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Treatment of 3 equiv of the potassium salts derived from the β-amino ketones 1-(dimethylamino)-3,3-dimethylbutan-2-one (L1H), 3,3-dimethyl-1-(pyrrolidin-1-yl)butan-2-one (L2H), and 3,3-dimethyl-1-(...

The feasibility of using selective thermal cobalt metal (Co) atomic layer deposition (ALD) as high density Cu–Cu interconnect bonding is demonstrated at a low temperature (200 °C) and with minimal surface pretreatment. A Cu/Gap/Cu structure, which emulates 3-D ICs stacking is fabricated. Cobalt ALD showing seamless interconnection between copper (Cu) pads with 30- $\mu \text{m}$ pitch is demonstrated with greater than 90% yield through electrical measurements, SEM inspection, EDS, and focused ion beam (FIB) cross section.

Treatment of the stable N-heterocyclic carbene 1,3-di-tert-butylimidazolin-2-ylidene with 2 equiv of AlH3(NMe3) afforded the structurally unusual ring-expanded dialane complex 1 in 72% yield after ...

An atomic layer deposition (ALD) process is reported for the growth of nanoscale PrAlO3 thin films for two-dimensional electronics and memory device applications using tris(isopropylcyclopentadieny...

The growth of rhenium nitride and rhenium metal thin films is presented using atomic layer deposition (ALD) with the precursors methyltrioxorhenium and 1,1-dimethylhydrazine. Saturative, self-limiting growth was determined at 340 °C for pulse times of ≥4.0 s for methyltrioxorhenium and ≥0.1 s for 1,1-dimethylhydrazine. An ALD window was observed from 340 to 350 °C with a growth rate of about 0.60 A/cycle. Films grown at 340 °C revealed an root mean square surface roughness of 2.7 nm for a 70 nm thick film and possessed a composition of ReN0.14 with low O and C content of 1.6 and 2.6 at.%, respectively. Enhanced nucleation on in-situ grown TiN, relative to thermal SiO2, enabled a conformality of 98% on high aspect ratio trenched structures. Subjecting the ReN0.14 thin films to thermal or chemical and thermal treatments reduced the nitrogen content to ≤1.6 at.%, yielding a film purity of about 96 at.% rhenium and resistivities as low as 51 µΩ cm. The Re metal film thicknesses on the trenched structures remained intact during the post-deposition annealing treatments and the films did not delaminate from the substrate surfaces.

A Cu-Cu bonding approach using low temperature (200 °C) selective Co ALD is demonstrated for Cu pads that are separated by 200 nm. The bonding testbed is characterized before and after Co ALD by SEM and EDS to confirm the feasibility of the approach. AFM and XPS are used to measure the selectivity of Co ALD on Cu and SiO 2 surfaces.

Taking the full advantage of the conformal growth characterizing atomic layer deposition (ALD), the possibility to grow Co thin films, with thickness from several tens down to few nanometers on top of a granular topological insulator (TI) Sb2Te3 film, exhibiting a quite high surface roughness (2–5 nm), was demonstrated. To study the Co growth on the Sb2Te3 substrate, we performed simultaneous Co depositions also on sputtered Pt substrates for comparison. We conducted a thorough chemical-structural characterization of the Co/Sb2Te3 and Co/Pt heterostructures, confirming for both cases, not only an excellent conformality, but also the structural continuity of the Co layers. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) analyses evidenced that Co on Sb2Te3 grows preferentially oriented along the [00ℓ] direction, following the underlying rhombohedric substrate. Differently, Co crystallizes in a cubic phase oriented along the [111] direction when deposited on Pt. This work shows that, in case of deposition of crystalline materials, the ALD surface selectivity and conformality can be extended to the definition of local epitaxy, where in-plane ordering of the crystal structure and mosaicity of the developed crystallized grains are dictated by the underlying substrate. Moreover, a highly sharp and chemically-pure Co/Sb2Te3 interface was evidenced, which is promising for the application of this growth process for spintronics. [Figure not available: see fulltext.].

We report the growth of nickel metal films by atomic layer deposition (ALD) employing bis(1,4-di- tert-butyl-1,3-diazadienyl)nickel and tert-butylamine as the precursors. A range of metal and insulating substrates were explored. An initial deposition study was carried out on platinum substrates. Deposition temperatures ranged from 160 to 220 °C. Saturation plots demonstrated self-limited growth for both precursors, with a growth rate of 0.60 Å/cycle. A plot of growth rate versus substrate temperature showed an ALD window from 180 to 195 °C. Crystalline nickel metal was observed by X-ray diffraction for a 60 nm thick film deposited at 180 °C. Films with thicknesses of 18 and 60 nm grown at 180 °C showed low root mean square roughnesses (2.5% of thicknesses) by atomic force microscopy. X-ray photoelectron spectroscopies of 18 and 60 nm thick films deposited on platinum at 180 °C revealed ionizations consistent with nickel metal after sputtering with argon ions. The nickel content in the films was97%, with low levels of carbon, nitrogen, and oxygen. Films deposited on ruthenium substrates displayed lower growth rates than those observed on platinum substrates. On copper substrates, discontinuous island growth was observed at ≤1000 cycles. Film growth was not observed on insulating substrates under any conditions. The new nickel metal ALD procedure gives inherently selective deposition on ruthenium and platinum from 160 to 220 °C.

