Chalcogen Research Articles

Mercury lands in marine ooze

Photosynthetic algae called diatoms can trap mercury in deep-sea sediments, a new study finds. These diatom-rich oozes may store up to 20% of the toxic metal released into the atmosphere by human activity over the past 150 years (Science 2018, DOI: 10.1126/science.aat2735). As a volatile metal, mercury easily enters the atmosphere from natural sources, such as erupting volcanoes, and human sources, coal burning in particular. Some of that mercury eventually dissolves in the oceans. A team led by Harald Biester, a geochemist at the Technical University of Braunschweig, has now found that diatoms somehow absorb a significant portion of the dissolved mercury, pulling it down to the seafloor when the microorganisms die. The researchers sampled diatom oozes in sediment cores taken from the bottom of the Southern Ocean at three locations around Antarctica. They found some of the highest mercury accumulation rates measured in marine environments. The scientists estimate that

In situ XPS study on atomic layer etching of Fe thin film using Cl2 and acetylacetone

Etching of transition metals is one of the major challenges in magnetic random-access memory fabrication. In this work, atomic layer etching of iron surfaces with halogen and an organic molecule was studied. The authors successfully etched Fe thin films by forming volatile metal complexes at low temperature with cyclic reactions of Cl2 and acetylacetone (acac). The mechanism of acac reacting on Cl-modified Fe surface was investigated: the surface was first activated with Cl2 gas, and then the top layer of metal was removed by acac reaction. The extent of Cl2 reaction determined the etching rate. At substrate temperatures lower than 135 °C, acac could not remove chlorine. In situ x-ray photoelectron spectroscopy and density functional theory simulation show that the reaction of acac on Cl-dosed Fe surface is likely following a complex pathway instead of simple acac substitution for Cl2. Acac decomposition may play an important role in the process.

Effect of Source-Classified Collection of Municipal Solid Waste on Heavy Metals and Pozzolanic Properties of Incineration Residues

The adoption of source-classified collection of municipal solid waste (MSW) systems has improved waste management and resource conservation in developing countries, including China. Here, we evaluated the effects of a new MSW source-classified collection system on the distribution and leaching of heavy metals in incineration residues as well as on the pozzolanic properties of residues used as additives in cement production. Cu, Cr, and Mn were found primarily in bottom ash, while the volatile metals Zn, Pb, and Cd became enriched primarily in fly ash during combustion. However, effective presorting of MSW prior to incineration reduced the heavy metal content of the MSW source material and increased the combustion efficiency and heat values of MSW. The system of source-classified collection of MSW resulted in decreased concentrations of heavy metals in bottom ash, as well as decreased leachate toxicity, which improved the viability of bottom ash for use as a non-hazardous raw material in cement production. The consistently high temperatures sustained during incineration of source-classified MSW increased the concentrations and leachate toxicity of Cd, Pb, Cu, Zn, and Cr in fly ash. Pozzolanic activity testing revealed that bottom ash may be used as a pozzolanic material in cement production, but that fly ash is not suitable. In contrast to bottom ash from the incineration of mixed MSW, bottom ash from the incineration of source-classified MSW fully satisfies China’s “Pozzolanic materials used for cement production” standards due to its low loss on ignition, high grindability, and the desired rupture strength, compressive strength, and stability that it adds to mortar mixtures.

A Series of Two-Coordinate Group-15 Element (P, As, Sb, Bi) Centered Radicals Having Bulky Alkyl Groups

Abstract Two-coordinate group-15 element centered radicals that bear a lone pair and an unpaired electron on the same group-15 atoms have received much attention in group-15 element chemistry. We previously synthesized an isolable dialkylphosphinyl radical, 2,2,5,5-tetrakis(trimethylsilyl)-1-phosphacyclopentane-1-yl (1P) and its antimony and bismuth analogues (stibinyl radical 1Sb and bismuthinyl radical 1Bi) as persistent radicals. We report herein (1) synthesis of an isolable cyclic dialkylarsinyl radical 1As that exists in the radical form both in solution and in the solid state and (2) comprehensive study of a series of neutral two-coordinate pnictogen-centered radicals (1P, 1As, 1Sb, 1Bi) including UV-vis spectra, redox properties, and reactions.

