摻雜元素X（B、Al、Sn、Co）對IDB-X/Diamond界面結(jié)合性能的影響

摘要 基于量子力學第一性原理，建立了IDB-B/Diamond、IDB-Al/Diamond、IDB-Sn/Diamond和IDB-Co/Dia-mond 4種膜基界面模型，計算了膜基界面結(jié)合能、差分電荷密度和布居數(shù)，以探究孕鑲金剛石鉆頭（impreg-nated diamond bits，IDB）基體中的常用元素X（X=B、Al、Sn、Co）對IDB-X/Diamond膜基結(jié)合強度的影響機制。計算結(jié)果表明：膜基界面結(jié)合能大小為Wad-Bgt;Wad-Algt;Wad-Cogt;Wad-Sn；B、Al是增強膜基結(jié)合強度的有益元素，因為B、Al原子的電荷主要轉(zhuǎn)移到摻雜位點附近的C1～C3原子，其與C1～C3原子的鍵合作用強；Sn、Co會削弱膜基結(jié)合強度，這是由于Sn、Co原子與C1～C3原子的鍵合作用弱，同時膜基界面間的其他C原子因俘獲電荷而相斥。壓痕對比的實驗結(jié)果與仿真結(jié)論相符。

關鍵詞 第一性原理；金剛石涂層；膜基結(jié)合；電荷轉(zhuǎn)移；布居數(shù)；壓痕實驗

中圖分類號 TQ164;TG58;TG74 文獻標志碼 A

文章編號 1006-852X（2025）01-0037-09

當前，地表資源接近枯竭，資源勘探和開采持續(xù)向地下深層擴張[1]，孕鑲金剛石鉆頭（impregnated dia-mond bits，IDB）以其優(yōu)異的切削性能和對高溫高壓環(huán)境優(yōu)良的耐受力，成為地下深層鉆進的主要工具[2]。

IDB一般是將金屬粉料與金剛石顆?；旌暇鶆蚝?，采用粉末冶金的方法熱壓燒結(jié)而成[3]。Sn和Co是IDB基體中常用的金屬黏結(jié)劑[2，4]，可增強基體對金剛石顆粒的把持力；在IDB基體配方中添加B元素可以提高金剛石顆粒的抗氧化性和IDB整體的耐磨性[2，5]，加強金剛石顆粒和基體之間的結(jié)合力[6]；添加Al元素可以提高基體強度[2]和致密度[4]，降低基體界面張力和表面張力[7]。

本課題組提出在IDB表面原位沉積一層CVD金剛石涂層，實現(xiàn)金剛石涂層的同質(zhì)外延生長和異質(zhì)外延生長，進一步提高IDB的工作壽命。大量宏觀實驗研究指出，在金剛石涂層與基底界面間引入B元素[8-9]或者在過渡層中引入Al元素[10-11]，有利于提高膜基結(jié)合力。關于Sn元素對膜基界面性能影響的研究較少。由于Co是IDB中綜合性能良好的金屬黏結(jié)劑，且會削弱膜基結(jié)合強度[12]，故本文引入Co元素作為對照。

基于量子力學第一性原理，借助CASTEP計算工具，從微觀角度研究IDB基體中常用的X（X=B、Al、Sn、Co）元素對孕鑲金剛石基底與CVD金剛石涂層膜基界面結(jié)合性能的影響機制，為優(yōu)化IDB基體配方和提高膜基界面結(jié)合強度提供理論參考與依據(jù)。

1模型建立與計算方法

1.1幾何模型

借助量子力學計算軟件Materials Studio，以IDB表層的金剛石顆粒為基底[13]，采用基底表層原子替代的方式[14]，建立含X（X=B、Al、Sn、Co）原子的IDB-X/Diamond膜基界面模型。其中，基底表層原子替代指在建立好孕鑲金剛石基底后，分別用B、Al、Sn、Co原子替代基底表層特定位點的C原子。

