as a Hf source and oxygen plasma as an oxygen source. Rapid annealing assisted by a 980 nm wavelength vertical cavity surface-emitting laser (VCSEL) was employed to assess the dielectric properties of the HfO2 thin films, compared to furnace annealing. Operational power and time of VCSEL was precisely controlled by computational simulation. In addition to decreased thickness of the interfacial layer, rapid annealing enabled reduced leakage current density as annealing temperature increased due to suppression of crystallization, resulting from the extremely short time duration of 0.98 s–8.14 s. Cross-sectional microstructures exhibited incomplete grain boundary formation of the rapidly annealed HfO2 thin film. VCSEL-based rapid annealing was verified to be an efficient process to enhance the dielectric characteristics of high-k dielectric oxide films.

Regioselective fluorination of allenes enabled by I(I)/I(III) catalysis

The prominence and versatility of propargylic fluorides in medicinal chemistry, coupled with the potency of F/H and F/OH bioisosterism, has created a powerful impetus to develop efficient methods to facilitate their construction. Motivated by the well-established conversion of propargylic alcohols to allenes, an operationally simple, organocatalysis-based strategy to process these abundant unsaturated precursors to propargylic fluorides would be highly enabling: this would consolidate the bioisosteric relationship that connects propargylic alcohols and fluorides. Herein, we describe a highly regioselective fluorination of unactivated allenes based on I(I)/I(III) catalysis in the presence of an inexpensive HF source that serves a dual role as both nucleophile and Brønsted acid activator. This strategy enables a variety of secondary and tertiary propargylic fluorides to be prepared: these motifs are prevalent across the bioactive small molecule spectrum. Facile product derivatisation, concise synthesis of multi-vicinal fluorinated products together with preliminary validation of enantioselective catalysis are disclosed. The expansive potential of this platform is also demonstrated through the highly regioselective organocatalytic oxidation, chlorination and arylation of allenes. It is envisaged that the transformation will find application in molecular design and accelerate the exploration of organofluorine chemical space.

Effects of hafnium sources and hafnium content on the structures and properties of SiBNC–Hf ceramic precursors

AbstractThe synthesis of SiBNC–M (M is metal element) multinary ceramic precursors has mainly been through chemical modification of the SiBNC ceramic precursors with the introduction of the metal element/compound. This misses the simplicity, efficiency, and combined benefits of single reactor synthesis routes. We herein adopt a one‐pot method to synthesize SiBNC–Hf ceramic precursors (PBSHZ) from different Hf sources, and with varying Hf content. The starting materials include hafnium tetrachloride, hafnium dichloride, trichlorosilane, hexamethyldisilazane, and boron trichloride. Fourier transform infrared spectroscopy (FT‐IR), nuclear magnetic resonance (NMR), X‐ray photoelectron spectroscopy (XPS), and thermogravimetric analysis are employed to characterize the structures and properties of the PBSHZ. The results reveal the successful incorporation of Hf into the precursors. Compared to the hafnium tetrachloride source, the precursor synthesized from hafnium dichloride yields more ceramics and shows better solubility, due to fewer Hf–Cl bonds available for reaction. Meanwhile, there is a positive correlation between the rise in the Hf content of PBSHZ and the ceramic yield. However, the solubility and processability of the precursors decline, due to the multiplication of the cross‐linking degree in the molecular structure. Further FT‐IR, NMR, XPS, and thermogravimetry–mass spectrometry (TG–MS) analysis indicate a full polymer‐to‐ceramic transformation at 1000°C pyrolysis temperature. At this point, the SiBNC–Hf ceramics mainly consist of an Si–B–N skeleton, HfN, and free carbon.

