Peer review of: Spatial defects nanoengineering for bipolar conductivity in MoS2 (2020)

Reviewers' comments: 

Reviewer #1 (Remarks to the Author): 

Calò et al report defects engineering in MoS2 flakes using thermochemical scanning probe 
lithography assisted with reactive gas, which can form either p- or n-type semiconductors. 
Understanding the formation nature of defects in 2D materials and their active control are of 
crucial importance for engineering different properties. Oxidation scanning probe lithography has 
also been reported to pattern MoS2 transistors (APPLIED PHYSICS LETTERS 106, 103503, 2015). 
This application of using thermochemical scanning probe lithography for creating defects in MoS2 
is new and gives different types of defects. The authors further applied XPS and DFT to give a 
molecular level understanding for the nature of these defects. Overall, to the reviewer, this work 
presents a good approach for engineering defects in MoS2 and controlling its electrical 
performance. However, the introduction and discussion are not clear to deliver the main 
contribution and novelty of the current work. Most importantly, although approaches like KPFM and 
DFT have been introduced, the current work lacks of high resolution characterization to support its 
conclusion about the atomic nature for the defects. The thermochemical scanning probe 
lithography approach for defect creation is similar to STM based method for engineering defects. 
The current way has advantages of higher throughput, but lacks of nanoscale resolutions. The 
authors need to compare this approach with STM tip induced electrochemical reaction, electron 
beam and laser induced defect patterning. Relevant references should be discussed. My detailed 
comments are listed below. 
The height profile of AFM image in Figure 1b needs to be provided to compare the thickness 
fluctuations of these layers. 
HR-TEM is suggested to image the atomic nature of the formed defects, where chemical structure 
can be easily revealed from the imaging contrast (Nat. Commun. 6:6293, 2015). The experiments 
are able to provide direct evidence for the main claims made in the XPS and DFT conclusion. 
Electrical measurements of n-type MoS2 made from N2–tc-SPL shall be shown in the current work 
to give the difference between patterned MoS2 and ‘natural’ n-type MoS2 (without treatment). For 
the diode junction in Figure 2, the reviewer believes the authors used unpatterned MoS2 flake as 
the n channel. This figure can be improved by using both HCl/H2O-tc-SPL and N2–tc-SPL 
patterned junction, and a higher rectification ratio can be expected. 

DFT calculation has large errors in correlating the results. The XPS result in Figure 3 does not 
involve the substitution of oxygen atoms. 
Why HCl/H2O/N2 has be preferentially chosen in the experiments. Its role in the thermochemical 
reactions needs to be further explored. Is there any other gas to be tested to demonstrate the 
controllability of this approach. 
The patterned density and spatial distribution of defects in MoS2 are not discussed in the current 
manuscript. 


Reviewer #2 (Remarks to the Author): 

In this article, the Authors report the realization of differently doped MoS2 layers with integration 
in a diode. One of the strengths of this approach is the experimental approach that may have 
potentials for better scalability with respect to other top-down methods. In my opinion this 
demonstration will serve as a basis for future developments along the area. 
The Authors supplement their work by a joint experimental and theoretical surface science analysis, 
reproducing in a controllable way the main findings achieved under less-controlled but more 
realistic conditions. This apparently suggests the main mechanisms beyond formation of p/n 
character. Especially the case of p-doped samples is discussed with detail, and atomistic models 
are proposed on the basis of XPS measurements and ab initio DFT simulations. 
The work appears to be robust and presented clearly and at a sufficient level of detail, with 
extensive use of references. There appear that the discussion of the nature of defects deserves 
some improvement and I recommend publication upon addressing the following comments: 

(1) The agreement between measured and calculated core level shifts (Fig.4e) is over-emphasized. 
It is clear that many model structures could be proposed, and that the Authors necessarily focus 
on few, and that the trend is in nice agreement, yet the computed values may double the 
experimental ones and no comment on this issue is provided. 

(2) The link of the DOS of Fig.4a-c with the p-character is not clear. What is the reader expected 
to look at? The fact that some DOS extends from the VB to the Fermi or slightly above? If so, is 
this robust with respect to the broadening scheme taken? The nature of the states at about the 
Fermi energy is not commented, and could be elucidated by projected DOS/bands as well as wave 
function amplitudes. And in the text, "the charge redistribution shows that each S atom at the 
surface", "at" means "above", I presume. 

(3) A much lower level of detail is provided for the structures of the n-doped samples. This is 
imputed to MoO3 species, but I recommend the Author provide additional explanation on the lines 
of the previous section, or in case state why this cannot be given. Do the Authors implicitly 
assume the additional O is imputed to come from the SiO2 substrate? What are the evidences? 
What is the nature of the states shown in Fig 

Various: 

Calculations: The cutoff of 100Ry is for the charge density, or for the wave function? What is the 
vacuum size in the simulation cell? How is the Brillouin zone sampled? Reporting the n x m lateral 
size would also be helpful. Do all calculation require spin polarization? 

Last line of page 3, just before Eq.(1): Ref35 would be more direct here than Ref34. 

At page 7, "(see Fig. S7 of the Supplementary Information)" should be Fig. S6. 

Figure 4f currently replicates Figure 3. Units are missing in the y-axes of the DOS in Fig.4. 

Supplementary Fig.S10 misses color scheme for the atoms. 



Reviewer #3 (Remarks to the Author): 

The authors use the thermochemical scanning probe lithography technique in presence of a 
reactive gas to achieve nanoscale control of the local thermal activation of defects in monolayer 
MoS2. The nanopatterns “drawn” by means of the above-mentioned technique can give rise to 
either p- or n-type conductivity on demand, depending on the reactive gas, therefore allowing to 
fabricate p-n junctions with a given precision and spatial control. Doping and defects formation 
mechanisms are studied by means of XPS and DFT, while the work function shift was measured by 
KPFM. 
Indeed, this work reports on quite fascinating findings with potential technological relevance but 
some major revisions are needed: 
1. The authors report the results of the electrical characterization only when p-type regions are 
patterned. 
In addition, they should characterize ELECTRICALLY the following cases: 
a. An FET device whose active area is an only n-doped region (please, report mobility and Vth) 
b. An FET device whose active area is an only p-doped region (please, report mobility and Vth) 
In case a. and b. the authors should also report the measured mobility and threshold voltage 
values and correlate them with the already-measured XPS, KPFM and DFT results. 
2. The Id-Vg curves in Figure 2 (especially 2b) should be plotted in logarithmic scale on the Y axis. 
As well, mobility and threshold voltage values must be calculated for devices in Figure 2a and 2b, 
respectively. The value of the threshold voltage should be related to doping and number of 
induced defects. 
3. The p-n device in Figure 2b is made by thermal “drawing” of a p-type region with respect to an 
otherwise n-type pristine region. How would the device characteristics change in Fig 2b with 
changing the p-type/n-type region in the channel? The authors should try to perform such an 
experiment. 
4. It would be preferable to have more details on reactive gas concentration in the tested cell. This 
piece of information would make the experiment easily reproducible in other laboratories.