Chemical, Electronic, and Electrical Properties of Alkylated Ge(111) Surfaces

Knapp, David; Brunschwig, Bruce S.; Lewis, Nathan S.

doi:10.1021/jp101375x

Cited by 48 publications

(60 citation statements)

References 56 publications

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“…The peak at 284.1 eV can be attributed to C−Ge from methyl groups covalently bonded to the Ge surface, similar to previous reports for CH 3 −Ge(111) and CH 3 −Si(111) surfaces. 7,21 In addition, to account for the vibrational fine structure, peaks were fit at fixed energy (+0.38, +0.76 eV) and relative area (49%, 11%) compared to the main C−Ge peak; these vibrational loss peaks are shown by the dotted peaks in Figure 5. The vibrational fine structure has been shown to produce an asymmetric peak shape for CH 3 −Si(111) surfaces, 21 and the same peak shape was found to provide the best fit for asprepared CH 3 −Ge(111) surfaces as well as for CH 3 −Ge(111) surfaces that had been annealed to remove adventitious hydrocarbons (vide infra).…”

Section: Journal Of the American Chemical Societymentioning

confidence: 99%

“…4,5 Applications for Ge in solar cells or in semiconductor electronics require a stable, low defect-density surface, which cannot be achieved by oxidation. 6 Methyl-terminated Ge(111) surfaces 7,8 have been prepared in a similar manner to that used to alkylate Si(111), 9 specifically through the use of a two-step halogen/alkylation process. Methyl termination of Ge(111) was demonstrated by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy, and surface recombination velocities of <100 cm s −1 were observed.…”

Section: ■ Introductionmentioning

confidence: 99%

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Synthesis and Characterization of Atomically Flat Methyl-Terminated Ge(111) Surfaces

et al. 2015

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Atomically flat, terraced H–Ge(111) was prepared by annealing in H2(g) at 850 °C. The formation of monohydride Ge–H bonds oriented normal to the surface was indicated by angle-dependent Fourier-transform infrared (FTIR) spectroscopy. Subsequent reaction in CCl3Br(l) formed Br-terminated Ge(111), as shown by the disappearance of the Ge–H absorption in the FTIR spectra concomitant with the appearance of Br photoelectron peaks in X-ray photoelectron (XP) spectra. The Br–Ge(111) surface was methylated by reaction with (CH3)2Mg. These surfaces exhibited a peak at 568 cm–1 in the high-resolution electron energy loss spectrum, consistent with the formation of a Ge–C bond. The absorption peaks in the FTIR spectra assigned to methyl “umbrella” and rocking modes were dependent on the angle of the incident light, indicating that the methyl groups were bonded directly atop surface Ge atoms. Atomic-force micrographs of CH3–Ge(111) surfaces indicated that the surface remained atomically flat after methylation. Electrochemical scanning–tunneling microscopy showed well-ordered methyl groups that covered nearly all of the surface. Low-energy electron diffraction images showed sharp, bright diffraction spots with a 3-fold symmetry, indicating a high degree of order with no evidence of surface reconstruction. A C 1s peak at 284.1 eV was observed in the XP spectra, consistent with the formation of a C–Ge bond. Annealing in ultrahigh vacuum revealed a thermal stability limit of ∼400 °C of the surficial CH3–Ge(111) groups. CH3–Ge(111) surfaces showed significantly greater resistance to oxidation in air than H–Ge(111) surfaces.

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Section: Journal Of the American Chemical Societymentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Synthesis and Characterization of Atomically Flat Methyl-Terminated Ge(111) Surfaces

et al. 2015

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“…This ambiguity in surface functionalization convolutes efforts to correlate the effects of surface functionalization on the optoelectronic properties of these single-atom thick semiconductors 9,20,[22][23][24] . Furthermore, it is well established that H-terminated Si(111) and Ge(111) surfaces are extremely air reactive, whereas the -CH 3 terminated surfaces can be resilient towards oxidation 25,26 . To bypass the potential air-reactive intermediates and create new organic-terminated materials, new single-step synthetic methods that can directly convert a precursor crystalline solid-state crystal into a crystalline, exfoliatable, organicterminated van der Waals solid in nonaqueous solvents is required.…”

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Improving the stability and optical properties of germanane via one-step covalent methyl-termination

et al. 2014

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Two-dimensional van der Waals materials have shown great promise for a variety of electronic, optoelectronic, sensing and energy conversion applications. Since almost every atom in these two-dimensional crystals is exposed to the surface, covalent surface termination could provide a powerful method for the controlled tuning of material properties. Here we demonstrate a facile, one-step metathesis approach that directly converts CaGe 2 crystals into mm-sized crystals of methyl-terminated germanane (GeCH 3 ). Replacing -H termination in GeH with -CH 3 increases the band gap by B0.1 eV to 1.7 eV, and produces band edge fluorescence with a quantum yield of B0.2%, with little dependence on layer thickness. Furthermore, the thermal stability of GeCH 3 has been increased to 250°C compared with 75°C for GeH. This one-step metathesis approach should be applicable for accessing new families of two-dimensional van der Waals lattices that feature precise organic terminations and with enhanced optoelectronic properties.

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“…10 For example, hydrogenated Ge(111) surfaces have been methylated using a two-step halogenation/alkylation process, creating well-ordered, air-stable surfaces with excellent electrical properties. 11,12 Recently, highly ordered, atomically flat CH 3 -Ge(111)-(1 × 1) surfaces have been prepared, resulting in improved chemical and electrical passivation. 13 Several standard surface analytical techniques have revealed the chemical composition, surface structure, surface conductance, and methyl vibrational modes of methylated Ge(111) surfaces.…”

Section: Introductionmentioning

confidence: 99%

“…[11][12][13] The vibrational modes of CH 3 -Ge(111) have been investigated by use of transmission infrared spectroscopy (TIRS), high-resolution electron-energy loss spectroscopy (HREELS), and density functional perturbation theory (DFPT).…”

Section: Introductionmentioning

confidence: 99%

Vibrational dynamics and band structure of methyl-terminated Ge(111)

Hund

Nihill

Campi

et al. 2015

The Journal of Chemical Physics

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Articles you may be interested inThe interaction of organic adsorbate vibrations with substrate lattice waves in methyl-Si (111) A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge (111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge (111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD 3 -Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH 3 -Ge(111) and CH 3 -Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers. C 2015 AIP Publishing LLC.[http://dx

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Chemical, Electronic, and Electrical Properties of Alkylated Ge(111) Surfaces

Abstract: Supporting Information1. Detailed C1s XPS of Decyl-terminated Ge prepared with Decylmagnesium Bromide.2. Python script for functional relationship between surface conductance and surface potential is available in separate file.

Cited by 48 publications

References 56 publications

Synthesis and Characterization of Atomically Flat Methyl-Terminated Ge(111) Surfaces

Synthesis and Characterization of Atomically Flat Methyl-Terminated Ge(111) Surfaces

Improving the stability and optical properties of germanane via one-step covalent methyl-termination

Vibrational dynamics and band structure of methyl-terminated Ge(111)

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