Recovery of Uranium, Thorium, and Other Rare Metals from Eudialyte Concentrate by a Binary Extractant Based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and Methyl Trioctylammonium Nitrate

Eudialyte-group minerals are of scientific interest as important concentrators of rare elements (mainly Zr and REE) in agpaitic alkaline rocks and a potential source of REE, Zr, Hf, Nb, and Ta for industrial use. Extraction of uranium(VI), thorium(IV), zirconium(IV), hafnium(IV), titanium(IV), and scandium(III) by a binary extractant based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyl trioctylammonium nitrate from eudialyte breakdown solutions is studied. Extraction isotherms were obtained and exhaustive extraction was investigated. It is shown that uranium, thorium, hafnium, zirconium, scandium, and titanium are almost completely recovered in two-stage extraction by a mixture of 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyltrioctylammonium nitrate in 1,2-dichloroethane. Quantitative characteristics were compared for uranium(VI), thorium(IV), zirconium(IV), hafnium(IV), titanium(IV), and scandium(III). It was shown that the extraction efficiency of the metals by the binary extractant based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyltrioctylammonium nitrate in 1,2-dichloroethane is much higher in comparison with the commercially available tributyl phosphate.

Skeletal Ring Contractions via I(I)/I(III) Catalysis: Stereoselective Synthesis of cis-α,α-Difluorocyclopropanes.

The clinical success of α,α-difluorocyclopropanes, combined with limitations in the existing synthesis portfolio, inspired the development of an operationally simple, organocatalysis-based strategy to access cis-configured derivatives with high levels of stereoselectivity (up to >20:1 cis:trans). Leveraging an I(I)/I(III)-catalysis platform in the presence of an inexpensive HF source, it has been possible to exploit disubstituted bicyclobutanes (BCBs) as masked cyclobutene equivalents for this purpose. In situ generation of this strained alkene, enabled by Brønsted acid activation, facilitates an unprecedented 4 → 3 fluorinative ring contraction, to furnish cis-α,α-difluorinated cyclopropanes in a highly stereoselective manner (up to 88% yield). Mechanistic studies are disclosed together with conformational analysis (X-ray crystallography and NMR) to validate cis-α,α-difluorocyclopropanes as isosteres of the 1,4-dicarbonyl moiety. Given the importance of this unit in biology and the foundational no → π* interactions that manifest themselves in this conformation (e.g., collagen), it is envisaged that the title motif will find application in focused molecular design.

Au(I) Fluorido Phosphine Complexes: Tools for the Hydrofluorination of Alkynes

AbstractThe reactivity of the Au(I) fluorido complex [Au(F)(SPhos)] (SPhos=dicyclohexyl(2’,6’‐dimethoxy[1,1’‐biphenyl]‐2‐yl)phosphine) (1) towards several alkynes was studied. The formation of fluorovinyl species by formal insertion of the alkyne in the metal‐fluorine bond was observed. Addition of HCl to vinyl complexes resulted in protodeauration and elimination of the hydrofluorinated alkynes. Treatment of1with the terminal alkyne 1‐hexyne resulted in clean formation of the alkynyl complex [Au(C≡CC4H9)(SPhos)] (15), whereas with an excess alkyne hydrofluorination was also observed. Various Au(I) phosphine complexes including1were then compared in their ability to catalyze hydrofluorination reactions of 1‐phenyl‐1‐propyne with Et3N ⋅ 3HF as HF source. Model reactions suggested a reaction mechanism, which imparts a pre‐coordination of an alkyne to a cationic gold center followed by nucleophilic addition of a fluoride. Mechanistic investigations included reactivity studies at [Au(SPhos)][B(C6F5)4)] (17), which was treated with 4‐phenyl‐3‐butyn‐2‐one and TMAF (TMAF=tetramethylammonium fluoride). The reaction led to the formation of the complex [Au(CH3C(O)C=C(F)Ph)(SPhos)] (13), but not the fluorido complex1.

Fluorination Reactions at a Platinum Carbene Complex: Reaction Routes to SF3 , S(=O)F and Fluorido Complexes.

