Professor Etienne Sicard
email: etienne.sicard@insa-toulouse.fr

Professor, Lionel Trojman
email: lionel.trojman@isep.fr

Introducing 3-nm Nano-Sheet FET technology in Microwind

Keywords: Nano-Sheet, NSFET, CMOS design, 3-nm, Ring oscillator, interconnects, SRAM, logic gates

This paper describes the implementation of the novel Nano-sheet FET (NS-FET) for the 3-nm CMOS technology node in Microwind. After a general presentation of the electronic market and the roadmap to the atomic scale, design rules and basic metrics for the 3-nm node are presented. Concepts related to the design of NS-FET and design for manufacturing are also described. The performances of a ring oscillator, basic cells, sequential cells and a 6-transistor RAM memory are also analyzed.

Introduction

Manufacturing smaller circuits begets the integration of more complex components to comply with a demand for an increased operating frequency and reduced power consumption. Continuous advances in process fabrication are enabling a vision of future nodes such as 5, 3.5, 2 and 1.5 nm for the next decade, reinforced by prospective roadmaps from giant semiconductor foundries such as Intel, TSMC & Samsung. Through 9 application notes, we have tried to illustrate the increased performances of devices, specifically for the 14-nm, 7-nm nodes [Sicard 2017] and more recently the 5-nm node [Sicard & Trojman 2021]. Two major silicon foundries, namely TSMC from Taiwan and Samsung from South-Korea have introduced 3-nm technologies in 2021, one of them implementing the novel nano-sheet approach, considered to be the successor of the FinFET, first introduced by Intel for its 22-nm technology. In this application note, we describe the main characteristics of the 3-nm node, by exploiting available scientific literature and information released by semiconductor manufacturers, with focus on the Nano-Sheet FET. We take the opportunity of this publication to outline the electronic market growth, the motivation for 3-nm process. Then, we review the basic design rules, describe the transistor characteristics, and detail the implementation of basic cells such as the inverter, the ring oscillator, and the static memory. We conclude this document by discussing the switching performances of this node. We recall in table 1 the main innovations over the past recent years.

Moving to nanosheet FETs varies depending on the foundries, a situation somehow similar to the transition from MosFET to FinFET initiated by Intel in 2011, soon followed by other major silicon companies. Samsung has announced it would introduce nanosheets for its new 3-nm process, with a mass production starting in 2022. In contrast, TSMC has announced it would extend the FinFET to 3nm node, and then move to nanosheet starting 20-Angstrom node (20A or 2nm), around 2025. From its side, INTEL has announced that its Intel 3 process would use while Intel 20A (A for "Angstrom") would use its own version of nano-sheet FET named RibbonFET starting 2024 [Intel2021]. It can be seen from Figure 2 that within a reduced silicon surface, process engineers have been able to fabricate much more efficient devices than the original MosFET, mainly in terms of equivalent channel width (W) that is nearly proportional to the switching current. Stacking nano sheets enable an equivalent channel width more than 3 times more area-efficient than the MosFET, in its 3 stacked nano-sheet configuration.

Introduction of Nano-Sheet FET in industry

The adoption of nano-sheet FET should follow the adoption of FinFET with a 10-years shift. Is it anticipated that the 3-nm node will announce the start of a migration from FinFET to NsFET, to enable further gains in current drive while reducing the device surface, thus enabling smaller, faster and more energy-efficient chips (Figure 3). The three different categories of applications should remain: high performance computing (severs, data centers), general purpose (laptops, gaming), and low power (mobile, IoT) with significant differences in terms of acceptable leakage current (IOFF). The demonstration of the full control of the channel was originally published by [Sung-Young Lee 2004] from Samsung, who described a "novel multi-bridge-channel MOSFET (MBCFET) with extremely high performance". However, the true industrial adoption of this novel device was shifted nearly 20 years after this publication. In more details, the industrial deployment is scheduled by Samsung for 3GAP node (an acronym which could stand for 3-nm Gate All Around -Production) in 2023. Two other IC suppliers should follow: TSMC for its future 2-nm "2N" node, with a device named Gate-All-Around FET (GAA), and Intel for its 2-nm "20A" node, with a device called RibbonFET

Limited scale down

One simple rule that drove the semiconductor industry over the past 40 years was to associate (at least in a first-order approximation) the technology with the minimum feature size. For example, in 90-nm technology, the narrowest feature such as the MOS gate was around 90 nm. Starting 32-nm node, the manufacturing of nano-scale patterns became so challenging that advanced patterning failed to enable further linear scaling. Therefore, the node generation could not be linked anymore with the minimum feature size. For example, concerning the 3-nm node, the minimum feature size is around 8-10 nm, that is nearly 3 times larger than what the node number would mean (Figure 4).

Improving performances by all means

Improving the performances in a significant manner at each new node generation is enabled by gaining silicon space, improving speed and saving power. As a significant shrink of the features is no more feasible, time has come to shrink the cell size by design, improve the device, and reduce parasitic capacitance & resistance, therefore improving speed and/or reducing power.

Reducing the cell height

The concept of cell height reduction with nearly no change of the cell width is illustrated in Figure 5 [ Weckx 2019]. The "Contacted Gate Pitch" (CPP) refers to the distance between 2 active gates, and this distance is the hardest to reduce from 14-nm (N14) to 2-nm (N2) node. It can be seen that no significant gain may be expected in terms of distance between vertical gates (in red in the figure, an heritage of the good old polysilicon that appeared light red in the microscope). In other words, the cell width cannot be shrinked significantly.

In contrast, the vertical dimension of the cell may the significantly reduced by replacing the FinFET by the Nano-sheet FET, which is more compact, and placing N & P devices closer to each other thanks to the suppression of n-well design rule constraints. In the future, replacing the power metal tracks by buried power rails would restore horizontal routing channels, a strategy already announced by Intel for node 20A (2-nm, 2024) and referred as PowerVia ™ [Intel2021].

Figure 5: Illustration of the limited contacted gate pitch scale down over the 14-nm to 2-nm node generations, and the aggressive scale down of the cell vertical dimension (7.5T to 5T) [Weckx 2019]

Improving Area Efficiency

Replacing the FinFET by the Nano-sheet FET has many advantages: the device is smaller for an equivalent current, the distance between N & P devices can be reduced as no n-well and no polarization is required, the intra-cell interconnects are shorter and lead to a capacitance & resistance reduction, and the full control of the 4 sides of the channel gives better Ion/Ioff performances than FinFET or MosFET. Given a 1mA ION current, nano-sheet FET require 50% less silicon as compared to FinFET, which was already 30% more area-efficient than the MosFET (Figure 6). The major step forward should be to stack the p-device over the n-device to decrease the device surface by 75% [Wang 2021]. The NsFET has a much more complex structure than the MosFET due to the stacking of nano-sheets.

Instead of growing a single channel, a superlattice of alternating Si and SiGe layer must be formed, followed by the selective removal of the sacrificed SiGe layer. The empty space in between the Si channels must be filled with the gate dielectric (usually a combination of SiO2, Si3N4 and high-K dielectric such as Hafnium oxide HfO2) and metal gate that will completely surround the nanosheets.

Equivalent channel width

Knowing the width W and nanosheet thickness TNS, and the number of nanosheets ns, we can get the effective channel width Weff using equation 1. The comparison between the NsFET (top) and MosFET (bottom) layouts with the same equivalent channel width and length is reported in Figure 7.

𝑊 = 𝑛𝑠 × (2𝑊 + 2𝑇𝑁𝑆) (eq. 1)
The illustration of the improved switching performances is illustrated in figure 8. Considering the logic levels 0 and 1 (0=VSS=0V, 1=VDD=0.65V), two important current values are often considered:

 IOFF (no channel but a parasitic leakage current)  ION (maximum current at maximum gate voltage)

Figure 7: the equivalent channel width is more than 3 times the MOS width thanks to a 4-side control of the channel, leading to very small footprint The ratio ION/IOFF is around 10 6 . Given a 1µm width, ION is within the 1mA range, IOFF the nA range.

The successive introduction of FinFET and later on NsFET have improved or at least maintained a satisfactory ION/IOFF ratio although the device dimensions have been drastically reduced. Some scientific publications define the current in mA/µm, some others refer to the device current itself.

Restoring the fine current tuning

One major drawback in the FinFET-based design is the discrete nature of fins, which do not give much choice for cell design: in the latest 5-nm FinFET technology [START_REF] Sicard | [END_REF]], the choice was limited between 1 or 2 fins, 1 for the "slow" device (or high-density), and 2 fins for "fast" devices (or high performance). Still, more fins could be added for increased current capabilities, for large drivers or power amplifiers for example. The continuous aspect of the NsFET restores the ability to adjust precisely the device ION according to the needs, which enable a more efficient design in terms of power consumption and speed, as compared to FinFET (Figure 9).

What about the supply

While the supply voltage has been steadily reduced from 0.35µm to 32-nm (3.3V down to 1V), the trend towards significant supply reducing is not valid anymore. What we observe from publications related for FinFET & NsFET is a saturation around 0.6-0.7 V (Figure 10). The end of n-well

No n-well layer is required anymore as the device channel is totally surrounded by the gate, without any influence of the substrate as for MosFET & FinFET. Therefore, no polarization is required too, which enables to place n & p devices much closer to each other than previous technologies. In Microwind's 3-nm implementation, the p-well layer is deactivated (Figure 11). A brief review of Nano-Sheet dimensions

We select 5 publications for which explicit values of the nanosheet FET dimensions are provided, as well as ION/IOFF performances. These parameters are listed in order to orient our own choices (last column of Table 2).

Summary of design rules

Depending on the publications, the number of nano-sheets oscillate between 2 and 7 stacked layers.

Until recently, Samsung & TSMC did not give much details on the physical dimensions of their nanosheet device. We have chosen to define 3 stacked layers, which is the most common number used in scientific publications regarding nano-sheet devices involved in the 3-nm node. 3 summarizes the main characteristics of the 3-nm design rules implemented in Microwind. The lambda unit is the same as for 7-nm & 5-nm node. VDD also remains at 0.65V. The number of nanosheets is defined as 4 stacked layers, with 5-nm thickness (TNS) and 10-nm spacing (TSP). The total device height is 60 nm. The number of nanosheets is defined in cmos3n.rul using parameter nsfet. Although any value between 1 and 7 is allowed, we assume the industry will use devices with 3 nanosheets. The nanosheet stack is constructed based on the nano-sheet thickness (tns) and the nanosheet spacing (tsp). The layout of two versions of the nsFET, one in "slow" mode (W=4 λ), the other in "fast" mode (W= 8λ) is shown in Figure 12, with the associated cross-section showing the 3 stacked nano-sheets.

