Wet Chemical Method for Black Phosphorus Thinning and Passivation

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Functional Inorganic Materials and Devices

A wet chemical method for black phosphorus thinning and passivation Shuangqing Fan, Jingsi Qiao, Jiawei Lai, Haicheng Hei, Zhihong Feng, Qiankun Zhang, Daihua Zhang, Sen Wu, Xiaodong Hu, Dong Sun, Wei Ji, and Jing Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b21655 • Publication Date (Web): 11 Feb 2019 Downloaded from http://pubs.acs.org on February 11, 2019

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ACS Applied Materials & Interfaces

A wet chemical method for black phosphorus thinning and passivation 1

Shuangqing Fan#, 2JingSi Qiao#, 3Jiawei Lai, 1Haicheng Hei, 1Zhihong Feng, 1Qiankun Zhang,

1

Daihua Zhang, 1Sen Wu, 1Xiaodong Hu, 3Dong Sun, 2Wei Ji* and 1Jing Liu*

1

State Key Laboratory of Precision Measurement Technology and Instruments, School of

Precision Instruments and Opto-electronics Engineering, Tianjin University, No. 92 Weijin Road, Tianjin, 300072, China 2

Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Material &

Micro-Nano Devices, Renmin University of China, Beijing 100872, China 3

International Center for Quantum Materials, School of Physics, Peiking University, No. 5

Yiheyuan Road, Beijing 100871, China

*Corresponding author emails: [email protected] and [email protected] #

These authors contributed equally to this work.

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Abstract Layered black phosphorus (BP) has been expected to be a promising material for future electronic and optoelectronic applications since its discovery. However, the difficulty in mass fabricating layered air-stable BP severely obstructs its potential industry applications. Here, we report a new BP chemical modification method to implement all-solution based mass production of layered air-stable BP. This method uses the combination of two electron-deficient

reagents

of

2,2,6,6-tetramethylpiperidinyl-N-oxyl

(TEMPO)

and

triphenylcarbenium tetrafluorobor ([Ph3C]BF4) to accomplish thinning and/or passivation of BP in organic solvent. The field effect transistor and photo detection devices constructed from the chemically modified BP flakes exhibit enhanced performances with environmental stability up to four months. A proof-of-concept BP thin film transistor fabricated through the all-solution based exfoliation and modification displays air-stable and typical p-type transistor behavior. This all-solution based method improves the prospects of BP for industry applications. Keywords: black phosphorus, covalent functionalization, chemical thinning, TEMPO, triphenylcarbenium tetrafluorobor


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Introduction Black phosphorus (BP) has attracted tremendous attentions since its discovery because of its thickness tunable band gap covering from visible to mid-infrared wavelength,1-3 high carrier mobility up to 20000 cm2/(V·s)4 and anisotropic properties.3-6 These fascinating properties make it a very promising semiconducting material for the next generation optoelectronics applications including nano-electronic devices/circuit,7 solar cells,8 photodetectors,9 and batteries.10 Nevertheless, the difficulty in mass production of layered air-stable BP has significantly hindered the development of BP in both fundamental research 11 and potential practical applications.12 So far, many efforts have been made to produce layered air-stable BP,13-17 which usually include several sequential steps of exfoliation, thinning and passivation. Two major methods to exfoliate atomic-layer-thin BP flake from its bulk counterpart are mechanical and solution-based exfoliations. Since both methods can hardly control the thickness of the prepared samples precisely, which plays an important role in determining its electrical and optical properties, additional thinning processes are usually applied. Mechanically exfoliated BP samples can be further thinned down by several physical thinning methods using plasma,13,18 laser19 and thermal annealing.20 which have been reported with high thinning rate and surface quality. For liquid-exfoliated samples, centrifugation is used to roughly separate flakes by thickness and size.21 Besides, BP forms oxides with oxygen in the air, which in turn absorbs water molecules to form phosphoric acid. Hence, passivation of BP is also extremely necessary, since BP actively reacts with species in air.22 The passivation methods are generally divided into two categories: using native oxide or a protective capping layer. The native oxide layer of P2O5 can be induced on top of BP by various well-controlled methods,13 while the protective capping layers include 2D materials, metal oxide, solvents, and inorganic molecules by transferring,23-25 atomic layer deposition (ALD),15,26-27 self-assembly17 and covalent functionalization14,16 approaches. Although they can successfully fabricate individual layered air-stable BP flakes, it is quite difficult for these reported methods to mass produce layered BP with environmental stability, which is of essential importance for industry applications. The bottleneck(s) may lie in the following two aspects: (1) low through-put of



one (or more) of these procedures, which may include mechanical exfoliation, physical thinning, and transferring protective layer; and (2) incompatibility among these procedures, for example mass produced BP flakes by liquid exfoliation are neither readily to be mass thinned by plasma/laser nor passivated by transferring or atomic layer depositing protective layer. Therefore, a manufacturing process comprising procedures that are all high through-put and compatible with each other is extremely desirable for flourishing BP in industry applications. In this work, we demonstrate an all-solution based method to mass produce layered air-stable BP, which is enabled by a new BP chemical modification method. This method implements BP thinning and passivation in the modification solution consisting of two electron-deficient organic reagents of 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) and triphenylcarbenium tetrafluorobor ([Ph3C]BF4), the former and latter of which have been reported to be grafted on graphene

28-32

and as a commonly used oxidant,33 respectively. The concentration of

[Ph3C]BF4 in the modification solution plays an important role in determining BP to be either thinned (high concentration) or passivated (low concentration). Here, we used dichloromethane and mixture of acetone and water (V:V=1:1) as the solvents to realize high and low concentration of [Ph3C]BF4 in the modification solution, and thus BP thinning and passivation, respectively. Consequently, we can accomplish BP exfoliation, thinning, and passivation all in liquid phase, and thus, mass production of layered air-stable BP. The chemical thinning shows very high selectivity towards BP with a comparable thinning rate of 2 min per layer to physical thinning.18The chemically thinned BP flake preserves high lattice crystalline confirmed by Raman spectroscopy and high-resolution transmission electron microscopy (HR-TEM), which improves the performance of field-effect transistor (FET) achieving Ion/Ioff ratio of ∼106, carrier mobility of 760 cm2/(V·s) and subthreshold swing of 0.44 V per decade at room temperature. On the other hand, the passivated BP exhibits increased p-type doping and no measurable morphological changes by atomic force microscopy (AFM) after four months of ambient exposure and comparable light responsivity to bare BP devices. Furthermore, an air-stable BP thin film transistor (TFT) is fabricated by all-solution based exfoliation and modification process, which shows typical p-type transistor


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behavior. In general, the all-solution based process is shown to facilitate the mass production of layered air-stable BP, and therefore boost its applications in industry.