參考文獻[13]的建模方法，首先，分別建立孕鑲金剛石基底和CVD金剛石涂層的單晶胞模型；其次，分別進行[100]晶向的切晶胞處理，因為在結(jié)構(gòu)優(yōu)化過程中膜基界面模型的原子相對位置變化主要集中于最外3層原子，為保證模型的穩(wěn)定性，經(jīng)表面能收斂性測試，切取C原子厚度定為5層；接著，建立3×3的孕鑲金剛石基底和CVD金剛石涂層超晶胞模型，其沿X、Y、Z方向的尺寸均為7.54?×7.54?×3.56?，分別添加厚度為12?的真空層后得到孕鑲金剛石基底模型和CVD金剛石涂層模型；然后，將孕鑲金剛石基底模型表面特定位點的C原子用X（X=B、Al、Sn、Co）原子進行替代，替代位點如圖1所示；最后，將X（X=B、Al、Sn、Co）原子替代后的IDB-X基底與CVD金剛石涂層模型沿[100]晶面結(jié)合，建立IDB-X/Diamond膜基界面模型，測試后，設置膜基界面間距為2?，如圖2所示。由于所建膜基界面模型中基底與涂層為同種晶胞構(gòu)建而來，且基底晶面和涂層晶面尺寸相同，故兩晶面之間的結(jié)合穩(wěn)定性優(yōu)異，界面適配度好。

1.2計算方法

基于密度泛函理論的CASTEP第一性原理計算方法，廣泛應用于研究包括金剛石材料在內(nèi)的陶瓷、金屬、半導體等各種晶體材料及其表界面性質(zhì)[15]。

本文采用Materials Studio的CASTEP模塊優(yōu)化X（X=B、Al、Sn、Co）原子摻雜的IDB-X/Diamond膜基界面模型，進而從膜基界面結(jié)合能、差分電荷密度、原子和化學鍵重疊布居數(shù)方面來分析4種膜基界面模型的性質(zhì)。選用廣義梯度近似下的交換關聯(lián)泛函GGA-PBE，平面波截斷能設置為400 eV，采用超軟贗勢（ultrasoft pseudopotential），布里淵區(qū)k點取樣精度為3×3×1，能量計算收斂判據(jù)為1×10?5 eV/atom，原子最大受力不超過0.3 eV/nm，原子最大位移不超過1×10?4 nm，原子最大應力為0.05 GPa，結(jié)構(gòu)優(yōu)化算法采用BFGS。結(jié)構(gòu)優(yōu)化后的IDB-X/Diamond膜基界面模型如圖3所示。

2計算結(jié)果與分析

2.1膜基界面結(jié)合能

膜基界面結(jié)合能可以反映涂層和基底的黏附效果，通常膜基界面結(jié)合能越大，膜基的黏附效果越好，其計算公式[16]為：

其中，Wad-X為X（X=B、Al、Sn、Co）原子摻雜的膜基界面結(jié)合能，EIDB-X、EDiamond、EIDB-X/Diamond分別為結(jié)構(gòu)優(yōu)化后的IDB-X基底、CVD金剛石涂層和IDB-X/Dia-mond膜基界面模型的能量，A為優(yōu)化后膜基界面的面積。膜基界面結(jié)合能計算結(jié)果如表1所示。

由表1可知，B、Al、Co、Sn原子摻雜的膜基界面結(jié)合能分別為11.68、9.94、7.38、6.85 J/m2。以膜基界面結(jié)合能的削弱相Co[13]為基準，則B、Al原子摻雜的IDB-B和IDB-Al基底與CVD金剛石涂層的膜基界面結(jié)合能明顯高于Co原子的，說明基底中的B、Al元素對于膜基結(jié)合強度的提高是有利的；而Sn原子摻雜的IDB-Sn基底與CVD金剛石涂層的膜基界面結(jié)合能與Co原子摻雜的相近，說明基底中的Sn元素同樣對膜基結(jié)合強度有削弱作用。

2.2電荷分析

2.2.1差分電荷密度分析

差分電荷密度能反映膜基界面間電荷轉(zhuǎn)移以及原子間成鍵情況，從電子云的相互作用入手，進一步揭示膜基界面結(jié)合的機理。由于每個膜基界面模型中2個摻雜原子呈對稱結(jié)構(gòu)，故取其中一個摻雜原子及其附近的C1～C3原子展開電荷分析，電荷取樣點位如圖4所示。圖5展示了B、Al、Sn、Co原子摻雜的膜基界面模型的差分電荷分布圖。

