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Towards a comprehensive understanding of the Si(100)-2×1 surface termination through hydrogen passivation using methylamine and methanol: a theoretical approach

  • Tanay Debnath
  • Tamalika Ash
  • Subhendu Sarkar
  • Abhijit Kr. DasEmail author
Original Paper
  • 84 Downloads
Part of the following topical collections:
  1. International Conference on Systems and Processes in Physics, Chemistry and Biology (ICSPPCB-2018) in honor of Professor Pratim K. Chattaraj on his sixtieth birthday

Abstract

Using density functional theory, we explored the termination process of Si (100)-2 × 1 reconstructed surface mechanistically through the dehydrogenation of small molecules, considering methyl amine and methanol as terminating reagents. At first, both the terminating reagents form two types of adduct through adsorption on the Si (100)-2 × 1 surface, one in chemisorption mode and the other via physisorption, from which the dehydrogenation process is initiated. By analyzing the activation barriers, it was observed that termination of the Si-surface through the dehydrogenation is kinetically almost equally feasible using either reagent. We further examined in detail the mechanism for each termination process by analyzing geometrical parameters and natural population analysis charges. From bonding evaluation, it is evident that hydrogen abstraction from adsorbates on the Si-surface is asymmetric in nature, where one hydrogen is abstracted as hydride by the electrophilic surface Si and the other hydrogen is abstracted as proton by the neucleophilic surface Si. Moreover, it was also observed that hydride transfer from adsorbate to the Si-surface occurs first followed by proton transfer. Overall, our theoretical interpretation provides a mechanistic understanding of the Si (100)-2 × 1 reconstructed surface termination by amine and alcohol that will further motivate researchers to design different types of decorated semiconductor devices.

Graphical Abstract

Surface termination process of Si(100)-2×1 through formation of non-polar Si–H bonds via dehydrogenation of methylamine and methanol as terminating reagents

Keywords

Si(100)-2 × 1 reconstructed surface Dehydrogenation Surface termination Potential energy surface Bonding evaluation 

Introduction

Chemical passivation of organic molecules on the surface of semiconductors unlocks the potential to fabricate organic functionalized hybrid devices [1, 2] that have broad application in chemical sensors, biological recognition, molecular and optical electronics, etc. [3, 4, 5, 6, 7, 8, 9, 10, 11]. Over the past several years, manufacturing of organic-modified semiconductor surfaces, especially the Si(100) surface, has been pivotal in attracting the attention of researchers because of its material importance in modern science and technology [12, 13, 14, 15, 16, 17, 18, 19, 20]. The Si(100) surface of silicon undergoes a 2×1 reconstruction, forming Si–Si dimers with partial double bond character consisting of a strong σ-bond and a weak π-bond. Due to significant strain, the π-orbital is poorly overlapped on the surface dimer, and thus the π -bond between the two Si-atoms in the dimer becomes very weak. The dimer on the surface becomes tilted in order to relieve the strain; thus the tilted dimer exhibits properties of both a weak π-bond and a zwitterion-like diradical. The tilting of dimers on the surface leads to a charge separation between the two surface Si-atoms. The lower Si-atom of the tilted dimer shows slightly greater positive charge compared to the upper atom, rendering the zwitterionic character of the surface dimer. The upper Si-atom has more s-character than the bulk sp3 bonds, while the lower surface Si-atom has more p-character. Thus, the electron density at the upper atom of the dimer is greater than that of the lower atom, and, consequently, the upper atom becomes nucleophilic and the lower atom becomes electrophilic in nature [21, 22, 23].

All hybrid devices consisting of organic molecules are manufactured by capitalizing on the specific properties of the Si(100) 2×1 surface. From several experimental as well as theoretical works, it is evident that the dimer undergoes facile addition reactions with different organic compounds such as hydrocarbons [24, 25, 26, 27], alkyl silane [28], alkyl halides [29, 30, 31], alcohols [32, 33, 34, 35, 36, 37, 38], amines [38, 39, 40, 41, 42, 43, 44], Lewis-acids [45], amino acids [9, 46], boranes [47], ammonia [48], etc. Organic modification of the Si(100) 2×1 surface is also a viable technique for surface termination as, in most cases, non-polar Si–C bond forms. Similar to the Si–C linkage, which is well known for its excellent surface terminator properties, Si–H should also be considered in this context because of its non-polar and inert nature. However, hydrogen passivation on the Si surface through molecular H2 is kinetically disfavored at ambient temperature and pressure, which encourages researchers to seek alternative solutions. Thus the passivation of organic molecules on the Si(100) surface, where the molecule is fragmented into two parts that are attached to the surface Si atoms, has become an enticing field of research. For instance, alcohol and amine dissociate into two parts via two different pathways, and the most feasible pathway shows that fragmentation occurs through the dissociation of the H···X–R (X = N,O) bond [33, 38, 44]. In these processes, although one of the surface Si atoms is terminated by inert hydrogen, the other Si remains polar and active in nature and overall forms a organic-decorated hybrid semiconductor device, which implies that 100% of the Si(100) 2×1 reconstructed surface termination through hydrogen remains untouched. Under these circumstances, our strategy is to acquire a fully hydrogen-terminated Si(100) surface with the help of the aforesaid small organic molecules.