Results Chemical thinning. Figure 1a and b are the AFM images of a BP sample transferred on SiO2/Si substrate before and after being immersed in chemical thinning solution composed of 10 mM TEMPO and 10 mM [Ph3C]BF4 in dichloromethane for 30 minutes, respectively. After chemical thinning, the thickness of the BP flake decreases from 10.6 nm to 2.7 nm. HR-TEM and the corresponding SAED pattern (as shown in Figure 1c and d) confirm the lattice structure integrity of the chemically thinned BP. We estimated the chemical thinning rate to be approximately 2 min per layer, by measuring the thickness differences of the BP samples before and after chemical thinning through AFM for a set of time durations (presented in Figure 1f), which is comparable to physical thinning methods.18 Various concentration combinations of TEMPO and [Ph3C]BF4 were also tried to figure out the optimum chemical thinning recipe (Figure S1-S4). Figure 1e shows the real-time Raman spectra of a BP flake during chemical thinning, in which the central frequencies of the three signature peaks, labeled as A1g , B2g and A2g , are consistent with mechanically exfoliated BP flakes.18,22 However, as the BP thickness decreases, the central frequency of A2g red shifts slightly due to the Davydov splitting,22 the shifting values of which are around 0.8, 1.3, and 2.5 cm-1 after being thinned for 80, 90,100 min, respectively. The full width at half maximum of all three signature peaks also increases as thickness decreases because of the increased freedom of the P atoms.22 We further examined the oxidation level of the BP sample after each chemical thinning cycle by measuring the peak integration ratio of A1g /A2g which are all greater than 0.38 (Figure 1g) indicating low oxidation levels.22 It is worth mentioning that chemical thinning possesses greatly enhances selectivity as compared to physical thinning. Three representative materials of graphene, MoS2 and Au electrode on SiO2/Si substrate were immersed in the same chemical thinning solution for 2 hours, after which their thicknesses remained the same (Figure S6).



Figure 1. Characterization of chemically thinned BP. AFM images of a BP flake that was (a) as-exfoliated and (b) thinned for 30 min. Scale bars: 1 μm. (c) HR-TEM image (scale bars: 2 nm) and (d) SAED pattern (scale bars: 5 1/nm) of the thinned BP flake. (e) Raman spectra of a BP flake after various thinning durations. (f) Thinned thicknesses of BP flakes as a function of the thinning duration. (g) Ratio of 𝐀𝟏𝐠 /𝐀𝟐𝐠 peak integration as a function of thinning duration. A ratio value greater than 0.2 indicates low oxidation level.

Chemically thinned BP FET. A mechanically exfoliated BP flake was transferred onto SiO2/Si substrate (SiO2 layer is 285 nm thick) (see Figure 2a) and immersed in 10 mM TEMPO and 10 mM [Ph3C]BF4 in dichloromethane for 30 min, during which the BP flake was thinned from 10 nm to 4 nm (shown in Figure 2b). Finally, the fabricated FET as presented in Figure 2c was tested in ambient environment. In the output curve of the FET shown in Figure 2d, the current Ids changes linearly and symmetrically with source/drain bias, suggesting an Ohmic contact between electrode and BP. The transfer curve in Figure 2e exhibits p-type dominant behavior which may attribute to the adsorption of metastable oxygen on the surface.34 This device not only has a decent hole mobility of 760 cm2/ (V·s) and Ion/Ioff current modulation of ~106 (the hole mobility and on-off ratio may varied 760 to 265.7 cm2/ (V·s) and from 106 to 2×105, respectively, for different devices as shown in Figure S7), but also achieves an ultralow subthreshold swing of ~0.44 V/decade, in comparison with previously reported subthreshold swing of BP FETs ranging from 1.5 to 17.2 V/decade.35 Possible


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reasons for achieving low subthreshold swing may due to the following aspects: (1) chemical thinning can remove the residual glue on BP surface (marked as light blue circles in Figure S8), (2) the wrinkles (marked as green circles in Figure S8) on BP flake can be expanded and flattened when it is immersed in the solution, and consequently the thinning solution can

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Figure 2. Characterization of chemically thinned BP FET. Optical microscopy images of (a) a bare BP flake on SiO2/Si, and (b) the same BP flake after being thinned for 30 min. Scale bars: 10 μm. (c) The fabricated BP FET. Scale bar: 4 μm. (d) Output characteristics of the device in (c) under various gate bias. (e) Transfer characteristic of the device in (c). The insert is the transfer characteristic of an un-thinned BP FET.

penetrate into the interface between BP and SiO2/Si substrate to remove the oxidized layer,35 (3) chemical thinning results in improved surface quality, such as less defects, than physically thinned samples. Chemical passivation. Figure 3a and b show the AFM images of a BP flake (3.2 nm thick) immediately and 120 days after chemical passivation, which is implemented by immersing the sample in chemical passivation solution composed of 10 mM TEMPO and 10 mM [Ph3C]BF4 in the mixture of acetone and water (V:V=1:1) for 12 hours. After being exposed under ambient condition for four months, the passivated BP flake shows no morphology



changes demonstrated by almost the same surface roughness of 0.656 nm (Figure 3a) and 0.676 nm (Figure 3b). In contrast, Figure 3c and d present the AFM images of a bare BP flake (5.1 nm thick) after being freshly exfoliated and exposed under ambient environment for 1 day, respectively. Drastically morphology change is observed and the surface roughness increases considerably from 0.357 nm (Figure 3c) to 6.26 nm (Figure 3d). Raman spectroscopy is further used to assess the air-stability and lattice crystalline of the passivated BP under air condition. In Figure 3e, the intensities of three signature peaks of functionalized BP flake keep almost unchanged after being exposed to air for 120 days, again indicating its excellent air-stability. On the contrary, the intensities of the A1g , B2g peaks of bare BP in Figure 3g decrease significantly after being exposed to air for just one day. We also investigated the transfer characteristics of a BP FET after chemical modification, which shows increased p-type doping as increased immersing time (as shown in Figure S14).