由圖5可知：B、Al、Sn、Co原子的電荷均有向周圍的C原子，尤其是向C1～C3原子轉(zhuǎn)移的傾向，且向C1原子轉(zhuǎn)移電荷的傾向更明顯，這表明4種摻雜原子與涂層中的C原子產(chǎn)生的電荷作用更強。從圖5a可以明顯看出B原子的電荷向C1～C3原子轉(zhuǎn)移，并且轉(zhuǎn)移的電荷密度均較高，這反映了B原子與C1～C3原子的電荷作用均較強，形成了緊密的鍵合作用，有利于膜基結(jié)合強度的提高。圖5b中Al原子轉(zhuǎn)移電荷的傾向主要集中于C1和C2原子，向C3原子轉(zhuǎn)移電荷的傾向不明顯，表明Al原子與C1和C2原子的鍵合作用可能更強，能有效黏結(jié)涂層和基底。圖5c中Sn原子向C1原子轉(zhuǎn)移電荷的傾向明顯，但是向C2和C3原子轉(zhuǎn)移電荷的傾向略弱，表明Sn原子與基底C原子的電荷作用力較弱，不利于提高膜基結(jié)合強度。圖5d中Co原子向C1和C3原子有較弱的電荷轉(zhuǎn)移傾向，向C2原子轉(zhuǎn)移電荷傾向不明顯，表明Co原子與涂層和基底的電荷作用均較弱，不能有效黏結(jié)涂層和基底。

2.2.2布居數(shù)分析

原子布居數(shù)可以反映各原子的得失電子情況，化學鍵重疊布居數(shù)可以反映原子間鍵合作用的強弱，其越大則原子間成鍵越穩(wěn)定[17]。本文按圖4所示點位，計算了X（X=B、Al、Sn、Co）摻雜原子與C1～C3原子的原子布居數(shù)（見表2）和化學鍵重疊布居數(shù)（見表3）。

由表2可知：B、Al、Sn、Co原子摻雜的膜基界面模型中，B、Al、Sn、Co均失去電子帶正電，其失電荷數(shù)分別為0.59e、1.89e、2.06e和1.71e，而4種摻雜原子附近的C1～C3原子均得到電子帶負電，4種摻雜原子與C1～C3原子之間存在明顯的電荷轉(zhuǎn)移，表明膜基界面間存在C?B、C?Al、C?Sn和C?Co 4種鍵合作用。C1～C3原子對B、Al、Sn、Co原子失去電荷的有效利用率分別為98%、58%、43%和39%，其中C1～C3原子對B原子失去電荷的有效利用率接近100%，表明B原子貢獻的電荷幾乎都用于和C1～C3原子成鍵，B原子起到膜基連接節(jié)點的作用，有利于膜基結(jié)合；C1～C3原子對Al原子失去電荷的有效利用率高于50%，表明Al原子與C1～C3原子成鍵的同時還與其他C原子成鍵，導致這一部分C原子因得電子而帶同種電荷產(chǎn)生斥力，然而Al原子用于產(chǎn)生引力的電荷數(shù)大于產(chǎn)生斥力的電荷數(shù)，故Al原子摻雜仍有益于膜基結(jié)合；C1～C3原子對Sn、Co原子失去電荷的有效利用率均低于50%，表明Sn、Co原子失去電荷中的大部分電荷被界面間其他C原子俘獲，導致膜基界面間C原子產(chǎn)生的斥力較多，既不利于Sn、Co原子與C1～C3成鍵，又會進一步削弱膜基結(jié)合強度。