Compounds such as amine, alcohol, etc. are dehydrogenated in the presence of certain substrates under certain specific conditions to form imine, aldehyde/ketone, respectively. By thorough investigation of the mechanism, it is well understood that, during the reaction, two hydrogens are eliminated from the respective systems in order to produce dehydrogenated derivatives. Now the question may arise whether the Si(100)-2×1 reconstructed surface can be terminated by the dehydrogenation of the aforementioned organic molecules taking up those two hydrogens. To answer this question, we explored the termination process of the Si(100) surface mediated by dehydrogenation of those small organic molecules, and further checked the kinetic as well as the thermodynamic feasibility of each process by determining the activation barrier and reaction enthalpy values. To achieve our goal of termination of the Si(100) surface by hydrogens, we also succeeded in dehydrogenating the organic molecules, which is not achievable in a unimolecular way at ambient temperature and pressure. The termination of Si(100) surface for methylamine and methanol systems was studied, and the feasibility of termination was compared from the perspective of activation barriers and reaction enthalpies. To provide mechanistic insights, we also performed a bonding evaluation for each process and interpreted the pattern of hydrogen transfer from adsorbate to sorbent.

To model the Si(100) 2×1 reconstructed surface, we have taken Si9H12—one of the most accurate representations of the Si(100) 2×1 reconstructed surface dimer [28, 33, 38, 45, 46]—as the template for exploring different types of reactions, except for the cases where extension of interactions leads beyond the cluster. In those cases, the one-dimer cluster was seen to underestimate the adsorption energy by ~20% compared to that calculated by larger clusters, although the nature of the reaction profile remains unchanged [46]. Overall, it was observed that, apart from significant charge transfer and strain parallel to the surface, the one-dimer cluster model correctly represents the Si(100)-2X1 surface. The Si9H12 cluster consists of two Si atoms in the top layer that represents the surface dimer, four Si atoms in second layer, two third-layer Si atoms, and one fourth-layer Si atom. The dangling subsurface bonds of the Si9H12 cluster are terminated by hydrogen atoms. The purpose of these terminating hydrogens is to preserve the sp3 bonding character of the subsurface silicon atoms, and they are necessary to avoid the nonphysical effects that stem from subsurface dangling bonds.

Computational details

All electronic structure calculations were carried out using the Gaussian 09 [49] suite of quantum chemistry programs. The participating reactants, transition states (TS) and products associated with both termination processes were optimized using the M06-2X [50, 51] hybrid functional in conjunction with the 6-311++G(d,p) basis set for all atoms, with no geometry or symmetry constraints. Zhao and Truhlar [50, 51] developed the M06 family of local (M06-L) and hybrid (M06, M06-2X) meta-GGA functionals, which show promising performance for the kinetic and thermodynamic calculations without the need to refine the energies by post Hartree-Fock methods. The M06-2X is well recommended for applications involving main group thermochemistry, non-covalent interaction, etc. The advantage of the M06-2X in studying reactions on the Si9H12 cluster is also evident from the work of Ferguson et al. [52]. Normal-mode analyses were performed at the same level of theory for reactants and products, as well as TS geometries, and minima were characterized with no imaginary frequency, whereas the presence of one imaginary frequency is the characteristic of TS. The TS between reactant and product was obtained by the synchronous transit-guided quasi-Newton (STQN) method and further confirmed by a parallel intrinsic reaction coordinate (IRC) calculation. The IRC [53, 54] calculations were performed to map out the reaction paths from the TS towards the directions of both reactant and product using the mass-weighted internal coordinate (Sb). This corroborates the connection between a particular TS with specific reactant and product. We further performed natural population analysis (NPA) to calculate the atomic charges of the participating atoms during the bonding evaluation process.