Herein, we will describe recent progress in our laboratory on the development of chemical precursors for the thermal atomic layer deposition (ALD) of cobalt metal, titanium metal, cobalt-titanium alloy, and other metal and metal alloy films. The nanoscale dimensions of current and future microelectronics devices now require alternative, ultrathin barrier materials for copper and other interconnect metals as well as new ultrathin liner materials. Sputtered cobalt-titanium alloys have been demonstrated to function as barrier materials and liners at dimensions as small as 1 nm. Hence, these materials may replace current barrier and liner materials such as TiN, TaN, and W metal. However, the narrow and deep nanoscale features require growth of cobalt-titanium alloy films by ALD to meet the strict conformality and thickness requirements. Moreover, thermal ALD is preferred over plasma-based processes, since recombination of atomic hydrogen on feature walls can afford poor conformal coverage. Thermal ALD processes for Co and Ti metal films are poorly developed, because the negative electrochemical potentials of the ions in precursors (Co2+ ↔ Co, E° = -0.280 V, Ti2+ ↔ Ti, E° = -1.628 V) require strong reducing co-reactants, which are not available. We will report new thermal ALD processes for cobalt metal films that employ various ligands, in combination with hydrazine-based co-reactants. These processes afford high purity cobalt metal films. We will also describe our efforts to develop new precursors for the thermal ALD of titanium metal films. Initial depositions of cobalt-titanium metal films will also be described.

Treatment of tetrakis(dimethylamido)zirconium or tetrakis(dimethylamido)hafnium with four equivalents of N-tert-butylacetamide, N-isopropylisobutyramide, N-isopropylacetamide, N-methylacetamide, or N-tert-butylformamide in refluxing toluene, followed by sublimation of the crude products at 105–125 °C/0.05 Torr, afforded tetrakis(N-tert-butylacetamido)zirconium (81%), tetrakis(N-isopropylisobutyramido)zirconium (87%), tetrakis(N-isopropylacetamido)zirconium (51%), tetrakis(N-tert-butylacetamido)hafnium (83%), tetrakis(N-isopropyliso-butyramido)hafnium (79%), tetrakis(N-isopropylacetamido)hafnium (67%), tetrakis(N-methylacetamido)zirconium (5%), and tetrakis(N-tert-butylformamido)zirconium (1%) as colorless crystalline solids. The structural assignments for the new complexes were based upon spectral and analytical data and by X-ray crystal structure determinations for tetrakis(N-tert-butylacetamido)zirconium, tetrakis(N-isopropylacetamido)zirconium, tetrakis(N-isopropylacetamido)hafnium, tetrakis(N-methylacetamido)zirconium, and tetrakis(N-tert-butylformamido)zirconium. These complexes are monomeric in the solid state, with eight-coordinate metal centers surrounded by four κ2-N,O-amidate ligands. Six of the eight new complexes undergo sublimation on a preparative scale from 130 to 140 °C at 0.05 Torr, with 84.5–95.8% sublimed recoveries and 0.68–3.06% nonvolatile residues. Tetrakis(N-methylacetamido)zirconium and tetrakis(N-tert-butylformamido)zirconium decompose extensively upon attempted sublimation. Solid state decomposition temperatures for the zirconium complexes range between 218 and 335 °C and 290–360 °C for the hafnium complexes. Tetrakis(N-isopropylisobutyramido)zirconium, tetrakis(N-tert-butylacetamido)hafnium, and tetrakis(N-isopropylacetamido)hafnium exhibit the highest solid state decomposition temperatures in the series, possess good volatility, and have useful properties for chemical vapor deposition and atomic layer deposition precursors.

The atomic layer deposition (ALD) of cobalt metal films is described using the precursor bis(1,4-di-tert-butyl-1,3-diazadienyl)cobalt and tert-butylamine or diethylamine. Platinum, copper, ruthenium, Si(100) with native oxide, thermal SiO2, hydrogen-terminated silicon, and carbon-doped oxide substrates were used with growth temperatures between 160 and 220 °C. Plots of growth rate versus pulse lengths showed saturative, self-limited behavior at ≥3.0 s for bis(1,4-di-tert-butyl-1,3-diazadienyl)cobalt and ≥0.1 s for tert-butylamine. An ALD window was observed between 170 and 200 °C, with a growth rate of 0.98 A/cycle on platinum substrates. A plot of thickness versus the number of cycles at 200 °C on platinum substrates was linear between 25 and 1000 cycles, with a growth rate of 0.98 A/cycle. A 98 nm thick film grown at 200 °C showed crystalline cobalt metal by X-ray diffraction. Atomic force microscopy of 10 and 98 nm thick cobalt metal films grown on platinum substrates at 200 °C showed rms roughness val...

Owing to its narrow band gap and promising magnetic and photocatalytic properties, thin films of zinc ferrite (ZFO, ZnFe2O4) are appealing for fabrication of devices in magnetic recording media and photoelectrochemical cells. Herein we report for the first time the fabrication of photactive zinc ferrites via a solvent free, conventional CVD approach, and the resulting ZFO layers show promise as a photocatalyst in PEC water-splitting. For large scale applications, chemical vapor deposition (CVD) routes are appealing for thin film deposition; however, very little is known about ZFO synthesis following CVD processes. The challenge in precisely controlling the composition for multicomponent material systems, such as ZFO, via conventional thermal CVD is an issue that is caused mainly by the mismatch in thermal properties of the precursors. The approach of using two different classes of precursors for zinc and iron with a close match in thermal windows led to the formation of polycrystalline spinel type ZFO. Un...