Structure and stability of propellane-like E[Formula: see text

Propellane-like structures are an important building block for group-14 compounds. Therefore, in the present work, we study theoretically various such structures of the form E[Formula: see text] starting with the pure molecules for which E = E' = E″ = C, Si, Ge, or Sn. Subsequently, we study the systems with E ≠ E' = E″ and finally, we consider some selected cases molecules for which E, E', and E″ all are different. Special emphasis is put on identifying structural trends for the molecules with at least two different group-14 elements. The resulting scheme is, we believe, generally valid for group-14 based systems with more than one type of group-14 elements.

Comprehensive Evaluation of Hazardous Chemical Exposure Control System at a Semiconductor Manufacturing Company in South Korea.

The goal of this study was to evaluate the hazardous chemical exposure control system in a semiconductor manufacturing company and recommend an appropriate exposure surveillance system for hazardous agents. We reviewed compliance-based chemical exposure data compiled between 2012 and 2014 by the study company. The chemical management system, characteristics of chemical use and hazardous gas monitoring system were also investigated. We evaluated the airborne isopropyl alcohol (IPA) and acetone generally used as cleaning solvents, volatile organic compounds and metals levels using internationally recommended sampling and analytical methods. Based on the results of past working environment measurement data and of our investigation, the overall current exposure to chemicals by semiconductor workers during routine production work appears to be controlled below occupational exposure limits. About 40% of chemical products used were found to contain at least one unidentifiable trade-secret substance. There are several situations and maintenance tasks that need special attention to reduce exposure to carcinogens as much as possible. In addition, a job-exposure matrix as a tool of surveillance system that can examine the exposure and health status of semiconductor workers according to type of operation and type of job or task is recommended.

Phase Equilibria in the ZnO-“FeO”-SiO2 System in Reducing Atmosphere and in the ZnO-“FeO”-SiO2-“Cu2O” System in Equilibrium with Liquid Copper Metal at 1250 °C (1523 K)

Recent experimental studies in the ZnO-"FeO"-SiO2 system in reducing atmosphere demonstrated significant discrepancies with the current FactSage thermodynamic model developed using previous experimental data in this system in equilibrium with metallic iron and air. The present experimental study on phase equilibria in the ZnO-"FeO"-SiO2-"Cu2O" system in equilibrium with liquid copper at 1250 A degrees C (1523 K) at low copper oxide concentrations in slag was initiated and undertaken to resolve these discrepancies. A high-temperature equilibration-rapid quenching-electron-probe X-ray microanalysis (EPMA) technique using a primary phase substrate support and closed system approach with Cu metal introduced to determine effective equilibrium oxygen partial pressure from the Cu-metal/Cu2Oslag equilibria was applied to provide accurate information on the liquidus and corresponding solid compositions in the spinel, willemite, and tridymite primary phase fields. The present results confirmed the accuracy of the FactSage model, resolved discrepancies, and demonstrated significant uncertainties in the recent studies by other authors on the system in the open reducing atmosphere. The present study shows how this closed system approach can be used to obtain key thermodynamic data on phase equilibria in systems containing volatile metal species, overcoming the limitations and uncertainties encountered in conventional open gas/condensed phase equilibration with these systems. The study highlights the importance of the focus on obtaining accurate experimental data and the risks of misleading information from inadequate experimental control and analysis. The study also demonstrates that continuing in-depth critical review and analysis of the elemental reactions taking place in complex systems is an essential step in phase equilibrium research.

Reduced graphene oxide bridged, TiO2 modified and Mn3O4 intercalated Ti3C2Tx sandwich-like nanocomposite as a high performance anode for enhanced lithium storage applications