Results and discussion

We explored the complete reaction mechanism for the simultaneous termination of Si(100)-2×1 surface along with the dehydrogenation of the terminating reagents methylamine (CH3NH2) and methanol (CH3OH). After exploration of the potential energy surface (PES), we further performed bonding evaluation by determining the geometrical parameters and NPA charges for the selected intunop geometries obtained from IRC calculation in order to understand the reaction mechanism in detail.

Si(100)-2×1 surface termination using CH3NH2

Reaction mechanism

Reviewing earlier reported works [37, 44], it was observed that the degradation of methylamine or other amine analogues on the Si(100)-2×1 surface have already been explored by several groups. Kato et al. [38] showed that methylamine can be degraded on the Si(100)-2×1 surface in two possible ways: through breakage of the C–N bond, i.e., segmentation of CH3 and NH2 units; or production of CH3NH and H units via breakage of the N–H bond. Wang et al. [44] investigated the degradation of unsaturated cyclic and aliphatic amines on the Si(100)-2×1 surface by exploring several pathways. To our knowledge, the dehydrogenation of methylamine to methyleneamine through the abstraction of hydrogens by the Si(100)-2×1 surface has not yet been revealed. The geometrical parameters of Si9H12 are presented in Scheme 1.
Scheme 1

Optimized geometry of Si9H12 with Si–Si bond lengths indicated (Å)

During study of the methylamine mediated termination process, we found two adsorption modes of methylamine on the Si(100)-2×1 surface: chemisorption and physisorption. In the chemisorption mode, methylamine is bound strongly to the Si surface through its N-site (dSi-N = 1.96 Å) and, consequently, the Si–Si distance increases to 2.34 Å. The associated chemisorption energy was found to be −33.3 kcal mol−1. In the case of the physisorption mode, methylamine interacts weakly with the Si-surface, with physisorption energy of −3.1 kcal mol−1, where one of the N–H and C–H hydrogens is facing towards the Si-surface and the Si–Si distance again reduces to 2.21 Å. By analyzing the structures of the adsorption modes, it is evident that, in the chemisorption mode, methylamine cannot participate directly in the dehydrogenation reaction, rather it is converted to the physisorption mode in order to take part in the dehydrogenation reaction. It should be noted that the transformation of chemisorption to physisorption mode can be achieved through controlled heat, otherwise it may not be detected experimentally. As depicted in Fig. 1, the dehydrogenation of methylamine via simultaneous abstraction of hydrogens from –NH2 and –CH3 groups by the Si(100)-2×1 surface occurs through the formation of a six-membered ring in the TS of activation barrier 11.0 kcal mol−1 with respect to the physisorption mode. The effective barrier height with respective to the chemsorption mode is 41.2 kcal mol−1, but, as in chemisorption mode, methylamine is not placed in a proper position for undergoing dehydrogenation, the effective barrier height was not considered here. The PES reported in previous studies, i.e., cleavage of H···NHCH3 and H3C···NH2 over the Si(100)-2×1 surface was obtained from chemisorption mode where the physisorption mode was not reported. In this study, for the first time we have identified the physisorption mode and also shown that the dehydrogenation pathway is initiated from that physiorption mode. The process was found to be highly thermodynamically feasible, with an exothermicity value of −24.3 kcal mol−1. Thus, it can be articulated that, if methylamine forms adducts with the Si-surface in physisorption mode, the dissociation of methylamine on the Si–Si surface will follow the newly explored dehydrogenation pathway along with the previously reported H···NHCH3 and H3C···NH2 segmentation pathways.
Fig. 1

Potential energy surface (PES) associated with the Si(100)-2×1 termination process using methylamine as a terminating reagent at M06-2X/6-311++G(d,p) level. The energy values are given in kcal mol−1

Bonding evaluation

To understand the mechanism in more depth, we studied bond formation and breakage thoroughly by analyzing geometrical parameters and NPA charge. In doing so, we first performed IRC calculations to select some unoptimized intermediate (intunop) geometries (not local minima) connecting the reactant and product via TS. Based on the analyses of geometrical parameters as well as NPA charge, we have monitored the entire bonding phenomenon. For the entire reaction pathway of methylamine, we chose a total of six intunop geometries as representative of the entire PES; these are designated ami1–ami6, where ami1 is the intunop closest to the reactant and ami6 is the intunop closest to the product. The geometrical parameters and NPA charges are presented in Table 1 and the associated geometries of the intunop are shown in Fig. 2. In the following section, we discussed the bonding evaluation in detail.
Table 1