從表3可以發(fā)現(xiàn)，C1與4種摻雜原子之間的化學鍵重疊布居數(shù)均大于C2、C3的，表明基底表層摻雜的B、Al、Sn、Co原子均更傾向于向金剛石涂層移動，與涂層中的C原子成鍵，這一點也與上文的差分電荷密度分析一致。C?B鍵的重疊布居數(shù)最大且鍵長最小，說明C?B鍵的鍵能更大，成鍵更穩(wěn)定，同時C?B鍵的長度最接近金剛石中C?C鍵的長度1.54?，表明B原子摻雜引起的晶格畸變很小，有利于維持金剛石構(gòu)型。C?Al鍵的重疊布居數(shù)次之，雖然C3?Al的重疊布居數(shù)小，但C1?Al與C2?Al的重疊布居數(shù)較大且比較接近，表明Al原子與涂層和基底中的C原子成鍵較為對稱，成鍵穩(wěn)定性較高，是連接涂層和基底的有益元素，同時C?Al鍵的鍵長較小，鍵能較大，有利于膜基結(jié)合。C?Sn鍵與C?Co鍵的重疊布居數(shù)均較小，就Sn元素而言，雖然C1?Sn的重疊布居數(shù)略大，但是C2?Sn與C3?Sn的重疊布居數(shù)均較小，表明Sn原子與基底的連接較弱，不利于膜基結(jié)合；對于Co元素來說，C?Co鍵的重疊布居數(shù)均較小，且C2?Co成反鍵，最能削弱膜基結(jié)合強度。

3壓痕實驗及結(jié)果

壓痕實驗可以直接表現(xiàn)涂層化合物的界面結(jié)合性能[18]，裂紋越多，壓痕凹坑越深，凹坑面積越大，則認為膜基結(jié)合強度越差。本文采用B、Al、Sn、Co元素引晶預處理的方式[19]將4種元素摻入膜基界面，進而使用微波等離子體化學氣相沉積（MPCVD）設備在孕鑲金剛石顆粒硬質(zhì)合金基底上沉積金剛石涂層，采用相同的實驗參數(shù)：CH4流量4 sccm，H2流量200 sccm，CO2流量6 sccm，Ar流量15 sccm，壓強7 kPa，溫度800℃，沉積時間9 h。然后使用HR-150A洛氏硬度儀，采用天然金剛石壓頭，施加588 N的試驗壓力進行壓痕實驗，進而使用VHX-2000超景深顯微鏡拍攝壓痕形貌來對比分析4種摻雜元素對膜基結(jié)合強度的影響。圖6展示了4種壓痕形貌。

從圖6a、圖6b可以發(fā)現(xiàn)，B、Al元素引晶預處理的金剛石涂層壓痕較淺，凹坑面積較小，表明IDB-B/Diamond和IDB-Al/Diamond的膜基結(jié)合強度高，其中B元素引晶預處理的金剛石涂層壓痕凹坑面積最小，表明B元素最利于增強膜基結(jié)合強度，Al元素次之。圖6c、圖6d中Sn、Co元素引晶預處理的金剛石涂層壓痕較深且壓痕凹坑面積較大，圖6d中凹坑面積最大，表明IDB-Sn/Diamond和IDB-Co/Diamond的膜基結(jié)合效果較差，膜基界面間引入Sn、Co元素會削弱膜基結(jié)合強度。

4結(jié)論

基于第一性原理探究了IDB基體中的常用元素X（X=B、Al、Sn、Co）對IDB-X/Diamond膜基界面結(jié)合性能的影響，計算了膜基界面結(jié)合能、差分電荷密度和布居數(shù)，揭示了能量和電荷的變化情況，并采用MPCVD設備沉積金剛石涂層開展壓痕實驗，得到以下結(jié)論：

（1）從能量方面來看，4種元素摻雜的膜基界面結(jié)合能大小為Wad-B（11.68 J/m2）gt;Wad-Al（9.94 J/m2）gt;Wad-Co（7.38 J/m2）gt;Wad-Sn（6.85 J/m2）。以膜基界面結(jié)合能的削弱相Co元素為基準，則B、Al元素摻雜有利于提高膜基結(jié)合強度，Sn元素摻雜的膜基界面結(jié)合能與Co元素相近，表明Sn元素摻雜同樣會削弱膜基結(jié)合強度。