Nano-Sheet device

Layout design in Microwind uses integer units called lambda (λ). This strategy is not optimum in terms of silicon area but makes the layout nearly independent of the technology. Design rules have remained nearly the same for the past 30 years. In our 3-nm implementation, λ is kept at 4 nm, the same value as for 7-nm and 5-nm nodes. In other words, no scale down has occurred, the space, speed and consumption benefits come from design & device innovations.

The minimum channel length is 2 λ as always, the contacted gate pitch (CGP) is 10 λ (quite similar to FinFET & MosFET nodes), and the metal pitch (MP) is 6 λ (3+3), same as always. In 3-nm technology, dummy gates are activated by default and added on both sides of the active device, with a gate pitch of around 10 λ (40 nm). The default width is 4 λ (16 nm). It corresponds to the slow speed. Notice that the effective width Weff is much larger than W, as the effective channel is more than 6 times higher, according to eq. 1 seen previously. The ID/VD curves of the slow and fast devices show an Ion current nearly double. Using the option layer, we may turn the device to high-performance mode for a supplementary boost of nearly 30% ION current, but at the cost of IOFF multiplied by 10 (Figure 15). The use of such device should be restricted to situations where the speed is critical (clock tree, critical logic path, needs for highest performances) and power saving is no more the priority.

In Nanosheet (NS) device architecture, it is much more challenging than FinFET or MosFET to provide multiple threshold voltage (multi-Vt) options for designer. Typically, low Vt devices are used for high performance, while high Vt devices are preferred for low power. Industrial processes usually propose up-to 4 different types of Vt to satisfy designer needs for optimized trade-off between speed and power consumption. For example [Cho 2016] from Samsung discussed the introduction of, sLVT, LVt, RVT, HVt variants of the same FinFET device in 10-nm technology, with Vt varying 200mV between the super-low and high-vt devices, thanks to adjustments in the thickness of metal layers used in the gate stack. Regarding NSFet, the metal gate boundary control is discussed by [Bao 2019] as a solution to enable multi-Vt devices.

In our 3-nm implementation of the NSFet, we may use either the High-Vt default device (Vt=0.30V), or the high-performance/low-Vt device (Vt=0.25V).

Modelling the NsFET

The reference model for simulating the Nano-Sheet FET is Berkeley BSIM-CMG, which stands for Common-Multi-Gate [BSIM-CMG 2021]. At the time of the writing of this application, BSIM-CMG 111.1 was not open source but BSIM-CMG 111.0 was available for download. Some details about the model may be found in [Dasgupta 2020]. It can be seen from Figure 16 that previous BSIM-CMG approaches were overestimating the drain current, whereas the updated model is able to capture the trend with high accuracy, matching measurements almost perfectly. Microwind uses a simplified version of the BSIM4 model for simulating the Nanosheet FET, for the shake of simplicity (Figure 17). The simplified version of BSIM4 follows the main equations detailed in the book [Liu 2001]. The BSIM4 model was not initially targeted to FinFET nor double-gate/nano-sheet devices. However, it may fit in first order the I/V characteristics of advanced devices. Using BSIM4 model instead of BSIM-CMG may lead to significant mismatch between simulations and measurements, specifically for analog & radio-frequency designs, as BSIM4 suffers from some nonsymmetrical equations, do not handle self-heating corrected in late versions such as BSIM6 [Agarwal 2013] & BSIM-CMG. Quantum effects are also ignored in BSIM4 models. The N & P devices use a 4 λ channel footprint, which corresponds to the "slow" design style. The nanosheet cross section can be displayed using the icon with a vertical selection corresponding to the active gate (A-A'). The 3 stacked nano-sheets appear (Figure 21), each with a thickness of 5 nm and spacing of 10 nm. The equivalent channel width Weff is

𝑊 = 𝑛𝑠 × (2𝑊 + 2𝑇𝑁𝑆) = 3 × (2 × 16 + 2 × 5) = 126 𝑛𝑚
where ns is the number of nano-sheets, W is the channel footprint and TNS the nano-sheet thickness.

Designing using 5T approach

Most publications related to 3-nm design refer to so-called 5T design where "T" stands for "horizontal metal tracks" [Mokuta 2018][Kim 2021]. The higher the number of "T", the taller the cell. The value of T is equal for the metal pitch Metal Pitch (MP) which is around 24 nm in 3-nm technology (3 λ minimum metal width, 3 λ minimum spacing). The "T" concept is illustrated by [Kim 2021] with a cell height reduced from 168 nm (6T with 5-nm design rules) to 120 nm (5T with 3-nm design rules), as shown in Figure 22. When adding an upper metal track for VDD supply, and a the lower track for VSS supply, we must ensure there is enough room for 4 intermediate metal tracks for horizontal routing. The VDD and VSS tracks are shared with upper and lower cells, so supply tracks account for half track each. In sum, this design style is called "5T design". In Microwind, it corresponds to 124 nm cell height (31 λ) and 80 nm cell width for an inverter. There is enough space to enlarge the device width for a faster switching (socalled fast design, with twice more device surface), as shown in Figure 23

Compile one inverter, 5T

Microwind includes a specific tool to handle the generation of a complete inverter. Other simple logic cells such as NAND, NOR, AND, OR can also be generated using this tool. The cell height corresponds to the "5T" approach. The device width can be either "Slow" (4 λ footprint) or "Fast" (8 λ). An example of three compiled inverters is reported in Figure 24. Each new cell is added at the right side of the existing layout. A closer look at the compiled layout reveals that the cell height is a little taller than expected. This is due to the internal routing strategy that do not rely of minimum width, minimum pitch (6 λ) but uses instead relaxed metal pitch of 8 λ, that simplifies the addition of contacts, but is not optimal. The cell height is 160 nm instead of 124 nm that is found in optimized 5T design (Figure 24).

Logic Design with Nano-Sheet

Ring Oscillator

Compiling 3 successive inverters enables to build a ring oscillator, that oscillates freely, without any external stimulation. The only work to do is to build the interconnections according to the schematic diagram shown below and to add the VSS and VDD supplies. The loading condition corresponds to the shortest possible wire and one single gate (the next input stage). The design corresponds to minimum parasitic resistance & capacitance, which corresponds to maximum performances. The observed frequency is approaching 120 GHz (Figure 25). Further boost may be obtained by enlarging the device width furthermore, or using the "high-speed" option, which is accessible using the option layer. Instead of the default "low leakage" option, we surround all 6 devices by as option layer and change the device option to "high speed". The resulting simulation shows an oscillating frequency of 160 GHz.

Ring Oscillator with Fan-Out

Many scientific publications include simulations of ring oscillators, such as [Wang 2020], [Ahmed 2020] or [Na 2021]. As the number of stages and operating conditions significantly vary among publications, direct comparison of the published results is not always possible. For example, [Na 201] uses 19 stages, each stage connected to M1, M2..M6 and then back to M1. In [Wang 2020], a 3-stage ring oscillator is used, each stage loaded by a metal track with a length corresponding to 25 × ( CGP + MP ), where CGP is the contacted gate pitch (48 nm) and MP is the metal pitch (28 nm), which intends to represent typical loading conditions. Comparison are possible only if similar operating conditions are used (VDD, loading, options, device size) and if power & frequency per stage is evaluated, instead of the ring oscillator itself. We use the following strategy for simulation: we consider a 3-stage RO with a 3-input load. This corresponds to a capacitance load around 1 fF (Figure 27). We extract the frequency per stage by multiplying the RO frequency by 3. We also extract the power per stage by dividing the total power consumption. In the following simulation, we use "fast" design approach and consider highperformance devices, instead of the default low power, to maximize the oscillating speed. Then, we iterate the simulation for VDD ranging from 0.5 to 0.8V, step 50 mV.

Interconnect delay

All these delays are optimistic as no charge has been connected to the outputs, which are just floating.

The connection of the outputs input gates through interconnects will be equivalent to a significant RC delay, which slows down the propagation. This is illustrated in figure 32: although the intrinsic delay is dominant for short & medium interconnects, the interconnect delay has a strong impact on the total switching delay for long interconnects. The metal resistance ranges between 500-1KΩ/µm [Wang 2020] [Seon 2021] according to authors and the metal capacitance is around 300aF/µm. Although no significant gain is observed between fast and slow inverter designs for short & medium interconnects, fast inverters limit the overall delay as compared to slow inverters when long metal wires (4 µm and above) are used. Figure 33 shows the simulation setup for evaluating the near-end delay of a 20-CGP metal interconnect. For the 100-CGP interconnect, we fold the wire into 5 parts (Figure 34). A 2KΩ virtual symbol has also been added to force the simulator to handle the RC delay, which is limited to capacitance C by default. Sequential Design with Nano-Sheet

XOR Gate

RS-Latch

The RS Latch is one of the simplest sequential circuits that may be built, but not the most useful. Two implementations of the RS-Latch are feasible, one based on NOR gates, the other one based on NAND gates (Figure 37-top). In the case of RS-NOR, the cell is sensitive to high levels of either Set or Reset, while for the RS-NAND, the cell is sensitive to low levels of either Set or Reset. We compile 2 NOR2 gates and add the necessary properties, as shown in Figure 37.

Memory

The 6-transistor static memory (also called SRAM 6T) consists of a 2-inverter stable loop that stores the data and 2 access transistors to either import or export the logic data through so-called bit lines. When the data is imported from outside to the cell (the data through BL, its opposite through ~BL), we refer to the write cycle, while when the data is exported, it is called the read cycle. The cell structure is optimized for multiplication in X, Y in order to create a matrix of cells, typically 1000 x 1000 that leads to 1 Mega-bit memory plane. The inverters are folded and the supply contacts are placed at the boundaries of the cell to enable to share VDD & VSS contacts with adjacent cells. The selection wire (Also called Word Line) is going through the cell using Metal3. The simulation reported figure 40 shows a memory state while the Selection is not active. At time 5, Sel is active but Data and ~Data are in 3-state mode. At time 6 ns, the memory is set to 0, and at time 7 ns, it is set to 1.

