Oxide-Free Three-Dimensional Germanium/Silicon Core–Shell Metalattice Made by High-Pressure Confined Chemical Vapor Deposition

Abstract

Metalattices are crystalline arrays of uniform particles in which the period of the crystal is close to some characteristic physical length scale of the material. Here, we explore the synthesis and properties of a germanium metalattice in which the ∼70 nm periodicity of a silica colloidal crystal template is close to the ∼24 nm Bohr exciton radius of the nanocrystalline Ge replica. The problem of Ge surface oxidation can be significant when exploring quantum confinement effects or designing electronically coupled nanostructures because of the high surface area to volume ratio at the nanoscale. To eliminate surface oxidation, we developed a core−shell synthesis in which the Ge metalattice is protected by an oxide-free Si interfacial layer, and we explore its properties by transmission electron microscopy (TEM), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The interstices of a colloidal crystal film grown from 69 nm diameter spherical silica particles were filled with polycrystalline Ge by high-pressure confined chemical vapor deposition (HPcCVD) from GeH 4 . After the SiO 2 template was etched away with aqueous HF, the Ge replica was uniformly coated with an amorphous Si shell by HPcCVD as confirmed by TEM-EDS (energy-dispersive X-ray spectroscopy) and Raman spectroscopy. Formation of the shell prevents oxidation of the Ge core within the detection limit of XPS. The electronic properties of the core−shell structure were studied by accessing the Ge 3d edge onset using STEM-EELS. A blue shift in the edge onset with decreasing size of Ge sites in the metalattices suggests quantum confinement of the Ge core. The degree of quantum confinement of the Ge core depends on the void sizes in the template, which is tunable by using silica particles of varying size. The edge onset also shows a shift to higher energy near the shell in comparison with the Ge core. This shift along with the observation of Ge−Si vibrational modes in the Raman spectrum indicate interdiffusion of Ge and Si. Both the size of the voids in the template and core−shell interdiffusion of Si and Ge can in principle be tuned to modify the electronic properties of the Ge metalattice.

Tunable Hollow Nanoreactors for In Situ Synthesis of GeP Electrodes towards High‐Performance Sodium Ion Batteries

“…As exhibited in Figure 4 g, the Ge/CN‐3 shows a main peak at 291.4 cm −1 , which is consistent well with the Raman spectrum of standard Ge powder (Supporting Information, Figure S7) [2, 24] . In the spectrum of GeP/CN‐3, two peaks corresponding to Ge‐P and Ge‐Ge stretching modes are observed at 361.0 and 200.4 cm −1 , respectively [20, 25] . The other three peaks located at 135.7, 246.3 and 308.1 cm −1 can be assigned to the plane deformation, rocking and skeleton stretching for Ge‐P‐Ge modes, respectively [26] .…”

“…In the Ge 3d XPS spectrum, three peaks located at 30.1, 31.4 and 31.8 eV are observed, which can be assigned to Ge‐Ge, Ge 3d 5/2 (Ge‐P) and Ge 3d 3/2 (Ge‐P), respectively (Figure 4 d). [19] The P 2p spectrum exhibits four peaks, the peaks at 129.3 and 130.6 eV can be ascribed to Ge‐P, [5, 20] and the other two peaks at 129.9 and 130.2 eV correspond to P‐P (Figure 4 e). [2, 21] The C 1s spectrum can be divided into three peaks.…”

Tunable Hollow Nanoreactors for In Situ Synthesis of GeP Electrodes towards High‐Performance Sodium Ion Batteries

“…[2,24] In the spectrum of GeP/CN-3, two peaks corresponding to Ge-P and Ge-Ge stretching modes are observed at 361.0 and 200.4 cm À1 ,respectively. [20,25] Theo ther three peaks located at 135.7, 246.3 and 308.1 cm À1 can be assigned to the plane deformation, rocking and skeleton stretching for Ge-P-Ge modes,r espectively. [26] Furthermore,t wo peaks appear at 1329.5 and 1581.8 cm À1 for both samples,w hich correspond to Da nd Gb ands of nitrogen-doped carbon, respectively.…”

“…In the Ge 3d XPS spectrum, three peaks located at 30.1, 31.4 and 31.8 eVare observed, which can be assigned to Ge-Ge,Ge3d 5/ 2 (Ge-P) and Ge 3d 3/2 (Ge-P), respectively (Figure 4d). [19] The P2 ps pectrum exhibits four peaks,t he peaks at 129.3 and 130.6 eV can be ascribed to Ge-P, [5,20] and the other two peaks at 129.9 and 130.2 eV correspond to P-P (Figure 4e). [2,21] The C1 ss pectrum can be divided into three peaks.T he strong peak at 284.6 eV can be indexed to C À C/C = C, while the other two peaks at 280.6 and 288.5 eV are the signals of C-N and C-O, respectively (Figure 4f).…”

Small-Angle X-ray Scattering Analysis of Colloidal Crystals and Replica Materials Made from l-Arginine-Stabilized Silica Nanoparticles

“…Stober et al 22 introduced the ammonia-catalyzed hydrolysis of silicon alkoxides in aqueous media in 1968, and this method and its modifications enabled the synthesis of monodisperse silica nanoparticles with diameters greater than 200 nm. A surfactant-assisted microemulsion approach was later developed to make silica colloids in the 30 range. 23,24 The use of non-polar organic solvents and large amounts of surfactants, however, limited the microemulsion approach to certain applications.…”