Ti3C2Tx, a novel two-dimensional metal carbide, is regarded as a promising candidate for lithium-ion batteries (LIBs) due to its unique layered structure, good conductivity and low barrier for Li+ diffusion. However, Ti3C2Tx has low capacity and poor rate capability due to the severe interlayer stacking and functionalization group of hydroxyl, oxygen or fluorine existing in Ti3C2Tx particles, limiting its widespread applications. Herein, we have firstly offered a relatively simple and rapid synthetic method to fabricate a 3D quaternary rGO/TiO2/Mn3O4/Ti3C2Tx nanocomposite as LIBs anode material. Ti3C2Tx acts as a conductive framework to enhance the electronic transport properties. Besides, this unique layered structure contributes partially to the enhancement of the total theoretical capacity of the active material. Mn3O4 functions as the dominant part of the active material to contribute an extraordinarily high theoretical capacity. TiO2 nanoparticles and rGO nanosheets can effectively shorten the electron/ion diffusion channels and construct a highly conductive matrix for the fast transfer of electron and Li+. Meanwhile, both of them can also efficaciously buffer the volume change effect during lithiation/delithiation process. As expected, rGO/TiO2/Mn3O4/Ti3C2Tx material has presented significantly outstanding lithium ion storage capabilities, high Coulombic efficiency, excellent long-term cyclability and superior rate capability. For an example, the rGO/TiO2/Mn3O4/Ti3C2Tx anode exhibits high specific capacity of 887.2 mA h g-1 at 0.05 A g−1, almost 2.2 times as much as that of raw Ti3C2Tx anode (404.9 mA h g-1). Even after 100 cycles at a current density of 0.5 A g−1, the rGO/TiO2/Mn3O4/Ti3C2Tx anode can still deliver a capacity of 221.5 mA h g−1. Thus the rGO/TiO2/Mn3O4/Ti3C2Tx anode can be ascribed to have a novel 3D sandwich-like collective benefit from the 0D/2D/3D particles/sheets/layers nanoarchitecture and can be used as a promising anode material for high performance LIBs.

Condensation behaviour of volatile trace metals in laboratory benchtop fumarole experiments

Volatile trace metals emitted from volcanoes condense in gas plumes and fumaroles. The transient nature of natural eruptions makes it challenging to isolate key variables affecting trace metal condensation in this complex natural system. To emulate these conditions in a controlled setting, we design a laboratory ‘benchtop’ fumarole to experimentally measure volatilization and condensation behaviour of volatile trace metals from magma. Synthetic silicate melt compositions in the Na2O-Al2O3-SiO2 and Na2O-Fe2O3-SiO2 systems doped with dissolved trace metals (V, Cu, Zn, As, Y, Mo, Cd, Sn, Tb, Pb and Bi) are degassed in a furnace at 900 °C over periods of days to weeks. The condensates from the gas phase form on a silica glass tube along a thermal gradient from 725 to 125 °C, and are examined by electron microscopy and chemical analysis. We observe variable crystallinity of condensates as functions of temperature. The concentrations of Li, Cu, As, Rb, Mo, Ag, Cd, Cs, W, Pt, Tl, Pb and Bi in leachates of the condensates change by orders of magnitude along the glass tube, and show maxima at various temperatures between 250 and 600 °C. A comparison of the experiments with natural examples shows similarities in the condensation pattern for Cu, As, Ag, and Tl. The enrichment of certain metals in the experimental gas condensates (e.g. Mo) is similar to that observed in natural systems, but differs greatly for other elements (e.g. Bi and Cd) likely due to lack of Cl, S or other complexing agents for metals in the experiments. Our experimental design is a starting point to investigate the role of these and other variables on trace metal condensation behaviour in natural volcanic emissions.

Developing a sustainable solution for recycling electric arc furnace dust via organic acid leaching

The current study demonstrates and proposes a new method for sustainable treatment of electric arc furnace (EAF) dust. The raw material is one of the largest and fast growing hazardous waste fractions produced. Globally, annual EAF production of steel generates more than 12 M tonnes of dust today. The dust is rich in Fe but also contains toxic and volatile metals. The main components in the dust include Fe, Mn, Zn, Pb, and Cr. However, Zn and Pb in the dust inhibits its recycling back to the steel process. The novel process approach employs alkaline roasting with NaOH at 450 °C, followed by organic acid leaching using 0.8 M citric acid at 40 °C under oxygen purging, for two hours. Zinc ferrite (ZnFe2O4), which is the main Zn carrier in the EAF dust is highly refractory making selective Zn vs. Fe leaching impracticable. Roasting was observed to transform EAF dust ZnFe2O4 mineralogy into favourable form of sodium zincate (Na2ZnO2) and sodium ferrate (NaFeO2), the former being an easily leachable Zn compound and the latter keeping Fe in solids. Under the optimized conditions, selective leaching of 100% of Zn vs. Fe (<10%) could be conducted, in addition ≥80% of Pb could be leached. Consequently, Fe and Zn rich recyclable secondary fractions were produced from hazardous EAF dust, both fractions being suitable raw materials for primary metal production.