Geometrical parameters (Å) and natural population analysis (NPA) charges of the separated reactants, intunop and separated products associated with the Si(100)-2 × 1 termination process using methylamine as a terminating reagent

Geometrical parameters

Geometry

Si–Si

Si-H(C)

Si–H(N)

C–H

N–H

C–N

 Si-dimer

2.19

 CH3NH2

1.10

1.01

1.46

 ami1

2.25

2.07

2.65

1.15

1.02

1.42

 ami2

2.32

1.84

2.41

1.28

1.03

1.36

 ami3

2.34

1.66

2.37

1.55

1.04

1.33

 TS

2.35

1.56

2.23

1.86

1.07

1.30

 ami4

2.37

1.52

2.09

2.13

1.13

1.28

 ami5

2.38

1.50

1.83

2.27

1.30

1.28

 ami6

2.37

1.49

1.47

2.32

1.82

1.26

 Hydrogenated Si-dimer

2.37

1.49

1.49

 CH2NH

1.29

NPA charge

Geometry

Si(C)

Si(N)

H(C)

H(N)

C

N

 Si-dimer

−0.044

−0.166

 CH3NH2

0.185

0.348

−0.370

−0.855

 ami1

0.071

−0.340

0.102

0.385

−0.304

−0.811

 ami2

0.067

−0.405

0.029

0.412

−0.218

−0.791

 ami3

0.027

−0.453

−0.082

0.432

−0.076

−0.744

 TS

−0.015

−0.457

−0.143

0.423

0.018

−0.704

 ami4

−0.035

−0.422

−0.153

0.383

0.059

−0.686

 ami5

−0.026

−0.294

−0.140

0.241

0.049

−0.665

 ami6

−0.011

0.004

−0.114

−0.006

−0.003

−0.638

 Hydrogenated Si-dimer

0.009

0.009

−0.075

−0.075

 CH2NH

0.04

−0.745

Fig. 2

Geometries of intermediates associated with the Si(100)-2×1 termination process with methylamine as a terminating reagent at M06-2X/6-311++G(d,p) level

Geometrical parameter analysis

We first discuss the geometrical parameters of the separated reactants, i.e., methylamine and the silicon dimer. In free methylamine, the C–H and N–H distances are calculated to be 1.09 Å and 0.96 Å, respectively, and the Si–Si dimer distance is 2.19 Å (Scheme 1). While examining the bond lengths associated with the participating atoms of all the intunop, it was observed that, at the beginning of the reaction, the hydrogen of –CH3 is abstracted by one of the surface silicon, whereas the hydrogen of –NH2 remains almost intact. During investigation of the geometrical parameters collected in Table 1, it was noted that the change in the N–H bond distance was almost insignificant from ami1 to TS (from 1.02 Å to 1.07 Å), whereas, for C–H, the bond distance increases significantly from 1.15 Å to 1.86 Å. In ami4, the hydrogen associated with –CH3 comes close to the surface silicon and forms strong non-polar covalent bond with the Si (Si-H(C) distance 1.52 Å). While moving from ami4 to ami6, dissociation of the N–H bond is prominent as the bond length increases from 1.13 Å to 1.82 Å. In ami6, the Si–H distance in the amine side becomes 1.47 Å, which is almost the same as that obtained on the methyl side, suggesting the completion of Si–H bond formation. Therefore, by analyzing the geometrical parameters, it was confirmed that the hydrogen transfer process from methylamine to Si(100)-2×1 surface is completely asymmetrical in nature.

NPA charge analysis

We first investigated the NPA charges of the separated reactants, i.e., methylamine and the silicon dimer of Si9H12. In the case of free methylamine, it was found that the hydrogen attached to nitrogen behaves like a proton, with NPA charge of 0.348, whereas the hydrogen bonded with carbon is less positive (0.185) and acts like hydride. While observing the free Si(100)-2×1 surface, it was noted that the electrophilic-Si is relatively less negative (−0.044) compared to the neucleophilic Si (−0.166). By analyzing the NPA charges on the participating atoms of ami1, it was observed that although both hydrogens remain positively charged, the positive charge on H(N) (0.385) was higher than that of free methylamine, while the reverse fact was noticed for H(C) (0.102). As evident from Table 1, for ami1, the NPA charge on N is −0.811, whereas for C the associated value is −0.304. As the reaction progresses up to the TS, the positive charge on H(C) decreases sharply, whereas the variation of charge on H(N) is almost negligible. After crossing the TS, when the reaction proceeds towards the product, the positive charge on H(N) decreases sharply and becomes almost neutral in ami6. From the NPA analysis, it was inferred that, at the initial stage of the reaction H(C), having relatively low positive charge acts like hydride, and is abstracted by the electrophilic Si to form an almost non-polar covalent Si–H bond in the product. On the other hand, H(N) behaves like a proton and is abstracted by the neucleophilic Si, where the charge transfer from Si(N) to H(N) leads to production of another covalent Si–H bond. Therefore, from NPA charge analysis for all the selected intunop geometries, it was apparent that hydrogen abstraction from methylamine by the Si-surface is asymmetric, and hydride transfer precedes the proton transfer process. For the hydrogenated Si(100)-2×1 surface, both the hydrogens become negative in the separated product state, while surface silicons are almost in neutral state.