Internet-of-things (IoT) objects are expected to exceed 75 billion objects by 2020, and a large part of the expansion is expected to be at a finer granularity than existing silicon-based IoT objects (i.e. tablets and cell phones) can deliver [1]. Currently, placing a room light or a thermostat on the internet for remote control is considered progressive. However, if printed electronics can achieve performance increases, then IoT objects could be affixed to almost anything, such as coffee creamer cartons, cereal boxes, or that missing sock. Each of these IoT objects could be driving a sensor, perhaps position, temperature or pressure, essentially a multitude of applications. In order for IoT objects to emulate a simple postage stamp, with self-powering from energy scavenging and local energy storage, all housed in a non-toxic flexible form factor, advances in solution processable devices need to occur. acceptedVersion

Treatment of [Ag((CF3)2pz)]3 or [Ag(tBu,C3F7)pz)]3 (pz = pyrazolate) with various stable N-heterocyclic carbenes (NHC) afforded silver(I) complexes containing pyrazolate and NHC ligands in 10–81% crystalline yields. These complexes were analyzed by spectral and analytical techniques and by X-ray crystal structure determinations. The solid state structures showed monomeric, dimeric, or tetrameric formulations, depending upon the pyrazolate and NHC substituents. To evaluate their potential as thin film growth precursors, [Ag((CF3)2pz)]3, [Ag(tBu,C3F7)pz)]3, and the new complexes were evaluated by thermogravimetric analyses, sublimation studies, thermal decomposition temperatures, and solution reduction experiments with potential reducing agents. The decomposition temperatures were higher for complexes containing (CF3)2pz ligands (203 to 293 °C) than for those containing (tBu,C3F7)pz ligands (160 to 200 °C). The complexes sublimed between 110 and 140 °C at 0.2 Torr. Solution reactions of several complexes with aqueous hydrazine, 1,1-dimethylhydrazine, formic acid, and tBuNH2 led to the formation of silver metal. Several of the new complexes have promising precursor properties for use in thin film growth by the atomic layer deposition and chemical vapor deposition techniques.

Ten peroxide compounds based upon the 3,6-di(hydroperoxy)-1,2-dioxane, 2-hydroxy-6-hydroperoxy-1,2-dioxane, 3,5-di(hydroperoxy)-1,2-dioxolane, and 3-hydroxy-5-hydroperoxy-1,2-dioxolane skeletons have been synthesized, structurally characterized, and fully evaluated for their energetic materials properties. The solid state structures of these compounds are dominated by hydrogen bonding interactions involving the hydroperoxy and hydroxy groups. Energetic materials testing shows that most of the compounds are highly sensitive toward impact and friction, with similar properties to highly sensitive peroxides such as triacetone triperoxide. 3,5-Diethyl-5-hydroperoxy-1,2-dioxolan-3-ol (3b) and 3,5-dimethyl-5-hydroperoxy-1,2-dioxolan-3-ol (5b) have lower impact and friction sensitivities than the other compounds, with values that are appropriate for use as primary explosives.

Atomic layer deposition (ALD) of ruthenium metal films is presented using (η4-2,3-dimethylbutadiene)(tricarbonyl)ruthenium [Ru(DMBD)(CO)3] with the coreactants 1,1-dimethylhydrazine, hydrazine, or tert-butylamine. The dependence of growth rate on precursor pulse lengths at 200 °C showed a saturative, self-limited behavior at ≥3.0 s for Ru(DMBD)(CO)3 and ≥0.1 s for 1,1-dimethylhydrazine. An ALD window was observed from 200 to 210 °C, with a growth rate of 0.42 A/cycle. Films grown at 200 °C showed rms surface roughnesses of

Aluminum dihydride complexes containing amido-amine ligands were synthesized and evaluated as potential reducing precursors for thermal atomic layer deposition (ALD). Highly volatile monomeric complexes AlH2(tBuNCH2CH2NMe2) and AlH2(tBuNCH2CH2NC4H8) are more thermally stable than common Al hydride thin film precursors such as AlH3(NMe3). ALD film growth experiments using TiCl4 and AlH2(tBuNCH2CH2NMe2) produced titanium carbonitride films with a high growth rate of 1.6-2.0 Å/cycle and resistivities around 600 μΩ·cm within a very wide ALD window of 220-400 °C. Importantly, film growth proceeded via self-limited surface reactions, which is the hallmark of an ALD process. Root mean square surface roughness was only 1.3 % of the film thickness at 300 °C by atomic force microscopy. The films were polycrystalline with low intensity, broad reflections corresponding to the cubic TiN/TiC phase according to grazing incidence X-ray diffraction. Film composition by X-ray photoelectron spectroscopy was approximately TiC0.8N0.5 at 300 °C with small amounts of Al (6 at%), Cl (4 at%) and O (4 at%) impurities. Remarkably, self-limited growth and low Al content was observed in films deposited well above the solid-state thermal decomposition point of AlH2(tBuNCH2CH2NMe2), which is ca. 185 °C. Similar growth rates, resistivities, and film compositions were observed in ALD film growth trials using AlH2(tBuNCH2CH2NC4H8).

1,4-Dimethyl-2,3,5,6-tetraoxabicyclo[2.2.1]heptane and several similar alkyl-derivatives were synthesized applying two different strategies. Crystal structures of the compounds were determined and their energetic properties including sensitivities towards impact, friction and electrostatic discharge as well as their thermal behaviour were determined and compared to tricacetone triperoxide (TATP). The enthalpies of formation and the resulting explosive properties were calculated using the EXPLO5 program.