Future steps

Intel has unveiled in 2020 [Huang 2020] a 3D stacked CMOS architecture to enable smaller standard cell and SRAM cell size, while providing better performance per Watt for future computing systems. The combination of nanoribbon, stacked N-FET and P-FET devices (as illustrated by [Huang 2020],

Figure 41) and further improvements in pitch scaling would divide by 10 the silicon surface in 20A node (2-nm) as compared to existing 10-nm FinFET technology. Further 2x boost in transistor would be achieved by die stacking, buried power layers and improved packaging. An illustration of the combined benefits of all these innovations is given by [Intel 2021], with an expected multiplication of the number of transistors per chip by nearly a factor of 50 as compared to 10-nm. PowerVia is Intel's industry-first implementation of backside power delivery, an approach proposed by IMEC as Buried Power Layer [Gupta 2020]. The Microwind implementation of the buried power layer appears in Figure 42 and should be proposed for the 2-nm/20-Å node, associated with an application note to appear early 2022. The stacked N&P should be introduced for the 1.5-nm/15-Å node, to appear late 2022.

Conclusion

This application note has described the implementation of the 3-nm technology in the educational tool Microwind, which is a major breakthrough as compared to previous nodes due to the introduction of the nano-sheet FET. We discussed in this paper about the NsFET characteristics, the performance tradeoff, the interconnect parasitic effects and the performances of basic cells such as logic gates, ring oscillators and memory cells.

Although limited gains are observed in terms of geometrical scale down, the NsFET efficiency has enabled considerable gains in terms of device surface, enabling a shrink of the logic cell height and the suppression of the n-well. The 3-nm node enables 20% speed improvement or 25% power saving as compared to the 5-nm FinFET-based node.

Figure 1 :

 1 Figure 1 : The processor die size has been reduced over the past node generationsAs shown in figure1, the processor die size has been steadily reduced over the past node generations. The same trend towards silicon surface reduction is anticipated for the next upcoming nodes. The main reason for introducing the Nano-Sheet (NS) FET is related to this quest for a more efficient device in a smaller area. The device has been called Gate-All-Around (GAA), Muti-Bridge-Channel (MCB) or RibbonFET depending on the manufacturers & researchers, but the principles for stacking channels fully surrounded by the gate is the same for all devices.

Figure 2 :

 2 Figure 2 : MosFET, FinFET & Nano-Sheet FET, with corresponding equivalent channel width

Figure 3 :

 3 Figure 3 : Increased current drive over 13 technology nodes including MosFET, FinFET & Nano-Sheet FET

Figure 4 :

 4 Figure 4 : Saturation effect in the technology scale down, the minimum feature size is no more related to the technology number

Figure 6 :

 6 Figure 6: Illustration of silicon surface benefits using innovative devices such as FinFET, NsFET, and stacked N-P NsFET, for the same switching current.

Figure 8 :

 8 Figure 8: Comparing ION/IOFF trade-off for MosFET, FinFET, & NsFET

Figure 9 :

 9 Figure 9: The discrete nature of fins limits the current tuning of FinFET, while the width of NsFET can be adjusted to the exact current needs

Figure 10 :

 10 Figure 10: The supply voltage is around 0.7 V for 7-nm, 5-nm & 3-nm nodes

Figure 11 :

 11 Figure 11: The 5-track implementation of the inverter do not include nwell layer nor associated polarization

Figure 12 :

 12 Figure 12: Slow and fast devices, layout view, cross-section & 3D view (nsFET.msk)

Figure 13 :

 13 Figure 13: in 3-nm nano-sheet technology, dummy gates are selected, and the default width is 16nm (Weff more than 6 times larger than W)

Figure 16 :

 16 Figure 16: Measured drain current as a function of the gate voltage for nanosheet FETs with NS thickness varying from 9nm to 4nm. The updated model is able to capture the trend with high accuracy [Dasgupta 2020]

Figure 17 :

 17 Figure 17: Simplified BSIM4 model implementation in Microwind used to simulate the 3-nm nanosheet devices

Figure 19 :

 19 Figure 19: Select a n-channel or p-channel NsFET

Figure 21 :

 21 Figure 21: Cross-section of the n-channel or p-channel NsFET generated by Microwind.

Figure 22 :

 22 Figure22: comparing the design of a 5-nm Inverter with 50nm contacted gate pitch (CPP), 6T and the 3-nm INV with 44nm CPP with 5T approach[Kim 2021]

  -right.

Figure 23 :

 23 Figure 23: Adding the VDD & VSS power rails in a 5T strategy, leading to a cell height of 120 nm, slow & fast inverters

Figure 24 :

 24 Figure 24: Two versions of the compiled inverter: slow at left, fast at right (invCompiled-Slow-Fast.MSK)

Figure 25 :

 25 Figure 25: A simple 3-stage ring oscillator based on compiled inverters "Fast" mode (RO3-FO1-Fast.MSK)

Figure 26 :

 26 Figure 26: Turning the device option to "High-speed" increases the oscillating frequency to 160 GHz (RO3-FO1-Fast.MSK)

Figure 27 :

 27 Figure 27: Each inverter output is connected to 3 inputs to emulate a significant load (RO3-FO3-Fast.MSK)

Figure 28 :

 28 Figure 28: VDD may be increased/decreased 50 mV directly from the simulation menu. For ring oscillators, the power & frequency per stage appear below the evaluation of the total power Figure 29 compares the performances of the Low-Power & High-Performance FinFET devices as published in [Sicard 2021] for VDD varying from 0.5 to 0.8 V. The circuit is a RO3-FO3 (3 stage, 3 connected inputs for each output). The same simulation performed in HP 3-nm NsFET shows improved speed at constant power consumption or reduced power consumption at constant speed, which demonstrates the benefits of the 3-nm technology. Further gains are expected for next generation 2nm and 15A nodes.

Figure 29 :

 29 Figure 29: Comparing the power & frequency per stage of 3-stage RO with Fanout 3 in 5-nm FinFET & 3-nm NsFET ring oscillators

Figure 30 :

 30 Figure 30: Compiled basic gates using the cell compiler in 3-nm NsFET technology, with 5T strategy (basicgates.MSK)

Figure 32 :

 32 Figure 32: The interconnect delay has a strong impact on the total switching delay for medium to long interconnects

  Several options exist for building the XOR gate, such as the 6-Transistor & 10-Transistor implementations reported in Figure34. The main problem of the 6T implementation (Figure35 -top) is the VT losses as the n & p-devices are used as pass transistors, leading to inappropriate delays and non-ideal logic levels. The 10T implementation is safer but consumes more silicon area. Its corresponding layout consists of 3 inverters and 2 transmission gates, as reported in Figure36. The worst-case delay in the simulation is around 4.8 ps.

Figure 35 :

 35 Figure 35: 6T and 10T schematic diagrams for the adder (XOR2_6T_10T.SCH)

Figure 37 :

 37 Figure 37: Compiled NOR gates to construct the RS-Latch (RSNor.MSK)

Figure 38 :

 38 Figure 38: Principles of the SRAM topology (Ram6T-array.SCH)

Figure 41 :

 41 Figure 41 : From FinFET to NanoRibbons and stacked CMOS devices [Huang 2020]

Figure 42 :

 42 Figure 42 : Introducing buried power rails will enable further reduction of the cell height while keeping similar routing capabilities (inv-7-5-4T.MSK)

Table 1 :

 1 Most significant technology nodes over the past 20 years and prospective vision for 2023-

	Technology node	Year of	Key Innovations	Application note
		introduction
	180nm	2000	Cu interconnect, MOS options, 6 metal layers
	130nm	2002	Low-k dielectric, 8 metal layers
	90nm	2003	SOI substrate	[Sicard2005]
	65nm	2004	Strain silicon	[Sicard2006]
	45nm	2008	2nd generation strain, 10 metal layers	[Sicard2008]
	32nm	2010	High-K metal gate	[Sicard2010]
	20nm	2013	Replacement metal gate, Double patterning,	[Sicard2014]
			12 metal layers
	14nm	2015	FinFET	[Sicard2017]
	10nm	2017	FinFET, double patterning	[Sicard2017]
	7nm	2019	FinFET, quadruple patterning	[Sicard2017]
	5nm	2020	FinFET enhancement, EUV	[Sicard2021]
	3nm	2021	Nano-Sheet FET, EUV	This application note
	20A	2023	Nano-Sheet FET, buried supply
	15A	2025	3D NS-FET, n/p co-engineering

Table 1 :

 1 [Intel 2021]. Introduction of the Nano-Sheet FET according to 3 semiconductor giants Samsung, TSMC & Intel

	COMPANY	NANO-SHEET DEVICE	TECHNOLOGY NODE	YEAR OF
		NAME		INTRODUCTION
	SAMSUNG	Multi Bridge Channel	3-nm (3GAP)	2023
		FET (MBCFET)
	TSMC	Gate-all-around FETs	2-nm (2N)	2024
		(GAAFETs) a
	INTEL	RibbonFET	2-nm (20A)	2024

Table 2 :

 2 Comparing the device dimensions & electrical characteristics for a selection of scientific publications

	DESIGN	UNIT	[KIM	[WECKX	[DAS 2020]	[JEONG	[YOON	OUR CHOICE
	PARAMETER		2021]	2019]		2020]	2020]
	DEVICE HEIGHT	nm	55	60	43	60	50
	GATE LENGTH	nm	11	15	8, 10	12	12	8
	NANOSHEET	nm	5	5	5	5	5	5
	THICKNESS
	NANOSHEET	nm	10	10	5	10	10
	SPACING
	NANOSHEET WIDTH	nm	24	13	20	42	26	16 (Slow)
								32 (Fast)
	NUMBER OF		3	4	4	3	3	3
	NANOSHEETS
	VDD	V	0.7	0.7	0.6	0.7	0.7	0.65
	IEFF NFET	µA	90 (LP)	70	20 (LP)	233 (HP)	30 (LP)	100 (LP-slow)
			180 (HP)		40 (Overdr)		60 (HP)	125 (HP-slow)
	SUBTHRESOLD	mV/Dec	70	75	60-70	100	n.a
	SLOPE

Table 3 :

 3

basic parameters of the 3-nm process implemented in Microwind (cmos3n.RUL)

Table

  Further improvements are forecast by introducing buried power layers (2-nm/20-Å node) and stacked P-FET & N-FET (1.5nm/15-Å). a B.S degree and a PhD in Electrical Engineering from the University of Toulouse in 1984 and 1987. Professor Sicard has authored or co-authored over 15 books, commercial software packages (Microwind, IC-EMC, Vocalab, Diadolab..) and more than 200 technical papers in the area of nano-scale CMOS technology, electromagnetic compatibility and digital signal processing for voice & speech therapy. He served as Deputy-Director of International Relations at INSA Toulouse 6 years and was elected Distinguished IEEE Lecturer of the EMC society. He is conducting research on speech & voice analysis at LURCO laboratory. the Aix-Marseille University. He received his Ph.D. degree in Electrical Engineering at the KULeuven in cooperation with IMEC, Belgium, in 2009. Since 2009, he was working as full time Professor and from 2015 also as director of the Master of Nanoelectronics to the electrical and electronics engineering department of the USFQ, Ecuador, where he also found the Institute of Micro and Nanoelectronics (IMNE) in 2013. He is currently working as full time professor for Isep, France, since 2019. He authored or coauthored more than 80 journal and conference papers on research work including transport for ultra-scaled MOSFET with UTEOT high-k dielectrics on bulk and UTTB-FDSOI, on ReRAM modelling, STT-MRAM circuits, GaN SBD-GET and HEMT devices, TFET and FinFET based SRAM circuits, ULP-OTA design, hardware implementation of IA algorithm on FPGA. He currently works on IC design coupled with sensor and Harvester energy devices and to implement Artificial Neural Network based IC.