The electron‐rich Pt complex [Pt(IMes)2] (IMes: [1,3‐bis(2,4,6‐trimethylphenyl)‐2‐imidazolinylidine]) can be used as precursor for the syntheses of a variety of fluorido ligand containing compounds. The sulfur fluoride SF4 undergoes a rapid oxidative addition at Pt0 to yield trans‐[Pt(F)(SF3)(IMes)2]. A photolytic reaction of SF6 at [Pt(IMes)2] in the presence of IMes gave the fluorido complexes trans‐[Pt(F)2(IMes)2] and trans‐[Pt(F)(SF3)(IMes)2] along with trans‐[Pt(F)(SOF)(IMes)2] and trans‐[Pt(F)(IMes’)(IMes)] (IMes’: cyclometalated IMes ligand), the latter being products produced by reaction with adventitious water. trans‐[Pt(F)(SOF)(IMes)2] and trans‐[Pt(F)2(IMes)2] were synthesized independently by treatment of [Pt(IMes)2] with SOF2 or XeF2. A reaction of [Pt(IMes)2] with a HF source gave trans‐[Pt(H)(F)(IMes)2], and an intermediate bifluorido complex trans‐[Pt(H)(FHF)(IMes)2] was identified. Compound trans‐[Pt(H)(F)(IMes)2] converts in the presence of CsF into trans‐[Pt(F)(IMes’)(IMes)].

Reactions

OPINION Reactions ShareShare onFacebookTwitterWechatLinked InRedditEmail C&EN, 2021, 99 (31), p 3August 30, 2021Cite this:C&EN 99, 31, 3Letters to the editorHydrogen fluorideIn the Aug. 24, 2020, issue of C&EN, a two-page feature article by Michael McCoy was published on “a new route to hydrogen fluoride” with the subheadline “In a first for the US, the fluorochemical raw material will be made from a fertilizer industry by-product” (page 24). While I agree that this is a very worthwhile undertaking to utilize an environmental pollutant for supplying an important raw material for fluorochemical makers, the article omitted important information on the history of this process. The concept of using the SiF4 by-product from fertilizer plants as a source of HF and using it as a starting material for the synthesis of fluorocarbons is neither new nor a first for the US. It was developed 60 years ago in the US at Stauffer Chemical in Richmond, California, by Albert Mohr. The Mohr process was utilized to prepare either concentrated HF or SiF4 and was reduced to practice on the pilot-plant scale. It is described in detail in US patent 3,257,167, issued on June 21, 1966.Furthermore, the use of SiF4 to produce fluorochemicals was extensively studied in the early ’60s at Stauffer and is described in US patent 3,287,426 by Attila Pavlath and me, issued on Nov. 22, 1966, and in the publication “Silicon Tetrafluoride, a New Fluorinating Agent” (J. Org. Chem. 1964, DOI: 10.1021/jo01033a052). The use of SiF4 for producing hydrohalocarbon and halocarbon compounds has also been patented by Bamidele Omotowa in 2009 in the world patent WO 2009/032849 A1.Karl O. ChristeCalabasas, CaliforniaFrank DavisAs a former graduate student of Frank Davis in the biochemistry department at Rutgers University, I appreciated your commemorating his invention of attaching polyethylene glycol to proteins to escape the body’s immune response (May 31, 2021, page 13).Before this work he was a nucleic acid chemist who discovered pseudouridine, the most abundant modification in RNA (J. Biol. Chem.1957, 227, 907).Philip BarnettNew York CityTitanium dioxide in foodThis letter is in response to the article on titanium dioxide in foodpublished in C&EN’s May 17, 2021, issue (page 13).I cannot think of any cogent reason for permitting any purely cosmetic additive in food unless it is a natural constituent of some other foodstuff generally recognized as safe. In my opinion, all artificial food colorings should be banned and the public should be educated to recognize, accept and—ultimately—prefer foods with their natural appearance.Alexander MoreLondon CorrectionAug. 16/23, 2021, page 38: The Talented 12 profile of Chern-Hooi Lim incorrectly says he raised $7 million for his company, New Iridium. The company has raised $2.5 million in nondilutive funding.