Extraction behavior of Mo and W from H2SO4 and HF/HCl solutions into toluene with Aliquat336: sulfate and fluoride complex formation of Mo and W towards chemical studies of seaborgium (Sg)

We have studied extraction behavior of group-6 elements Mo and W to search for suitable conditions for an on-line extraction experiment of their heavier homolog, seaborgium (Sg). Batch-wise extraction of carrier-free radiotracers 93mMo and 177,179,181W were carried out from 0.10 – 8.6 M H2SO4 and 1.0 × 10−4 − 5.0 M HF/1.0 M HCl into toluene with a quaternary ammonium compound, Aliquat336. Anionic sulfate complexes of Mo and W with charge − 2 were extracted with Aliquat336 from H2SO4 solutions with concentrations of [H2SO4] > 2 M. In HF/1.0 M HCl, oxyfluoro complexes of Mo and W with charge − 1 were interpreted to be formed and extracted with Aliquat336. From these results, favorable conditions for the extraction of Sg are discussed.

Coexistence of a metastable double hcp phase in bcc–fcc structure transition of Te under high pressure

The structural phase transitions of tellurium (Te) are investigated at pressures of up to 330 GPa at 298 K using an X-ray powder diffraction technique. In the experiments, it was found that the high-pressure bcc phase (Te-V) transitioned to the fcc phase (Te-VI) at 99 GPa, although a double hcp phase (dhcp) coexisted with the fcc phase. As the pressure was increased and decreased, the dhcp phase vanished at 255 and 100 GPa, respectively. These results suggest that the dhcp phase is metastable at 298 K and the structure of the highest-pressure phase of Te is fcc. The present results provide important information regarding the high-pressure behavior of group-16 elements.

Decomposition of the ISA-card under steam for valorized polymetallic raw material

The complete 3Com TokenLink Velocity ISA 16/4 3C319 waste card was gasified under steam at atmospheric pressure in the allothermal process by heating up to 900 °C. The product was easily partitioned according to size and magnetic properties into 5 fractions. Each fraction was analyzed for content of metals by classical chemical route (aqua regia/ICP-OES). With exception of bulky steel parts, these fractions were also investigated by XRD and SEM-EDS methods It was found that there were no bromides in the solid product of gasification. Aqueous condensates, collected in six periods, were individually analyzed for content of bromine and potentially volatile metals (Sn, Zn, and Pb). The composition of tars and oils from condensates and proportions between contents of detected species were also evaluated (GC–MS). Condensation of the excess of steam appeared efficient in the cleaning of the gas from tars, oils, and HBr − final form of bromine. Results of the experiment were discussed and supplemented by the thermodynamic assessment of oxygen potential of the system as well as speciation and volatilization of metals and bromine. Finally, the process was shortly discussed in terms of zero-emissions + zero-waste model as well as the valorization of the waste due to transformation into metal-mineral resource enriched in valuable metals.

Kinetic study of heavy metals Cu and Zn removal during sewage sludge ash calcination in air and N2 atmospheres

Heavy metal control is essential during the thermochemical recovery of phosphorus (P) from sewage sludge ash (SSA). For medium volatile heavy metals, i.e. Cu and Zn, the effect of chlorine additive was complicated and more sensitive to temperature variation. So, in the in-depth study on the removal kinetics of Cu and Zn was necessary. Thus, the studies described in this paper considered the experiments and kinetic models of Cu and Zn removal in SSA through calcination under different atmospheres and temperatures. The results showed that within 15 min, the removal of Cu and Zn was more effective at the same temperature in air than in N2. The result is consistent with kinetic analysis: Reaction activation energy of both Cu and Zn in an air atmosphere is lower than in N2. In addition, the reaction orders, energy and frequency factors of Cu and Zn removal reaction during SSA calcination at high temperature with air and N2 atmosphere were calculated.

Impact of snow deposition on major and trace element concentrations and elementary fluxes in surface waters of the Western Siberian Lowland across a 1700 km latitudinal gradient