Acknowledgements

We gratefully acknowledge the numerous students, researchers and engineers who have used our applications notes related to 90..5-nm technologies, and published more than 600 scientific papers using Microwind. This motivates us to release new application notes dedicated to the nano-cmos technologies of the future.


Ekaterina K Khrapova

Valery L Ugolkov

Elena A Straumal

Sergey A Lermontov

Vasily A Lebedev

Daniil A Kozlov

Tatyana S Kunkel

Alexandre Nominé

Stephanie Bruyere

Jaafar Ghanbaja

Thierry Belmonte

Andrei A Krasilin

Thermal behavior of Mg-Ni-phyllosilicate nanoscrolls: An emerging materials for hydrogenation

Keywords: nanotubes, hydrothermal synthesis, reduction, metal, nanoparticles, heterogeneous catalysis

Here we report on the thermal properties of Mg-Ni-phyllosilicate nanoscrolls as a promising precursor for production of Ni/silicate composite catalysts. Spontaneous scrolling of the phyllosilicate layer originating from size difference between metal-oxygen and silica sheets provides an increased surface area of future catalyst support. Metal nanoparticles can be obtained directly from the matrix by H2 reduction. Despite the system has already been used for methane reforming, little attention has been paid to the control of size distribution of Ni nanoparticles, as well as to the reduction process itself. In order to close the gap, we carried out a thermal study of (Mg1-xNix)3Si2O5(OH)4 nanoscrolls in air and in H2 environments. The phyllosilicate structure passed through a number of transformations including partial dehydroxylation with formation of sepiolite-like phase followed by silicate or oxide crystallization. Temperature ranges of these transitions overlapped with the reduction process sophisticating the H2 consumption profiles. In particular, some amount of Ni 2+ got sealed up by the sepiolite structural features, that opened a path for the tuning of Ni 0 :Ni 2+ ratio of the catalyst. An increase of Ni content in the system yielded a decrease in the metal nanoparticles sizes due to both high intensity of nucleation and type of residual matrix (mostly amorphous or crystalline). In turn, size distribution and specific surface area of the composite catalysts governed conversion rate of hexene-1 and acetone hydrogenation.

INTRODUCTION

A number of layered hydrosilicate particles can gain spontaneous curvature due to an excess of strain energy and difference in chemical composition on the opposite sides of the layer. [START_REF] Krasilin | Comparative Energy Modeling of Multiwalled Mg3Si2O5(OH)4 and Ni3Si2O5(OH)4 Nanoscroll Growth[END_REF][START_REF] Guimarães | Electronic, and Mechanical Properties of Single-Walled Halloysite Nanotube Models[END_REF][START_REF] Thill | How the Diameter and Structure of (OH)3Al2O3SixGe1-xOH Imogolite Nanotubes Are Controlled by an Adhesion versus Curvature Competition[END_REF][START_REF] Dódony | Serpentines Close-Up and Intimate: An HRTEM View[END_REF] In 1:1 phyllosilicate like chrysotile and halloysite, strain originates from size difference between covalently bounded metal oxide and silicon oxide sheets. In addition, surface of metal (magnesium, aluminum) oxide sheet is highly hydroxylated causing large surface energy difference between the two surfaces. [START_REF] Shchipalov | Surface Energy of Crystalline and Vitreous Silica[END_REF][START_REF] Evarestov | HF and DFT Calculations of MgO Surface Energy and Electrostatic Potential Using Two-and Three-Periodic Models[END_REF][START_REF] Churakov | Ab Initio Study of Dehydroxylation-Carbonation Reaction on Brucite Surface[END_REF] As a result, those hydrosilicates form multi-walled nanotubes and nanoscrolls, that could be found in nature [START_REF] Dódony | Serpentines Close-Up and Intimate: An HRTEM View[END_REF][START_REF] Bloise | DSC Study of the Thermal Behaviour of Hazardous Mineral Fibres[END_REF][START_REF] Joussein | Halloysite Clay Minerals -a Review[END_REF] or synthesized by a hydrothermal process. [START_REF] Falini | Tubular-Shaped Stoichiometric Chrysotile Nanocrystals[END_REF][START_REF] Lafay | Dissolution-Reprecipitation and Self-Assembly of Serpentine Nanoparticles Preceding Chrysotile Formation: Insights into the Structure of Proto-Serpentine[END_REF][START_REF] Korytkova | Influence of the Physicochemical Parameters of Synthesis on the Growth of Nanotubes of the Mg3Si2O5(OH)4 Composition under Hydrothermal Conditions[END_REF][START_REF] Krasilin | Effect of the Structure of Precursors on the Formation of Nanotubular Magnesium Hydrosilicate[END_REF][START_REF] Bloise | Hydrothermal Alteration of Glass to Chrysotile[END_REF] Synthesis allows the tuning of chemical composition of phyllosilicates by doping them with Fe, [START_REF] Bloise | Synthesis of Fe-Doped Chrysotile and Characterization of the Resulting Chrysotile Fibers[END_REF][START_REF] Krasilin | Formation of Variable-Composition Iron(III) Hydrosilicates with the Сhrysotile Structure[END_REF][START_REF] Ogorodova | The Synthesis and Thermochemical Study of (Mg,Fe)3Si2O5(OH)4 Nanotubes. Russ[END_REF] Co, [START_REF] Korytkova | Hydrothermal Synthesis of Nanotubular Co-Mg Hydrosilicates with the Chrysotile Structure[END_REF][START_REF] Park | Synthesis of Co/SiO2 Hybrid Nanocatalyst via Twisted Co3Si2O5(OH)4 Nanosheets for High-Temperature Fischer-Tropsch Reaction[END_REF] Ni, [START_REF] Krasilin | Comparative Energy Modeling of Multiwalled Mg3Si2O5(OH)4 and Ni3Si2O5(OH)4 Nanoscroll Growth[END_REF][START_REF] Korytkova | Synthesis of Nanotubular Mg3Si2O5(OH)4-Ni3Si2O5(OH)4 Silicates at Elevated Temperatures and Pressures[END_REF][START_REF] Mcdonald | Hydrothermal Preparation of Nanotubular Particles of a 1:1 Nickel Phyllosilicate[END_REF][START_REF] Bloise | Influence of Synthesis Conditions on Growth of Ni-Doped Chrysotile[END_REF][START_REF] Maslennikova | Influence of Synthesis of Physicochemical Parameters on Growth of Ni3Si2O5(OH)4 Nanotubes and Their Filling with Solutions of Hydroxides and Chlorides of Alkaline Metals[END_REF][START_REF] Yang | X. Ni3Si2O5(OH)4 Multi-Walled Nanotubes with Tunable Magnetic Properties and Their Application as Anode Materials for Lithium Batteries[END_REF][START_REF] White | Morphological Control of Synthetic Ni3Si2O5(OH)4 Nanotubes in an Alkaline Hydrothermal Environment[END_REF][START_REF] Bian | A Highly Active and Stable Ni-Mg Phyllosilicate Nanotubular Catalyst for Ultrahigh Temperature Water-Gas Shift Reaction[END_REF][START_REF] Krasilin | Cation Redistribution along the Spiral of Ni-Doped Phyllosilicate Nanoscrolls: Energy Modelling and STEM/EDS Study[END_REF] Ti, [START_REF] Bloise | Hydrothermal Alteration of Ti-Doped Forsterite to Chrysotile and Characterization of the Resulting Chrysotile Fibers[END_REF][START_REF] Maslennikova | Hydrothermal Synthesis of Ti-Doped Nickel Hydrosilicates of Various Morphologies[END_REF] Ge, [START_REF] White | Spontaneous Scrolling of Kaolinite Nanosheets into Halloysite Nanotubes in an Aqueous Suspension in the Presence of GeO2[END_REF][START_REF] Perbost | Influence of Cation Size on the Curvature of Serpentine Minerals: Hrtem-Aem Study and Elastic Theory[END_REF][START_REF] Krasilin | Effect of Hydrothermal Treatment Conditions on Formation of Nickel Hydrogermanate with Platy Morphology[END_REF] and other cations, which yields change in properties [START_REF] Yang | X. Ni3Si2O5(OH)4 Multi-Walled Nanotubes with Tunable Magnetic Properties and Their Application as Anode Materials for Lithium Batteries[END_REF][START_REF] Piperno | Characterization of Geoinspired and Synthetic Chrysotile Nanotubes by Atomic Force Microscopy and Transmission Electron Microscopy[END_REF][START_REF] Krasilin | Magnetic Properties of Synthetic Ni3Si2O5(OH)4 Nanotubes[END_REF] and morphology up to stabilization of platy particles. [START_REF] Krasilin | Formation of Variable-Composition Iron(III) Hydrosilicates with the Сhrysotile Structure[END_REF][START_REF] Perbost | Influence of Cation Size on the Curvature of Serpentine Minerals: Hrtem-Aem Study and Elastic Theory[END_REF][START_REF] Krasilin | Effect of Hydrothermal Treatment Conditions on Formation of Nickel Hydrogermanate with Platy Morphology[END_REF] High specific surface area becomes one of the results of the scrolling process making the nanoscrolls suitable for adsorp-tion [START_REF] Li | Comparative Study of Synthetic Tubular Kaolinite Nanoscrolls and Natural Halloysite Nanotubes[END_REF][START_REF] Ferrante | Adsorption Studies of Molecules on the Halloysite Surfaces: A Computational and Experimental Investigation[END_REF][START_REF] Yuan | Properties and Applications of Halloysite Nanotubes: Recent Research Advances and Future Prospects[END_REF][START_REF] Krasilin | Crystal Violet Adsorption by Oppositely Twisted Heat-Treated Halloysite and Pecoraite Nanoscrolls[END_REF][START_REF] Yu | Synthesis of Magnetic Chrysotile Nanotubes for Adsorption of Pb(II), Cd(II) and Cr(III) Ions from Aqueous Solution[END_REF] and catalytic applications. [START_REF] Bian | Characterization and Catalytic Application of Phyllosilicate: A Review[END_REF] Lafay et al. [START_REF] Lafay | Influence of Trace Elements on the Textural Properties of Synthetic Chrysotile: Complementary Insights from Macroscopic and Nanoscopic Measurements[END_REF] reported on 250 m 2 /g for chrysotile nanoscrolls, and Belkassa et al. [START_REF] Belkassa | Physicochemical and Adsorptive Properties of a Heat-Treated and Acid-Leached Algerian Halloysite[END_REF] demonstrated an increase of the specific surface area from 61 to 503 m 2 /g by chemical etching. High values up to 315 m 2 /g were achieved for Ni phyllosilicates. [START_REF] Sivaiah | Nickel Based Catalysts Derived from Hydrothermally Synthesized 1:1 and 2:1 Phyllosilicates as Precursors for Carbon Dioxide Reforming of Methane[END_REF][START_REF] Bian | Highly Carbon Resistant Multicore-Shell Catalyst Derived from Ni-Mg Phyllosilicate Nanotubes@silica for Dry Reforming of Methane[END_REF] In comparison with 3D zeolites and other porous materials, nanotubes and nanoscrolls have quasi-1D channel pore, that gives rise to controllable release of its contents (for example, drugs and corrosion inhibitors) by sealing up the nanoscroll's inner channel. [START_REF] Lvov | Halloysite Clay Nanotubes for Loading and Sustained Release of Functional Compounds[END_REF][START_REF] Cavallaro | Halloysite Nanotubes: Controlled Access and Release by Smart Gates[END_REF] Abundance of OH-groups on the nanoscrolls surface facilitates its further chemical modification by organic molecules or inorganic nanoparticles boosting up adsorption, [START_REF] Mahrez | Improving of the Adsorption Capacity of Halloysite Nanotubes Intercalated with Dimethyl Sulfoxide[END_REF][START_REF] Li | Chitosan Modified Halloysite Nanotubes as Emerging Porous Microspheres for Drug Carrier[END_REF][START_REF] Grabka | Modified Halloysite as an Adsorbent for Prometryn from Aqueous Solutions[END_REF] sensing, [START_REF] Zhang | Synthesis of Au Nanoparticles Dispersed on Halloysite Nanotubes-Reduced Graphene Oxide Nanosheets and Their Application for Nitrites Electrochemical Sensing[END_REF] and catalytic performance. [START_REF] Krasilin | On an Adsorption/Photocatalytic Performance of Nanotubular Mg3Si2O5(OH)4/TiO2 Composite[END_REF][START_REF] Carrillo | Cu and Co Oxides Supported on Halloysite for the Total Oxidation of Toluene[END_REF][START_REF] Vinokurov | Formation of Metal Clusters in Halloysite Clay Nanotubes[END_REF][START_REF] Zhao | Supported Ni Catalyst on a Natural Halloysite Derived Silica-Alumina Composite Oxide with Unexpected Coke-Resistant Stability for Steam-CO2 Dual Reforming of Methane[END_REF][START_REF] Li | Halloysite Nanotube Supported Ag Nanoparticles Heteroarchitectures as Catalysts for Polymerization of Alkylsilanes to Superhydrophobic Silanol/Siloxane Composite Microspheres[END_REF][START_REF] Zhang | Application of MnOx/HNTs Catalysts in Low-Temperature NO Reduction with NH3[END_REF][START_REF] Massaro | Palladium Supported on Halloysite-Triazolium Salts as Catalyst for Ligand Free Suzuki Cross-Coupling in Water under Microwave Irradiation[END_REF][START_REF] Barrientos-Ramírez | Use of Nanotubes of Natural Halloysite as Catalyst Support in the Atom Transfer Radical Polymerization of Methyl Methacrylate[END_REF] An intriguing feature of d-element based nanoscrolls is the metal nanoparticles formation during H2 heat treatment. In addition to relatively high specific surface area of initial phyllosilicate, these particles are tightly bounded with the support. Ni, Cu, and Co-based phyllosilicate materials demonstrated good catalytic activity in dry reforming of methane, [START_REF] Sivaiah | Nickel Based Catalysts Derived from Hydrothermally Synthesized 1:1 and 2:1 Phyllosilicates as Precursors for Carbon Dioxide Reforming of Methane[END_REF][START_REF] Zhang | Sintering-Resistant Ni-Based Reforming Catalysts Obtained via the Nanoconfinement Effect[END_REF][START_REF] Ashok | Ni-Phyllosilicate Structure Derived Ni-SiO2-MgO Catalysts for Bi-Reforming Applications: Acidity, Basicity and Thermal Stability[END_REF][START_REF] Bian | Highly Carbon-Resistant Ni-Co/SiO2 Catalysts Derived from Phyllosilicates for Dry Reforming of Methane[END_REF]