The atomic layer deposition (ALD) of Cu metal films was carried out by a two-step process with Cu(OCHMeCH2NMe2)2 and BH3(NHMe2) on Ru substrates and by a three-step process employing Cu(OCHMeCH2NMe2)2, formic acid, and BH3(NHMe2) on Pd and Pt substrates. The two-step process demonstrated self-limited ALD growth at 150 °C with Cu(OCHMeCH2NMe2)2 and BH3(NHMe2) pulse lengths of ≥3.0 and ≥1.0 s, respectively. An ALD window was observed between 130 and 160 °C, with a growth rate of about 0.13 A/cycle. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed rough Cu films that likely originate from the Cu nanoparticle seed layer. The Cu films exhibited poor electrical conductivity because of their nanoparticulate natures. The three-step process showed self-limited ALD growth on Pd and Pt at 150 °C with Cu(OCHMeCH2NMe2)2, formic acid, and BH3(NHMe2) pulse lengths of ≥3.0, ≥ 0.3, and ≥1.0 s, respectively. ALD windows were observed between 135 and 165 °C on both Pd and Pt, with growth rates o...

Treatment of MCl2 (M = Cu, Ni, Co, Fe, Mn, Cr) with 2 equiv of α-imino alkoxide salts K(RR'COCNtBu) (R = Me, tBu; R' = iPr, tBu) afforded M(RR'COCNtBu)2 or [Mn(RR'COCNtBu)2]2 in 9-75% yields. These complexes combine volatility and high thermal stability and have useful atomic layer deposition (ALD) precursor properties. Solution reactions between Ni, Co, and Mn complexes showed that BH3(NHMe2) can reduce all to metal powders. ALD growth of Ni, Co, Fe, and Cr films is demonstrated. Mn film growth may be possible, but the films oxidize completely upon exposure to air.

Treatment of MCl2 (M = Ni, Co, Fe, Mn, Cr) with 2 equiv of the hydrazonate salts K(tBuNNCHCtBuO), K(tBuNNCHCiPrO), or K(tBuNNCMeCMeO) afforded the complexes M(tBuNNCHCtBuO)2 (M = Ni, 65%; Co, 80%; Fe, 83%; Mn, 68%; Cr, 64%), M(tBuNNCHCiPrO)2 (M = Ni, 63%; Co, 86%; Fe, 75%), and M(tBuNNCMeCMeO)2 (M = Ni, 34%; Co, 29%; Fe, 27%). Crystal structure determinations of Co(tBuNNCHCtBuO)2, M(tBuNNCHCiPrO)2 (M = Ni, Co), and M(tBuNNCMeCMeO)2 (M = Ni, Co, Fe) revealed monomeric complexes with tetrahedral geometries about the metal centers. To evaluate the potential of these new complexes as film growth precursors, preparative sublimations, thermogravimetric analyses, solid state decomposition studies, and solution reactions with reducing coreagents were carried out. M(tBuNNCHCtBuO)2 sublime between 120 and 135 °C at 0.05 Torr, whereas M(tBuNNCHCiPrO)2 and M(tBuNNCMeCMeO)2 sublime between 100 and 105 °C at the same pressure. All complexes afforded ≥96% recovery of sublimed material, with ≤3% of nonvolatile residues. The solid state decomposition temperatures were highest for M(tBuNNCHCiPrO)2 (273-308 °C), intermediate for M(tBuNNCHCtBuO)2 (241-278 °C), and lowest for M(tBuNNCMeCMeO)2 (235-250 °C). Treatment of Co(tBuNNCHCtBuO)2 in tetrahydrofuran with hydrazine, BH3(L) (L = NHMe2, SMe2, THF), pinacol borane, and LiAlH4 led to rapid formation of cobalt metal, while analogous reductions of Mn(tBuNNCHCtBuO)2 with BH3(THF), pinacol borane, and LiAlH4 appeared to afford manganese metal. The new complexes M(tBuNNCHCtBuO)2, M(tBuNNCHCiPrO)2, and M(tBuNNCMeCMeO)2 have very promising properties for use as precursors for the growth of the respective metals in atomic layer deposition film growth processes.

Treatment of metal(II) halides (metal = Cu, Ni, Co, Fe, Mn, Cr) with the potassium salts of carbohydrazides L1–L6 afforded Cu(L1)2 (75%), Cu(L2)2 (51%), Cu(L3)2 (23%), Co(L1)2 (57%), Cr(L1)2 (62%), Ni(L1)2 (76%), Ni(L2)2 (62%), Ni(L3)2 (62%), Ni(L4)2 (13%), Ni(L5)2 (11%), Ni(L6)2 (29%), [Fe(L1)2]2 (28%), and [Mn(L1)2]2 (12%) as crystalline solids, where L1 = Me2NN C(tBu)O−, L2 = Me2NN C(iPr)O−, L3 = Me2NN C(Me)O−, L4 = (CH2)5NN C(tBu)O−, L5 = (CH2)5NN C(iPr)O−, and L6 = (CH2)5NN C(Me)O−. These complexes were characterized by spectral and analytical techniques, and by X-ray crystal structure determinations for Cu(L1)2, Co(L1)2, Cr(L1)2, Ni(L1)2, and [Fe(L1)2]2. Cu(L1)2, Co(L1)2, Cr(L1)2, and Ni(L1)2 exist as square planar, monomeric complexes, whereas [Fe(L1)2]2 is a dimer. A combination of sublimation studies, thermal decomposition temperature determinations, and thermogravimetric/differential thermal analysis demonstrate that the Cu, Co, and Ni complexes Cu(L1)2, Cu(L2)2, Co(L1)2, Ni(L1)2, and Ni(L2)2 have the lowest sublimation temperatures and highest decomposition temperatures among the series. Additionally, these compounds have higher volatilities and thermal stabilities than commonly used ALD and CVD precursors. Hence, these new complexes have excellent properties for application as ALD precursors to Cu, Co, and Ni metal films.