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Figure 3. Characterization of passivated BP. AFM images of (a) functionalized BP flake and (b) the same BP flake exposed under ambient environment for 120 days. AFM images of (c) freshly exfoliated BP flake and (d) the same BP flake exposed under ambient environment for 1 day without any passivation. (e) Raman spectra of the BP flake in (a) (black line) and (b) (red line). (f) Raman spectra of the BP flake in (c) (black line) and (d) (red line). Scale bars are 1 μm.

Chemically passivated BP photodetector. A mechanically exfoliated BP flake was transferred onto a SiO2/Si substrate and immersed in chemical passivation solution for 12 hours. The fabricated FET device presented in Figure 4a was characterized by spatially resolved scanning photocurrent microscopy (SPCM) under ambient environment. Figure 4c/e


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and d/f show the room temperature SPCM images of the device under laser illumination at 632.8 nm/800 nm with laser power of 400 mW, after 0 day and 30 days exposure to air, respectively. With both wavelengths, the photon response patterns of the device are similar indicating the current generation is mainly around the interface between the sample and the metal electrode, where the built-in electric field exists to efficiently separate the photo-excited electron-hole pairs. The responsivities of the device at the maximum response position are calculated to be 1.25 mA/W and 0.26 mA/W for 632.8 nm and 800 nm excitations, respectively, which is fairly good considering that the device was immersed in chemical passivation solution for 12 hours, and the responsivity was derived from a 2-μm spot size. After 30 days ambient exposure, the device remains the same responsivity of 1.25 mA/W under 632.8 nm excitation, while the responsivity decreases slightly from 0.26 mA/W to 0.14 mA/W under 800 nm excitation. These results demonstrate that the chemical passivation not only enables BP long-term stability under ambient environment but also successfully preserves its efficient light response. Therefore, chemical passivation may be a promising route to fabricate air-stable BP devices for environmental interactive applications.

Figure 4. Photocurrent measurements of the chemically passivated BP FET. (a) Schematic diagram of the SPCM setup. (b) Optical microscopy image of the passivated BP FET (10 nm thick). Scale bar: 20 mm. SPCM images of the BP FET under 400 mW laser illumination at (c) 632.8 nm and (d) 800 nm. SPCM images of the same BP FET exposed under ambient environment for 30 days under 400 mW laser illumination at (e) 632.8 nm and (f) 800 nm. Scale bars in (c)-(f): 8 μm.



BP TFT. We accomplished all-solution based mass production of layered air-stable BP and fabricated a proof-of-concept BP TFT. Bulk BP material was first exfoliated through ultra-sonication in the mixture of acetone and water (V:V=1:1). The resultant dispersion was centrifugated under 2000 rpm for 30 min. Top 80% of the suspension was collected for further modification by adding 10 mM TEMPO and 10 mM [Ph3C]BF4 in the dispersion. After being placed under room temperature overnight, the suspension was filtered through an ester membrane, resulting in a thin layer of BP film deposited on the top which is thoroughly washed by acetone and IPA before transfer. Figure 5a and b show the semi-transparent and flexible BP thin film transferred onto a polydimethylsiloxane substrate. We also fabricated BP TFTs by transferring the BP thin films onto a SiO2/Si substrate with pre-fabricated interdigitated electrodes as shown in Figure 5c. The transfer characteristic of the modified BP TFT (Figure 5e) shows a typical p-type transistor behavior which remains almost the same after two weeks ambient exposure. In contrast, another BP TFT, made from the same process except without chemical modification, shows an ambipolar transfer characteristic (Figure 5d), which deteriorates rapidly within one week, resulting in a complete loss of switching property. We further compare the source-drain current of three modified and three non-modified BP TFTs as plotted in Figure 5f. Initially, all TFTs have similar channel current ranging from several to several tens of mA. As time progresses, the modified BP TFTs keep the channel current variation within one order of magnitude for two weeks, while the non-modified BP TFTs have their channel current drop drastically by around six orders of magnitude within a week.


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Figure 5. Characterization of BP TFT device. (a,b), Optical microscopy image of air-stable BP thin film fabricated by all-solution based process on PDMS substrates. (c), SEM images of fabricated BP TFT. The BP thin film was deposited across the source (S) and drain (D) electrodes. Transfer characteristics of BP TFTs made from (d) non-modified BP thin film and (e) modified BP thin film, over the course of ambient exposure. (f), Source-drain current of chemically passivated BP TFTs (lines in pink green and grey) and bare BP TFTs (lines in black, red and blue) versus ambient exposure time.

Discussion In order to investigate the working mechanism of the chemical thinning and passivation, we carried out further experiments, including density functional theory (DFT) calculations, Raman, AFM, X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) spectroscopy. The DFT calculation was carried out to model the bonding of TEMPO molecules on BP surface. Initially, we used TEMPO in Configuration B1 adsorbed on a 2L BP as an exemplary structure, since Configuration B1 is the most stable configuration of TEMPO adsorbed on the non-oxidized BP surface among all possible product structures (see Figure S20-21). On a pristine BP surface, the lone electron pair of an uncharged P atom repulses the dangling bond of TEMPO, making TEMPO weakly chemisorbed or physisorbed on the BP surface (length and adsorption energy of P-O bond between P0 atom and TEMPO are 2.84 Å and -0.85 eV, respectively) as shown in Figure 6a, leading to unsuccessful passivation. However, when TEMPO molecules are adsorbed on BP with P vacancies (Figure 6b) or locally oxidized (Figure 6c), the nearest P-O bonds shortens to 1.75 Å /1.67 Å, and the adsorption energy



decreases to -1.22 eV/-2.11 eV, respectively (see more information in Figure S22-23). These results indicate that the lowered local electron density may substantially reduce the repulsion or even favor attractive interactions between the dangling bonds of TEMPO and lone electron pair of BP.