Etching of Si3N4 by SF6/H2 and SF6/D2 plasmas

Selective plasma etching of silicon nitride (Si3N4) over silicon oxide (SiO2) is one of critical steps in the nanofabrication processes, where a direct plasma etching of Si3N4 is required for some applications. It was reported recently that Si3N4 etching by remote plasma source can be initiated by the vibrationally excited HF(v) molecules at the low concentration of atomic fluorine. Generally, the main source of HF(v) in plasma is reaction of atomic fluorine with H2 molecule. Due to this fact, the kinetic isotope effect should be observed during Si3N4 etching if replace the H2 source gas on deuterium gas (D2). The data presented here are the Si3N4 and SiO2 etching by the SF6/H2 and SF6/D2 plasmas. A different amount of H2 and D2 have been added to the SF6 discharge during the Si3N4 and SiO2 etching. It was shown that at low H2/D2 flow rate the Si3N4 etch rate is lower in the SF6/D2 discharge. This one confirms the hypothesis about Si3N4 etching by HF(v) and indicates on the fact that HF(v) gives contribution to Si3N4 etching by the direct plasma (not only by the remote plasma) at relatively high concentration of atomic fluorine.

Distribution, contamination status and source of trace elements in the soil around brick kilns

This study reports the distribution, contamination level, and possible sources of 54 metal (oid)s in the soils found around brick kilns in south-western Bangladesh. In total, 40 soil samples were collected from the vicinity of five brick kilns in four directions at 250 m intervals. This study reveals that the mean respective concentrations of caesium (Cs), beryllium (Be), lead (Pb), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), dysprosium (Dy), holmium (Ho), terbium (Tb), erbium (Er), thulium (Tm), ytterbium (Yb), thorium (Th), germanium (Ge), yttrium (Y), zirconium (Zr), niobium (Nb), silver (Ag), hafnium (Hf), tantalum (Ta), and tungsten (W), were 7.83, 3.19, 22.93, 85.93, 9.61, 36.86, 7.30, 1.23, 5.76, 1.13, 0.99, 3.14, 0.45, 2.91, 17.72, 3.04, 30.07, 185.13, 13.99, 0.30, 5.34, 1.26, and 2.61 μg g−1. Furthermore, those amounts exceeded their respective shale values. The pollution evaluation indices indicated a moderate level of contamination by Cs, Pb, Th, Ag, Hf, Ta, W, and lanthanides but excluding lanthanum (La) and lutetium (Lu). The pollution load index revealed pollution at two brickfields. Multivariate statistics reported that coal combustion in the brick kilns is the primary source of lanthanides, actinides, Y, Zr, and Hf in the soil, while other elements derived mostly from natural sources. A portion originated from coal combustion in brick kilns and agricultural activities. Changes in metal (oid)s concentrations were non-linear with the distance between the kilns and sampling points. Consequently, further studies are required and should consider meteorological factors and severity of human impact in the study area.

Genesis of baddeleyite and high δ18O zircon in impure marble from the Tongbai orogen, Central China: insights from petrochronology and Hf–O isotope compositions

Coexistence of baddeleyite and zircon is rarely documented in metacarbonate rocks and poorly understood. In this study, metamorphic baddeleyite and zircon were recognized in marbles from the Tongbai orogen, central China. We carried out high spatial resolution analysis of trace element geochemistry and U‒Pb‒Lu‒Hf‒O isotope systematics for the zircon and baddeleyite. SIMS (Secondary Ion Mass Spectroscopy) U‒Pb analysis yields weighted average 207Pb/206Pb ages of 1848.0 ± 3.3 Ma (MSDW = 1.2, n = 12) for baddeleyite and 1840 ± 13 Ma (MSWD = 1.7, n = 13) for zircon. The baddeleyite grains have relatively low REE (Rare Earth Element) contents (ΣREE = 1.30–47.3 ppm) with flat chondrite-normalized patterns and moderate contents of HFSE (High Field Strength Element), which are ascribed to the nature of its host metacarbonate rock and mineral assemblage. The zircon grains have low Ti contents (1.63–3.56 ppm), positive Ce anomalies (Ce/Ce* = 1.91–6.96), and mineral inclusions of hematite, calcite, dolomite, lizardite and H2O. These characteristics indicate zircon formation in a relatively low-temperature setting under oxidizing and water-rich conditions. The baddeleyite and zircon have similar ranges of eHf(t) values of – 7.7 to – 10.5 and – 7.8 to – 11.6, respectively, which suggest their derivation from a relatively uniform Hf source. The high δ18O values of these zircon grains (20.0–21.0‰) preclude any percolation of external meteoric fluids during their crystallization. Therefore, a “detrital-zircon-dissolution” reaction is preferred to provide the Zr for the metamorphic zircon and baddeleyite in this study. The O isotope disequilibrium between whole-rock (δ18O = 16.2–16.3‰) and metamorphic zircon is most likely caused by metamorphic devolatilization or interaction with an H2O-dominant fluid during later metamorphism. On the other hand, the baddeleyite grains yield δ18O values ranging from 4.5 to 8.7‰, which is in disequilibrium with metamorphic zircon at the temperature of “detrital-zircon-dissolution” reaction (ca. 660–710 °C; Zircon + Dolomite → Baddeleyite + Forsterite + Calcite + CO2). The genesis of metamorphic zircon can be interpreted by a baddeleyite-to-zircon reaction of ZrO2 + SiO2 → ZrSiO4 at a retrograde stage, consistent with the low Ti-in-Zircon temperatures. The results highlight the importance of integrating trace element and multiple isotopic compositions in studying the genesis of metamorphic baddeleyite and zircon. Additionally, the U–Pb geochronology data also indicate that the protoliths of the marble were deposited in the early Paleoproterozoic and experienced a metamorphism at 1.85 Ga. The ca. 1.85 Ga high-grade metamorphic event might have been induced by the coeval magmatism in an extensional setting.