Si(100)-2×1 surface termination using CH3OH

Reaction mechanism

Similar to methylamine, several degradation pathways on the Si(100)-2×1 surface have also been reported in the case of methanol. Kato et al. [38] reported the degradation of methanol in two different ways, one is degradation via the breakage of CH3 and OH units, which proceeds through high activation barrier and, in another pathway, the CH3O···H bond is cleaved to produce CH3O and H fragments, for which the barrier height is extremely low. Later, Zhang et al. [33] also confirmed the greater feasibility of alcohol degradation through O–H cleavage rather than C–O cleavage. Similar to methylamine, for methanol also, dehydrogenation through hydrogen abstraction by the Si(100)-2×1 surface has not yet been revealed. Here also, along with the chemisorption mode, with energy of −18.8 kcal mol−1, we found the physorption mode, with energy −3.5 kcal mol−1, where the participating hydrogens are oriented towards the Si surface. Similar to methylamine, in this case also the Si–Si distance is significantly elongated (dSi-Si = 2.32 Å) compared to the physisorption mode (dSi-Si = 2.21 Å). Initiation of the dehydrogenation reaction from the physisorption mode proceeds via simultaneous hydrogen abstraction from –CH3 and –OH through the six-membered TS activation barrier of 13.0 kcal mol−1 (Fig. 3) with respect to physisorption mode. In this case, the effective barrier height (28.3 kcal mol−1) was also calculated with respect to chemisorption mode but, as the dehydrogenation process cannot be achieved directly from the chemisorption mode, the effective barrier height was not considered here. Here also, the physisorption mode of methanol on the Si(100)-2×1 surface is reported for the first time, as is the dehydrogenation process on the silicon surface. Hence, along with the O–H cleavage pathway, methanol can also be degraded through the hydrogen abstraction pathway on the Si-surface if the physisorption mode is formed through controlled thermal heating. The thermodynamic feasibility of this process is apparent from its high exothermicity value (−29.2 kcal mol−1).
Fig. 3

PES associated with the Si(100)-2×1 termination process by methanol as a terminating reagent at M06-2X/6-311++G(d,p) level. The energy values are given in kcal mol−1

Bonding evaluation

For methanol also, we have performed IRC to understand the mechanistic pathway of hydrogen abstraction from methanol by the Si(100)-2×1 surface. Here also, with the help of geometrical parameters and NPA charges, we were able to show whether the hydrogen abstraction process is symmetrical or asymmetrical. Along with the TS geometry, a total of six intunop geometrieswere selected to describe the entire reaction pathway (Fig. 4).
Fig. 4

Geometries of the intermediates associated with the Si(100)-2×1 termination process by methanol as a terminating reagent at M06-2X/6-311++G(d,p) level

Geometrical parameters analysis

The geometrical parameters of free methanol were first examined, with the C–H and O–H distances observed as 1.09 Å and 0.96 Å, respectively. In the reactant-like intunop (ol1), the hydrogen of –OH interacts with nucleophilic silicon, where the Si–H(O) bond distance is 2.61 Å and the hydrogen associated with the –CH3 group interacts with electrophilic Si center from a distance of 2.61 Å. As the reaction progresses, it was observed that at first the hydrogen of –CH3 becomes detached from the carbon center, while the hydrogen of –OH remains strongly bonded with the oxygen center. From ol1 to ol3, it was observed that the C–H bond distance increases from 1.11 Å to 1.25 Å, whereas for the O–H bond, the enhancement is not prominent. After crossing the TS, the hydrogen of –OH starts to detach, and breakage of both the C–H and O–H bonds occur in parallel until the formation of Si–H bonds is complete in the product-like intunop (ol6). Overall, analyzing the geometrical parameters of the intunop, it can be inferred that methanol dehydrogenation by the silicon surface is also an asymmetrical process, where the Si-surface maintains heterogenic character throughout the reaction. In the product state, the Si–Si distance becomes 2.37 Å, indicating that it becomes single bonded in nature.