Abstract. In order to better understand the chemical composition of snow and its impact on surface water hydrochemistry in the poorly studied Western Siberia Lowland (WSL), the surface layer of snow was sampled in February 2014 across a 1700 km latitudinal gradient (ca. 56.5 to 68° N). We aimed at assessing the latitudinal effect on both dissolved and particulate forms of elements in snow and quantifying the impact of atmospheric input to element storage and export fluxes in inland waters of the WSL. The concentration of dissolved+colloidal (&lt; 0.45 µm) Fe, Co, Cu, As and La increased by a factor of 2 to 5 north of 63° N compared to southern regions. The pH and dissolved Ca, Mg, Sr, Mo and U in snow water increased with the rise in concentrations of particulate fraction (PF). Principal component analyses of major and trace element concentrations in both dissolved and particulate fractions revealed two factors not linked to the latitude. A hierarchical cluster analysis yielded several groups of elements that originated from alumino-silicate mineral matrix, carbonate minerals and marine aerosols or belonging to volatile atmospheric heavy metals, labile elements from weatherable minerals and nutrients. The main sources of mineral components in PF are desert and semi-desert regions of central Asia. The snow water concentrations of DIC, Cl, SO4, Mg, Ca, Cr, Co, Ni, Cu, Mo, Cd, Sb, Cs, W, Pb and U exceeded or were comparable with springtime concentrations in thermokarst lakes of the permafrost-affected WSL zone. The springtime river fluxes of DIC, Cl, SO4, Na, Mg, Ca, Rb, Cs, metals (Cr, Co, Ni, Cu, Zn, Cd, Pb), metalloids (As, Sb), Mo and U in the discontinuous to continuous permafrost zone (64–68° N) can be explained solely by melting of accumulated snow. The impact of snow deposition on riverine fluxes of elements strongly increased northward, in discontinuous and continuous permafrost zones of frozen peat bogs. This was consistent with the decrease in the impact of rock lithology on river chemical composition in the permafrost zone of the WSL, relative to the permafrost-free regions. Therefore, the present study demonstrates significant and previously underestimated atmospheric input of many major and trace elements to their riverine fluxes during spring floods. A broader impact of this result is that current estimations of river water fluxes response to climate warming in high latitudes may be unwarranted without detailed analysis of winter precipitation.

Magmatic controls on the genesis of porphyry Cu–Mo–Au deposits: The Bingham Canyon example

Bingham Canyon is one of the world's largest porphyry Cu–Mo–Au deposits and was previously used as an example to emphasize the role of magma mixing and magmatic sulphide saturation in the enhancement of ore fertility of magmatic systems. We analyzed whole rocks, minerals, and silicate melt inclusions (SMI) from the co-genetic, ore-contemporaneous volcanic package (∼38 Ma). As opposed to previous propositions, whole-rock trace element signatures preclude shoshonite–latite genesis via mixing of melanephelinite and trachyte or rhyolite, whereas core to rim compositional profiles of large clinopyroxene phenocrysts suggests the amalgamation of the ore-related magma reservoir by episodic recharge of shoshonitic to latitic magmas with various degrees of differentiation. Major and trace element and Sr and Nd isotopic signatures indicate that the ore-related shoshonite–latite series were generated by low-degree partial melting of an ancient metasomatized mantle source yielding volatile and ore metal rich magmas. Latite and SMI compositions can be reproduced by MELTS modeling assuming 2-step lower and upper crustal fractionation of a primary shoshonite with minimal country rock assimilation. High oxygen fugacities (≈NNO+1) are prevalent as evidenced by olivine-spinel oxybarometry, high SO3 in apatite, and anhydrite saturation. The magma could therefore carry significantly more S than would have been possible at more reducing conditions, and the extent of ore metal sequestration by magmatic sulphide saturation was minimal. The SMI data show that the latites were Cu rich, with Cu concentrations in the silicate melt reaching up to 300–400 ppm at about 60 wt% SiO2. The Au and Ag concentrations are also high (1.5–4 and 50–200 ppb, respectively), but show less variation with SiO2. A sudden drop in Cu and S concentrations in the silicate melt at around 65 wt% SiO2 in the presence of high Cl, Mo, Ag, and Au shows that the onset of effective metal extraction by fluid exsolution occurred at a relatively late stage of magma evolution. Overall, our results show that fluid exsolution during simple magmatic differentiation of oxidized alkaline magmas is capable of producing giant porphyry Cu deposits.

New tetrahedral polymorphs of the group-14 elements

In this short communication we present the main results of an ab initio structural search for new polymorphs of the group-14 elements C, Si, and Ge, with a focus on low-density and energetically favorable sp 3-bonded tetrahedral polymorphs which could constitute candidate phases to be synthesized in the laboratory. We propose new orthorhombic and tetragonal polymorphs with enthalpies that are lower or comparable to those of other polymorphs of the group-14 elements that have either been experimentally synthesized or recently proposed as the structure of unknown phases obtained in experiments. The new phases have interesting structural and electronics properties. These include an orthorhombic phase that in Si is found to have a quasi-direct band gap at the zone center of about the right size for optimal photovoltaic applications, and a tetragonal phase with a chiral topology that displays an exotic pentagonal pattern and whose vibrational properties match those of an unknown phase of Si.

