Field Effect and Photoconduction in Au₂₅ Nanoclusters Films

Abstract

Quantum‐confined Au nanoclusters exhibit molecule‐like properties, including atomic precision and discrete energy levels. The electrical conductivity of Au nanocluster films can vary by several orders of magnitude and is determined by the strength of the electronic coupling between the individual nanoclusters in the film. Similar to quantum‐confined, semiconducting quantum dots, the electrical coupling in films is dependent on the size and structure of the Au core and the length and conjugation of the organic ligands surrounding it. Unlike quantum dots, however, semiconducting transport has not been reported in Au nanocluster films. Here, it is demonstrated that through a simple yet careful choice of cluster size and organic ligands, stable Au nanocluster films can electronically couple and become semiconducting, exhibiting electric field effect and photoconductivity. The molecule‐like nature of the Au nanoclusters is evidenced by a hopping transport mechanism reminiscent of doped, disordered organic semiconductor films. These results demonstrate the potential of metal nanoclusters as a solution‐processed material for semiconducting devices.

Structural order enhances charge carrier transport in self-assembled Au-nanoclusters

“…Strikingly, a field-effect can be observed, indicating semiconducting behavior of the metal NC assemblies. The tri-butyl-phosphine ligands covering the cluster cores limit the electronic coupling enough to prevent metallic behavior 26 . Figure 4e shows the FET transfer curve of a polycrystalline thin film of Au 32 -NCs on interdigitated electrodes with channel dimensions of L = 2.5 µm, W = 1 cm and h = 30 ± 2 nm.…”

“…3a) is consistent with earlier reports on other Au NCs and the expected degree of quantum confinement. Specifically, for NCs with 11 and 25 Au atoms and, thus, stronger quantum confinement, HOMO-LUMO transitions of 2.97 and 1.84 eV have been reported 26,42 . In line with this, (AuAg) 34 -NCs exhibit a HOMO-LUMO transition of around 1.4 eV 20 .…”

“…Previous studies on Au-NC ensembles have yet either reported conductivity measurements of polycrystalline assemblies 25 , along with the first observation of semiconducting properties 26 , or the formation of highly ordered microcrystals 20 , 24 , 27 , 28 . However, attempts to quantify the influence of perfect order on the electronic properties of such microcrystals have remained unsuccessful 29 .…”

Solvent-mediated assembly of atom-precise gold–silver nanoclusters to semiconducting one-dimensional materials

“…18). As a comparison, recently reported photoconductive two-dimensional (2D) films of phosphine-thiolate-stabilized Au 25 clusters 36 showed ON/OFF ratio of about 50 000 for V SD = 6 V, charge carrier mobility approaching 10 −5 cm 2 V −1 s −1 at V SD = 20 V, and n-type field effect. The mobility of our polymeric crystal of nanoclusters is in the range of traditional p-type single-crystal organic semiconductors 56 and close to the mobility of supercrystal of CdSe Quantum Dots (Supplementary Table 6) 57,58 .…”

“…Early successful realizations included gold nanoparticle assemblies where individual particles were linked by dithiols 10 , DNA 11,12 , or using viral proteins as scaffolds 13,14 . Gold nanoclusters stabilized by thiolates 15 have for a long time served as a prototype, and the first successful structural determinations of their atomic structures led to breakthroughs in understanding the structure of the gold-ligand interface, the interactions in the ligand layer, the organic surface, and the principles that govern their electronic structure and optical response [16][17][18][19][20][21] , This has inspired efforts towards nanoscale and macroscale assemblies of gold [22][23][24][25][26] , silver 27,28 , and copper clusters [29][30][31][32] that might have a variety of applications in the fields of (bio)chemical sensing [33][34][35] , and optoelectronics [29][30][31][32][36][37][38] .…”