NPA charge analysis

To get a clearer picture, we also performed NPA charge analysis. As evident from Table 2, in the separated state the hydrogen of the C–H bond, having less positive charge (0.153), acts like a hydride center, whereas the hydrogen attached to oxygen center, having comparatively more positive charge (0.455), acts like a proton. In the initial intunop state (ol1), the –OH hydrogen becomes more positive (0.475), whereas the positive charge of H(C) decreases (0.142). As the reaction proceeds, Si(C), which was initially positive (0.090 in ol1), tends to form a bond with comparatively less positive hydrogen, i.e., hydrogen of methyl, and the positive charge consequently decreases. On the other hand, the negatively charged Si(O) (−0.313 in ol1) tends to form a bond with the hydrogen of –OH, and, here also, the negative charge decreases with the progress of the reaction. By analyzing the NPA charges, it can be argued that the comparatively higher positively charged hydrogen, i.e., H(O) acts as a proton, whereas the H(C) participates as a hydride in the termination process. Thus, here also, hydrogen abstraction from methanol by the silicon surface is asymmetrical in nature, as the transfer of hydridic hydrogen from –CH3 to electrophilic Si center is much faster than the other half.
Table 2

Geometrical parameters (Å) and NPA charges of the separated reactants, intunop and separated products associated with the Si(100)-2×1 termination process by methanol as a terminating reagent

Geometrical parameters

Geometry

Si-Si

Si-H(C)

Si-H(O)

C-H

O-H

C-O

 Si-dimer

2.19

 CH3OH

1.09

0.96

1.41

 ol1

2.22

2.61

2.61

1.11

0.97

1.40

 ol2

2.24

2.07

2.31

1.13

0.98

1.38

 ol3

2.30

1.78

1.94

1.25

1.05

1.32

 TS

2.30

1.65

1.76

1.41

1.23

1.28

 ol4

2.31

1.58

1.63

1.50

1.38

1.26

 ol5

2.31

1.50

1.48

1.63

1.60

1.23

 ol6

2.33

1.47

1.46

1.94

2.01

1.20

 Hydrogenated Si-dimer

2.37

1.49

1.49

 CH2O

1.26

NPA charge

Geometry

Si(C)

Si(O)

H(C)

H(O)

C

O

 Si-dimer

−0.044

−0.166

 CH3OH

0.153

0.455

−0.200

−0.738

 ol1

0.090

−0.313

0.142

0.475

−0.191

−0.735

 ol2

0.053

−0.346

0.105

0.480

−0.143

−0.723

 ol3

0.078

−0.351

0.021

0.426

−0.027

−0.735

 TS

0.072

−0.266

−0.053

0.285

0.086

−0.693

 ol4

0.069

−0.169

−0.089

0.165

0.136

−0.655

 ol5

0.058

−0.036

−0.124

0.029

0.197

−0.606

 ol6

0.026

0.018

−0.131

−0.026

0.265

−0.557

 Hydrogenated Si-dimer

0.009

0.009

−0.075

−0.075

 CH2O

0.279

−0.511

Conclusions

In summary, we have conducted a DFT study to explore the termination process of Si(100)-2×1 surface through the dehydrogenation of methylamine and methanol. To explore the mechanism in detail, we have also performed the bonding evaluation by analyzing the geometrical parameters and NPA charge associated with each intunop. When methylamine and methanol are used as terminating reagents, we found two types of adsorption mode on the Si(100)-2 × 1 surface, namely chemisorption and physisorption modes. Because the orientation of methylamine on the Si-surface in the physisorption mode is suitable for undergoing dehydrogenation, prior to the surface termination process, the chemisorption mode is transformed to the physisorption mode. From NPA charge calculations, it is evident that the hydrogen attached to nitrogen/oxygen is abstracted by the silicon surface as a proton, whereas the hydrogen of the methyl is transferred to the silicon surface as hydride. From bonding evaluation, it was noted that the hydrogen abstraction processes are asymmetrical in nature, with hydride transfer occurring first followed by proton transfer on the silicon surface. In brief, the present work will motivate researchers to investigate the activity of different semiconductor surfaces as well as their termination processes in future.