The atomic layer deposition (ALD) of films with the approximate compositions Mn3(BO3)2 and CoB2O4 is described using MnTp2 or CoTp2 [Tp ¼ tris(pyrazolyl)borate] with ozone. The solid state decomposition temperatures of MnTp2 and CoTp2 are 370 and 340 C, respectively. Preparative-scale sublimations of MnTp2 and CoTp2 at 210 C/0.05 Torr afforded >99% recoveries with

Treatment of MCl4(4-tBupy)2 (M = Nb, Ta) with 3 equiv of potassium 3,5-di-tert-butylpyrazolate afforded (2,2,6,6-tetramethyl-5-ketimidehept-3-en-3-imide)bis(3,5-di-tert-butylpyrazolate)chloroniobium(V) (1; 24%) and (2,2,6,6-tetramethyl-5-ketimidehept-3-en-3-imide)bis(3,5-di-tert-butylpyrazolate)chlorotantalum(V) (2; 27%) as deep red and yellow crystalline solids, respectively. Analogous treatment of NbCl4(THF)2 with 3 equiv each of 4-tert-butylpyridine and potassium 3,5-di-tert-butylpyrazolate and excess Na/Hg in diethyl ether afforded (2,2,6,6-tetramethyl-5-ketimidohept-3-en-3-imide)bis(3,5-di-tert-butylpyrazolate)niobium(V) (3, 32%) as deep red crystals. X-ray crystallography established that 1 and 3 each contain two intact η2-3,5-di-tert-butylpyrazolate ligands as well as one 3,5-di-tert-butylpyrazolate ligand that has undergone N–N bond oxidative addition to the niobium center. In 1, one of the nitrogen atoms abstracted a hydrogen atom from tetrahydrofuran solvent, whereas no hydrogen atom abstraction...

The aromaticity of a series of metallapyrimidines involving second row transition metals was examined using density functional theory. Nucleus independent chemical shifts (NICS) placed above the ring (NICS(1)zz) were used to gauge the amount of aromaticity. Natural chemical shielding analysis (NCS) was employed to decompose the chemical shifts in terms of diamagnetic and paramagnetic contributions from individual molecular orbitals. While NICS(1)zz for niobapyrimidine, [(pz)2(Nb-pyr)](0), suggested slightly aromatic character, the NCS analysis shows this is due to the diamagnetic (field-free) contribution. Instead, the positive paramagnetic (field-induced) contribution suggests that niobapyrimidine may be slightly antiaromatic. A series of d(0) metallapyrimidines, [(pz)2(M-pyr)] with M = Y(III), Zr(IV), Nb(V), Mo(VI), Tc(VII), demonstrated similar behavior. Variation of the number of metal d electrons in a series of M(V) metallapyrimidines, [(pz)2(M-pyr)] where M = Mo, Tc, Ru, and Rh, showed strong evidence for aromaticity, with NICS(1)zz values of -15.4, -36.0, -31.6, and -22.4, respectively, that are comparable to benzene (-28.7). NCS analysis of the Tc(V), Ru(V), and Rh(V) complexes shows that aromaticity is favored by an unoccupied d-π orbital that serves as an acceptor to facilitate conjugation in the metallapyrimidine ring. This unoccupied orbital is not sufficient as the d(0) series of complexes demonstrated, and we propose that the occupied d-δ orbital prevents bond localization and enables aromaticity in these metallacycles.

Treatment of MCl2 (M = Cr, Mn, Fe, Co, Ni) with 2 equiv of lithium metal and 1,4-di-tert-butyl-1,3-diazadiene (tBu2DAD) in tetrahydrofuran at ambient temperature afforded Cr(tBu2DAD)2 (38%), Mn(tBu...

The atomic layer deposition (ALD) of strontium borate films is carried out using bis(tris(pyrazolyl)borate)strontium (SrTp2) and water as precursors. Self-limiting ALD growth is established at 350 °C with SrTp2 and water pulse lengths of ≥ 2.0 s and ≥ 0.3 s, respectively. An ALD window is observed from 300 to 375 °C, in which the growth rate is 0.47 A per cycle. The thin film compositions are assessed by elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS). ERDA suggests compositions of SrB2O4 at growth temperatures of

