Negative ion clusters in self‐condensation of GeH₄

Abstract

Formation of negative ion clusters from GeH4 has been studied as a function of germane pressure, in the 25-450 mTorr range, by chemical ionisation mass spectrometry. At the lowest pressures, only the GeHn- (n = 0-3) ion family is formed, whilst at increasing pressures GemHn- (m = 1-9) ion clusters of increasing size are observed in the mass spectra. A variable contribution of the ions with different hydrogen content is observed as a function of the pressure of germane in all the GemHn- (m = 1-9) clusters. Increasing pressures induce a general increase of ion species with a low content of hydrogen atoms. In fact, at 450 mTorr, 38% of the ion current is due to the bare Gem- (m = 2-5) clusters and 83% to the sum of abundances of the GemHn- ions without hydrogen (n = 0) and with a number of hydrogen atoms not higher than the number of germanium atoms (n = 0-m). This trend suggests that a contribution of negative clusters to the deposition of the amorphous solid a-Ge:H from gaseous systems containing GeH4, activated by radiolytic methods, can enhance the formation of solids with a low hydrogen content, which show better photoelectrical properties.

Negative gas‐phase ion chemistry of GeH4: a quadrupole ion trap study

“…This suggests that negative ions may play a considerable role in the polymerization process that ultimately leads to deposition of Ge‐based amorphous solids. The present results are in good agreement with previous studies,24 where it was shown that the content of hydrogen in the Ge n H ion clusters decreases with increasing cluster size. This is also a positive outcome for application purposes, as it was found that the best photoelectrical properties of a‐Ge:H materials are achieved when the percentage of hydrogen atoms is not higher than 10% 39…”

“…Self‐condensation reactions10, 11 and gas‐phase mixtures of germane or methylgermane with hydrides of C and/or N, P were studied in order to obtain information on the early ion clustering reactions that eventually lead to deposition of doped germanium carbides 12–23. Recently, our attention has shifted to negative germane ions, which were observed to give extensive condensation reactions in the relatively high‐pressure environment of a triple quadrupole mass spectrometer 24. A correlation was drawn between abundances of ions containing a large number of Ge atoms (up to 9) and GeH 4 pressure in the source, but no reaction sequences were studied.…”

Gas-Phase Ion Chemistry of GeH4/B2H6 Mixtures

“…In both positive and negative ionization modes, we observed an appreciable formation of Ge-B bonds. Even if we might have expected a higher contribution given by negative ions, on the basis of what we have observed in the SiH 4 / B 2 H 6 system, 38 and in self-condensation of germane in negative ionization, 34,36 we have to conclude that germane anions display a higher affinity for self-condensation processes rather than for reactions with diborane. However, it is noticeable that the ionized GeH 4 / B 2 H 6 mixture represents a well-balanced system in view of formation of Ge-B bonds, as positive and negative ions give a comparable contribution.…”

“…While our interest has been traditionally focused on positive ions, quite recently we have also shifted our attention to the less investigated field of gas-phase negative ions. Preliminary results on the structure and reactivity of germanium [34][35][36] and silicon 37,38 hydride anions were very interesting and disclosed a new intriguing research area. Stimulated by these recent results, we have undertaken the study of the gas-phase ion chemistry of germane/diborane mixtures, in both positive and negative ionization modes.…”

Ge3Hn- Anions (n = 0−5) and Their Neutral Analogues: A Theoretical Investigation on the Structure, Stability, and Thermochemistry

“…On the other hand, the information about anionic germanium hydrides is less abundant and includes few studies on GeH n -(n ) 1-3), 25,[30][31][32][33][34][35][36][37][38][39][40] GeH 5 -, 41 Ge 2 H 6 -, 42 and the systematic DFT investigation by Schaefer and co-workers 43 on GeH n -(n ) 0-4) and Ge 2 H n -(n ) 0-6). More recently, to obtain theoretical support to the mass spectrometric experiments on the anionic self-condensation of GeH 4 , 9 we have investigated the experimentally observed Ge 2 H n -(n ) 0-5) at the DFT and ab initio level of theory. 44 As a further contribution to the study of the species involved in the negative ion chemistry of GeH 4 , we report here density functional theory (DFT) and Gaussian-2 (G2) calculations on various Ge 3 H nanions (n ) 0-5) and on their neutral analogues.…”