Geochemistry, Sm–Nd, Rb–Sr, and Lu–Hf Isotopes, Sources, and Conditions of Formation of Early Paleozoic Plagiogranitoids in the South of the Lake Zone in Western Mongolia

Abstract —We present results of geochemical and isotope (Rb–Sr, Sm–Nd, and Lu–Hf) studies of the early Paleozoic plagiogranitoid associations in the south of the Lake Zone in Western Mongolia, which formed at the island-arc and accretion–collision stages of the regional evolution. According to the petrogeochemical composition, the early Paleozoic plagiogranitoid associations of the island-arc (Tugrug, Hatan-Hunga, Udzur-Hunga, and Bayasgalant plutons, 531–517 Ma) and accretion–collision (Tugrug, Mandalt, and Dut Uul plutons, 504–481 Ma) stages are high- and low-alumina rocks. The recognized types of plagiogranitoids, with regard to their trace-element composition, indicate that their parental melts were generated from MORB-type metabasites at ≥10–12 kbar, in equilibrium with garnet-containing restite, and at ≤8 kbar, in equilibrium with plagioclase-containing restite. The Sr–Nd isotope data on the rocks and the Lu–Hf isotope parameters of their magmatic zircons show two groups of plagiogranitoids, with different sources of melts. The first group includes plagiogranitoid associations of most plutons (Tugrug, Udzur-Hunga, Hatan-Hunga, Bayasgalant, and Dut Uul) with isotope parameters (εNd = 8.5–4.6, (87Sr/86Sr)0 = 0.7034–0.7036, and εHf = 14.7–11.9) indicating the juvenile nature of their sources. The second group includes plagiogranitoids of the Mandalt pluton; their isotope parameters (εNd = 1.4–0.2, (87Sr/86Sr)0 = 0.7053, and εHf = 7.2–5.4) indicate that the parental melts were generated mostly from enriched-mantle metabasites. The Hf isotope data on inherited and xenogenic zircons (664–519 Ma) from the early Paleozoic plagiogranitoid associations of the southern Lake Zone permit us to separate these rocks into three groups according to their εHf values (14.5–12.8, 2.9, and 10.6–6.7). The Hf isotope parameters of magmatic and inherited zircons, with regard to their age, indicate that the source of the parental melts lacked rocks with a long crustal history, such as the early Precambrian associations of the Dzavhan microcontinent.

Gold-Catalyzed Hydrofluorination of Internal Alkynes Using Aqueous HF.

The gold-catalyzed hydrofluorination reaction of internal alkynes using hydrofluoric acid is reported. Notably, those conditions use one of the most economical sources of HF and are free of additional additives. Both symmetrical and unsymmetrical internal alkynes can be utilized, and the use of alkynes bearing a fluorinated group at the propargylic position as substrates allowed for a regioselective hydrofluorination reaction.