Thermal behavior of Mg-Ni-phyllosilicate nanoscrolls and performance of the resulting composites in hexene-1 and acetone hydrogenation

Fischer-Tropsch process, [START_REF] Park | Synthesis of Co/SiO2 Hybrid Nanocatalyst via Twisted Co3Si2O5(OH)4 Nanosheets for High-Temperature Fischer-Tropsch Reaction[END_REF] and hydrogenation process. [START_REF] Yue | A Copper-Phyllosilicate Core-Sheath Nanoreactor for Carbon-Oxygen Hydrogenolysis Reactions[END_REF][START_REF] Wang | Ni Nanoparticles Entrapped in Nickel Phyllosilicate for Selective Hydrogenation of Guaiacol to 2-Methoxycyclohexanol[END_REF] In perspective, initial nanoscrolls could be designed on the basis of multiple d-element cations, thus supporting advantages of bimetallic catalysis. [START_REF] Bian | Highly Carbon-Resistant Ni-Co/SiO2 Catalysts Derived from Phyllosilicates for Dry Reforming of Methane[END_REF][START_REF] Bian | A Review on Bimetallic Nickel-Based Catalysts for CO2 Reforming of Methane[END_REF][START_REF] Ellert | Bimetallic Nanoalloys in Heterogeneous Catalysis of Industrially Important Reactions: Synergistic Effects and Structural Organization of Active Components[END_REF] Hydrogen treatment results in metal nanoparticles formation, but the heat action itself causes the phyllosilicate layer structural transformation. Thermal studies carried out on natural 8 and synthetic [START_REF] Bloise | Synthesis of Fe-Doped Chrysotile and Characterization of the Resulting Chrysotile Fibers[END_REF][START_REF] Bloise | Influence of Synthesis Conditions on Growth of Ni-Doped Chrysotile[END_REF][START_REF] Malkov | Effect of Heat Treatment on Structural-Chemical Transformations in Magnesium Hydrosilicate [Mg3Si2O5(OH)4] Nanotubes[END_REF][START_REF] Foresti | Morphological and Chemical/Physical Characterization of Fe-Doped Synthetic Chrysotile Nanotubes[END_REF] phyllosilicate nanoscrolls reported on two principle effects: intense endothermic dehydroxylation at around 630 °C and exothermic forsterite crystallization around 820 °C. First effect was often interpreted as structure collapse, however, nanotubular morphology can still be preserved [START_REF] Krasilin | Crystal Violet Adsorption by Oppositely Twisted Heat-Treated Halloysite and Pecoraite Nanoscrolls[END_REF] until silicate crystallization.

The aim of this work was to study peculiarities of Ni reduction in Mg-Ni-phyllosilicate nanoscrolls in the view of their catalytical application, in particular, to distinguish between the effect of temperature increase and H2 chemical action on the nanoscrolls structure and morphology.

EXPERIMENTAL SECTION

Nanoscrolls synthesis

Phyllosilicate (Mg1-xNix)3Si2O5(OH)4 nanoscrolls with nominal x = 0, 0.33, 0.5, 0.67, and 1 were synthesized by hydrothermal treatment of initial composition. The latter was prepared as follows. About of 4 g of amorphous SiO2 (Aerosil A-300) were mixed with 100 ml of 2 M NaOH water solution. The suspension was stirred by magnetic stirrer for 24 h at room temperature until SiO2 dissolution. Then 500 ml of 1 M (1-x)MgCl2 and xNiCl2 water solution was added dropwise at constant stirring. The precipitate was washed with distilled water from NaCl byproduct and excess of NaOH by decantation and vacuum filtration, dried at 90 °C in air, and grinded in an agate mortar. About of 2.0 g of initial composition was put in 400 ml stainless steel autoclave with titanium liner. The autoclave's volume was filled by 160 ml of 0.1 M NaOH water solution. The vessel was sealed, and heat treated at 350-353 °C and 21-24 MPa (the pressure was measured by U-type and digital pressure gauges) for 10 h. After cooling, the product was washed from NaOH by decantation and dried at 90 °C in air.

Heat treatment techniques

Thermal properties of the nanoscrolls obtained were investigated by synchronous thermal analysis and temperatureprogrammed reduction (TPR). Netzsch STA 429 CD was used as thermal analyzer working in differential scanning calorimetry and thermogravimetry regime (DSC-TG). The device was equipped with quadrupole mass spectrometer Netzsch QMS 403 C for detection of thermal decomposition products. A tablet containing about 20 mg of sample was produced by hydraulic press (the pressure was 1 kg/mm 2 ). Tablets were analyzed in open corundum crucible in the 40-1100 °C temperature range with 20 °/min heating speed. Compressed air or 5 vol.% H2-Ar mixture (99.995% purity) were used as a dynamic (50 ml/min) atmosphere.

