Colloidal Synthesis of Air-Stable Crystalline Germanium Nanoparticles with Tunable Sizes and Shapes

Abstract

Nanoparticles of elemental germanium have interesting optical and electronic properties and relatively low toxicity, making them attractive materials for biological and optoelectronic applications. The most common routes to colloidal Ge nanoparticles include metathesis reactions involving Zintl salts, hydride reduction of Ge halides, and thermal decomposition of organogermane precursors. Here we describe an alternative “heat-up” method for the synthesis of size- and shape-tunable Ge nanoparticles that are both crystalline and air stable. The readily available reagents GeI4, oleylamine, oleic acid, and hexamethyldisilazane are combined in one pot and heated to 260 °C, where a rapid nucleation event occurs and multifaceted nanoparticles of crystalline Ge form. By varying the concentration of GeI4, the nanoparticle size can be tuned from 6 to 22 nm with narrow size distributions. Adding trioctylphosphine yields cube-shaped particles, and switching the solvent to octadecene yields one-dimensional nanostructures. The Ge nanoparticles, which are fully air stable for more than 6 months, were characterized by XRD, TEM, HRTEM, EDS, XPS, DRIFT, and UV−visible spectroscopy.

Size and emission color tuning in the solution phase synthesis of highly luminescent germanium nanocrystals

“…[14][15][16][17][18][19][20][21] Other methods include thermal co-reduction of Ge(II) and amido based precursors, 6,22,23 aqueous phase reduction of GeO 2 powders by NaBH 4 , 24 and other high temperature chemical reduction methods. [25][26][27][28][29][30][31] However, disadvantages associated with these methods include synthetically involved precursor synthesis, long reaction times, high temperatures and pressures, and extensive post synthetic purification procedures. 1,29 As well as the variation in size distribution, morphology and surface chemistries reported above, significant inconsistencies also exist in the photophysical properties of these nanostructures, precluding a detailed understanding of their size-dependent characteristics.…”

Synthesis of Nanoamorphous Germanium and Its Transformation to Nanocrystalline Germanium

“…Bottom-up solution-phase synthetic chemistry methods offer better control of the size and shape of the nanoparticles, but often do not provide the good crystallinity required for many applications, and require the use of longchain ligands and surfactants to stabilize the particle surface and control growth. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Due to their ease of preparation, these solution-phase methods are also more accessible to many researchers and more amenable to scaling. As a result, their development is in great demand to prepare high-quality materials for detailed chemistry and physical studies, essential for their eventual integration into practical devices.…”

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] The germanium sources in these investigations are usually the germanium halides, GeX n , or organogermanes [23,24] in which the Ge center is either in the 4 + or 2 + oxidation state (e.g., GeCl 4 , GeBr 4 , GeI 2 ), and long-chain phosphines and alkenes are often used as surface protection ligands for nanoparticle stabilization. The reducing agents used in these investigations are usually the strong ones, such as LiAlH 4 , NaBH 4 , sodium, sodium naphthalide, butyllithium, and Ge Zintl salts.…”

“…The reducing agents used in these investigations are usually the strong ones, such as LiAlH 4 , NaBH 4 , sodium, sodium naphthalide, butyllithium, and Ge Zintl salts. [12][13][14][15][16][17][18][19][20][21][22][23][24] In these reactions, the strength of the reducing agent and the reduction reaction rate are related to each other, and usually these strong reducing agents react very quickly such that the reaction kinetics and nanocrystal growth rates cannot be explored and are not under fine control. Slowing these reduction steps and collecting kinetic information will be very beneficial for the synthesis of Ge nanoparticles and will gainfully contribute to the nanochemistry of these systems.…”

Solution-processed photodetectors using colloidal germanium nanoparticles

“…Ge NPs were synthesized using a "heat-up" synthesis method, which has been previously reported to produce airstable crystalline nanoparticles with tunable size and shapes [5]. In this method, GeI 4 , oleylamine, oleic acid, and HMDS are slowly heated until a distinct color change from yellow to reddish-brown indicates that Ge NPs have been formed.…”