Figure 6. DFT modeling for BP thinning and passivation mechanisms. (a) Geometric structure of TEMPO physically adsorbed on pristine BP surface. (b) Geometric structure of TEMPO adsorbed on BP surface, when P0 atom is oxidized by 1.0 e. P0 is the phosphorus atom closest to O atom on TEMPO. (c) Geometric structure of TEMPO connects to P vacancy. The distance between P0 and nearest O atom is marked on each panel. (d) Band structure of BP adsorbed with TEMPO when P0 atom is oxidized by 1.0 e. The states of valence band maximum (VBM), conduction band minimum (CBM) and two defect states (DS1 and DS2) are marked. (e-f) Visualized wavefunctions for the VBM and CBM states along xz and yz plane using an isosurface of 0.00025 e bohr-3.

We then proposed two possible free radical mechanisms for the chemical modification: Path A and B, as shown in Figure 7. Path A corresponds to free radical addition reactions induced by TEMPO incorporated with Ph3C+. Firstly, TEMPO molecules undergo free radial addition to BP surface, while Ph3C+ breaks neighboring P-P bonds subsequently. Consequently, TEMPO molecules take away P atoms from BP matrix and create P vacancies on BP. Then, the exposed P radicals on BP surface further capture TEMPO molecules. When the reactions take


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place in the solvent of water/acetone (V:V=1:1), the formation rate of P vacancies is controllable because the concentration of Ph3C+ can be reduced to very low level by the hydrolysis reaction between Ph3C+ and water. As a result, the TEMPO molecules adsorbed on P vacancies protect BP surface from further oxidization. On the other hand, when dichloromethane is used as solvent, the concentration of Ph3C+ is too high to control the formation of P vacancies, which leads to the collapse of BP surface (thinning of BP). Path B corresponds to TEMPO radical covalently functionalized on the oxidized BP surface. As [Ph3C]+ and O2 in the solution oxide BP, TEMPO molecules can be chemisorbed on the oxidized BP surface (BP radical). The existence of ionic fluorine (demonstrated in Figure S9) keeps the system electrically neutral and stabilizes the TEMPO-BP compound. When water/acetone (V:V=1:1) is used as the solvent, the low concentration of Ph3C+ ensures that the oxidation process is controllable, so that TEMPO molecules are covalently functionalized on BP surface for passivation. When dichloromethane is used as the solvent, the concentration of [Ph3C]+ is high, which oxidizes BP surface quickly, leading to weakened P-P bonds and structural distortion of BP surface (DFT calculations are presented in Figure S27-S31). In this case, TEMPO molecules bond with oxidized P atoms forming TEMPO-P complex. The complex is highly soluble in the organic solvents, which favors the dissociation of surface P atoms from the BP matrix, and thus, layer-by-layer thinning of BP. We propose that BP radical is involved in this mechanism because room-temperature ESR spectrum of BP and Ph3C+ in the solution of water/acetone (V:V=1:1) displays a signal with a g factor of 2.000 (Figure S10).



Figure 7. Schematic of plausible reaction pathways of chemical passivation and thinning mechanisms. We performed AFM and Raman measurements to experimentally demonstrate that BP is functionalized after being treated by TEMPO and [Ph3C]BF4 in water/acetone (V:V=1:1). In the AFM measurement, the thickness of the BP flake increases from 2.5 nm (before) to 3.8 nm after passivation (see Figure S12), which is consistent with the thickness change when BP is functionalized by aryl diazonium.[14] Additionally, the Raman spectrum of the BP flake after passivation exhibits split in the A1g mode corresponding to out-of-plane P atom vibration, [18,22]

(purple line in Figure S13), which potentially indicates the presence of functional groups

attached to the P atoms. We then used XPS to demonstrate the main molecule functionalized on P atoms to be TEMPO, instead of Ph3C·. We prepared bare, passivated and oxidized BP samples for XPS


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measurements, all of which were thoroughly rinsed by IPA and acetone and dried under nitrogen flow before measurements to remove any potential chemical residuals. Figure 8 presents the XPS spectra of bare, passivated and oxidized BP samples, the chemical states of which are probed with core levels of P 2p, C 1s, N 1s, and O 1s. In the N 1s spectrum, two peaks at 399.5 eV and 401.6 eV corresponding to C-N-O bond of TEMPO, emerge in the passivated BP sample, instead of bare and oxidized BP samples, which demonstrates the attachment of TEMPO molecules (other than [Ph3C]BF4) on the passivated BP.30,32 This inference is also confirmed by C1s spectra, in which the peak at 285.5 eV bonding energy is only observed in passivated BP. This peak can be attributed to the C-N bond corresponding to the TEMPO piperidine ring.28,31 Moreover, in the O 1s spectra, an additional peak at 534.2 eV is only observed in passivated BP, which may be assigned to P-O-N bond, as referencing the P-O-H bond position in the XPS spectra of OH functionalized BP prepared by ball-milling.36 The observation of P-O-N bond indicates that the passivated BP is covalent functionalized by TEMPO. Table 1 also lists the concentrations of P, C, N, O elements in each BP sample. It shows that the concentrations of C and N, mainly from TEMPO, in bare and oxidized BP are much lower than in passivated BP. Additionally, the measured N/P concentration ratio of 7.4% for passivated BP is similar to the DFT calculated ratio of 6.3% when TEMPO molecules fully cover BP surface (Figure S25) and the ratio of N/C for TEMPO modified graphene reported in previous literatures,30,31 indicating high level coverage of TEMPO on BP surface. In addition, we tried using [Ph3C]BF4 alone (10 mM in the passivation solution) to treat BP



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flake, after which the treated BP flake degraded after two-day ambient exposure (see Figure

S18b and d). It indicates that the main molecule bonding to and passivating P atom is not likely to be Ph3C·. Figure 8. High-resolution P 2p, C 1s, N 1s, and O 1s XPS spectra of bare BP, passivated BP and oxidized BP. The inset shows structure of the covalent bonding of TEMPO to BP.