TPR experiments were carried out on Chemosorb ("Neosib", Novosibirsk). About of 0.1 g of the sample was pressed into tablet and put into gas flow reactor. The reactor was fed with 60 ml/min 10 vol.% H2-Ar mixture (of 99.995% and 99.998% purity, respectively). Hydrogen consumption profiles were recorded in the 25-900 °C range at 20 °/min heating rate.

Catalysis of hydrogenation reactions

The nanoscrolls samples with maximal nominal Ni load (x = 0.67, 1) were put into the quartz gas flow reactor (a tube of 6 mm inner diameter) and exposed to 99.995 % H2 50 ml/min flow for 1 hour at a number of given temperatures. The exposure temperatures were chosen in the 400-900 °C range on the basis of thermal analysis. The furnace has been heated in advance up to the chosen temperature. Catalytical tests were carried out right after exposure in the same set up. Hydrogen was bubbled through one of the initial reagents, then the gaseous mixture was passed through the sample at 120 and 240 °C. Initial reagents were preheated in the case of their low volatility. Since the reaction occurred at a gas/solid interface, compliance of constant contact time between the gaseous mixture and the solid was considered to be of first priority. For that purpose, the solid sample apparent volume that had been put in the reactor was kept constant at 0.45 cm 3 . Three hydrogenation reactions were studied: hexene-1 to hexane conversion, acetone to isopropanol conversion, and the transformation of benzene into cyclohexane. The reaction product was cooled (in ice bath) and collected for ex situ nuclear magnetic resonance ( 1 H NMR) analysis.

Ex situ characterization

Hydrothermal and heat treatment products were characterized by powder X-ray diffraction (RXPD, Rigaku SmartLab 3 operating in the Bragg-Brentano geometry, 1.5406 Å CuKa radiation, Kb filtered, D/TEX ULTRA 250 detector working in 1D mode) in the 5-80° 2q range with a 0.01° step. The Crystallography Open Database [START_REF] Gražulis | Crystallography Open Database (COD): An Open-Access Collection of Crystal Structures and Platform for World-Wide Collaboration[END_REF][START_REF] Gražulis | Computing Stoichiometric Molecular Composition from Crystal Structures[END_REF] (COD) was used for the phase analysis. The PXRD peak files (for visualization purposes) were simulated by the VESTA 70 powder diffraction utility. Size distributions of Ni nanoparticles were calculated involving the most intense (111) reflection of metallic nickel by Rigaku SmartLab Studio II software. Fundamental Parameter method [START_REF] Cheary | Fundamental Parameters Approach to X-Ray Line-Profile Fitting[END_REF] was used for the peak's convolution assuming lognormal distribution of nanoparticles size. The (Mg1-xNix)3Si2O5(OH)4 nanoscrolls lattice constants were refined by the Whole Powder Pattern Decomposition 72 assuming ellipsoidal shape of crystallite.

FEI Quanta 200 scanning electron microscope equipped with EDAX energy dispersive X-ray spectrometer (SEM/EDS) was used for element content evaluation. Average sizes and morphology of the nanoscrolls and Ni particles were studied by Zeiss Libra 200 transmission electron microscope (TEM) in the bright field mode. About 200 nanoscrolls for each x value were used to estimate their mean length, outer and inner diameters on the basis of volumetric distribution. The volume of every nanoscroll was calculated in the hollow cylindrical approximation. Then, a weighted average value was calculated for each parameter. Ni nanoparticles size distributions based on TEM micrographs analysis accounted for at least 500 particles for each sample. Simple numerical weighted average was used to calculate the particles mean diameter.

JEOL -ARM 200 F Cold FEG was used for high-resolution microstructure characterization and element mapping (JEOL Centurio Silicon Drift Detector). The microscope was operated at 200 kV in TEM and scanning TEM (STEM) bright field and high-angle annular dark field (HAADF) modes. Gwyddion open-source software [START_REF] Nečas | An Open-Source Software for SPM Data Analysis[END_REF] was used for fast Fourier transform (FFT) of TEM micrographs. Change in the specific surface area of the samples exposed to hydrogen was studied by N2 adsorption and desorption in the 0.01-0.99 P/P0 range using Micromeritics ASAP 2020. Prior measurements, samples were vacuum heated at 110 °C until constant mass. Specific surface area was evaluated within the Brunauer-Emmett-Teller (BET) theory approximation.

Product content (W, at.%) after each type hydrogenation reaction was estimated by normalizing the 1 H NMR spectra integral peak intensity of product on sum of product and initial substance peak intensities. Spectra were acquired by liquid phase 1 H NMR (Bruker DPX-200, 200 MHz working frequency). Tetramethylsilane was used as an external standard.

RESULTS AND DISCUSSION

Nanoscrolls structure and morphology

Figure 1.a shows PXRD patterns of hydrothermal treatment products. All patterns were well described by the synthetic chrysotile (COD ID 1552115) obtained by Foresti et al. [START_REF] Falini | Tubular-Shaped Stoichiometric Chrysotile Nanocrystals[END_REF] Mg 2+ to Ni 2+ cations substitution yielded minor crystal structure change due to the fact that these cations have close values of ionic radii: 72 pm and 69 pm, [START_REF] Shannon | Effective Ionic Radii in Oxides and Fluorides[END_REF] respectively. That substitution led to gradual decrease in the lattice volume.(Figure 1.b) Table 1 represents chemical composition of nanoscroll samples measured by SEM/EDS. The nickel content, measured by EDS (xEDS), corresponded to its nominal content within the error.

Figure 2.a-c shows TEM micrographs of nanoscrolls as well as change in mean values of size parameters as functions of nominal x. In all cases hydrothermal process yielded different nanoscrolls fractions starting from particles with aspect ratio close to 1 up to highly anisotropic nanofibers. In this case the all dependencies of size parameters upon nominal Ni content demonstrated a maximum at x = 0.5. This maximum could be related to chemical composition features revealed in previous works, [START_REF] Krasilin | Cation Redistribution along the Spiral of Ni-Doped Phyllosilicate Nanoscrolls: Energy Modelling and STEM/EDS Study[END_REF][START_REF] Krasilin | Formation of Conical (Mg,Ni)3Si2O5(OH)4 Nanoscrolls[END_REF][START_REF] Krasilin | Redistribution of Mg and Ni Cations in Crystal Lattice of Conical Nanotube with Chrysotile Structure[END_REF] such as growth of conical nanoscrolls and redistribution of Mg and Ni cations along the nanoscroll's spiral. This feature can be possible because of the nanotubular phyllosilicate crystal growth, in addition to conventional crystal growth processes, is guided by a strain energy. [START_REF] Krasilin | Comparative Energy Modeling of Multiwalled Mg3Si2O5(OH)4 and Ni3Si2O5(OH)4 Nanoscroll Growth[END_REF][START_REF] Guimarães | Electronic, and Mechanical Properties of Single-Walled Halloysite Nanotube Models[END_REF][START_REF] Demichelis | Serpentine Polymorphism: A Quantitative Insight from First-Principles Calculations[END_REF] The latter is a function of size difference between octahedral and tetrahedral sheets, in other words, a function of ionic radii of cations which constitute the layer.

Thermal behavior features

Heat treatment in air Figure 3 shows DSC-TG curves obtained in air and in H2-Ar atmosphere, and PXRD patterns of samples after the thermal analysis. Temperature increase in air (Figure 3.a,c) was accompanied by three principle heat effects in the ranges of 100-400 °C, 400-800 °C, and 800-1100 °C. Below 200 °C there is a small endothermal effect related to adsorbed water removal up to 4% of initial mass. The interval of 200-400 °C was characterized by small continuous mass loss without pronounced heat effects, that could be related to both removal of strongly coupled water and dehydroxylation of nanoscroll outer layers.

The 400-800 °C range contained intense but broad endoeffect with mass loss up to 9% in air. This effect could be caused by volume dehydroxylation [START_REF] Bloise | Influence of Synthesis Conditions on Growth of Ni-Doped Chrysotile[END_REF] together with structural transformation of sample into sepiolite-like Mg4Si6O15(OH)2 phase shown by Krasilin et al. [START_REF] Krasilin | Crystal Violet Adsorption by Oppositely Twisted Heat-Treated Halloysite and Pecoraite Nanoscrolls[END_REF] Because sepiolite differs from Mg3Si2O5(OH)4 chrysotile by Mg:Si ratio, this transformation could also be accompanied with partial amorphization. Increase in Ni content split the peak (see inset on Figure 3.a) into at least two parts. Temperature of the shoulder was ap-proximately equal to that of the sample with x = 1, while the main peak's temperature shifted from 635 °C (x = 0) to 649 °C (x = 0.33) and 637 °C (x = 0.5). We attributed this splitting to the effect of cations redistribution along the nanoscroll's spiral as mentioned elsewhere. [START_REF] Krasilin | Cation Redistribution along the Spiral of Ni-Doped Phyllosilicate Nanoscrolls: Energy Modelling and STEM/EDS Study[END_REF] The Ni-rich shell of the nanoscroll could dehydroxylate at lower temperature (585-587 °C) thus serving as a sacrificial layer against heat action. If, on the contrary, Mg and Ni cations were distributed nonuniformly between the particles but homogeneously in the scrolled layer of every particle, then one should expect gradual decrease in the peak temperature without occurrence of the shoulder peak. As far as the sepiolite-like phase still contained some number of OH-groups, it dehydroxylated continuously in the 640-800 °C range, which could be confirmed by the mass loss curves. (Figure 3.c)

Strong and narrow exo-effect in the 800-1100 °C range was related to (Mg,Ni)2SiO4 (COD ID 900053578) forsterite crystallization. The effect was very sensitive to the Ni content: its increase hindered crystallization of the silicate phase or even cancelled it at x = 1. PXRD analysis (Figure 3.e) showed that there was an admixture of (Mg,Ni)SiO3 (COD ID 154855179) enstatite, which could crystallize at temperature higher than 1000 °C. Exo-effect of this process should be very weak because the stoichiometry of the system treated in air lies far beyond Mg:Si=1:1 favorable for MgSiO3 formation. Nanocrystalline NiO (COD ID 101038180) was formed instead of forsterite-like phase with very weak exo-effect at 1020 °C in case x = 1. This effect could also be attributed to a-SiO2 crystallization, but this phase was hardly visible on the PXRD pattern. (Figure 3.e) All samples contained amorphous phase, most likely, SiO2 together with crystalline phases.

