Synthesizing Amorphous Precursors through Control of Local Composition

Synthesizing compounds predicted to have exceptional properties that are close to or below the ground-state convex hull has proven to be very challenging because avoiding the formation of more thermodynamically or kinetically stable mixtures of known compounds is often required. A homogeneous amorphous phase has been suggested as a very general reaction intermediate. However, the preparation of amorphous phases with controlled composition is also very challenging. We postulated that amorphous intermediates with controlled composition can be made by avoiding the formation of regions with compositions close to those of the known compounds. Specifically, we demonstrated that we could avoid the formation of PbSe and MoSe2 by sequentially depositing nonstoichiometric ultrathin submonolayer thickness layers on a nominally room-temperature substrate. The substrate temperature needs to be low enough to minimize surface diffusion, preventing the agglomeration of elements and resultant concentration gradients. The amount of diffusion required to form nucleation embryos can be controlled by changing the difference between the composition of the film and the stoichiometry of the compound in question. Large enough differences should result in amorphous intermediates in most systems. The presence of more than two elements will further suppress the nucleation of binary compounds, making this approach particularly useful to prepare amorphous precursors for the synthesis of metastable ternary and quaternary compounds

Insights into the Charge-Transfer Stabilization of Heterostructure Components with Unstable Bulk Analogs

Solid state chemists have yet to find a targeted approach based on simple rules to predict new materials with desired physical properties. Recent advances in computational high-throughput methods have led to the creation of large databases with predicted new compounds. While many of these compounds are unstable, some may be stabilized inside heterostructures. BiSe is an example for such a compound where the rock-salt structure is unstable in bulk but can be found in misfit layer compounds and ferecrystals. In some of these heterostructures, BiSe also exhibits antiphase boundaries (APBs), periodic Bi–Bi pairings that interrupt the alternating pattern of the rock-salt structure. Understanding the behavior of BiSe may aid in the discovery of new heterostructure components where no stable bulk analog exists. We used density functional theory (DFT) and crystal orbital Hamilton populations (COHPs) to explain the different stabilities of rock-salt structured BiSe. COHPs show that rock-salt structured BiSe has occupied antibonding states at the Fermi level, which destabilize the structure. In heterostructures, these states can be depopulated by donating electrons into an adjacent layer or by forming APBs to localize electrons into a Bi–Bi bond. The results suggest that the depopulation of antibonding states is crucial to stabilizing rock-salt structured BiSe, and that BiSe needs to be paired with a suitable electron acceptor. We predict that this is a general principle that can be applied to other compounds with unstable polytypes and suggest that COHPs should play a larger role in the discovery of new heterostructure components

Structure, Stability, and Properties of the Intergrowth Compounds ([SnSe]_1+δ)_<i>m</i>(NbSe₂)_<i>n</i>, where <i>m</i> = <i>n</i> = 1–20

Intergrowth compounds of ([SnSe]_1+δ)_<i>m</i>(NbSe₂)_<i>n</i>, where 1 ≤ <i>m = n ≤ </i>20, with the same atomic composition but different <i>c</i>-axis lattice parameters and number of interfaces per volume were synthesized using the modulated elemental reactant technique. A <i>c</i>-axis lattice parameter change of 1.217(6) nm as a function of one unit of <i>m</i> = <i>n</i> was observed. In-plane X-ray diffraction shows an increase in distortion of the rock salt layer as a function of <i>m</i> and a broadening of the NbSe₂ reflections as <i>n</i> increases, indicating the presence of different coordination environments for Nb (trigonal prismatic and octahedral) and smaller crystallite size, which were confirmed via scanning transmission electron microscopy investigations. The electrical resistivities of all 12 compounds exhibit metallic temperature dependence and are similar in magnitude as would be expected for isocompositional compounds. Carrier concentration and mobility of the compounds vary within a narrow range of 2–6 × 10²¹ cm^–3 and 2–6 cm² V^–1 s^–1, respectively. Even at a thickness of 12 nm for the SnSe and NbSe₂ blocks, the properties of the intergrowth compounds cannot be explained as composite behavior, due to significant charge transfer between them. Upon being annealed at 500 °C, the higher order <i>m</i> = <i>n</i> compounds were found to convert to the thermodynamically stable phase, the (1,1) compound. This suggests that the capacitive energy of the interfaces stabilizes these intergrowth compounds