（2）從電荷方面來看，B、Al原子的電荷主要轉(zhuǎn)移到摻雜位點附近的C1～C3原子，其有效電荷利用率分別為98%和58%，C?B、C?Al鍵的重疊布居數(shù)均較高，表明B、Al原子與C1～C3原子的成鍵較強，起到了膜基連接節(jié)點的作用，能提高膜基結(jié)合強度；Sn、Co原子的有效電荷利用率均﹤50%，表明大量電荷轉(zhuǎn)移到膜基界面間除C1～C3原子之外的其他C原子，導致Sn、Co原子與C1～C3原子的成鍵較弱，同時其他C原子由于得電荷而相斥，削弱膜基結(jié)合強度。

（3）從壓痕實驗來看，B元素引晶預處理的金剛石涂層與孕鑲金剛石基底的結(jié)合強度最高，Al元素次之，Sn、Co元素較差。

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作者簡介

通信作者：簡小剛，男，1975年生，博士、副教授。主要研究方向：涂層制備與性能檢測。

E-mail：jianxgg@#edu.cn

（編輯：趙興昊）

Effect of doped elements X（B，Al，Sn，Co）on binding performance of"IDB-X/Diamond interface

JIAN Xiaogang，YAO Wenshan，ZHANG Yi，LIANG Xiaowei，HU Jibo，CHEN Zhe，CHEN Maolin

（School of Mechanical Engineering，Tongji University，Shanghai 201804，China）

Abstract Objectives：At present，resource exploration and mining continue to expand to deep underground.Impreg-nated diamond bits（IDB）with excellent performance have become the main tool for deep underground drilling.Our re-search group has found that depositing a layer of CVD diamond coating in situ on the surface of IDB can achieve homo-geneous epitaxial growth and heterogeneous epitaxial growth of diamond coatings，which can improve the working life of IDB.This article is based on the first principles of quantum mechanics and uses the CASTEP computational tool to study the influence mechanism of X（X=B，Al，Sn，Co）elements commonly used in the IDB on the interfacial bonding performance of CVD diamond coatings on IDB from a microscopic perspective.It provides a theoretical reference and basis for further optimizing the formulation of drill bit substrates and improving the interfacial bonding strength between the film and substrate.Methods：This article uses the CASTEP module of the quantum mechanics computing software Materials Studio to study the influence mechanism of X（X=B，Al，Sn，Co）elements commonly used in IDB on the in-terfacial bonding performance of CVD diamond coatings on IDB from a microscopic perspective.Firstly，establish[100]crystal orientation，3×3 size IDB，and CVD diamond coating supercell models，with dimensions of 7.54?×7.54?×3.56?along the X，Y，and Z directions.After adding a vacuum layer with a thickness of 12?，the IDB model and CVD diamond coating model are obtained.Then，replace the C atoms at specific locations on the surface of the IDB model with X（X=B，Al，Sn，Co）atoms.Afterwards，the IDB-X substrate is combined with the CVD diamond coating"model along the[100]crystal plane to establish an IDB-X/Diamond film substrate interface model.After testing，the film-substrate interface spacing is set to 2?.Next，the CASTEP module is used to optimize the IDB-X/Diamond film-substrate interface model doped with X（X=B，Al，Sn，Co）atoms.The properties of the four film-substrate interface models are analyzed from the aspects of film-substrate interface binding energy，differential charge density，and Mul-liken population.Finally，verification is conducted with indentation experiments.Results：（1）From the perspective of film-substrate interface binding energy，the binding energies of B，Al，Co，and Sn atom doping are 11.68，9.94，7.38，and 6.85 J/m2，respectively.Based on the weakening phase Co of the film-substrate interface binding energy，the film-sub-strate interface binding energy doped with B and Al atoms is significantly higher than that of Co atoms，indicating that the B and Al elements in the substrate are beneficial for improving the film-substrate interface binding energy.The film-substrate interface binding energy doped with Sn atoms is similar to that of Co atoms，indicating that the Sn element in the substrate also weakens the bonding strength between the film and substrate.