Heat treatment in H2-Ar

Heat treatment in H2-Ar mixture (Figure 3.b,d) was accompanied by Ni 2+ cations reduction. It was assumed that the reduction reaction was slightly exothermic by the analogy with NiO reduction. [START_REF] Galwey | The Mechanism and Kinetics of NiO Reduction by Hydrogen[END_REF] This process perturbed heat effects curves with weak and hardly visible exo-effects. Only some of them could be successfully correlated with hydrogen consumption profiles presented in Figure 4. However, the effect of Ni reduction was distinctly seen by an almost two-fold increase in mass loss in the 400-800 °C range. Hydrogen treatment extracted nickel out from the oxide part of the system thus decreasing the metal to silicon ratio. In the case of x = 0.33 the final Mg:Si ratio was 1:1, and crystallization of MgSiO3 (Figure 3.f) enstatite with exo-effect at 1080 °C (Figure 3.b) followed by forsterite crystallization. For other cases this effect was less articulated. In the case of x = 1 the only one option -crystallization of a-SiO2 (COD ID 900157882) -could cause weak exo-effect at 1020 °C.

The reduction of Ni began after 300 °C in a stepwise manner. (Figure 4) At x = 0.33, there were two distinct regions of reduction with maxima at 400 °C, 445 °C, and 677 °C with a gap between them where almost no H2 consumption occurred. Temperature range of this gap coincided with the chrysotileto-sepiolite transition. (Figure 3.b and Table 2) In contrast to 1:1 sheet arrangement in chrysotile, sepiolite is 2:1 phyllosilicate (Figure S1), in which tetrahedral sheets surround octahedral ones from both sides. [START_REF] Falini | Tubular-Shaped Stoichiometric Chrysotile Nanocrystals[END_REF][START_REF] Post | Synchrotron Powder X-Ray Diffraction Study of the Structure and Dehydration Behavior of Sepiolite[END_REF] This feature could serve as sterical hindrance for the reduction process and grant an increased thermal stability to those Ni cations that had not been reduced. In addition, sepiolite layers were surrounded by Mg-rich amorphous substance, which should be produced due to stoichiometry requirements. x is nominal Ni content; Tmax is temperature of the peaks extremum; (h) points that the value was obtained in the H2-Ar atmosphere; (tpr) means that the value was obtained on the basis of the TPR experiment. (Figure 4) Relative intensities of the thermal effects are denoted as follows: 'v.w.' -very weak, 'w.' -weak, 'm.' -medium, 's.' -strong. The effect's type is denoted as follows: 'en.' -endothermic, 'ex.'exothermic. Other designations are: 'sh.' -shoulder of the main peak.

In fact, among the samples studied the chrysotile-tosepiolite transition could be possible without segregation of Ni into the amorphous only for x = 0.33, in an extreme case. In terms of metal to silicon ratio the transition is the ratio change from 3:2 to 2:3, or 6:4 Me6Si4O10(OH)8 chrysotile-like to sepiolite-like 4:6 Me4Si6O15(OH)2. To accomplish this transition, a phase with the 4:1 ratio has to be withdrawn:

4Mg ! NiSi ! O $ (OH) " % → Ni " Si & O '$ (OH) ! + 2Mg " SiO &()*.) + 8H ! O ↑
Potentially, all nickel cations could be preserved in the sepiolite-like phase only in case x ≤ 0.33 or else they would end up in the amorphous 4:1 phase and would be reduced immediately. At x = 0.5, the reduction process did not disrupt namely because the amorphous 4:1 phase contained sufficient amount of Ni cations. With further increase in the x value up to 0.67 and 1 the beginning of chrysotile-to-sepiolite transition and amorphization, on the contrary, acted like a driver for reduc-tion. Finally, in these cases high temperature peaks of reduction appeared (Figure 4), which were attributed to Ni reduction in bulk sepiolite-like phase or to amorphous phase formed right after continuous dehydroxylation of sepiolite-like phase. The results of heat effects assignments are summarized in Table 2.

Structure and morphology of Ni-containing composites

Thermal analysis demonstrated the possibility of metallic Ni particles formation from the nanoscrolls by H2 treatment. TPR (Figure 4) and STEM/EDS analysis of the products (Figure 5) showed that Ni could be completely extracted at high temperature. Nickel nanoparticles were embedded in residual matrix (Figure 6) consisting of amorphous silica or combination of silica and forsterite depending on presence of magnesium cations. General cylindrical morphology of the composite was preserved; however, the inner channel was eliminated completely at high temperature. 7 shows PRXD patterns of the samples with highest Ni content (x = 0.67, 1), reduced by pure H2 at given temperatures. Besides TPR (Figure 4) showed start of reduction process at 400 °C, it was complicated to confirm it by PXRD or TEM. Reliable presence of Ni nanoparticles (COD ID 901302484) was found in the samples treated at 540-600 °C. Crystal structure of the nanoscrolls first also changed to sepiolite-like phase (COD ID 901014883) with temperature increase (Figure 7) and then eliminated gradually.

Figure 8 shows degradation of the nanoscroll layered structure and its transformation to composite material. In the first step, hydrosilicate layers thickened and lost their periodicity. In hydrogen atmosphere this process came along with growth of Ni nanoparticles. Further decomposition of the layers yielded amorphous substance, and its subsequent crystallization depended on the initial chemical composition. (Figure 6)

Figure 9 compares PXRD and TEM size distributions of Ni nanoparticles. Generally, Ni particles size distributions broadened, and their weighted average value grew with the temperature increase. Both types of distributions were in a good agreement with each other. Decrease in Ni content yielded increase in Ni particles size, which could be clearly seen in the high temperature region. This feature could be the consequence not only of the higher nucleation speed in the Ni-rich system but also of but also of the crystallization of residual matrix components that try to take room for themselves, force out Ni particles and move them closer to each other. On the other hand, presence of amorphous phase like SiO2 usually hindered the mass transfer and crystallization of any other component in the system up to high temperature of 1500 ºC. [START_REF] Almjasheva | Effect of ZrO2 Nanocrystals on the Stabilization of the Amorphous State of Alumina and Silica in the ZrO2-Al2O3 and ZrO2-SiO2 Systems[END_REF]

Hydrogenation performance

Figure 10 demonstrates change in BET surface area with increase in H2 treatment temperature. Decrease in surface area occurred in same manner as it was shown before for the case of Ni3Si2O5(OH)4 nanoscrolls treated in air. [START_REF] Krasilin | Crystal Violet Adsorption by Oppositely Twisted Heat-Treated Halloysite and Pecoraite Nanoscrolls[END_REF] The decrease had Z-form curve with slight value recovery in the area of chrysotile-to-sepiolite transition. This recovery could be related with features in the nanoscrolls wall alteration (Figure 8) as a kind of thickening and exfoliation of the layers, which could open additional sites for adsorption. The sample with nominal x = 0.67 suffered greatly from the heat action probably because of its partial crystallization in the high temperature range. (Figure 7.a) Figure 10. BET surface area of initial nanoscrolls (heat treated in vacuum at 110 °C) and the reduced samples.

Table 3 shows hexane and isopropanol content W after hexene-1 and acetone hydrogenation at two temperatures. Attempts to hydrogenate benzene also have been carried out, but without success: conversion efficiency did not climb over 2%. Both series of samples demonstrated high performance in hydrogenation of hexene-1. The effect took place even in case of samples treated at 400 °C, that indirectly confirms the presence of Ni nanoparticles. These facts are in a good agreement with the literature data. Mokhov et al. [START_REF] Mokhov | Hydrogenation of Alkenes over Nickel Nanoparticles under Atmospheric Pressure of Hydrogen[END_REF] revealed that Ni nanoparticles were an effective catalyst for alkene-into-alkane transformation under mild conditions. Moreover, such catalysts were selective and did not lead to reduction of arenes. The W value decreased with an increase in the reaction temperature. One of the reasons could be the hydrogenationdehydration of acetone, as it was shown for the cases with Ni/zeolite 87 and Ni/SiO2 88 catalysts. In particular, Sooknoi et al. [START_REF] Witsuthammakul | Selective Hydrodeoxygenation of Bio-Oil Derived Products: Ketones to Olefins[END_REF] revealed that dehydration rate increased, that lowered the isopropanol content in the products mixture, significantly above 150 °C. This process involves two sequential reactions -hydrogenation of initial acetone to iso-propanol over metal sites of catalyst and dehydration of the alcohol over SiO2 (or zeolite) sites. Thus, propene could be one of possible dehydration products. The selected experimental conditions and research methods did not allow to capture propene in the reaction products because of its -47.7 °C boiling temperature. So, the observed W value decrease could be assigned to the formation of propene instead of isopropanol at 240°C.

Overall drop of the W value with H2 treatment temperature increase from 400 °C to 900 °C was likely related to decrease in specific surface area and Ni nanoparticles growth. An increase of the W value with increase in Ni content was related to the particle size decrease, i.e. to increase their surface-tovolume ratio. Accumulative H2 consumption profiles (

100%

(2)

where lower index means nominal Ni content.

These two equations were applied to weighted average diameter (Figure 9.b) and W value (Table 3) of the samples reduced at 600 ºC and used as acetone hydrogenation catalysts at 120 ºC. It was found that Δ𝑠 &66 = 54% and Δ𝑊 &66 = 43%. In the case samples were reduced at 900 ºC, the equations yielded Δ𝑠 766 = 58% and Δ𝑊 766 = 56%. The proximity of these two values spoke in favor of the decisive role of the particles surface-to-volume ratio in the hydrogenation process.