Table 1. Element analysis of bare, passivated and oxidized BP. Sample Bare BP Passivated BP Oxidized BP

P (%) 85.95 45.32 29.15

C (%) 9.09 21.84 13.36

N (%) 0.51 3.37 0.72

O (%) 4.45 29.46 56.77

We further conducted several control experiments to demonstrate the proposed mechanisms. Firstly, the AFM (optical) images in Figure S17 (Figure S18) show that the BP flakes cannot be thinned (passivated) when they are immersed in the dichloromethane (water/acetone) with only 10 mM TEMPO or 10 mM [Ph3C]BF4. It demonstrates that thinning (passivation) is the result of combined action of TEMPO and Ph3C+. Secondly, when NMP, IPA and acetone are used as solvent (concentrations of TEMPO and [Ph3C+]BF4 are both 10 mM), the treated BP flakes can be thinned (see Figure S15), but not passivated (degraded within 4 days as shown in Figure S16). In contrast, if the solvent are replaced by water/acetone (V:V=1:1), no obvious degradation sign are found after 20 days exposure in air (see Figure S16). Furthermore, by decreasing the [Ph3C]BF4 concentration to 1 mM and keeping the TEMPO concentration at 1 mM in acetone, the treated BP flake remain stable under ambient condition for 2 days (see


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Figure S19). These results are consistent with the proposed mechanism that the low (high) concentration of [Ph3C]BF4 leads to BP passivation (thinning). Thus, the concentration of [Ph3C]BF4 plays a key role to determine BP to be passivated or thinned. It is also interesting to find that the electronic carrier mobility and other electrical transport properties of BP maintain almost the same after the surface being functionalized by TEMPO. Figure 6d shows the band structures of the Configuration B1 when 2L BP with 1.0 e removed from P0 atom and functionalized with TEMPO. All the defect states reside within either the conduction or valence bands, and over 1.0 eV away from the band edges (Figure S26). Therefore, the main features of VBM and CBM nearly remain (Figure 6e and f), which guarantees the high mobility of TEMPO functionalized BP. These results manifest that TEMPO is a highly promising molecule for BP protection. Conclusion We demonstrate an all-solution process to mass produce layered air-stable BP. This process is enabled by a new chemical modification method for BP by immersing it in modification solution containing both TEMPO and [Ph3C]BF4. Two possible radical mechanisms are proposed based on DFT calculations and various characterizations, which indicates that the concentration of [Ph3C]BF4 determines the solution to either thin down or passivate BP. The chemical thinning attains comparable thinning rate with physical thinning and enhances semiconductor performance of BP, with the fabricated FET possessing improved carrier mobility, on/off ratio and subthreshold swing. The passivated BP leads to increased stability in air up to four months, while preserving its electronic properties and efficient interactivity with light. A BP TFT, fabricated by the all-solution based exfoliation and modification, shows stable and typical p-type transistor behavior under ambient environment. Further research is required to fully understand of the modification mechanisms and further optimization of this method, which is expected to boost the development of high performance BP thin film devices and its industry applications.

Methods Sample characterization. AFM characterization was conducted in tapping mode on a Dimension Icon (Bruker, German). The Raman spectra were obtained with a Renishaw InVia



Raman microscope using a 532 nm laser at ∼1.38 mW power. For both experiments, the mechanically exfoliated BP flakes were transferred on a SiO2/Si substrate and immersed in the chemical modification solution for corresponding treatments. XPS measurements were performed in ultrahigh vacuum in an ESCALAB 250 Xi (Thermo Scientific, USA) with a nominal spot size of 400 µm. XPS sample was prepared by ultrasonicating BP in the mixture of water and acetone (V:V=1:1) followed by adding 10 mM TEMPO and 10 mM [Ph3C]BF4 in the mixture. Then, the precipitation was collected for XPS measurement after the solution was placed overnight. The bare BP sample was tested immediately after being deposited on the substrate, while passivated and oxidized BP samples were placed in air environment for 5 days before XPS measurements. The BP samples were deposited on the aluminum foil with conducting resin on its surface, and the thickness of the BP flakes range from 20 nm~200 nm. HR-TEM images were taken by a Tecnai G2 F20 (FEI, USA) at an acceleration voltage of 200 kV. HR-TEM sample was prepared by micro-pipetting liquid exfoliated BP onto a copper grid with carbon mesh which was then immersed in the solution composed of 10 mM TEMPO and 10 mM [Ph3C]BF4 in dichloromethane for 30 min. ESR spectra were tested on a Bruker EMXplus EPR Spectrometer. ESR sample was prepared by adding [Ph3C]BF4 and BP into water/acetone (V:V=1:1) mixture, follow by ultrasound for 20 min. Chemical thinning of BP. Pristine BP flakes were obtained by mechanically exfoliating bulk BP (Smart Elements, USA) onto a SiO2/Si substrates, which was then immersed in the solution composed of TEMPO and [Ph3C]BF4 in dichloromethane for a period time. After that, the samples were sequentially and thoroughly washed by 2-propanol and acetone to remove the residual chemicals. Finally, the samples were dried under N2 flow. Chemical passivation of BP. The exfoliated pristine BP flakes were immersed in the solution which was composed of TEMPO and [Ph3C]BF4 in water/acetone (V:V=1:1) for a period of time. After that, the samples were sequentially and thoroughly washed by 2-propanol and acetone to remove the residual chemicals. Finally, the samples were dried under N2 flow. Fabrication of chemically treated BP FET. All chemically thinned/passivated BP samples were obtained by aforementioned methods. Then electron-beam lithography was used to define metal contacts on the chemically treated BP flakes. Cr/Au (10 nm/60 nm) electrodes were deposited by an e-beam evaporator. The device electrical measurements were performed