Notes

Acknowledgments

T.D. and T.A. are thankful to Council of Scientific and Industrial Research (CSIR) and S.S. is thankful to the University Grants Commission (UGC) for providing them with research fellowships.

Supplementary material

894_2018_3809_MOESM1_ESM.docx (195 kb)
ESM 1 (DOCX 195 kb)

References

  1. 1.
    Bent SF (2002) Surf Sci 500:879–903CrossRefGoogle Scholar
  2. 2.
    Filler MA, Bent SF (2003) Prog Surf Sci 73:1–56CrossRefGoogle Scholar
  3. 3.
    Lu X, Lin MC (2002) Int Rev Phys Chem 21:137–184CrossRefGoogle Scholar
  4. 4.
    Whaley SR, English DS, Hu EL, Barbara PF, Belcher AM (2000) Nature 405:665–668CrossRefGoogle Scholar
  5. 5.
    Loscutoff PW, Bent SF (2006) Annu Rev Phys Chem 57:467–495CrossRefGoogle Scholar
  6. 6.
    Peelle BR, Krauland EM, Wittrup KD, Belcher AM (2005) Langmuir 21:6929–6933CrossRefGoogle Scholar
  7. 7.
    Estephan E, Larroque C, Cuisinier FJG, Bálint Z, Gergely C (2008) J Phys Chem B 112:8799–8805CrossRefGoogle Scholar
  8. 8.
    Lopez A, Heller T, Bitzer T, Richardson NV (2002) Chem Phys 277:1–8CrossRefGoogle Scholar
  9. 9.
    Ardalan P, Davani N, Musgrave CB (2007) J Phys Chem C 111:3692–3699CrossRefGoogle Scholar
  10. 10.
    Hamers RJ, Hovis JS, Lee S, Liu H, Shan J (1997) J Phys Chem B 101:1489–1492CrossRefGoogle Scholar
  11. 11.
    Kasemo B (2002) Surf Sci 500:656–677CrossRefGoogle Scholar
  12. 12.
    Buriak JM (2002) Chem Rev 102:1271–1308CrossRefGoogle Scholar
  13. 13.
    Ulman A (1996) Chem Rev 96:1533–1554CrossRefGoogle Scholar
  14. 14.
    Maboudian R (1998) Surf Sci Rep 30:207–269CrossRefGoogle Scholar
  15. 15.
    Linford MR, Chidsey CED (1993) J Am Chem Soc 115:12631–12632CrossRefGoogle Scholar
  16. 16.
    Faber EJ, de Smet LCPM, Olthuis W, Zuilhof H, Sudhölter EJR, Bergveld P, van den Berg A (2005) ChemPhysChem 6:2153–2166CrossRefGoogle Scholar
  17. 17.
    Liu YJ, Yu HZ (2003) ChemPhysChem 4:335–342CrossRefGoogle Scholar
  18. 18.
    Scheibal ZR, Xu W, Audiffred JF, Henry JE, Flake JC (2008) Electrochem Solid-State Lett 11:K81–K84CrossRefGoogle Scholar
  19. 19.
    Kilian KA, Böcking T, Gaus K, Gal M, Gooding JJ (2007) Biomaterials 28:3055–3062CrossRefGoogle Scholar
  20. 20.
    Zhu XY, Houston JE (1999) Tribol Lett 7:87–90CrossRefGoogle Scholar
  21. 21.
    Liu Q, Hoffmann R (1995) J Am Chem Soc 117:4082–4092CrossRefGoogle Scholar
  22. 22.
    Konečný R, Doren DJ (1997) J Chem Phys 106:2426–2435CrossRefGoogle Scholar
  23. 23.
    Collin M, Joseph HH, Wang GT, Musgrave CB, Bent SF (2002) J Am Chem Soc 124:4027–4038CrossRefGoogle Scholar
  24. 24.
    Addamiano A, Klein PH (1984) J Cryst Growth 70:291–294CrossRefGoogle Scholar
  25. 25.
    Shibahara K, Nishino S, Matsunami H (1986) J Cryst Growth 78:538–544CrossRefGoogle Scholar
  26. 26.
    de Smet LCPM, Zuilhof H, Sudhölter EJR, Lie LH, Houlton A, Horrocks BR (2005) J Phys Chem B 109:12020–12031CrossRefGoogle Scholar
  27. 27.
    Sieval AB, Opitz R, Maas HPA, Schoeman MG, Meijer G, Vergeldt FJ, Zuilhof H, Sudhölter EJR (2000) Langmuir 16:10359–10368CrossRefGoogle Scholar
  28. 28.
    Qu YQ, Li J, Han KL (2004) J Phys Chem B 108:15103–15109CrossRefGoogle Scholar