Treatment of Cb ∗ Co(CO) 2 I (Cb ∗ = η 4 -C 4 Me 4 ) with one equivalent of potassium 3,5-dimethylpyrazolate (Me 2 pzK) or potassium 3,5-bis(trifluoromethyl)pyrazolate ((CF 3 ) 2 pzK) in tetrahydrofuran at 0 °C afforded (η 4 -C 4 Me 4 (Me 2 pz))Co(CO) 2 and Cb ∗ Co((CF 3 ) 2 pz)(CO) 2 in 90 and 71% yields, respectively. Treatment of Cb ∗ Co(CO) 2 I with one equivalent of Me 2 pzH followed by the addition of one equivalent Me 2 pzK in tetrahydrofuran afforded Cb ∗ Co(Me 2 pzH)(Me 2 pz)(CO) in 74% yield. The reaction of Cb ∗ Co(CO) 2 I with one equivalent of potassium phenyl tetrazolate (PhtetzK) in tetrahydrofuran at 0 °C afforded [Cb ∗ Co(Phtetz)(CO)] 2 in 44% yield. The solid state structure of (η 4 -C 4 Me 4 (Me 2 pz))Co(CO) 2 revealed nucleophilic addition of a pyrazolate nitrogen atom to a Cb ∗ ligand carbon atom to afford a novel tetradentate ligand that bonds to the cobalt ion through an η 3 -π-allyl interaction and one pyrazolyl nitrogen atom. Two carbonyl ligands are also present. An X-ray crystal structure determination of Cb ∗ Co((CF 3 ) 2 pz)(CO) 2 showed η 1 -coordination of the (CF 3 ) 2 pz ligand and η 4 -coordination of the Cb ∗ ligand. The solid state structure of Cb ∗ Co(Me 2 pz)(Me 2 pzH)(CO) is monomeric with one η 1 -Me 2 pz, one η 1 -Me 2 pzH, two carbonyl, and one η 4 -Cb ∗ ligands. The η 1 -Me 2 pz and η 1 -Me 2 pzH ligands are linked by a hydrogen bond involving the uncoordinated nitrogen atoms. The X-ray crystal structure determination of [Cb ∗ Co(Phtetz)(CO)] 2 showed a dimeric molecular structure with two μ:η 1 ,η 1 -Phtetz ligands connected to the cobalt ions through the 2- and 3-nitrogen atoms, one η 4 -Cb ∗ ligand, and one carbonyl ligand per cobalt center. (η 4 -C 4 Me 4 (Me 2 pz))Co(CO) 2 is highly volatile and sublimes at 60 °C/0.03 Torr.

Treatment of a solid mixture of KBH4 with six equivalents of 3,5-diisopropylpyrazole (iPr2pzH) at 180 °C afforded KTpiPr2(iPr2PzH)3 in 53% yield. KBpiPr2 was synthesized in 56% yield by treatment of a 1:2 M ratio of KBH4 and iPr2PzH in refluxing dimethylacetamide. Treatment of MI2 (M = Ca, Sr, Ba) with two equivalents of KBp or KBpiPr2 in tetrahydrofuran afforded MBp2(THF)2 (M = Ca, 64%, M = Sr, 81%), BaBp2(THF)4 (32%), and M(BpiPr2)2(THF)2 (M = Ca, 63%; M = Sr, 61%, M = Ba, 48%) as colorless crystalline solids upon workup. These complexes were characterized by spectral and analytical techniques and by X-ray crystal structure determinations of all complexes except KBpiPr2. KTpiPr2(iPr2PzH)3 contains one κ3-N,N,N-TpiPr2 ligand and three κ1-iPr2pzH ligands, with overall distorted octahedral geometry about the K ion. The iPr2PzH nitrogen–hydrogen bonds are engaged in intramolecular hydrogen bonding to the 2-nitrogen atoms of the TpiPr2 ligand. The solid state structures of MBp2(THF)2, BaBp2(THF)4, and M(BpiPr2)2(THF)2 contain κ3-N,N,H Bp and BpiPr2 ligands, which form through metal–nitrogen bond formation to the 2-nitrogen atoms of the pyrazolyl fragments and metal–hydrogen bond formation to one boron-bound hydrogen atom per Bp ligand. SrBp2(THF)2has the shortest metal–hydrogen interactions among the series. A combination of preparative sublimations, solid state decomposition temperatures, and thermogravimetric analysis demonstrated that MBp2(THF)2, BaBp2(THF)4, and M(BpiPr2)2(THF)2 undergo solid state decomposition at moderate temperatures.

Our laboratory is developing new chemical precursors for the growth of electropositive metal and element thin films by atomic layer deposition (ALD). We are also interested in processes that exhibit area selective growth. ALD has many current applications in copper metallization, diffusion barriers, liners, and transistor fabrication. Thermal ALD is often preferred because plasmas can afford low conformal coverage due to radical recombination on the walls of deep and narrow features. There has been extensive progress in the thermal ALD of copper and noble metal films in recent years, because the positive electrochemical potentials allow relatively easy reduction of precursor ions to the metals. Thermal ALD approaches to most other metals and elements in the periodic table are not well developed, due to the negative electrochemical potentials of the ions and a current lack of ALD co-reagents that can convert the ions to the metals or elements. Herein, we will describe the thermal ALD growth of electropositive metals such as nickel, cobalt, aluminium, and others. The ALD of nickel and cobalt metal films has been achieved using precursors containing diazadienyl ligands (precursors 1 and 2). These precursors enable the deposition of cobalt and nickel metal films at temperatures below 200 °C and use alkylamines as benign co-reagents. Growth rates are high (0.60 Å/cycle for nickel, 0.98 Å/cycle for cobalt), high purity, low resistivity metal films are obtained, and the films have low rms roughnesses. The processes exhibit inherent selective growth on metal substrates such as platinum, ruthenium, and copper. By contrast, no growth is observed on insulating substrates. We will also overview a new thermal ALD process for the growth of aluminum metal films. This process entails treatment of surface-bound AlCl3 with a thermally stable, volatile aluminium hydride co-reagent. The growth rate for the aluminium metal ALD process is high, and high purity, low resistivity aluminium metal films are obtained. Prospects for the area selective growth of aluminum metal films will be presented. These examples demonstrate that ALD processes can be enabled for electropositive metals through careful design of precursors and chemistry. Moreover, many of the metal ALD processes exhibit area selective growth. Figure 1

The atomic layer deposition (ALD) growth of Ta2O5 films was demonstrated using Ta(NtBu)-(iPrNC(Me)NiPr)2(NMe2) and water with substrate temperatures between 225 and 400 °C. At 325 °C, self-limited ...