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using an Agilent B1500A semiconductor parameter analyzer under ambient conditions. All the ambient conditions mentioned in the manuscript refer to the temperature of 20 oC and relative humidity ranging from 20%. Photoelectronic measurements. Scanning photocurrent measurements were performed in ambient conditions using a 632.8 nm He-Ne laser and 800 nm Coherent Mira 900 running in continuous wave mode. The beam is focused by a 40× objective lens (NA=0.6) with spot size around 2 μm. The reflection signal and photocurrent were recorded simultaneously to obtain the photocurrent mapping. A scanning mirror was used to allow the beam to be scanned on the sample. The laser beam was modulated with a mechanical chopper, and the short-circuit photocurrent signal was detected with a current preamplifier and a lock-in amplifier. Fabrication of BP TFT. Layered BP suspension was obtained by ultrasonic exfoliating bulk BP in water and acetone, followed by centrifugating the suspension at 2000 rpm for 30 min. Top 80% of the suspension was collected for further modification by adding 10 mM TEMPO and 10 mM [Ph3C]BF4. The suspension was set aside for one night before use. The suspension was then vacuum-filtrated through a mixed cellulose ester membrane with pores diameter of 0.22 mm, resulting in a layer of BP thin film deposited on the top. The BP deposited membrane was cut into desirable sizes, and pressed against the substrate (the BP side in contact with the substrate). The membrane was removed after one-hour pressing. DFT calculations. DFT calculations were performed using the generalized gradient approximation for the exchange-correlation potential, the projector augmented wave method,37,38 and a plane wave basis set as implemented in the Vienna ab-initio simulation package (VASP).39 The kinetic energy cutoff for the plane-wave basis set was up to 400 eV for all calculations. A k-mesh of 2×3×1 was adopted to sample the first Brillouin zone of a 3×5 supercell of few-layer black phosphorus. The armchair and zigzag directions were denoted x and y axis, respectively. In geometry optimization, van der Waals interactions were considered at the van der Waals density functional (vdW-DF)40,41 level with the optB88 functional for the exchange potential (optB88-vdW)42,43 The shape and volume of each supercell were kept fixed to the monolayer values and all atoms in it were allowed to relax until the residual force per atom was less than 0.02 eV·Å-1. Spin polarization was considered



and dipole correction was applied along the z direction (normal to the BP layer). The inclusion of dipole correction shows no appreciable change to the geometry and slightly varies the adsorption energy by 0.01 ~ 0.02 eV (less than 2% variation). The potential-energy profiles along the dissociative reaction pathways from physisorbed O2 molecules to chemisorbed O atoms on monolayer BP were calculated using the climbing image nudged elastic band (CI-NEB) technique,44 which exactly locates the saddle points of the reaction pathways. Five images were adopted in CI-NEB calculations and calculated with the optB86b-vdW functional.42,43 Charge transfer effects resulted from radicals and cations were simulated using the ionic potential method,45 which successfully modeled various charged systems.46,47 Acknowledgments This work is supported by National Science Foundation of China (No. 21405109, 91433103, 11622437 and 61674171), Seed Foundation of State Key Laboratory of Precision Measurement

Technology and Instruments, China (No. Pilt1710) and the Fundamental Research Funds for the Central Universities of China and the Research Funds of Renmin University of China (16XNLQ01). Calculations were performed at the Physics Lab of High-Performance Computing of Renmin University of China.

Supporting information 1. Dependency of the thinning rate on solute concentration 2. Peak intensity ratio of A1g to Si in BP Raman spectrum 3. Selectivity of chemical thinning 4. Characterization of chemically thinned BP FET 5. Improved surface quality after chemical thinning 6. Nuclear magnetic resonance (NMR) of chemically thinning solution 7. Electron spin resonance (ESR) test on the solution containing BP and [Ph3C]BF4 sonicated in mixture of water and acetone 8. XPS test of TEMPO functionalized BP 9. Characterization of chemically passivated BP 10. Chemically passivated BP FET 11. Impact of organic solvent on BP chemical modification 12. The necessary of coexistence of TEMPO and [Ph3C]BF4 in solution for chemical modification


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13. Effect of Ph3CBF4 concentration on chemical passivation 14. Investigation of passivation mechanism by DFT calculations 15. Investigation of thinning mechanism by density functional theory (DFT) calculations

Author contributions J. L. conceived the experiments, analyzed the experiment data with the assistance of D. S., W. J. and S. W., and prepared the manuscript. S. F. executed the BP chemical thinning and passivation, fabricated BP FETs under supervision of J.L., and analyzed the device data with assistance of Z. F., X. H., D. Z. and J. L.. J. W. L. performed the BP FET photocurrent measurement and data analysis under supervision of D. S.. H. H. performed AFM measurements and data analysis under supervision of S. W., W. J. and J. Q. performed DFT calculations.



References [1] Ge, S.; Li, C.; Zhang, Z.; Zhang, C.; Zhang, Y.; Qiu, J.; Wang, Q.; Liu, J.; Jia, S.; Feng, J.; et al. Dynamical Evolution of Anisotropic Response in Black Phosphorus under Ultrafast Photoexcitation. Nano Lett. 2015, 15 (7), 4650–4656.

[2] Huber, M. A.; Mooshammer, F.; Plankl, M.; Viti, L.; Sandner, F.; Kastner, L. Z.; Frank, T.; Fabian, J.; Vitiello, M. S.; Cocker, T. L.; et al. Femtosecond Photo-Switching of Interface Polaritons in Black Phosphorus Heterostructures. Nat. Nanotechnol. 2017, 12 (3), 207–211.

[3] Wang, X.; Jones, A. M.; Seyler, K. L.; Tran, V.; Jia, Y.; Zhao, H.; Wang, H.; Yang, L.; Xu, X.; Xia, F. Highly Anisotropic and Robust Excitons in Monolayer Black Phosphorus. Nat. Nanotechnol. 2015, 10 (6), 517–521.

[4] Xia, F.; Wang, H.; Jia, Y. Rediscovering Black Phosphorus as an Anisotropic Layered Material for Optoelectronics and Electronics. Nat. Commun. 2014, 5, 4458.