  29. 29.
    Lee JY, Kim S (2001) Surf Sci 482–485:196–200CrossRefGoogle Scholar
  30. 30.
    Romero AH, Sbraccia C, Silvestrelli PL, Ancilotto F (2003) J Chem Phys 119:1085–1092CrossRefGoogle Scholar
  31. 31.
    Debnath T, Sen K, Ghosh D, Banu T, Das AK (2015) J Phys Chem A 119:4939–4952CrossRefGoogle Scholar
  32. 32.
    Cho J, Choi CH (2008) J Phys Chem C 112:6907–6913CrossRefGoogle Scholar
  33. 33.
    Zhang L, Carman AJ, Casey SM (2003) J Phys Chem B 107:8424–8432CrossRefGoogle Scholar
  34. 34.
    Zhou JG, Hagelberg F, Xiao C (2006) Phys Rev B 73:155307CrossRefGoogle Scholar
  35. 35.
    Lee JH, Cho JH (2007) Phys Rev B 76:125302CrossRefGoogle Scholar
  36. 36.
    Bae SS, Kim KJ, Lee HK, Lee H, Kang TH, Kim B, Kim S (2010) Langmuir 26:1019–1023CrossRefGoogle Scholar
  37. 37.
    Hahn JR, Jang SH, Jeong S (2010) J Phys Chem C 114:17761–17767CrossRefGoogle Scholar
  38. 38.
    Kato T, Kang SY, Xu X, Yamabe T (2001) J Phys Chem B 105:10340–10347CrossRefGoogle Scholar
  39. 39.
    Naitabdi A, Bournel F, Gallet JJ, Markovits A, Rochet F, Borensztein Y, Silly MG, Sirotti F (2012) J Phys Chem C 116:16473–16486CrossRefGoogle Scholar
  40. 40.
    Carman AJ, Zhang L, Liswood JL, Casey SM (2003) J Phys Chem B 107:5491–5502CrossRefGoogle Scholar
  41. 41.
    Cho J, Choi CH (2011) J Chem Phys 134:194701CrossRefGoogle Scholar
  42. 42.
    Davies BM, Craig JH (2003) Surf Interface Anal 35:1060–1064CrossRefGoogle Scholar
  43. 43.
    Wang Y, Hwang GS (2004) Chem Phys Lett 385:144–148CrossRefGoogle Scholar
  44. 44.
    Wang GT, Mui C, Tannaci JF, Filler MA, Musgrave CB, Bent SF (2003) J Phys Chem B 107:4982–4996CrossRefGoogle Scholar
  45. 45.
    Ferguson GA, Das U, Raghavachari K (2009) J Phys Chem C 113:10146–10150CrossRefGoogle Scholar
  46. 46.
    Ardalan P, Dupont G, Musgrave CB (2011) J Phys Chem C 115:7477–7486CrossRefGoogle Scholar
  47. 47.
    Konecny R, Doren DJ (1997) J Phys Chem B 101:10983–10985CrossRefGoogle Scholar
  48. 48.
    Sniatynsky R, Janesko BG, El-Mellouhi F, Brothers EN (2012) J Phys Chem C 116:26396–26404CrossRefGoogle Scholar
  49. 49.
    Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE et al (2009) Gaussian 09, Revision D.01. Gaussian, Inc., WallingfordGoogle Scholar
  50. 50.
    Zhao Y, Truhlar D (2006) J Chem Phys 125:194101–194118CrossRefGoogle Scholar
  51. 51.
    Zhao Y, Truhlar D (2008) Theor Chem Accounts 120:215–241CrossRefGoogle Scholar
  52. 52.
    Ferguson GA, Ramabhadran RO, Than CTL, Paradise RK, Raghavachari K (2014) J Phys Chem C 118:8379–8386CrossRefGoogle Scholar
  53. 53.
    Gonzalez C, Schlegel HB (1989) J Chem Phys 90:2154–2161CrossRefGoogle Scholar
  54. 54.
    Gonzalez C, Schlegel HB (1990) J Phys Chem 94:5523–5527CrossRefGoogle Scholar

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  • Tanay Debnath
    • 1
  • Tamalika Ash
    • 1
  • Subhendu Sarkar
    • 1
  • Abhijit Kr. Das
    • 1
    Email author
  1. 1.School of Mathematical & Computational SciencesIndian Association for the Cultivation of ScienceKolkataIndia

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