Treatment of MI2 (M = Ca, Sr, Ba) with two equivalents of thallium bis(3,5-di-tert-butylpyrazolyl)borate (TlBptBu2) in tetrahydrofuran at ambient temperature afforded CaBptBu22 (67%), SrBptBu22 (79...

The atomic layer deposition (ALD) of tungsten carbide films is described with a thermal process employing WCl6 and AlMe3 as precursors. WCl6 has not been previously reported as an ALD precursor. Furthermore, WCl6 has favorable precursor characteristics and advantages over the widely used WF6, which is corrosive and toxic. The process displays an ALD window between 275 and 350 °C and a high growth rate of 1.5–1.8 A/cycle within the ALD window. High purity tungsten carbide films with low Al and Cl contaminants were deposited at 300 °C. Film resistivities decreased with increasing growth temperature, reaching a minimum value of 1500 μΩ cm at 375 °C. The as-deposited films are amorphous, which could indicate superior performance as a Cu diffusion barrier over previously studied polycrystalline tungsten carbide barrier layers.

Treatment of M(allyl)(Cl)(CO)2(py)2 (M = Mo, W) with 1 equiv. of potassium pyrazolates in tetrahydrofuran at −78 °C afforded M(allyl)(R2pz)(CO)2(py)n (R2pz = 3,5-disubstituted pyrazolate; n = 1, 2) in 68–81% yields. X-ray crystal structure analyses of Mo(allyl)((CF3)2pz)(CO)2(py)2 and W(allyl)(tBu2pz)(CO)2(py) revealed η1- and η2-coordination of the (CF3)2pz and tBu2pz ligands, respectively. Analogous treatment of Mo(allyl)(Cl)(CO)2(NCCH3)2 with 1 equiv. of tBu2pzK in tetrahydrofuran at −78 °C afforded [Mo(allyl)(tBu2pz)(CO)2]2 in 79% yield. An X-ray crystal structure analysis of [Mo(allyl)(tBu2pz)(CO)2]2 showed a dimeric structure bridged by two μ-η2:η1-tBu2pz ligands. Treatment of M(allyl)(Cl)(CO)2(py)2 with 1 equiv. of lithium 1,3-diisopropylacetamidinate or lithium 1,3-di-tert-butylacetamidinate in diethyl ether at −78 °C afforded M(allyl)(iPrNC(Me)NiPr)(CO)2(py) and M(allyl)(tBuNC(Me)NtBu)(CO)2(py), respectively, in 68–78% yields. The new complexes were characterized by spectral and analytical methods and by X-ray crystal structure determinations. M(allyl)(iPrNC(Me)NiPr)(CO)2(py) adopt pseudo-octahedral geometry about the metal centers, with the 1,3-diisopropylacetamidate ligand nitrogen atoms spanning one axial site and one equatorial site of the octahedron. By contrast, M(allyl)(tBuNC(Me)NtBu)(CO)2(py) adopt pseudo-octahedral structures in which the two 1,3-di-tert-butylacetamidinate ligand nitrogen atoms span two equatorial coordination sites. Sublimation of M(allyl)(tBuNC(Me)NtBu)-(CO)2(py) at 105 °C/0.03 Torr afforded ⩽7% yields of M(allyl)(tBuNC(Me)NtBu)(CO)2, along with sublimed M(allyl)(tBuNC(Me)NtBu)(CO)2(py). W(allyl)(tBuNC(Me)NtBu)(CO)2 exists in the solid state as a 16-electron complex with distorted square pyramidal geometry. Many of the new complexes undergo dynamic ligand site exchange in solution, and these processes were probed by variable temperature 1H NMR spectroscopy. The volatilities and thermal stabilities were evaluated to determine the potential of the new complexes for use as precursors in thin film growth experiments.

Treatment of MI(2) (M = Ca, Sr) or BaI(2)(THF)(3) with 2 equiv of potassium tris(3,5-diethylpyrazolyl)borate (KTp(Et2)) or potassium tris(3,5-di-n-propylpyrazolyl)borate (KTp(nPr2)) in hexane at ambient temperature afforded CaTp(Et2)(2) (64%), SrTp(Et2)(2) (64%), BaTp(Et2)(2) (67%), CaTp(nPr2)(2) (51%), SrTp(nPr2)(2) (75%), and BaTp(nPr2)(2) (39%). Crystal structure determinations of CaTp(Et2)(2), SrTp(Et2)(2), and BaTp(Et2)(2) revealed monomeric structures. X-ray structural determinations for strontium tris(pyrazolyl)borate (SrTp(2)) and barium tris(pyrazolyl)borate ([BaTp(2)](2)) show that SrTp(2) exists as a monomer and [BaTp(2)](2) exists as a dimer containing two bridging Tp ligands. The thermogravimetric analysis traces, preparative sublimations, and melting point/decomposition determinations demonstrate generally very high thermal stabilities and reasonable volatilities. SrTp(2) has the highest volatility with a sublimation temperature of 200 degrees C/0.05 Torr. [BaTp(2)](2) is the least thermally stable with a decomposition temperature of 330 degrees C and a percent residue of 46.5% at 450 degrees C in the thermogravimetric analysis trace. SrTp(Et2)(2), BaTp(Et2)(2), CaTp(nPr2)(2), SrTp(nPr2)(2), and BaTp(nPr2)(2) vaporize as liquids between 210 and 240 degrees C at 0.05 Torr. BaTp(Et2)(2) and BaTp(nPr2)(2) decompose at about 375 degrees C, whereas MTp(Et2)(2) and MTp(nPr2)(2) (M = Ca, Sr) are stable to400 degrees C. Several of these new complexes represent promising precursors for chemical vapor deposition and atomic layer deposition film growth techniques.