Preparation, Formation, and Structure of [(SnSe)_1.04]_<i>m</i>(MoSe₂)_<i>n</i> Intergrowth Compounds (0 < <i>m</i> and <i>n</i> < 32) from Designed Precursors

A detailed synthetic approach, using the method of modulated elemental reactants, is described for the preparation of MX–TX₂ (M = metal, X = chalcogen, and T = transition metal) solid-state intergrowths with <i>m</i> and <i>n</i> values significantly larger than previously reported. As a specific example, we demonstrate the ability to synthesize more than 500 distinct intergrowth compounds in a single ternary system, Sn–Mo–Se. A simple method for determination of the chemical composition of the constituent layers in the precursor and product is described for cases in which both structural components contain one or more common elements. X-ray reflectivity, laboratory and synchrotron X-ray diffraction, scanning transmission electron microscopy, and high-resolution transmission electron microscopy imaging, and electron microprobe analysis provide conclusive evidence of the formation of layered intergrowths with well-defined structure and composition. The ability to access a large range of monochalcogenide thicknesses allows a size-dependent structural transition in the SnSe component to be controlled and tracked and indicates that intergrowth materials such as those described here comprise novel material systems in which size-dependent phenomena can be precisely controlled

Effect of Local Structure of NbSe₂ on the Transport Properties of ([SnSe]_1.16)₁(NbSe₂)_<i>n</i> Ferecrystals

([SnSe]_1.16)₁(NbSe₂)_<i>n</i> ferecrystals were synthesized through the modulated elemental reactants technique by increasing the number of Nb|Se layers in the precursor from 1 to 4. The <i>c</i>-lattice parameter of the intergrowth was observed to change as a function of <i>n</i> by 0.635(2) nm. The <i>c</i>-lattice parameter of SnSe was observed to be 0.588(8) nm and independent of <i>n</i>. The electrical resistivity does not decrease as <i>n</i> increases as expected from simple models, but instead the trend in the resistivity is (1,3) > (1,4) ≥ (1,1) > (1,2). The carrier concentration increases with <i>n</i> as expected, so the unusual trend in resistivity is a result of the carrier mobility decreasing with increasing <i>n.</i> In-plane X-ray diffraction line widths and STEM images of the (1,4) compound show that it has small in-plane grain sizes and a large diversity of stacking sequences respectively, providing a potential explanation for the reduced carrier mobility

The Influence of Interfaces on Properties of Thin-Film Inorganic Structural Isomers Containing SnSe–NbSe₂ Subunits

Inorganic isomers ([SnSe]_1+δ)_<i>m</i>(NbSe₂)_<i>n</i>([SnSe]_1+δ)_<i>p</i>(NbSe₂)_<i>q</i>([SnSe]_1+δ)_<i>r</i>(NbSe₂)_<i>s</i> where <i>m</i>, <i>n</i>, <i>p</i>, <i>q</i>, <i>r</i>, and <i>s</i> are integers and <i>m</i> + <i>p</i> + <i>r</i> = <i>n</i> + <i>q</i> + <i>s</i> = 4 were prepared using the modulated elemental reactant technique. This series of all six possible isomers provides an opportunity to study the influence of interface density on properties while maintaining the same unit cell size and composition. As expected, all six compounds were observed to have the same atomic compositions and an almost constant <i>c</i>-axis lattice parameter of ≈4.90(5) nm, with a slight trend in the <i>c</i>-axis lattice parameter correlated with the different number of interfaces in the isomers: two, four and six. The structures of the constituents in the <i>ab</i>-plane were independent of one another, confirming the nonepitaxial relationship between them. The temperature dependent electrical resistivities revealed metallic behavior for all the six compounds. Surprisingly, the electrical resistivity at room temperature decreases with increasing number of interfaces. Hall measurements suggest this results from changes in carrier concentration, which increases with increasing thickness of the thickest SnSe block in the isomer. Carrier mobility scales with the thickness of the thickest NbSe₂ block due to increased interfacial scattering as the NbSe₂ blocks become thinner. The observed behavior suggests that the two constituents serve different purposes with respect to electrical transport. SnSe acts as a charge donor and NbSe₂ acts as the charge transport layer. This separation of function suggests that such heterostructures can be designed to optimize performance through choice of constituent, layer thickness, and layer sequence. A simplistic model, which predicts the properties of the complex isomers from a weighted sum of the properties of building blocks, was developed. A theoretical model is needed to predict the optimal compound for specific properties among the many potential compounds that can be prepared

Different detergents and dilution of cell extracts does not destabilize gB-gH/gL complexes.