Геохимия марганценосных отложений палеовулканогенных комплексов Южного Урала

Research subject . This article is devoted to the geochemistry of manganese deposits referred to the Devonian paleovolcanic complexes of the Magnitogorsk belt in the Southern Urals. Materials and methods . A series of studies was conducted using materials collected from the Kyzyl-Tash, Kazgan-Tash, Kozhayevskoye, Bikkulovskoye and Southern Fayzuinskoye deposits. The content of main elements and rare-earth elements was determined using the X-ray spectral fluorescent and ICP-MS methods, respectively. Results. It is shown that the values of indicator lithochemical modules in the manganese rocks under study are comparable to those in the modern metal- and ore-bearing sediments. The manganese rocks are characterized by low concentrations of rare-earth elements, as well as by a negative Ce anomaly (Ce/Ce* = 0.20-0.85) in their spectrum and an insignificant prevalence of heavy lanthanides over light ones. In terms of the REE spectrum configuration, the rocks under study are close to modern ferromanganese deposits of a hydrothermal genesis. Conclusion. The most probable source of Li, Be, Sc, Cr, Rb, Zr, Nb, Hf and Th in the manganese deposits was the detrital material of background sediments. Co, Ni, Ge, As, Mo and Sb, which concentration in the studied rocks is higher compared to that in the detrital component, are most likely to have been produced by hydrothermal solutions. Other rare elements could have been brought into the sediments through different routes. In general, according to the distribution of main, rare and rare-earth elements, the manganese rocks in the Southern Urals are comparable to the deposits of low-temperature hydrothermal sources, which developed within the arc system of the modern ocean. Our findings agree well with the concept of the hydrothermal-sedimentary origin of manganese deposits in the Southern Urals, thus supplementing this hypothesis by the data obtained using independent sources.

Enhanced reactivity of fluorine with para-hydrogen in cold interstellar clouds by resonance-induced quantum tunnelling

Chemical reactions are important in the evolution of low-temperature interstellar clouds, where the quantum tunnelling effect becomes significant. The F + para-H2 → HF + H reaction, which has a significant barrier of 1.8 kcal mol-1, is an important source of HF in interstellar clouds; however, the dynamics of this quantum-tunnelling-induced reactivity at low temperature is unknown. Here, we show that this quantum tunnelling is caused by a post-barrier resonance state. Quantum-state-resolved crossed-beam scattering measurements reveal that this resonance state has a collision energy of ~5 meV and a lifetime of ~80 fs, which are in excellent agreement with a recent anion photoelectron spectroscopic study. Accurate quantum reactive scattering calculations on the new iCSZ-LWAL potential energy surfaces provides a detailed explanation of the experimental results. The reaction rate for this system was also theoretically determined accurately at temperatures as low as 1 K.

Neutron capture cross sections of Hf178 leading to Hfm2179

Cross sections for radiative neutron capture have been measured for the formation of 25-d $^{179}\mathrm{Hf}^{{m}_{2}}$ (${J}^{\ensuremath{\pi}}=25/{2}^{+}$) using targets of enriched $^{178}\mathrm{Hf}$. Based on irradiations using pure epithermal neutrons as well as mixed thermal + epithermal neutrons, the thermal cross section has been determined to be $\ensuremath{\sigma}=6(5)\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{b}$ and the resonance integral $I=1.63(5)\phantom{\rule{0.16em}{0ex}}\mathrm{mb}$. To enhance the determination of the cross sections, the energies and intensities of the $\ensuremath{\gamma}$ rays from the decay of $^{179}\mathrm{Hf}^{{m}_{2}}$ have been re-determined with improved precision. The half-life of $^{179}\mathrm{Hf}^{{m}_{2}}$ has been measured to be 24.91(27) d, in agreement with the previously accepted value. The analysis of the $^{179}\mathrm{Hf}^{{m}_{2}}$ decay required more precise spectrometry on competing $\ensuremath{\gamma}$ rays from the decay of $^{181}\mathrm{Hf}$, whose results are presented (along with that of the decay of $^{175}\mathrm{Hf}$) from irradiation of a source of natural Hf. The measured cross sections are compared with those of other high-spin neutron captures.