[5] Sofer, Z.; Sedmidubský, D.; Huber, Š.; Luxa, J.; Bouša, D.; Boothroyd, C.; Pumera, M. Layered Black Phosphorus: Strongly Anisotropic Magnetic, Electronic, and Electron-Transfer Properties. Angew. Chemie - Int. Ed. 2016, 55 (10), 3382–3386.

[6] Tao, J.; Shen, W.; Wu, S.; Liu, L.; Feng, Z.; Wang, C.; Hu, C.; Yao, P.; Zhang, H.; Pang, W.; et al. Mechanical and Electrical Anisotropy of Few-Layer Black Phosphorus. ACS Nano. 2015, 9 (11), 11362–11370.

[7] Liu, H.; Du, Y.; Deng, Y.; Ye, P. D. Semiconducting Black Phosphorus: Synthesis, Transport Properties and Electronic Applications. Chem. Soc. Rev. 2015, 44 (9), 2732–2743.

[8] Dai, J.; Zeng, X. C. Bilayer Phosphorene: Effect of Stacking Order on Bandgap and Its Potential Applications in Thin-Film Solar Cells. J. Phys. Chem. Lett. 2014, 5 (7), 1289–1293.

[9] Guo, Q.; Pospischil, A.; Bhuiyan, M.; Jiang, H.; Tian, H.; Farmer, D.; Deng, B.; Li, C.; Han, S. J.; Wang, H.; et al. Black Phosphorus Mid-Infrared Photodetectors with High Gain. Nano Lett. 2016, 16 (7), 4648–4655.

[10] Guo, Q.; Pospischil, A.; Bhuiyan, M.; Jiang, H.; Tian, H.; Farmer, D.; Deng, B.; Li, C.; Han, S. J.; Wang, H.; et al. Black Phosphorus Mid-Infrared Photodetectors with High Gain. Nano Lett. 2016, 16 (7), 4648–4655.

[11] Liu, H.; Neal, A. T.; Zhu, Z.; Luo, Z.; Xu, X.; Tománek, D.; Ye, P. D. Phosphorene: An Unexplored 2D Semiconductor with a High Hole Mobility. ACS Nano 2014, 8 (4), 4033–


Page 22 of 26

Page 23 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4041.

[12] Yasaei, P.; Behranginia, A.; Foroozan, T.; Asadi, M.; Kim, K.; Khalili-Araghi, F.; Salehi-Khojin, A. Stable and Selective Humidity Sensing Using Stacked Black Phosphorus Flakes. ACS Nano 2015, 9 (10), 9898–9905.

[13] Pei, J.; Gai, X.; Yang, J.; Wang, X.; Yu, Z.; Choi, D. Y.; Luther-Davies, B.; Lu, Y. Producing Air-Stable Monolayers of Phosphorene and Their Defect Engineering. Nat. Commun. 2016, 7, 10450.

[14] Ryder, C. R.; Wood, J. D.; Wells, S. A.; Yang, Y.; Jariwala, D.; Marks, T. J.; Schatz, G. C.; Hersam, M. C. Covalent Functionalization and Passivation of Exfoliated Black Phosphorus via Aryl Diazonium Chemistry. Nat. Chem. 2016, 8 (6), 597–602.

[15] Wood, J. D.; Wells, S. A.; Jariwala, D.; Chen, K. S.; Cho, E.; Sangwan, V. K.; Liu, X.; Lauhon, L. J.; Marks, T. J.; Hersam, M. C. Effective Passivation of Exfoliated Black Phosphorus Transistors against Ambient Degradation. Nano Lett. 2014, 14 (12), 6964–6970.

[16] Artel, V.; Guo, Q.; Cohen, H.; Gasper, R.; Ramasubramaniam, A.; Xia, F.; Naveh, D. Protective Molecular Passivation of Black Phosphorous. npj 2D Mater. Appl. 2017, 1 (1), 6. (1) Artel, V.; Guo, Q.; Cohen, H.; Gasper, R.; Ramasubramaniam, A.; Xia, F.; Naveh, D. Protective Molecular Passivation of Black Phosphorous. npj 2D Mater. Appl. 2017, 1 (1), 6.

[17] Zhao, Y.; Zhou, Q.; Li, Q.; Yao, X.; Wang, J. Passivation of Black Phosphorus via Self-Assembled Organic Monolayers by van Der Waals Epitaxy. Adv. Mater. 2017, 29 (6), 1– 5.

[18] Jia, J.; Jang, S. K.; Lai, S.; Xu, J.; Choi, Y. J.; Park, J. Two-Dimensional Black Phosphorus and Its Electronic Transport Properties. 2015, No. 9, 8729–8736.

[19] Castellanos-Gomez, A.; Barkelid, M.; Goossens, A. M.; Calado, V. E.; Van Der Zant, H. S. J.; Steele, G. A. Laser-Thinning of MoS2: On Demand Generation of a Single-Layer Semiconductor. Nano Lett. 2012, 12 (6), 3187–3192.

[20] Luo, W.; Yang, R.; Liu, J.; Zhao, Y.; Zhu, W.; Xia, G. Thermal Sublimation: A Scalable and Controllable Thinning Method for the Fabrication of Few-Layer Black Phosphorus. Nanotechnology 2017, 28 (28), 1–17.

[21] Nicolosi, V.; Chhowalla, M.; Kanatzidis, M. G.; Strano, M. S.; Coleman, J. N. Liquid Exfoliation of Layered Materials. Science (80-. ). 2013, 340 (6139), 72–75.



[22] Favron, A.; Gaufrès, E.; Fossard, F.; Phaneuf-Laheureux, A. L.; Tang, N. Y. W.; Lévesque, P. L.; Loiseau, A.; Leonelli, R.; Francoeur, S.; Martel, R. Photooxidation and Quantum Confinement Effects in Exfoliated Black Phosphorus. Nat. Mater. 2015, 14 (8), 826–832.

[23] Favron, A.; Gaufrès, E.; Fossard, F.; Phaneuf-Laheureux, A. L.; Tang, N. Y. W.; Lévesque, P. L.; Loiseau, A.; Leonelli, R.; Francoeur, S.; Martel, R. Photooxidation and Quantum Confinement Effects in Exfoliated Black Phosphorus. Nat. Mater. 2015, 14 (8), 826–832.