<p>(A) ARPE-19 cells were transduced with Ad vectors expressing gB, gB and gH/gL, or gH/gL and GFP for 20 hrs then radiolabeled for 4 hrs. Cell extract were made using IP buffer containing 1% NP-40. Some of each extract was then diluted with 4 times the volume of the same buffer (4X). Proteins were precipitated from cell extracts using either anti-gB MAb 27–156 or anti-gH MAb 14-4b then proteins analyzed by SDS-PAGE under reducing conditions. (B) ARPE-19 cells were transduced as described for panel A and extracts were prepared with IP buffer containing 1% digitonin. IP’s were performed with either anti-gB MAb 27–156 or anti-gH MAb 14-4b with undiluted samples (1X) or after samples were diluted with 4 times the volume (4X) of IP buffer containing 1% digitonin. (C) IPs were performed as described for panel B except cell lysates were prepared and diluted with IP buffer containing 1% octyl glucoside. The antibodies used for the IPs and the Ad vectors used to transduce cells are indicated above each panel. The detergents used in the IPs and whether samples were used neat or diluted is indicated below each panel. The positions of gB and gH/gL are indicated on the left side of the panels and molecular mass markers (MW) are indicated on the right.</p

HCMV gB-gH/gL complexes detected by IP-western blots.

<p>ARPE-19 or MRC-5 cells were transduced with Ad vectors expressing HCMV gB, gH/gL, both gB and gH/gL, or with Ad-tet-trans (tet, as a negative control) as indicated at the top part of each panel. After 20 hrs the cells were lysed in IP buffer containing 1% NP-40. (A) Proteins were IP’d from ARPE-19 or MRC-5 cell extracts with anti-gH MAb 14-4b, separated by SDS-PAGE under reducing conditions, transferred to membranes, and then analyzed by western blot using rabbit polyclonal sera specific to gB or anti-gH MAb AP86. (B) Proteins from ARPE-19 cell lysates were IP’d with anti-gB MAbs 9C1, 13H10, or 15H7 and the IPs analyzed by western blot as described above using anti-gH AP86. Input represents 5% of the extract loaded directly onto gels then blotted. (C) ARPE-19 cells were transfected with an Ad vector expressing gB with a C-terminal FLAG epitope tag or wild type gB and co-transduced with Ad vectors to express gH/gL as indicated along the top of the panel. Proteins were IP’d with an anti-FLAG antibody and analyzed by western blot as described above with rabbit polyclonal gB-specific serum or anti-gH MAb AP-86 to detect gB and gH, respectively. The percent of gB and gH/gL that was co-IP in these experiments was quantified using NIH ImageJ software by comparing the relative band intensities from the IP’d proteins to the 5% input and are indicated under the lanes. Molecular mass (MW) markers are indicated on the left.</p

HSV-1 glycoproteins do not interact with HCMV glycoproteins.