Impact of Hf and Al Co-Incorporation into the Atomic-Layer-Deposited ZnO Active Channel for the Thin-Film Transistor Applications

ZnO-based oxide semiconductors have attracted much attention as active layer for thin film transistors (TFTs) due to their special features such as low-temperature process compatibility, high transparency, and wide bandgap (~3.37 eV). However, the instability and difficulty in controlling the electrical conductivity of ZnO still remain as critical issues. To solve these problems, various metal atoms have been introduced in ZnO, such as In, Ga, Sn, Al, and Hf. Among them, Hf and Al can be acted as stability enhancer by suppressing oxygen vacancies formation and as conductivity modulator by adjusting doping concentration, respectively. To effectively exploit their advantages, the composition control is one of the important parameters to be carefully adjusted. Furthermore, the active channel layer should have homogenous and smooth surface for forming good interface between Hf-Al-Zn-O (HAZO) active and Al2O3 gate insulator layers. From these viewpoints, atomic layer deposition (ALD) can be an optimum method to deposit the HAZO thin films because of such benefits as excellent conformality and good controllability for composition and film thickness. Thus, in this work, we fabricated top-gate transparent oxide TFTs using newly presented HAZO active channels deposited by ALD method and investigated the effects of Hf and Al concentration on the device performance including basic characteristics such as carrier mobility, subthreshold swing (SS), and turn-on voltage (Von), and reliability characteristics. The ALD temperature of HAZO was fixed at 100 oC. Tetrakis(ethylmethylamino)hafnium (TEMAHf), trimethylaluminium (TMA), diethylzinc (DEZ), and H2O were used as Hf, Al, Zn, and O2 sources, respectively. In this work, the composition control of Hf and Al was selected as main strategy to modulate device property. The atomic composition of 20-nm-thick HAZO thin films was controlled by adding TEMAHf and TMA cycles among a total 100 cycles. Total ALD cycles were designed so that the HfO2 and Al2O3 were located in the intervals of ZnO. For the HAZO thin film with 2-at%-Hf and 2-at%-Al, the position of two TEMAHf cycles were placed on 40th and 80th cycles, and two TMA cycles were placed on 20th and 60th cycles of total 100 cycles, separately. The incorporated amounts of Hf and Al were modulated into 2, 4, 6, 8, and 10 at% and 2 and 4 at%, respectively. The data figure shows the comparisons in transfer characteristics for the fabricated top-gate TFTs using HAZO active layers with various amounts of incorporated Hf when the incorporated Al amount was fixed at 2 at%. The fabricated devices show distinct differences in device characteristics depending on the incorporated Hf and Al compositions. When the Hf amounts were varied from 2 to 10 at%, the Von’s shifted to positive direction from negative side toward 0 V and SS values were improved from 1.12 to 0.37 V/dec. In contrast, the carrier mobility was slightly decreased from 2.97 to 1.24 cm2/Vs. The post-annealing effects were also investigated. The fabricated TFTs were thermally treated at the temperature range from 150 to 250 oC for 1 h in oxygen atmosphere. The Von shifted toward positive direction and SS were improved as the increase in annealing temperature, although the on-current and carrier mobility showed decreasing trend. In conclusion, we successfully confirmed that the new composition of oxide semiconductor, HAZO, can be utilized as an active layer for the oxide TFT, and that the electronic natures of the HAZO channel layers can be well controlled by adjusting the ALD conditions. The top-gate TFT using the HAZO channel with 10-at%-Hf and 2-at%-Al showed the best device characteristics such as low SS value of 370 mV/dec, low-voltage operation at around 0 V, and comparable carrier mobility of 1.24 cm2/Vs. It was also found that thermal treatment in oxygen atmosphere markedly influenced on the transfer characteristics including the location of Von. Here, we believe that the device performance can be far improved by simultaneously optimizing the Hf and Al incorporating amounts and the post annealing process condition. Optimum ALD conditions for preparing the HAZO channel layers will also be important for better device performance for the HAZO TFTs. Furthermore, we have plans to investigate the device reliability, which is one of the most important factor in evaluating device characteristics, such as positive bias temperature stress stability (PBTS), and negative bias illumination stability (NBIS). As results, highly-stable TFTs will be implemented with practical value of carrier mobility by employing HAZO channel with appropriate incorporating amounts of Hf and Al at optimum ALD conditions. Figure 1

Ordered Topographically Patterned Silicon by Insect-Inspired Capillary Submicron Stamping.