（2）From the perspective of differential charge density，the charges of B，Al，Sn，and Co atoms all tend to transfer to the surrounding C atoms，especially to the C1?C3 atoms in CVD diamond coatings，and the tendency to transfer charges to C1 atoms is more pronounced.This in-dicates that the four doped atoms have a stronger effect on the charges generated by the C atoms in the film.The dens-ity of charge transfer from B atom to C1?C3 atom is relatively high，which reflects the strong charge interaction between B atom and C1?C3 atom.The tendency of Al atoms to transfer charges is mainly concentrated in C1 and C2 atoms，and the tendency to transfer charges to C3 atoms is not obvious，indicating that the bonding between Al atoms and C1 and C2 atoms may be stronger.The tendency of Sn atoms to transfer charges to C1 atoms is obvious，but the tendency to transfer charges to C2 and C3 atoms is slightly weaker，indicating that the charge interaction force between Sn atoms and C atoms in the substrate is weak.Co atoms have a weak tendency to transfer charges to C1 and C3 atoms，while their tendency to transfer charges to C2 atoms is not significant，indicating that the charge interaction between Co atoms and the film and substrate is weak.（3）From the perspective of atomic and chemical bond Mulliken population，B，Al，Sn，and Co all lose electrons and carry positive charges，with charge loss numbers of 0.59e，1.89e，2.06e，and 1.71e，respectively.Meanwhile，the C1?C3 atoms near the four doping elements all receive negative charges，indicating signi-ficant charge transfer between the four doped atoms and C1?C3 atoms.This suggests the existence of four types of bonding interactions between the film-substrate interface interface：C?B，C?Al，C?Sn，and C?Co.The effective utilization rates of the lost charges of B，Al，Sn，and Co atoms by C1～C3 atoms are 98%，58%，43%，and 39%，respect-ively.The Mulliken population of the C?B bond is the largest and the bond length is the smallest，followed by the Mulliken population of the C?Al bond.The Mulliken populations of the C?Sn bond and C?Co bond are relatively small.（4）From the indentation experiment，it can be seen that the indentation of diamond films pretreated with B and Al elements is shallow and the pit area is small，indicating that the film-substrate interface binding strength of IDB-B/Dia-mondand IDB-Al/Diamond is high.Among them，the indentation pit area of diamond films pretreated with B element is the smallest，indicating that B element is most conducive to enhancing the film-substrate interface binding strength，fol-lowed by Al element.The diamond coatings pretreated with Sn and Co elements have deeper indentation and a larger in-dentation pit area，indicating poor film-substrate interface effect of IDB-Sn/Diamond and IDB-Co/Diamond.Conclu-sions：（1）From the perspective of energy，the binding energy of the film-substrate interface doped with four elements is Wad-B（11.68 J/m2）gt;Wad-Al（9.94 J/m2）gt;Wad-Co（7.38 J/m2）gt;Wad-Sn（6.85 J/m2）.Based on the weakening phase of the film-sub-strate interface binding energy of the Co element，the doping of B and Al elements are conducive to improving the film-substrate interface bonding strength.The film-substrate interface binding energy of Sn element doped is similar to that of Co element，indicating that Sn element doped also weakens the film-substrate interface bonding strength.（2）From the perspective of charge，the charges of B and Al atoms mainly transfer to the C1?C3 atoms near the doping site，with"effective charge utilization rates of 98%and 58%，respectively.In addition，the Mulliken populations of C?B and C?Al bonds are relatively high，indicating that the bonding between B and Al atoms and C1?C3 atoms is strong，playing the role of film substrate connection nodes and improving the film substrate interface binding strength.The effective charge utilization rates of Sn and Co atoms are both less than 50%，indicating that a large amount of charge is transferred to other C atoms at the film substrate interface except for C1?C3 atoms，resulting in weak bonding between Sn and Co atoms and C1?C3 atoms.At the same time，other C atoms repel each other due to the charge obtained，weakening the film substrate interface binding strength.（3）From the indentation experiment，it can be seen that the film-substrate inter-face bonding strength of B element-induced crystal pretreatment is the highest，followed by Al element，while Sn and Co elements are relatively poor.

Key words first-principles；diamond coating；membrane-based binding；charge transfer；Mulliken population；indenta-tion experiments