<p>(A) ARPE-19 cells were transduced with Ad vectors expressing Ad-tet-trans alone (tet, as a negative control), HSV-1 gH/gL, or HSV-1 gH/gL along with HCMV gB (as indicated along the top of the panel). HCMV gB was IP’d from cell lysates with MAb 15H7 then blots probed with HCMV gB polyclonal serum (upper panel) or anti-HSV-1 gH polyclonal serum R137 (lower panel). (B) ARPE-19 cells were transduced with Ad vectors expressing HSV-1 gD alone or with HSV-1 gD and HCMV gH/gL or with Ad-tet-trans (tet, a negative control) then lysates IP’d with HCMV gH/gL-specific MAb 14-4b. Proteins were analyzed by SDS-PAGE under reducing conditions and western blots were probed with rabbit anti-HSV-1 gD polyclonal serum (R45) or anti-HCMV gH MAb AP86. (C) ARPE-19 cells were transduced with Ad vectors expressing HSV-1 gB, gH/gL, gD, and nectin-1. After 24 hrs proteins were IP’d from cell lysates with anti-HSV-1 gB MAb SS10, anti-HSV-1 gH MAb 53S, or irrelevant control MAb (15H7). The IP’d proteins were separated by SDS-PAGE under reducing conditions, transferred to membranes, and blotted with polyclonal rabbit serum R137 or R67 against HSV-1 gH/gL and gB, respectively. (D) Proteins were IP’d from ARPE-19 lysates with anti-HSV-1 gB MAb SS10, anti-HSV-1 gH MAb 53S, anti-HSV-1 gD MAb DL6, or irrelevant control MAb (15H7). The proteins were separated by SDS-PAGE under reducing conditions, transferred to membranes and blotted with rabbit anti-HSV-1 gD polyclonal serum (R45). The arrow with asterisk indicates cross reactivity of R45 with IgG heavy chain. (E) Proteins were IP’d from cell lysates, separated by SDS-PAGE and transferred to membranes as described above and then probed with rabbit polyclonal serum R45, R137, or R67 against HSV-1 gD, gH/gL, and gB, respectively. Input represents 5% of the total amount of lysate used for the IPs. Molecular mass (MW) markers are indicated on the left.</p

HCMV gH/gL/gO and gH/gL/UL128-131 do not significantly complex with gB in virions.

<p>HCMV BADrUL131 extracellular virus particles were partially purified from cell supernatants harvested10 days post -infection then solubilized in 1% NP-40 and insoluble proteins removed by centrifugation. (A) Proteins from virion extracts were IP’d using rabbit polyclonal anti-peptide antibodies specific for UL130 or a gM-specific MAb as a negative control and the IP’d proteins separated by SDS-PAGE and analyzed by western blot with gH-specific MAb AP86 or gB-specific MAb 15H7. (B) Proteins were IP’d from detergent extracts of HCMV virions with rabbit polyclonal antibodies specific for UL130, rabbit polyclonal anti-peptide serum specific for gO (TBgO) [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005564#ppat.1005564.ref023" target="_blank">23</a>] or with a gM-specific MAb and the IP’s analyzed by western blot as described above with the gH-specific MAb AP86. (C) Detergent extracts of extracellular HCMV virus particles were solubilized then extracts IP’d with anti-gM MAb or anti-gB MAb 15H7 (as indicated along the top of the panel). The precipitated proteins were analyzed by western blot with anti-gH MAb AP86, rabbit anti-gO (TBgO) sera, rabbit anti-UL130 sera, or a gM-specific MAb (as indicated along the right side of the panel). (D) IP-western blot analyses of solubilized BADrUL131 extracellular virions as described for panel C, except that the membrane blotted for gH from the gB IP was exposed along side a linear range of input samples derived from a gH/gL expressing cell lysate. (E) Linear curve of the gH signal generated after exposure of the membrane containing the increasing doses of the gH-gL expressing lysate. The y-axis indicates the relative density of the protein bands and the x-axis indicates the amount of lysate loaded into each well. (F) Shown is the exposure of the western blot containing the increasing amounts of the gH-gL expressing lysate. The amount to gH/gL expressing lysate loaded into each well is indicated below the panel. (G) Western blot analyses as described for panel D except IP’s were performed with solubilized extracellular virions derived from the clinical strain TR. (H) Linear curve of the gH signal containing the increasing doses of the gH-gL expressing lysate as described for panel E. (I) Shown is the exposure of the western blot containing the increasing amounts of the gH-gL expressing lysate. The amount to gH/gL expressing lysate loaded into each well is indicated below the panel. To assess the relative quantity of IP’d proteins, we compared the signal intensities of the IP’d proteins to the input protein signal intensities. Analysis was performed using ImageJ software (panel C) or Image Studio software (Licor) for panels 7D-7I. For all blots, input refers to 5% of the virion lysate loaded directly into gels. The percent of the total protein IP’d compared with the total in the virion extract is shown under each lane. Molecular mass (MW) markers are indicated on the left. All samples were analyzed by SDS-PAGE under reducing conditions with the exception of samples involving the detection of gO, which required that that SDS-PAGE be performed under non-reducing conditions, thus the signal for gO represents the gH/gL/gO disulfide linked >250 kDa trimer. ND indicates not detected.</p