Insect-inspired capillary submicron stamping and subsequent surface-limited metal-assisted chemical etching (MACE) with ammonium bifluoride as a HF source are employed for the high-throughput production of ordered topographically patterned silicon (tpSi). Insect feet often possess hairy contact elements through which adhesive secretion is deployed. Thus, arrays of adhesive secretion drops remain as footprints on contact surfaces. Stamps for insect-inspired capillary submicron stamping having surfaces topographically patterned with contact elements mimic the functional principles of such insect feet. They contain spongy continuous nanopore networks penetrating the entire stamps. Any ink (organic or aqueous) may be supplied from the backside of the nanoporous stamps to the contact elements. We generated ordered arrays of submicron AgNO3 dots extending square millimeters on Si by manual stamping with cycle times of a few seconds under ambient conditions; at higher load, ordered holey AgNO3 films were obtained. Surface-limited MACE correspondingly yielded either macroporous tpSi or Si pillar arrays. Inkjet printing of polymer solutions onto the tpSi yielded patterns of polymer blots conformally covering the tpSi. Such blot patterns could potentially represent a starting point for the development of persistent and scratch-resistant identity labels or quick response codes on silicon surfaces.

Magmatic age of rare-earth element and zirconium mineralisation at the Norra Kärr alkaline complex, southern Sweden, determined by U–Pb and Lu–Hf isotope analyses of metasomatic zircon and eudialyte

The agpaitic Norra Kärr alkaline complex in southern Sweden is rich in heavy rare-earth elements and zirconium. Despite generally containing high concentrations of Zr, agpaitic rocks sensu stricto are devoid of igneous zircon. During the late stages of magmatic activity at Norra Kärr, metasomatic Na- and F-rich fluids transporting Zr complexes caused fenitisation (syn-magmatic alkali metasomatism) of the granitic wall rocks, which formed new metasomatic zircon. Fenite zircon was dated by LA-MC-ICP-MS with the U–Pb method at 1.49±0.01Ga, while the unaltered country rock granite was dated at 1.79±0.01Ga. Zircon in the fenites exhibits εHf+6.58±0.36 at 1.49Ga; significantly above the expected value for Svecofennian crust at that time (ca. −5±2), but identical, within error, of that measured in eudialyte from Norra Kärr. This suggests a common source of Hf for fenite zircon and eudialyte from Norra Kärr, which isotopically strengthens the genetic link between fenite and nepheline syenite. The 1.49Ga age dates not only the fenitisation, but also the relatively small agpaitic intrusion, which caused the fenitisation. This also dates the origin of the rare-earth element and Zr ore within the agpaitic nepheline syenite, which probably formed from an evolved magma derived from the mantle. A few zircon xenocrysts, which survived in the agpaitic nepheline syenite magma, may indicate the presence of an Archaean component in the basement.

Reaction of N-heterocyclic carbene (NHC) with different HF sources and ratios – A free fluoride reagent based on imidazolium fluoride

Treatment of N-heterocyclic carbene (1,3-Bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene; (LDipp)) with different sources of hydrofluoric acid (Et3N∙3HF, anhydrous hydrofluoric acid and KHF2) in 1:1, 1:2, 1:3 ratios affords [(LDipp)H]+[F]− (1), [(LDipp)H]+[(HF)F]− (2) and [(LDipp)H]+[(HF)2F]− (3) salts respectively. Different fluoride sources all yield the same products, but ease of manipulation and isolation can influence the choice in the future use.Compound (1), which shows characteristics of a free fluoride reagent, can be obtained with good yield and without the contaminants usually present in such compounds. All products were characterized by X-Ray crystallography, NMR spectroscopy and free fluoride (Ff−) chemical analysis.