Emergent Interface in Heterostructured Thin Films of Cu(II) and Cu(I) Coordination Polymers

Abstract

In this work we report fabrication of high-quality AB- and BA-type heterostructured thin films of cubic Cu­(II) (A-type) and tetragonal Cu­(I) (B-type) coordination polymers (CPs) on the functionalized Au substrate by the layer-by-layer method. Successful growth of Cu­(I)-CP on top of Cu­(II)-CP was assigned to be due to the interfacial reduction reaction (IRR). Notably, electrical transport measurements across AB- and BA-type heterostructured thin films revealed rectification of current in opposite directions. We have attributed such an interestingly new observation to the formation of a well-defined interface of Cu­(II)-CP and Cu­(I)-CP resembling a p–n junctiona hitherto unreported phenomenon that is anticipated to open enormous opportunities for the heterostructured thin films of CPs, likewise celebrated interfaces of oxide heterostructures.

Direct Layer-by-Layer Growth of Crystalline Ag-TCNQ Thin Films on Functionalized Au Substrate: How Critical Is the pH of Ag(I) Solution?

“…Briefly, a Au substrate (functionalized with a self-assembled monolayer (SAM) of mercaptoundecanoic acid (MUDA)) was sequentially dipped into AgOAc (silver acetate) and TCNQ solutions in ethanol to grow the Ag-TCNQ thin film at ambient conditions (see the Supporting Information for experimental details). Note that in each LbL growth cycle, multilayers of Ag-TCNQ were deposited, which is consistent with our earlier observations on thin films of CPs, in general. ,− Visual inspection of the bare functionalized Au and the Ag-TCNQ thin film revealed a distinct change in color from golden to dark blue (Figure ).…”

“…The here presented growth of Ag-TCNQ thin films is not as precise as covering the entire surface with one layer of Ag-TCNQ in one cycle of LbL, as in our earlier studies on the LbL growth of Cu-TCNQ thin films under similar conditions. 7,18,19,21 That is why we need to keep the pH of the Ag(I) solution at ≥6.5 and continue LbL cycles until the surface is completely covered with Ag-TCNQ crystallites followed by formation of a thin film in subsequent cycles. Interestingly, upon mixing the TCNQ solution with the AgOAc solution (Figure S9) as well as the TCNQ solution with the AgNO 3 solution (Figure S10), solid Ag-TCNQ was consistently isolated from both the mixtures (Figure S9 and Figure S10).…”

Charge-transfer interface of insulating metal-organic frameworks with metallic conduction

“…In view of poor electrical conductivity of MOFs coupled with fabrication challenges of downsizing these materials into crystalline thin film configurations, investigations on electron transport across hetero-structured thin films of MOFs are rarely explored 23 , except the recent studies on the realization of p-n hetero-junction diodes 24 , 25 . Herein, we present an emergence of metallic conduction at the interface of a Mott and a band insulating MOFs.…”

“…1 ). Fabrication of such Cu(II)-Cu(I) (3 d 9 –3 d 10 ) interface is attributed to the interfacial reduction reaction (IRR) 24 , 27 , 28 whereby solution of Cu(II)(OAc) 2 was consistently introduced as the metal ion precursor during two consecutive LbL growth with the BPyDC and TCNQ ligands.

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Chemistry at the Solid–Gas Interface: Direct Crystalline Thin-Film to Thin-Film Chemical Transformation

“…The Au substrate was thiolate functionalized by dipping the substrate into 1 mM solution of MUDA in ethanol and acetic acid (v/v = 9:1) for approximately 2 days followed by washing with ethanol and drying in a stream of N 2 gas. ,,− …”