Synthesis and characterization of hybrid nanostructures

Abstract

There has been significant interest in the development of multicomponent nanocrystals formed by the assembly of two or more different materials with control over size, shape, composition, and spatial orientation. In particular, the selective growth of metals on the tips of semiconductor nanorods and wires can act to couple the electrical and optical properties of semiconductors with the unique properties of various metals. Here, we outline our progress on the solution-phase synthesis of metal-semiconductor heterojunctions formed by the growth of Au, Pt, or other binary catalytic metal systems on metal (Cd, Pb, Cu)-chalcogenide nanostructures. We show the ability to grow the metal on various shapes (spherical, rods, hexagonal prisms, and wires). Furthermore, manipulating the composition of the metal nanoparticles is also shown, where PtNi and PtCo alloys are our main focus. The magnetic and electrical properties of the developed hybrid nanostructures are shown.

Keywords: Electrical and magnetic properties; Hybrid Nanocrystals; MOCVD; Nanowires; synthesis.

Fig. 1

Au overgrowth on semiconductor nanomaterials. (A) CdSe-Au nanorods, (B) CdS-Au nanorods, (C) CdTe-Au nanorods, (D) Cu₂S-Au hexagonal nanoprisms, (E) PbSe-Au nanocrystals, (F) GaN-Au nanowires.

Fig. 2

Growth of different metals and binary metals on CdSe nanowires. (A) CdSe-Au nanowires, (B) CdSe-Pt nanowires, (C) CdSe-PtNi nanowires, (D) CdSe-PtCo nanowires.

Fig. 3

Characterization of metal and binary metal overgrowth on CdSe nanowires. (A) XRD data, (B) EDS data, (C) SQUID magnetometry results for CdSe-PtCo showing temperature-dependent magnetization measurements (magnified in upper inset). Lower inset shows traces of magnetization as a function of temperature in zero-field cooled (triangles) and field-cooled (squares) modes.

Fig. 4

Growth of different metals and binary metals on CdSe nanowires. (A) CdSe-Au nanowires, (B) CdSe-Pt nanowires, (C) CdSe-PtNi nanowires, (D) CdSe-PtCo nanowires.

Fig. 5

TEM image of CdSe nanocrystal before (A) and after (b) Au tip growth. SEM image (c) and schematic (e) of a single nanocrystal two-terminal device. After a silicon wafer test chip was submersed in a toluene-nanocrystal solution, the evaporating solvent orients individual nanocrystals across predefined Au electrodes fabricated via e-beam lithography. (d) Solution phase optical spectra indicate onset of first exciton absorption at 2 eV for both CdSe (red) and Au-tipped CdSe heterostructure (green) samples.

Fig. 6

(A) Histogram of room temperature device resistance near 0 V applied bias. (B) Representative two-probe I-V trace of a CdSe device (red) and an Au-tipped CdSe device (green) at room temperature. Note the color-coded axes correspond to picoampere (red) and microampere (green) scales. (C) Simplified energy-band diagram of proposed barrier structure across a device under bias. The dashed blue line shows the barrier lowering due to the image potential - not drawn to scale.