Solution Synthesis of Germanium Nanocrystals:  Success and Open Challenges

Abstract

We present a two-step synthesis route that yields nanometer-size crystalline germanium in the form of a black powder. It relies on high temperature decomposition of tetraethylgermane (TEG) in organic solvents. The presence of pure germanium with diamond structure is unambiguously attested by powder XRD measurements. Low-resolution TEM indicates that the particles are between ∼5 to 30 nm in size, depending on the synthesis conditions. The as-synthesized Ge powders can be stored in air for months and no oxidation occurs. The Ge powders are sparingly soluble in conventional solvents because Ge nanocrystals are likely embedded in a matrix composed mainly of CdC, C−C, and C−H bonds. The presence of residual organic byproducts impedes probing of the optical properties of the dots. Also, we discuss drawbacks and open challenges in high-temperature solution synthesis of Ge nanocrystals that could also be faced in the synthesis of Si nanocrystals. Overall, our results call for a cautious interpretation of reported optical properties of Ge and Si nanocrystals obtained by high-temperature solution methods.

Solution Synthesis of Germanium Nanowires Using a Ge2+ Alkoxide Precursor

“…16 One reason for the scarce exploration of Ge 0 nanowires as an advanced material is due to the lack of a simple and benign synthetic pathway to this morphology. 17 The previously reported routes cover a myriad of processes, including chemical vapor deposition (CVD), 6, 18 laser ablation, 19 vapor-liquid-solid (VLS) growth, 20 templated supercritical fluid, 21-24 and combination of these techniques. The VLS technique is most widely used amongst these methods.…”

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.…”

Hollow, Branched and Multifunctional Nanoparticles: Synthesis, Properties and Applications

“…Zanella et alh i g hlight that this is quite suspicious, and propose the emission could result from excess capping agent or even polymeric species formed during the synthesis of the hybrid nanoparticles. 131,136 Hybrid AuPbS nanoparticles do not exhibit unusual shifts in the photoluminescence emission maxima, but the intensity of the emission for Au-PbS is at least 30 times less intense than that for PbS. 119 The decrease in luminescence intensity is attributed to the direct contact between the two nanoparticles, where the contact promotes charge separation via electron transfer from the PbS nanoparticles to the Au nanoparticle.…”