WO3 and W Thermal Atomic Layer Etching Using "Conversion-Fluorination" and "Oxidation-Conversion-Fluorination" Mechanisms.

The thermal atomic layer etching (ALE) of WO3 and W was demonstrated with new "conversion-fluorination" and "oxidation-conversion-fluorination" etching mechanisms. Both of these mechanisms are based on sequential, self-limiting reactions. WO3 ALE was achieved by a "conversion-fluorination" mechanism using an AB exposure sequence with boron trichloride (BCl3) and hydrogen fluoride (HF). BCl3 converts the WO3 surface to a B2O3 layer while forming volatile WOxCly products. Subsequently, HF spontaneously etches the B2O3 layer producing volatile BF3 and H2O products. In situ spectroscopic ellipsometry (SE) studies determined that the BCl3 and HF reactions were self-limiting versus exposure. The WO3 ALE etch rates increased with temperature from 0.55 Å/cycle at 128 °C to 4.19 Å/cycle at 207 °C. W served as an etch stop because BCl3 and HF could not etch the underlying W film. W ALE was performed using a three-step "oxidation-conversion-fluorination" mechanism. In this ABC exposure sequence, the W surface is first oxidized to a WO3 layer using O2/O3. Subsequently, the WO3 layer is etched with BCl3 and HF. SE could simultaneously monitor the W and WO3 thicknesses and conversion of W to WO3. SE measurements showed that the W film thickness decreased linearly with number of ABC reaction cycles. W ALE was shown to be self-limiting with respect to each reaction in the ABC process. The etch rate for W ALE was ∼2.5 Å/cycle at 207 °C. An oxide thickness of ∼20 Å remained after W ALE, but could be removed by sequential BCl3 and HF exposures without affecting the W layer. These new etching mechanisms will enable the thermal ALE of a variety of additional metal materials including those that have volatile metal fluorides.

Synthesis of quenchable amorphous diamond

Diamond owes its unique mechanical, thermal, optical, electrical, chemical, and biocompatible materials properties to its complete sp3-carbon network bonding. Crystallinity is another major controlling factor for materials properties. Although other Group-14 elements silicon and germanium have complementary crystalline and amorphous forms consisting of purely sp3 bonds, purely sp3-bonded tetrahedral amorphous carbon has not yet been obtained. In this letter, we combine high pressure and in situ laser heating techniques to convert glassy carbon into “quenchable amorphous diamond”, and recover it to ambient conditions. Our X-ray diffraction, high-resolution transmission electron microscopy and electron energy-loss spectroscopy experiments on the recovered sample and computer simulations confirm its tetrahedral amorphous structure and complete sp3 bonding. This transparent quenchable amorphous diamond has, to our knowledge, the highest density among amorphous carbon materials, and shows incompressibility comparable to crystalline diamond.

Group-13 and group-15 doping of germanane.

Germanane, a hydrogen-terminated graphane analogue of germanium has generated interest as a potential 2D electronic material. However, the incorporation and retention of extrinsic dopant atoms in the lattice, to tune the electronic properties, remains a significant challenge. Here, we show that the group-13 element Ga and the group-15 element As, can be successfully doped into a precursor CaGe2 phase, and remain intact in the lattice after the topotactic deintercalation, using HCl, to form GeH. After deintercalation, a maximum of 1.1% As and 2.3% Ga can be substituted into the germanium lattice. Electronic transport properties of single flakes show that incorporation of dopants leads to a reduction of resistance of more than three orders of magnitude in H2O-containing atmosphere after As doping. After doping with Ga, the reduction is more than six orders of magnitude, but with significant hysteretic behavior, indicative of water-activation of dopants on the surface. Only Ga-doped germanane remains activated under vacuum, and also exhibits minimal hysteretic behavior while the sheet resistance is reduced by more than four orders of magnitude. These Ga- and As-doped germanane materials start to oxidize after one to four days in ambient atmosphere. Overall, this work demonstrates that extrinsic doping with Ga is a viable pathway towards accessing stable electronic behavior in graphane analogues of germanium.