CONCLUSIONS

Here we considered chemical and structural transformations occurring in (Mg1-xNix)3Si2O5(OH)4 nanoscrolls, obtained by hydrothermal synthesis, under heating in air and in H2-Ar flow. In air, the nanoscrolls passed through a number of dehydroxylation steps with endothermic transition to a sepiolitelike phase in the 580-650 °C range following by exothermic silicate, silica, or nickel oxide crystallization depending on the initial chemical composition. In H2-Ar, nickel can be fully or partially reduced out from nanoscrolls in a tunable manner. The reduction process overlapped with endothermic dehydroxylation stages and did not show obvious thermal effects even though it was distinctly detected on the TG curves. Transition to sepiolite-like phase influenced on the reduction process by sealing up a part of nickel-containing octahedrons cations with SiO2 sheets from both sides. This feature modulated the shape of H2 consumption profiles resulting in appearance of gaps and peak splitting. Mean diameter of Ni nanoparticles obtained by the reduction decreased with increase of Ni content in the initial nanoscrolls, that was attributed to increase in nucleation rate and quantity of amorphous phase, which hindered mass transfer between Ni nanoparticles at high temperature. Difference in the size-to-volume ratio of Ni nanoparticles distribution, as well as specific surface area decrease during heat treatment, produced an optimal 600 °C reduction temperature in the view of the hydrogenation conversion rate.

Figure 1 .

 1 Figure 1. (a) PXRD patterns and (b) change in lattice constants of (Mg1-xNix)3Si2O5(OH)4 nanoscrolls vs Ni content measured by EDS.

Figure 2 .

 2 Figure 2. TEM micrographs of nanoscrolls with nominal Ni content x = (a) 0, (b) 0.5, and (c) 1. (d) Weighted mean values of nanoscrolls size parameters based on their mass contribution vs nominal Ni content x.

Figure 3 .

 3 Figure 3. DSC curves obtained (a) in air and (b) in H2-Ar atmosphere. TG curves obtained (c) in air and (d) in H2-Ar atmosphere. PXRD patterns obtained after thermal analysis (e) in air and (f) in H2-Ar atmosphere.

Figure 4 .

 4 Figure 4. (a) H2 consumption profiles obtained by the TPR method and (b) cumulative H2 consumption profiles showing relative quantity of Ni being reduced at certain temperature.

Figure 5 .

 5 Figure 5. STEM HAADF micrographs and EDS maps of nickel distribution in samples after TPR analysis. Nominal x was (a) 0.5 and (b) 1.

Figure 6 .

 6 Figure 6. TEM micrographs of TPR products with nominal x (a) 0.5 and (b) 1 with FFT images of selected areas. (c) FFT profiles of selected areas after radial integration.

Figure 7 .

 7 Figure 7. PXRD patterns of Mg-Ni-nanoscrolls with x = (a) 0.67 and (b) 1 reduced in pure H2 at given temperatures.

Figure 8 .

 8 Figure 8. TEM micrographs of Mg-Ni-nanoscrolls with (a) x = 0.67 and (b) 1 reduced at certain temperatures. HAADF image and Ni EDS map of Mg-Ni nanoscrolls with (c) x = 0.67 reduced at 600 °С and (d) x = 1 reduced at 540 °C showing partial Ni reduction.

Figure 9 .

 9 Figure 9. (a) PXRD (solid line) and TEM (chart) size distributions of Ni nanoparticles. Total number of the particles measured is given in brackets. (b) Weighted mean diameter of the nanoparticles according to PXRD and TEM analysis.

Figure

  Figure7shows PRXD patterns of the samples with highest Ni content (x = 0.67, 1), reduced by pure H2 at given temperatures. Besides TPR (Figure4) showed start of reduction process at 400 °C, it was complicated to confirm it by PXRD or TEM. Reliable presence of Ni nanoparticles (COD ID 901302484) was found in the samples treated at 540-600 °C. Crystal structure of the nanoscrolls first also changed to sepiolite-like phase (COD ID 901014883) with temperature increase (Figure7) and then eliminated gradually.Figure8shows degradation of the nanoscroll layered structure and its transformation to composite material. In the first step, hydrosilicate layers thickened and lost their periodicity. In hydrogen atmosphere this process came along with growth of Ni nanoparticles. Further decomposition of the layers yielded amorphous substance, and its subsequent crystallization depended on the initial chemical composition. (Figure6)Figure9compares PXRD and TEM size distributions of Ni nanoparticles. Generally, Ni particles size distributions broadened, and their weighted average value grew with the temperature increase. Both types of distributions were in a good agreement with each other. Decrease in Ni content yielded increase in Ni particles size, which could be clearly seen in the high temperature region. This feature could be the consequence not only of the higher nucleation speed in the Ni-rich system but also of but also of the crystallization of residual matrix components that try to take room for themselves, force out Ni particles and move them closer to each other. On the other hand, presence of amorphous phase like SiO2 usually hindered the mass transfer and crystallization of any other component in the system up to high temperature of 1500 ºC.[START_REF] Almjasheva | Effect of ZrO2 Nanocrystals on the Stabilization of the Amorphous State of Alumina and Silica in the ZrO2-Al2O3 and ZrO2-SiO2 Systems[END_REF] Hydrogenation performanceFigure10demonstrates change in BET surface area with increase in H2 treatment temperature. Decrease in surface area occurred in same manner as it was shown before for the case of Ni3Si2O5(OH)4 nanoscrolls treated in air.[START_REF] Krasilin | Crystal Violet Adsorption by Oppositely Twisted Heat-Treated Halloysite and Pecoraite Nanoscrolls[END_REF] The decrease had Z-form curve with slight value recovery in the area of chrysotile-to-sepiolite transition. This recovery could be related with features in the nanoscrolls wall alteration (Figure8) as a kind of thickening and exfoliation of the layers, which could open additional sites for adsorption. The sample with nominal x = 0.67 suffered greatly from the heat action probably because of its partial crystallization in the high temperature range. (Figure7.a)

Figure 4 .

 4 b) showed that at any temperature lower than 650 °C equal quantities of Ni have been reduced in samples with x = 0.67 and 1. Assuming spherical form of Ni nanoparticles, the surface-to-volume ratio could be written as follows: where d is a weighted average diameter. Relative change of a value v was written as follows: Δ𝑣 = |1 ".$% /1 & | 234(1 ".$% ,1 & )

Table 1 . Nanoscrolls chemical composition according to SEM/EDS measurements.

 1

	nomin al x	Ni content by EDS, xEDS	Mg	normalized element concentration, at.% Ni Si O	Approximate chemical formula
	0	0	23±4	0	15±3	62±7	Mg2.98Si2O5(OH)4
	0.33	0.32±0.03	15.6±0.2	7.4±0.1	16.2±0.3	60.8±0.5	Mg1.93Ni0.92Si2O5(OH)4
	0.5	0.45±0.05	11.5±0.7	9±2	16.5±0.5	63±3	Mg1.40Ni1.33Si2O5(OH)4
	0.67	0.64±0.05	8.5±0.2	15.1±0.2	15.9±0.2	60.5±0.3	Mg1.06Ni1.90Si2O5(OH)4
	1	1	0	23±3	16±2	60±5	Ni2.97Si2O5(OH)4

Table 2 . Thermal effects in (Mg1-xNix)3Si2O5(OH)4 nanoscrolls in the 100-1100 °C range.

 2

	T range, °C x	mass loss, %	Tmax of the effect, °C assignment
	100-400	0	3-4; 2 (h)
		0.33	1-2; 1-2 (h)	-	Removal of adsorbed water, dehydroxylation
		0.5	2; <1 (h)
				340 (tpr) 390 (tpr)	Ni reduction in chrysotile layers
		0.67	1-2; <1 (h)	-	Removal of adsorbed water, dehydroxylation
				274 (tpr)	Ni reduction in chrysotile layers. Probably,
				335 (tpr)	reduction of Ni(OH)2 byproduct
		1	2; <1 (h)	-	Removal of adsorbed water, dehydroxylation
	400-800	0	11; 11 (h)	628 m. en. (h) 635 m. en.	Chrysotile-to-sepiolite transition
		0.33	9; 16 (h)	400 (tpr) 445 (tpr)	Ni reduction in chrysotile layers
				579 sh. w. en. (h) 584 sh. w. en.	Chrysotile-to-sepiolite transition of Ni-rich part
				641 m. en. (h) 649 m. en.	Chrysotile-to-sepiolite transition of Mg-rich part
				677 (tpr)	Ni reduction during and after the transition
		0.5	9; 16 (h)	472 (tpr)	Ni reduction in chrysotile layers
				579 sh. w. en. (h) 583 sh. w. en.	Chrysotile-to-sepiolite transition of Ni-rich part
				633 m. en. (h) 637 m. en.	Chrysotile-to-sepiolite transition of Mg-rich part
				667 (tpr)	Ni reduction of amorphous phase formed during the chrysotile-to sepiolite transition
		0.67	8; 16 (h)	449 (tpr)	Ni reduction in chrysotile layers
				596 (tpr)	Ni reduction of amorphous phase formed during the

Table 3 . Product (hexane or isopropanol) content W (at.%) depending on Ni content and nanoscrolls reduction tem- perature.

 3

	x	T, °C	hexene-1 120 °C 240 °C	120 °C	acetone 240 °C
		400	100	100	71	13
	1	600	100	100	79	27
		900	100	63	45	14
		400	-	-	23	8
	0.67	600	100	100	45	15
		900	100	50	20	12

ACKNOWLEDGMENT

The research was partially supported by the Russian Science Foundation (Grant 19-13-00151). A.N., S.B. and J.G. are thankful to the French Ministry of Higher Education, Research and Innovation for financial support through Program Hubert Curien-Kolmogorov. A.N. is thankful to "ITMO Fellowship and Professorship" program. X-ray studies were carried out on the equipment of the Engineering Center of Saint-Petersburg State Technological Institute (Technical University). The authors would like to thank E.V. Kryachko, K.I. Timoschuk, D.P. Danilovich, and Prof. V.V. Gusarov for assistance and fruitful discussions.

ASSOCIATED CONTENT

Supporting Information

The Supporting Information is available free of charge on the ACS Publications website.

Crystal structures of chrysotile and sepiolite (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: ikrasilin@mail.ioffe.ru

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

ABBREVIATIONS

TPR, temperature-programmed reduction; DSC, differential scanning calorimetry; TG, thermogravimetry; NMR, nuclear magnetic resonance; PXRD, powder X-ray diffraction; COD, Crystallography Open Database; SEM, scanning electron microscopy; TEM, transmission electron microscopy; STEM, scanning transmission electron microscopy; EDS, energy dispersive X-ray spectroscopy; HAADF, high-angle annular dark field; FFT, fast Fourier transform; BET, Brunauer-Emmett-Teller; .