Treatment of M(N(SiMe3)2)2(THF)2 with 2 equiv of 4-(2,2-dimethylhydrazino)dimethylhydrazone-3-penten-2-one (LNMe2H) in toluene at ambient temperature afforded Ca(η2-LNMe2)2 (88%), [Sr(η5-LNMe2)(μ-η1:η5-LNMe2)]2 (85%), and [Ba(η5-LNMe2)(μ-η2:η3-LNMe2)]2 (83%) as colorless or pale yellow crystalline solids. The formulations of the new complexes were assigned from spectral and analytical data and by X-ray crystal structure determinations. In the solid state, Ca(η2-LNMe2)2 exists as a tetrahedral monomer. [Sr(η5-LNMe2)(μ-η1:η5-LNMe2)]2 is a dimer that contains a terminal η5-LNMe2 ligand on each strontium ion. The dimer is held together by two μ-η1:η5-LNMe2 ligands, in which one dimethylamino moiety per LNMe2 ligand acts as a donor ligand to the adjacent strontium ion. [Ba(η5-LNMe2)(μ-η2:η3-LNMe2)]2 crystallizes as a dimer that contains a terminal η5-LNMe2 ligand on each barium ion. The two bridging LNMe2 ligands adopt a μ-η2:η3-coordination mode, where each LNMe2 ligand is bonded to one barium ion through the...

Treatment of dibutylmagnesium with two equivalents of 4-(2,2-dimethylhydrazino)dimethylhydrazone-3-penten-2-one (L1H) in diethyl ether afforded Mg(L1)2 (76%), which contains η2-L1 ligands with tetrahedral coordination at the magnesium ion. Similar treatment of dibutylmagnesium with 4-(2,2-dimethylhydrazino)-3-penten-2-one (L2H) or 5-(2,2-dimethylhydrazino)-2,6-dimethyl-4-hepten-3-one (L3H) and 4-tert-butylpyridine (4-tBupy) in diethyl ether afforded the octahedral complexes Mg(L2)2(4-tBupy)2 (85%) and Mg(L3)2(4-tBupy)2 (79%). Treatment of dibutylmagnesium with two equivalents of L2H or L3H in the absence of 4-tBupy afforded [Mg(L2)2]2 and Mg(L3)2, however, these complexes were difficult to isolate due to the sticky nature of the crude products. A better synthetic approach entailed sublimation of Mg(L2)2(4-tBupy)2 or Mg(L3)2(4-tBupy)2 at 95–100 °C/0.05 Torr, which afforded [Mg(L2)2]2 (94%) and Mg(L3)2 (80%) as colorless crystalline solids that were easily isolated. Treatment of [MgCp(CH3)(OEt2)]2 with two equivalents each of 4-tBupy and L1H afforded MgCp(L1)(4-tBupy) (65%). Similar treatment of [MgCp(CH3)(OEt2)]2 with two equivalents of L2H or L3H afforded the dimeric complexes [MgCp(L2)]2 (81%) and [MgCp(L3)]2 (84%), respectively. [MgCp(L2)]2 and [MgCp(L3)]2 decompose upon attempted sublimation at 125–130 °C/0.05 Torr to afford Cp2Mg (47–53%) and [Mg(L2)2]2 (67%) or Mg(L3)2 (74%). The X-ray crystal structures of Mg(L1)2, Mg(L3)2(4-tBupy)2, [Mg(L2)2]2, Mg(L3)2, MgCp(L1)(4-tBupy), [MgCp(L2)]2, and [MgCp(L3)]2 are described. The thermal stability and volatility of the complexes were determined through preparative sublimation experiments. Many of the complexes sublime without decomposition at moderate temperatures and low pressures, and thus represent new potential precursors for thin film growth using chemical vapor deposition and related techniques.

A series of sodium, potassium, rubidium, and cesium complexes of methyl tetrazolate was prepared and structurally characterized. Treatment of methyl tetrazole (MetetzH) with the group 1 hydroxides in water at ambient temperature afforded Na(Metetz)(H2O)2 (92%), K(Metetz) (92%), Rb(Metetz) (97%), and Cs(Metetz) (97%) as colorless solids after workup. These complexes were characterized by spectral and analytical methods, thermogravimetric analysis, and by X-ray crystallography. Na(Metetz)(H2O)2 adopts a structure that consists of approximately octahedrally coordinated sodium ions that form infinite chains built up by two μ2-aqua ligands and two μ2-N1,N2-tetrazolate ligands between each sodium atom. The aqua ligand hydrogen atoms engage in hydrogen bonding with uncoordinated nitrogen atoms to hold the chains together. K(Metetz) and Rb(Metetz) are isostructural, with eight-coordinate metal ions and two metal–nitrogen bonds per nitrogen atom in each Metetz ligand. Cs(Metetz) has 10-coordinate cesium ions with two cesium–nitrogen bonds to two of the Metetz ligand nitrogen atoms and three cesium–nitrogen bonds to the other two nitrogen atoms. K(Metetz), Rb(Metetz), and Cs(Metetz) exhibit new coordination modes for the tetrazolate ligand.