[24] Uk Lee, H.; Lee, S. C.; Won, J.; Son, B. C.; Choi, S.; Kim, Y.; Park, S. Y.; Kim, H. S.; Lee, Y. C.; Lee, J. Stable Semiconductor Black Phosphorus (BP)@titanium Dioxide (TiO2) Hybrid Photocatalysts. Sci. Rep. 2015, 5, 8691.

[25] Zhao, Y.; Wang, H.; Huang, H.; Xiao, Q.; Xu, Y.; Guo, Z.; Xie, H.; Shao, J.; Sun, Z.; Han, W.; et al. Surface Coordination of Black Phosphorus for Robust Air and Water Stability. Angew. Chemie - Int. Ed. 2016, 55 (16), 5003–5007.

[26] Illarionov, Y. Y.; Waltl, M.; Rzepa, G.; Kim, J. S.; Kim, S.; Dodabalapur, A.; Akinwande, D.; Grasser, T. Long-Term Stability and Reliability of Black Phosphorus Field-Effect Transistors. ACS Nano. 2016, pp 9543–9549.

[27] Na, J.; Lee, Y. T.; Lim, J. A.; Hwang, D. K.; Kim, G. T.; Choi, W. K.; Song, Y. W. Few-Layer Black Phosphorus Field-Effect Transistors with Reduced Current Fluctuation. ACS Nano 2014, 8 (11), 11753–11762.

[28] Avila-Vega, Y. I.; Leyva-Porras, C. C.; Mireles, M.; Quevedo-López, M.; Macossay, J.; Bonilla-Cruz, J. Nitroxide-Functionalized Graphene Oxide from Graphite Oxide. Carbon N. Y. 2013, 63, 376–389.

[29] Geneste, F.; Moinet, C.; Ababou-Girard, S.; Solal, F. Covalent Attachment of TEMPO onto a Graphite Felt Electrode and Application in Electrocatalysis. New J. Chem. 2005, 29 (12), 1520–1526.

[30] Deng, Y.; Li, Y.; Dai, J.; Lang, M.; Huang, X. An Efficient Way to Functionalize Graphene Sheets with Presynthesized Polymer via ATNRC Chemistry. J. Polym. Sci. Part A Polym. Chem. 2011, 49 (7), 1582–1590.

[31] Lai, W.; Xu, D.; Wang, X.; Wang, Z.; Liu, Y.; Zhang, X.; Li, Y.; Liu, X. Defluorination and Covalent Grafting of Fluorinated Graphene with TEMPO in a Radical Mechanism. Phys. Chem. Chem. Phys. 2017, 19 (35), 24076–24081.


Page 24 of 26

Page 25 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[32] Choi, J.; Lee, H.; Kim, K. J.; Kim, B.; Kim, S. Chemical Doping of Epitaxial Graphene by Organic Free Radicals. J. Phys. Chem. Lett. 2010, 1 (2), 505–509.

[33] Nesterov, V.; Qu, Z. W.; Schnakenburg, G.; Grimme, S.; Streubel, R. Selective Phosphanyl Complex Trapping Using TEMPO. Synthesis and Reactivity of P-Functional P-Nitroxyl Phosphane Complexes. Chem. Commun. 2014, 50 (83), 12508–12511.

[34] Doganov, R. A.; O’Farrell, E. C. T.; Koenig, S. P.; Yeo, Y.; Ziletti, A.; Carvalho, A.; Campbell, D. K.; Coker, D. F.; Watanabe, K.; Taniguchi, T.; et al. Transport Properties of Pristine Few-Layer Black Phosphorus by van Der Waals Passivation in an Inert Atmosphere. Nat. Commun. 2015, 6, 6647.

[35] Liu, X.; Ang, K. W.; Yu, W.; He, J.; Feng, X.; Liu, Q.; Jiang, H.; Tang, D.; Wen, J.; Lu, Y.; et al. Black Phosphorus Based Field Effect Transistors with Simultaneously Achieved Near Ideal Subthreshold Swing and High Hole Mobility at Room Temperature. Sci. Rep. 2016, 6 (April), 8.

[36] Zhu, X.; Zhang, T.; Sun, Z.; Chen, H.; Guan, J.; Chen, X.; Ji, H.; Du, P.; Yang, S. Black Phosphorus Revisited: A Missing Metal-Free Elemental Photocatalyst for Visible Light Hydrogen Evolution. Adv. Mater. 2017, 29 (17), 1–7.

[37] Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B, 1994, 50, 17953–17979. [38] Kresse, G.; Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B. 1999, 59, 1758–1775. [39] Kresse, G.; Furthmüller. J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B. 1996, 54, 11169–11186. [40] Lee, K.; Murray, É. D.; Kong, L.; Lundqvist, B. I..; Langreth, D, C.; Higher-accuracy van der Waals density functional. Phys. Rev. B. 2010, 82, 3–6 . [41] Fuhr, J. D.; Saúl, A.; Sofo, J. O. Scanning Tunneling Microscopy Chemical Signature of Point Defects on the [Formula Presented] Surface. Phys. Rev. Lett. 2004, 92 (2), 4.

[42] Klimeš, J.; owler, D. R.B.; Michaelides, A. J.; Chemical accuracy for the van der Waals density functional. Phys. Condens. Matter. 2010, 22, 22201. [43] Klime, J.; Bowler, D. R.; Michaelides, A.; Van der Waals density functionals applied to solidsPhys. Rev. B - Condens. Matter Mater. Phys. 2011, 83, 1–13 [44] Henkelman, G.; Uberuaga, B. P.; Jónsson, H.; A climbing image nudged elastic band



method for finding saddle points and minimum energy paths. Chem. Phys. 2000, 113, 9901–9904. [45] Ji, W.; Lu, Z. Y.; Gao, H. Electron Core-Hole Interaction and Its Induced Ionic Structural Relaxation in Molecular Systems under X-Ray Irradiation. Phys. Rev. Lett. 2006, 97 (24), 1– 4.

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Wet Chemical Method for Black Phosphorus Thinning and Passivation

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